Method of joining thermoplastic parts.

The invention relates to a method for joining thermoplastic parts, the end to be joined portions are heated by contact with a heating element, such as metallic sword, until it softened.

Although be possible in one piece in plastics technology typically components such. As housing, troughs for liquids, diaphragms for batteries and the like., Plastic parts have either to achieve certain spatial configurations, bulky structures or large-scale structures, the corresponding to keep mold costs within economic limits, or in order to obtain plastic parts of different composition and thus properties, are joined together. With thermoplastic resins, these can be joined together at the surfaces to be joined by the action of heat and subsequent printing. In the case of thermosetting plastics is the possibility either to prepare this compound by conventional elements such as screws, rivets or the like., Or to achieve the connection by means of adhesives. A further possibility in thermosetting plastics is that to use the normally existing, if not strongly formed thermoplastic properties of thermosetting plastics, to obtain a thermoplastic compound.

In the case of the thermoplastic compound of thermoplastics may also be a thermoplastic welding filler material, which is in particular species matched as the materials to be joined, can be used.

As with known metallic compounds, generally represents the seam z. B. weld between the to be bonded materials not weak point, but there are usually adjacent to the weld areas of the parts to the vulnerability, which is either a breaking the connection between the parts is caused by or cause together with the weld undesirable geometric distortions. Such geometric distortions are particularly present when either plastics with different filler z. B. polypropylene without fillers and polypropylene with glass, carbon black or the like. Or with other plastics such. As polyethylene are connected. However, such structures are, for example, in particular bipolar electrodes as required with circulating electrolytes for rechargeable zinc-bromine batteries, is particularly advantageous. Hiebei is the electrochemically active area of ​​the inner electrode, which is electrically conductive and thus has a high thermal conductivity is surrounded by an electrically non-conductive frame and thus provided with a lower thermal conductivity polypropylene part. Alone due to the different thermal conductivities of the two plastic parts to be joined together in particular the welding stresses in the parts to be after completion of bonding, causing thereby a premature destruction of the compound and that next to the weld and also geometric distortions z. B. unwanted undulations of planseienden surfaces conditionally.

The present invention has for its object to provide a method for joining plastic parts with thermoplastic areas along their end faces, which realizes a high strength of the connected parts and this causes a very small deformation of the connected parts.

The inventive method is based on a state of the art, as taught, for example, by the Austrian Patent 185 570. In this patent, a method of joining thermoplastic parts is described, wherein a welding member along the parts to be connected is performed. This welder element has a sword-like extension which in turn contributes to the softening of the to be interconnected end parts of the plastic components concern. The, obtained by merging the softened areas, weld is smoothed by an integral with the sword part which lags the sword, the weld is in turn fused to smooth.

The inventive method for joining thermoplastic parts, which is to be connected, thermoplastic end portions are heated in particular by contact with a heating element, such as metallic Sword, especially simultaneously, up to the softening, whereupon the softened plastic areas caused to contact with each other, in particular the plastic parts are pushed to each other whereby a weld between the plastic parts is formed, which is mechanically applied, consists mainly in the fact that the still softened and cooling weld and possibly the subsequent edges of the plastic parts, in pulses with a constant temperature below the melting temperature of the joining plastic parts pressure element, in particular by at least one mechanical impulse is applied. By doing so, either the flow into one another end portions of connected plastic parts or the one into the plastic areas are pressure and tension-equalizing interconnected, so that a balance of impurities which are caused by the weld are opposite to be bonded plastic parts particularly effectively avoided, simultaneously is particularly favorable avoided a lacy force introduction of a plastic parts for other plastic part, resulting in, for example, to faults or the like.. By lying below the melting temperature of the joining plastic parts temperature of the pressure element is achieved that not only a lying at the surface of equalization of the forces, but one up to the inside of the weld seam continuous balancing of the forces may be present.

If the pulse loading, based on the weld step by step and the weld each newly formed acted so subject to the weld particularly low thermal stress, at the same time a particularly economical method of equalizing forces tips can be achieved in the region of the weld.

If the weld the parts to be connected with regions of different thermal conductivity by melting of plastic parts with different thermal conductivity, z. B. formed plastics with different filler or fillers, may without welding consumables a weld with different composite plastics even be obtained different plastics that do not additional voltage compensations between the individual plastic parts needed so that a weld with very high strength and uniform introduction of force into the plastic parts can be achieved with each other.

If the pressure member maintained at room temperature, the Druckegalisierung occurs particularly advantageous since the plastic parts to be joined together, are generally also at room temperature, so that the surface of the weld and to use plastic parts have only low force peaks even at room temperature. About Attack the another, in particular at an angle greater than 0 ° z. B. 90 ° subsequent welds the pulsed applying a weld, so can thereby present, application of force peaks, are particularly effective achieved a balance of, especially in corners of welded joints.

If the weld from both sides, in particular applied the same pulse-like, it is not only the reflection of the forces if a unilateral impingement takes place and a rigid support is given, achieved, it is on both sides a deeper adjustment of the pressure peaks in a particularly simple fashion performed.

If the weld held approximately to the material thickness to be joined plastic parts in the compound may also requires at later force, for example, by application of heat, a particularly uniform transfer of forces from a plastic part in the other plastic part without power peaks to create the weld, be achieved.

In the following the invention is explained in more detail in the Examples:

Example 1: Two polypropylene sheets of the same composition with a material thickness of 1.2 mm were prepared by a metal sword, which was heated to 230 ° C, to one of its end faces, which had a length of 20 cm, heated. The end faces were melted thereby, after which the sword was returned out of contact with the end faces. Then the two front sides were played down and brought into contact with each other, whereby a slightly raised weld was formed. This weld was supported on the lower side by a base plate and against the weld and also against the adjacent portions of the two polypropylene plates a striking element was driven at a speed of 3 m / per second. The movement of the striking element was set so that this 1.1 mm was pressed against the polypropylene plates. From the thus-joined plates a sample was taken with dimensions 100 mm x 20 mm, with the normal to the weld

Longitudinal extension was placed and subjected to a tensile test. The strength showed hiebei> 95% of the material underlying.

For similar material with corresponding welding conditions without additional pulse-like action on the weld strength was 65%.

Above experiment is thus clear from that a pulse-like action on the still molten weld provides a substantial strengthening of the weld.

Example 2 A compound was prepared from polypropylene plates according to Example 1 was conducted, wherein a pulse-like actuation of the still softened weld according to Example 1, however, in a frequency of 5 Hertz, 10 seconds was carried out for. The striking element was similar to Example 1, wherein the large mass of the striking element prevented a heating above the room temperature. The periodic pulse-like stress the weld exhibited a further increase in strength to more than 95% of the material underlying.

Example 3: A split frame made of polyethylene with a thickness of 1.5 mm, which had a reinforced edge, has in its inner region, of the 200 mm x 200 mm having a rectangular recess of the dimensions, a polypropylene filled with carbon was gradually connected. Both the welding, and the pulse-like application of impact element having room temperature, in the corner regions overlap welds was given. The so welded inner area of ​​the cell was despite the different thermal conductivity, after all four end portions were welded to the frame, perfectly flat, so that could be particularly accurately dimensioned in a manufactured with this electrode zinc-bromine battery, which the internal resistance of zinc bromo-battery particularly small and their capacity could be held up very effectively.

Further experiments with polyethylene were also carried out with polyvinyl chloride with plasticizers, foamed polypropylene polyvinyl acetate and other thermoplastics, where in each case the strength of the weld could be substantially increased and at the same time was able to be effectively prevented warping of the interconnected parts.