Friction is defined as the resistance to relative motion that opposes the travel direction of an object. It is created by contact of one solid body with a divergent surface.
Friction materials are manufactured forms, used to harness friction in order to slow down or stop an object or machine.
Friction materials are essential to the safe and controlled usage of all types of machinery. They induce resistance and decreased speed or movement in a number of different systems, such as industrial machinery, automotive brake systems, industrial brake systems, and operating systems. They also transfer power.
Because of their important functions, the friction material market is quite robust, and there are several applications for which friction materials are essential. Some of the products that rely on friction materials to function are: brake pads, clutch sets, brake bands, brake lining, clutch facings, disc brake pads, clutch discs and friction discs, brake shoes and brake block.
These materials are utilized by a variety of industries such as automotive manufacturing, general manufacturing, aircraft, aerospace, railroad, mining, defense, oil and gas, forestry and construction.
The History of Friction Materials
Friction is a natural occurrence, and we have a record number of people trying to either combat or use it since the time of the ancient Greeks. Greek and Roman scientists like Aristotle, Pliny the Elder and Vitruvius all studied the cause and mitigation of friction.
The classic laws of sliding friction were discovered by Leonardo da Vinci in 1493, but he did not publish the notebooks in which he wrote about them. They were rediscovered 206 years later by Guillaume Amontons, and became known as Amonton’s three laws of dry friction. Other scientists went on to elaborate on this, making important discoveries like the difference between static and kinetic friction. In 1734, John Theophilus Desaguliers uncovered the role of adhesion in friction, proposing that friction was the force necessary to tear adhering surfaces apart. In 1833, Arthur Jules Morin developed the concept of sliding versus rolling friction, and around 30 years later, Osborne Reynolds worked out the equation of viscous flow. These developments completed the classic empirical model of friction (static, kinetic and rolling) still used in engineering today.
Using knowledge like this, Bertha Benz invented brake linings and brake pads while driving across Germany in one of the first long-distance car trips ever taken (August 1888). The earliest manufactured brake linings were made from asbestos; this trend continued into the late 1900s, until 1989, when the National Institutes of Health (NIH) announced that asbestos exposure was dangerous to human health. (It can cause lung disease and cancer.) Since then, asbestos has been dropped from the friction material lineup, largely replaced by fibers like synthetic aramids.
Although it is an important aspect of many markets, the production of friction materials has recently become an industry in its own right. The friction material industry of today is competitive and thriving. Because of major changes in the industry throughout the years, such as the introduction of ceramics, many companies try to protect their own advancements and formulas, in order to beat out competitors. Friction materials continue to advance, and developments are a consistent occurrence in the industry market.
When making friction materials, manufacturers design for important product characteristics, such as: heat resistance, a high coefficient of friction, good energy absorption, durability, and resistance to wear and tear. To that end, they usually produce rough or textured surfaced materials, as smooth surfaces create little friction and are not efficient. They also design for application-specific requirements, such as torque capacity and speed of stopping. For example, applications that require quick stopping, they must choose a material that creates a large amount of friction.
Another thing they think about is the type of frictional force they are looking to create, as the type of material suited to a given task is dependent upon the type of friction. There are three main types of frictional force: static, kinetic and rolling.
- Static friction is found between two solid objects that are not moving relative to each other, preventing movement entirely. Slope is an important consideration when utilizing this particular type of friction.
- Kinetic friction, also known as dynamic friction, occurs between two objects moving relative to each other. Both surfaces may be moving or one may be sliding along a stationary object.
- Rolling friction involves wheels or balls. The rough texture of friction materials catches the wheel and stops it from sliding or slipping. A car tire spinning on ice or snow, for instance, is an example of low rolling friction and thus the tire does not catch on the ground, but keeps moving around.
Materials for Friction Material
The raw materials available for friction material production range from organic to ceramic to fibers and metallic materials. Ceramic materials are used in heavy loads and high temperature applications. Ceramic can withstand thermal energy higher than any other alternative, however, it wears pretty fast. Organic friction material makes use of fiberglass and other materials, since asbestos proves to be a hazardous material for humans. Aramide fibers such as Kevlar is also used for making friction materials, it has the property of organic material that helps in smooth engagement of components and braking ability of ceramic pads. The other options involve high-end metallic materials, such as, sintered steel and phosphate steel. No other additives are required for making metallic pads; however, they take heavy toll on the machinery, therefore, used only in performance vehicles. Finally, semi-metallic brake elements are also available using copper, brass and steel wool bonded by resin as these compounds share many of the long-lasting characteristics of ceramic options.
Depending on your market, your friction materials may work a little different.
Brakes, for example, use friction materials to slow and stop wheels and other mechanisms from moving. When you press the brake, it activates a system that places friction material against the moving disc, which slows down the connected tire.
A traditional braking system prevents motion by means of friction, converting kinetic energy of the vehicle or a moving object to heat. However, in regenerative braking, which is relatively a new concept, the kinetic energy is converted into electrical energy. This is found in hybrid or electric vehicles.
A friction disc, or a friction plate, is a plate bonded with friction material, used in automotive braking systems. Friction plates are usually constructed of durable metal, and because they can be noisy, manufacturers often coat them with rubber and other high friction materials.
Clutch discs are a type of friction disc, used to connect a vehicle engine to the input shaft of the transmission. This connection allows for the temporary separation required to shift gears.
