Structure of rice cooker barrel is relatively complex. There is a round hole on the top for placing inner pot of rice cooker. There are buckles of various structures on its outer surface. There is a buckle 1 for installing control panel on the front, and a buckle 2 for installing button above buckle 1. There are buckles 3 and 4 on the left and right sides of plastic part for installing handle, as shown in Figure 1 (a) and (b). There are buckles 5 and 6 on the left and right sides of upper back of plastic part for installing rotating shaft of rice cooker cover. There is a flat plastic cup buckle 7 on the back of plastic part for installing water vapor, as shown in Figure 1 (b). Outer dimensions of rice cooker barrel are 349 mm×265 mm×162 mm, and inner hole diameter is φ207 mm, as shown in Figure 1 (c).

 

Figure 1 Rice cooker barrel

According to structure of plastic part, mold adopts a two-plate mold structure, and pouring system uses 4 latent gates for pouring. Since diameter of circular hole on plastic part is large, area of special-shaped hole where control panel is installed is also large, these two areas need to be set with parting surfaces. Plastic part has 3 parting surfaces, as shown in Figure 2. Among them, main parting surface is a plane, located at maximum contour of plastic part mouth step; parting surface of circular hole on plastic part is a plane, located at minimum contour of circular hole; parting surface of special-shaped hole of control panel is located on inner surface, so that flash generated there is not obvious.

 

Figure 2 Parting surface design

Since contour mark of slider is not allowed on plastic part, 7 buckle positions above rice cooker barrel must be demolded using a fixed mold slider mechanism. Except for slider structures of two symmetrical buckle positions of buckle position 3 and buckle position 4, buckle position 5 and buckle position 6, other buckle positions all use different side core pulling structures, as shown in Figure 3.

 

Figure 3 Fixed mold side core pulling structure

Since buckle position 1 is located on the front of plastic part, no slider mark is allowed. Fixed mold slider structure is used for demoulding, which is composed of a slider and a T-shaped wedge, as shown in Figure 4. In order to increase strength of slider, slider and slider seat are combined into a whole. T-shaped wedge is connected to slider through a T-shaped slot. When mold is opened, T-shaped wedge drives slider to demould, and when mold is closed, T-shaped wedge drives slider to reset.

 

Figure 4 Slider ① structure

Buck position 2 is used to install button that locks upper cover. There are multiple ribs at the bottom, there is a cylindrical hole on each of left and right sides, as shown in Figure 5 (a). Double-sided T-shaped wedges are used here to drive two inner core pulling structures to demould. Each inner core pulling structure is provided with two pressure blocks to form a T-shaped slide, as shown in Figure 5 (b). Ribs at the bottom of buckle position 2 are formed by end faces of double-sided T-shaped wedge, cylindrical holes on the left and right sides are formed by two inner core pulling cores. Double-sided T-shaped inclined wedge is connected to inner core through an inclined T-shaped groove. When mold is opened, double-sided T-shaped inclined wedge rises and drives the two inner core pulling structures to move closer to the center, so that cylindrical holes on both sides are demolded. When mold is closed, double-sided T-shaped inclined wedge is pressed down and drives two inner core pulling structures to reset to both sides.

 

Figure 5 Slider ② structure

There is a cylindrical hole on the left and right sides of rice cooker barrel for installing rice cooker handle. Location of cylindrical hole belongs to appearance surface, and no slider mark is allowed. Fixed mold slider structure is used for demolding, which consists of a pressure strip, a slider, a slider seat, a spring and an inclined wedge. Slider is connected to slider seat through a dovetail groove, and inclined wedge is connected to slider seat through a T-shaped groove, as shown in Figure 6. In order to simplify mold structure and increase strength of cylindrical hole core, cylindrical hole core and dovetail tenon are combined into a whole. When mold is opened, T-shaped wedge rises, driving slider seat and slider to demold in horizontal direction. When mold is closed, T-shaped wedge drives slider seat and slider to reset. Function of spring is to keep slider moving smoothly when mold is opened.

 

Figure 6 Structure of sliders ③ and ④

There is a buckle position for installing rotating shaft of upper cover of rice cooker on the left and right sides of back of rice cooker barrel, as shown in Figure 7 (a). Buckle position adopts a fixed mold slider structure for demolding, which is composed of a T-shaped wedge, a slider seat, a core-pulling slider, a pressure strip, a spring, etc., as shown in Figure 7 (b). When mold is opened, T-shaped wedge rises, driving slider seat and core-pulling slider to demold in horizontal direction. When mold is closed, T-shaped wedge drives slider seat and core-pulling slider to reset. Function of spring is to keep slider seat moving smoothly when mold is opened.

 

Figure 7 Slide block ⑤ and slider block ⑥ structure

Rib position shown in Figure 7 (a) is far away from parting surface and located above plastic part, so it is suitable for demolding with a fixed mold slider structure, which consists of a T-shaped wedge and a slider. In order to facilitate processing and increase strength of slider, slider and slider seat are connected as a whole, as shown in Figure 8. Due to large size of rib position, in order to prevent insufficient filling, insert molding is adopted, and insert on slider is fixed to slider by a cylindrical pin.

