MU Mechanical Engineering Department

TABLE OF CONTENT

1. Background and Justification.........................................................................................................1

2. Introduction.....................................................................................................................................3
3. Objective.........................................................................................................................................4
4 .Literature Review...........................................................................................................................4
4.1 Manufacturing Methods and Quality Control...........................................................................9
4.2 Concrete Manufacture............................................................................................................10
4.3 Block making Machinery.......................................................................................................10
4.3 .1 Concrete blocks and concrete brick................................................................................14
4.3.2 Raw Materials..................................................................................................................14
4.3.3 Existing process description for hollow concrete blocks................................................15
4.4 curing......................................................................................................................................15
4.5 Palletising and Packaging.......................................................................................................16
5. Design of multi-hollow concrete block producing machine.........................................................18
5.1 Design considerations.............................................................................................................18
5.2 Identification of design problems of the existing machine under consideration....................19
5.3 Design concepts for improve technology...............................................................................19
5.3.1 Design matrix...................................................................................................................20
5.3.2 Design analysis................................................................................................................25
5.3.2.1 Design of belt................................................................................................................29
5.3.2.2 Design of pulley............................................................................................................33
5.3.2.3 Design of shaft..............................................................................................................35
5.3.2.4 Design of key................................................................................................................37
5.3.2.5 Bearing selection..........................................................................................................39
5.3.2.6 Design of spring............................................................................................................39
5.3.2.7 Design of bolt...............................................................................................................42
5.3.2.8 Design of pins and link levers (cotter joint).................................................................42
COST ESTIMATION.......................................................................................................................45
ASSEMBLY TIP..............................................................................................................................46
LIMITATION...................................................................................................................................47
CONCLUSION.................................................................................................................................48
RECOMMENDATION....................................................................................................................49
APPENDICES..................................................................................................................................50
REFERENCE:..................................................................................................................................51

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

1. Background and Justification

A concrete block is primarily used as a building material in the construction of walls. It is

sometimes called a concrete masonry unit (CMU). A concrete block is one of several
precast concrete products used in construction. The term precast refers to the fact that the
blocks are formed and hardened before they are brought to the job site. Most concrete
blocks have one or more hollow cavities, and their sides may be cast smooth or with a
design. In use, concrete blocks are stacked one at a time and held together with fresh
concrete mortar to form the desired length and height of the wall [5].

Concrete mortar was used by the Romans as early as 200 B.C. to bind shaped stones
together in the construction of buildings. During the reign of the Roman emperor
Caligula, in 37-41 A.D., small blocks of precast concrete were used as a construction
material in the region around present-day Naples, Italy. Much of the concrete technology
developed by the Romans was lost after the fall of the Roman Empire in the fifth century.
It was not until 1824 that the English stonemason Joseph Aspdin developed Portland
cement, which became one of the key components of modern concrete [5].

The first hollow concrete block was designed in 1890 by Harmon S. Palmer in the United
States. After 10 years of experimenting, Palmer patented the design in 1900. Palmer's
blocks were 8 in (20.3 cm) by 10 in (25.4 cm) by 30 in (76.2 cm), and they were so heavy
they had to be lifted into place with a small crane. By 1905, an estimated 1,500 companies
were manufacturing concrete blocks in the United States [5].

These early blocks were usually cast by hand, and the average output was about 10
blocks per person per hour. Today, concrete block manufacturing is a highly automated
process that can produce up to 2,000 blocks per hour [5].

There is a self-evident need for adequate and durable housing, especially in the urban
and peri-urban areas of developing countries. The poor are most adversely affected by
this housing shortage. Assuming land availability and planning permission for further
development, the need is to deliver more durable housing at lower cost.

The cost of a dwelling can be split into a number of separate areas as follows:

1. Initial land survey

2. Land preparation on paper – division into plots with access, (needs approval)
3. Physical preparation of ground – clearing vegetation, debris, boulders, etc.
4. Installation of services (optional) – water, sewerage, electricity and telephone
5. Purchase of the plot – cost direct to the homebuilder
6. House erection – foundations and walling (entailing materials and labour)
7. Roofing – spanning beams and roof material
8. Openings – windows and doors with fittings

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

9. Services – connection up to services if available, (optional, may require approval)

Items 6 to 8 constitute the most significant part of the total cost of the dwelling [5].
Furthermore, the walling constitutes the most significant part of the physical structure,
60% according to [2]. From this it makes sense to concentrate work on low-cost walling.
Research recently conducted at Warwick University has indicated that dynamic
compaction may provide a method of improving the performance of stabilised soil blocks
for walling and at reduced cost. A further motivation for research into stabilised soil
blocks is their environmental sustainability. Cement Stabilised Soil Blocks (CSSB) use low
quantities of cement, locally available soil and have a low energy requirement. Currently
popular alternatives such as clamp fired brick and concrete blocks do not have these
advantages. Environmentally unsustainable practices are also sometimes used in their
production such as burning firewood and dredging river sand, [2], [4].

Earth construction is very successful in arid areas, but significant stabilization is required
for adequate performance in humid areas. Research conducted at Warwick by Kerali
indicated that a six-fold increase in wet compressive strength could be achieved using
improved curing regimes for CSSB, [2]. With good production control CSSB can perform
quite adequately, but further improvements in material performance will help to
outweigh sloppy production practices.

 Construction development in Ethiopia

Construction is second to agriculture in generating employment in Ethiopia. Capacities in

construction, as well as in manufacturing of construction materials, are in a better setting
than in other sectors. This is because fairly reasonable institutional and infrastructural
bases exist for design and construction in both the public and private sectors. The sector
can also be said to have better developed skilled labour.

At present, research and development in the construction sector is conducted mainly in

the production of wall and roofing materials. Research and development on domestic
raw materials to reduce the sector's dependence on imported materials is far from what it
should be. Research and development has been conducted by various institutions,
departments, and units in a scattered and uncoordinated manner. Little progress has
been made in generating efficient and effective indigenous technologies to fit the
available material and human resources, especially in low-cost housing construction. The
sector has no centrally organized institution to support and carry out research and
development.

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

2. Introduction

This is a short note that briefly explains how a concrete block is manufactured, the raw
materials of it and outlines the history of concrete block machine. Researches in this area
are being done; this is done by broadly outlining the problem of housing shortage
specifically in our country. Like that of ministry of trade and transport industry of
regional Tigray.

