A Dynamic Duo: Thermoplastics and Compressed Air Systems

April 23, 2001

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Automation technology is on the rise -- and so is the need for extremely durable materials within these systems. After much trial and error, an ideal plastic has been engineered that fits the bill.

In the age of automation, the use of contaminant-free compressed air systems has become commonplace. Paint and protective coating sprays, robotic assembly tools and heavy-duty packaging machinery all utilize this type of pneumatic technology. Alongside this proliferation of compressed air systems has arisen the need for a durable material from which to construct them.

Because of needs specific to the dynamics of these systems, trusted plastics such as PVC and CPVC are out of the running. The use of these materials in a compressed air system means that, in the case of a failure, air within the pipe could suddenly decompress and send shards of the shattered plastic flying in all directions. Commonly used metals, such as black iron and galvanized steel, bring another set of problems due to the rust and corrosion particles that develop within the systems. The resulting debris can cause manufacturing problems. Copper piping and stainless steel, while free of corrosive particles, are still likely to leak simply because pipes made of these materials must be connected by threading. In addition, there is the expensive cost associated with these materials.

Specially engineered and modified thermoplastic, known as ABS, proves to be the best solution. This material is ideally suited to compressed air systems due to its strength, durability and, most importantly, due to its trait of responding to severe impacts with little more than a crack or a split. The fissure that opens in the material serves the purpose of releasing the air pressure with considerably less danger than would be present in the event of a bursting PVC shaft.

Since threading its ends would compromise its optimal pressure rating, ABS piping needs to be connected by applying an adhesive solvent. Any place in the system where plastic needs to be connected to plastic must be secured in this fashion. Incidentally, the ABS plastic should never be connected directly to the air compressor. Rather, it should be attached downstream from the air receiver or after cooler. The expansion and contraction of the plastic material must also be taken into account when gluing the plastic fittings together. Thus the piping should not be connected when it is either too cold (below 40 degrees Fahrenheit) or too warm (above 90). In addition, a primer is necessary to disinfect the area of the pipe that is to be glued and the adhesive should be applied to the primer-coated area before it dries. Of course, only the proper adhesive should be used. This holds true for the applicator as well (oftentimes a brush located on the underside of the lid to the adhesive's container.)

Source: Using Plastic for Compressed Air Piping
Don Hoffman
Plant Engineering, January, 2001
http://www.manufacturing.net/articles/ple/2001/0101/article17.html

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