Structure of plastic part is shown in Figure 1. Length is 374mm, outer diameter of small end is φ51mm, wall thickness is 2mm, aspect ratio is 7.3:1, shape is slender, and bilateral slope along axis is 0.25°. Inner diameter of small end of plastic part is φ36mm, and there are 6 protrusions on the inner surface of small end. Three long grooves with a width of 7mm are evenly distributed on the outer surface of plastic part. There is a groove-shaped hole inside one of long grooves, and there are two depressions on both sides of long groove. There are two square holes near small end of plastic part, with a size of 28mm*20mm. Angle between cross-section center lines of two square holes is 120°. Buckle positions ① and ② are located at both ends of square hole. There are several ribs on outer cylindrical surface of large end of plastic part. There are two difficulties in mold design: first, square hole, buckle position ①, and buckle position ② are close to each other, so an independent demoulding mechanism cannot be designed, and a linkage demoulding mechanism must be designed; second, ejection distance of long core-pulling mechanism is relatively long. Considering molding accuracy, long core cannot be extracted from plastic part at one time, and a non-standard ejection mechanism needs to be designed.

 

Place plastic part to be formed laterally on parting surface of mold, with slotted hole, long slot where slotted hole is located, depressions on both sides of long slot are placed downward and are formed by movable mold insert; the other two long grooves of plastic part are located diagonally above left and right sides. Mechanism of hydraulic cylinder + slider is used to pull core and eject mold obliquely above; for buckle position ①, a structure in which slider and movable mold insert collide is used for forming; square hole and the buckle position ② connected to square hole are formed by using a linkage slider mechanism to pull core diagonally downward to demould; core pulling on inner surface is divided into two sections: small end core pulling and large end core pulling. Facing surface of two core pulling sections is located at arc edge of inner surface of small end. Both sections of core are driven by hydraulic cylinders, and mold core pulling structure is shown in Figure 2.

 

Buckle position ① is located on left side of square hole. Since the two sides of buckle position ① are inclined planes, a structure in which slider and movable mold insert collide is used for demoulding. Butting surface is located in the middle of buckle position ①, and buckle position ① is separated from middle. Upper part of butting surface is slider, and the lower part is movable mold insert. Buckle position ② is located on the right side of square hole. Since square hole and buckle position ② are close to each other, a linkage mechanism is used to demould, as shown in Figure 3.

 

Small-end core-pulling mechanism of plastic parts mainly includes a hydraulic cylinder, a hydraulic cylinder bracket, a limit switch, a core-pulling seat, a core fixing plate, a core, etc., as shown in Figure 4. In order to ensure reset accuracy with long core, a circular table for positioning is set on the end face of small core.

 

Large-end core-pulling mechanism of plastic parts includes long core, core fixing plate, core-pulling seat, core-pulling hydraulic cylinder, jacking hydraulic cylinder, chute plate, guide post, guide bush, etc., as shown in Figure 5. Since plastic part is long, if long core is completely pulled out of plastic part during demoulding, distance between piston rod of hydraulic cylinder and chute will be longer, which will affect molding accuracy of plastic part. Set demoulding distance of long core to 2/3 of length of plastic part, then use hydraulic cylinder piston rod to lift the entire core-pulling mechanism and plastic part, and finally take out plastic part along axial direction. In order to keep core-pulling mechanism balanced when moving up and down, four pairs of guide posts and guide bushes are installed on chute and movable mold plate.

The two long grooves distributed on both sides of plastic part cannot be demoulded directly, and oblique core pulling method needs to be used to move diagonally upward to demould. Oblique core pulling structure includes a hydraulic cylinder, slider seat, slider, limit switch, etc., as shown in Figure 6.

 

Buckle position ② is close to square hole. Due to limited mold space, it is impossible to set up two independent demoulding mechanisms. Instead, slider of buckle position ② is placed in square hole slider, and square hole slider drives slider of buckle position ② to move, forming a linkage demoulding mechanism, including a hydraulic cylinder, a bracket, a square hole slider seat, and a square hole slider, a buckle position ② slider seat, a buckle position ② slider and a compression wedge, etc., as shown in Figure 7 ( a), and its cross-sectional structure is shown in Figure 7(b).

