Brake disk (ventilated)
Motor cars in the lower price-ranges which still have drum-brakes on the rear wheels, are only seldom found nowadays. In cars right up to the middle class, solid brake-disks in the rear are found much more often
than in the front. Also in the case of drum-brakes, in the rear they are nearly always ventilated. How the air flows between the two disks, can be seen in the pictures with the cut-open disks. All in all, today's brake-disks,
together with the tyres that have become much wider, have shortened the braking distances e.g., from a speed of 100 km/h, by several meters.
Brake-disks are made of cast iron, that means a lot of carbon and alloy substances. If aluminium is found, then only in the brake-disk chamber because it is not suitable as a friction partner. One would very much like
to reduce the unsprung mass in this manner. Perhaps one day, there will be an alloy that is much lighter than cast iron, apart from expensive carbon of course. Because the frictional heat is almost exclusively taken in
by the brake-disk and can reach temperatures of up to 700° C, is another reason why aluminium is not suitable.
The 'Power-Disk' shown in the above picture has a so-called endless groove on the ring surface. This reduces not only the sensitivity to moisture but also the noises which occur with other groove shapes. Apart from
this advantage, one can see the wear and tear limit more easily through the rim, however, only if the wear is relatively even on both the outside and the inside. Apparently, the groove also serves to prevent fading.
The disk-chamber makes it necessary, that when seen from the front, the brake disk has an asymmetrical mounting, which can lead to unwanted deformation if they are heated strongly. If this heat is not evenly
distributed around the circumference, sectional friction and thus, juddering may be the result. For this reason, high-demand disks are floating-mounted. They may then be made from a different material.
Thus, there is only a form fitting between the chamber and the disc in circumferential direction. Therefore the disc remains a ring, which expands evenly and which can correct a one-sided contact with the brake-lining.
The floating disc also creates a heat shield for the wheel bearing and its grease-filling. Additionally, the piston or pistons in the calliper are not pressed unnecessarily far back. A small amount of play remains for the
next braking action.
These two discs clearly show the form-fitting in the circumferential direction. They are used for light railway vehicles. If you look very closely, the concentric division in the front disk can be seen. This is because in
railway vehicles, the wheels are solidly joined to the axles, it would therefore, not be possible to mount them using the same method that is used for road vehicles. This is why only the front disks are one-piece. 06/15