Hot-cut pelletizer

Details Hot-cut pelletizer Hot-cut pelletizer

1996-12-06

1998-09-29

Woo, Jay H.

Plastic article or earthenware shaping or treating: apparatus

Immersed shaping orifice discharging directly into liquid...

264142, 264143, 425313, B29B 906

Patent

active

058143505

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to a hot-cut pelletizer for thermoplastics, having a housing which is designed as a hollow rotational body and the interior space of which is supplied with polymer melt, which is forced through channels passing radially through the housing wall and is cut into pellets by cutters which rotate in a substantially water-free space and slide over the openings of the channels along a cutting face running around the housing wall.


BACKGROUND OF THE INVENTION

Such a hot-cut pelletizer is described in German Offenlegungsschrift 1,454,753. The rotational body used in this pelletizer is of a conical design, there opening out at its conical surface radially directed channels for the passage of polymer melt, which is cut up into pellets by cutters passing over the surface. In the publication, reference is made with respect to the cooling of the pellets to the possibility of accomplishing this cooling by liquid sprayed onto the pellets or by air. Particular attention is paid to a special type of air cooling, which consists in providing fan blades which rotate with the cutters and produce an air stream, which additionally accelerates the pellet particles flung outward by the centrifugal action of the cutters. This is intended to achieve the effect that the pellets sliding off the cutters are directed onto the fan blades without impact, that is to say do not strike hard against the fan blades, the pellets being cooled by the air flow produced by the blades. Additional cooling is accomplished by the fact that in the region of the fan blades there are provided outlet openings for a cooling liquid, through which liquid is directed onto the fan blades and forms a protective film on them and on the inside wall of a collecting housing surrounding the hollow rotational body with the cutters. The outlet openings for the cooling liquid are arranged in the vicinity of the cutting edges of the cutters. Owing to the centrifugal force acting on the cooling liquid, the region of the cutters lying between the cutting edges of the cutters and the outlet openings consequently remain free from cooling liquid, since the latter immediately flows off radially outward over the fan blades on account of the rotation of the cutters and of the outlet openings. Cooling of the cutting edges particularly exposed to heating and of the regions directly adjacent thereto is thus not possible in this way, which on the one hand does not adequately protect the cutting edges against overheating and on the other hand significantly increases the risk which always exists during hot cutting that pellets will remain adhering directly to the cutting edges, initially still in a molten state and not cooled at all directly at the outlet from the rotational body, owing to the water being radially flung out there. It therefore tends to smear over the rotational body. Some types of plastic cannot be pelletized in this way. Therefore, a practical implementation of this known hot-cut pelletizer has not become known.
Also disclosed, by U.S. Pat. No. 3,792,950, is an underwater pelletizer, in which there rotates around the outer face of a cylinder passed through by radial polymer dies in a pelletizer housing filled with cooling water a cutter plate with cutters passing over the polymer dies. The filling of the pelletizer housing with cooling water in this case takes place via a ring nozzle, which is formed by the outer face of the cylinder and the inner face of the cutter plate and introduces into the interior of the pelletizer housing a stream of cooling water along the outer face of the cylinder with the polymer dies. This stream of cooling water is used not only to fill the interior space of the pelletizer housing but also to rinse away from the polymer dies the pellets just cut, which then leave together with the cooling water through an outflow fitted onto the pelletizer housing in the manner of a flue. The intensive and direct rinsing over of the outer face of the cylinder with the polymer dies by the cooling water resul

REFERENCES:
patent: 3295469 (1967-01-01), Vassalli
patent: 3415917 (1968-12-01), Watanabe et al.
patent: 3792950 (1974-02-01), Cuff
patent: 4245972 (1981-01-01), Anders
patent: 4285652 (1981-08-01), Anders
patent: 4300877 (1981-11-01), Anderson

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