Injection molding splay

A new GPPS resin was tested at a customer s injection-molding plant as an Improvement over an incumbent resin manufactured by a competitor. The new resin performed well in the process except that it created parts with a 5% rejection rate due to a splay defect. The competitive resin was reported to run well but with a lower... 

Many of the contamination defects that typically occur in extrusion processes can also occur in injection-molded parts. The most obvious defects are caused by foreign material contamination, resin degradation, and surface defects known as splay. The next sections provide case studies where contamination caused defects in injection-molded parts. 

Splay is a common term for surface imperfections that occur on injection-molded parts. Like the term gels for films, splay can occur from several root causes. Many of the root causes originate from the plasticating system and are related to moisture in... 

Injection-Molded Parts with Splay and Poor Resin Color Purge... 

The modified screw was placed back into the injection-molding press and evaluated for performance. The barrel temperatures were maintained at 245, 255, 260, and 260 °C for the feed zone through the last barrel zone, respectively. This temperature setting was lower than that used for the original screw. The screw was rotated at a speed of 235 rpm, and the back pressure was set so that the pressure at the tip was 10 MPa. The 0.244 kg part and runner system was plasticated in 4.2 s for a specific rate of 0.89 kg/(h-rpm). All parts produced were completely free of the splay defect. The modifications were able to eliminate the bubbles and the unmelted material. 

The automotive indushy is an extremely competitive market for the injection molding industry. Automotive manufacturers are reducing the number of supphers which produce components for their vehicles. To stay competitive, injection molders need to be proactive in both technology and pricing. Interior trim is a very competitive market for the injection molding industry. Much of the interior of an automobile is comprised of plastic parts molded from many different materials. The variety of plastics used in interior trim makes it very difficult for the assembler to obtain color match between all components. Each type of base resin requires a different formulation of colorant to achieve the same finished color. This problem is further complicated by the addition of additives such as UV stabilizers, lubricants, fillers, etc. Other problems include molding faults such as flow lines, weld lines, sink, splay, and blush... 

Need for Drying TPEs. Many TPEs can absorb sufficient moisture in a short time to cause difficulties such as poor surface appearance (or splay) on injection molded parts and rough surfaces and porosity in extrusions. A moisture pickup of 0.10 percent or greater can give highly significant problems, even in the case of nonpolar hydrocarbon TPEs. An exposure of less than one day can be unacceptable. 

Gate blush (gate splay) n. A blemish or disturbance in the gate area of an injection-molded article. It occurs when the melt fractures as it emerges from the gate due to sudden release of large elastic stresses. 

Processing can be done on standard injection molding machines at normal residence times. Longer residence times should be avoided since they cause chemical reactions, affecting Vicat and other properties. Drying of this blend is more important than for example, PC/ABS blend because PET component is very sensitive to moisture. Drying prevents splay. 

Problems and Troubleshooting - Injection Molding Flow chart 5.2.15 - Splay marks/Delamination... 

Splay Mark Also called silver streak. Fan-like or streaking on the surface of fabricated plastic parts. Causes include moisture in the plastic material, thermal degradation of plastic material, relatively cold plastic on mold or die surface due to fast an operation (called jetting), injection mold gate restriction, foam molding, etc. 

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