This article will try and answer all the above questions, but for ease of reading not in the order shown, you can jump to any answer just by clicking the question. If you require an Abrasive wheel training course try this link.
An abrasive wheel is a wheel, cup or cone consisting of abrasive particles bonded together with various substances.
There are two main types of bonding agent, inorganic and organic. Only organic-bonded wheels should be used for portable and hand-held grinding machines. Those intended for cutting-off operations should additionally have some form of reinforcement, usually fibre glass.
Inorganic bonds are 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. Such wheels are tough, shock-resistant and self-dressing, and are most suited to non-precision applications, for example fettling and cutting off.
To answer the question of why must abrasive grinding wheels be inspected we need to examine the risks of using an abrasive wheel. All covered fully in Abrasive wheel training course
Contact with the Wheel
The abrasive wheel rotates at high speed and is capable of causing severe injuries if it comes into contact with flesh. This is particularly important for hand held tools such as angle grinders which have abrasive wheels that rotate at extremely high speed.
Should the wheel break the resulting pieces are likely to be ejected at high speed and are capable of causing severe wounds or even death. The speeds of ejection can be as high as 80 to 100 miles per hour.
Ejection of Particles or the workpiece.
The abrasive wheel sheds particles as it works and wears down. These are usually seen as sparks and are capable of causing damage to bare skin and are particularly damaging if in contact with the eyes. The workpiece can also be ejected from the machine at high speed.
Any item which comes into contact with the rotating wheel may be wrapped around it and drawn into the wheel. If this is something attached to the operator they will be drawn into the wheel and injured.
Unfortunately many accidents do occur whilst using abrasive wheels, in particular injury resulting from either wheel breakage or contact with a running wheel. The risk of breakage is inherent in every abrasive wheel and if the number of breakages is to be kept as low as possible and hence accidents also reduced. Then the initial care exercised in the design, manufacture and testing by abrasive wheel and machine makers must be coupled with the adoption of an inspection of abrasive grinding wheels before and during use by the users of abrasive grinding wheels. Which leads onto the next questions:
Abrasive wheels must be marked in accordance with Annex A of BS EN 12413.
Knowing which wheel to use for each task and type of machinery is a vital skill. Using the incorrect wheel for a task can have potentially fatal consequences. So, the first test would be to select the correct wheel for the job and machine, and ensure you and staff are trained. Abrasive wheel training course
Annex A of BS EN 12413 and BS ISO 5255 specify how wheels should be marked to indicate the restrictions for their use:
All organic bonded wheels for hand-held applications will bear a use-by date of three years from the date of manufacture.
A code number should be marked on the wheel to indicate the source and manufacturing details of the wheel.
The maximum permitted speed should be marked on all abrasive wheels over 80mm in diameter. The speed should be marked in revolutions per minute (rpm) and meters per second (m/s). For wheels under 80mm in diameter it is not practical to mark the wheel due to the size, so the maximum permitted speed should be marked on a notice in the workshop which can be easily seen. For speeds of 50m/s and over a colour coded stripe will appear on the wheel.
Also on the label is a manufacturer’s code.
What does the code number on an abrasive wheel show? It is simply construction details of the wheel. Usually the first letters show the type of abrasive eg. A = Aluminium Oxide, then a number denoting the grain size eg 24, then a letter to denote the hardness of the bond for example R = medium and finally some more letters to show the type of bond for example RF = resinoid reinforced. There is not a standardised system for this, so the manufacturers own nomenclature should be consulted.
Additional information may be included on the wheel or its packaging, for example detailing the main areas of use. If the wheel is unsuitable for the job, ‘loading’ may result, i.e. the abrasive wheel face becomes clogged with particles of the material being ground or cut. A wheel may also be either too hard or too fine, resulting in ‘glazing’. The operator is then tempted to use excessive pressure for the work on the wheel, a contributory cause of wheel breakage.
After ensuring the correct wheel has been selected for the job in hand, then how the wheel has been handled and stored needs to be considered.
Manufacturers go to great lengths to ensure wheels are manufactured to the correct standards and quality. It is vital that wheels are handled and stored correctly to protect their integrity.
The following practices should be adopted to ensure the integrity of the cutting wheel is maintained:
Do not expose wheels to direct sunlight or other thermal stresses during transport and storage;
Stack cutting wheels flat, on a level surface, in the original packaging and in a dry place where the temperature is as constant as possible;
Store cutting wheels in a frost-free place;
Do not store cutting wheels in the vicinity of aggressive fluids (acids, alkalis, petrol, diesel or other solvents);
Avoid jolting and impacts.
Diamond cutting wheels are more resilient than composite and less prone to thermal shock but it is still good practice to follow the above list.
Here is a list of what tests should be performed on an abrasive wheel.
Has it been stored and handled correctly? (A cutting wheel that has been dropped must not be used)
Does the label show it is approved for free hand cutting?
If it is an organic/resin bonded wheel is it within the use by date?
