A comminuting apparatus may typically be used for example for comminuting wood, paper, plastic material, rubber, textiles, production residues or waste from trade and industry, but also for dealing with bulky refuse, domestic refuse, collections of paper and other waste materials for example from organisations set up to dispose of waste and such like in an environmentally friendly fashion, as well as more specialist waste such as hospital and clinical waste. A comminuting apparatus for such a purpose may comprise a drive unit with at least one electric motor having a drive shaft operatively connected to a comminuting shaft. At its periphery the comminuting shaft has comminuting tools over its working width. The tools co-operate with a counterpart means adapted in respect of shape to the rotational surface of the comminuting shaft, for comminuting the material to be processed. In such an apparatus the material to be comminuted is comminuted by cutting, shearing, squeezing, tearing and/or rubbing, between rotor members or in the co-operation between a rotor member and a fixed transverse member operatively associated therewith. Such an apparatus may be found for example in EP 0 419 919 B1.
There are also forms of comminuting apparatus comprising a plurality of rotors each with a respective stationary transverse member associated therewith, between the respective rotors.
To perform an operation of roughly pre-comminuting waste material, a rotary speed of the comminuting shaft of between about 20 and 50 rpm is appropriate. Hydraulic drives are generally used for that purpose. When dealing with material which is easy to comminute or which is already sufficiently pre-comminuted, such as for example films, sheets, packaging residues and the like, the comminuting apparatus can in principle be operated at higher rotary speeds in order to increase the waste material throughput, and in that respect presentday comminuting apparatuses are equipped with comminuting shafts which may be driven at between about 80 and 500 rpm. The electrical drive power of such an apparatus is between about 30 and 450 kW.
Various drive configurations may be adopted for such comminuting apparatuses. Conventional apparatuses generally include an asynchronous motor which is preferably of a 4-pole configuration and which accordingly operates at a motor speed of 1500 revolutions at a mains frequency of 50 Hz. To set the specified speed of rotation of the comminuting shaft, the transmission of force thereto from the motor is effected by way of a belt drive or a universally jointed shaft or a clutch to a transmission in which the rotary speed, depending on the respective demands involved, is reduced to between about 90 and 200 rpm, whereby the torque at the comminuting shaft is increased in comparison with that of the motor in the same relationship.
In regard to a further design configuration of a comminuting apparatus, it has a drive in the form of an electric motor which is generally of a 4-pole or 6-pole design and which accordingly operates at 1500 rpm or 1000 rpm respectively at a mains frequency of 50 Hz. Connected downstream of the electric motor is a transmission operating with a pulling means such as a belt or chain transmission. That arrangement makes it possible to attain rotary speeds for the comminuting shaft of between about 200 rpm and 500 rpm, by means of a simple drive, although it will be noted that belt pulleys which are very large and usually expensive have to be used.
As the large belt pulleys employed have a high moment of inertia, a load-limiting or load-separating clutch or coupling unit is generally fitted at or in a hub between the comminuting shaft and the belt pulley, preferably a slipping clutch, depending on the material to be comminuted, in order to avoid breakage of the comminuting shaft. At even lower rotary speeds, it is necessary to use a double-run belt transmission. In that case, very high levels of torque can be produced at the comminuting shaft, which however require suitable dimensioning of the drive elements, so that such a design configuration is very expensive and maintenance-intensive, while at the same time the comminuting apparatus takes up a great deal of space, by virtue of its bulky structure. The fluid couplings which are generally used in both the above-discussed drive configurations optimise the known disadvantageous start-up characteristic of an asynchronous motor and make it easier for the comminuting shaft to start under load. In addition, in the event of a sudden blockage, for example due to the presence of a foreign body in the material being comminuted, the coupling arrangement has a damping effect and reduces the load peaks which are produced by the apparatus in the supply mains network.
A further conventional drive arrangement for a comminuting apparatus employs an asynchronous electric motor, a hydraulic pump and an oil motor. The moment produced by that drive assembly is passed to the comminuting shaft with or without an interposed transmission. That design configuration is highly expensive and maintenance-intensive, and comparatively unfavourable in terms of level of efficiency, while in addition the apparatus is very noisy. On the other hand that configuration affords the advantage that the rotary speed of the comminuting shaft can be adjusted over a predetermined range.
What is common to all those conventional drive configurations is that they include a plurality of drive members for connecting a motor to a comminuting shaft. They are comparatively expensive, they increase the amount of space required and in addition increase the level of noise generated by the apparatus. Connecting a plurality of drive members in succession results in the machine suffering from a power loss. In other words, the machine has an unfavourable level of efficiency, with a corresponding energy loss. As the entire drive consists of a plurality of drive members, those drive members in combination exhibit a high level of mass moment of inertia, which, in the event of load peaks which suddenly occur, can result in problems in regard to strength and operating life and under some circumstances can result in parts of the machine being broken and destroyed. Load peaks of that kind can occur on the one hand due to pieces of material which cannot be comminuted, for example metal, stones, rocks and so forth, in the material being processed, but they can also occur when comminuting tough resilient materials with a high level of tearing strength such as for example fiber mesh or web, cables, cords and the like.
Depending on the material being comminuted, the rotor blades adopted and the rotary speed of the rotor or rotors, rotary oscillations often occur, in particular when gear transmissions are used in the drive assembly. Such oscillations generate a large amount of noise and reduce the service life of the drives.