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Hand arm vibration in Foundries (HAVS)

Introduction

This information is aimed at all levels of management, safety officers, safety representatives and others within the foundry industry who may require guidance on how to reduce the risks of hand-arm vibration syndrome (HAVS).  It outlines the requirements for ensuring that the risks from vibration in the Foundry environment are eliminated or controlled.

What you need to know….

Vibration experienced in many foundry processes can cause a range of disabling health complaints that are known collectively as 'hand-arm vibration syndrome' (HAVS). The best known of these is 'vibration white finger' (VWF) which is caused by the effects of vibration on the body's blood circulation. Other damage may be caused to the nerves and muscles of the fingers and hands causing numbness and tingling, reduced grip strength and sensitivity. Damage to nerves is invisible to observers but the sufferer may appear increasingly clumsy as the use of their hands, sense of touch and perception to thermal changes is slowly and progressively lost.

The Control of Vibration at Work Regulations 2005 require employers to prevent or reduce risks to health and safety from exposure to vibration at work. Employees have duties under the regulations too.

HAVS is a reportable disease under the Reporting of Injuries, Diseases and Dangerous Occurrences (RIDDOR) Regulations 1995

What you need to do….

Risk assessment

To help you decide what you need to do, start by assessing the risks from vibration within your foundry.  When you have identified processes and tasks that pose a vibration risk, you can then work out how to eliminate or reduce this risk to ensure the health and safety of your employees who are exposed to vibration.

Your risk assessment should:

You must record the findings of your risk assessment.  When you have identified the work processes which expose your employees to vibration, you should decide what can be done to eliminate or reduce the risks, with a timetable identifying who will be responsible for the work.

What are the risks – vibration exposure?

The Control of Vibration Regulations set an Exposure Action Value (EAV) of 2.5 m/s2 exposure, averaged over an 8 hour working day (A(8)), and Exposure Limit Value (ELV), of 5 m/s2 A(8).

The Exposure Limit Value (ELV) is the maximum amount of vibration an employee may be exposed to on any single day.   

The Exposure Action Value (EAV) is a daily amount of vibration exposure above which employers are required to take action to control exposure.

However the EAV is not an entirely safe level, so the regulations require risk to be eliminated or reduced even where exposure is below the EAV if further reductions can be achieved at a reasonable cost.

Exposure estimates provide a guide to the risk to health created by vibration at the workplace.  Exposure describes:

Vibration exposure equation

It is not important to obtain a precise daily exposure (it will probably vary from day to day anyway).  You just need enough information to establish whether it is likely that the EAV or ELV will be exceeded.  You may be able to do this without having to make vibration measurements in your workplace.  This can be estimated using machinery vibration data or by carrying out measurements if no suitable vibration data is available.

Where is there a risk of HAVS in the foundry?

Risks of HAVs in the Foundry are generally highest in the dressing/fettling shop. There are other areas/jobs you need to consider such as refractory wrecking and relining work on ladles or furnaces.

The whole foundry process should be considered and the following questions asked:

You will need to review your risk assessment if circumstances in your workplace change and affect exposures. You should also review it regularly to make sure that you continue to do all that is reasonably practicable to control the vibration risks. Even if it appears that nothing has changed, you should not leave it for more than about two years without checking whether a review is needed.

More detailed information on how to assess the risks from vibration and estimating employee exposures can be found on the HSE Vibration web pages.

Hierarchy of control

Elimination

There are various methods by which fettling can be eliminated, so reducing exposure to vibration along with the possible benefits of reducing dust and noise.  All need close co-operation between the different foundry departments for these solutions to be effective.

A few minutes thought at the design stage can save hours of expensive and hazardous fettling!

Casting Design

The removal of the runner/feeder system (commonly known as knock-off or cut-off depending on the method used) and grinding down the resulting stubs are usually manual operations. They can lead to significant vibration exposure. Improving the design of the casting and running system can minimise the effort required to knock-off.

You should aim to design casting and runner systems to allow for non-manual cut-off/knock-off. Correct positioning of runners and risers can allow the use of semi-automatic cut-off machines, knock-off guns, hydraulic wedges or other non-manual methods.

Castings can be designed so that the gates, risers and feeders easily break off just clear of the casting. This helps prevent break-in as well as minimising the effort needed for stub removal. It can be achieved by using breaker cores, Connor block runners, or wide, thin section in-gates. With small to medium-sized castings it is likely that the runner system will be detached during any vibratory or tumble shake-out.

Added benefits of improved design can include:

Common cut-off methods such as use of a pedestal grinder or an angle grinder will lead to transfer of vibration from the casting to the operator.  It may be possible to use alternative cut-off methods such as laser cutting or water jet cutting.  Thermal cutting may be considered but this can lead to dust/fume and noise problems which will all have to be controlled.

