JOINING OF METAL ELEMENTS WITH MOULDED PIECES FROM PLASTICS

Transcription

1 JOINING OF METAL ELEMENTS WITH MOULDED PIECES FROM PLASTICS Elżbieta Kopciuszewska Stanisław Borkowski Technical University of Częstochowa, Department of Management, Division of Production Engineering, St. Armii Krajowej 19B, Częstochowa, POLAND Abstract In the paper there are compared some properties of plastics with some properties of metals and the results determine applications of joinings of moulded pieces from plastics with metal elements. Joining of metal elements with plastics makes some tasks connected with problems of co-operating two different materials in a whole construction. Advantages and problems coming into being at creation of these constructions are discussed. In the paper there are also described producibility of usages of metal inserts. The main reason of utilisation of metal inserts is superiority of value of endurance on extension of metals over artificial materials. However several times greater coefficient of thermal expansibility and contraction of materials creates tensions round the metal inserts metal inserts. It can cause the crack of the metal insert. Suitable selection of thickness of side of material round metal insert and technological interventions (e.g. heating up before foundation) permit to solve the problem. In the paper there are presented some technological solutions which are indispensable for article to be peaceable ( in the aim of protection of metal insert from drawing out and from turning it executes on its area some grooves, incisions, of flattening etc, in the case of usage of large metal inserts with large areas one should use cuts of openings etc). 1. INTRODUCTION At quality investigations of articles from plastics [1] it often appears some problems of realising of possible requirements which are not to success by usage of plastic only. That is why, joining of elements is applied to obtain definite properties of articles. Settling in injection's articles from plastics metal - elements so-called. Metal inserts found a lagre use. First of all, there are all armatures stiffening the articles, enlarging strength properties eg of thread opening, of catch elements, of practical elements in wheels, of pegged heels etc. Metal inserts one can divide on: connecting elements such as funnels and pins with thread, joints such as connectors, tin plates and soldering lugs, river-bed elements such as naves, river-beds, elements stiffening such as funnels of plate {shallow}, cores of sheet metal, independent elements such as axles, strings, blades. Joinings of metal with mould pieces from plastics takes place through: ironing of metal - element placed in form before bringing it materials, pressing metal - parts in ready mould pieces, mechanical folding and sticking.

2 Materials recommended on metal inserts are steels, aluminium alloys, copper alloys (two last from regard on resistance on corrosion, greater coefficient of thermal expansibility and on diminution of results of possible crumpling forms). Making up own mind on use metal inserts one should notice, that every insertion of metal - parts to injection's forms is time consuming (enlarges the laborious) and causes elevation of costs. Especially unprofitable is settling metal inserts in injection's forms, because it decreases of efficiency of injection moulding machines. Only in rare events such form can work automatically. Manual, inevitable insertion involves also potential threat of worker. Fastening of metal - parts in ready mould pieces are in general more profitable than settling them in forms. It eliminates some unprofitable acts of manual settling in form and it does not cause any tensions in mould pieces. It is less expensive and time-consuming. In mould pieces from some elastic thermoplastic materials e.g. PP metal - parts one can settle also by pressing, but endurance such connections grows enough quickly together with height of temperature. At 60 o C, it obtains some values twice smaller than values obtained at temperature 20 o C. To obtain some joints it also uses riveting of mechanical connections, thread connections, joinings by circumferential wrapping up the edges of metal insert and connections with rivet pins and with thread-forming screws. 2. THE COMRISON OF SOME PROPERTIES OF PLASTICS AND OF METALS 1a) kp/cm 2 PC POM kp/cm 2 Tensile strength

3 1b) cm/cm o C PC POM cm/cm o C Linear coefficient of heat expansion 1c) kp/cm PC POM kp/cm 2 Modulus of elasticity