 

1. Hydraulic cylinder 2. Chute plate 3. Square hole slider seat 4. Buckle position 2) Slider seat 5. Cylindrical pin 6. Square hole core-pulling slider 7. Buckle position ② Core
Figure 7 Linkage demoulding mechanism of square hole and buckle position ②
Pressing wedge of slider mechanism is generally located above demoulding mechanism. However, in order to avoid long slot demoulding mechanism above it, pressing wedge of this mechanism is set below square hole slider seat and fixed on movable mold base plate. In order to remove pressing wedge before demoulding, mold is designed to be opened twice, the first mold opening is located between movable mold base plate and movable mold plate. Demoulding mechanism of buckle position ② is composed of buckle position ② slider, cylindrical pin, buckle position ② slider seat, etc. The two ends of cylindrical pin are placed on steps of slider seat of buckle position ②, as shown in Figure 7 (c). Since buckle position ② slider seat is fixed on movable mold plate, when hydraulic cylinder piston rod drives square hole slider to demould, buckle position ② slider seat remains stationary, 75° slope in square hole slider will drive buckle position ② slider to move sideways along step of buckle position ② slider seat, so that buckle position ② is ejected from mold.

Mold adopts a pouring system that converts hot runner to ordinary runner, and material is injected from small end of plastic part, as shown in Figure 8(a). Since hot runner is located at meeting surface of two long groove slide blocks, main flow channel of ordinary runner is set on meeting surface of two long groove slide blocks, then open a ring of annular shunt channels around small-end core-pull on parting surface of small-end core-pull, and set up three feed ports, as shown in Figure 8(b). Cross-section of gate is small, while cross-sectional area of longitudinal runner is large, which can be regarded as a cold material cavity, effectively prevent undesirable phenomena such as flow marks on the surface of plastic part.

 

Cooling system plays an important role in maintaining mold temperature balance. Main parts of mold are relatively flat and are suitable for use of straight-through conforming water channels. Long core and short core are cooled by spacers + well-type water channels, and a straight-through water channel is set up on core-pulling seat, as shown in Figure 9 (a) and (b). Long groove slider uses two straight-through waterways, as shown in Figure 9(c). Cooling water channel of movable mold insert needs to avoid two core-pulling mechanisms that move diagonally downwards. Therefore, layout of cooling water channels at both ends of movable mold insert is inconsistent. One end adopts a horizontally arranged straight-through water channel, and the other end adopts a longitudinally arranged straight-through waterway, as shown in Figure 9(d).

 

Cooling water channels of movable mold insert all adopt one-way straight-through water channels, which can effectively prevent heat from being brought in from other locations and causing uneven mold temperature.

Mold structure is shown in Figure 10. A special-shaped mold base is used, push plate, push rod fixed plate and two backing plates are eliminated, and movable mold plate is directly connected to movable mold base plate. Mold movement process: After injection is completed, under action of auxiliary mold opening mechanism 36, mold is first separated from movable mold base plate 1 and movable mold plate 18. At this time, wedge 21 leaves slider seat 22, and the first mold opening is performed. Mold continues to be opened, movable mold plate 18 and fixed mold plate 25 are separated, forming second mold opening. After movable mold and fixed mold are completely separated, hydraulic cylinder piston rod drives each core-pulling mechanism to perform ejection movement. Long core-pulling ejection distance is 250mm, which is about 2/3 of length of plastic part. Plastic part is placed on long core 12, then lift up piston rod of hydraulic cylinder 32 to lift up all long core-pulling demoulding mechanism (including long core 12, long core-pulling seat 13, slide groove 16, hydraulic cylinder 17 and other parts), and manipulator takes out plastic part along axial direction of long core. Finally, injection molding machine starts to push mold to close, and mold closing process is opposite to mold opening movement. After mold is closed, next production cycle begins.

 

1. Moving mold base plate 2. Pad 3. Bracket 4. Hydraulic cylinder 5. Inclined wedge 6. Core-pulling seat 7. Core 8. Hot runner tube 9. Fixed mold base plate 10. Hot runner electrical components 11. Positioning ring 12. Long core 13. Long core seat 14, inclined wedge 15. Slide guide post 16. Slide groove 17. Hydraulic cylinder 18. Moving mold plate 19. Hydraulic cylinder 20. Bracket 21. Incline 22. Slider seat 23. Small core 24. Large core 25. Fixed mold plate 26. Hot runner plate 27. Slider 28. Slider seat 29. Hydraulic cylinder 30. Bracket 31. Moving mold insert 32. Jacking hydraulic cylinder 33. Heat insulation board 34. Fixed mold guide post and guide bush 35. Moving mold guide post and guide bush 36. Auxiliary mold opening mechanism
Figure 10 Mold structure
For read some mold structure that Gud Mould has finished for long round tube, please refer to Mould for Plastic Wall Plug.