First, the principle of thimble arrangement The ejector should be arranged so as to balance the top output.
The structure of complex parts of the required release force is larger, the number of thimble should be correspondingly increased. (2) The thimble should be placed in an effective position, such as bone position, column, step, metal insert, local thick plastic structure and other complex parts.
Bone position, the column on both sides of the thimble should be as far as possible symmetrical arrangement, thimble and bone position, the column edge spacing generally take d=1.5mm, as shown in Figure 5.5.8, in addition, should try to ensure that the center of the pin on both sides of the column center connection through the column centre. (3) To avoid crossing the stairs or set the thimble on the bevel, the top of the ejector should be as smooth as possible, the thimble should be placed in the plastic parts of the structural parts of the better.
As shown in Figure 5.5.9. (4) A flat thimble should be used in the case of deep bone (depth ≥20mm) or difficulty in arranging the dome needle. When a flat thimble is needed, the flat thimble is used as a form of insert to facilitate processing.
As shown in Figure 5.5.10 (5) Avoid sharp steel, thin steel, especially the top surface of the ejector can not touch the front die surface.
As shown in Figure 5.5.11 (6) The thimble arrangement should consider the distance between the thimble and the transport channel, to avoid affecting the processing and leakage of the waterway.
See chapter Tenth, Section 10.2 for specific requirements. (7) Consider the exhaust function of the ejector, in order to eject the exhaust, in the easy formation of vacuum parts should be arranged thimble.
For example, the larger surface of the cavity, although the adhesive is less compact, but easy to form a vacuum, resulting in increased release force.
(8) The appearance of the plastic parts, the thimble can not be arranged in the appearance of the surface, should use other ejection method.
(9) For transparent plastic pieces, the thimble can not be placed in the need for light transmission parts.
Two. Ejector pin selection principle (1) Select the larger diameter thimble.
That is, if there is enough to top out the position, should choose the larger diameter, and the size of the first thimble. (2) The selection of thimble should be as small as possible specifications.
When selecting a thimble, the size of the thimble should be adjusted to the minimum size, and the preferred size series should be chosen. (3) The selection of Thimble should meet the top-out strength requirements.
Ejector, the thimble to withstand greater pressure, in order to avoid the small thimble bending deformation, when the thimble diameter is less than 2.5mm, should be used with a thimble.
Mold demoulding difficult, easy to break the thimble problem can be reduced through a variety of ⼿ segments but always can not be eliminated, high maintenance costs, and some of the reasons and recommendations are as follows:
1. High temperature of production environment, resulting in fatigue, ejector material annealing thus failure
2. Does the dimensional accuracy meet the requirement of use
3. Stress concentration.
The shaft is prone to stress concentration in the area of sudden change in diameter (other workpiece in the sudden change of shape), thus cracking or breaking when encountering external forces (especially radial forces) in the work.
4. Heat Treatment
Most of the thimble in the manufacturing process must be heat treatment, quenching after tempering or tempering time is not enough products easy to appear, such as excessive residual stress and other quality problems;
5. Surface treatment, in order to improve wear resistance, more use of nitriding treatment, check whether the nitriding process is standardized, high nitriding temperature resulting in material tempering or even annealing and failure
6. Try to avoid the radial force of the thimble during use.
7. When designing the mold, consider the circular angle transition or increase the stress relief groove in the variable diameter area of the hole.
8. Install the thimble before checking the size and roughness of the aperture, if the thimble hole hinge after the thimble installed is very loose, the thimble hole is easy to feed, the thimble is easy to break, if very tight, in the high temperature is easy to burn, so the thimble and hole of the coordination degree must be mastered well.
9. Mold Daily maintenance and process commissioning It is better to apply anti-sticking oil to the mold each time, and the daily maintenance is mainly to apply lubricant or thimble oil regularly.
Mold thimble are 3-5μ clearance, ⼀-like lubricant can be applied up to ⽀ support 3-5 days, with dust, mold friction formed metal powder accumulated into the thimble, sliding block, oblique-top tunnel cracks in the gap between the smaller, less and less, the final complete ablation die until the break. It is therefore necessary to wipe the thimble and the mold surface dirt to re-apply the clean lubricant.
Care to pay attention to the oblique top and thimble as far as possible to apply high-temperature lubricant paste, the formation of ⼀ film can be, do not use the brush to apply, otherwise very easy to cause oil pollution injection molded parts
10. In pursuit of a shorter cycle, the ejection and jacking speed is set too fast to exceed the mold withstand capacity. 11. Demoulding is too fast, the bottom of the product is insufficient, it will form the damping state of negative pressure, increase the resistance of demoulding.
The top bar will be subject to great resistance.
12. If the top bar is relatively thin, it is also prone to damage.
13. When the ejection resistance is too large, check the beer pieces have no strain deformation of the place, appropriate to improve the mold slope, the first few molds will open the mold time, a two seconds, is not a system problem, is the product buckle force is too big reason.
14. The cooling water is not shut down after the shutdown, the mold temperature drops, the ⼀ die, the cooling time Long pack tight force is big, the opening time shortens 15. Ejector material problem, can choose new material Sweden SSAB Steel Group Toolox44 to solve the material and heat treatment problems, Toolox is the world's hardest pre-hard steel, ⼚ pre-hard to 45-48HRC, reduce heat treatment risk and cycle, excellent nitriding performance, almost no stress,
No deformation, 2-3 times higher than the traditional material toughness, can resist 640°c the following high temperature, can completely solve the problem of fracture or deformation, is currently the best selection of high temperature stability. Why is the injection mold thimble always prone to breakage?