THE SECRETS OF THE BRAKE DISC

The friction coefficient (the force applied to the disc and the disc-pad materials) varies according to the sliding speed and decreases as pressure is applied. Heat and friction stimulate the system and lead to wearing on both the pads and the disc itself, sometimes even provoking the permanent deformation of the two components. Maintenance is essential in order to avoid having problems. Starting by checking that the disc is straight, which is performed by positioning a dial gauge on the braking tracks: when rotating the disc, the oscillation must be less than 0.1 mm, otherwise it must be replaced (grinding is not recommended as there is a risk of excessively reducing the thickness, the minimum size of which is usually specified on the disc itself).
In order to counteract stresses, the geometry, thicknesses and materials must be carefully chosen when designing discs and pads. With regard to materials, cast iron (malleable grey or spheroidal cast iron, with a hardness of around 250 HB, or white cast iron, which is much harder, albeit more brittle) is most commonly used for discs. In some cases, special cast iron is used, for example "GJS600" spheroidal cast iron, whose tensile strength is typical of steel (about 600 N/mm2). Another material used in kart discs is stainless steel of the "AISI 400" family, which can be subjected to hardening in order to obtain a hardness of around 50 HRC. Stainless steel works well with sintered pads (copper, etc.), while pads made of organic material (traditional, black) are more suitable with cast iron.