Notes on Compressed Air

The most common energy systems used by Industry are Electric, Hydraulic, and Pneumatic. Of these, the Pneumatic or compressed air system has the most readily available medium – air.

Compressed Air is a clean, safe, reliable and versatile source of power which is simple and economical to use and can be harnessed in numerous ways to make light work of many industrial operations. You can overload compressed air equipment, even to stall, without damaging the motor or actuator.

There are no sparks or electric shocks with compressed air systems so they are more suitable for use in inflammable environments.

Generally compressed air equipment is smaller, simpler in operation, and more robust than equivalent electrically powered equipment. With fewer moving parts, wear and tear is less and maintenance costs are lower. For these reasons compressed air is widely used in the Manufacturing, Process and Service Industries as well as in Construction and Mining.

Why Use Air Tools?

You can use Compressed Air for drilling, screwdriving, bolt tightening, nut running, grinding, sanding, polishing, chipping, deburring, wire brushing, descaling, deslagging, scabbling, compacting, cutting, sawing, pumping, paint spraying, blast cleaning, pressure lubricating, lifting and more.

The following advantages of Air Tools will help to improve productivity and product quality:

  • SAFE no sparks, no electric shocks
  • CLEAN do not leak oil
  • STRONG long lasting metal and composite construction
  • COMPACT smaller than electric tools of equivalent power
  • DURABLE do not burn out with overloading
  • RELIABLE simple in operation
  • ERGONOMIC high power-to-weight ratio
  • CONVENIENT no electric lead regulations
  • VERSATILE can be used under water and in explosive conditions
  • SECURE not so easy to use at home

Safety With Compressed Air

Compressed Air stores energy which if released accidentally is capable of causing serious injury or even death to persons in the area of the incident.

When using compressed air and compressed air equipment the following precautions must be taken:

  • Ensure all hose fittings are tightened at the tool, at the compressed air source and wherever they occur between these two points, before connecting the hose.
  • When connecting air hoses, check for wear in the fittings so as to avoid accidental release leading to hose-whip which can cause serious injury.
  • In the case of long lengths of hose install an in-line check valve to prevent hose whip.
  • Do not drive vehicles or machinery over hose or fittings as this can result in damage to the fittings and kinking or nicking of the hose which can lead to failure and cause serious injury.
  • Do not allow a jet of compressed air to blow on any part of the body. This is especially dangerous to the eyes but can also injure other parts of the body. Eliminate the danger of the jet by deflecting it in another direction.
  • Never point blow guns or air hoses directly at any part of the body or at somebody else. Always use the Personal Protective Equipment (PPE) recommended for any particular task.
  • Avoid inhalation of airborne substances e.g. oil fog from exhausts, condensation and rust particles from the pipe work, dirt picked up by hose ends and condensation from the air receiver.
  • Appoint a responsible person to ensure the compressed air system is properly maintained. Air lines and air receivers should be drained daily. Air receivers should be checked by a qualified boiler inspector every 2 years.

Safety with Air Tools

Drills

Always exercise caution when using large air drills. Place yourself in a position where you have ample and safe footing.

Large drills should always be equipped with safety, self releasing throttles which shut off the air supply to the drill as soon as the handle is released.

The following points should be remembered when using twist drills, taps or reamers:

  • Properly sharpened twist drills and reamers, and the proper selection of drill speed reduce the feed pressure required and also the risk of breakage due to high breakthrough torque.
  • It is very easy to vary the speed of an air drill. Start at low speed until the drill is well centred, then increase to full operating speed for the remainder of the operation.
  • Reduce dangerous kickback by easing up on feed pressure at the instant of breakthrough.

Put on eye protection before using a drill. Beware of chips lodged in drill bit flutes that can easily become embedded in your eyes. Never wear loose clothing when operating a drill. Clothing is easily caught by the drill bit or the chuck. Where necessary, use barriers behind the work to prevent people from being injured as the drill breaks through the other side of the work.

