Plastic part structure is shown in Figure 1. Cap body and anti-theft ring are connected to form an integrated cap. Through connection between cap body and anti-theft ring, inner wall of cap body has its own internal thread, which forms a screwing torque action with outer thread of bottle. Anti-theft ring is injection molded into an oblique angle. After cutting ring and folding inward, it is highly locked with anti-theft ring at the bottle mouth to achieve disconnection type opening anti-theft function. Both materials are made of HDPE, which has excellent physical properties and durability, a shrinkage rate of 2.0%, light weight, good chemical resistance, and is suitable for non-carbonic plastic packaging.

 

Figure 1 Plastic part structure
Main features of anti-theft threaded cap: ① Outer side of cap is evenly distributed with knurled anti-slip ribs, 360°/2.67°=135, to increase friction of opening cap and increase grip area of hand to facilitate closing and opening cap; ② Inner side of cap is designed with trapezoidal arc double threads, n=0.9 turns, thread size M40.0mm, thread depth 1.1mm, thread width 1.7mm, thread pitch 3.7mm, forced demoulding angle 40°, forced demoulding transition radius R0.7mm. Structural design and size setting of thread are conducive to forced demoulding of thread after mold forming. Corresponding mold structure is designed to be pushed out synchronously with double actions, that is, push plate (demolding ring), inner core sleeve and gas-assisted push rod in mold are pushed out synchronously to realize forced demoulding; ③ Cap body and skirt anti-theft ring are designed with an inner bevel angle of 55°, which is conducive to forced demoulding. The thinnest wall thickness at connection position between the two is 0.26mm. This thin-walled discount position is a skirt anti-theft ring structure with an inward reverse bevel angle of 8.55° after ring is cut and folded, providing fixed size and inner support form required for invisible folding. When cap is screwed into bottle mouth thread until corresponding height positioning circle, reverse skirt anti-theft ring is buckled and enters bottle mouth height positioning circle, realizing interference fit of cap and bottle at this position in upper and lower heights, inner and outer diameters. When cap is opened with force, cap cutting point is disconnected and separated under external force of vertical unscrewing, cap body and skirt anti-theft ring are completely separated to realize opening of cap. The key is that this opening process is a disconnection-type anti-theft action.

Plastic parts are non-carbonated general-purpose caps, which are in high demand. A 8-cavity (2 horizontal and 4 vertical) needle valve hot runner balanced cap top feeding layout is adopted. Mold features: ① In limited mold space, due to forced demolding requirements of thread and oblique long-size skirt anti-theft ring, a grouped insert and double-action synchronous sequential ejection combined structure are designed, and an auxiliary air blowing design is also used to ensure demolding of molded plastic parts; ② A set of ejection and reset error-proof structures are designed to prevent disordered ejection and disordered reset of double actions of synchronous ejection, so as to prevent interference in action of mold parts and ensure stable output; ③ A set of reasonable conformal cooling devices are designed, namely conformal cooling structure of fixed mold hot runner and cavity, conformal cooling structure of push plate (ejection ring) of movable mold and core, movable and fixed molds form an effective cooling system mechanism.

Double-action synchronous ejection combination mechanism is shown in Figure 2. Threaded core 19 has 0.9 turns of double thread, with a tooth depth of 1.1mm>1mm, plus a circle of inner oblique skirt. How can demoulding structure be demoulded smoothly in limited space of threaded core 19 and inner oblique skirt sleeve 20, and molded plastic parts can be effectively produced? The key is to design inlay structure and ejection action of multifunctional component on the molding core, and it is also necessary to meet requirements of the thinnest molding of 0.26mm at connection position without deformation, subsequent cutting and folding of ring. Double-action ejection combination structure device is composed of inner core 18, threaded core 19, skirt sleeve 20, push plate sleeve 21, inner core sleeve 22 inlaid inside and outside in sequence. Inner core 18 is fixed on first push plate 2, threaded core 19 is fixed on second push plate 5, skirt sleeve 20 and inner core sleeve 22 are fixed on mold plate 8, push plate sleeve 21 is fixed on push plate 9, push plate sleeve 21 and skirt sleeve 20 are assembled at a combined angle of 13° at mold line position, which is conducive to ejection of molded plastic parts, skirt sleeve 20 and threaded core 19 are assembled at 55°, which is conducive to forced demolding of inner oblique skirt. First sequence of ejection action is to leave a 6mm half-open demoulding space for inner oblique skirt. First group of push plates 2 synchronously drives second group of push plates 5. One step is to drive reset rod 25 to push push plate 9 and push plate sleeve 21 to push out edge position of plastic part. The other step is to drive threaded core 19 and inner core 18 to synchronously push out inner end face of plastic part. At this time, skirt sleeve 20 fixed on mold plate 8 does not move. Double-step action mold parts are synchronously pushed out 6mm with plastic part to achieve separation from skirt sleeve 20. At this point, first parting surface PL1 is in place. Second sequence of ejection action: After second group of push plates 5 runs 6mm, it stops at stroke position, and first group of push plates 2 continues to push forward. One step is to drive reset rod 25 to push push plate 9 and push plate sleeve 21 to push out edge position of plastic part, and the other step is to drive inner core 18 to synchronously push out inner end face of plastic part. At this time, threaded core 19 fixed on second group of push plates 5 does not move. Mold parts of double-step action are synchronously pushed out 24mm with plastic part to achieve forced thread demoulding with threaded core 19. At the same time, injection molding machine synchronously releases blowing signal, and high-pressure airflow follows surface annular air path of inner core sleeve 22 to assist air pressure to blow down molded plastic part. At this point, second parting surface PL2 runs an effective stroke of 6+24=30mm. Above design functions: ① Power of all actions such as secondary ejection and limiting comes from injection molding machine. With help of ejector rod, all back and forth actions are driven in sequence, with synchronous actions, accurate and time-saving; ② Multi-insert functional combination is opened, and design of air blowing device is simultaneously launched and assisted, while ensuring success rate of forced demolding of thread and extending service life of mold; ③ Forced demolding boundary angle of 55° on one side is designed, and skirt is first realized in a semi-demolding state when mold opening stroke is 6mm, with small clamping force to avoid friction and non-locking. In addition, all parts of this core pulling structure can be processed separately, which is simple to manufacture and easy to assemble.