 

Figure 8 Slide block ⑦ structure

There are 4 buckle positions on inner surface of lower port of plastic part, as shown in Figure 9 (a), and it cannot be demolded normally. Since top of plastic part is uneven, if oblique push structure is used for demolding, oblique push rod will interfere with molded plastic part. In addition, it is suitable to use inner slider mechanism for demolding, which consists of an oblique wedge, an inner slider and a spring, as shown in Figure 9 (b). Since buckle is on inner surface of plastic part, inner slider is a single-sided T-shaped structure. After penetrating inner surface from bottom of plastic part to be molded, buckle is formed with raised part of slider. Positions of four inner sliders in mold are shown in Figure 9 (c). When mold is opened, inclined wedge rises, and spring drives inner slider to move toward center to demold buckle; when mold is closed, inclined wedge presses down, driving inner slider to expand around mold to reset inner slider.

 

Figure 9 Inner slider mechanism and position in mold

There are 4 buckles and another 2 buckles on the edge of inner hole on upper part of plastic part. Oblique push structure is used for demolding. Due to large size of buckle, an oblique push block structure is used. Oblique push rod and oblique push seat are connected by a cylindrical pin, as shown in Figure 10. Inclined push seat is fixed between push plate and push rod fixed plate. When inclined push rod makes a push-out movement, inclined push seat is driven to move horizontally between push plate and push rod fixed plate. At the same time, inclined push rod and inclined push seat will rotate around cylindrical pin to correct processing error.

 

Figure 10 Oblique push demoulding mechanism

According to structure of plastic part, a common runner casting system is used to extend vertical flow channel below parting surface. Extended part is regarded as a cold material well. Four circular (φ12 mm) diverter channels are set on parting surface of circular hole at upper end of plastic part. Diverter channels are located directly below vertical flow channel, and then four latent gates are used for feeding, as shown in Figure 11 (a). Diameter of latent gate is φ2 mm, and it is evenly set on inner wall of upper circular hole of plastic part to be molded, as shown in Figure 11 (b).

 

Figure 11 Casting system

In order to cool and shape plastic parts as quickly as possible, cooling system should be designed according to shape of plastic parts and mold structure. In mold fixed mold insert, a water well-type water channel (φ25 mm) is used in front of plastic part, and a water trough is opened on the back of mold to connect water wells in series, which is conducive to avoiding slider in front of plastic part①. There is a fixed mold slider⑦ behind plastic part, which is not suitable for opening a water channel. Three independent straight water channels (φ8 mm) are used on the left and right sides of plastic part, and a circular straight water channel (φ8 mm) is designed at the mouth of plastic part. Fixed mold cooling water channel is shown in Figure 12 (a). 12 spacer-type water well water channels (φ25 mm) are set along contour of plastic part on movable mold insert. Since 12 water wells are arranged in a circular pattern, it is not appropriate to connect water wells with a straight water channel. A water trough is opened on the back of movable mold insert to connect water wells in series. In order to maintain uniform water temperature, dynamic mold water circuit is composed of 5 groups of independent water circuits, which can shorten length of cooling water circuit and help prevent cooling water from bringing heat from one area to another during circulation process, resulting in uneven mold temperature. Movable mold cooling water circuit is shown in Figure 12 (b).

 

Figure 12 Cooling system

According to structure of plastic part, mold adopts a two-plate mold structure with two mold openings. In order to enable fixed mold slider to move, the first mold opening is set between fixed mold plate and fixed mold base plate. In order to enable fixed mold plate to move smoothly, a fixed mold guide column and guide sleeve are installed between fixed mold plate and fixed mold base plate, and an auxiliary mold opening mechanism is installed on the side of mold frame, so that fixed mold plate and fixed mold base plate can be separated during mold opening process, and fixed mold slider is driven to perform demolding movement. Mold structure is shown in Figure 13.

 

Figure 13 Mold structure
1. Moving mold base plate 2. Push plate 3. Push rod fixing plate 4. Limiting column 5. Reset rod 6. Moving mold plate 7. Guide block 8. Pull rod 9. Moving mold large insert 10. Fixed mold plate 11. Oblique push rod 12. Fixed mold slide 13. Oblique push block 14. T-shaped oblique wedge 15. Fixed mold base plate 16. Fixed mold insert 17. Moving mold small insert 18. Positioning ring 19. Gate sleeve 20. Fixed mold guide column and guide sleeve 21. Auxiliary mold opening mechanism 22. Push rod 23. Guide column 24. Oblique push seat 25. Pad
Mold working process: After injection, slider of injection molding machine drives movable mold to retreat, and mold is first separated at PL1. Since T-shaped inclined wedge 14 is fixed on fixed mold base plate 15, and slide groove of fixed mold slider 12 is set on fixed mold plate 10, when fixed mold plate 10 is separated from fixed mold base plate 15, T-shaped inclined wedge 14 will drive fixed mold slider 12 to demold. When separation distance between fixed mold plate 10 and fixed mold base plate 15 reaches 100 mm, hook of auxiliary mold opening mechanism 21 hooks fixed mold plate 10, and fixed mold plate 10 is no longer separated from fixed mold base plate 15, completing the first mold opening. Then mold will separate movable mold plate 6 from fixed mold plate 10, and complete second mold opening at PL2. When mold is completely separated, slider of injection molding machine drives ejection mechanism of mold (including push plate 2, push rod fixing plate 3, inclined push rod 11, inclined push block 13, pull rod 8, push rod 22, etc.) to perform demolding movement. After plastic parts are taken out, slider of injection molding machine will drive movable mold of mold to reset. Reset process of mold is opposite of mold opening process. When mold is completely reset, next injection can begin.