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  • Why is the ejector pin of injection mold always easy to break?

Why is the ejector pin of injection mold always easy to break?

I. Ejector arrangement principles

(1) The ejector pin arrangement should make the ejection force as balanced as possible. Complex parts of the structure required to release forces are larger, the number of ejector pins should be increased accordingly.

(2) the ejector pin should be set ineffective parts, such as bone position, column position, step, metal inserts, local thick rubber, and other structural complex parts. Bone position, column position on both sides of the thimble should try to symmetrically arranged, thimble and bone position, column position side spacing is generally taken D = 1.5mm, as shown in the figure, in addition, should try to ensure that the column position on both sides of the thimble centerline through the center of the column position.

(3) Avoid setting the thimble across the step or on the slope, the top surface of the thimble should be as gentle as possible, and the thimble should be arranged in the structural parts of the rubber parts with better stress. As shown in the figure.

(4) In the deeper bone position of the rubber parts (depth ≥ 20mm) or difficult to arrange the round thimble, should use the flat thimble. Need to use flat thimbles, flat thimbles in the form of inserts as far as possible to facilitate processing. As Figure

(5) to avoid sharp steel, thin steel, especially the top surface of the thimble should not touch the front mold surface. As shown in the figure

(6) ejector arrangement should consider the side spacing between the ejector and the waterway, to avoid affecting the processing of the waterway and leakage. For specific requirements see Chapter 10, section 10.2.

(7) Consider the ejector pin exhaust function, in order to eject the exhaust, in the easy formation of vacuum parts should be arranged ejector pin. For example, at the larger plane of the cavity, although the clamping force of the plastic parts is small but easy to form a vacuum, resulting in increased release force.

(8) The plastic parts with appearance requirements, the ejector pin can not be arranged on the appearance surface, other ejecting methods should be used.

(9) For transparent plastic parts, the ejector can't be arranged in the part that needs light transmission.

II. Thimble selection principles

(1) choose a larger diameter of the thimble. That is, in the case of sufficient ejector position, should choose a larger diameter, and size priority of the thimble.

(2) the choice of thimble specifications should be as little as possible. Selection of thimbles, the size of the thimble should be adjusted so that the size of the minimum specifications while trying to use the preferred size series.

(3) the choice of ejector pin should meet the ejector strength requirements. Ejector, ejector pin to withstand greater pressure, in order to avoid small ejector pin bending deformation, when the ejector pin diameter is less than 2.5mm, should be selected with a butt ejector pin.

Mold release difficulties, easy to crush the problem of broken ejector can be reduced by various hands but always can not be eliminated, high maintenance costs, some of the reasons and recommendations are as follows.

1. high temperature of the production environment, resulting in fatigue, ejector pin material annealing, and thus failure

2. dimensional accuracy to meet the requirements of use

3. stress concentration.

Shaft in the processing step is easy in the diameter of the sudden change in the part (another workpiece in the sudden change in the shape of the part) the formation of stress concentration so that in the use of engineering encounter external force (especially radial force) when cracking or fracture.

4. Heat treatment

Most of the ejector pin in the manufacturing process to heat treatment, quenching without tempering or tempering time is not enough products prone to, such as excessive residual stress and other quality problems;

5. surface treatment, in order to improve wear resistance, more nitriding treatment, check whether the nitriding process is standardized, higher nitriding temperature causes material tempering or even annealing and failure

6. in the use of the process as far as possible to avoid the ejector pin radial force.

7. in the design of the mold to consider the hole reducer parts using rounded transition or increase the stress relief groove.

8. check the size and roughness of the aperture before installing the ejector pin, if the ejector pin hole reamed after the ejector pin is installed very loose, the ejector hole is easy to feed, the ejector pin is easy to break if it is very tight, it is easy to burn at high temperatures, so the ejector pin and hole fit must be mastered.

9. mold daily maintenance and process debugging

Each time the mold is installed with anti-seize oil effect is better, where the daily maintenance is mainly regular application of lubricant or ejector oil. The ejector pin of the mold are 3-5μ gap, at most can support 3~5 days after the general lubricating oil is applied, with the accumulation of dust, metal powder formed by mold friction into the ejector pin, slider, slant top tunnel gap caused by the gap of the mating surface is getting smaller and smaller, the finish is getting lower and lower, and finally completely ablated and stuck until fracture.

Therefore, it is necessary to wipe the ejector pin and mold surface dirt reapplication of clean lubricant. When maintenance, pay attention to the diagonal top and ejector pin as much as possible to apply high temperature resistant lubricating paste, forming a film, do not use a brush to apply, otherwise, it is very easy to cause oil pollution injection molding parts

10. pursue shorter cycle time, set the speed of ejecting and ejecting too fast than the capacity of the mold.

11. If the ejection speed is too fast, the product will not have enough air inlet at the bottom, which will form a negative pressure damping state and increase the resistance of the ejection. The top bar will be subject to large resistance

12. If the ejector rod is thin, it will be easily damaged.

13. when the ejector resistance is too large, check the beer parts have no strains deformation, appropriate to improve the mold slope, the first few dies will open the mold time is short, one or two seconds can be, not the system problems is the product buckling force is the too large reason.

14. the cooling water is not turned off after the machine is stopped, the mold temperature drops, the pressure of the first mold, the cooling time is long, the clamping force is large, the mold opening time is shortened

15. the material of the thimble, you can choose the new material Sweden SSAB Steel Group Toolox44 Topaz steel to solve the material and heat treatment problems, Toolox is the world's hardest pre-hardened steel, pre-hardened to 45-48HRC, reducing the risk of heat treatment and cycle, excellent nitriding performance, almost no stress, no deformation, 2-3 times higher than the traditional material toughness, can resist It is the best choice of material for high-temperature resistance and stability.
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