 Construction material methods

Many different materials are used around the world for walling. Where quarried stone
and timber are not readily available, earth is the most common material used. Earthen
architecture has been used for centuries in many different parts of the world. [4] States:
“Thirty percent of the world’s population, or nearly 1,500,000,000 human beings, live in a
home of unbaked earth.” Accounts from the Bible (Exodus 1:11-14, 5:6, 7) indicate that
around 1500BC earth mixed with straw was a typical building material. Earlier accounts
from the Bible (Genesis 11:3) also speak of burning bricks and using slime as mortar.
Archaeological evidence in very dry areas has also shown that earth building was a
highly popular material for dwelling construction. Earth is still used today in many parts
of the world where access to other forms of building material is restricted by location or
by cost. Each building material has its own advantages and disadvantages. Some of the
problems with existing materials are their poor use of environmental resources, poor
quality control of the finished product and consequently a significant variation in
durability. The long-term sustainability of some methods is being questioned in many
places. Other alternatives are being sought after that is environmentally sustainable
whilst also being of a suitable strength and durability for use in humid areas. [4]

 Intent of the project

The specifications and the characteristics of a concrete block depend on the machine
used to manufacture concrete blocks. The most common size of solid concrete blocks
is 300mmx200mmx150mm. The basic raw material is cement, sand, and fine
aggregate and coarse aggregate. Very little water is used. This is possible only with
mechanized compaction and vibration and gives the block high quality inspite of the
lean mix, which uses very little cement. Weight of a concrete block is about 18-19
kgs. Concrete blocks can be surface engineered by using pieces of stone or ceramic
waste on their face. Another common type is hollow concrete blocks. They are made
with a richer mix, but offer a number of advantages, such as lighter weight, easier
handling, less cost and facility for conduiting or reinforcement through the hollows.

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

Unique features of Concrete Block Technology

 Cost effective compared to other traditional walling systems
 Maximum utilization of wastes and local resources
 Structural performance can be engineered
 Decentralized local production
 Cost effective compared to other traditional walling
 Offers business opportunities

3. Objective

Today more than one billion of the world's city residents live in inadequate housing;
worldwide, 18% of all urban housing units are non-permanent structures and 25% do not
conform to building regulations [11]. Between 40 and 70% of the population in most
African cities live in informal settlements (Towards sustainable urban development, 2000,
p.5).This implies that there has to be a solution to wards this big problem.

Generally, the objective of this project is to design efficient and productive hollow
concrete block producing machine, which means that to provide a low cost housing
which is the big issue of our government.

4 .Literature Review
Masonry construction is one of the oldest forms of construction used by man. Structures
of stone, mud brick and clay brick, some built thousands of years ago; remain to bear
witness to the durability of masonry. Not until the nineteenth century, with the
development of hydraulic cements, did concrete masonry begin to evolve. It began in the
United States, where large heavy solid blocks were made of a moulded mixture of
quicklime and moist sand cured by steam [1].

The next developments were seen in England, where solid blocks were made using
powdered lime, fine aggregates and boiling water to give rapid set. Some of these blocks
were used in London, in houses in Pall Mall and in the Royal College of Surgeons’
building. Solid blocks, however, proved unpopular and impractical because of their
weight. About 1866, the development of techniques of moulding hollow blocks began.
During the following ten years, a number of patents on hollow blocks were granted in
England and the United States. These did not cover manufacturing methods, as blocks
were usually moulded in wooden moulds. By about 1900, a number of ‘machines’ for
making blocks began to appear in the United States. These were nothing more than
moulds with removable sides, cores and bases, in some cases with arrangements for
turning the freshly moulded block to permit its removal. Mould filling and concrete
tamping were by hand. In the early moulds, the face of the block was formed on the
removable mould bottom, which could, if desired, be provided with a patterned or rock-
face finish. The cores were supported horizontally. To remove the block, the mould sides
4

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

had to be demounted, core extracted and the block taken away on the mould base to be
cured. For the next block, a fresh mould base, referred to as a pallet, was inserted and the
process repeated. Later ‘machines’, about 1904, had vertical cores, fold-down moulds
sides, and a pallet with cut-outs so it would fit over the cores. The pallet was placed on
the bottom of the mould and was used to lift the freshly moulded block out of the mould
after hand tamping [1].

Although the early blocks were much the same height and thickness as the largest sizes
now made, they were up to twice as long and therefore correspondingly heavier and
difficult to handle. The early ‘machines’ could make only about two hundred blocks per
ten-hour day with three men (Figure4.1). Between 1914 and 1924, power tamping
replaced hand tamping, improving density, strength and uniformity. One manufacturer
developed and sold a semi-automatic machine capable of making 1800 blocks per day
with the same number of men as had made only 200 blocks on the older machines.
During this period, the dimensions of units were standardized gradually, leading to the
full modular coordination we have today [1].

Figure4. 1 The early hand mould machine [1]. Figure4. 2 Illustrate a block making machine of
this days [1].
Perhaps the greatest single advance in block making machinery was made in 1924 with
the introduction of the first successful ‘stripper’ machine using plain pallets that did not
have to be profiled around the cores. In this machine, the block was extruded downwards
through the mould, exactly the same as in modern machines. Apart from feeding empty
pallets and removal of the freshly made blocks, the machine was fully mechanized and
automatic in operation. It used power tamping and could produce 3000 blocks per day.
Today’s fully automatic block making machines are descended from the 1924 machine.

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

During the following fifteen years, productivity and automation developed. A 1929
machine is illustrated in (Figure 4.3). In 1939, tamping was superseded by mould
vibration while the “green” concrete in the mould was under pressure. This greatly
improved face texture and sharpness of arrises and gave higher block strength. These
machines could make 5000 blocks per day (Figure 4.4). Since 1939, there have been
progressive improvements in productivity and product quality, resulting initially from
the introduction of automatic controls to regulate block height and density and later from
the automation of ancillary equipment such as raw materials handling, weigh batching
and mixing. Further productivity improvements have been gained by developing
automatic equipment to remove green blocks from the block making machine and place
them either on racks or directly in the curing chambers. This is achieved by the
introduction of rack transfer systems to move racks to the curing chambers, and by other
equipment which will withdraw cured blocks from the curing chambers and package
them ready for dispatch. Figure 4.5 shows a modern plant incorporating a transfer system
[1].

Figure 4. 3 A1929machine [1].

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com

Figure 4. 4 The improved machine that could Figure 4. 5A modern plant incorporating a
make 5000 blocks per day [1]. transport system [1].
 MU Mechanical Engineering Department

From air curing with occasional water sprays used early in this century, curing
techniques have also been developed and refined. Low- and high pressure steam curing
systems and burner curing systems are used now. In some cases, these are supplemented
by the introduction of carbon dioxide into the curing chambers after curing is completed,
to reduce block shrinkage [1].

