For flat plastic parts with flanges, if a push plate is used to eject mold, ejection mechanism should be used. Because push block is part of cavity, it should have higher hardness and lower surface roughness. There are two types of reset: one is to rely on plastic pressure, and the other is to use a reset lever.

Some plastic parts are not suitable for ejection mechanism such as ejectors, push plates, push blocks due to structural shape and plastic used. At this time, plastic inserts can be used to bring out plastic parts. Pushing block mentioned earlier belongs to ejection mechanism of shaped insert.

It refers to integration of several ejection mechanism mentioned above to achieve purpose of ejection. Commonly used are jacks and plates, jacks and plates.

Compressed air passages and valves are required to use air pressure demoulding. Processing is relatively simple, suitable for demoulding of light and thin soft plastics.

When plastic parts have inner and outer holes or undercuts that are different from direction of mold opening to prevent plastic parts from being demolded directly, an oblique slider demoulding mechanism must be used. That is, forming a side hole or undercut into a movable core.
When plastic parts are ejected from mold, movable core is first pulled out, then plastic parts are ejected from mold. Mechanism to complete extraction and reset of movable core is called core pulling mechanism.
Purpose of ejection system in plastic mold is to eject product from mold core. Common ejection structures are round ejector pin, Rectangular E.P., ejector sleeve, ejector bar, lifter, push plate, push block, secondary ejection and so on. Following introduces essentials of ejection system design.

 

Ejector pin with a diameter of less than 2.5MM has an effective length of 10-15MM. Following parts can be avoided to prevent ejector pin from being mismatched and burned. Effective length is 15-30MM, which increases correspondingly according to size of ejector pin.

 

 

Ejector pin that forms plastic position, and ejector pin that has a different direction need to be positioned. There are three common positioning methods, which are determined according to factory habits. When third method is adopted and supporting height of ejector pin is 4MM, pin diameter is 1.5MM. When supporting height is greater than 4, pin diameter is 2.5MM. As shown below:

 

(1) Ejector pin should be as large as possible, and specifications should be as uniform as possible. Ejector pin should be at least 0.5MM away from back die side, and should not exceed 3.0MM as much as possible, as shown in the figure.

 

(2) Ejector pin should be placed as far as possible at the bottom of finished product, such as A pin, try to be 0.3mm away from mold core, avoiding placing it at the top, such as B pin.

 

(3) Try not to make ejector pin on inclined surface. If necessary, add an anti-slip position to ejector pin on inclined surface.

 

(4) There are two ways to eject rubber column. One is to add a ejector pin directly under rubber column to perform two functions of ejection and exhaust. Second is add a ejector pin next to rubber column. Bottom of rubber column can choose whether to add an exhaust pin.

 

(5) There are two ways to push out ejector sleeve: if height is below 6MM, you can choose middle insert pin and add ejector on both sides. For heights above 6MM, use ejector sleeve directly to push out. For ejects of deep bone, Rectangular E.P. is preferred, and finally round ejector pin is added at the bottom.

 

Whether there is guiding C angle in middle hole position. There are two ways to form C angle. One is forming on ejector sleeve. When it is formed on a ejector pin, it is processed by a grinder. When it is formed on a ejector sleeve, it is processed by EDM. Minimum wall thickness of ejector pin should be no less than 0.8, otherwise it is difficult to process. There are two ways to fix ejector pin on bottom plate. One is to fix it directly with a headless reel, which is usually suitable for case of fewer ejector pins. Second is to use 8- 12MM thick pressure plate plus M5 or M6 reel fixed.

 

Inner side of parts is not suitable for ejection pin. When parts is deep, you can use a push plate to eject. When it cannot be ejected whole cycle, you can use a push block to eject. These two are essentially same. There are several points when designing:
(1) Place where inner insert contacts push plate should be 3-5 degrees to reduce wear.
(2) There should be a distance of 0.3 from hard core on the inside of parts to prevent damage to mold core.

 

Lifter mechanism can take off produce and eject product, so do not use ejector pin in the area of lifter. Angle of lifter is determined by product's undercut. Generally, it takes 3-12 degrees, as shown in figure. :