Every time you use your shot blast machine, wear will take place on anything the abrasive comes into contact with. In the blast wheel itself, over a given period this will result in changes that will affect your blast pattern (how and where the abrasive is thrown).
Wear parts in your shot blast machine are the: blades/vanes, control cage, impellor and side / top wear plates in the blast wheel(s) themselves and the wear protection plates in the blast zone (in the area calculated to have the most impact from the abrasive when it is thrown from the wheel).
The blast media in your shot blast machine is provided as a “working mix” to achieve your required process. After a period of blast time it will not perform to the required standard as it has now reduced in size. If it remains in your machine, you can expect to increase the wear and degradation of the blast wheel components together with the recovery system of your machine. It will increase production times and power consumption because of the longer blast duration required. An efficient separator will remove unwanted contaminants and undersized media without carrying out good, usable abrasive. It is vital you regularly check the efficiency of your separator and the size at which media, fines and dust are being removed.
Just as abrasive circulates in your shot blast machine so will any contaminants that aren’t removed by screens (if fitted), by the air wash separator and/or dust collector.
When larger oversized particles are allowed to remain in the machine they can cause damage to the blast wheels (giving a high risk of blast wheel part breakage) and can affect the finish produced and process times adversely.
As abrasive is recycled and re-used within your shot blast machine it is affected by impact. It will gradually reduce in size as a result of a combination of: splintering, spalling (peeling), deformation (i.e. rounding) or smoothing (i.e. grit becoming blunt).
Irrespective of the starting size of your media in your blast machine (i.e. S110, S230, etc…) within a very short time that media will reduce in size as a result of abrasion, deformation as a result of impact (i.e. rounding) and/or fracture/splintering. This will cause a drop in the abrasive level which needs to be topped up with new media (as per tip 1).
It is critical you maintain a balanced abrasive particle size to obtain a consistent, quality finish. When a machine is first installed it should be filled with new abrasive constituting a “working mix” of different sizes of media.
Sometimes things change … including the starting condition of your parts. Worn tooling, changes in manufacturing methods or materials or investment in a new manufacturing machine can result in you no longer getting a result from your mass finishing machine like the one you have been used to and/or need. We would typically recommend a sample starting condition part is kept by the machine for reference each time parts are to be processed. Should the starting condition prove to be different often this can be accommodated in the mass finishing process itself (i.e. extended time, changes in machine amplitude and drive power, different media, etc…). Should the change be dramatic though the mass finishing process will need to be re-evaluated. It may be that a different media, compound and/or setting will still get you there – and we’d be delighted to help make a recommendation for that using our process development service.
It is said that where a human being is involved in a process there is typically a 3% risk of error. This is because we lose focus, become distracted and invariably seek to find a way to make our lives easier. Worse still with variables such as media, water, compound, volumes of parts to be processed and process time with a mass finishing process there is often too much to tamper with! Our experience is that people love to change things. Whilst you will always be the masters of your own parts and know them better than us, we do know that through many years of experience process parameters need to be set and then adhered to. Where your finish requirement isn’t being met and you’ve checked the above list of possible causes and find nothing there is a good chance someone has changed something. Check through your parameters and ensure they are being followed. If they are and you still have an issue give us a call and we’ll visit to see how we can help. If they aren’t and you find something that has changed, simply change it back and your problem should be resolved. The beauty with mass finishing is that it is consistent and what you will produce in any one day will be the same as any other providing the parameters are the same.
Over time the lining of the vibro machine will wear. This will happen more quickly with highly abrasive process media and with sharper / heavier components and very slowly with polishing processes (providing the correct ratios of parts-to-media are adhered to).