In the production of single and multiple layer rubber strips for the manufacture of tires, for example protector or tire sidewall profiles, not only high quality but also high frequency of cuts per unit time must be obtained in order to meet the production requirements of tire production. The cut quality is of particular importance in the production of radial tires and the cut frequency is necessary in order to obtain economical production.
Cutting apparatus according to the state of the art, almost without exception, uses a fast rotating circular knife which during the cut must be lubricated with steam or by a liquid vapor. There are embodiments in which the circular knife is mounted directly on the shaft of the driving motor which then must be moved with the knife and protection devices transversely of the profile strip. In order to make a cut on a moving profile strip, such cutting machine had a carriage which through coupling to the transport device during the cutting operation moved synchronously with the rubber profile strip to be cut. With higher production rates, this cutting apparatus soon became inoperable because the return movement of the carriage with the cutting apparatus could not be accomplished in the short time period.
The further development of the cutting apparatus was to the effect that the rubber strip to be cut would be stopped for a short period of time for the cutting operation, which required braking and accelerating mechanism for the transport element and raised serious problems of precision which, however, could be solved. However, it showed the limits of performance in the transverse movement of the rotating cutting knife, since because of the relatively great mass, in particular of the knife motor, the speed of movement could not be as high as required for efficient operation, in particular the required cutting frequency desired for the extrusion apparatus. However, not only the weight of the driving motor for the knife set limits on increase in speed of production, but also the transport mechanism, for the most part rotating screw spindles, which were driven by brake motors and which, on account of the frequent acceleration and braking, were subject to serious abrasion. The starting and braking operations of the transverse movement involved strong forces which affect the entire cutting machine and are not endurable.
It has been sought to carry out the cutting operation in both directions by making one cut from left to right and the next cut from right to left. However, this gave dissimilar cut pictures which led to problems in the packaging of tires. It is, hence necessary, in the return movement of the knife, to raise the knife together with the knife holder over the profile strip to be cut at the end of a cut, then draw it back over the profile strip and then, for carrying out the next cut, again lower the knife, as is described for example in DE-OPS 11 86 209.
The apparatus known through this publication has, as the cross feed mechanism, a carriage which is displacable on guide rails and is shoved back and forth by a chain between two guide wheels. The carriage has a cradle with bearings for the knife shaft. The movement of the cradle is derived from a rocker arm which is linked to the chain and the carriage and which transmits the chain movement to the carriage. On account of the inexact cradle height adjustment, there are additionally provided pivot adjustments. The driving motor is connected wit the knife shaft by a flexible shaft. With this arrangement an exact cut is not possible. The nonuniformities which occur lie in somewhat like positions and hence largely compensate one another, but this is not sufficient for modern requirements of tire quality.
The use of pneumatic thrust cylinders instead of threaded spindles leads to an almost abrasion free method of operation but does not achieve the desired result, since, because of the short time of the entire operation, the thrust of acceleration and braking cannot be sufficiently damped. Moreover, these pneumatic transport devices have the objection that they cannot be brought to a uniform transverse velocity during the cut, since at the moment of cutting, the resistance-responsive forward velocity is decreased. This leads to unclean cuts. Hydraulic drives for the transverse movement of the knife are prohibited, not only by reason of cost, but also because of the hard thrust which occurs with hydraulic mechanism in fast acceleration and braking.
USPTO Backgrounds
USPTO Backgrounds