In Australia, concrete masonry followed American developments, although the

introduction of modern high-production extrusion machines occurred much later. Blocks
were originally made in primitive moulds. This practice continued until the 1950s when
the first modern block making plant was established in Adelaide. The introduction of
similar machinery to other Australian cities and towns followed [1].
Several types of block-, brick- and paver-making machines are used in Australia. Typical
modern block making machines are shown in Figures 4.6, 4.7 and 4.8.With the
introduction of segmental paving into the Australian market in 1974, a new type of
concrete unit machine began to make its appearance. Originating in Europe, these
dedicated paving machines featured larger pallet areas (0.5 to 1.0 m2) but slower cycle
times (20 to 30 seconds). The long cycle times mean that the surface can be more
effectively compacted, resulting in better wear characteristics. The dedicated paving
machines are particularly suited to producing units with complex plan shapes (such as
dentate interlocking pavers) and thicknesses in the range of 60 to 80 mm. The paving
machines were generally used to augment the older hollow-block machines, which
concentrated on the production of hollow blocks and rectangular pavers [1].

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com

Figure4. 6 Figure4. 7
 MU Mechanical Engineering Department

Figure 4. 8

Figure4. 6, 4. 7, 4. 8 are typical modern block making [1].

machin [1].e

4.1 Manufacturing Methods and Quality Control

Most concrete masonry units used in Australia are manufactured by automatic

machinery of advanced design and capable of a very high output with a high degree of
uniformity. A typical flow diagram, Figure 4.1.1, illustrates the sequence of
manufacturing operations and the points of regular quality control checks employed by
well-managed factories. These checks cover raw materials, manufacturing operations,
methods and processes as well as the finished product. Figures 10 to Figure 26 illustrate
some of these features in more detail [1].

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com

Figure 4.1.1concrete masonry manufacture – typical flow diagram [1].

 MU Mechanical Engineering Department

4.2 Concrete Manufacture

Raw materials are delivered to silos and bins, with the various aggregates separated, see
Figure 4.3.1. Cement and aggregates are weighed automatically to predetermined
quantities. Figure 4.3.2 shows typical control panels for automatic weigh batching and
mixing [1].

The concrete ingredients are proportioned to produce the desired properties in the
finished units. If incoming raw materials change in grading or moisture content, the mix
proportions are adjusted to compensate. Very ‘dry’ cohesive concrete is used in masonry
manufacture, in conjunction with powerful mould vibration at the same time as pressure
is applied to the concrete in the mould. As freshly moulded units are extruded down

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

from the machine mould approximately every ten seconds, they must have sufficient
‘green strength’ to permit them to be handled without damage or distortion
The mixing of concrete is controlled automatically in most plants and is linked with the
batching plant to provide a concrete output suited to the consumption of the block
machine. A typical mixer for masonry concrete is shown in Figure 4.3.3. A moisture
sensor controls the addition of water. It maintains the correct moisture content and
consistency in the concrete as it is delivered from the mixer to the block making machine.
In some plants, automatic compensation of fine aggregate weight for moisture content is
provided by feedback from the moisture sensor to the batch weigher, but in others the
operator will note changes and compensate manually.

4.3 Block making Machinery

From the mixer, concrete of the correct proportions and workability is transported either
by gravity or mechanically to the block making machine. Machine pallets are heavy steel
plates designed to act as a mould bottom. Before each new cycle of the machine, a fresh
machine pallet is placed under the mould. The mould is filled and the blocks vibrated.
The blocks are then extruded downwards from the mould, remaining on the pallet which
travels with them to form a tray on which they are transported until they are cured and
about to be assembled into ‘cubes’ at the packaging station.
Figure 4.3.4 shows a concrete block mould, with cores, stripper shoes and head. The latter
are lay back at an angle in this photograph to show the details. They normally occupy a
vertical position. During mould filling, the head and shoes are raised clear of the mould
to allow concrete to enter. When the mould is filled and while it is being vibrated, the
head and shoes press on the top of the ‘green’ blocks. At the end of the vibration period,
they are moved down to extrude the blocks from the mould. This particular mould is
fitted to make four 400 x 150 x 200 mm hollow blocks and is quite small by modern
standards. At the lower left and right of the mould, the drive pulleys for the two vibrator
units may be seen. The latter are attached to the mould body and are driven by two
powerful electric motors by means of belts.

Figure 4.3.1 Aggregate silos [1]. Figure 4.3.2 Auto weigh batching and mixing
controls [1].

10

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com

Figure 4.3.3 typical mixer for concrete masonry Figure 4.3.4 Concrete block mould [1].
manufacture [1].
 MU Mechanical Engineering Department

Most high production block machines used in Australia employ similar mould, core,
stripper shoe and machine pallet arrangements. They differ only in size, the number of
units that can be made per machine cycle (i.e. on each machine pallet), the system of
actuation (electro-mechanical or electro hydraulic) and the method by which vibration is
applied to the mould and the ‘green’ blocks. Mould vibration systems are either vibrator
units directly attached to the mould or remote units connected to the mould by rods.
Most concrete segmental pavers are manufactured using specialized paving machines of
European origin, as described previously. Hollow-block machines are also widely used
for the production of some types of concrete segmental pavers. Rectangular units can be
manufactured ‘on edge’ in the block machine, ensuring that the whole of the machine
cavity is effectively used. Thus, for each machine cycle a larger number of units may be
manufactured in this way than would otherwise result from units manufactured ‘on the
flat’. Checks are made frequently on both moulds and cores for correct setting and wear.
Machine controls are provided to set the height of the blocks. These checks ensure
dimensional accuracy. Frequent checks are made for density, vibration and machine cycle
time to ensure that the finished units will have satisfactory physical properties.
11

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

Moulded ‘green’ blocks are transported mechanically from the block machine on the
machine pallets to the curing chambers. Several alternative systems for handling ‘green’
blocks are employed. These are shown in Figures 4.3.5, 4.3.6, 4.3.7 and 4.3.8. As well as
loading ‘green’ blocks into the curing chambers, these systems also unload the cured
blocks coming from the curing chambers, see Figure 4.3.9. The process flow may be briefly
described as follows. Freshly moulded or ‘green’ concrete units are deposited on a steel
pallet. These may be: _ loaded into steel racks for transport by forklift or kiln car to and
from the kilns or curing areas; _ loaded directly onto an automatic transfer car; or _
transported to and from the kiln or curing area by a conveyor system.

When the hardened concrete units have been returned from the kiln or curing area, they
are automatically removed from the steel pallets, realigned and pushed into a cubic shape
using an automatic cubing machine. In some factories, cubes of finished product are
shrink-wrapped. When required, units may be split, rumbled or polished using
equipment installed at the factory.

