High-performance cold gas coating for wear protection and emission reduction for brake discs
Brake discs endure exceptionally heavy loads and rank among the most stressed components of an automobile. Not only do they require frequent replacement due to rapid wear and tear, but they also contribute significantly to environmental impact through particulate emissions.
While modern vehicles have made strides in emission control, the extent of particulate matter generated by tire and brake abrasion remains largely overlooked. Tire and road abrasion account for approximately half of the particulate matter in German road traffic, with brake pad abrasion adding another quarter to the equation.
Brake wear emissions, encompassing brake dust and particulate matter, have emerged as a mounting concern for the automotive industry in light of stricter environmental regulations set by the EU.
Brake discs predominantly originate from gray cast iron infused with embedded graphite. These gray cast iron brake discs not only offer cost-effective manufacturing but also encompass the essential mechanical attributes required.
Yet, challenges persist in the form of subpar corrosion resistance and excessive disc wear during operation. While no other material currently matches the cost efficiency of gray cast iron for vehicle brake discs, coating such discs provides a practical and budget-friendly solution.
However, traditional thermal coating methods remain costly in terms of both materials and expenses, and they are unable to consistently meet the required criteria for coating adhesion, corrosion resistance, and resistance to cracking. In contrast, the cold spray process, unlike laser cladding, is unencumbered by patent restrictions from any major automotive manufacturer.
Tests and results
- With a high-performance cold gas coating with the Impact Cold Spray System EvoCSII, there is no delamination or severe cracking in the coating and the particle emission is reduced drastically.
- The performance of the coating was evaluated in terms of corrosion resistance, wear resistance, and tensile bond strength between the coating and the brake disc.
- The cold gas sprayed composite coating of the cast iron brake disc showed a 95% reduction in wear in the SAE J2522 test
- The coating showed excellent adhesion even after extreme bench test runs without any delamination.
- In addition, 720 hours of salt spray tests were successfully completed without corrosion.
- The cold spray process wins over other coating technologies with its simplicity, high performance and low costs.
- As it is a cold process all process parameters are always constant independent of the dimensions and shape of the brake discs.
- There is no thermal distortion of the discs, and the layer build-up stands out with its uniformity. Thus, the coating thickness can be reduced to a minimum and the subsequent grinding costs are minimized.
- A standard brake disc can also be coated in a one-layer system (no intermediate layer) in less than 30 seconds.
The present results show a cost-effective and resource-saving solution for the brake disc application with cold sprayed composite coatings.