Pump manufacturers have a long, successful history of working with metals and are familiar with the beneficial properties they deliver in a variety of pumping applications. Similarly, the pump industry has been using thermoplastics in pump designs for several decades because of their low cost, light weight, superior chemical resistance, manufacturability and other valuable—and profitable—advantages. While unmodified thermoplastic resins have many inherent benefits, they also pose many limitations for pump applications if used in an unmodified form. Chief among these limitations are strength, impact, wear resistance and flame-retardant properties that can often fall short of those same properties in metals. Despite these setbacks, manufacturers have a broad range of options for enhancing the properties of unmodified resins. Compounders can add combinations of reinforcing fibers, fillers and additives to a carefully selected base resin to create a high-performance compound with a host of distinct properties instilled into a single material. Many manufacturers are frequently surprised at the diversity of properties that can be readily built into a compound—including flame retardancy, impact resistance, strength, wear and friction resistance, conductivity, temperature resistance, chemical resistance, corrosion resistance and colorability—to deliver the exact performance criteria that they have specified.
Reinforcing additives combined with a carefully selected base resin can create a high-performance compound for any application.
03/26/2015
Figure 1. Wear resistance of unmodified vs. modified materials (Graphics courtesy of RTP Company).
Another common scenario for pumps used in corrosive environments is selecting PPS—a highly chemically resistant thermoplastic with excellent thermal stability—and building in required wear resistance with the addition of carbon fibers used in conjunction with PTFE. This particular type of compound has been highly successful in pump vane applications.
All fiber reinforcement, fillers and additives have some considerations, and the compounder must understand them. For example, mating surfaces, applied loads and speeds, and operating temperatures influence wear and friction along with the wear package used.
Figure 2. Centrifugal pump impeller utilizing PPS with carbon fiber and PTFE for maximum strength and wear resistance
Figure 3. ATEX-compliant pump utilizing a conductive PP with glass fiber reinforcement
ATEX is a legal guideline based on two European Union directives that describe what equipment and protective systems are allowed in an environment with a potentially explosive atmosphere. Derived from the French title of the 94/9/EC directive Appareils destinés à être utilisés en ATmosphères Explosives, ATEX is a concern for thousands of manufacturers worldwide. Often, it is a race to meet stringent conductivity standards so that products can continue to be used in mines and other potentially explosive environments. Ironically, these are many of the same environments where the light weighting, strength and corrosion resistance provided by thermoplastic compounds have become so valuable (see Figure 2).
To maintain the use of thermoplastics in these applications, manufacturers can work with compounders to find the appropriate conductive technology from possibilities such as carbon fibers, carbon nanotubes, inherently conductive polymers and carbon black. Some of these impact the strength of thermoplastics, so the compounder must create the right formula to maintain all the properties required by the application. The compounder also needs to understand that ATEX compliance might require a combination of several other properties, such as flame retardancy, impact resistance and thermal resistance—most of which are well within reach of compounded thermoplastics.