Strand cutter with bed knife that can be replaced during operati

Details Strand cutter with bed knife that can be replaced during operati Strand cutter with bed knife that can be replaced during operati

1988-11-16

1990-10-02

Watts, Douglas D.

Cutting

Processes

With reorientation of tool between cuts

83349, 83906, 83950, B26D 708

Patent

active

049600206

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a strand cutter, more particularly for granulating plastic materials.
Strand cutters are machines with which materials or stream of materials, in the present case strands, are cut into short segments. As a rule, when manufacturing plastic molding compounds, they are used for converting the plastic, after synthesis and compounding, into a form in which it can be simply divided into portions and packed up and reprocessed by almost any current machine.
Unexamined West German Patent Applications No. 25 12 899, 26 46 309, and 28 09 680 disclose granulators used to carry out granulating plastic materials in so-called hot die-face cutting. With this method, the plastic melt is extruded in water through a breaker plate. The thus formed strands ar cut by knives rotating at the breaker plate. These granulators are primarily employed when granulating bulk plastic materials and provide the throughput capacity necessary for this purpose. High-grade plastic materials, so-called engineering plastics, which often tend to form filaments, cannot be satisfactorily granulated in this manner. Strand cutters for such applications have been disclosed in Unexamined West German Patent Applications (DE-OS) No. 27 24 464 and DE-OS No. 29 01 018, the said strand cutters being preferably used with somewhat low throughput capacities and for filled and reinforced plastic materials. The melts are extruded through multi-orifice dies into a water bath or flowing water, and after passing through a cooling section the strands forming upon cooling are fed into the granulatingunit proper in which they are cut into granules by means of a cutting rotor with a plurality of knives on a fixed bed knife.
It became evident, however, that the conventional mechanical concepts for strand cutters have a serious disadvantage: When granulating filled, reinforced and often even corrosive plastic materials, the knife edges are subject to considerable wear This is particularly true if the fillers or reinforcing materials are very hard and a corrosive component is added for abrasive stress. Contingent upon the fact that the bed knife, in comparison with the knives on the cutting rotor, is in contact in each cut, its wear is particularly high. Even after a few hours of operation, the cutting quality and thereby the shape of the granules can become so poor that it is necessary to replace the worn bed knife. Continuous processes or processes extending over a rather long period must be interrupted for this purpose; this often entails technical problems and economic losses.
The invention has as its object the manufacture of a strand cutter in which the fixed bed knife can be changed without interrupting the granulating process.
The object is achieved according to the invention by keeping the bed knife free from play in a guide at right angles to the strand direction and moving the bed knife forward at a relatively low feed rate or replacing it during the granulating process. The feed rate must be so low that the position of strands in the granulator is not affected. The fixing of the bed knife according to one embodiment has the advantage that given an appropriate design the guide and the attendant bed-knife require only a small space. This makes it possible to rebuild existing granulators. To do this, the guide must be screwed in instead of the bed-knife. A prerequisite is for the existing design to offer lateral room for inserting and pushing forward the the bed-knife. The fixing of the bed knife according to a further embodiment enables one to vary the frictional forces as required, e.g., when securing the bed knife in position or when moving it forward.
If a very long bed-knife is used, there is the advantage that there are no abutting surfaces in the region where the strands are granulated. If a very long knife cannot be used for reasons of space, a new knife is inserted from the side of the granulator into the guide and brought by means of a feeding unit into the area where the strands are cut. At the same time, the old, worn bed knif

REFERENCES:
patent: 3837586 (1974-09-01), Perschbacher et al.
patent: 3852144 (1974-12-01), Parry
patent: 4208931 (1980-06-01), Collins
patent: 4474336 (1984-10-01), Fleming
patent: 4590978 (1986-05-01), Kintz et al.
patent: 4693157 (1987-09-01), Looser

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