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4.0 Process Development
4.1 Process Types
Fluent Mass
:
The fluent mass is employed within the barrel to provide an impinging force upon the
parts during rotation of the barrel. The types of fluent mass are often referred to as “Media”. The
parameters that define the preferred fluent mass are determined by the type of process to be
performed.
4.1.1 Cut
The cut process is used for removal of material from the surface of the parts, usually to remove milled
or coarse sanding marks. Ideally, a cut process produces a surface texture of between 32 and 10 micro-
inches. In a cut process, the individual particulate of media ranges from 0.0625” to 1.25”. The size of the
particulate as well as the media make-up or “bond” will greatly influence the aggression of the process
and the outcome of the surface texture of the part. In conjunction with the bond of the media, the
density of the media affects the aggression of the process. This is because the centrifugal barrel finishing
system is capable of generating 10 to 30 times the force of the individual media particulate. The higher
the density of the media particulate, the greater the impacting force applied to the part.
In setting the parameters which define the size of the fluent mass for the rough cut process keep in
mind the following rules: If the fluent mass particulate is too large, too much energy is imparted to the
fluent mass so that the parts are damaged when the media impinges the surface. This causes a rough
surface texture and a high peak to valley surface reading. Alternatively, if the particulate size is too small,
insufficient energy is imparted to the fluent mass. An inability to impart sufficient energy to the fluent
mass prevents the media from effectively removing a significant amount of material, thereby rendering
the process ineffective. The density of the fluent mass for the rough cut process may range from 10 to
300 lbs/ft
3
, wherein the optimal range is from 85 to 150 lbs/ft
3
, and the preferred density of the fluent
mass for the rough cut process is approximately 95 lbs/ft
3
.
4.1.2 Refinement
The refinement process is used to improve the surface texture of a part after a cut process. This may be
necessary to prep the part for plating, painting, or burnishing. This operation is similar to the cut process
with the exception of media bonds that are usually mild or non-abrasive, slower turret speeds, and
abrasive compounds between 240 and 1000 mesh. The surface texture of the part may have a low
micro-inch finish, between 4 and 10 Ra, with a dull or matted surface appearance.
4.1.3 Burnishing or Dry Buffing
To achieve deep luster and a bright polished color, a burnishing or dry buffing step must be used. The
fluent mass for this process ranges from low density media, such as ground and treated Walnut Shell
or Corn Cob used in Dry Buffing, to very high density media such as Steel or Stainless Steel shot or pin
utilized in a burnishing operation. The preferred fluent mass is between 100 lbs/ft
3
to 150 lbs/ft
3
, such
