Silicone products are becoming more and more common and important in daily life. How are silicone products produced? Designing a complete set of molds is an important part of it.
A complete set of molds covers multiple related systems, which complement each other. Only when the various systems achieve the best combination can the normal use and precision of the mold be guaranteed. Because the structure of the mold must meet the requirements of the product, different products have different requirements, and the product has variability and diversity, which determines the diversity of the mold.
Generally speaking, a typical plastic mold includes: gating system, ejection system, cooling system, exhaust system, core pulling system, etc.
Related elements of mold design
1. Parting surfaceIn order to take the product out of the mold, the mold must be divided into two parts, the male and female sides, and this interface is called the parting surface. It has the function of parting and exhausting, but due to the difference in mold precision and molding, it is easy to produce burrs and knots, which hinder the appearance and precision of the product. When choosing the parting surface, pay attention to:
- It cannot be located in an obvious position to affect the appearance of the product.
- When opening the mold, the product should be left on the side with the demoulding mechanism.
- Located in the place where mold processing and product post-processing are easy.
- For products with high coaxiality requirements, design the cavity on the same side as much as possible.
- Avoid long core-pulling, consider placing it in the mold opening direction of the male mold, if necessary, set the core-pulling mechanism as far as possible on the male mold side.
- Generally do not use arc part parting, which will affect the appearance of the product.
- For plastics with good fluidity and easy to overflow edges, the type of breaking should be used to prevent the generation of burrs.
- For products with high height and small demoulding slope, it is advisable to split the mold in the middle and divide the cavity into two sides to facilitate demoulding.
2. Draft angle
In order to make the product easy to come out of the mold, the mold must be provided with a draft slope. Its size varies depending on product shape, plastic, mold structure, surface accuracy and processing methods. Generally, it is 1-3°. The larger the demoulding slope, the better without affecting the appearance and performance of the product.
3. Thick flesh
The thickness of the product will directly affect the molding cycle and production efficiency, and will cause shrinkage and stress due to uneven thickness. When designing the mold, you should pay attention to the following:
- Whether the mechanical strength of the product is sufficient.
- Can the impact force and demoulding force be evenly dispersed without cracking.
- When there are embedded parts, it must be prevented from breaking, and whether the strength will be affected by the joint line due to the thin flesh.
- The thickness of the meat should be as consistent as possible to prevent shrinkage and subsidence.
- Whether the meat is too thin will cause insufficient filling or hinder the material flow.
4. Convex column
Generally, it is a protruding cylinder on the product, which can enhance the peripheral strength of the hole, and is used for assembling holes and local heightening. It is necessary to prevent shrinkage due to increase in meat thickness and insufficient filling or scorching due to air accumulation. Points to be noted during design:
- Its height should not exceed twice its own diameter, otherwise reinforcing ribs must be added
- Its position should not be too close to the corner or side wall to facilitate processing
- The round shape is preferred to facilitate processing and material flow. For example, the bottom can be 0.3-0.5mm higher than the bottom surface.
There are holes on most products, and there are three main methods to obtain them:
- Forming directly on the product.
- The reserved holes are formed on the product first, and then the machining is completed.
- After the type is completely drilled by machining.
The following points should be paid attention to when designing:
- The distance between holes must be more than 2 times the hole diameter
- The distance between the hole and the edge of the product should be more than 3 times the hole diameter
- The thickness of the flesh should be increased around the hole
- The distance between the hole and the side wall of the product should be more than 0.75 times the hole diameter
- When the diameter of the hole is less than 1.5mm, it is easy to produce bending deformation. It should be noted that the depth of the hole should not exceed 2 times the diameter of the hole
- For the through hole in the middle of the parting surface, in order to prevent eccentricity, the hole diameter on the unimportant side can be enlarged.
For assembly purposes, there are sometimes thread designs on the product, which can be formed directly or machined after forming. For threads that are often disassembled or subjected to high stress, metal thread inserts are used, and the following principles should be paid attention to when designing:
- Avoid the use of threads with a pitch less than 0.75mm, and threads with a maximum pitch of 5mm can be used
- Due to plastic shrinkage, avoid direct molding of long threads to prevent pitch distortion
- When the thread tolerance is less than the plastic shrinkage, avoid using
- If the internal and external threads are matched, a gap of 0.1-0.4mm must be left
- The threaded part should have a 1-3° demoulding slope
- The screw teeth cannot be extended to the end of the product, and a 0.8mm or so polished rod position must be provided to facilitate mold processing and thread life
- On some similar bottle cap products, there will be some vertical knuckles, and the spacing should be large, the minimum is 1.5mm, generally 3.0mm, and a flat part of at least 0.8mm should be set on the parting surface.
