During ejection, white ejector mark usually appears on the plastic parts in contact with the ejector pin and such ejector mark will easily crack during actual use of the products. The causes thereof comprise:
1 Overhigh injection pressure, overfast dwell time, overlow mold temperature, accompanied with overfast cooling speed of products in the mold as well as unbalanced cooling, which altogether lead to the increase of internal stress of products;
2 Oversmall draft, incorrect or insufficient spraying of mold release agent, overlarge ejection resistance;
3 Improper design of ejector unit, overfast ejection speed, resulting in large ejection stress at the contact area of plastic parts and ejector parts (mainly for ejector pin or ejector tube);
4 Improper design of structure for the products.
According to the above causes, measures should be taken to minimize the internal stress for the molding of products and to reduce the ejection resistance and the ejection stress applied on the plastic parts by the ejector pin; proper reinforcing measures should be adopted for the contact area of product and ejector pin. The specific measures therein are as follows:
1 Avoid excessive injection of melt.
2 Reduce injection pressure and dwell pressure, shorten dwell time.
3 Reduce injection rate, optimize design of feed system, and realize sound mold filling.
4 Properly improve mold temperature, prolong cooling time, properly reduce cooling speed,
optimize mold temperature control system and structure of products and try to keep uniform cooling of products in the mold.
5 While ensuring proper retaining mode of plastic parts in the mold, increase draft.
6 According to the structural features of plastic parts, carefully analyze the ejection resistance and its distribution, use suitable ejection mode, properly arrange position of ejector pin, and try to achieve balanced ejection; increase number of ejector pins at places with large ejection resistance, and meanwhile expand section dimension of ejector pin, reduce ejection stress at contact area of product and ejector pin; properly increase wall thickness at places where ejector mark will easily occur, to strengthen the resistance of products against destructivity of stress.
7 Increase smoothness for the surface of cavity, and at the final stage of polishing for molding parts, the polishing should be done along the ejection direction of plastic parts to reduce ejection resistance; for molds whereto the ejector mark has already occurred, it is recommended that polishing be applied to the surface of molding parts corresponding to the ejector mark.
8 Properly spray the mold release agent.
How to improve ejector marks defect injection molding?
1） If sample has scratch at boss, rib -> lapping the mold at these position.
2） If ejector pin is too small, change to new ejector pin with bigger diameter, or change ejector pin to new position, we can change to rib area.
3） Increase cooling time.
4） Increase thickness of product at ejector mark if we can.
5） Reduce holding pressure, holding pressure time, or mold temperature.
6） Check the mold, if ejector is over core surface, re-set ejector system.
When the ejector pins try to push the part out of the mold, sometimes the mold sticks, which causes the pin marks to appear on the finished part. However, the issue may not always be with the mold itself, but rather the molding process, machine, or materials.
The most common culprits include:
Over-high injection pressure, over-fast dwell time, overflow mold temperature accompanied by an over-fast or unbalanced cooling speed, which altogether increase the internal stress of products.
Over-small draft, incorrect or insufficient spraying of the mold-release agent or an over-large ejection resistance.
Improper design of the ejector unit and over-fast ejection speeds can result in large ejection stress among the plastic and ejector parts.
Improper design of structure for the products.
they create unnecessary internal stress for the molding of products, so we need to reduce the ejection resistance and stress being applied by the ejector pins on the plastic parts.
Avoid excessive injection of melt.
Reduce injection pressure and dwell pressure. Shorten dwell time.
Reduce injection rate, optimize the design of the feed system and realize a sound mold filling.
Properly improve mold temperature, prolong cooling time and reduce cooling speed. Optimize temperature control and product structure to encourage uniform cooling of products in the mold.
Increase draft while ensuring proper retaining mode of plastic parts in the mold.
Analyze the ejection resistance and distribution, then use a suitable ejection mold with properly arranged ejector pins, trying to achieve a balanced ejection. If you see large ejection resistance, increase the number of ejector pins in those areas and expand the section dimensions of the ejector pin. Increase wall thickness where the ejector mark can easily occur in an effort to strengthen the products’ resistance to stress.
Increase smoothness for the cavity surface. Polish along the ejection direction of plastic parts in the final stage of polishing. If you’re polishing a mold that already has ejector pin marks, apply polish corresponding to the ejector mark.
Properly spray the mold-release agent.
Causes of ejector pin marks and solutions
1. Product design:
Whether the product wall thickness is appropriately designed is dependent on the raw material and product structure. Usually, the thickness of a simple-structured product needs to be no less than 2.5mm. Comparatively speaking, for some complex-structured products, i.e., products with more ribs in the cavity, the thickness must be no less than 2.8mm.
2. Mold design:
1). In order to save raw materials and facilitate subsequent mold changes, the sizes of the nozzle and runner are usually not too large when they are first designed. When ejector marks occur on the product, the sizes of the sprue and the runner can be appropriately increased to alleviate the overshooting of the injection pressure and other parameters caused by filling difficulty (note: the sizes of the sprue and the runner can only be changed and increased when the injection parameters are too high, or other severe issues may occur; design vents at the runner end). The internal stress around the gate is the highest, so the gate should be located where it is easy to fill the cavity and as far away as possible from the ejector, while resin filling should be as uniform as possible to ensure uniform stress distribution.
2). The type, arrangement, size, location and number of ejectors all have a lot to do with the occurrence of ejector marks. The design should ensure that the properly sized ejector pin is uniformly stressed when the product is ejected. For example, the areas with deep ribs, that is, the areas where it is more difficult to eject the product, need to be ejected with higher force. Also, the ejector pins need to be designed on the ribs.
For products with deep ribs, it is necessary to put the stress points on those deep ribs, so as to avoid ejector marks caused by excessive force during product ejection.
The design of the ejector pin location should take the following two factors into consideration: whether it is ejected at the maximum stress point and whether it is balanced.
All the causes create unnecessary internal stress for the molding of products, so we need to reduce the ejection resistance and stress being applied by the ejector pins on the plastic parts.
Avoid excessive injection of melt.
Reduce injection pressure and dwell pressure. Shorten dwell time.
Reduce injection rate, optimize the design of the feed system and realize a sound mold filling.
Properly improve mold temperature, prolong cooling time and reduce cooling speed. Optimize temperature control and product structure to encourage uniform cooling of products in the mold.
Increase draft while ensuring proper retaining mode of plastic parts in the mold.
Analyze the ejection resistance and distribution, then use a suitable ejection mold with properly arranged ejector pins, trying to achieve a balanced ejection. If you see large ejection resistance, increase the number of ejector pins in those areas and expand the section dimensions of the ejector pin. Increase wall thickness where the ejector mark can easily occur in an effort to strengthen the products’ resistance to stress.
Increase smoothness for the cavity surface. Polish along the ejection direction of plastic parts in the final stage of polishing. If you’re polishing a mold that already has ejector pin marks, apply polish corresponding to the ejector mark.
hai,
Am having a problem in spots of ejector pin , having dark white spots facing ejector pins . It disappear while lubricating with spary.Please tell me some solution without using spray to eliminate white spot .
hi
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