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).
Occasionally vibro machines are disconnected and wired back in (following relocation, repair, etc…). Often machines can have the electrical phases reversed and can run backwards. Whilst the machine will process you will find the result isn’t as good as it should be, movement will be slow (this may look similar to when the drains are blocked) and unloading the machine can be very slow – to the point where all parts will not unload automatically over a separation screen (where fitted). Key here is to look at the ‘roll’ of the mass in the machine. If you see parts and media are rolling to the outer wall of the machine more than into the centre (which is the correct rotation) then there’s every chance the phases have been reversed. In this case disconnect the machine from the supply, reverse the phases and restart – you should see the media roll into the centre immediately as a result.
When your process is first established a full load of parts should be calculated (be it 5,500 or even 5,000). This number of parts will be equivalent to a volume which then be added to the media to fill the machine to the correct level ensuring that all operates as it should.
Put too few components in the machine and besides being an unusually expensive process where this is the case you may also experience issues where the machine mass (media and parts) don’t move the way they should which in extreme cases could affect the quality and consistency of your finish. More of an issue though would be to put too many parts in the machine (where people think they are doing the right thing for the company as it would equate to a lower per-part finishing cost) and you may end up causing severe problems for yourself. Where too many parts are loaded the machine can become overfilled, this will affect the ratio of consumables-to- parts which will absolutely affect the quality and consistency of the finish and worse still, where the machine has a separation screen then it could result in components being damaged as they ‘catch’ on the underside of the screen or ‘chatter’ against each other on top of the media fighting against each other to be submerged back in the mass.
Drains allow the process water, particles and any contaminants to be carried out of the bowl so the process can operate and perform to its optimum capability consistently. Depending on the process if unchecked drains can get blocked. Once this happens the water level in the bowl will increase, with compound added this can create foam (and mess) and the process time and surface finish will again suffer as a result. If the quantity of particles in the bowl is high then this can contaminate (and even ruin the media) as well as coating the lining of the bowl causing a loss in drive of the media.