In order to prevent the product from cracking, increase the mechanical strength, or serve as a medium for conducting current and decoration, inserts are often embedded when the product is formed. Points to note:
- To ensure the reliability of the insert, the adhesive layer around the insert should not be too thin
- The fit between the insert and the insert hole must be tight enough to not affect the pick-and-place
- In order to make the insert and the plastic tightly combined, the embedded part is often designed in a rough or concave-convex shape (Embossing, drilling, punching, grooving, undercut, etc.)
8. Other points
- The ribs should not be too thick, generally no more than half the thickness of the meat to prevent shrinkage
- As long as the appearance and function are not affected, the smooth surface should be changed to the textured surface as much as possible, which can reduce the difficulty of mold processing, increase the aesthetic feeling, and prevent shrinkage
- Around the convex column, part of the flesh thickness can be removed to prevent shrinkage and subsidence
- For holes with thinner flesh, the edge and height of the hole should be increased for reinforcement
- The core tip is affected by the contraction force, and it is easy to cause rupture when the product is ejected. A convex edge can be set to withstand the ejection force
- Setting R at the corner can improve the strength, prevent stress concentration and facilitate material flow
- Avoid sharp angles, the thin part is easy to cause insufficient material filling
- Products with ripples on the outside can be changed to strengthen the edge for the convenience of post-processing
- When the parting surface has a stage shape, the mold processing is not easy, so consider changing to a slash or curved parting
- The through core pull is prone to failure, it is better to change the core pull on both sides
- Because the round shape is easier to process than other shapes, it can reduce costs and is preferred
- When adding etched characters or patterns on the product, if there is no special requirement, try to design concave characters to facilitate mold processing.
Gating system design
The gating system is an important link in the mold design, and it is often divided into ordinary and non-runner gating systems. It is closely related to the shape, size, machine and parting surface of the plastic product used.
Pay attention to the following principles when designing:
- The runner should be as straight as possible, as short as possible, to reduce bending, and the finish should be between Ra=0.8-1.6um
- Consider the number of mold cavities, design according to the layout of the mold cavity, try to be symmetrical with the center line of the mold
- When the projected area of the product is large, avoid opening gates on one side to prevent uneven injection force
- The position of the gate should be easy to remove, leaving no obvious traces on the product, and not affecting the appearance of the product
- When designing the sprue, avoid direct impact of plastic on small cores or small inserts to avoid bending or breaking.
- Machining or correction margins are reserved for the main channel in order to ensure product accuracy.
Ejection system design
After the product completes a forming cycle and the mold is opened, the product will be wrapped on one side of the mold and must be removed from the mold. This work must be done by the ejection system. It is an important part of the whole mold structure, and generally consists of three parts: ejection, reset and ejection guide.
1. According to power
- Manual ejection: After the mold is opened, the ejection system is manually operated to eject the product. It simplifies the structure of the mold, the demoulding is smooth, and the product is not easily deformed. However, the labor intensity of workers is high, the productivity is low, and the scope of application is not wide. It is generally used when screwing out the threaded core manually.
- Motorized ejection: The ejection mechanism is driven to eject the product by the power of the injection machine or an additional motor. It can push the ejector plate through the ejector rod on the machine table to achieve the purpose of ejection. It is also possible to install fixed-distance tie rods or chains on the male and female templates, and rely on the mold opening force to drag the ejector mechanism to eject the product. When adjusting the mold, care must be taken to control the mold opening stroke. It is suitable for molds where the ejector system is on the female mold side.
- Hydraulic ejection: A special oil cylinder is installed on the mold, and the action of the oil cylinder is controlled by the injection machine. The speed and time of the ejection force can be adjusted by the hydraulic system, and the ejection system can return to its position before the mold is closed.
- Pneumatic ejection: Use compressed air to set air passages and small ejection holes on the mold to directly blow out the product. No ejection marks are left on the product, suitable for thin or long cylindrical products.
