Braking for the future
Most brake suppliers use generic marketing terms such as “ceramic” or “semi-metallic” or “NAO” (nonasbestos organic) to describe their products, but they don’t give you any details as to what exactly these terms mean. That’s because no two brake suppliers agree on what these terms actually mean. Ceramic, semi-metallic and NAO are all buzzwords that imply a particular friction material contains an unspecified percentage of the named ingredient.
The Brake Business, in Detail
All that the term, “NAO” tells you is that the friction material contains no asbestos fibers. In other words, the term NAO does not tell you what a friction material contains, only what it does not. Typically, NAO friction materials have a low metallic content, usually less than 30%, but that percentage can vary with the product and application.
Semi-metallic tells you a friction material has a high metallic content, typically 50-to-60 percent or more chopped steel wool fiber. But it says nothing about any other ingredients that may be in the material.
“Ceramic” is the most misleading and confusing term of all. The word implies the friction material contains ceramic fiber, of which there are various types and particle sizes. But how much? And does the actual amount really matter? The size of ceramic fibers or particles can range from 0.4 to as much as 80 microns in diameter. Some say smaller is better because the brakes run more quietly, but others disagree and say size doesn’t matter. It’s the other ingredients that go into the mix that have more of an impact on noise and performance.
One reason why there are no standard definitions for these terms is because there are literally hundreds of different friction formulas being produced by aftermarket and OE suppliers. Within a given product line, there may be dozens of variations of NAO or ceramic friction materials for different vehicle applications. For the last decade or so, brake suppliers have realized that a one-size-fits-all friction material just doesn’t cut it in today’s world.
Replacement brake pads and shoes have to closely match the friction characteristics of the original equipment brake materials, Otherwise it may upset the operation of the antilock brake and stability control systems. It may impact the vehicle if the replacement brake pads and shoes don’t feel and perform the same or better than the original equipment brakes.
The point is the actual friction formula doesn’t really matter as long as the replacement brakes deliver the kind of braking performance your customer expects.
What Really Counts
When a brake supplier develops a new friction formula for a particular vehicle application, they look at what your customer really wants. According to a JD Power survey, the most important features that customers want from their brakes are as follows:
1. Stopping power
2. Good pedal feel
3. Quiet operation
4. No brake pulsation
Brake suppliers take these factors into consideration, along with technical and safety requirements such as the hot and cold friction characteristics of the material, resistance to fading after repeated hard braking, the strength of the material itself, fatigue resistance, weather resistance, noise characteristics, dust generation and wear properties. They also take into consideration how the vehicle will be driven and the type of driver who will most likely buy their product.
Someone who drives a Ford Focus is obviously a different kind of customer than someone who drives a Corvette or a BMW M3.
With so many variables to take into account, one friction formula is often not enough for a given vehicle application. Some vehicle owners may want a high-performance replacement product rather than a standard replacement product. So the brake supplier may offer a standard replacement line, and a premium line, and/or a performance line to provide a range of options for different customers.
Some brake suppliers also offer different product lines that are specially formulated for a particular type of vehicle. For example, many late-model Japanese vehicles are factory-equipped with ceramic brake linings. As a rule, ceramic friction materials perform well at low-to-moderate brake temperatures (up to 500° F), to deliver long pad life, quiet braking, reduced rotor wear and little visible brake dust.
Many European performance cars and sedans, by comparison, are factory-equipped with more aggressive low- or semi-metallic pads. The original equipment Euro brakes are notorious for producing lots of ugly black brake dust that sticks to alloy wheels. Rotor wear can also be a problem. So a different type of replacement pad would be offered for European applications compared to Asian applications.
One thing no brake supplier will ever reveal is the exact formula for any of its friction products. These are closely guarded trade secrets that only a few people have access to. The labels on the containers are coded so a casual observer can’t tell what exactly they contain. There are various kinds of powders, fibers and resins that can be blended together to create all kinds of friction materials.
Back in the days when asbestos was still used in brakes, most friction materials usually contained a simple mix of asbestos fibers, some filler material and a binder such as linseed oil, cashew resin or phenol resin to glue it all together.
Today, a typical NAO or ceramic friction material may have as many as 20 different ingredients, including various sizes and types of carbon or ceramic fibers, metallic fibers, graphite or coke particles, inorganic fillers and resins.
Copper is one ingredient that has been added to friction materials to help reduce noise, dissipate heat and reinforce the pads. But environmentalists say copper in brake dust can pollute water and harm algae and fish. Some US states have banned copper in their mix and all states may cap the copper to five percent copper content by model year 2021.
How Pads are Made
When a brake manufacturer makes a production run using a particular recipe, the various ingredients are carefully weighed and blended together in a giant mixer. A uniform mix is very important for consistent friction characteristics. The powder is then pressed into a mold to create a raw unfinished brake pad. Some brake suppliers also insert a noise control shim into the pad itself as it is being molded. Others attach the metal or fiber shim to the back of the steel backing plate after the pad has been baked and attached to the plate with adhesive or rivets. Some manufacturers use mechanical retaining systems, which use hook-like serrations or welded mesh on the face of the backing plate to lock and hold the friction material in place.
The molded pads (which are called “green” pads at this stage of the process) are then placed on a conveyor belt and sent through a long oven to harden the resins. The time and temperature of the baking process must also be closely controlled for consistent quality.
After the bake oven comes any final machining such as cutting slots and/or chamfers on the pads. Some pads may also have a top coating applied at this point to aid break-in and suppress noise. Some pads may also receive a final heat treatment to fully cure the resin. Most pads, however, are not fully cured until they are installed on a vehicle and driven a few hundred miles. The break-in process must be done correctly to burnish and seat the pads: gradual braking with sufficient time between applications for the pads to cool down. Hard braking should be avoided until the pads are fully cured as this can overheat, glaze and ruin a new set of pads.
Developing New Materials
The development of new friction materials is an ongoing and time-consuming process. As one brake supplier said, “We are always trying to make our current products obsolete with even better products.”
It’s important to note that the development, testing and manufacturing processes I’ve described are those generally followed by name-brand brake manufacturers. They have a reputation to maintain, and are liable for the products they produce. That’s not the case with every brake supplier you may encounter. Some replacement pads have had little or no testing, and may or may not deliver satisfactory braking performance, noise control or wear. The quality may be inconsistent, and you may end up with a dissatisfied customer and a comeback if you take a chance and install these kinds of pads on a customer’s vehicle. Don’t take chances. Choose brand-name products you’re familiar with and a supplier who stands behind their products.
Also, follow your brake suppliers’ recommendations as to what type of friction material should be used for various kinds of driving applications. For hard-use applications, premium-grade replacement pads and shoes are usually best. Premium-grade products generally provide better wear than standard or economy-grade products. Premium products also tend to perform better in terms of stopping distance, fade resistance, pedal feel and noise control. They deliver the kind of “like-new” performance that makes most customers happy.
Much, much more in the print addition of Auto Atlantic.
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