HARVESTING AND THRESHING MACHINERY

Harvesting – process of gathering the useful portion of the crop from the field.
Threshing – process of separating the grains from the straw. Additionally, it may include
cleaning the grains.
Systems of harvesting and threshing of rice:

Manual harvesting Manual threshing

 Use of hand tools: sickle,  Use of flails or sticks
scythe, yatab  Hampasan
 80 – 160 man-hrs/ha  Foot threshing
 Animal treading
 140 – 220 man-hrs/ha

Field losses = 5 – 16 %
Manual harvesting Mechanized threshing
 Same as above  Use of pedal thresher at 100 man-hrs/ha
 Power thresher at 12 man-hrs/ha
Field losses = 3 – 10 %
Mechanical harvesting Mechanical Threshing
 Use of manually operated  Same as above
harvester at 50 man-hrs/ha
 Power harvester at 5 man-
hrs/ha

Field losses = 3 – 6 %
Combine harvesting – both operations done by a single machine-combine
 3 – 21 man-hrs/ha
 Field losses – 1.5 – 6 %
Stripping harvesting – removal of grains from panicle without cutting the straw –
stripper
 3 – 21 man-hrs/ha
 Field losses – 2 – 6 %

Fig. 1. Traditional harvesting, threshing, and cleaning

 Operations done by a combine and stripper
COMBINE STRIPPER
1. Separating the rows 1. Separating the rows
2. Cutting the standing crop 2. Stripping
3. Conveying the cut materials 3. Cleaning the grains
into the threshing section 4. Conveying the grains to the
4. Shaking the straw to separate tank or sack
loose grains from the straw
5. Cleaning the grains of chaff
6. Conveying the grains to the
tank or sack

 Factors affecting the choice of system

o Kind of crop
o Timeliness of operation
o Topography
o Farm size
o Type of culture (row or broadcasted, upland or lowland)
o Availability and cost of labor
o Availability of capital
 A major factor affecting choice of system is timeliness of operation because it
affects field losses, time available for the next crop and grain quality.

Time of harvesting Field losses (%)

 One week before maturity  0.77
 At maturity  3.35
 One week after maturity  5.63
 Two weeks after maturity  8.64
 Three weeks after maturity  40.70
 Four weeks after maturity  60.46

 If the crop is harvested too early, it will have a large percentage of imperfectly
formed kernels
 The field should be drained 1 – 1.5 weeks before harvesting to harden the soil.

HARVESTING MACHINERY
 Groupings of harvesters:
1. Hand tools – include sickle, scythe, yatab, lingkao, and cradle (Figure 2)

Fig. 2. Harvesting hand tools

2. Reaper – windrower – a machine that cuts the standing crop, conveys the cut crop
to one side, and lays them down in an orderly manner (Figure 3).

Fig. 3. Reaper -windrower

3. Reaper – binder – a machine that cuts the standing crop, binds the cut crop and
lays down the bound crop to one side(Figure 4).

Fig. 4. Reaper – binder

 Cutting mechanisms:

1. Slicing/tearing action – employed in hand tools (Figure 5).

Slicing action Tearing action

(Sharp smooth edge) (Serrated edge)

Fig. 5. Slicing and tearing action

2. High velocity, single element, impact action – use of sharp or dull-edge blades
moving at high velocity of 2000 fpm to 9000 fpm (Figure 6).

Fig. 6. High velocity, single-element, impact action

3. Two-element, scissor type action – shearing action between the moving and
stationary blades (Figure 7).

Fig. 7. Double-element, Scissor type action

 THRESHING MACHINERY

 Methods of threshing
1. Rubbing action – grains are detached from their panicles because of a rubbing
action as in treading by man, animal and vehicle.
- Output of man treading is 14 kg/hr
2. Impact action – grains are accelerated faster than their panicles and are detached
as in hampasan and mechanical threshers.
- Output of hampasan is 34 kg/hr
- Output of mechanical threshers vary with size of machine and power source.
3. Stripping action – grains are detached from their panicles when a straw is pulled
through a “V” configuration or a comb – like device is passed through the
panicles.

 Mechanical threshers:
o Mechanical threshers employ the impact action
o Variability of threshers came from:
1. Power source – manual as in pedal thresher or power thresher as in engine-
driven thresher.

Figure 8. Pedal thresher

Figure 9. Power thresher

2. Type of feeding:

a. Hold-on feeding – straws don’t pass through the threshing section

(Figure 10)

i. Low power requirement

ii. Lightweight construction
iii. Examples: pedal thresher and Japanese combine

Figure 10. Hold-on feeding type of thresher

b. Throw-in feeding – Straws pass through the threshing section (Figure

11).

i. High power requirement

ii. Heavyweight construction
iii. Examples: Axial – flow thresher and US combine

Figure 11. Throw-in feeding type of thresher

3. Direction of threshing materials (Figure 12):

a. Tangential-flow – Materials are fed between the revolving cylinder

and stationary concave and go straight out of the thresher tangentially.
i. About 60% of the grains pass through the concave and the rest
are separated in subsequent operations.

b. Axial-flow – Materials are fed between the revolving cylinder and

stationary concave on one end, go around the cylinder several times
axially and discharge at the other end.
 i. About 90% of the grains are separated from the straw at the
cylinder.

Figure 12. Flow of materials

4. Types of cylinder teeth (Figure 13):

a. Wire-loop
b. Peg-tooth
c. Rasp-bar

Figure 13. types of threshing teeth

 Cleaning systems:
o Separation of the bulky straw, chaff, empty kernels and very light
impurities from the grains.
o Light materials can be separated from the grains by winnowing using
natural wind or blower.
o For hold-on threshers, straws do not pass through the thresher and only the
removal of the chaff and light materials are needed using blowers and
screens
o For throw-in threshers, straws pass through the thresher and cleaning is
done using a straw walker, blower and screens.
Sample Problem 1.
A 5-m self-propelled combine makes an average stop of 4 minutes every time its
2-ton grain tank is to be unloaded. The yield of the 20-ha field is 40 tons. The operating
speed is 4.8 kph. The time for turning on the headland at the ends of the 500-m field is 15
seconds.
Find: a. theoretical field capacity
b. actual field capacity
c. Field efficiency

Solution:

a. Theoretical field capacity =

b. Actual field capacity = where,

A = 20 ha
T = t1 + t2 + t3 where
t1 = actual working time in the rows at 100%
efficiency
t2 = time for turning at headland
t3 = time for unloading of tank

c) Field efficiency =

Sample problem 2:

A 4-m combine travelling at 5 kph can empty its 1.64-ton grain tank in 60
seconds. When unloading on-the-go, it has 82% field efficiency. Field yield is 3 tons/ha.

Find: What would be the field efficiency if the combine stopped to unload?

Solution:

a. Unloading on-the-go:

Actual field capacity (on-the-go) =

b. No. of unloadings/hr =
 c. Time for unloading = t2 =

d. Eff =

e. New Eff =

PAES:

PAES 204:2000 Agricultural Machinery – Mechanical Rice Thresher – Specifications

PAES 205:2000 Agricultural Machinery – Mechanical Rice Thresher – Methods of Test
PAES 212:2004 Agricultural Machinery – Rice Reaper – Specifications
PAES 213:2004 Agricultural Machinery – Rice Reaper – Methods of Test