 

1. Moving mold seat plate 2. Push plate of the first group 3. Push rod fixing plate 4. Pad 5. Push plate of the second group 6. Threaded core fixing plate 7. Mold plate 8. Mold plate 9. Push plate 10. Cavity plate 11. Mold plate 12. Hot runner plate 13. Fixed mold seat plate 14. Valve needle seat 15. Valve needle 16. Cavity plate 17. Cavity plate 18. Inner core 19. Threaded core 20. Skirt sleeve 21. Push plate sleeve 22. Inner core sleeve 23. Push-out connecting sleeve 24. Valve needle hot runner 25. Reset rod 26. Slide seat 27. Oblique pin 28. Spring 29. Push block
Figure 2 Double action synchronous push-out combination mechanism

Error-proofing structure for ejection and reset sequence is shown in Figure 3.

 

1. Mold plate 2. Mold plate 3. Mold plate 4. Mold plate 5. Mold plate 6. Mold plate 7. Skirt sleeve 8. Push plate sleeve 9. Threaded core 10. Slide 11. Oblique pin 12. Spring 13. Push block
Figure 3 Error-proof structure for push-out and reset sequence
Push-out error-proofing structure design: Threaded core 9 and push plate sleeve 8 are the key force-bearing forming parts in mold structure, and are important parts for forced demoulding. Inlay structure design of push-out component is that threaded core 9 and skirt sleeve 7 are designed with an assembly angle of 55°; skirt sleeve 7 and push plate sleeve 8 are designed with an assembly angle of 13°. This design maintains coaxiality while ensuring a reasonable forced demoulding angle, avoiding friction with linear end faces of adjacent molded parts, and increasing sealing force area of parting surface. While improving coaxiality, it eliminates hidden dangers of friction heating and easy burns caused by uneven reset force and push-out deviation in advance.
Combined structure of limiting mechanism is composed of a slide 10, an inclined pin 11, a spring 12, and a push block 13 arranged in sequence. Slide 10 is fixed on mold plate 6, inclined pin 11 and spring 12 are fixed on the second push plate group, and the push block 13 is fixed on the first push plate group. Head of inclined pin is designed to have two force contact surfaces, one of which is a vertical plane, which contacts plane of push block 13, and plays a delay role in action time difference. This delay time allows second push plate group that fixes inclined pin 11 to run a 6mm push-out stroke to achieve first sequence action, and the other side is a 35° inclined surface, which contacts inclined surface of slide 10. According to inclined surface compression principle, straight-line distance of 6mm, mechanical power is greater than spring power, which can make inclined pin 11 compress spring 12 and run vertically inward until it is flush with side of mold plate. After flushing, push block 13 can achieve continuous push-out action, that is, first push plate group fixed by push block 13 can continuously push out a stroke distance of 24mm to achieve second sequence action of mold. When ejection action is finished, as first and second push plate groups retreat, they are reset in retreat order, and push block 13 retreats. Push block 13 leaves pressed inclined pin 11, inclined pin 11 is reset under action of spring 12, and maintains inclined surface contact with retreating slide 10. Design function: ① Ejection component and its embedded structure meet requirements of easy forced demoulding and avoid friction heat burns in anti-error design of ejection and reset activities; ② Structural design of limit mechanism meets requirements of easy forced demoulding and avoids friction heat burns in anti-error design of order of back and forth sequence and moving distance. Travel sequence and ejection distance of first and second push plate groups meet action sequence and distance accuracy of forced demoulding and demoulding of plastic parts.

