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  • Long Fiber Compound Puts the Brakes on Secondary Processes

Master CylinderHydraulic brake systems for trailers are only one of the many items that Demco-Dethmers Manufacturing Company has been manufacturing for years. “Originally, the master cylinders were done in cast iron, which can rust, then most of the auto industry went to aluminum, but that still needed secondary machining. We wanted something that would not rust nor require the secondary processes which would lower costs and help with lead times,” said Tim Lammers, Engineering Manager for Demco-Dethmers Manufacturing. They turned to molder, Riverside Plastics and RTP Company for help.

“When you are dealing with this type of application, your primary concern is rupture,” discussed Michael Meek, General Manager of Riverside Plastics. “RTP Company was our first stop. We’ve worked with RTP Company for many years and have had nothing but good experiences. Overall, we trust RTP Company’s ability to match materials with applications.”

The material chosen for this application was an RTP 200 Series long fiber reinforced nylon. When performance is critical, Long Fiber Compounds are a smart choice. They provide high strength-to-weight ratios with very low creep. This particular compound provided Riverside Plastics and Demco with increased impact strength plus the benefit of increased flexural modulus. Notched impact strength of the compound is 5.0 ft lbs/in at 1/8 inch (267 J/m at 3.18 mm) while the flexural modulus is 1.70 x106 psi (11,713 MPa).

Tooling for this project was done in stages. The strength of the plastic played a vital role in each stage. Stage one was to prove that a bore could be produced smooth enough to function with the piston and seals and that the molded part had the strength to handle the pressure that was applied. The plastic cylinder was pressure tested to ten times the maximum working pressure. A stroke wear test was also conducted and found very little wear after 1 million cycles at 75-100 percent of the maximum pressure output of the master cylinder.

The next step was to mold the reservoir on the top of the bore without distortion. The reservoir capacity was increased by twenty percent and was able to be retro-fit to older models, allowing older brake systems to be updated with the new master cylinder.

“Using plastic allowed us to mold this part to an exact size, shape, and surface finish so that processes like painting and machining could be eliminated. You can also add features that are not possible with other processes and materials, like the site gauge window with a fluorescent float ball to check fluid levels without opening the reservoir. We also added a baffle to the bleed back port to prevent fluid spills when bleeding the brakes.” Stated Lammers, “We use this master cylinder in many of our own products, and also sell them to other manufacturers. We tried other materials but did not get the surface texture and piston seal life we needed.”

“We needed help in finding the right material and thought of RTP Company” commented Allen Gunn, Vice President of Riverside Plastics. “Our account rep really knows the materials and is always willing to help.”

Visit Demco-Dethmers Manufacturing Company at, they are located in Boyden, Iowa. Riverside Plastics is a full service injection molder located in Bonaparte, Iowa contact them at (319) 592-3166.