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 Modifiers. 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 FormulaFX™ product line covers the full spectrum of carbonaceous materials which are used in organic as well as sintered brake pads or linings.

FormulaFX™ product line includes:

Calcined Petroleum Coke (CPC)

CPC has always been a major constituent of brake pads and is the base of the mechanical strength and an optimal “carrier” for other ingredients. Due to its relative hardness, CPC is responsible for the base coefficient of friction (CoF). Usually relatively coarse CPC is used, but very fine grades can also be used as a “soft” abrasive and cleaning material in some formulas.

Fig. 01

SEM of Calcined Petroleum Coke

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. 02

SEM of Natural Graphite

Synthetic Graphite

Synthetic graphite, being primary or secondary in origin, is used in almost all formulations for its lubrication properties and for its excellent thermal conductivity, which is related to its high level of crystallinity and purity.

Fig. 03

SEM of Synthetic 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™ product line, Superior Graphite offers purified flake and synthetic grades.

Fig. 04

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 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. 05

Resiliency Comparison: Graphitic Materials at Different Pressures

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