Safe Working Practices- Abrasive Wheel

SAFE WORKING PRACTICES:ABRASIVE WHEEL

Presentation Prepared by:Efren Echague

I. Introduction An Abrasive Wheel is a wheel consisting of an abrasive

particles bonded together with various substances. They are mounted to Grinding Machine before it can be used for the work intended for them.

The wheels are generally made from a matrix of coarse particles pressed and bonded together to form a solid, circular shape. Various profiles and cross sections are available depending on the intended usage for the wheel. They may also be made from a solid steel or aluminium disc with particles bonded to the surface.

SAFETY IN USING ABRASIVE WHEELS

A grinding machine, often shortened to grinder, is any of various power tools or machine tools used for grinding, which is a type of machine using an abrasive wheel as the cutting tool, Each grain of abrasive on the wheel's surface cuts a small chip from the workpiece via shear deformation.

Grinding is used to finish work pieces that must show high surface quality (e.g., low surface roughness) and high accuracy of shape and dimension.

Manufacture of these wheels is a precise and tightly controlled process, due not only to the inherent safety risks of a spinning disc, but also the composition and uniformity required to prevent the disc from exploding due to the high stresses produced during rotation.

Characteristics of an Abrasive WheelThere are five characteristics of an Abrasive wheel: material, grain size, wheel grade, grain spacing, and bond type. They will be indicated by codes on the wheel's label.1. MaterialThe actual abrasive material, is selected according to the hardness of the material being cut.• Aluminum Oxide(A)• Silicon Carbide (S) Ceramic (C) Diamond (D, MD, SD) Cubic Boron Nitride (B)

Grinding wheels with diamond or Cubic Boron Nitride (CBN) grains are called super abrasives. Grinding wheels with Aluminum Oxide (corundum), Silicon Carbide or Ceramic grains are called conventional abrasives.

2. Grain SizeGrain size, from 8 (coarsest) 1200 (finest), determines the physical size of the abrasive grains in the wheel. A larger grain will cut freely, allowing fast cutting but poor surface finish. Ultra-fine grain sizes are for precision finish work.

3. Wheel GradeWheel grade, from A (soft) to Z (hard), determines how tightly the bond holds the abrasive. Grade affects almost all considerations of grinding, such as wheel speed, coolant flow, maximum and minimum feed rates, and grinding depth.

4. Grain SpacingGrain spacing, or structure, from 1(densest) to 16 (least dense). Density is the ratio of bond and abrasive to air space. A less-dense wheel will cut freely, and has a large effect on surface finish. It is also able to take a deeper or wider cut with less coolant, as the chip clearance on the wheel is greater.

5. Bond TypeHow the wheel holds the abrasives, affects finish, coolant, and minimum/maximum wheel speed. There are two main types of bonding agent: inorganic and organic. See example with Specs. on next 2 slides. ◦ INORGANIC BOND ORGANIC BOND

◦ Inorganic bonds are mainly vitrified, ie the wheel is generally fired in a furnace to give the bond a hard, strong but brittle structure. These wheels are used for precision grinding applications as they hold their shape, but require dressing.

Organic bonds are not fired but are cured at low temperature; the bond agents are resinoid (B), rubber (R) and shellac (E). Such wheels are tough, shock-resistant and self-dressing, and are most suited to non-precision applications, for example fettling (trimming or cleaning rough edges) and cutting off.

Example of Bonded Abrasive Wheel with Complete Label

II. Several Uses of Abrasive Wheel◦ Grinding of Surface for welding preparation (e.g. Beveling,

surface cleaning)◦ Grinding of welded joints to clean out excess metals or to

cut-out welded joint◦ Grinding of work pieces that must show high surface

quality (low surface roughness and high accuracy of shape and dimension

◦ Surface reduction◦ Cutting◦ Sharpening of Tools◦ Various uses in manufacturing Jewelries, Stone works and

metal works III. Hazards in using Abrasive Wheels

Grinding wheels can pose many health and safety hazards:

Health hazards:◦ Breathing in dusts caused by grinding can cause

respiratory problems.◦ Contact with lubricating oils and metallic dusts can irritate

the skin.

