Metal-polymer joint

Abstract The formation of stable metal/polymer joints is an enormous challenge in material sciences. Good adhesion requires an interphase which is able to specifically interact with the metal substrate as well as with the second component. Furthermore, the interphase should compensate thermally generated mechanical tensions between the two adhering components. It will be shown that statistic copolymers of poly(vinyl formamide) and poly(vinyl amine) (PVFA-co-PVAm) are potential candidates for adhesion promoters. The polyelectrolyte character of the copolymers allows to apply them from its aqueous solutions. The primary amino groups exhibit the copolymers as highly reactive to metal surfaces as well as to the second joint partner. The... 

L.S. Pinchuk. Investigations of capillary liquid permeation into metal-polymer joints. Trans. Belarus AS, ser. Phys.-Tech. Sci, 1978, No. 2, pp. 119-122. 

Structural inhibited plastics have found application in the sealing of movable and stationary metal-polymer joints operating in hostile environment. They are most efficient in weakly and moderately loaded friction joints, plain bearings and seals. Their main role in metal-polymer friction joints is the reduction or suppression of mechanochemical wear. 

It should be emphasized that use of inhibited plastics in metal-polymer friction joints assists in a number of cases in solving the problem of fighting mechanochemical wear through the suppression of corrosion processes in the friction zone by Cl liberated by the polymer counterbody. Yet inhibited plastics are not the only means of corrosion inhibition in metal-polymer joints. 

Let us examine some examples of improved service characteristics of metal-polymer friction joints with the help of electrical fields. A metal-polymer joint (MPJ) is a combination of metal and polymer parts operating in coordination [66]. The durability of an MPJ depends on its design, the properties of constituent materials and the operation conditions, including temperature, pressure, mutual displacement velocity, ambient media, physical fields, radiation etc. During operation, an MPJ undergoes certain changes in its material structure, wearing, etc. that impair its performances and life of the joint as a whole (Fig. 4.18, solid arrows). 

Fig. 4.18. Schematic diagram of monitoring serviceability of a metal-polymer joint dnring its operation...

The primary challenge facing adhesive bonding of metals is to obtain sufficient durability of a bonded structure. Initial bond strength in metal-polymer adhesive joints is almost invariably excellent. Challenging the application of adhesives in polymer-polymer joining, however, is the problem of obtaining a joint that is... 

The predominant applications of present day metal/polymer adhesion technology are for the development of strong metal-to-metal structural adhesive joints and durable protective coatings. 

The contacting metals are subject to a specific effect due to the polymer materials. This effect should be considered during the design of anticorrosion metal-polymer parts and joints and when predicting their service parameters. 

One of the reasons for local corrosion at the metal-polymer interface is sorption of electrolytes by polymers and permeability of the polymer barrier towards electrolytes. Sorption of electrolytes (acid solutions, bases and salts) leads to essential variation in the service characteristics of the protecting polymer coatings and anticorrosion packaging films under mechanical loads. These variations under mechanical loads, especially in seals and friction joints, are much deeper and can affect mechanisms of contact interactions. 

Parts of friction joints and seals are often made from inhibited structural plastics (see Chap. 4). Their main role in metal-polymer friction joints is to abate Mechano-chemical wearing of metal counterbodies. Application of inhibited antifrictional materials is considered to be a promising trend for extending the life of friction joints operating in hostile media. The structural polymers or their blends most often contain plasticizers. Cl, fillers and modifiers as additional components. The inhibited plastics are employed in plain bearings, sealing elements and other members of oil-extracting equipment and vehicles. 

Another group of compositions of this type is used to protect metal friction joints during transportation and preservation. They represent compositions thickened by polymers of soap, silica gel and soap-hydrocarbon lubricants impregnated with anti-frictional fillers (molybdenum or graphite disulfide), oil-soluble Cl, anti-seizure additives and surfactants. To this type of Fluids belong such compositions as Tenox Film 30 (Sophes Co., France), Koral 530 (Hungary), SACI 500 and Shell Ensis Fluid 256 (Shell, GB). 

Despite the fact that the peculiarities of metal wearing in contact with polymers were determined more than 30 years ago [35], the serviceability of metal-polymer friction joints has resisted estimates for a long time. The origin of this corrosion wear mode was considered only for plastics processing equipment, in which metals are in contact with the moving polymer melt [36]. 

