Shotblast Batch Barrels: How Full is Full?

This question is one of the most frequently asked by operators of batch type cleaning machines, most commonly called a “tumble blast” or “barrel blast” machine, of which there are probably more in operation than any other style of blast cleaning machine in the market.

Tumble blast machines employ either an endless rubber belt or a metal slat and chain conveyor as the main carrier of the components being cleaned. If the sidewalls of the machine were see-through, the upper portion of the conveyor would appear in roughly the shape of the letter “J”, with the rounded area of the “J” serving as the cradle in which the materials being processed are contained during the cycle. The “J” is formed into a closed loop by a three point conveyor support arrangement, combined with the continuous belt or chain.

The two sides of this endless conveyor are closed off and supported by round plates, commonly referred to as barrel heads or drum end plates, which rotate along with the slow moving conveyor.

So, going back to the question, how does a machine operator know if this type of machine is “Full”, or being filled with parts to a correct level? To determine where the “Full Load” line is, the easiest and most reliable way is to form an imaginary line along the face of either barrel head, with the ends of the line located at the those points where the belt/chain conveyor first makes contact with the barrel head, and up to the point where the conveyor leaves contact with the barrel head to follow its return path. Note that this line will generally not exactly bisect the barrel head in half, but will split it approximately 60/40. This 40% side is the lower side and is the area which the parts being processed will nest when the conveyor is motionless. A “Full Load” approaches this imaginary line but does not cross it.

Batch Barrel

If the quantity of parts is too great, then when the conveyor is moving and the parts are tumbling, the parts will fall or climb outside of this line. Conversely, when there are not enough parts loaded in the machine, the tumbling action (if the parts are even tumbling) will not move the parts even close to the imaginary line.

A machine operated with excessive batch loads will have problems, and so too will a machine that is routinely operated with less than full loads. An overloaded machine will suffer from parts getting trapped or jammed in the “wedges” created where the conveyor engages the barrel head in the front portion of the machine, which can either cause a rubber belt to tear or cause a chain link to crack or worse– break. The machine operated with less than full loads will also suffer increased wear on the conveyor parts and barrel heads due to exposed surfaces, and it is also likely that insufficient tumbling of a small batch load will result in parts not being completely processed in one cycle, necessitating reblast and increasing process costs.

Keep in mind that most rubber belt conveyor tumble blast machines have a weight restriction, so a combination of quantity plus weight is required data to calculate what comprises a “Full Load”. Most machines equipped with a slat and chain conveyor are not weight restricted, or have a much higher density limit, so volume is usually the key determinant in the calculation.

Keep costs down and machine operation optimum by running “Full Loads” in your tumble blast machine!

 

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