NVH Rubber Bumper Design: A Case Study

NVH Rubber Solution: Rubber Bumper Case Study

A while back one of our customers was designing a rubber part for an automotive OEM and was looking for solutions to the rubber part’s squeaking problem. This part was meant to be a shock absorber on a vehicle bodyside, but previous iterations of the rubber bumper made unpleasant squeaking noises when the car was in motion. For the new part design, the company looked to Coi Rubber to assist in solving the rubber part’s noise control issue as Coi Rubber has a long history of servicing the NVH (Noise, Vibration, and Harshness) industry in custom NVH rubber components.

Internal vs. External Lubricant for NVH Rubber

The client wanted the new rubber bumper to provide a constantly oily or self-lubricating surface that is clear of color and offer just the right amount of lubricity, or friction reduction, that is beneficial for its final use. At first, the client engineer considered EBS (ethylene bis-stearamide, or ethylene wax) and WD-40 (multi-purpose lubricating oil) as lubricating additives into the rubber compound, but neither of these additives would serve to provide the constant self-lubricated surface the client was looking for.

EBS is a processing agent that improves the material mix’s dispersion and product mold release, but it is not a surface conditioner that can provide a constantly blooming surface lubricant in the final product. WD-40 can be applied to an NVH component’s rubber surface for temporary lubrication. This is considered an external lubricant, but applying external lubricants like WD-40 to each of the NVH rubber bumpers would neither be cost effective nor accomplish the customer’s product performance requirements.

Experienced engineers at Coi Rubber Products recommended either erucamide or oleamide, both fatty acid amides, as an internal lubricant for this client’s NVH rubber bumper. Erucamide is a “slow blooming” lubricant, while oleamide is a “fast blooming” lubricant. Now the question came down to which of these internal lubricants – erucamide or oleamide – is more suitable for this client’s product.

Slow Blooming vs. Fast Blooming Lubricant

The release of the internal lubricant to the surface of the rubber for its final use is dictated by the amount of blooming that takes place giving the rubber surface an “adequate” amount of constant lubrication. Therefore, the type of blooming required is dependent on the form, fit, and function of the specific NVH rubber component. Other considerations for the lubricant choice are the mold equipment and mold temperature required for the rubber. For this client’s particular product, the primary concerns were low cost and fast lead time for mass production.

While erucamide does provide better lubrication than the same amount of oleamide, the slow blooming would not be adequate for the size of this client’s product and to meet their fast lead time for large scale production to market. Due to its chemical stability, erucamide also has a lower rate of color formation or yellowing than oleamide, but because the final product did not have a light color requirement this was not a concern. Oleamide is less expensive than erucamide and its lower molecular weight allowed the lubricant to migrate to the molded rubber surface more quickly, i.e. “fast blooming.” Ultimately, experienced engineers at Coi Rubber and the client engineers decided on oleamide as the appropriate internal lubricant for this vehicle’s bodyside NVH rubber bumper.

Learn More: Erucamide vs. Oleamide

About Coi Rubber

Coi Rubber Products, Inc. is a custom manufacturer of molded rubber and plastic components. Coi Rubber has over 28 years of experience in Engineering, Design, Compounding, Prototyping, and Production of molded rubber and plastics. Our capabilities include custom compounding, injection molding, compression molding, transfer molding, extrusions, rubber-to-metal bonding, insert over-molding, and more. We provide large scale production and engineering support to the Automotive, Industrial, Agriculture, Appliance, HVAC industries, and many more. Coi Rubber is ISO/TS 16949:2009 and MBE certified.