EXTRUSION HEAD FOR PLASTIC TUBING
Charles E. Carter, Easrliampton, and Stanley C. Wells, Jr., Southampton, Mass., assignors to United Plastic Corporation, Easthanipton, Mass., a corporation of Massachutts玛咖的功效与作用
This invention relates to an improved extrusion apparatus and method for extruding tubing of plastic and more particularly of plastic having a short extrusion range.猪肝怎么去腥
In the past the extrusion of tubing of plastics of long extrusion range, such as polyethylene has been effected in an apparatus in which the polyethylene, melted to a suitable viscosity, is introduced in the form of a round rod into the side of an extrusion head which is provided with a hollow mandrel and an extrusion die forming with the mandrel an accurately dimensioned and positioned annulus. The plastic is forced in under pressure and is extruded in the form of a tube. Since the plastic is not sufficiently hardened to be completely lf-supporting the end of the tube is aled tight at the start of any extrusion and a small pressure of air is maintained through the hollow bore of the mandrel. This distends the tube slightly, supporting it and it is then t by cooling with air or by other well k
nown means. Take-up rolls pull the tube out and may, if desired, stretch it, determining the tube wall thickness. Different extrusion dies may be bolted on to the head for producing tubing of different sizes. No problem is encountered with a plastic such as polyethylene which is sufficiently flowable so that it forms a uniform tube which is perfectly clear. The method and the apparatus have been ud on a very large scale and constitute one of the standard methods of producing tubing from suitable plastics, such as polyethylene.
When it is attempted to extrude tubes of polyurethane by the method and the apparatus described above for polyethylene, problems are encountered. Polyurethane does not have the long extrusion range of polyethylene and has to be introduced at more perfectly controlled viscosities. As a result when the solid rod of polyurethane is forced to turn and fill the annular space between the mandTel and the extrusion head, and further down the extrusion die the results are unsatisfactory. At the point of maximum change of direction optical and dimensional imperfections in the tubing result. The imperfections do not necessarily affect the strength of the tube but they do produce a am becau the zone
of imperfections is not perfectly homogenous and hence not transparent. The tubes, although they may be mechanically of suitable strength, do not look well and in order to avoid this drawback it is customary to pigment the polyurethane or otherwi color it so that the am is masked. Where an opaque tube is acceptable polyurethane tubing produced with pigmentation or coloring has been sold and is a practical, though not so perfect product. However, for many purpos it is desirable to have a perfectly uniform, clear, transparent tubing of maximum strength and this has hitherto not been practical at least on a reliably reproducible schedule. It is with the problem of producing uniform, transparent tubes of polyurethane or similar type of plastic that the prent invention deals.
Esntially the prent invention utilizes an extrusion die mandrel and air pressure for supporting the tube until it is hardened in exactly the same manner as in the extrusion method and apparatus ud for polyethylene tubing. However, instead of introducing a solid rod of polyurethane into the extrusion head the polyurethane introduced is formed into a somewhat flattened ribbon.
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Now when the ribbon has to change direction in order to flow down through the annular space between the mandrel and the extrusion head and further down the extrusion die, the curvature, which is coaxial with the thin 5 dimension of the ribbon, does not produce imperfections which show up as a am. On the contrary, perfectly clear polyurethane tubing can be extruded continuously and reliably without any off-grade material.
In order to produce the tubing by the method described above, a different form of extrusion head and channel for the introduction of the polyurethane is required and this combination constitutes the apparatus pha of the prent invention. The u of a removable die, while desirable, and provided in the prent invention, does not constitute the distinction from the prior art. The dies may be of substantially the same design as ud with polyethylene type materials for the production of tubing. Preferably they are removable in order to accommodate tubing of different sizes. As far as the main part of the head is concerned, the prent invention eliminates production of an undesirable am in the finished tubing but the easier curving of the ribbon shaped polyurethane coming in also minimizes pressure drop and turbulence in the head. This is
欢喜坨however, of less major importance than the production of uniform, transparent tubing which is the main advantage of the prent invention. The fact that no disadvantages result, and no compromis are needed is an added advantage of the prent invention. The exact means by which the extrusion head is made forms no part of the prent invention in its broader aspect. There will be described however, a method of forming the extrusion head and design therefor which is advantageous and so in a more specific aspect of the invention this is an additional feature. The preferred method involves a split block head which is then bolted or otherwi fastened together. However, any other method of producing the cavities necessary to introduce a ribbon may be ud, for example by an inrt plug, and so in the broader aspect the prent invention includes an extrusion head having the desired configuration regardless of the method by which the head is made.
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Institutions diagram
The invention will be described in greater detail in conjunction with the drawings in which:感恩节在几月
FIG. 1 is a vertical ction through extrusion head die and material supply;
FIG. 2 is an elevation of the material supply element along the line 2—2 of FIG. 1 looking toward the left; FIG. 3 is an elevation of a portion of the extrusion head at the point where the material supply is attached and is situated along the line 3—3 of FIG. 1 looking toward the right; and
FIG. 4 is an isometric view of the two blocks of which the extrusion head is formed the said blocks being shown parated.
The extrusion head in FIG. 1 has a main casting which is shown as 1A becau in the view it is this block. The other block, IB, is shown in FIG. 4 but does not appear in FIG. 1.
A mandrel tip 2 is screwed into the hollow mandrel 8 and a die 26 is held in two rings 3 and 5. The former is bolted to the extrusion head by bolts 4 and the latter is bolted to the ring 3 by bolt 6. An adjusting t screw 7 rves to position the die accurately with its central part, which is the mandrel tip 2, screwed to the mandrel 8 as described above.
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