Maintaining Consistent Surface Finish on Delicate Die Cast PartsMar 09 2017, by Transmet Blog in
Transmet Cast Aluminum Shot and Cast Zinc Shot are widely used media for abrasive shot blasting die cast parts. Both are relatively soft when compared to other blast media; which can be advantageous or challenging depending on the application.
Through many years of successful (and unsuccessful) partnerships, we have encountered a few similar situations where an organization approached us with a challenge: the surface finish on die cast parts is different when the shot blasting machine is loaded with a brand new bag of shot.
To first understand how this is possible, let’s examine how Transmet Cast Shot is made.
How It’s Made: Transmet Cast Shot
Transmet Cast Aluminum Shot and Cast Zinc Shot are cast in air; resulting in a teardrop shape that can shock customers at first. No worries: the initial teardrop shape typically only lasts 50 to 100 cycles before the tail is pounded into the shot, making it round. The metallic shot has the ability to work-harden or work-soften as it becomes a working mix (or operating mix) of shot.
How to Maintain Consistent Surface Finish
As it turns out, the organizations that approached us with the above problem were running their blast machine down to empty before filling it up completely with brand new shot. Not only does this habit harm shot blasting efficiency, it also opens up the shot blasting process to potential problems and inconsistencies.
Transmet Cast Aluminum Shot and Cast Zinc Shot are both engineered to last well over 8,000 cycles. Because of this, machine operators should make small, periodic additions to their blast machines every day (as opposed to large dumps of fresh shot). Small additions ensure approximately 90% of the media in the machine will be conditioned (rounded) and less than 10% will be new shot (teardrop shape). Surface finish results are repeatable day after day.
Many of our customers have determined the daily additions needed in order to keep the Amp load on the blast wheel consistent. These additions can be added on a specific interval (such as the beginning of every shift). We encourage all shot blasting operations to track additions of media and monitor the Amp gauge throughout operation.
Once you have found the right interval to add new shot, you will have a shot blasting operation producing consistent, repeatable results for your company and your customers.