Weld line

Developments. A variety of process modifications aimed at improving surface finish or weld line integrity have been described. They include gas assisted, co-injection, fusible core, multiple Hve feed, and push—pull injection mol ding (46,47). An important development includes computer-aided design (CAD) methods, wherein a proposed mold design is simulated by a computer and the melt flow through it is analy2ed (48). 

Weld-seam defects. Failure to fuse the metal fully along the weld line in welded tubes may result in a linear open seam or crevice. 

Moulded plastics will also have crack initiation sites created by moulding defects such as weld lines, gates, etc and by filler particles such as pigments, stabilisers, etc. And, of course, stress concentrations caused by sharp geometrical discontinuities will be a major source of fatigue cracks. Fig. 2.72 shows a typical fatigue fracture in which the crack has propagated from a surface flaw. 

W a = air inleakage resulting from metal porosity and cracks along weld lines, Ib/hr... 

Fig. 3 -29 Injection molded test specimens that include weld lines.

Fabricating techniques can be used to reduce this problem in a product. However, the approach used in designing the product, particularly its mold (relocate gates), is most important to eliminate unwanted orientation or weld lines. This approach is no different from that of designing with other materials like steel, aluminum, or glass. 

A meld line is similar to a weld line except the flow fronts move in parallel rather than meet head. Usually the meld line is identified as a weld line. 

Weld line With moldings that include openings (holes), problems can develop. In the process of filling a cavity the flowing melt is obstructed by the core, splits its stream, and surrounds the core. The split stream then... 

Opposite flow fronts produce a weld line that could also contain entrapped air. 

Fig. 3-31 Examples of melt flow patterns to consider during the design stage to eliminate or at least minimise weld lines to obtain maximum strength.

Weld line Weld or knit fines where two parts of a melt join while flowing into the mold cavity can result in problems. The quality of the weld depends on the temperature of the material at the weld point and the pressure present in the melt after flowing from the gate. The higher the temperature and pressure, the more complete the weld and the better the product performance and appearance. Bringing the material to the weld point at a higher temperature and pressure requires rapid filling of the mold cavity (Chapter 3, BASIC FEATURE, Weld Line). 

The RP tank just reviewed that was removed in 1988 met these requirements, but two steel tanks unearthed from the same site at that time failed to meet them. There was no record of how long the steel tanks had been in service, but one was dusted with white metal oxide and the other showed signs of corrosion at the weld line. Rust had weakened this joint so much that it could be scraped away with a pocketknife. 

Fig. 8-23 Example of weld lines where the gate was located at the top center of the telephone handset.

These are usually self-adhesive, precut, printed patterns on a substrate that are simply adhered to the surface of a product. Decals generally use a transparent plastic film while labels are usually on an opaque plastic, metallic and multilayer sandwich base. Labels of sufficient thickness are useful for hiding unavoidable appearance problems such as gate and sprue removal areas, sink marks, blushes, splays, and weld lines. 

The silicon map shows the distribution of slag inclusions, while the position of the weld lines can be seen to be marked by boundaries between areas of high and low phosphorus content and by enrichments of nickel and/or arsenic at the weld lines. Higher resolution maps can be made of welds to reveal their fine structure. 

An example of a higher resolution map from the EPMA is given in Figure 5.11, where the sample is again an archaeological specimen - a pair of shears from the same site as the specimen shown in Figure 5.10. Here the weld lines are marked by lines of sulphide and slag particles in an area depleted of phosphorus. 

Formed domed heads are made with a short straight cylindrical section, called a flange or skirt Figure 13.10. This ensures that the weld line is away from the point of discontinuity between the head and the cylindrical section of the vessel. 

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