When the car is braking, kinetic energy is converted into thermal energy of the braking element, due to friction on the pad-disc interface. Hence, it is extremely important for the braking element to work properly with different vehicle weights (both vehicle with only a driver, but also with a full set of passengers and a loaded trunk) and at different speeds. It is also worth noting that the heat energy produced during braking (which is the result of the friction between the lining and the disc) is absorbed mainly by the brake disc. Therefore, its structure, ability to absorb heat generated due to braking, and quick dissipation of thermal energy thus formed is of extreme importance to safety.
Theoretically, the use of brake discs of a material which has a minimum heat absorption (ceramic disks) is most preferable. However, this solution is quite expensive and car manufacturers offer it only as an alternative in sport model (for example, the purchase of a AMG ceramic brake system in a Mercedes AMG GT 462 HP worth over EUR 250,000 is associated with an additional cost of about EUR 20,000). Therefore, without going into detail about “top-shelf solutions”, let’s focus on conventional metal brake discs used in most cars.
Of course, heat absorption depends on the heat capacity of the disc, i.e. the larger and thicker the disc, the better (more material means more heat capacity). At the same time, however, it is necessary to be able to quickly lower the temperature of the disc in order to prevent fading*. Therefore, special R&D laboratories are hard at work trying to choose the appropriate cast iron for brake discs. Mechanical solutions and shapes are continuously being developed, and more and more cars use brake discs with internal ribbing, which provides faster cooling. The result of research conducted in Master-Sport laboratories, focused on new solutions in materials and workmanship is e.g. reducing disc warmth by fitting it with air vents, which also determines the flow of the air stream (this technology, also used in professional sports cars, is available in the Master-Sport offer under the name Extreme Sports).
However, even the best brake disc is exposed to improper operation and faster wear. Although it is impossible to eliminate wear and tear, it can be reduced.
Never forget about good friction linings
When designing any mechanism, the ultimate goal of an engineer is such structure, as to make sure that any possible quick damage occurs in cheaper parts. This is the case in developing the brake pad – brake disc system. Because the pads are cheaper and easier to replace, they are the weaker part, prone to faster wear than the disc cooperating with them. However, one should optimize the braking performance and abrasion resistance of the pads (i.e. the effective course of operation). For example, Master-Sport laboratories have developed the special Keramik pads, whose technology optimizes these requirements.
In low-cost alternatives, where laboratory tests are omitted, the pad often has the wrong friction piece composition, resulting in damage (scratches, uneven wear) of the brake disc. (For more info on pads, see separate text “Brake pads are more than a panel with a friction lining”).
Remember the chassis and steering
Unfortunately, few are aware that damaged parts of the suspension, steering rods, badly set convergence, and even the imbalance of wheels, have a direct impact on the damage to the brake discs. In this case, the geometry parameters of the system are changed, and in addition to the force exerted by the pad linings on the disc, there are also additional forces not taken into account in the design. In practice, damage to the suspension and the occurrence of additional forces acting on the wheel is manifested in grooves and depressions on the disc, or even deformation.
The brake is not a footrest
Another bad habit due to the drivers’ ignorance is keeping one’s foot on the brake after prolonged braking, and vigorous braking before a stopover in the winter. In the first case we are dealing with heating up the brake discs (remember that the temperature at the disc/pad interface exceeds 500 degrees, and the outer layer of the disc is heated to about 400 degrees) and inability to discharge temperature at the point of pad contact/pressure. In the second case, we have the effect of blocking the brakes and… no pad rollback effect (usually it occurs automatically when the tire moves). As a result, the pad is adjacent to the disc, sticks to it and leaves a scratch on the pad/disc interface.
In each of the reported cases we will have damage to the brake discs in the form of dents, scratches or warping of the surface. Of course, this may be remedied by “lathing the discs” or mechanically gathering irregularities and restoring the factory parameters. However, this is not recommended by the manufacturer, and if someone decides to take such a measure, it is worth remembering that the disc has a minimum thickness, the reduction of which may result in damage to the system. In addition, “lathing the discs” is only a temporary and partially successful treatment. First of all, by gathering more material layer, we further decrease the heat capacity of the disc, thereby the unit’s heating/cooling will be worse. Secondly, a thinner disc (lower heat capacity) is more susceptible to the above effects, which will quickly bring the issue back.
Therefore, in case of mechanical damage to the discs (deep scratches, small thickness, and sometimes even “rattling” due to overheating and deformation of the material), the brake discs should be replaced with new ones. In this respect, one should focus on a few parameters that describe the discs.
Secondly, regardless of whether we choose the cheapest disc, or a more expensive one, we must pay attention to the type of material used to manufacture the product and the quality control during the manufacturing process. Of course, the composition of the alloy will tell us close to nothing, and quality control during the manufacturing process is a secret (for example, at Master-Sport, each brake disc is tested by X-ray during production), but the important information for a client to note is that the product meets the OE requirements, since this guarantees the quality demanded by the car manufacturer. In addition, each product approved for sale must have a permanent ECE marking. The ECE symbol guarantees quality confirmed by accredited laboratories, which have carried out comprehensive product tests.
Thirdly, let us remember: only laboratory testing allows us to offer a good quality product on the market. Hence, it is worth considering whether the manufacturer conducts laboratory tests, or is your car going to be a testing ground. (more info on the laboratory work, see the text “Braking is not only the discs and brake pads, or in the Master-Sport laboratory”)
The purchase of the product, taking into account only the minimum price, usually results in poor quality, and thus quick wear and reduced braking efficiency.
At the end it is worth paying attention to the correct assembly of products. Doing this unprofessionally, carelessly and without proper assessment of the technical quality of the working components may result not only in a faster deterioration of parts, but also damage other components. Hence, it is worth commissioning the replacement to authorized specialists whose employees are properly qualified.
*(Fading is produced by high temperature (when braking, the temperature on the pad/disc interface exceeds 500 degrees Celsius) as a result of gas generating from abrasive material due to physical change in the heated abrasive material. As a result, an “airbag” is formed at the disc/pad interface and/or the structure of the material changes. This results in a decrease in the friction coefficient, hindering the effectiveness of the friction lining and proper deceleration of the vehicle)