Figure 4.3.7 Block making machine with manually-

Figure 4.3.5 Block makingoperated
machineoff bearer, loading and
with unloading
Figure Racks truck handling racks of
4.3.6 Forklift
automatic rack loading and unloading equipment blocks from automatic loading and unloading
equipment, to and from curing chambers

12

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
Figure 4.3.8 Automatic rack-transfer car system, Figure 4.3.9 Cured blocks on machine pallets being
handling loaded racks to and from curing transported to the ‘Cubing’ machine after unloading
chambers from the kilns
 MU Mechanical Engineering Department

4.3 .1 Concrete blocks and concrete brick

They can be hollow or massive with mortar or interlocked as a dry-stack masonry system.
The masonry could be a non-reinforced or reinforced load-bearing wall, depending on
local conditions and standards. Construction could achieve efficiency if well supervised
and performed. The mortar can be traditional Portland cement or cement mix with lime
and/or rice husk ash.

Negative aspects with masonry:

- Long term shrinkage of units placing wall under tension thereby increasing cracking
- Mixing of mortar must be done under control to obtain good results or cracks may
appear
- Necessary to plaster and paint with waterproof painting
- Requires on site supervision
- Methods of jointing must be controlled
13

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

Concrete blocks masonry is a common solution for low-income houses in Ethiopia. Types vary
from mass, hollow, interlocking and dry-stack systems.

4.3.2 Raw Materials

The concrete commonly used to make concrete blocks is a mixture of powdered Portland
cement, water, sand, and gravel. This produces a light gray block with a fine surface
texture and a high compressive strength. A typical concrete block weighs (17.2-19.5 kg).
In general, the concrete mixture used for blocks has a higher percentage of sand and a
lower percentage of gravel and water than the concrete mixtures used for general
construction purposes. This produces a very dry, stiff mixture that holds its shape when
it is removed from the block mold.

If granulated coal or volcanic cinders are used instead of sand and gravel, the resulting
block is commonly called a cinder block. This produces a dark gray block with a medium-
to-coarse surface texture, good strength, good sound-deadening properties, and a higher
thermal insulating value than a concrete block. A typical cinder block weighs (11.8-15.0
kg).

Lightweight concrete blocks are made by replacing the sand and gravel with expanded
clay, shale, or slate. Expanded clay, shale, and slate are produced by crushing the raw
materials and heating them to about 2000°F (1093°C). At this temperature the material
bloats, or puffs up, because of the rapid generation of gases caused by the combustion of
small quantities of organic material trapped inside. A typical light-weight block weighs
(10.0-12.7 kg) and is used to build non-load-bearing walls and partitions. Expanded blast
furnace slags, as well as natural volcanic materials such as pumice and scoria, are also
used to make lightweight blocks.

In addition to the basic components, the concrete mixture used to make blocks may also
contain various chemicals, called admixtures, to alter curing time, increase compressive
strength, or improve workability. The mixture may have pigments added to give the
blocks a uniform color throughout, or the surface of the blocks may be coated with a
baked-on glaze to give a decorative effect or to provide protection against chemical
attack. The glazes are usually made with a thermosetting resinous binder, silica sand, and
color pigments.

4.3.3 Existing process description for hollow concrete blocks

Hollow concrete block are with graded sand and large amounts of cement (12-17% by
weight). If manufactured properly they can have very high strength and good durability.
Significant cost and weight reduction is achieved by removing material from the central

14

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

region of the block. Machinery for production requires a vibrating table to settle the
cement mix into the mould. Sometimes, instead, a heavy hinged lid slammed a couple of
times or low pressures are applied to compress the material.
Good dimensional accuracy means that these blocks can be laid on a 10mm mortar joint. However,
due to the voids in the block, mortar falls down these holes and is wasted. (In calculating the
required mortar it has been assumed that the mortar actually used is closer to that needed for the
surface area of the entire top surface of the block rather than just the edges where a joint is made
with the neighboring block.) These blocks are sometimes rendered for aesthetic reasons, which we
will omit from any calculations for the time being.

4.4 curing

In the early days of concrete masonry, units were usually cured by being left in the
storage yard for at least four weeks and sprinkled occasionally with water. Curing was
doubtful and variable and depended on weather conditions. Extreme colour variations,
caused by differential surface drying, resulted from this method of curing. With the
arrival of high production manufacturing and handling equipment, accelerated curing
techniques became necessary to avoid enormous accumulation of stock.

Low-pressure steam curing was one of the earliest accelerated curing methods used. In
this system, saturated steam, at atmospheric pressure and at temperatures above about
70°C, is introduced into insulated chambers containing racks of ‘green’ blocks. Hydration,
the chemical reaction between cement and water which causes hardening, is accelerated
at high temperature in a vapour saturated atmosphere. About 70 to 80% of the 28-day
atmospheric-temperature cured strength of the concrete is developed in 18 to 24 hours by
this process. Units may thus be handled and packaged the day after moulding other low-
pressure curing systems use gas or oil burners to heat the curing chamber. Steam is
generated by spraying water on a hot plate that is heated by the burner. These systems
offer economies in capital expenditure, as a steam boiler is not needed. They can be
programmed for automatic operation without the need for an attendant, resulting in
economy in operation. The results achieved are generally similar to those available with
medium temperature low-pressure steam curing. Burner systems have the advantage that
a drying period may be added at the end of the curing cycle. A typical installation of this
type is shown in Figures 4.4.1 and 4.4.2. Figure 4.5.1 shows a modern installation
employing automatic handling of 20-high racks.

15

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
Figure4.4.1Typical low-pressure Installation using
Figure4.4.2 Rear view of above installation
burners to heat the Chamber and produce the
steam
 MU Mechanical Engineering Department

4.5 Palletising and Packaging

After being cured, blocks are unloaded from the racks or curing chambers. They are
removed mechanically from the machine pallets and transported by conveyor to the
palletising station, where they are assembled into ‘cubes’ of standard sizes, usually
measuring approximately 1.2 x 1.2 x 1.2 m. Figures 22 and 23 show typical cubing
equipment. Between the machine pallet stripping station and the cuber, inspection is
often made for units of substandard appearance. If any are found, they are rejected and
removed. Sampling for testing for compliance with Australian Standards AS/NZS 4455
andFigure4.4.1Typical
AS/NZS 4456, low-pressure Installation
as appropriate, using out also at this stage.
is carried
burners to heat the Chamber and produce the
steam

Figure 4.5. 2‘Cuber’ with magazine of pallets on right

16

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com

Figure 4.5. 3‘Cuber’ with two finished ‘Cubes’ of

blocks on wood pallets
 MU Mechanical Engineering Department

Figure 4.5.1 Low-pressure installations with

automatic handling of 20-high Racks

5. Design of multi-hollow concrete block producing machine

Design is the formulation of a plan for the satisfaction of a human need. Design of multi-hollow
concrete block producing machine is towards this plan. The solution to design problem is not
unique. Often, many alternative solution are considered and the optimal one is selected, this is
what was tried in every part of the design.

