Joint design surface preparation

The design of pipework has to be such as to allow access to welds and bends for weld and surface preparation. It is preferable to use seamless tubing conforming to BS 806 1986. Where this is impractical, tubing in accordance with BS 1387 1985 is acceptable provided that the butt-welded joint seam does not restrict the bore by more than 0-25 mm. 

Important Processing Issues. As with conventional adhesive bonding, there are several important issues that cannot be overlooked with weldbonding. Two of the most important issues are joint design and surface preparation. 

Much of what we know about bonding to composite materials has come through the aerospace industries. The early studies on adhesives, surface preparation, test specimen preparation, and design of bonded composite joints reported for the PABST Program76 gave credibility to the concept of a bonded aircraft and provide reliable methods of transferring loads between composites and metals or other composites. 

Morris, C. E. M., Strong, Durable Adhesion Bonding Some Aspects of Surface Preparation, Joint Design, and Adhesive Selection, Materials Forum, vol. 17, 1993, pp. 211-218. 

As with all bonding operations appropriate surface preparation and joint design is essential to obtain a good bond. Surface preparation is achieved by carrying out a suitable surface pre-treatment such as ... 

For the best possible performance, joints should be specifically designed for adhesive bonding. In a few cases only can an adhesive be used on a joint not specifically designed for adhesives - mainly cylindrical joints. Bond stresses, materials, type of adhesive, surface preparation, methods of application and production requirements can then all be considered in relation to each other at the outset. The designer should consider especially the effect of shear, tension, cleavage and peel stresses upon the joint (Fig. 1) (see Joint design strength and fracture perspectives). 

The term primer is used to describe any liquid preparation used to modify the surface of an adherend. While there are some primerless systems, the sealants used in construction often require primers as the surface condition may be extremely variable (See Sealant joint design, Seaiants in doubie giazing and Selection of joint sealants). 

The choice of joint design should also take account of the fact that the lifetime of the chosen sealant may well be less than that of the building and that at some future date the sealant will have to be replaced. If such an operation is likely, a design of joint must be used that allows defective sealant to be removed and the joint surfaces cleaned and prepared before reapplication of fresh sealant. Because this procedure is fairly straightforward in the butt joint, this is the solution most frequently adopted by designers. In the discussion of some other aspects of joint design that follows, it is assumed that the butt joint is the option chosen. 

Joints must be designed to eliminate peel and cleavage stresses. Careful surface preparation often required. 

F. D. Petke The problem is probably due to surface preparation rather than the adhesive design. Care should be taken to remove any moisture from the surface of substrates. Silane adhesive promoting agents can be used to improve adhesive joint strength and resistance to environmental moisture for many adhesives. 

An overview is presented of the reasons for construction sealants failing in the real world . These reasons are categorised by design errors, such as improper joints sizing, application errors, such as lack of surface preparation, and lastly material failures. 1 ref. 

From the viewpoint of the adhesive technologist, plastics are an anomaly bonded joints can be made in which the plastic fails before the adhesive, but certain plastics are very difficult to bond. Although plastics often present difficulties in adhesive bonding (Table 4.2), all can be joined successfully with the correct choice of adhesive, joint design, and surface preparation [28] ... 

Most materials can be bonded with the correct selection of adhesive, surface preparation and joint design. Metals, plastics, composites, wood, glass, paper, leather and ceramics are bonded commonly. 

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