Screen Separating Basics

There are a couple of ways to separate parts from media. Basically, a screen is used to separate out smaller items from larger items. The best separation is achieved when the media and parts (or whatever is being separated) are different enough in size and shape to make separation simple.

A tubular rotary screen separator will tumble the items to be separated while the load passes through the screen tube and the smaller items are separated. This type of process can be used for separating almost anything and works great for parts that 'hold' the media and need to be over-turned to be emptied. A tubular rotary screen separator can also process high volume loads (hundreds of pounds per minute if necessary). Multiple tubes in sequence can be used for multiple separations.

A flat vibrating screen is a good general purpose method to separate parts and media. Loads are simply emptied onto the vibrating screen and the smaller pieces fall through the screen. This is more of a batch process and ideal for small load sizes. A flat vibrating screen can be incorporated into vibratory tumbling systems for automated separation of media and parts in process.

The biggest challenge with screen separating is identifying a screen opening (size and shape) that will quickly and efficiently separate the load. If parts and media (or whatever is being separated) are very close in size and shape the optimal results will be much more difficult to achieve.

Hurricanes, Oil & Shipping

It is absolutely upsetting to see the pictures and read the stories of those affected so dramatically by the hurricanes in the Gulf of Mexico. The devastation in some of these communities seems irreversible.

A silver lining with these 2008 storms is the minimal damage to the oil refineries in the Gulf. The anticipated but un-materialized damage to infrastructure has taken some of the crazy speculation out of the global oil market.

With the price per drum dropping below $100 per barrel from a high of nearly $150 I suspect that the inflationary pressures on many products will weaken. More importantly the cost of shipping and fuel surcharges should start to come down - although I'm sure not as quickly as they went up in the past 12 months.

Tumbling with Abrasive Grit

Tumbling parts to achieve a deburred, deflashed or rounded edge is a common process. Both vibratory and barrel tumblers are used for this purpose. Choosing the proper media type is critical to achieving the desired finish.

Most applications require the use a preformed tumbling media. These media contain abrasives that are released into the tumbling process to remove the burr, etc. The (relatively) large mass of the media assists in this process by acting as a sanding block of sorts on the edge and surface of the part. After this abrasive process, parts can be tumbling in other media (including grits) to achieve a smoother or polished surface finish.

Tumbling parts simply with an abrasive grit such as Aluminum Oxide, Silicon Carbide or Walnut Shell does not typically achieve the deburring, deflashing or edge rounding required. While the grit may be very sharp, hard and abrasive, there is very little force acting against the edge of the part. The surface finish will probably be affected (roughening, smoothing or even polishing) but the edges will be left mostly untouched.

There are some exceptions to this 'rule' (see this post) but generally preformed tumbling media is superior to grit media for deburring, deflashing and edge rounding.

Log Home Blasting

Here is a great picture of a do-it-yourself log home blasting project. The blaster being used is a relatively small KF100DM Portable Pressure Blaster with a 3/16" nozzle. Fine Corn Cob Grit is the media being blasted. The objective was to take off the old stain and sealant so that the logs could be re-stained and sealed. I believe the job was completed in one weekend.