CL Sintered Technology FAQ05.01.2012
What is sintering, and how are sintered pads different from other pads currently on the market?
While most pads are formed from fibers and organic materials bonded together by resins, CL Brakes Sintered Pads begin as powdered metals such as iron, bronze, and copper, mixed with roughly ten other constituent materials including graphite and carbon. The mix is compressed in a tool under extreme pressure to give it shape, and then brazed onto a backing plate in an oven at 1800F. The resulting material is characterized by a consistently high coefficient of friction, stability at high temperatures, and an extremely low wear rates.
Where else has sintered brake pad technology been used?
CL Brakes originally created sintered brake materials for military applications such as tanks, helicopters, and airplanes, as well as high speed freight and passenger trains like France's TGV (see the video at the bottom of this page). After extensive development, the technology was successfully introduced in motorcycle applications. The most recent development has focused on aligning the sintered technology with racecars. CL Brakes have now been used successfully at the highest levels of motorsport, including World Rally Championship (WRC) and NASCAR Sprint Cup.
How do they have so much cold bite, when most other race pads need a lot of heat to produce bite?
In order to achieve their maximum coefficient of friction, most resin-based semi-metallic race pads need to be operated at elevated temperatures, and must be thoroughly bed-in or burnished prior to heavy use. That type of pad generates the greatest amount of friction when rubbing against the thin layer of pad material transferred to the rotor face during the bed-in cycle.
CL Sintered Brake Pads are quite different. Their extremely high metal content and slightly porous nature provides a high coefficient of friction without needing any extensive preparation steps. They contain more abrasive metallic material per pad puck, and less resins and fillers, which means more bite when cold. That also means you're getting more of the 'good stuff' per pad vs. the competition. More metal, more brakes.
Why do they last so long?
The metallic matrix generated during the sintering process is more heat resistant than the binding agents, resins, fillers, and additives used to construct other types of pads. The high metal content and unique forming process makes them extremely durable during high heat conditions such as those experienced on a racetrack.
The sintered pad material is also more porous and ductile than other brake pad materials, particularly at temperature (ductile means that the pad can deform without fracture; the opposite of brittle). When you apply the brakes on your car, the pads press against the rotors and generate friction. That friction causes pad particles to loosen and separate from the friction puck (the body of the pad attached to the backing plate). Since most brake pads are not porous or ductile, those dislodged particles typically end up as brake dust on your wheels, the side of your car, or in the air. With the unique metallurgy of CL Sintered Pads, the bonds between particles have a greater capacity to bend without breaking, and some of the particles that are released fill in the pores of the friction puck, helping to retain the overall pad mass. A very simple way to explain it would be to say that as the pad breaks itself apart, it fills itself back in. This characteristic is also one of the reasons why CL Sintered Pads produce less dust than many other race pads.
If the pad material is ductile, wouldn't that make the brake pedal feel soft or spongy?
While the ductility of the material aids in mass retention, it doesn't negatively impact drivability. Even though some density is lost during the pressurized sintering process, the overall density of CL Sintered Brake Pads remains much higher than other pad types. Since the powdered metal particles are packed so tightly together when the pad is formed, CL Pads have extremely low compressibility. In fact, one of the first things you'll notice when you try CL Sintered pads is the rock-hard pedal feel.
Why are they so tough to fade?
Most track day cars and club racers won't see pad or rotor temps above 1300?F. In fact, pure race cars rarely see brake temps above 1600?F. CL Sintered pads are formed at 1800?F. That means that no matter what you throw at them, you're never even going to get the pads back to the temperatures they saw when they were originally formed.
Why is it so easy to bed CL pads in, and why is there less risk of vibration or judder?
With most pad types, the goal of bed-in is to heat the pad to the point where material from the pad puck will stick to the rotor face, forming a pad transfer layer. The pad on the rotor face and the pad itself then generate greater friction than if the pad was riding on a clean iron rotor face. This situation is similar to dragster doing a burnout. The like materials of the rubber on the track and the rubber on the tires create more friction than the tires would if clawing at a bare road surface.
Unfortunately, when these types of pads are heated beyond their ideal temperature range, they tend to smear the face of the rotor with a thick, uneven layer of pad material, called an uneven pad deposit. Those pad deposits create high spots on the rotor, which you then feel as vibrations or judder every time you step on the brakes. Nothing can be more distracting when entering a turn at a high speed.
Because of their higher metal content, CL Sintered Pads don't rely on a pad transfer layer to generate high levels of friction. The only recommended bed-in after install is to do a few moderately hard stops to seat the pads flush with the rotor face. That's it. When the pads heat to a certain point, they will deposit a layer material on the face of the rotors, just like other pad types. That pad transfer layer is extremely thin however, and contains graphite (a lubricant), which protects the rotors from wear. Because of the abrasive nature of the sintered material when cold, that thin transfer layer will quickly be removed from the rotors during any cold brake applications. The transfer layer of CL pads is essentially self-curing, and only develops when required to protect the rotors.
Won't CL pads wear out my rotors and make noise if they're almost pure metal?
As described above, one of the constituent materials in CL Sintered Pads is graphite. The graphite in the pads acts a lubricant when the pads are heated and pressed against the rotor face. The thin graphite transfer layer will appear on the rotor face when the brakes see heavy use, and will protect the rotors from wear. It will also diminish noise, particularly for the compounds with more graphite in their mix. In most cases CL pads aren't any noisier than other semi-metallic race pads.
What is brazing, and how is this method of attaching the pad to the backing plate different from other types of pads?
When CL Sintered Pads are formed, the pad puck and backing plate are heated, and a filler metal is drawn into the joint to bond them together via capillary action. This process is different from welding because the temperature is considerably lower, and the base metals being joined are not actually melted. The brazing process creates a metallurgical bond between the filler metal, the pad puck, and the backing plate. In other words, the pad and backing plate essentially become one solid piece of metal. Just like welding, the strength of the bond between the parts often exceeds that of the individual parts. Because temperatures remain relatively low during the process, the physical properties of the pad remain unaffected: distortion and warping are nominal, and stress in the joint area is minimized. That means it's almost impossible for the backing plate to separate from the pad puck (delaminate).
Other pad types typically attach the pad puck to the backing plate with glue or rivets. Some also use a series of raised hooks on the backing plate to augment the strength of the bond. The reality is however, that the metallurgical bond on CL pads is stronger, and resists shear more than other types of attachment. Because of the incredibly strong brazed bond, the edges of the pad puck are also less likely to lift from the backing plate, which is a common source of noise and vibration.
Click Here to determine which CL Sintered Pad Compound is right for you.
I received my CL Sintered Pads, and they appear to be a bit smaller than my OEM pads.
Sintered materials tend to expand more than other types of pads under high heat track conditions. CL allows for greater expansion by manufacturing the pad to a smaller initial size. You therefore may experience some movement of the pad within the caliper, which can result in a clunking sound, and is most noticeable when changing directions (front to reverse, etc.). Please keep in mind that these pads are race pads, and some NVH can be expected.