In put parameters:

 Motor 3.4 kW
 2800 rpm
 with capacity of different concrete patterns
 4 blocks (400mmx200mmx200mm)
 5 blocks (400mmx200mmx150mm)
 7 blocks (400mmx200mmx100mm)
 And different products according to the different moulds.

17

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

5.1 Design considerations

Most engineering designs involve a multitude of considerations. It is a challenge to the engineer to

recognize all of them in proper proportions .some times the strength of an element is an important
factor in the determination of the geometry and dimensions of the element. In such the case it is
said that strength is an important design consideration. Design consideration refers to some
characteristics, which influences the design or an element or the entire system. Usually, a number
of these have to be considered in any given design situation. The following list shows some of the
design consideration.

Strength
Operating condition
Cost
Availability Make Proper function
Manufacturing ability the Good performance
Aesthetic(good appearance) design Adequate reliability
Material optimal Low cost
Safety solution.
Reliability and Maintainability
Ergonomics(human and machine
interaction)

Figure 5.1.1the correlation of design consideration and optimal solution

5.2 Identification of design problems of the existing machine under consideration

In Ethiopia, the existing single of Hollow block producing machine technology could
not meet the increase demand building construction, that is not efficient, time taking, it is
not quantified in mathematics (not in design paper) and energy consuming. To solve these
problems, it is; thus, important to evaluate the existing design and go one step forward
towards designing, manufacturing and testing multi-hollow block producing machine.

5.3 Design concepts for improve technology

We may examine an implement's safety (absence of failure) by one of three approaches:-

1. Try it with care, an approach which is not possible if failure could be hazardous or
cause significant financial loss, or

18

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

2. Analyse it via a mathematical model of the implement, from which the stresses and
deflections may be calculated for the known loading and the existing implement's
size (dimensions) and material (strength, modulus), thus indicating whether the
implement is safe or not; or
3. Synthesise it, i.e. analyse in reverse, where the material is chosen and the minimum
dimensions necessary to avoid failure are calculated before the implement is later
made to suit.

Figure 5.3.1Major aspects of the analysis and synthesis

thus involve four implement [7]

An implement in mechanical engineering is more complex than those above, and requires
careful design to ensure that everyone who is associated with it is satisfied with it. A well
designed artefact is cheap to manufacture, and is easy and safe to use and to maintain,
among other things.

Although safety is just one aspect of design, it is a fundamental necessity for all designs

Implement safety can of course be assured by building a physical model and testing it, but this is
usually uneconomical and so one of the major aspects of this design is to demonstrate the
formation of mathematical models of various mechanical components - bits and pieces such as
shafts, spring, welds, bearings and the like, which are assembled into machine for transforming
mechanical power outside the human performance envelope. These models may be analysed to
predict the prototypes' behaviour and safety before they are built, and in conjunction with sketches
enable component design to be carried out. It must be appreciated that the techniques of
(mathematical) model building which are introduced in the context of one particular component
are usually applicable to many other components which cannot be considered in the design, and
therefore the design emphasis is as much on how we arrive at a result as on what that result is.

 Safety factor
A component subjected to a solitary load will be considered in the first instance. There
are two completely different manifestations of the load, which have important
consequences for the component:
 the extrinsic actual load is the load exerted on the component by its surrounds,
and

19

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

 The intrinsic maximum load is the largest load that the component can withstand
without failure; the maximum load is a property of the component, a function of
its dimensions and material.

5.3.1 Design matrix

The Design Matrix allows additional constraints to be placed on the real parameter
estimates through the definition of the beta parameters, or to specify individual
covariates to be included in the model. The best way to explain the use of the Design
Matrix is to illustrate its use.
Beta parameters are parameters that are estimated directly in the likelihood function
based on the columns of the design matrix. Each column of the design matrix causes a
beta parameter to be estimated. Each row of the design matrix generates a real parameter
estimate. Derived parameters are parameter estimates that are derived from either the
real parameter estimates or the beta parameter estimates.
Real parameters are parameters that are estimated through the likelihood function based
on the rows of the design matrix.
To weigh up using the derived parameters assigned a rank from (1-5) points.

 Lifting mechanism for the mould board

Concept A:
Using U-shape steels for the carriage of mould board sliding over the RHS fixed
support.

Concept B:
Using the circular hollow cylinder for carriage of mould board and sliding over the
fixed circular hollow or solid cylinder.

Concept C:
Using U-shape steels for guide of sliding to the metallic flat bar which the carriage of
mould board over it.

Concept D:
The rope and two pulley mechanism for the lifting of mould board.

Table 5.3.1.1
Design Material Manufacturing assembly maintenance operation strength total
matrix availability feasibility
concept A 5 4 4 5 5 5 28
concept B 5 5 5 5 5 5 30
20

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

concept C 5 5 5 5 5 4 29
concept D 3 4 4 3 3 5 22

There fore concept B was chosen.

 Lifting mechanism for the impactor assembly

Concept A:
The pin attachment is on the external additional weld element (RHS)

Concept B:
The pin attachment is direct on the fixed structure of the machine.

Table 5.3.1.2
Design Material Manufacturing assembly maintenance operation strength total
matrix availability feasibility
conceptA 5 5 5 5 5 5 30
concept B 5 5 5 5 4 5 29

There fore concept B was chosen.

 Mechanism for take off product

Concept A:
The sliding mechanism, this concept is sliding the wooden carriage over vibrator plate
assembly to the collector.

Concept B:
Simply take the concrete block from the vibrator plate by manual.

Concept C:
Using the four bar mechanism, the top element (vibrator plate) will no change the
angle it keep its horizontal surface after and before sliding.

Table 5.3.1.3

Design Material Manufacturing assembly maintenance operation strength total

matrix availability feasibility
concept 4 3 3 3 5 5 23
A
concept 5 5 5 5 1 5 26
B
21

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

Concept - 4 4 4 4 4 20
C

According to the result concept B was selected.

 The element linkage mechanism

Figure5.3.1. 1 for concept A, B, C respectively

Concept A:
Using RHS

Concept B:
Using fabrication metallic bars, bolts and nuts instead of pins

Concept C:
Using casting

Table 5.3.1.4

Design Material Manufacturing assembly maintenance cost strength total

matrix availability feasibility
concept 5 4 5 4 3 5 26
A
concept 5 5 5 5 5 5 30
B
Concept 5 3 5 5 2 5 25
C

According to the result concept B was selected.

 Mechanisms for he source of vibration

In this design there are two types of vibration sources.

Concept A:
Using the eccentric circular cam

22

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

The eccentric circular cam is one of the simplest cams used to produce the simple
harmonic motion. The shape of the cam is perfect circle, and the offset distance for the
cam shaft is equal to one-half the follower displacement. Since this type of cam does not
provide a dwell period, it can use for vibration application.
In the design of HCBPM the follower has flat surface and the eccentric cam is not a plate
shaft.