Ask if your customer requires a high standard of fettling. If not, you can lower your costs as well as reduce your employees exposure to vibration

Control and removal of flash

Flash is the unwanted penetration of metal into joints of a mould.  Any reduction in flash or its subsequent removal will reduce exposure to vibration per casting, and save money spent in unnecessary fettling.

Flash can be caused by:

To reduce excessive flash, all aspects of the casting process, from initial design to pouring, may need to be examined. Communication between designers, moulders/coremakers, patternmakers and fettlers is needed. They should be aware of how their activities affect others in the process so that an effective solution can be found.

Questions to ask

  • Does the design minimise the need for fettling, eg minimum number of cores, joint lines accessible?
  • Can a triangular section be designed onto the joint line to give an aesthetically acceptable joint with minimal fettling?
  • Are the core/core print tolerances minimised, taking into account pattern production methods? (CNC machined patterns should allow tighter tolerances than handmade ones.)
  • Are core dressers/setters trained to use the minimum of core rubbing needed to give a good fit?
  • Is the sand/binder system appropriate for this casting, and well compacted and fully cured?
  • Is the mould reinforcement adequate?
  • Are the mould/core components set firmly to prevent movement under pressure from the molten metal?
  • Is wall support adequate to prevent break-out?
  • Are locating pins, lugs and prints set accurately to allow proper alignment?
  • Are the weighting/clamping arrangements adequate to prevent cope lift?
  • To allow proper alignment and prevent metal seepage are pattern equipment and core/moulding boxes in good condition?
  • By modifying the design or casting process can other defects requiring remedial fettling, such as sand burn-on, be minimised?

These approaches to elimination can be fully utilised by mechanised foundries with long production runs, but some may be used by jobbing foundries to good effect.

Hierarchy of control

Substitution

It is unlikely that flash will be completely eliminated, especially at jobbing foundries, so it is important that its removal is properly managed.  With any substitution or alternative method, you should assess the risks from both the original and proposed new operation so that the overall benefit can be determined.

Depending on the metal being cast, it is often possible to remove flash in relatively large pieces using knock-off guns or manual hammer blows. While this is the preferred method, the risk of work related upper limb disorders (WRULDS) should be managed.

The alternatives for removing substantial amounts of flash include:

The method of flash removal should be chosen to minimise vibration exposure.  

You should look for alternatives to the manual fettling tools below or reduce their use where possible:

Automated or semi-automated methods can reduce employees’ exposure to vibration.

The mechanical alternatives below can save a great deal of fettling and cost BUT they often involve repetitive manual loading/unloading of castings. You should make sure that you reduce the handling of castings as far as possible and look into the potential use of magnetic/vacuum lifting devices.

Automatic or semi-automatic cut-off machines

These consist of an enclosure containing a slitting wheel and a moveable clamping mechanism to hold the casting and the runner system. The clamping mechanism is then moved to apply each runner to the wheel. Such systems have been used successfully in both long-run and jobbing situations. But the casting and runner systems must be designed to allow access of the runners to the wheel to give minimal stub at cut-off.

Cropping machines

These are small presses used to clip off joint line flash, used for smaller castings. Dies have to be prepared for each individual casting type, so this technique is favoured for long production runs.

Manipulators

Manipulators are moveable jigs which either hold castings against a grindwheel, or hold a grinding tool against a casting. They are a form of remote manual operation, usually with a feedback system to the operator to prevent over-fettling. This technique does not have the set-up programming problems of other methods and can be applied to a jobbing situation. Where several grinding operations are required on each casting, manual handling can be considerably reduced. Manipulators could be particularly beneficial to jobbing foundries which have an identified HAVS problem.

Automated grinding stations

These can range from automatic single operations without programming through to a full robot fettler which can pick-and-place and carry out a range of grinding operations. A range of simpler (and cheaper) autofettlers to cover the range of castings produced are more commonly used.

Bowl or tub vibrators

These are heavy duty large vibrating bowls, troughs and tubs used with abrasive media. They are are primarily used for deburring, removing tool marks and polishing but can be used for the removal of small amounts of flash.

Hierarchy of control

Engineering

Fettling/Dressing

Manufacturers are constantly improving tools used in the fettling/dressing shop. Your supplier should be able to provide you information about these improvements as well as the 'in-use' vibration data for each tool.  You can use this data to work out possible employee vibration exposure.

You should select and use grinders with built-in vibration reduction such as automatic spindle balancing (ASB). Generally vibration levels will be lower with lighter more powerful machines.  Where heavier machines are used consideration should be given to tool balancing systems.

Users of pedestal grinders are exposed to vibration from the workpiece.  This vibration effect is exacerbated when the work rest is mounted directly to the pedestal grinder, so it is a good idea to isolate this.  Vibration exposure may be further reduced by use of a jig to hold the workpiece against the wheel as this reduces the grip forces needed, or eliminated by use of an automated system to offer up the work pieces to the wheel.