Does the label show that the permissible speed of the cutting wheel is equal to or greater than the maximum spindle speed of the cut-off machine.
Carry out the same checks as for a new cutting wheel but in addition;-
Check spindle hole for damage. Do not use cutting wheels with a damaged spindle hole.
Check that it is not cracked, chipped, or uneven, and does not display any signs of core fatigue or overheating (discolouration).
Check also that there are no damaged or missing segments
Next, whether the wheel is new or used, it should be checked that it has been mounted correctly.
Check the rotation of the machine and ensure the wheel is fitted so that it rotates in the direction indicated on the label of the wheel.
The flanges that hold the wheel should be at least a quarter of the wheel diameter.
Turn cutting wheel by hand, making a visual inspection for radial and axial run out.
Deviations in axial run-out (Picture 2) result in higher thermal loading and wider cuts.
All of the tests and checks are covered in Abrasive wheel training course
Finally, a commonly used test is the ‘ring’ test, what is a ring test on an abrasive wheel? We have answered that as a separate section as it is a unique test on grinding wheels rather than cut off wheels.
Grinding wheels must be inspected and "ring-tested" before they are mounted to ensure that they are free from cracks or other defects. Wheels are tapped gently with a light, nonmetallic instrument. A stable and undamaged wheel will give a clear metallic tone or "ring."
The ring comes from the hardness of the material in the wheel and its ability to transmit sound vibrations. If the wheel is cracked, the vibrations stop at the crack and there is no ring. However, a ring test may not detect all defects in a wheel, so a careful visual inspection is also necessary.
To perform a ring test make sure the wheel is dry and free of sawdust or anything that could deaden the sound of the ring. Then get a hard plastic or hard wood object, such as the handle of a screwdriver or other tool, but make sure not to use metal objects.
Suspend the wheel on a pin or a shaft that fits through the hole so that it will be easy to turn, but do not mount the wheel on the grinder. If the wheel is too large to suspend, stand it on a clean, hard surface.
Imagine a vertical plumb line up the center of the wheel.
Tap the wheel about 45 degrees on each side of the vertical line, about one or two inches from the wheel’s edge. (Large wheels may be tapped on the edge rather than the side of the wheel.)
Turn the wheel 180 degrees so that the bottom of the wheel is now on top.
Tap the wheel about 45 degrees on each side of the vertical line again.
The wheel passes the test if it gives a clear metallic tone when tapped at all four points. If the wheel sounds dead at any of the four points, it is cracked and must not be used.
Abrasive grinding wheels and cut off wheels are dangerous things in the wrong hands, correct storage, handling, selection and use are essential if risks are to be minimised. Safety awareness training is therefore essential. Abrasive wheel training course
These questions are interrelated, but first let’s examine any legislation that specifically applies to abrasive wheels. HSG 17 published by the HSE, is a guidance document relating to abrasive wheels. It is not legislation, however where guidance is given by the HSE it should be followed, as if an accident occurs and it was found that guidance had not been followed then you may face prosecution under the Health and Safety at Work Act. Below, is an extract from HSG 17:
There is no substitute for thorough practical training in all aspects of the mounting and use of abrasive wheels. Any training programme should cover at least the following:
It is recommended that a record of training in the safe mounting of abrasive wheels is kept, showing the trainee’s name and date of training.
Commodious offer an online training course that complies with all the above recommendations. Abrasive wheel training course
Further regulations and advice that apply directly to abrasive wheels are Provision and Use of Work Equipment Regulations 1998 (PUWER 98) the purpose of these regulations is to ensure that work equipment, including abrasive wheels, does not give rise to risks to health and safety, regardless of the work equipment’s age, condition or origin. PUWER 98 applies to all workplaces and work situations subject to the Health and Safety at Work Act 1974 (HSW Act).
There are also the Control of Substances Hazardous to Health (COSHH) Regulations 2002 these cover all substances that are hazardous to health including fumes and dust that can be created from the use of abrasive wheels. The HSE guidance CIS 54 covers exposure to respirable crystalline silica (RCS) dust, associated with stone and concrete cutting.
Additional safety and training guidance can be found in the following regulations and guidance.
Abrasive wheel training is not in itself mandatory or a legal requirement, but there are many regulations and legislation that by implication include abrasive wheels and the associated health and safety hazards that they can create. Therefore in practical terms abrasive wheel safety awareness training is mandatory and also a legal requirement. Abrasive Wheel Training Course
There is no legal or mandatory retraining dates for how long abrasive wheel training or a certificate of training lasts because in general there is no formally recognised period of validity for any health and safety training.
The HSE web site states that refresher training should be carried out whenever it is felt necessary (for example a change in working condition, the introduction of new equipment, staff or working practices or when it is felt necessary to undertake refresher training).
The view of Commodious is that every 3 years is good practice and definitely every 5. It really comes down to your own view and who you work for or are contracted to. More details here
Commodious offer a 15 course great value bundle deal that has been put together by Trades people, Contractors and specialists from the trade and construction sectors.