Selecting Friction Material
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Know the Terms
- Static/Breakaway Coefficient:
Quantifies the ability of a material to avoid slipping. The higher the coefficient, the more force (torque) it takes to begin slipping
- Dynamic/Midpoint Coefficient:
Quantifies the relative force required to maintain a constant slip. The higher the coefficient, the less force (apply pressure) and time it takes to modulate or control slipping
- Thermal Capacity/Durability:
The amount of thermal distress a material can tolerate before it can no longer function as intended. In short, can it take the heat?
- Elasticity (Shudder Resistance):
The ability to conform to variations in running surfaces. The elasticity of the material impacts surface contact (area) and loading (force). It is sometimes referred to as Shudder or NVH Resistance.
- Shear Strength:
The amount of force the friction material can handle before it fails or fractures.
The amount of oil the friction material can hold.
The terms above have one thing in common: they are all well-established physical properties by which any piece of friction material can be analyzed and evaluated.
What matters? Which is of greatest importance? That depends on how you intend to use the friction material. For example, in a straight on or off lockup system, static coefficient and shear strength would surely top the list, and thermal capacity and porosity may be on the lower end of importance. As you move further toward a system designed to slip continuously, static coefficient and shear strength become less important considerations compared to thermal capacity and porosity.
In general, these are the levels of importance within the three general lockup categories:
|Static Coefficient||Dynamic Coefficient||Thermal Capacity||Elasticity Resilience||Shear Strength||Porosity|
|Limited Slip Lockup||Medium||Medium||Medium||Medium||Medium||Medium|
|Continuous Slip Lockup||Medium||High||High||High||Medium||high|
Once you know what properties are important, how do you select the right friction material? The charts below represent a comparative analysis of a variety of BorgWarner friction material offerings (HTE, HTS, HTL and XTL), along with analysis of materials offered by a major competitive brand (T, K, HC, PT). The superior materials offered by BorgWarner – used appropriately based on application criteria – will consistently provide you with the best quality lining for your torque converter rebuilds.
Elasticity (Shudder Resistance)
Click here to learn more about BorgWarner friction rings.
Chart data provided by BorgWarner.
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