4 1d) 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 kcal/mh 0 C PC POM 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 kcal/mh 0 C kcal/mh 0 C Heat conducfivity Figure1. The comparison of some properties of plastics and of metals. 3. CONDITIONING AND TECHNOLOGICAL PROPERTIES OF USAGES OF METAL INSERTS The main reason of utilization of metal inserts is showed on figure 1a. It is clear that of tensile strength of metals has a superiority over artificial materials (the exception are polyesters which are strengthened glass - fibre). Metal inserts are applied to improvement of some strength properties in mould pieces from plastics. Because plastics have several times greater coefficient of heat expansion and contraction is several times greater than of metals, (in the range of temperatures of transformation of materials and of chilling of mould pieces, some contractional tensions round metal insert are inevitable. It can cause the crack of metal insert. The suitable selection of thickness of side of material round the metal insert and technological interventions are in a position to diminish some values of contractional tensions of material. For diminutions of differences of contraction and successes correct structures of material it is indispensable the initial heating up mould pieces, before foundation them to forms (900 o C o C). Too large mass of cold mould pieces can receive heat from flowing materials too quickly. In effect it can come into being some shorts or irregular structure of crystal (figure 2a). Thickness of side round metal - parts in mould pieces selects with dependencies on materials e.g.:

5 Polyethylene PE mm, Urea plastic or melamine plastic 6-10 mm, for diameters mm Fenol plastic 3,5-6 mm, Polypropylene PP thickness of basic sides of mould pieces. If it is unsuitable proportion of thickness of side the layer of material will crack (too little layer of material) or some blisters and some drops will rise (too large layer of material). 2a,n) 2a,t) The metal insert with too big mass cause too early freezing of plastic. 2b,n) 2b,t) Dangerous arterial opening with thread causes pouring of plastic. 2c,n) 2c,t) Differences in thickness of layers of plastic on either side of metal insert are the reason of unevens of contraction and bend of mould pieces.

6 2d,n) 2d,t) 1- metal insert 2- form The thread should be protected Figure 2. Technological properties of construction of metal inserts (t technological, n not technological) [2]. The shape of metal inserts must prevent from the creation of hail, the bending of metal inserts (figure 2d) and the influence of material e.g. rolls of thread (figure 2b). The layer of plastic has to surround the metal insert symmetrically to avoid of twists and of distortions (figure 2c), if flat metal inserts are given. When thread arterially passes through the metal insert it uses the metal inserts with through- thread opening. The height of metal insert has to be compactly tolerated in the aim of avoidance of flooding of opening with material or of crumpling of metal insert. In closed form the metal inserts are squeezed by surface of nest. If metal insert is completely sunk, the material can put into the rolls of thread, that is why it uses more expensive metal inserts with nonarterial opening. Sometimes it uses the metal inserts which are infatuated with little hood or with disc from sheet metal. In the case of usage of metal inserts in the form of rods, of wires, of tin plates and of plates one should take note of splinters and exact tolerance in places compressed with form. In the aim of protection of metal insert from drawing out or turning it executes on its of area some grooves, incisions, of flattening etc. In the case of usage of large metal inserts with large areas one should use some cuts of openings. The high exactitude of arrangement of axis one can obtain from regard on ten times lower heat expansion of metal than of plastic. Then it uses the bearing plate determining one metal insert for many material elements injected in separate nests. Bearing plate coats with material and finally it obtains the article, for which in one plate the row of elements e.g.: river-beds, cams, brackets, runners etc. is executed. 4. SUMMARY The usage of metal inserts in some articles from plastics solves the problem of realisation of requirements of the article, regarding to unattainable proprieties of plastic: mostly strength. Joining of metals with material places before technologist some problems connected with co-operation of two different materials in one joint construction. Technological properties of such construction depends mostly from expertise of properties of joined materials. Different properties can realise some new requirements in article, but also may cause some problems with eliminating incidental disagreements. LITERATURE 1. KOPCIUSZEWSKA E. The Analysis of Influence of Polymer Material PP Parameters on Quality of Injection Products. W: Materialove vedy na prahu 3 Milenina, Brno ZAWISTOWSKI H., FRENKLER D. Konstrukcja form wtryskowych do tworzyw termoplastycznych. PWN, Warszawa SIKORA R. Tworzywa wielkocząsteczkowe. Rodzaje, właściwości i struktura. Politechnika Lubelska, Lublin 1991.