Vibrator plate

Shaft
Eccentric cam

Figure5.3.1.2 eccentric cam and shaft

23

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

Figure5.3.1.3 displacement diagram of the follower

Concept B:
Using the attachment of unbalanced mass

If the cause of vibration is unbalanced mass attached to the shaft like fig below.

Figure5.3.1. 2unbalanced mass attached to the shaft like

Design Material Manufacturing assembly maintenance operation strength total

matrix availability feasibility
concept A 2 3 2 3 2 2 14
concept B 5 5 5 5 5 5 30

According to the result concept B was selected.

24

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

5.3.2 Design analysis

 Motion analysis for the eccentric circular cam

25

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

MODELING

M eq X (t)

Y (t)
Base excitation by simple harmonic motion (SHM)
Figure 5.3.2.1 Base excitation by
simple harmonic motion (SHM)
model mass and spring system

This problem has two solutions

 For the complementary function
 For the particular integral

26

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

Figure 5.3.2.2 Figure 1vibration response

It need time extra study as an alternative this way could be analysed.

 Using the attachment of unbalanced mass

If the cause of vibration is unbalanced mass attached to the shaft like fig below.

Figure 5.3.2.3 unbalanced mass attached to the shaft like

27

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

This is way Concept B is chosen.

5.3.2.1 Design of belt

The last 50 years have brought rubber belt drives to high state of technological requirement. The
result is higher, more compact drive capable of carrying higher load at low cost.

V –BELT

V-belt remains the basic workhorse of industry, available from virtually every distributor and
adaptable to practically any drives. They are presently available in a wade variety of standardized
sizes and types for transmitting almost any amount of load power. Normally v-belt derives operate
best at belt speeds between (8-30m/s). For standard belts, ideal (peak capacity) speed is
approximately 23m/s, narrow v-belt, however, will operate up to 50m/s

Figure5.3.2.1.1 cross section of v-

belt and pulley [7]
28

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

 Limitations
Because they are subjected to a certain amount of creep and slip, v-belt should not be used where
synchronous speeds are required.
 Standard geometric dimensions
Cross section industrial and agricultural v-belt is always made to standard cross section.V-belt
drives are essentially short centre drives. If in drive design the centre distance C is not
specified, preferably not less than D2. Since the diameters and belt length are discrete
variables so also is the theoretical centre distance, though in the absence of idlers the
nominally fixed centre distance must be capable of slight variation by motor slide rails for
example, to allow for belt installation and subsequent take-up (initial tightening) before
rotation commences. This capability also allows for manufacturing tolerances on belt
length, L. From the geometry:-

This is used to find the belt length, L, for given centre distance, C (and pulley diameters).
Conversely, to find the centre distance corresponding to a certain belt length must be
solved iteratively - a very close first approximation is given by:-

The wrap angle (or "arc of contact") on each pulley is evidently π.

Any particular cross-section of the belt traverses alternately the slack and tight strands
and is subject to bending when in way of one of the pulleys.

This relation specifies the maximum ratio of belt tensions which given belt/pulley
interfaces can support without gross slip. The ρv2 term, often conveniently if erroneously
referred to as the centrifugal tension, detracts from the interface's useful tension ratio
capabilities. It is convenient to define f ≡ μ∗cosec β as the effective coefficient of
friction which reflects the amplification of the actual coefficient μ by wedging action in
the groove of angle β.
29

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

A drive comprises two pulleys, potentially with different values of μ, β, and θ -

although the slack and tight strand tensions are common to both pulleys. The maximum
tension ratio which the drive can support without slip on either of the two pulleys is
therefore:

(F max - ρv2) / ( F min - ρv2 ) ≤ e ( f θ)

min

where f ≡ μ ∗ cosecβ and ( f θ)min = min ( (fθ)1 , (fθ)2 )

A representative coefficient of friction is 1/6, and this together with a wedge angle 2β =
38o and a wrap angle of 180o in a 1:1 drive, corresponds to a static tension ratio

F max /F min = e0.512π = 5.0

 Industrial v-belt

These are made in two types: heavy duty (convectional narrow) and light duty.
Convectional belts are available in A, B, C, D and E sections.
 Length- although endless v-belt can be manufactured in any length with in a fairly
wide range, manufacturers have standardized on a certain length that are
produced for shock.

V-belt specification:

o A 3.4KWmotor running at 2800rpm used to drive multi- hollow concrete block

producing machine. The machine is operating 10 and under hours per day.
o No speed redaction i.e. D2/D1=1
o Center distance was selected to be 160mm

Analysis

We first make the following decisions.

 An over all load service factor is 1.4 which is heavy shock and normal torque.
 A –belt was selected using power and angular velocity from figure 1.
 ƒ is 0.512.
 F=3216N, M=2393Nm, ρ=.09682kg/m, 11= ∆mm, Lo=1717mm from table 2.

P*=Ks P
=1.4x3.4
30

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

=7.6KW

=
But, it has been found that for the efficient transmition of power the belt speed should be
(20-22.5m/s) taking 20m/s.

=136.4mm

The recommended pulley pitch diameter 140mm from the standard size.

=20.52m/s
Then:
L=
= π140 + 2x160
= 759.82mm
From the standard the nearest value for A-type is 790mm.Then C=175mm.

From table of power rating of A-section v-belt is 4.13KW at a belt speed greater than
20m/s and shaft speed of 2800rpm.additional power for speed ratio1:1is 0KW.
The total power rating per belt is 4.13KW. The total power rating per belt is must be
corrected for contact angle and belt length, the correction factors are1and 0.83
respectively.

P=.83x1x4.13
=3.4279KW

Then the number of belts required is,

=1.388 belts
31

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

Two belts be specified

We know also

=144.32N

=61.47N

5.3.2.2 Design of pulley

As the belt passes around the pulley, it flexes, and bending stresses are induced as a
result of the reduced radius of curvature, bending stresses are higher for small
pulley .because of the reduced fatigue stresses, a large pulley result in an increased belt
life. Pulley should not be so large, however, as to cause excessive belt speeds.

Pulleys are usually used cast iron material. If there is no availability it is better to use
machined aluminum pulley. Since aluminum is available and easy to machine.
Pulley:
 The type of pulley is V-grooved
 Number of grooves on the pulley are two
 The power rating per belt is 4.13KW
 β=380

If cast iron is available:

From standard for A-belt groove pulley

32

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

= 15(1) +2x10
=35mm
For aluminum pulley: It is better to approximate

Note: Take B=100mm it is determined due to the key length.