Grinders

General

Accidents with grinders can be fatal. The greatest hazard when using grinders is wheel breakage. Attention is drawn to Australian Standard 1788.1 – 1987 Abrasive Wheels – Design, Construction and Safeguarding and Australian Standard 1788.2 – 1987 Abrasive Wheels – Selection, Care and Use.

Accidents can be minimized by observing the following rules:

  • Store wheels properly and handle carefully.
  • Select the right wheel for the job.
  • Always use a correctly designed wheel guard.
  • Inspect the wheel visually before mounting.
  • Mount wheels correctly.
  • Use correct Personal Protective Equipment (PPE).
  • Avoid excessive wheel speed.
  • Do not "bump" the wheel when starting to grind or when grinding.
  • Do not use excessive pressure. Allow the wheel to do the work.

Suitable racks, bins or drawers should be provided for wheels and tools. Stored wheels must not be subject to extremes of temperature and humidity. Wheels should be stored according to type, size and speed with all bins clearly marked. Particular care should be exercised, when handling wheels, to avoid dropping and bumping. The finest crack can cause some wheels to explode in use.

Portable grinders should have the Manufacturer’s nameplate attached, indicating the rated speed and rated air pressure of the tool. The label on the grinding wheel should show the Maximum Safe Operating Speed (MOS).

Always use a wheel with a Maximum Safe Operating Speed that is equal to or greater than the rated speed of the grinder. Never use a wheel with a missing label. Straight wheels, cupped wheels and depressed centre wheels must be used with protective guards. Always use the guard supplied with the grinder. If the type of wheel being used is changed, obtain a suitable guard from the tool manufacturer.

Personal Protective Equipment (PPE)

Personal Protective Equipment should be selected in accordance with SAA HB9 – 1994 Occupational Personal Protection and subsequent related Australian Standards. In general, with respect to grinding:

  • Always wear eye protection.
  • Always wear face protection.
  • Always wear hearing protection.
  • Always wear breathing protection.
  • Always wear protective clothing.
Using Straight Grinding WHeels (Type 1)

When mounting straight, unthreaded wheels always use heat treated inner and outer wheel flanges with equal outside diameters and matched recesses in accordance with AS 1788.1 – 1987. These flanges are supplied with the tool by the tool manufacturer. Never substitute soft washers which spread when tightened.

Always observe the following points:

  • Never use a straight wheel without labels (also known as blotters). Wheel flanges should always clamp against labels, never against the bare wheel. On properly manufactured grinding wheels the labels or blotters are designed to distribute the clamping force evenly around the wheel.
  • The inside diameter of the wheel and the outside diameter of the grinder spindle must always be the same nominal size. The threaded portion of the spindle should allow full nut mounting and the thread should extend inside the outer flange. Tighten the spindle end-nut carefully with a hand wrench. Over tightening can cause wheel breakage.
  • Always use a wheel guard that is designed for use with the grinder. Make sure the guard is the correct size for the wheel being used.
  • When flanges are not matched, stresses are set up in the wheel which can cause wheel breakage and possible serious damage or injury.

Wheel breakage can also occur when:

  • An outer flange is omitted.
  • An outer flange is reversed.
  • A washer is substituted for a flange.
Using Straight Cutting Off Wheels (Type 1)

When using straight cutting off wheels the tool being used must meet the following requirements:

  • Have adequate power. It is best to have reserve power to ensure efficiency.
  • Have adequate speed. Abrasive cutting operations generate a great deal of localized heat which causes rapid expansion of the piece being cut. Wheels being operated at speeds significantly lower than the recommended Maximum Operating Speed will generate excessive heat leading to rapid wheel deterioration and breakage.
  • Have heavy duty bearing support for the spindle. Spindle run-out will result in rough cutting causing rapid wheel wear leading to wheel breakage and possible serious damage or injury.
  • Have correct wheel flanges with outside diameters and recesses in accordance with AS 1788.1 – 1987.
  • Have correct wheel guarding in accordance with AS 1788.1 – 1987.
  • Be maintained in first class condition.
  • All of the above points should be routinely checked and substandard conditions corrected.