Cooling and exhaust optimization scheme of mold is shown in Figure 4: ① Fixed mold cavity is designed as a combination of a cavity plate and a gate mold plate, cavity plate 5 and gate template 6 are separately annularly cooled; main core molding parts of movable mold are synchronously designed as an inlaid splicing combination, and inner core sleeve 1, skirt sleeve 2, and push plate sleeve 3 are all designed with imitation cooling water channels; threaded core 4 and inner core 1 are both inlaid, and waterfall-type conformal cooling is designed inside inner core 1; above cooling methods are all designed in group series, so that contact area of cooling water channel is maximized, mold cold and heat balance achieves a reasonable cooling effect, while preventing heat expansion and burn damage caused by mutual friction, improving production efficiency and extending service life of mold; ② Running-in contact section between each main core insert is all designed with a surrounding exhaust groove, especially outer surface of inner core 1 is designed with a conformal blowing channel, which can exhaust and meet function of air blowing molding plastic parts. Design of above exhaust system optimizes exhaust channel, injection feeding and cavity exhaust achieve the best air pressure balance, reducing quality defects of molded plastic parts such as gas marks and burning caused by trapped air.

 

1. Inner core 2. Skirt sleeve 3. Push plate sleeve 4. Threaded core 5. Cavity plate 6. Gate mold plate

Figure 4 Conformal exhaust and cooling integrated device
Optimized design of comprehensive cooling and exhaust system not only improves appearance and dimensional accuracy of molded plastic parts, but also improves production efficiency. Not only molding cycle is shortened by 2~3s and optimized within 16s, but also mold life is extended, plastic part molding efficiency is improved, and production capacity is maximized.

Designed injection mold structure is shown in Figure 2. The overall dimensions of mold are 400mm×550mm×516mm. During first parting, main parting surface is opened, movable and fixed molds are separated, and molded plastic parts leave mold cavity. Then, for second parting, two push plates of mold are pushed out simultaneously by ejector rod of injection molding machine. Limit mechanism is set at a 6mm position. The first push plate continues to push forward, second push plate is in place and does not move. At this time, plastic part is in a semi-demolded state. As it continues to be pushed out, threaded core and other molded parts fixed on first push plate are demolded under action of push plate and inner core being pushed out synchronously and auxiliary air blowing. Mold opening action is completed, limit mechanism and push plate are reset immediately during mold closing process, thereby completing a molding cycle. Specific working process is as follows.
(1) Mold valve needle hot runner 24 receives signal from injection molding machine. Valve needle 15 in valve needle seat 14 is pushed by air pressure to instantly and synchronously close 8 point gates of mold cavity. Mold enters pressure holding and cooling state, waiting for next action signal.
(2) Under action of slider of injection molding machine, movable and fixed molds of mold are opened at the first parting surface PL1 first, and molded plastic part is separated from fixed mold cavity plate. Opening action of first parting surface PL1 is completed, fixed mold does not move at this time. Movable mold starts to move, and ejection connection sleeve 23 fixed on first group of push plates 2 starts to eject. At this time, inclined pin 27 is subjected to force on both sides. One side comes from push block 29 fixed in upper limit mechanism of first group of push plates 2 pushing right angle surface of inclined pin 27 fixed on second group of push plates 5, and the other side comes from inclined surface of slide seat 26 of auxiliary positioning mechanism at same angle pressed on inclined surface of inclined pin 27 fixed on second group of push plates 5. Right angle surface is subjected to greater force than inclined surface. At this time, spring 28 built into inclined pin 27 is compressed by angle pressure and gradually moves inward until end face of inclined pin 27 is flush with side of mold plate. At this time, right angle surface of inclined pin 27 is no longer subjected to thrust of push block 29 fixed in upper limit mechanism of first group of push plates 2, and second group of push plates 5 fixedly connected by inclined pin stops moving.
(3) At the same time, under action of push-out connecting sleeve 23 pushing first push plate 2, reset rod 25 fixed on first push plate 2 synchronously pushes push plate 9 and push plate sleeve 21 fixed on push plate 9 to move with threaded core 19 and inner core sleeve 22 fixed on first push plate 2, pushes molded plastic part out 6mm synchronously, and separates from skirt sleeve 20 fixed on mold plate 8, leaving 6mm of demolding space for molded plastic part. At this time, skirt sleeve 20 fixed on mold plate 8 does not move, and second parting surface PL2 is molded 6mm.
(4) Under action of ejector rod of injection molding machine, push-out connecting sleeve 23 continuously pushes first group of push plates 2, reset rod 25 fixed on first group of push plates 2 synchronously pushes push plate 9 and push plate sleeve 21 fixed on push plate 9, threaded core 19 and inner core sleeve 22 fixed on first group of push plates 2 are synchronously pushed out 24mm. That is, under double forced pushing action of push plate sleeve 21 and inner core sleeve 22, molded plastic part realizes forced thread demoulding with threaded core 19. At the same time, injection molding machine synchronously releases blowing signal, high-pressure airflow follows surface annular air path of inner core sleeve 22, auxiliary air pressure blows off molded plastic part and closes it. At this point, second parting surface PL2 completes an effective stroke of 6+24=30mm.
(5) After all opening and ejecting actions of mold are completed, injection molding machine sends a signal, and mold parts begin to close mold under force of injection molding machine slider. Two sets of push plates of movable mold are reset, and limit mechanism slide 26 retreats 6mm. Under action of spring 28, push block 29 and inclined pin 27 are reset. When all mold parts are reset, mold completes an injection cycle.