Chapter 4
Factories and Industrial Undertakings (Abrasive Wheels) Regulations
Abrasive Wheels
Abrasive wheels (火石碌, “AW”) are used extensively in industries for grinding
of tools such as cutters and drill bits.
Bursting of Wheels
• Defective wheel
• Over-speeding
• Faulty mounting
• Misuse, including grinding on the side instead of the perimeter of the wheel
• Other dangers include contact with the wheel and injury to the eyes from
flying particles
Interpretation
An AW that is regulated under this piece of legislation needs to be power driven.
Hence, a manual foot-operated grinding wheel (for sharpening of kitchen choppers)
is not within the purview of this Regulation. An AW must also contain abrasive
material. Hence, a buffing wheel does not contain any abrasive material and is
hence not considered an AW.
Abrasive
An abrasive is a material, often a mineral, that is used to shape or finish a
workpiece through rubbing which leads to part of the workpiece being worn away
by friction. While finishing a material often means polishing it to gain a smooth,
reflective surface, the process can also involve roughening as in satin, matte or
beaded finishes. In short, the ceramics which are used to cut, grind and polish
other softer materials are known as abrasives.
Application
Apart from grinding, some AW, such as abrasive cutters, are used for cutting,
which, according to the definition of AW, is a legitimate use and not misuse.
This is also true for a portable grinder used for cutting cleats (栓), though by its
very name, it is also used for grinding.
Speed of AW
A reduction in diameter could be the result of wear and tear.
Increased speed in rpm = original speed in rpm x original dia. / reduced dia.
The maximum permissible speed of a wheel may also change upon the aging of the
bonding material of the wheel after prolonged use. The manufacturer or supplier
should be consulted in case of doubt.
Pneumatic AW
A suitable pressure reducing regulator shall be fitted between the governor (限速
器) and the air supply outlet if the working pressure of the outlet is greater than
that of the grinding machine. Where a filter is incorporated in the air supply
system, it should be properly maintained to prevent clogging by dust or grits. To
prevent accidents caused by snaking hoses when severed under high pressure of
air, it is also recommended that an automatic hose brake valve be fitted to the hose
before joining the grinder.
Mounting
• A wheel should not be mounted on a machine for which it is not intended
and certainly not on any makeshift (臨時) apparatus or where there is
vibration of the machine
• The soundness of the wheel should be checked before it is mounted
• Washers, either paper or other compressible material, should be used with
all bonded abrasive wheels, except tapered wheels, threaded-hole wheels,
discs, cylinder wheels, and the hub section of depressed-centre wheels
• Washers should be slightly larger than the flanges and there should be no
wrinkles in them
• The bush (軸襯), if any, should not project beyond the sides of the wheel
• The wheel should fit freely but not loosely on the spindle
• Clamping nuts and screws should be tightened uniformly in pattern formation
(diametrical sequence) and only sufficiently to hold the wheel firmly
• Screws for inserted nuts for the mounting of discs, cylinders or cones should
be long enough to engage a sufficient length of thread, but no so long as to
contact the abrasive material
• When re-mounting factory-mounted wheels and points, the overhang for a
particular diameter of mandrel, speed and size of a wheel should not be
exceeded. Also there should be sufficient length of the mandrel in the
collet or chuck. The manufacturer should be consulted for details of
overhang permissible for a particular wheel
• For depressed-centre wheels, when the adaptor has been tightened, there
should be a slight clearance between the flange and the wheel to ensure that
the clamping pressure is exerted only at the centre of the hub centre. The
outer part of the face of the flange adjacent to the wheel should be tapered to
allow the full width of the flange to support the wheel during the grinding
operation
Depressed-centre Wheels
Depressed center wheels (also known as raised hub wheels) are designed to handle
tough right angle grinding applications on metal, masonry and other building
materials. Wheels are designated by shape “type”. Available in various grit and
abrasive options, these wheels cut, grind, remove stock, chamfer edges, bevel and
blend with aggressive cut rate and long life.
Competent Person
All mountings shall only be done by CPs appointed in writing by the proprietors.
CPs should be well trained and have the practical experience in the mounting job.
Construction and Maintenance of Guards
The guard should be of rigid construction, proper dimensions and securely
anchored to the machine frame. It also serves to prevent an oversized wheel from
being fitted.
Tapered Wheels
Where the work which is ordinarily done at any AW requires that the exposed
area of the wheel shall exceed 180 degrees measured at the centre of the wheel
then, where practicable, the wheel shall be tapered from its centre towards its
periphery by at least 6 per cent on each side and shall be mounted between
suitable protection flanges.
Protection Flanges
• The diameter of flanges should according to the diameter of the wheels and
their bearing surfaces should be true and free from burrs
• With the exception of the single flange used for threaded-hole wheels, all
flanges should be properly recessed or undercut
• Flanges on both sides of the wheel should have the same outside diameter
and diameter of recess
Selection of AW
In case of doubt, the manufacturer may be consulted on the proper type of wheels
to suit a particular job. Generally, soft wheels are more suitable for hard
materials and hard wheels for soft materials. Defective wheels should not be used.
Ring Test
The soundness of wheels can be checked by a “ring test” (suspend the wheel
vertically and tap the two opposing positions on the same side of the wheel with a
light non-metallic tool, such as a wooden screwdriver handle). A clear sound
indicates that the wheel is healthy.
Storage of AW
Wheels should be kept dry, not exposed to extreme temperatures and be stored
properly in suitable racks.