Points for basic cutting procedure:

  • Be sure the work is securely clamped - both sides of the cut, if practical.
  • Start the cut gently. Do not "bump" the wheel to make a start.
  • Feed the wheel through the work as fast as possible without slowing it.
  • Feed the wheel through the work as smoothly as possible. Don’t "baby" the wheel through the cut. If the wheel is fed through the work unevenly the cutting edge could be damaged leading to fraying, "grabbing" and wheel breakage.
Using Cup Wheels (Type 11)

Most cup wheels that are mounted on vertical grinders have threaded steel bushings moulded into the wheel. These wheels are simply screwed on to the end of the threaded tool spindle, which is usually 5/8” (16mm) in diameter. The back flange for such wheels should be flat and unrelieved. Never use a recessed flange with a cup wheel as this has the tendency to pull the bushing out of the wheel when it is tightened down on the shaft. See AS 1788.1 – 1987 for the correct way to mount cup wheels.

Using Cone and Plug Wheels (Types 16, 17, 18 & 19)

Cone and plug wheels have blind threaded bushings which screw on to the spindles of straight grinders. In this case the grinder spindle must be shorter than the depth of the hole in the bushing. When the spindle is longer than the hole in the bushing it pushes on the bottom of the hole and tends to crack the top off the cone or plug.

If the spindle is too long, use a properly machined flat spacer to give the required thread clearance and to support the back of the threaded bush. Never use relieved flanges or spacers as these will pull the bushing out of the wheel. Never use a spacer that makes the engagement of the threaded spindle too short. When this is done it is almost certain that the bushing will break and pull out of the wheel.

Using Depressed Centre Wheels (Types 27 & 28)

Because of their shape and usage Type 27 & 28 wheels require specially designed backing flanges and locking nuts as described in AS 1788.1 – 1987.

For type 27 & 28 wheels the locking nut fits within the depressed centre of the wheel to prevent interference when side grinding, and serves to drive the wheel by clamping it against the depressed portion of the backing flange.

Mounts which are fixed to the wheel by the manufacturer should not be re-used as back-up flanges for un-mounted wheels.

Type 27 & 28 wheels must only be used with a safety guard mounted on the tool between the wheel and the operator.

The variation in flange diameters, the fact that the locking nut is less than one third of the wheel diameter and the exertion of side pressure during the grinding process limits the construction of depressed centre wheels to reinforced organic bonded types.

When using reinforced depressed centre grinding wheels the minimum recommended angle between the wheel and the work is 15 degrees.

Using Mounted Wheels (Points)

The Maximum Safe Operating Speed for mounted wheels is determined by the following factors:

  • Shape and size of mounted wheel.
  • Size of mandrel (shank).
  • Overhang of mandrel.
  • Wheel specifications.

The Maximum Operating Speeds for medium and high strength mounted wheels having 2.4mm, 3.2mm, 4.8mm or 6.4mm diameter mandrels operating with various overhangs from 12mm to 125mm are given in AS 1788.1 – 1987. The wheel manufacturer’s specifications must be checked to see whether the wheels are low, medium or high strength. If the specification indicates a low strength wheel, the Maximum Operating Speed recommended by the wheel manufacturer must not be exceeded.

When using mounted wheels always observe the following points:

  • Before selecting air tool, check wheel manufacturer’s instructions for correct operating speed.
  • Before starting grinder, read the operating instructions supplied with the tool.
  • Before starting job, put on the necessary Personal Protective Equipment (PPE) as earlier described.
  • Before engaging work, run grinder under bench at full speed for one minute.
  • Do not use wheels that have been dropped or show any evidence of damage.
  • Regardless of shank length have at least 10mm of shank clamped in the collet of the grinder.
  • Wheels with long shanks should be placed inside the hollow work piece or groove before starting grinder.
  • Do not continue to use a wheel that evidences hammering when first engaging the work. This indicates excessive spindle run-out, damage to the head of the wheel or a bent shank, all of which can cause wheel breakage leading to property damage or serious injury.
Using Tungsten Carbide Burs

The recommended cutting speeds for Tungsten Carbide Burs vary with the material being machined and the desired finish. The bur manufacturer’s operating instructions should be consulted with respect to these factors in order to determine the correct bur speed for a particular job and therefore the correct tool to be used.

