Figure 1 — Torque converter reactors made from molded phenolic composites. These units have integral thrust washers.

Most electric motor engineers know that phenolic composite materials offer excellent electrical insulation in commutators and brush holders. Less well known, however, is that molded phenolic components also replace metal assemblies in a variety of automotive applications.

These applications suggest other opportunities to use plastic industrial drive components, especially those produced in highvolume. Some examples of phenolic composite parts include transmission reactors, brake pistons, pulleys, and sprockets.

Figure 2 — Separately molded transmission thrust washers.

Molded phenolic composites offer several advantages over metals, including smooth surfaces, uniform density, weight reduction, and ability to damp vibration. These fiber-reinforced plastics handle applications that demand stiffness, chemical resistance, and dimensional stability at temperatures from 120 to 200 C. Particularly in high temperature stiffness and creep resistance, they outperform other plastic composites. Designers can tailor their properties to the needs of particular applications by adjusting the amounts of resin, fibers, fillers, and other additives.

Here are some application examples, which may stimulate other PT application ideas for plastic materials.

Electrical insulation

In motors, molded phenolic material holds the commutator on the motor shaft. In addition to holding the copper bars in place, the material provides electrical insulation between adjacent copper bars and between the bars and the shaft. Applications include automotive starter motors as well as automotive auxiliary, appliance, and industrial motors.

The dimensional stability of phenolic materials enables the commutators to remain virtually stable at spin speeds of 25,000 to 50,000 rpm, operating temperatures of 150 to 250 C, and soldering temperatures of 400 C for up to 30 sec. Because the commutator resists creep, bar movement is held to less than 0.0002 in.

These materials also encapsulate electrical and electronic components, providing electrical insulation along with strength. For example, the molded component in an automotive fuel injector can withstand 1,400 psi spikes for millions of cycles without excessive degradation or creep.

Corrosion resistance

Environments where water causes corrosion result in other applications for these materials. For example, a Japanese heavy-equipment manufacturer uses a corrosion-resistant, glass-reinforced phenolic water pump impeller that is molded to net shape. A boat manufacturer uses a bracket made of similar material in a tilt mechanism. This bracket resists corrosion, electrically insulates the brush holders, eliminates machining, and does not require a bearing as do metal brackets.

Metal replacement

Figure 3 — Tensile strength retention of plastics at 200 C.
Select figure to enlarge.

Plastic materials, including phenolics, have replaced metal components in various automotive applications. The driving force in these high-volume applications is lower cost.

Plastics save money mainly through production process advantages. Injection molded fiber-reinforced plastic composites produce complex shapes with smooth and precise surfaces, thereby reducing finishing costs associated with metal. In addition, metal components consisting of several metal parts are often replaced by a single molded plastic component, reducing machining and assembly costs.

Replacing metal with plastic reduces weight, and enhances performance characteristics such as chemical and corrosion resistance, thermal insulation, and vibration and sound damping.

Automotive applications in which phenolic composites have replaced metal parts include torque converter reactors (also called stators), as well as other engine, transmission, and brake components.

Torque converter reactors. In the U.S. and Japan, glass-reinforced phenolics are used in reactors that direct transmission fluid within torque converters. These reactors are molded to net shape. Selecting phenolics rather than aluminum results in 20% weight reduction; elimination of crimping and other machine steps; part integration (some reactors incorporate an integral thrust washer); and reduced manufacturing costs.

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