Solving White Bloom on NBR 85 Brake Pedal Bumpers for Racing Simulators

How we removed surface bloom and fixed the root cause in the compound.

If you build racing game controls or simulator pedals, you know the brake pedal has to feel solid—and last. We manufacture a hard NBR rubber bumper for a customer in the racing game control industry. It sits at the brake pedal stop. When the driver presses the brake all the way down, the bumper cushions the impact and prevents metal-on-metal contact. That reduces wear and protects the pedal assembly from damage. (Chicarubber)

The material is NBR, 85 Shore A. It is abrasion-resistant and very hard—close to plastic. That hardness is great for durability, but it makes production more demanding. Deflashing and trimming are difficult, so the mold must be made from harder steel.

Then we ran into a common issue: white bloom.

The parts started showing a white, powdery film. NBR is more prone to this than some other rubbers. Silicone can bloom too, but it usually happens more slowly. The customer returned some parts, and we went to work.

First, we tumble-washed the returned parts to remove the white surface film. Then we placed them in an oven for post-curing, also called secondary vulcanization. After that, the white bloom was gone. We also talked with our raw material supplier and asked them to improve the compound so future production would not have the same problem.

Why Does Rubber Bloom?

White bloom usually comes from ingredients inside the rubber that have not fully reacted or volatilized. In this case, sulfur powder and white powdered accelerators—acting as cure catalysts—were not completely driven off. Post-curing in an oven helps evaporate those residues. If they remain in the part, those white additives can migrate to the surface at unpredictable times.

The fix is not just cleaning the surface. It has to include the compound and the cure. We can reduce the amount of those additives and switch to black additives where possible. That lowers the risk of bloom and gives the part a clean, consistent finish.(Chicarubber)

What This Means for Racing Pedal Brands

A white film on a brake pedal bumper may look like a small issue, but it can affect appearance, customer perception, and sometimes performance. For a premium racing simulator, every touchpoint matters. A clean, durable bumper helps the pedal feel right and protects the hardware inside.

Our approach for hard NBR pedal bumpers includes:

  • Selecting an NBR compound with the right hardness and abrasion resistance
  • Using harder mold steel to handle 85 Shore A material and difficult deflashing
  • Controlling cure and post-cure to drive off volatile ingredients
  • Tumble washing when surface bloom needs to be removed
  • Working with the compound supplier to reduce bloom-causing additives and use black alternatives

If you need NBR rubber bumpers for racing pedals or other control hardware, the goal is simple: a part that cushions the stop, resists wear, and stays clean. Contact us to discuss your project. We can help you choose the right compound, mold, and post-cure process for your application.

Solving White Bloom on NBR 85 Brake Pedal Bumpers for Racing Simulators

If you need to customize silicone products, please contact us at chicarubber