FormulaFX™: Innovative Friction Products
Modern brake pad formulations are a mix of many ingredients, which can be classified in 5 categories: fibers, fillers, friction modifiers, phenolic resin, steel wool and other metals. Together with inorganic materials like clays, rubber and abrasives like aluminum oxide, graphite and cokes belong to friction modifying products and materials. Depending on applications being non-asbestos organics (mainly Asia, North and South America), low steel (mainly Europe) and semi-metallic, the carbonaceous fraction can represent up to 25% in weight of friction materials. Regarding the carbonaceous aspect, formulators are using a mix of calcined petroleum coke (CPC), synthetic graphite and natural graphite to balance the specific performance of each individual ingredient. The Superior Graphite FormulaFXTM friction product line covers the full spectrum of carbonaceous friction materials which are used in organic as well as sintered brake pads or linings.
Natural Graphite
Natural graphite can be divided in 2 categories: amorphous and flake. Amorphous graphite is a micro-crystalline material, whereas flake graphite is macro-crystalline. Both have good lubrication properties allowing an adjustment of the CoF. However both have relatively low purity in the range with a maximum of 85% for amorphous (Mexican origin for example) and 95% for flake (mainly Chinese origin). This will limit future usage due to increased regulations, especially on SiO2, which is classified as a carcinogen.
Fig. 01
SEM of Natural Graphite
Thermally Purified Grades
Superior Graphite’s unique Electro-Thermal Treatment/Purification Technology is an ideal tool to overcome the purity deficit of natural materials like flake graphite. An improvement of the crystalline structure resulting in electrical or thermal conductivity enhancement of synthetic graphite is also achieved at temperatures approaching 3,000°C. In the FormulaFX™ friction product line, Superior Graphite offers purified flake and synthetic grades.
Fig. 03
SEM of Flake Graphite after Heat Treatment
Graphitic Coke Grades
The Electro-Thermal Treatment/Purification Technology also imparts graphitic properties of amorphous feed stocks like CPC, resulting in unique materials like Resilient Graphitic Carbons (RGC™), which have proven advantages in brake pad behavior (see Compressibility Application page). Depending on the morphology or other characteristics of the feed material, other specialty graphitic materials can be produced using this technology. RGC™ can easily be differentiated from other carbonaceous friction material by the extremely high resiliency (spring back effect) that RGC™ exhibits under high pressure (see Figure 5).
First Image
SEM of Graphitic (Purified) Coke
Fig. 04
Resiliency Comparison: Graphitic Materials at Different Pressures
