HU206487B - Tool for working up synthetic materials and process for producing the tool - Google Patents

Abstract

In a plastics working tool, esp. for extruding or rolling thermoplastics, in which at least the major part of the plastics-contacting surface of the tool is a ceramic surface, the novelty is that the ceramic surface is formed by a 0.3-0.5 mm thick ceramic layer deposited on the rotational face of a metallic tool body. Prodn. of the tool involves (a) preparing a metallic tool body having dimensions, at any place where a ceramic face is to be formed, which differ from the nominal tool dimension by the intended thickness of the ceramic layer; (b) subjecting the tool body to degreasing, conditioning by powder blasting, and preheating; (c) depositing a base layer and an at least 0.7 mm thick ceramic layer by flame or plasma spraying; and (d) grinding the ceramic layer to the final thickness of 0.3-0.5 mm. USE/ADVANTAGE - The tool is useful as an extruder nozzle or foil roller e.g. for processing molten polyolefins such as linear polyethylene. It is resistant to baked-on eg-deposits so that cleaning operations can be eliminated, has a thin ceramic layer so that thermal conductivity of the tool is not significantly affected, and is not significantly more expensive than conventional tools since the expense of usual operations such as polishing and Cr plating is avoided.

Description

The present application relates to a process for extruding and rolling a tool, in particular a thermoplastic, which is coated with a plastic layer on a plastic-contacting surface of a tool, and a method for producing a plastic processing tool in which a metal die body is formed. size, and then apply a ceramic layer on this surface and grind it.

The relevant literature emphasizes abrasion resistance as the most critical feature of plastic processing tools, and new solutions in tool design are always aimed at increasing the abrasion resistance.

Extrusion tools suitable for processing plastics are generally made of steel with a tensile strength of 80-90 kp / mm and harden the working edges (mouthpieces). According to the literature, only corrosion-resistant or hard chrome-plated tools can be used for extrusion of PVC (Sors-Bardócz-Radnóti: Plastic forming tools, page 216; MK, Budapest).

DE 3633 966 discloses a process in which the plastic-contacting surfaces of an extruding die are coated with a high abrasion-resistant coating by flame or plasma spraying and subsequently machined. Powder metals, metal alloys, carbides, metal oxides are used as materials to be sprayed. The description does not provide guidance on the appropriate thickness of the coating.

According to the technical literature on the application of technical ceramics, successful attempts have been made to use metal ceramics, including as materials for plastic extrusion tools (Kunststoffe 1985/12, pages 913-919). According to the literature, the wear protection of a 45 mm cylinder was successfully solved with a 4 mm ceramic sleeve. The biggest mistake of the solution, according to the literature, is that its thermal conductivity is four times lower than that of the steel cylinder.

Economical Consumption of Materials (OMFBOMIKK) 1989/1 issue, 913-919. According to pages 1 to 5, the zirconium oxide ceramic is most recently spread, which is used to make stickers. Such stickers are usually fixed by shrinkage in the forming tool. According to the literature, ceramic thicknesses of less than 1 mm should be avoided due to the risk of cracking or fracture. These tools are still not widespread due to their imperfections and cost.

Literature barely addresses another major problem with tools, the risk of burning plastic. There is an increased risk of burns when processing linear polyethylene, but a similar problem is the temporary machine shutdown, when the flow of plastic stops in the heated tool and there is no continuous heat extraction. The burn phenomenon is considered by experts to be an inevitable defect; in the event of burn, the tool is disassembled and mechanically cleaned. Frequent tool assembly, cleaning also carries the risk of malfunction and injury and leads to faster tool wear.

In order to reduce the risk of burns, tool surfaces in contact with the plastic melt are made with polished surfaces because the smooth surface has less tendency for the plastic to burn.

SUMMARY OF THE INVENTION It is an object of the present invention to partially overcome the shortcomings of the prior art by providing a tool and a method for producing it which substantially improve the burn properties of plastic processing tools and eliminate the disadvantages of poor thermal conductivity and stiffness of the ceramic.

The present invention has led to the discovery that the metal ceramic surface and the polyolefin melt develop similar conditions to the behavior of the Teflon surface and this "Teflon effect" prevents the thermal degradation of the polyolefins from burning on the work surfaces, and its disadvantageous properties do not prevail.

In the embodiment of the present invention, a significant portion of the plastic contacting surfaces of the tool is formed as a 0.3 to 0.5 mm thick ceramic layer applied to a rotationally symmetrical surface of the metal tool body.

The ceramic surface is preferably delimited by a metal flange forming a continuation thereof, the metal flange forming the working edge of the tool being made of hard metal.

The present invention further provides a process for producing a plastic processing tool comprising preheating the degreased and blast-molded tool body, then applying a primer layer and a ceramic layer at least 0.7 mm thick to a final size of 0.3 mm. Grind to a thickness of 0.5 mm.

Preferably, the ceramic layer is a mixture of alumina and titanium dioxide containing from 97% to 60% alumina.

The main advantage of the present invention over the known solutions is that the ceramic surface of the tool does not exhibit any burning of the plastic even after overheating, which prevents frequent tool disassembly, cleaning and consequent loss of production.

The advantage of the process is that it provides a relatively thin ceramic layer which does not significantly affect the thermal conductivity of the tool. A further advantage of the process is that it does not significantly increase the cost of producing the tool, since it does not involve expensive operations of the conventional method, such as polishing, chroming, etc.

The effect of the disadvantageous properties of the ceramic coating on the life of the tool has been eliminated by making the edges of the ceramic surfaces edged with metal and the working edges of the tool with hard metal.

The invention will now be described in more detail by way of example. 1 is a partial sectional view of a plastic machining roller.