When using carbide burs always observe the following points:

  • Before selecting air tool, consult bur manufacturer’s instructions for correct operating speed for the bur to do the particular job on hand.
  • Refer to the bur manufacturer's instructions for the power of the tool to be used.
  • Before starting grinder, read the operating instructions supplied with the tool.
  • Before starting the job put on the necessary Personal Protective Equipment (PPE) as earlier described. In particular use the correct type of respirator as recommended by the bur manufacturer.
  • Do not use burs that have been dropped or show any evidence of damage to the flutes.
  • Burs can be damaged by dropping, using a grinder with excessive spindle run-out or running with too much shank out of the collet.
  • Do not continue to use a bur which evidences hammering when first engaging the work. This indicates excessive spindle run-out, damage to the head of the bur or a bent shank.
  • Misuse of burs can cause weakening of the brazing between the head and the shank and lead to the head coming off while in use and causing serious injury.
Grinder Speeds

Check grinder speeds regularly with a tachometer. If the grinder exceeds the speed on the name plate, or body of the tool, have it serviced immediately. An increase in the sound output of a tool is an indication that its operating speed may have increased. Speed changes can be caused by dirty compressed air fouling the speed governor inside the tool. Always use filters and lubricators on air lines.

Lock-Off Throttles

Always prefer a lock-off throttle if this is an available option. This should especially be the case on larger, more powerful grinders. Lock-off throttles prevent accidental start-up as the operator must unlock the throttle before starting the tool. The throttle automatically returns to the locked-off position when released.

Mounting a New Wheel

When mounting a new grinding wheel onto a tool remember the following points:

  • Check the speed of the tool with a tachometer.
  • Always check recommended wheel speed against grinder speed.
  • Never use a wheel with a Maximum Safe Operating Speed less than the free speed of the tool.
  • Select correct wheel guard before using tool.
  • Re-install the guard when a new wheel is mounted.
  • It is a good idea to colour code wheels, guards, flanges and machines.
  • After the wheel has been fitted, run the grinder under a steel bench, in a steel pipe or in a steel casting for at least one minute at full throttle. If the wheel breaks under these conditions, re-check the wheel speed, the grinder speed and the method of mounting the wheel. This test should also be applied to grinders that have been dropped or have been out of use.
Grinding Practice

Even properly mounted and guarded grinding wheels can be fractured by misuse. Wheels should make smooth contact with the work without any bumping action. Forced grinding which slows down the air motor should also be avoided. Never grind against the side of a straight wheel.

Safety goggles or face shields are a must when sanding and grinding. Safety aprons, and properly fitted protective clothing should be used in prolonged grinding. Never wear loose clothing.

Protective barriers should be used to prevent grinding operations from causing damage or injury to others.

When grinding, the following points should also be remembered:

  • Sparks are hot molten metal.
  • Respirators should be used if ventilation is not adequate and always with tungsten carbide burs.
  • Never grind in flammable atmospheres or near flammable mixtures or materials.
Noise

Apart from being a nuisance, noise can also cause permanent hearing damage. Even when a grinding tool has been designed to minimize its sound output, the combined sound level of the grinder plus the work noise could still be damaging to the operator’s ears and ear protection should always be worn. Where an operator is exposed to high sound levels, the time of exposure may also have to be limited.

Impact Wrenches

When installing or removing large bolts and nuts, the use of hand wrenches with extensions can cause accidents. It is usually safer to use an impact wrench.

Impact wrenches have little reaction or kick. They deliver a large amount of torque for their size and weight. A 100kg man on the end of a 1.5 metre bar cannot deliver as much torque as an impact wrench weighing 11.5kg.

Impact grade sockets should always be used with impact wrenches.

When winding out a bolt or nut in a confined space make sure your hand does not get jammed as the tool moves back.