The recycling of old rubber tires presents a very difficult problem. In the first place, there is considerable difficulty in separating embedded metal parts from the rubber of the tire before the tire runs through the pulverizing machine. Moreover, there is a possibility of reusing the rubber only when the rubber is reduced practically to powder form because it is only in this form that old rubber can be used as an additive in the rubber industry for the production of new rubber ware.
In order to comminute old rubber tires, cutting and shredding tools have been used. According to DE 29 11 251 C2, the tire is clamped in a clamping device, with three outwardly slidable pins, whereupon a tangential cut is made with rotating disk knives to remove the tread with the side strips from the metal inlay containing beads and subsequently other circular disk-form knives are used to cut the rubber into strips which are then fed into cross cutting apparatus. The rubber pieces thus obtained required further comminuting.
Other old rubber tire disintegrating machines are shredders which, with rotating knife cylinders, attack the circumference of the tread and comminute the tread as well as the side strips to chips (SU 36 93 894 A1). A machine according to SU 13 88 294 A1 works in a similar manner. Here the tire is gripped on both sides by saucers and is stressed and pressed so that the tread is bent and deformed and in this narrowed form is subjected to the knives of a shredding cylinder. Comminuting is effected in a similar manner by the comminuting machine of DE 37 04 725 A1, in which the comminuting tools arranged on the rotating comminuting cylinder are small, hard plates, and the comminuting tools themselves are arranged in a particular form.
The old rubber pieces obtained from all of these comminuting processes are technically not yet usable in the rubber industry as an additive. The rubber pieces thus obtained are so large, of such a dissimilar shape and so nonhomogeneous that further working and comminuting presents great difficulty.
Rubber scrap is also produced in the production of new rubber ware when, through production error or mixing error or through use of unsuitable mixtures, damaged goods are produced.
Apparatus for further working such rubber scrap is known through DD 265 855 A1. With this known apparatus, an extruder with several work zones is connected by a radial discharge pipe with a mill having grinding disks defining a conical grinding gap. Different work zones are formed in the extruder through different formation of different screw sections. Bringing the compressed rubber scrap from the extruder into the grinding space is difficult and the grinding of the rubber is problematic.
For rubber is an extremely difficult to comminute material, which is in many respects nonhomogeneous. Through different exposure to the sun's rays, and different loading during the life of an automobile tire, as well as different life spans, the old rubber scrap to be worked on is differently aged. The pieces of old rubber scrap have strongly aged portions, which are relatively easy to pulverize. Other, less aged parts, on the contrary, still have a high degree of elasticity and can hence be comminuted by grinding only with great difficulty or not at all. In most cases, strongly aged portions are integral with less aged portions. They thereby present particular difficulty in comminuting. This difficulty is increased by the presence of foreign material in the form of metal parts in the rubber scrap which are not removable prior to grinding because they are in part surrounded by the rubber and in part the rubber is vulcanized to them. These metal parts have a destructive effect on the grinding disks.