CH669555A5 - - Google Patents

Description

DESCRIPTION

The invention relates to a plastic screw press according to the preamble of claim 1. With such plastic screw presses, both the cylinders and the screws can be made in one or more parts. The invention is concerned with measures to increase the wear resistance in such plastic screw presses by coating them with tungsten carbide (WC).

The method of increasing the wear resistance by coating with tungsten carbide (WC) is known per se (company publication UCAR “Metal & Ceramic Coatings” from Union Carbide Deutschland GmbH, 77.09.06 CS.G). One mainly works with tools such as deep-drawing dies, dies, cutting tools, milling cutters, punching dies or hard metal cutting inserts, and with injection molds. One makes use of the fact that the phenomena that otherwise interfere with tools, such as built-up cutting edge, cold welding, cold wear, crack formation in the cutting edge of the tools, do not occur or occur to a very reduced extent. The coating is applied by a plasma spraying process or by a detonation spraying process. In the plasma spraying process, a plasma burner controls a high-temperature inert gas jet of, for example, 20,000 ° C at extremely high speeds. There is no combustion. Rather, a non-transmitted electric arc with a high energy density releases its heat potential to the flowing, dissociating inert gas stream. The powdered spray material melts in this hot gas stream. At the same time, it experiences high acceleration before it is hurled onto the surface of the workpiece to be coated. The impacting material particles form an extremely dense, self-adhering coating that adheres securely to the surface of the pretreated base material. A detonation gun is used in the detonation spraying process. The detonation cannon essentially consists of a tubular elongated reaction chamber which, like a gun, protrudes from a control block for gases, material powder and electronics. While precisely metered amounts of oxygen, acetylene and powdered spray material get into the reaction chamber, the detonation of this mixture is triggered by an electrical ignition spark. The hot gas jet generated in this way melts the material particles slightly and accelerates them in the tubular,

long outlet opening to a multiple of the speed of sound. The particles hitting the surface of the workpiece at this speed weld to the surface in the sense of micro-welding to form a tough connection with the base material. Through rapid successive detonation intervals, the layer thicknesses of 0.03 to 0.5 mm can be generated on the mostly automatically moved and controlled workpiece surface, depending on the application. In both the plasma spraying process and the detonation spraying process, the temperature of the workpiece surface remains at 150 ° C and below, except for a thin transition layer. The workpiece is not disturbed.

The method of increasing wear resistance by coating with the abovementioned substances has (in practice) also been proposed for cylinders and for the screw tips of the screw of plastic screw presses, but not with tungsten carbide but with titanium nitride or titanium carbide as the coating material. The coating was applied either to the cylinder or to the screw tip at different points where the signs of wear occurred on the cylinder or on the screw tip. The success was not satisfactory. The service life of the unit consisting of worm and cylinder, and thus the service life of the machine as a whole, cannot be improved sufficiently by these measures. In practice, work is therefore different to increase the service life of the screw and cylinder in plastic screw presses. In particular, surface hardening measures, e.g. B. realized by nitriding or bushings made of special metals, especially hard metals, are used in the cylinder. One also knows so-called bimetallic cylinders, which are thrown out with a corresponding material.

The invention is based on the object of specifying how the service life and thus the service life of the entire machine can be considerably improved in a plastic screw press.

The solution to this problem according to the invention is the subject of patent claim 1. The basic concept of the invention is that, within the framework of the measures according to the invention, both the cylinder and the screw, which are at least on the screw webs, are coated in opposite areas, specifically there, where the wear would occur without a coating. This does not exclude that other areas and not only opposite ones are coated.

A preferred embodiment of the invention is characterized in that the cylinder and the worm shaft are edge-hardened. Another embodiment is characterized in that the cylinder and the worm shaft are hardened. You can also combine both measures and z. B. use the worm shaft in the fully hardened state, the cylinder in the hardened state - or vice versa. If only surface layer hardening is used, the hardening depth should be between 0.3 and 3 mm. The coating should have a layer thickness of approximately 0.1 mm and a roughness depth of approximately 10 μm. The coating can be applied with the aid of a plasma spraying process, to be precise on the hardened base material. However, the coating can also be applied using a detonation spraying process and is then applied to the fully hardened base material. After the coating has been applied, it is generally not necessary to cure again.

The advantages achieved can be seen in the fact that a surprising improvement in the service life and thus the life of the

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entire plastic screw press is reached. If the material combinations are otherwise the same, the service life or service life can be improved by more than 25% simply by coating. The machine can then continue to be operated because even after the coating has been removed, the components made of the hardened base material can still be used for a long time.

The usual steel alloys can be used as base materials for the worm shaft and for the cylinder. Particularly good results are obtained with the materials of the material numbers given in the following table with the reference:

1.2379-DIN 17350 1.7225-DIN 1654/17200 1.7707-DIN 17200 1.2344-DIN 17350 s 1.8550-DIN 17211 1.8515-DIN 17211

1.7735 - StahlKey (1983), p. 389, Verlag StahlKey Wegst io The cylinder can also consist of a base body and an inserted bush; then all information and measures refer to the socket.

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Claims (6)

669 555 1. Plastic screw press with cylinder and screw shaft made of a base material made of steel with a hardness of 40 to 70 HRC in accordance with DIN 50103, characterized in that both the cylinder and the screw shaft both have at least in opposite sections for the purpose of increasing wear resistance with tungsten carbide (WC ) are coated, true to the contour, and in the opposite sections with fit tolerances in the range between 0.15 to 1%, based on the nominal diameter, and that the base material has a surface accuracy of 2 to 4 (in as well as a profile load proportion according to DIN 4765 in 0.25 Jim has depth ranging between 40 and 80%. 2. Plastic screw press according to claim 1, characterized in that the cylinder and the screw shaft are edge-hardened. 2nd PATENT CLAIMS 3. Plastic screw press according to claim 1, characterized in that the cylinder and the screw shaft are hardened. 4. Plastic screw press according to one of claims 1 to 3, characterized in that the coating has a layer thickness of about 0.1 mm and a surface roughness of about 10 p.m. 5. Plastic screw press according to claim 1, characterized in that the base material has a profile load proportion according to DIN 4765 in 0.25 (depth of about 60%) before coating. 6. The method for producing the plastic screw press according to one of claims 1 to 5, characterized in that the tungsten carbide coating is applied with the aid of a plasma spraying process or a detonation spraying process.