Clutch facings are used to maintain systems with a lower coefficient of friction. The lower coefficient facilitates smooth and stable clutch engagement and disengagement. It also creates a quieter system.
Brake pads, also known as brake bands, are friction mechanisms of brakes. They slow down the system when they are pressed against the friction disc. Like friction discs, they consist of a friction surface bonded to a metal plate. There are many types of brake pad, including disc brake pad and ceramic brake pad varieties.
Brake lining is another component of brakes. This friction material is heat resistant, which is important in friction systems, since they create so much heat. Brake lining is used on many brake varieties, including the drum brake and the disc brake.
Friction Shoe/Brake Shoe
Friction shoes, or brake shoes, along with friction pads, are the most well-known forms of friction materials used in braking mechanisms. In disc braking systems, they are placed in brake calipers and touch the disc to convert kinetic energy into the thermal energy that slows the automobile.
Friction Clutch Set
Friction columns, or blocks, have specialized movement regulation applications in mining and oil rigging industry. To use them, manufacturers attach them to crane components, such as winches and hoists. regulate the movement.
Proper Care for Friction Materials
Friction materials are heavily used products, so it is not easy to care for them, so watch out for signs of wear or damage.
Due to the nature of their work, your friction materials, regardless of wear resistance, will become worn at some point. When this happens, you need to replace them. If you don’t, in the case of automobiles, the backing or rivets will rub up against the rotors or drums during braking, and eventually cause expensive damage. You will likely have to re-machine or replace the damaged parts. Avoid this by looking out for the classic warning sign of brake wear, squealing. If you wait too long, your next warning sign (suggesting damage) will be an unpleasant grinding sound or sensation.
Another peril for brake friction material is contamination by leaked brake fluid or oil. If you hear brake chatter, like brake pads are vibrating as you use them, they’re probably contaminated. Fix this by finding and repairing the leak source and replacing the brake pad. Note: you must always replace both of your brake pads at the same time. This is because unmatched lining thicknesses or materials will cause uneven braking, which can be both dangerous and inefficient. Fortunately, friction materials like these are easy and inexpensive to replace.
We recommend that you purchase RoHS compliant friction materials. RoHS (Restriction of Hazardous Substances) is an EU directive that restricts the use of certain hazardous materials. While RoHS compliance is not required in the United States, if you work with products to be shipped overseas, you need this certification. Also, it’s just a good guide to follow. In the United States, make sure that your friction materials comply with standard regulations put out by the EPA. Also talk to your manufacturer about SAE International and FMSI (Friction Materials Standards Institute).
Things to Consider
Since there are a number of options in friction material, it is necessary to consider factors that determine its functionality and life. Before buying a friction material, you need to find out:
- Whether the material provides smooth engagement
- Whether the material can resist brake fade as the temperature rises
- Whether the material endures temporary exposure to water
If your supplier can answer “yes” to all of these questions, then you can go ahead feeling confident that this friction material will serve you for longer periods.
Speaking of suppliers, the key finding the friction material you need is working with the right manufacturer. Find this manufacturer by scrolling up to the top of this page and checking out the proven friction material companies we’ve listed for you. Visit their individual websites and browse their products and services. Pick three or four that you believe could serve you best, and then reach out to each of them with your specifications and questions. Compare and contrast not only their answers, but their attitudes. Look for a friction material manufacturer who will provide you not with a barebones product, but the best product possible, no matter your budget.
Friction Materials Terms
- Refers to the stability between the
front and rear brakes.
- The process by which overheated or spoiled brake fluid
and air bubbles are removed from the brake system.
- Metal housing bolted to an axle and vehicle wheel
that looks like a large jar lid. Brake shoes are forced against the drum
to stop rotating wheels.
friction material that presses against the disc/drum to create braking
- Made of friction materials and bonded to metal plates.
Brake pads need to be replaced occasionally due to heavy wear.
- Process of wearing in brakes so that the contact between
the friction material and the rotor or drum becomes stable.
- The assembly that
houses the brake pad(s) and applies them to the rotor. This also houses
the hydraulically operated pistons
to which the pads are bonded.
- Any of various contraptions used to engage and disengage
two moving parts of a shaft or shaft and driving mechanism. When changing
gears, the clutch pedal is pressed, disengaging the clutch and allowing
the gear change; when released, the clutch engages and transfers the
rotating motion throughout the entire driveshaft.
- The ratio of force necessary to move
an object compared to the weight of the object itself.
- Consists of brake pads, caliper and rotor. This is
the part of the brake system that actually stops the vehicle.
- A large circular metal
housing that looks like an oversized jar lid and is bolted to a vehicle's
axle and wheel. Brake shoes are forced against the inner section of the
drum, which then stops the
- Apparatus in a laboratory used to test brake system
- Temporary reduced braking power. Fade results from overheating
of the friction material.
- Grooves on friction material that help dispel
heat, get rid of fluid and eliminate noise.
- The cylinder that contains hydraulic fluid and
a piston. It is connected directly to the brake pedal and transmits pressure
to the brake operating system.
- The return of braking performance to a normal level
after fade has diminished. This measures friction materials' ability
to perform after overheating.
- Also referred to as a disc or drum, this is the circular
metal object to which the brake pads are applied, creating friction to
slow and stop the vehicle.
- A steel semicircular form coated with a friction agent that
presses against the inside of a drum when activated.
- High-pitched noise made when braking. Squeal indicates
that brakes should be inspected for wear.