1. Safety Design of Slider Spring
After mold opening, slider will move backward a certain distance with mold. To ensure slider can safely return to its original position, a limiting device must be installed to ensure that slider remains stationary after moving required distance. Considering safety factors, springs are usually used in conjunction with inclined guide pillars or bent pins. Springs cannot be used alone as driving element of slider, as they are prone to fatigue and breakage, leading to mold failure and accidents. In particular, built-in springs inside mold are prone to failure at high temperatures, and failure of built-in springs is not easily detected, easily damaging mold or even causing accidents. European customers generally do not like built-in springs.
There are two safety design methods for external springs on slider, as shown in Figure 9-1 and Figure 9-2. For larger sliders, spring force must not be less than 1.5 times weight of slider. Figure 9-1 shows use of a bolt sleeve as a limiting device for external spring, with bolt sleeve 7 fixed to slider by bolt 5. Bolt sleeve is made of 638 mold steel with good toughness and cannot be heat-treated. This design is safe and reliable, avoiding danger of spring breakage and ejection caused by directly fixing spring with plug bolts.

 

Figure 9-1 External Spring and Bolt Sleeve
1 - Cavity; 2 - Slider Insert; 3 - Angled Guide Post; 4 - Slider Seat; 5 - Bolt; 6 - Spring; 7 - Bolt Sleeve; 8 - Slider Baffle
Figure 9-2 shows design of external spring and protective device. Left side adds protective device 10, a typical design for an external spring on moving mold slider. Right side shows external spring protection device 8 on fixed mold slider. This design effectively provides safety protection.

 

Figure 9-2 External Spring and Protective Device
1 - Bent Pin; 2 - Wear-resistant Block; 3 - Slider; 4, 14 - Stop Block; 5, 13 - Bolt; 6, 11 - Spring; 7, 12 - Washer; 8, 10 - External Spring Protective Device; 9 - Limiting Pin; 15 - Slider Seat; 16 - Wedge; 17 - Slider Insert; 18 - Angled Guide Post
For bolt 5 specifications, M8 is selected for small sliders, and M10 or larger for large sliders. In Figure 9-1, single-sided gap between bolt sleeve 7 and slider baffle 8 is 0.5mm. No countersunk hole is made at bolt sleeve installation location; it only needs to be aligned with tail of slider. There is no gap between bolt and bolt sleeve; that is, inner hole of bolt sleeve for an M10 bolt is 10mm. 8.8 grade bolts are used; limit screws (plug screws) cannot be used.
2. Design of Pre-Reset Device
When ejector pins are present at the bottom of slider, ejector plate must return to its pre-ejection state before mold closing. Figure 9-3 shows circular pre-reset device of DME. Figure (a) shows mold closed state, and Figure (b) shows mold open state, at instant pre-reset rod just contacts elastic sleeve. If ejection distance is L, distance from head of inclined guide post to point of action of slider's inner hole should be L + 5. Length of pre-reset rod must ensure that ejector plate is pushed back before inclined guide post enters slider. This pre-reset device, designed inside mold, has reliable reset action, good durability, and is suitable for long-life mold designs. Care should be taken to arrange it inside mold during design to prevent it from obstructing robot's movement.

 

Figure 9-3 DME’s circular first reset device
1 - pressure plate; 2 - first reset rod; 3 - elastic sleeve; 4 - ejector plate; 5 - ejector pin; 6 - core; 7 - inclined guide post; 8 - wear-resistant block at the bottom of the slider; 9 - slide block; 10 - wear-resistant block; 11 - inclined wedge
3. Design of Slider Safety Pin
Designing a slider safety pin is a unique design concept in European molds. Due to need for product ejection, if ejector pins are arranged under slider, if ejector plate does not return to its pre-ejection state before mold closing, mold slider may collide with ejector pins or other ejection elements, as shown in Figure 9-4(a). Slider safety pin is designed to solve this problem. It's typically located at the bottom of slider and mounted on ejector plate, similar to ejector pin. Its function is to prevent ejector plate from accurately resetting if ejector plate doesn't return to its proper position. If ejector plate doesn't return to its proper position, safety pin will protrude above slider's pressure plate. During mold closing, safety pin will obstruct slider's forward movement, thus protecting slider and its bottom ejector pin from collision (diameter of safety pin must not be less than 5mm). There are two design options for slider safety pin. For smaller sliders, safety pin is designed at the front end of slider's positioning step to block slider's forward movement, as shown in Figure 9-4(b). For larger sliders, a hole is drilled in slider, and during ejection, safety pin passes through this hole, obstructing slider's forward movement, as shown in Figure 9-4(c).

