Polishing or burnishing soft metal (brass, copper, aluminum, etc.) parts with Corn Cob Grit in either a barrel or vibratory tumbler is a popular process. Selecting the proper grit size for small parts or parts with complex geometry can be a real challenge.
The initial testing used for this part (only portion of part shown) used the same medium grit size as is used for larger, less complex parts also being tumbled by the customer. Due to the size of the many slots, holes and grooves in this part, this medium grit size media got stuck in many areas making the cleaning process timely and expensive. There are two options.
Using a larger grit size to prevent the media from getting stuck in the first place will address the problem and still provide the required burnishing action. Of course, as the media wears and breaks down, there is an increasing risk of media getting stuck.
Using a very fine grit will prevent the problem completely. Unfortunately, finer media sizes (i.e., lighter particles) can sometimes not provide the force/work necessary to achieve the desired surface finish. In addition, finer media can ‘pack’ into the interior areas of the part – like the inside diameter of the part pictured – making the media removal just as difficult.
There is no right answer to this problem. Balancing the required surface finish with the effort (time, labor, etc.) to achieve that finish will determine the appropriate process for each situation.