Machine Controls
This concerns fitting an emergency stop switch to the wheel.
Rest
For bench and floor stand grinders, the clearance between the work-rest and the
wheel should not exceed 3.2 mm (1/8 inch). Lack of adjustment is the cause of
many serious accidents in that the workpiece is jammed between the wheel and the
work-rest which may force the operator’s fingers against the wheel face.
Warning Notice
When operating an AW, an approved warning notice must be posted in the
vicinity.
Condition of Floor
The floor should be even and clear of material to avoid slipping, tripping and
falling on the machine.
Responsibilities of Employees
Some operators take the guard down and grind at the side of the AW. This
weakens the integrity and uniformity of the wheel and may result in the shattering
of the wheel. An unbalanced wheel should be properly trued and dressed, or
disposed of if truing and dressing cannot provide a useful remedy.
Safety and the Operator
• Do not grind on the sides of straight-sided wheels
• Install protective screen or wear eye protectors
• Do not apply sudden pressure to the wheel
• Do not allow the wheel to revolve unattended
• The wheel should be trued or dressed when necessary to remove loading or
glazing at the wheel surface, both of which reduce the cutting action.
Eccentric force (離心力) will be created at wheels used for hand grinding
rendering them out of balance if not trued, and if the force becomes excessive,
it may damage the spindle and cause the wheel to burst
Exception
There has also been a general consensus that the F&IU (Abrasive Wheels)
Regulations is NOT applicable to a portable grinder or cutter (when the abrasive
disc is replaced by a stainless-steel disc used for cutting aluminium strips or angle-
iron, or cutting wood. However, the exception in Regulation 4(4) of this piece of
regulation is only applicable to a portable grinder that is manufactured of rubber.
Employee
Means a person who in an industrial undertaking is employed in using any
abrasive wheel in any grinding or cutting operation.
Mounted Wheel or Point (端點)
Means a wheel or point consisting in either case of abrasive particles held together
by mineral, metallic or organic bonds whether natural or artificial and securely
and permanently mounted on the end of a mandrel (心軸) or quill (套筒軸).
Overhang (外露軸段)
In relation to a mounted wheel or point, means that part of the mandrel or quill
which is exposed between the collet in which the mandrel or quill is held and the
part of the abrasive material nearest to that collet (筒夾).
Application
The F&IU (AW) Regulations shall apply to any abrasive wheel used for any
grinding or cutting operation in any IU.
Exemption
• Manufactured of metal, wood or rubber and having any surface consisting
wholly or partly of abrasive material
• Which does not exceed 235 mm in diameter, is manufactured of rubber and
has any surface consisting wholly or partly of abrasive material, when that
abrasive wheel is used n a portable machine
• Having separate segments of abrasive material
• Not apply to any wheel, disc or saw to any surface of which, in each case, is
attached a rim or segments consisting of diameter abrasive particles
Speeds of Spindles
Mounting
Provision of Guards
A guard shall be provided and kept in position at every AW in motion except
where, by reason of the work being done, or of the work which is ordinarily done,
or the nature of the wheel, the use of a guard is impracticable.
Guard
• So far as is reasonably practicable, be of such design and construction as to
contain every part of the AW in the event of fracture of the abrasive wheel
or any part thereof occurring while the AW is in motion
• Be properly maintained and so secured as to prevent its displacement in the
event of fracture
• Enclose the whole of the AW except such part as is necessarily exposed for the
purpose of work being done at that AW or, where a guard which is not
adjustable is used, for the purpose of the work which is ordinarily done thereat
Selection of AW
All practicable steps shall be taken to ensure that any AW used is suitable for the
work for which it is used to the extent necessary to reduce the risk of injury to
employees.
Machine Controls
No AW shall be used in a machine unless the machine is provided with an
efficient device for starting and cutting off the power to the machine and the
control of the device shall be in such a position and of such design and
construction as to the readily and conveniently operated by the person operating
the machine.
Rest
• Where at an abrasive wheel there is a rest for supporting a workpiece, that
rest shall at all times while the wheel is in motion be properly secured and
adjusted so as to be as close as practicable to the exposed part of the AW
• Every rest shall be of substantial construction and properly maintained
Warning Notice
A warning notice, in English and Chinese and in a form approved by the
Commissioner, concerning the dangers arising from the use of AW and the
precautions to be observed shall be affixed in every room in which grinding and
cutting by means of AW is ordinarily carried out, or, where such grinding or
cutting is not ordinarily carried out in a room, at a place and in such a position
where it may be easily read by employees.
Condition of Floors
• The floor immediately surrounding every fixed machine on which an AW is,
or is intended to be mounted shall be maintained in good and even condition
and shall, so far as practicable, be kept clear of loose material and prevented
from becoming slippery
• All reasonably practicable steps shall be taken to ensure that the floor of any
room or place in which any portable machine on which an AW is mounted is
in good and even condition, is kept clear of loose material and is prevented
from becoming slippery
Responsibilities of Employees
• No employee shall willfully misuse or remove any guard, or willfully misuse
any protection flange, machine control, governor or other device provided in
pursuance of the F&IU (AW) Regulations or any rest for a workpiece
• Every employee shall make full and proper use of guards, protection flanges,
machine controls, governors and other devices provided in pursuance of the
F&IU (AW) Regulations and of rests for work-pieces and if he discovers
any defect in the same shall forthwith report such defect to the proprietor