Electrical polarization of friction joints is an effective means of fighting mechanochemical wear. Polarization parameters are chosen so as to transfer the metal into a stable passive state. In other words, the metal potential maintained during operation of the friction joint is different from a standard electrode one. The sources of such polarization can be metal-polymer parts and joints of machines and equipment containing M1-P-M2 pairs. 

Properties of engineering materials are known to vary under the action of electromagnetic fields. For instance, wear of metal-polymer friction joints was found to reduce substantially in response to exposure to a flow of charged particles in conditions of electrochemical reactions. Besides, methods of regulating the conductivity of materials and polarization of crystals by electrical fields, as well as by so-called training methods of semi-conducting substances and many others are known in the art. 

The brief information on polymer transformations under tribochemical effects cited above can be used for estimation of mechanochemical processes in the metal-inhibited plastic tribojoints only in the first approximation. A unified theory of tribochemical transformations of pol3Tuers has not yet been developed and the mechanisms of macromolecular conversions during friction are still to be studied comprehensively. Some investigation results of tribochemical phenomena in metal-polymer friction joints are discussed below. 

The composition of the products of tribochemical reactions depends on the service load and velocity regimes of the metal-polymer friction joint and the origin of the contacting materials. As has been indicated earlier, the... 

It is quite apparent that Cl are able to function as efficient wear inhibitors and contribute to extending the lifespan of metal-polymer friction joints. 

L.S. Pinchuk, V.A. Goldade and A.S. Neverov. About electrical phenomena in metal-polymer moving joints. Proc. of Soviet Conf. Theory of friction, wear and lubrication , Tashkent, 1975, Vol. 2, pp. 145-146. 

Both electronic and medical applications of plasma polymers have been reported [54-61]. Most of these investigations are on the interface between polymers and inorganic materials, for instance, metal/polymer interfaces in structural adhesive joints, and cation diffusion along polymer/metal interfaces under an applied electric potential. In another reference, more specific aspects for electrical and electronic applications [59] were treated, wherein protective films for microcircuitry, and for wettability were explained. The use of such film for surface treatment has also been examined. 

This combination of materials has had a profound effect upon the development of surgery for the treatment of Joint disease and prostheses are readily available, not just for the hip joint but also for the knee, ankle, shoulder and other joints. It is the good biological acceptability of UHMWPE coupled with its mechanical properties that has led to this widespread acceptance. In particular, the tribological characteristics appear to be the most satisfactory for use in a metal-polymer combination. Prosthesis designs utilising alumina ceramic also incorporate an acetabular component of UHMWPE in consequence of the low rate of wear observed. 

ISO (2001) Standard test method for mode I interlaminar fracture toughness, GIC, of unidirectional fibre-reinforced polymer matrix composites. ISO 15024 ISO (2009) Adhesives - Detemination of the mode I adhesive fracture energy GIC of structural adhesive joints using double cantilever beam and tapered double beam specimens. ISO Standard 25217 Kawashita LF, Moore DR et al (2005) Comparison of peel tests for metal-polymer laminates for aerospace applications. J Adhes 81 561-586... 

In due course a full numerical solution to the elastohydrodynamic problem for Chamley type, metal-on-polymer Joints was reported [9]. It was confirmed that the theoretical film thickness in natural Joints was about 1 pm, while films of only about 0.2 pm were predicted for the gold-standard form of Joint replacement The latter films were too small to ensure separation of the metallic femoral heads and polyethylene acetabular cups and it was concluded that boundary, or at the best mixed lubrication, would prevail. This theoretical finding... 

In describing the components of total joint prostheses and their interaction with adjacent tissues, many authors identify the articulating interface (metal/polymer), the metallic prosthesis - polymethylmethacrylate bone cement interface and the bone cement-bone interface. Unfortunately, the bone cement-bone interface may be transient with a fibrous capsule eventually interposing itself between the bone cement and the bone to create the bone cement-fibrous capsule-bone interface (19,20). As described earlier, the formation of a fibrous capsule around implants is a common occurrence. In the case of total joint prostheses where situ polymerizing methyl methacrylate is used as bone cement, this fibrous capsule formation may be accelerated by the heat of polymerization or the toxicity of the monomer, both of which may lead to localized tissue destruction and cell death (21,22). 

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