The roller shown in the figure has a step-shaped tool body (1). Operating surface of tool (4)

20 the peripheral surface of the middle step shown in the drawing, wherein a smaller diameter nest is formed between the two edges (2) of the tool body step, which is filled with a metal ceramic layer (3).

The inner side wall of the flanges (2) has an angle of inclination of 45 ° with respect to the axis line, the cylindrical surface of the flanges (2) being a continuous continuation of the surface (4) of the metal ceramic layer (3). The metal ceramic layer (3) has a thickness of 0.3 to 03 mm.

Various tools are known for processing plastics; extrusion nozzle, film roll, etc. may be formed in accordance with the invention.

A substantial portion, 9798%, of the plastic contact surfaces of any tool formed in accordance with the present invention is a ceramic surface where the ceramic surface is a 0.3-0.5 mm thick metal ceramic layer deposited on a rotationally symmetrical surface of the metal die body. The ceramic surfaces are bounded by annular metal surfaces, the metal flange (2), which are made of the material of the tool body. The edges (2) which form the working edges of the tool are particularly resistant to abrasion and are generally brazed on the tool body.

The metal ceramic is a brittle material that is not capable of forming a working edge, generally having an angle of less than 120 ', and has the highest strength against compression. The metal ceramic also has a relatively poor thermal conductivity, which is preheated and / or heated. an important factor to consider in terms of the thermal balance of the tool, which is heated by the heat to be removed during the working of the heated material.

In the embodiment of the present invention, the ceramic surface is a relatively thin layer of 0.3-0.5 mm thick which, despite its high specific heat resistance, remains low in heat resistance due to the shortness of the heat path in the ceramic. The ceramic surface is bordered by a 2-3mm wide metal border flange, which protects the ceramic from local overload and provides well-defined contours for the ceramic surface.

The ceramic surface is more abrasion resistant than the steel or chrome surface. Therefore, the working edges are preferably made of hard metal, which has better dimensional stability and abrasion resistance than the working edges made of hardened steel of known design tools. The working edge carbide flange, which is usually annular, is fastened to a die body of steel or other suitable metal by brazing, AWI (argon shielding, argon, tungsten electrode arc welding) or plasma welding. Suitable carbides are e.g. cobalt-based HR-1HR-12 Stellite fillers. The ceramic layer may also be bounded by a carbide tile.

In a method for producing a tool according to the invention, the degreased and blast-molded body is preheated, then a primer layer and a ceramic layer at least 0.7 mm thick are applied by flame or plasma spraying and finally the ceramic layer to a final size of 0.3 Grind to a thickness of -0.5 mm. Preferably, the ceramic layer material is a mixture of alumina and titanium dioxide containing from 97% to 60% alumina.

First, the tool body is machined, the dimensions of which, at the locations (rotating surfaces) where the ceramic surface is intended to be formed, are of a size (0.3-0.5 mm) corresponding to the intended thickness of the ceramic layer. The optimum film thickness is 0.3-0.4 mm. A 2-3 mm wide surface is bounded with a grinding margin.

The die body is machined to form a 1.2 mm deep, 3 mm wide annular slot receiving the carbide element of the working edge, usually at the periphery of the die body, and then embedded therein to form a carbide flange.

Then the entire surface of the tool body is degreased and the surface on which the metal ceramic layer is to be applied is blasted.

Blasting produces a surface roughness of 250-400 μη.

The die body prepared by cutting and blasting is preheated to 80-90 ° C. Unwanted surfaces are protected by covering and shading.

In the first spraying operation, e.g. Using a UTP-UNI-Spray-Jet gun, an EXOBOND 1001 powder is applied to the die body in a thickness of 0.10 to 0.15 mm. Meanwhile, the tool body must not warm up to 180-200 ° C and must be cooled to 90-100 ° C before the next operation.

In a further spraying operation by flame spraying with a UTP spray gun

AI ₂ 0 ₃ / Ti 0 ₂ = 60/40%, or

Al ₂ O ₃ / TiO ₂ = 87/13% ceramic powder is sprayed on the surface in a thickness of 0.7-0.8 mm.

Allow the workpiece to cool in a draft-free, still air.

The cooled workpiece is ground with a diamond disk. By grinding, on the one hand, the ceramic surface is worked to a final size (optimum ceramic layer thickness of 0.3-0.4 mm), and on the other hand, the carbide insert produces a working life.

In our experience, a ceramic material with a composition of the following limits: alumina 97% -60% and titanium dioxide provides a good wear-resistant layer.

It is advisable to give the ceramic surface a mirror-like surface quality of 0.32.

In accordance with the invention, not only external surfaces, but also internal surfaces (6> 160mm, h = <450mm) can be coated with a ceramic layer.

Claims (4)

1. A tool for processing plastics, in particular for extruding and rolling thermoplastic materials, the plastics contacting surface of which is coated with a ceramic layer, characterized in that The ceramic surface (4) of its plastic-contacting part is in the form of a ceramic layer (3) of 0.3-0.5 mm applied to a rotating surface of a metal tool body (1). The tool according to claim 1, characterized in that the surface of the ceramic is delimited by a metal flange (2) forming a continuation thereof. Tool according to claim 2, characterized in that the metal flange (2) forming the working edge of the tool is made of hard metal. 4. A method of producing a tool for plastics processing, comprising forming a metal tool body having a size at locations where a ceramic surface is formed with a size corresponding to the intended thickness of the ceramic layer, and applying and subsequently grinding a ceramic layer thereto. preheating the degreased and pre-blasted die body, then applying a flame or plasma spray primer and a ceramic layer of at least 0.7 mm thickness, and finally grinding the ceramic layer to a final thickness of 0.3-0.5 mm. 5. The method of claim 4, wherein the ceramic layer is a mixture of alumina and titanium dioxide containing from 97% to 60% alumina.