Figure 5.3.2.1.1 cross section of

pulley

5.3.2.3 Design of shaft

Continuous mechanical power is usually transmitted along and between rotating shafts.
The transfer between shafts is accomplished by gears, belts, chains or other similar means
for matching the torque/speed characteristics of the interconnected shafts - e.g. A
H.C.B.P.M needs belt between the electric motor drive and driven pulley-shafts.
33

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

The shafts rotating at constant speed n (rev/m) are considered here, and as shafts are usually
statically determinate they examined by the techniques of elementary statics. Also, since
 power = force ( N) ∗ linear velocity ( m/s) in translational applications and
 power = torque ( Nm) ∗ angular velocity ( = 2π n rad/s) in rotational applications,
Then it follows that torque is a major load component in power transmitting rotating
shafts.

Torque may be transferred to or from the end of one shaft by a second coaxial shaft - this
is a pure torque, a twist about the shaft axis.

The shaft carries the two unbalance mass or eccentric circular cam, pulley and bearing.
The motor drive the belt and the belt drives the shaft pulley, which is keyed to the
rotating shaft.

Figure 5.3.2.2.1 bending and reaction force diagram

M A =0
 205.79 x 280+1547.55x100=200R B
 R B  1061.88 N
there  ore :
RA  1753.34 N  R B
RA  691.46 N 34
M C  Rof
Design A x.01m
CBPM By: Haftay Atsbeha
M C  year
Final 69.146 Nm
project ibgmf@yahoo.com
M B  205.79 Nx.08m
M B  16.4632 Nm
 MU Mechanical Engineering Department

Since the torque on both belts are the same

35

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

5.3.2.4 Design of key

A key is a piece of steel lying partly in a groove in the shaft and extending in to another
groove in the hub. The groove in the shaft is referred to as a key seat, while the groove in
the pulley or surrounding part is referred to as a key way. A key is used to secure gears,
pulley, cranks, handles and similar machine parts to shaft, so that motion of the part with
out slippage.

Figure 5.3.2.3.1 key assembly

36

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

There are many kinds of keys. The most common types are square and flat keys are
widely used in industry. For this case the square key was selected because of equally
strong in shear and crushing.

=144.32N+1547.55N
=1630.4N

(i) Considering shear of the key

(ii) Considering the crushing of the key, the tangential crushing force of key is Ftot.

………………. (1)

(iii) The tensional shear strength of the shaft is

…………… (2)

Equating (1) and (2)

For both shafts l=94mm say 100mm

37

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

5.3.2.5 Bearing selection

Machine designers have a large variety of bearing types and size from which to choose, each of
these types have characteristics that make if best for a certain application. Roller bearing was
selected because roller bearing is more satisfactory under shock or impact load than ball bearing
and less expensive.

Cylindrical roller bearing is applicable in the design, and has high radial capacity and provides
accurate guidance to the rollers, their low friction permits operation at high speed.

Dimensional selection depends on the diameter of the shaft.

From table 4
d=30mm
D=62mm
B=20mm
r=1.5mm
r1=1mm
F=38.5mm
Maximum permissible speed=13000rpm

Figure 5.3.2.3.1 Nomenclature of bearing

5.3.2.6 Design of spring

A is defined as an elastic body, whose function is to distort when loaded and to recover its original
shape when the load is removed. There are many various important application of spring like to
cushion, absorb or control energy due to either shock or vibration as in the Hollow Concrete Block
Producing Machine (H.C.B.P.M) and car.

There are many types of spring like coil, volute, bar, flat, leaf and Belleville. From the above
different types of spring coil spring was selected .coil spring may be tortional, power, compression
and extension. But compression coil spring is applicable in the H.C.B.P.M. there are also many
types of ends of compression coil spring, in this design it was selected the square and ground end
to holed the vibrator horizontally and with maximum stability.
38

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

Spring nomenclature

Figure5.3.2.4.1compression coil
spring [7]

 Material for the helical compression sprig

The material of the spring should have high fatigue strength, high
durability, high resilience, it should be creep resistance and they are
used for sever service.

 Specification of the compression coil spring

Figure 5.3.2.4.2spring nomenclature [7]
F=1393.02N of the total load

The velocity of the vibrator shaft is around 4.39m/s.

Assuming the load is distributed equally in to the individual spring i.e. Fi=139.302N

Where c (spring index) =D/d and n=№ of active turns

(1) diameter of the spring wire

We know that the kinetic energy of the vibrator is

39

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

Let F’ be the equivalent load which when applied gradually on each spring causing a deflection
of 40mm since there are ten springs therefore energy stored in the springs.

We know that the torque transmitted by the spring

T=F’D/2 but D = c x d = 4d
= 2F’d
We also know the torque transmitted by the spring

Equating the two equations

(2) number of the turns of the spring coil

Say n=4

(3) free length of the spring

(4) pitch of the coil

40

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

5.3.2.7 Design of bolt

Bolt is required at the impactor; the bolts are under tension due to the load of the impactor. Four
bolts are specified and the weight of the impactor is around 300N so each bolt is carry 75N.

Mild steel bolts was selected having tensile stress as t=56MPa

A free body of the nut and bolt demonstrates that the external load on them is the force P
or F due to contact over annular areas with the two fastened components.

Figure5.3.2.5.1 free body diagram of bolt ,nut and impactor assembly[7]

Although minimum diameter of bolt can with stand to carry the impactor .the bolt is
assembled and disassembled every time to change the different types of impactors and it
is under dynamic so it was selected M14 of bolt it is good resistive to the damage of the
tooth.

5.3.2.8 Design of pins and link levers (cotter joint)

Considering the pin (bolt and nut) which attaches the carriage of the mould, and the link
lever, Selecting suitable dimensions for the separable cotter joint illustrated, which
transmits a tensile load, F. The allowable stresses, τ in shear σ t in tension and σ c in crush,
are known for each ductile component.

41

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

Figure5.3.2.6.1 cotter joint[7]

The first step is to evaluate the external effects on each component - then, for each component,
the force paths can be traced, the possible modes of failure identified and the corresponding design
equations applied. To illustrate the technique, we shall consider only the left component; the right
component is very similar. The joint is statically determinate, so the free body of the component
with simplified lines of force will be as shown in Figure A below.

Figure 5.3.2.6.2 Some of the failure modes[7]

81N 325.25N

F=406.25N

42

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

The safe value of d and t are concluded from the above calculations.
There fore say d is 10mm and t is 15mm.

4mmm

d +2t

Figure 5.3.2.6.3 lever arm

We know that all the linkages required less than the calculated values because of the low rest
linkages are subjected lower forces. That means it is safe to take a material with the above
dimension.

43

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

COST ESTIMATION

The visibility of the machine is dependent on the total cost of the machine which is the
variable cost and fixed cost. Estimation of the cost or the total expenses for manufacturing
the machine is significant. Cost may be material, process (labour, machine) and time.
Labour cost (daily worker, qualified worker) is for welding, cutting bending, and
machining.

