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Analysis on the design of plastic bottle cap mould parts and structure


On the basis of analyzing the structural characteristics of plastic parts, the structure design of the mold was elaborated, the working process of the mold was introduced, and the demoulding process of the mold was simulated in the form of illustration.

1 Plastic structure analysis

A beverage bottle cap made of PE (polyethylene) and weighs 2.9g. The outer side of the main body of the bottle cap is evenly distributed with 120 anti-slip ribs for increasing friction, and the top of the bottle cap has the name of the trademark name ZSM. There is a security ring on the lower part of the cap and the cap body is connected by 8 small cylinders with a diameter of φ1mm and a height of 1mm. There are 8 semi-circular bosses with a uniform length of 3mm and a diameter of φ1.5mm on the inside of the security ring. Inside the cap, the thread has a semi-circular thread and a height of 4mm, and the cross-section diameter of φ1mm is closely matched with the inner diameter of the bottle. The height of the anti-counterfeit ring of 1mm and the cross-sectional diameter of φ1mm closely matches the outer diameter of the bottle to prevent water leakage.

2 mold structure design

According to the shape, precision, size, process requirements and production batch of the plastic part, the following aspects should be considered in the mold design.

2.1 Number and arrangement of cavities

The bottle cap is mass-produced as a packaging container. It is advisable to use a multi-cavity. Considering the clamping force of the existing injection molding machine, the injection volume and the precision and economic factors of the cap mould parts, it is determined to be a 1-mode 10-cavity and a cavity arrangement. The way is "inline shape".

2.2 Pouring system design

According to the structure of the plastic part, the mold is designed to adopt a three-plate type point gate, and the gate is arranged at the center of the top of the plastic part. The point gate can significantly increase the shear rate of the melt, and the melt viscosity is greatly reduced to facilitate the filling. It is especially effective for PEs that are sensitive to shear rate. As a packaging container, the plastic parts have high appearance quality requirements, and the residual traces of the point gates are small, which can ensure the surface quality of the plastic parts, and the gates are automatically broken when the mold is released, which facilitates the automation of the production process and improves the production efficiency. Increased economic benefits. The non-equilibrium gating system uses a compact cavity arrangement to reduce the size of the mold. In order to enable the various cavities to be simultaneously and evenly filled, the BGV (Balanced Gat Value) method is used to manually adjust the size of each cavity gate to achieve balance. Use a cold hole to store the front cold material.

2.3 Cooling system design

The mold temperature regulation system directly affects the quality and production efficiency of the product. In order to improve the cooling efficiency of the cavity, the cooling circuit shown in Figure 2 is used, and the inlet of one circuit is located near the outlet of the other circuit; according to the shape of the plastic part and the structure limitation of the mold, the diameter of the cooling water channel of the fixed mold is φ12 mm, and the outside of the mold The hose connection forms a circulating cooling. The dynamic model core has a relatively small diameter, and the steel tube cooling method shown in FIG. 3 is adopted. A soft copper core rod having good thermal conductivity is pressed into the center of the core, and one end of the core rod is extended into the cooling water hole for cooling.

2.4 Demoulding mechanism design

The plastic part (cap) has a semi-circular coarse thread in the main part, and the plastic material is polyethylene (PE), which has good flexibility. Considering forced release, in order to simplify the mold structure and reduce the closing height of the mold, A stripping mechanism combining a limit plate and a pusher plate.

1. Positioning ring 2. Screw 3. Fixed mold seat plate 4. Limit screw 5. Guide post 6. Spring 7. Flow path pull plate 8. Guide sleeve 9. Pusher plate 10. Guide post 11. Screw 12. Support Plate 13. Water nozzle 14. Movable seat plate 15. Soft copper core rod 16. Seal ring 17. Core 18. Slant guide post 19. Plastic part 20. Limit plate 21. Screw 22. Huff block 23. Screw 24. Water channel 25. Cavity plate 26. Limit pin 27. Water channel 28. Spring 29. Gate sleeve 30. Cold material hole 31. Point gate 32. Shunt channel 33. Main channel

2.5 parting surface selection

The body of the cap is connected to the security ring only through 8 small cylinders along the circumference, and two semi-circular haval blocks (lateral) are used to form the security ring. Combined with the structural characteristics of the plastic parts, the plastic parts must remain on the core after molding, so the mold parting surface is set at the largest part of the cross-sectional contour between the security ring and the cap body, perpendicular to the mold opening direction.

2.6 lateral core pulling mechanism

The lower part of the plastic part has an anti-counterfeiting ring, and the two half blocks of the forming anti-counterfeiting ring form a cavity together with the main part of the cap, and are arranged in the fixed part, and the two Huff blocks are mounted in the guiding trough of the cavity plate. When demoulding, the inclined guide column is opened by two Huff blocks to complete the side core. When the mold is closed, the Hough block is locked by the wedge block mounted on the movable mold, and the undercut of the formed security ring is only 0.6 mm. The required pulling force is not large, the core pulling distance is small, and the Hough block is designed so as not to be separated from the oblique pin, so it is not necessary to set the positioning device of the Hough block.

3 mold working process

The mold is clamped, and the viscous fluid plastic melt after plasticization is injected, held, cooled and fixed. After the nozzle of the injection machine moves backward, the main flow condensate is released from the sprue bushing due to the rebound action of the spring 28, and the mold is opened along the I-I parting surface under the action of the spring 6, when the limit screw 4 acts as a limit position, The flow channel puller 7 pulls off the dot gate, and pulls the aggregate out of the cavity plate 25 to automatically fall. The cavity plate 25 continues to move backward under the moving template of the injection machine, and the limit screw 26 is limited. When the action is fixed, the fixed part stops moving; due to the shrinkage effect of the melt cooling, the plastic part is wrapped on the core, and the movable part continues to move backwards under the driving of the moving template of the injection machine, and the plastic part is released from the cavity, at the same time The inclined guide post 18 is opened by the Hough block 22 to complete the side core pulling action, and the movable mold part continues to move backward. When the limiting plate 20 functions as a limit, the pusher plate 9 causes the plastic part to be disengaged from the core. The mold clamping, the demolding mechanism, and the side core pulling mechanism are reset, and an injection cycle is completed.

4 Conclusion

The production practice proves that the mold is beneficial to the filling flow of the plastic melt, the demoulding mechanism is simple and reliable, the cooling system layout and the side core pulling mechanism are designed reasonably, and the quality of the plastic parts is stable and meets the user requirements after being put into use.

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