 

Figure 9-4 Two forms of slider safety pin design
Slider safety pin design example shown in Figure 9-5. Left side shows mold closed state, and right side shows hole where safety pin enters slider after mold opening. After designing slider safety pin, a reset rod is still needed to reset ejector plate. Most European molds use a strong pull and strong push structure to force ejector plate to reset. In addition, a return confirmation electronic limit switch must be designed on ejector plate to ensure accurate mold reset.

 

Figure 9-5 Slider Safety Pin Design
1 - Cavity; 2 - A Plate; 3 & 9 - Push Rod; 4 - Angled Guide Pillar; 5 & 8 - Slider Safety Pin; 6 - Slider; 7 - Core; 10 - Push Rod Fixing Plate; 11 - Push Plate; 12 - Ejector Roller; 13 - Moving Mold Base Plate
4. Ejector Reset Confirmation
Reset confirmation of ejector device is generally achieved by installing an electronic limit switch. Electronic limit switches have various structures; European molds often use HASCO proximity switches. This non-contact electronic switch has a simple structure, no wear, and a long lifespan, and is widely used in Europe.

When a plastic part requires a slider core-pulling mechanism, if an angled guide pillar core-pulling mechanism can be designed, it must be designed as such. Slider mechanism with angled guide pillar core-pulling should be used as a priority whenever possible. This principle applies to export molds exported to Europe, North America, and Japan, and is also suitable for domestic precision, high-efficiency, and long-life plastic injection molds.

Considering factors such as slider processing technology, maintenance after wear, ease of setting up water-cooling rings, and fixing small slider inserts, an inlay structure is used for side core and slider seat, offering many advantages. For smaller plastic parts with multiple cavities, multiple slider cores can be embedded in same slider seat, facilitating processing, adjustment, replacement, and maintenance. Figure 9-6 shows a four-part mold, where four independent sliders are assembled on same slider seat. Mounting bosses on sliders are perpendicular on three sides, with a 3° bevel on the top surface to tightly fit groove of slider seat. Bolt holes (not shown in figure) are drilled on beveled surface of slider seat to lock slider inserts in place.

 

Figure 9-6 Slider insert and slider seat
1 - Slider seat; 2 - Slider insert
Figure 9-7 shows design of moving mold for a printer cover. Printer cover has three small snap-fit positions on each of its two long sides, requiring slider design, and one small snap-fit position on each of its two short sides. To facilitate processing, moving mold is designed with a fully inlaid structure, with small sliders passing through inserts on four edges. This fully inlaid structure allows slider parts of mold to be directly CNC machined, avoiding EDM processing.

 

Figure 9-7 Design drawing of moving mold for printer cover plate
Figure 9-8 shows inlaid structure of slider for a fax machine front cover. Product structure is complex, and multiple heat dissipation holes on the side of plastic part require slider molding. Slider is divided into two parts: slider base 7 and slider insert 6, which facilitates machining and avoids EDM processing.

 

Figure 9-8 Assembly of fax machine front cover slider
1-A plate; 2-Cavity; 3-Core; 4-Push rod; 5-B plate; 6-Slider insert; 7-Slider seat; 8-Wear-resistant plate; 9-Angled guide post; 10-Limit pin; 11-Spring baffle; 12-Spring; 13-Screw

Generally, sliders with a width of 60mm or more must have cooling water channels machined. Ensure water inlet at the rear of slider is properly positioned. Cooling water channels should be as close as possible to molding surface to facilitate rapid cooling of plastic part. Cooling water channels should avoid oblique guide post holes, spring holes, and threaded holes as much as possible. If slider molding surface is a complex curved surface, depth of each cooling hole and entire water channel route should be fully represented by a 3D drawing, then machining data and water hole codes should be marked on a 2D drawing to avoid errors during machining. If there are related molding inserts at slider head, water channels should avoid insert holes.

There should be a reasonable gap between slider and pressure bar, especially when molding plastic materials at high temperatures. Thermal expansion caused by high temperatures can cause slider mechanism to jam or malfunction, and in severe cases, lead to bending or breakage of oblique guide post. Large sliders are more prone to jamming during high-temperature forming. Solution is to design a guide strip at the center of slider's bottom increase gap between slider and pressure strips on both sides. Value of gap needs to be calculated based on linear expansion coefficient of steel.