• Compressed air (used on air-powered grinders) can cause body injury due to its high pressure.

◦ Vibration can cause feeling of discomfort even after work.◦ Noise can damage hearing and be stressful.◦ Electric shock can kill.

Safety hazards◦ A wheel that shatters can seriously injure the operator and

those working or passing nearby.◦ Shooting fragments of a wheel can injure the eyes and

face. ◦ Contact with a wheel can cause cuts and scrapes.◦ If a portable grinder drops, it can injure the legs and feet.◦ Sparks can cause skin burns, and fire.

IV. Safety Procedure –Mounting an Abrasive Wheel (Lee Engineering HSSE Handbook Section 6.14)

No person is permitted to mount, change or dress abrasive wheels/disc, unless trained, competent and authorized. Prior to use always ensure that the guard is in place and the wheel is in good condition.

The following procedure should be followed when mounting an abrasive wheel: Ensure that the wheel/disc you are using is appropriate to

the material that you are grinding. Use only tools issued by the supplier for changing

wheels/disc. Always wear eye protection to the correct standard. Keep the work area neat and tidy. Ensure that the power to the tool (Grinder) is OFF. Clean the abrasive wheel with brush and check for any

signs of damage Under no circumstance should a damage wheel be used. Check that the spindle bearing is not worn. Check that the maximum abrasive wheel speed is greater

than the maximum spindle speed of the grinder.

V. Warnings: Do not use Equipment with faulty or missing guards Do not mount, change or dress wheels/disc unless you are suitably trained,

competent and authorized. Always wear Eye protection (Eye Goggle or Face Shield) when grinding Stop the Machine if abnormal vibration was noticed during operation,

disconnect it from power source and check for wheel damage and worn bearing.

Pay attention to the Job (Grinding) you are doing and do it safely. Do not leave the Grinder while it is running. Make sure that the Grinder Switch is in OFF position before plugging it in an

outlet.VI. Abrasive Wheel Expiration:

Safety requirements for bonded abrasive products,  with type of bond B (Resin) and BF (Resin/Reinforced) for use on hand-held grinding machines or hand-held cutting-off machines shall be marked with a date of expiry. The date of expiry shall at the longest be within 3 years from the date of manufacture. It is expressed as month and year e.g. 04/2009.Reccomendation (St Gobain Norton –Abrasive Disc Manufacturer); Resinoid Bonded grinding wheels be used up within 2 years from the date of manufacture. This recommendation assumes that Resinoid Bonded grinding wheels have been stored under ideal storage conditions.These same comments also apply to rubber and shellac bonded grinding wheels. As for vitrified or glass bonded grinding wheels, the shelf life is less influenced by humidity and adverse storage conditions as compared to resinoid, rubber or shellac, but even vitrified grinding wheels do not have an infinite shelf life. The best procedure and the best rule of thumb is to have any wheel that is two years old or older re-speed tested and re-inspected to ensure it is fit for use.

Even when a grinding wheel is tested and equipped with all possible safety devices, grinding is still a hazardous activity. It is important to always follow below safe working practices:

Safety goggles or safety spectacles shall be worn by all personnel exposed to grinding operation (ILL.3)

Where necessary, additional personal protective equipment shall be used, such as face protection, ear protection, respiratory devices, aprons, protective footwear, and protective gloves (ILL.3).

Never wear loose clothing, ties, rings or other jewelry.Keep long hair in a hair net.Let the machine run at full speed for one minute while

everyone stands clear.

VI. Safety at Work:

Bring the workpiece slowly and smoothly into contact with the wheel (don’t bump the wheel). Bring a cold wheel a chance to warm up.

Don’t force work against the wheel so that the motor slows down excessively or stalls.

Don’t side grind on the flat side of a straight wheel; use wheels designed for this purpose (ILL. 4).

If a grinder appears to be defective or unsafe, tag it and report the problem immediately to your supervisor.

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