Mold-ejector mark

Slider, Jaw, and ejector Fretting of the elements Contaminations on the molded part surface brown wreaths around the ejector markings... 

Ejector pins often leave compression marks on the molded article. They should not be used on the visible part of the article, if this can be avoided. Another example of an ejector is the sleeve-ejector (Figure 4-12), which is able to transmit greater ejection force. Slccvc-ejectors are primarily employed with moldings, which are axially symmetrical. 

Ejector locations. Ejection devices for plastic parts can range from screwdrivers used to pry parts out of a hand mold to mechanized stripper plates and elaborate mechanisms which also retract collapsible cores. All of them share one common characteristic they exert pressure on a newly formed part. That pressure can distort the part to the point of disturbing its function or appearance if it occurs while the part is still too soft to withstand it. Therefore, the processor must delay ejection until the moldment can endure it. The more ejectors there are, the more ejection surface there is to distribute that pressure and the sooner the part can be removed from the mold, thereby shortening the molding cycle. However, ejectors cost money and leave marks on the surface of the moldment. Therefore, there is a mold cost associated with a faster molding cycle. (Differences between bidders on a project are often based on variations in cooling and ejection systems.) Additional ejectors leave more marks on the surface and their number and location may be limited by functional and appearance concerns. 

Problems and Troubleshooting - Injection Molding Flow chart 5.2.17 - Ejector pin marks... 

A diagram of the injection molding process is shown in Figure 6.22. The extruder is similar to other fabrication techniques where the granular resin enters a hopper, where the material is transferred to a heated barrel and a reciprocating screw moves the molten plastic to the molding cavity. The molding cavity is unique to this process. The molten polyethylene is forced xmder pressure into a closed mold that is continually cooled. After the molded part cools, the mold opens and the fabricated part is ejected from the mold. An injection molded article can usually be identified by the ejector pin marks that are usually present on the molded part. 

With a curved tunnel gate (also called submarine gate or cashew gate, Figure 1.38) it is possible to position the gate on the back of the molded part where the appearance is as little affected as by the markings of the ejector pins. 

The position of the ejector pins is regulated by the geometry of the molded part. To prevent markings, it has to be ensured that the pins push against ribs, shoulders, and hidden molded part surfaces. 

These ejectors, or combinations, are advantageous because the injection molding machines are designed for them speciflcally, and the cycle times are kept short. Gate marks and deformations of thin-walled parts have to be taken into consideration with these solutions. 

Ejection is the name given both to the process of removing the molding from the mold and to the means by which it is done. Ejectors inevitably leave witness marks on the molding, and this alone may determine the disposition of the part in the mold. Once that basic choice has been made, there is usually not much further freedom to position ejectors in cosmetically acceptable positions. The choices are much constrained by other features in the mold and the need to put ejectors where they are most needed to overcome the resistance of the molded part. 

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