Material cost

 Bolts, there are 28bolts and nuts with M12x1.75

The cost per piece is 3birr
Total cost is 98 birr
Bolts, there are 22bolts and nuts with M8x1.25
The cost per piece is 2.5birr
Total cost is 55 birr
Cost for bolt 153 birr
 For angle iron in the market there is 6000x30x30x3 it costs 40 birr so the total cost
estimated in this case is 120 birr.
 Bearing there are four bearings each costs 40 birr totally 160 birr.
 Spring, there are ten springs costs 35 birr for each totally 350 birr.
 Motor having the running power of 3.4KW at 2800 rpm costs 1800 birr.
 Solid round bar it costs 70 birr.
 Hollow round bar is costs 40 birr.
 Flat bar there are many different sizes for all it is assumed that it costs for 120 birr.
 Belt 45birr per piece totally 90 birr.
 RHS(rectangular hollow section) 60000x30x30x3 it costs 40 birr for the total
assembly it is approximated 80 birr.
 Lath machine Aluminum pulley it costs 150 birr per piece totally 300birr.
 Key is costs 12 birr.
 Arc welding electrode it is required 4 boxes totally it costs 44 birr.
 Circlipe there are 8 in number 4birr for each totally it costs 32 birr.
 Wooden carriage it costs for 50 birr.
 Shaft it is solid round bar it costs 100 birr.

Process cost

For The manufacturing of the machine it is assumed that it take 32 hours.

 Labour cost
Two daily workers 20 birr per each totally 120 birr, and two qualified worker (certified
welder) 50 birr per each totally 300 birr.
 Machine cost

44

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

For the manufacturing of the machine there are many machine required, just like welder,
grinder, bender, roller, cutter, if so lath machine and so on. It is assumed that it would
take 300 birr.

The total machine cost is then 4241birr

ASSEMBLY TIP

After the concrete block machine parts are fully manufactured the way of assembly
follows with procedure .The core to assemble is the structural frame which guides the
assembly steps, the assembly procedure has two parts, assembly of accessories and
assembly of lifting mechanism.
 Put the springs over the angle iron at the right position of spring.
 Place the vibrator plate over the spring then bolt with the vibrator assembly.
The second stage of assembly is assembling the lifting mechanism,
 Assemble the mould lifter over the wooden concrete carriage. After the vibrator
assembly is bolted to the vibrator plate.
 Assemble the impactor lifter to the impactor holder.
The vibrator assembly is assembled as follows:
 Assemble independently the vibrator assembly one by one.
 Insert the shaft to the casing then the bearing holder after that the bearing, lastly
bolt the bearing cover to the casing and the bearing holder.
 the independent vibrator assembly should assembled to the pulley with help of
key ,then insert the belt,
 Lastly bolt the two assemblies with the vibrator plate.
The belt is attached to the two pulleys (motor and vibrator) and slide the motor till the
keep tightness of the belt, to do so slide the motor over the slider then after bolt the motor
to make is fixed over the structure.

45

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

LIMITATION

Though there are many facilities of materials and finance, for the success of full design
the hollow concrete block producing machine, there are limitations just like full survey of
the existing technology in our home country, shortage of time. Infact these limitations
have influence in the project work.

46

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

CONCLUSION

The delivery system of low-income housing projects can be vastly improved by

considering options for alternative design and materials. The project considers on
choice of design and materials as arriving at, the optimal and efficient design. The new
design is alternative concepts to provide the optimal design. A less expensive and less
complex machine would be more amenable to local production and small-scale capital
investment. These are the areas where hollow concrete block production technology
needs to be taken and dynamic compaction shows promise. Working with this
alternatives play an important role in the economic development path for construction
sector.

47

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

RECOMMENDATION

The co-operation amongst institutions and governmental organizations should Increase to access
information, education and finance support. Technical sustainability, such as energy efficiency,
diversification, control, impacts on nature and health, should receive more attention in order to the
way development. Secure a common understanding (professionals, politicians, authorities, users,
etc.) of the definitions of "adequate house", structural stability, safety and control to achieve a
quality structure. Authorities should initiate programs to produce materials and structures locally in
order to create jobs. Finally I will recommend that any concerned person has to provide available
material property to any project work.

48

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

APPENDICES

Table 2 v-belt and pulley dimension

Minimum pitch diameter

Belt section Width(mm) Thickness(mm) of the pulley (mm)
A 13 8 125

Table3 bearing standard dimensions

(DESIGN DATA PSG College of Technology Combatore, DPV
printers)

Maximum permissible
d D B r r1 F Speed (rpm)
25 52 18 1.5 1 32 13000
30 62 20 1.5 1 38.5 13000
35 72 23 1 1 43.8 10000

Figure 1standard cross-sectional

Table 4 values of factor of safety (gupta)
Material Steady load Live load Shock load
steel 4 8 12 to16
Wrought iron 4 7 10 to 15
Cast iron 5 to 6 8 to 12 16 to 20
Soft material and alloy 6 9 15

49

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com
 MU Mechanical Engineering Department

REFERENCE:

[1]. Concrete Masonry Association of Australia

Table of contents.doc

[2]. Agevi, E. (1999) "Technology Dissemination in Kenya", Development

Alternatives Newsletter, Vol: 9 (11), 7-9.

[3]. Kerali, A. G. (2001) Durability of Compressed and Cement-Stabilised Building

Blocks, University of Warwick, UK

[4]. Mumbai, L., Mertens de Wilmars, A., & Tirlocq, J. (2000) "Performance
Characteristics of lateritic soil bricks fired at low temperatures: a case

[5]. University of Warwick, School of Engineering, January 2002

http://www.eng.warwick.ac.uk/dtu/pubs/rn/build/demthesis.pdf
[6].Houben, Hugo and Guillaud, Hubert Earth Construction: A Comprehensive
Guide, Intermediate Technology Publications, UK.

[7].Department of Mechanical and Materials Engineering, The University of Western

Australia Notes on DESIGN AND ANALYSIS OF MACHINE ELEMENTS
doug@mech.uwa.edu.au

[8] CECIL JENSEN AND JAY D.ELSEN, Engineering Drawing and Design, fifth edition,
New York, MC Graw-Hill

[9] RS.KHURMI AND J.K.GUPTA, A Text of Machine Design, New Delhi, 2002

[10] DESIGN DATA PSG College of Technology Combatore, DPV printers

[11] Habitat, 2001a, United Nation Human Settlement: State of world's city - 2001, "Urban
settlements: housing", http://www.unchs.org/documents (2001-11-28)
[12] Habitat, 2001b, United Nation Human Settlement:” Urban population trends",
http://www.unchs.org/
hd/hdv7n2/index.htm

50

Design of CBPM By: Haftay Atsbeha

Final year project ibgmf@yahoo.com