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Rubber Insulated Bushings and Method of Manufacture

One of the most frequently asked questions we receive from customers who visit us on line, or call in - is with regards to bushing design, and specifically – What method of manufacture is best for my bushing application?  In this blog, we’ll examine two different approaches to bushing manufacturing design.

Silent-Bloc Design vs. Center Joint Bonded Design
Silent-Bloc Bushings generally consist of three (3) distinct pieces.  An outer steel sleeve, and an inner steel sleeve, which sandwiches a piece of molded rubber (a “shot” bushing). Or a long rubber tube assembled over a steel inner tube, which is funneled into an outside steel tube and cut to length (a “Torflex” bushing).

The Silent-Bloc or Torflex Bushings described above rely on a mechanical bond-compression-and friction between the rubber and metal sleeves for adhesion. Center Joint Bonded Bushings have the rubber vulcanized to the insert.  This chemically bonded over mold, is then assembled into the outer sleeve.

Bushings Inc. manufactures both Silent-Bloc and the Center Joint Bonded design bushings, in fact we also manufacture bushings using several other methods – we will cover these other design types in another blog.

When properly designed both silent-bloc, and center joint bonded bushings accommodate oscillating movement without lubrication in dusty and dirty environments, they relieve mis-alignment, reduce noise, and absorb linear and torsional vibration.  

Which of these two designs is the best?

Bushings Inc. has numerous rubber molds accumulated during our 65+ years in business, and when a Silent-Bloc bushing can be fabricated from existing rubber mold tooling, a properly designed Silent-Bloc bushing can provide a good low cost (no rubber mold tooling expense) solution for your application requirement.

A Center Bonded bushing does have additional radial load capacity when compared to a Silent-Bloc bushing.  Initial tooling costs can be slightly higher for the rubber mold, but with volume applications, this cost is typically minimized.  Tighter tolerances can be maintained with this design as well.  But perhaps the biggest advantage of the Center Bonded design is greater fatigue life.

Fatigue Test Results

We will examine fatigue test results of our Center Bonded bushings versus one of our competitors Silent-Bloc bushings which demonstrate this in the next blog.

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What Our Clients Say About Us

Testimonial Image
"I want to take this opportunity to thank the Bushings Incorporated team that recently helped us get our automated assembly line up and running.  For years our line required our rubber insulated overmolds be manually inserted due to several failed attempts to get an automated press to properly insert the bushings.  The Bushings Incorporated team was able to help by working with our manufacturing engineers to develop fixtures, and procedures that were able to get the automated press up and running.

With the new press up and running, the consistency has been great, and the operator is very happy with the new process.  The operator says that the new press and fixturing is doing a good job at installing the bushings straight and consistent.  He has experienced no “mushrooming” or tearing of the bushings with the automated press (this was the reason for manually inserting them for so many years).  The operator also says that the job is much easier on him, and the production level is up due to the new process.

The help that was received to improve our process was above and beyond.  That kind of support is needed and appreciated, and while most vendors lack in their support, it is my feeling that Bushings Incorporated and their team have gone one step above.

Thanks again for the support!"

Steven A.
Engineering Product Manager
Motion Control Division


Our Company

Established in suburban Detroit in 1942, Bushings Inc. is an ISO 9001:2015 certified manufacturer of rubber insulated bushings, and marine/industrial engine mounts, with headquarters in Rochester Hills, Michigan.

Our rubber molded products, including engine mounts, rubber insulated bushings, and rubber overmolds are world class quality, and are specified by leading Original Equipment and Aftermarket Manufacturers.


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