DE1729183A1 - Process for the production of molding trains consisting of concentrically arranged layers of polytetrafluoroethylene - Google Patents

Description

Method for the production of ivons which are arranged centrically to one another Layers of molded strands consisting of polytetrafluoroethylene The invention relates refers to a method for producing from concentric to one another Layers of polytetrafluoroethylene existing molding strands, in particular with such layers insulated wires, strands or cables, with individual layers Contain additives, preferably in the form of fillers.

In the process, the powdery polymer is first by means of a press pressed into cylindrical shaped bodies and these are then in a Piston extruder pressed into shaped strands.

It is known that polytetrafluoroethylene does not become plastic when heated, but at about 325 C it changes into a jelly-like, non-flowing mass that cannot be processed with screw presses. For production of Molded strands are then made from the crystalline powdery polymer first Cylindrical moldings are pressed, which are then closed in a piston extruder Form strands are pressed. Before pressing the moldings, the powdery Polymer with a lubricant and other additives - for example asbestos or Glass fibers, colored powder, graphite, molybdenum disulfide or other metal powder, each according to the application of the molded strands - mixed. Pressing to form the molded body is possible both in the roller extruder, which is used for pressing the shaped bodies into shaped strands is used, as well as, uncl (read is for economic reasons cheaper to do in a second press.

In many cases, molded strands are desired that extend beyond their cross-section a certain sicyndendent nature in terms of physical, mechanical or have electrical properties, such as molded strands with a certain color coating, molded strands with a core made of polytetrafluoroethylene and an outer layer made of, for example, a polytetrafluoroethylene-molybdenum disulfide mixture for self-lubricating axles or with the reverse structure for tooth, running or riding) wheels that should have a self-lubricating layer in their axle bores, Wires, strands or cables with a polytetrafluoroethylene insulation and a conductive outer layer, for example made of a polytetrafluoroethylene-graphite mixture etc. The production of such molded strands has been done so that for each layer A piston extruder was used - continuous production - or the molding strand Depending on the number of layers, a piston extruder ran through a dif-continuous one several times Production. The molding strands obtained in this way, however, have the disadvantage that the individual Layers are not firmly bonded together; they are therefore only suitable in certain areas Cases for further processing into axles, gears etc .. In addition, a such production is very expensive and time-consuming.

The invention now shows a simple way of producing such Form strands and insulation that do not have these disadvantages and that are simple and can be manufactured cheaply. The method according to the invention consists in that before the powdered polymer is poured into the press, this -speaking the number of layers-by tubular, coaxial to the press axis arranged stakes is divided, then into the individual, by the stakes spaces formed the powdery, optionally mixed with additives is poured, then the inserts are removed and finally the powder is pressed into a cylindrical shaped body. This shaped body is now so far it is not already in the piston extruder, inserted into it and pressed in a known manner to form strands. By the method according to the invention a continuous manufacturing process for molded strands is thus created, those made up of concentrically arranged, firmly connected layers consist of polytetrafluoroethylene with and without additives. From the molded strands can then through simple machining the desired parts, such as Achéen, Gears, running or friction wheels or the like can be manufactured.

In the same way it is possible with the method according to the invention To insulate wires, strands and cables with small layers; this is what it is only required that the piston extrusion to pass through the wires, strands or cables are designed accordingly.

When pulling out the inserts, make sure that it is in the individual spaces formed by the tubular inserts, and at least Partly with additives, do not mix up a large polymer powder at the interfaces Shear forces is exposed, otherwise a mixing of the interfaces at the interfaces different powder occurs and thus a clear separation of the individual layers is no longer given. This can occur especially when the diameter reduction from molded bodies to the molded strand is relatively large, i.e. molded strands with a small diameter, as is the case, for example, with insulation layers for wires and strands, the end. Moldings of large diameter are pressed. A mix of the different Powder at their interfaces would then result in a molded strand that is no longer for example, has two layers, but only one of the two layers resulting mixed layer. In order to avoid such mixing, therefore, on Most appropriate the insert is withdrawn slowly and at a steady rate.

When using several inserts, i.e. when producing from It recommends molding strands consisting of several layers arranged in relation to one another the individual inserts on the pouring side by one or more struts to connect with each other into one unit. This has the advantage that all stakes can be pulled out of the press at once and also a centering of the inserts is facilitated in the press. The latter can happen, for example, by that a tubular, an outer diameter corresponding to the inner diameter of the Press-owning insert is provided, which is connected to the other inserts via struts connected is.

The distance between the individual inserts or when used only a single insert - with a two-layer molded strand-v the spacing of the use of the press wall is in a corresponding ratio v to the to choose the desired layer thickness. This relationship generally becomes empirical can be determined, as it depends heavily on the shape of the press and the shape of the plunger.

To explain the invention, reference is made to two figures which in a partly schematic representation, an exemplary embodiment of one with the one according to the invention Methods include making a molding strand and an inset press. In Figure 1 is a cross-section through one consisting of two concentric layers Form strand drawn. The layers are denoted by 1 and 2.

FIG. 2 shows a cross section through a press 3 with three therein Located inserts 4, 5 and 6. Here, the roll-shaped insert 6, the has an outer diameter corresponding to the inner diameter of the press, than Centering means. The three inserts are connected to one another on the pouring side by means of struts 7 tied together.

Claims (3)

Claims @ Method for producing from concentric stacked layers of polytetrafluoroethylene formed strands, in particular of wires, strands or cables insulated with such layers, wherein individual layers contain additives, preferably in the form of fillers, beicem first the powdery polymer by means of a press to form cylindrical shaped bodies pressed and these are then pressed into shaped strands in a piston extruder, characterized in that # before the powdered polymer is poured into the press this according to the number of layers through tubular, coaxial to the press axis arranged inserts is divided, then into the individual, The powdery spaces formed by the inserts, optionally with additives mixed polymer is poured, then the inserts are removed and finally the powder is pressed into a cylindrical shaped body. 2. The method according to claim 1, characterized in that the inserts removed slowly and at a steady rate. 3. The method according to claim 1 or 2, characterized in that the individual inserts on the pouring side by one or more struts with one another be connected to one unit.