It is important to choose the correct type of grinding wheel as this can reduce noise, dust and vibration as well as reducing fettling costs.  It is a false economy to use a wheel that is too hard.  You may think that the life of the wheel is extended but in fact the abrasiveness of the wheel becomes reduced and so the time spent fettling actually increases.  Because the wheel is less abrasive Fettlers may press the casting more firmly against it to try and achieve some cutting or grinding.  This may lead to distortion in the wheel and increased vibration exposure.  More seriously it may lead to the wheel breaking which can have fatal consequences.

Grinding wheels should be selected for maximum cutting efficiency and not maximum life.  In conjunction with other approaches to HAVS reduction this should significantly reduce exposure, limit dust and noise, and give cost savings per casting

Alternatives to conventional abrasive wheel grinding

There are some alternative grinding techniques that eliminate the problems associated with out-of balance wheels and discs, although there could still be resonance effects. They should be considered as part of a HAV control programme.

Abrasive belts

Abrasive belt fettling is a well-established technique which normally exposes the operator to less vibration than conventional abrasive wheel grinding. It is frequently seen in finishing fettling such as the final joint line skim, which might involve a small portable linisher. Larger belts can be used for initial rough dressing.

Metal burrs

Equally well established is the use of metal burrs or rotary files instead of stone points for interior or fine fettling. Because the abrasion is only at the surface of the tool the potential for becoming out of balance is reduced. Excessive sideways forces on these relatively small tools can cause the shaft to bend, resulting in increased vibration. The burrs should be replaced if there is any evidence of this occurring.

Alternatives to manual wrecking or relining

Preformed crucibles/linings for furnaces and ladles should be used wherever it is reasonably practicable. The use of such preformed linings and crucibles can completely eliminate or significantly reduce the use of vibratory tools and:

Additional benefits can also include:

With some furnaces spent preformed linings can be automatically pushed out using large rams.  With many smaller furnaces and ladles the linings can be released and eased out using simple tools.

Where it is not possible to use preformed linings and wrecking out has to be carried out manually, automated machine mounted equipment should be used instead of hand held picks and other vibratory equipment.

Where work has to be carried out with hand held equipment, low vibration chisels and rammers should be used and all appropriate management controls in place.

Hierarchy of control

Management controls

There are a number of management controls available which can help reduce the effects of vibration exposure, or limit the exposure itself. These can include:

Training

You should be open and share the results of your vibration risk assessment with your exposed workers and their safety and employee representatives. Employees should be properly trained to carry out their jobs safely.

Employers should ensure employees fully understand the level of risk they may be exposed to, how it is caused and the possible health effects, ie:

You should also educate employees potentially exposed to vibration on the increased risk associated with smoking as it affects blood circulation and encourage healthy lifestyle choices

Health Surveillance

Health surveillance is about detecting work-related ill health at an early stage and acting on the results. The aims are to check the long-term effectiveness of control measures and to safeguard the health of employees (including identifying and protecting people at increased risk).

In the case of hand-arm vibration, one of the aims is to prevent employees developing hand-arm vibration syndrome (HAVS) associated with loss of hand function. It is possible that your employees who are exposed to vibration may have mild symptoms of HAVS. If they are not aware that they have the disease, health surveillance can help them to recognise that the first symptoms of HAVS have started to develop.

Appropriate health surveillance must be provided for vibration-exposed employees who:

Further information on health surveillance for HAVs can be found on the HSE Vibration web pages.

Further information on health surveillance can be found on the HSE Health surveillance web pages

Health surveillance is vital to detect and respond to early signs of damage

Hierarchy of control

Personal Protection

Gloves marketed as "anti-vibration", which aim to isolate the wearer's hands from the effects of vibration, are available .They are not particularly effective at reducing the frequency-weighted vibration associated with risk of HAVS and they can increase the vibration at some frequencies. Gloves cannot be relied upon to reduce an operator’s exposure to vibration, even when the vibration characteristics of the tool are known and you attempt to match this with the attenuation data supplied by the glove manufacturer.

However, gloves and other warm clothing can be useful to protect vibration-exposed workers from cold, helping to maintain circulation.  Low hand or body temperature increases the risk of finger blanching because of the reduced blood circulation. You should therefore make sure employees working outdoors in cold weather have adequate protection. The temperature in an indoor workplace should provide reasonable comfort without the need for special clothing and should normally be at least 16 °C. If this is not reasonably practicable, you should provide warm clothing and gloves. (More than one set may be required for each employee if the gloves or clothing are likely to become wet). Gloves and other clothing should be assessed for good fit and for effectiveness in keeping the hands and body warm and dry in the working environment. You should also ensure that gloves or other clothing you provide do not stop employees working safely and do not present a risk of entanglement with moving parts of machinery.

Updated 2014-09-01