2. According to the mold structure
It can be divided into primary ejection mechanism, secondary ejection mechanism, master mold ejection mechanism, pouring system ejection mechanism, thread ejection mechanism, etc.
- When choosing the parting surface, try to keep the product on the side with the demoulding mechanism
- Ejection force and position are balanced to ensure that the product is not deformed or broken
- The thimble must be set at a place that does not affect the appearance and function of the product
- Try to use standard parts, safe, reliable and conducive to manufacture and replacement. The ejection system has various forms, which are related to the shape, structure and plastic properties of the product. Generally, there are ejector rods, ejector tubes, push plates, ejector blocks, air pressure, and composite ejectors.
It is the simplest and most common form in the ejection mechanism, and its cross-sectional area mainly includes the following forms: Round shape: because the round shape is easy to manufacture, process and repair, and the ejection effect is good, it is the most widely used in production. However, the circular ejection area is relatively small, which is prone to stress concentration, top-through products, and top deformation. Try to avoid using it in tubular and box-shaped products with small demoulding slope and high resistance. When the ejector rod is slender, it is generally set as a stepped ejector pin to strengthen the rigidity and avoid bending and breaking.
- The ejection position should be set at a place with high resistance, not too close to inserts or cores, for box-shaped and other deep cavity molds. The side resistance is the largest, and the top and side ejection methods should be adopted at the same time to prevent the product from being deformed and broken.
- When the product resistance is balanced, the ejector pin should be set symmetrically to balance the force.
- When there are thin and deep ribs, the ejector rod is generally installed at the bottom.
- If there is an insert on the mold, the effect of setting the thimble on it is better.
- Avoid setting thimbles at the glue inlet of the product to avoid rupture.
- When the surface of the product is not allowed to have ejection marks, the ejection ears can be set and then cut off.
- For thin meat products, set the thimble on the runner, and the product can be taken out.
- The thimble fits with the thimble hole, generally a clearance fit. If it is too loose, it will easily produce burrs, and if it is too tight, it will easily cause jamming. In order to facilitate processing and assembly and reduce the friction surface, generally 10-15mm of matching length is reserved on the mold core, and the rest of the holes are reamed by 0.5-1.0mm to form escape holes.
- In order to prevent the thimble from rotating during production, it must be fixed on the thimble plate. There are various forms, which must be determined according to the size, shape, and position of the thimble, which will not be listed here.
- After the ejection system supports the mold, it must be returned to the original position in the next cycle of production. The main forms include forced return, pull rod return, spring return, oil cylinder, etc.
4. Pipe jacking
Also called cylinder or sleeve thimble, it is suitable for the ejection of products with a ring shape or a center hole. Because it is in full-circumference contact, the force is uniform, the product will not be deformed, and it is not easy to leave obvious ejection marks, which can improve the concentricity of the product. However, avoid using products with thinner flesh around them to avoid processing difficulties and weakened strength, resulting in damage.
5. Push plate
This form is suitable for various containers, box-shaped, cylindrical and thin products with a central hole. It ejects smoothly and evenly, with high ejection force and no ejection marks. Generally, there is a fixed connection to prevent the push plate from being pushed down during production or when pushing the mold. However, as long as the guide column is long enough and the stroke of the supporting mold is strictly controlled, the push plate may not be fixed.
The cooperation between the push plate and the core must be smooth to prevent friction or jamming, and it is also necessary to prevent the plastic from seeping into the gap. When the product is a blind hole, it will cause difficulty in demoulding and product deformation due to vacuum adsorption. A fungus valve is set on the top, and the fungus valve opens when ejecting, and air enters to make demoulding smooth. It can be returned by a spring, and it can also be connected with the ejector device and act as a ejector rod.
6. Eject block
Some products with flanges or larger sizes are often designed to be ejected in the form of ejector blocks in order to facilitate processing and demoulding. Most of its plane is the parting surface, and there are two or several larger-diameter ejector rods connected below, and the ejection area is large and stable. It is widely used in molds with forming surfaces and larger sizes.
7. Air pressure ejection
When the product is a deep cavity and thin meat, it is simple and effective to eject it with compressed air. Some small air inlets can be set on the male mold core, and mushroom-shaped rods can also be set. After the mold is opened, 5-6 atmospheres of compressed air are introduced to make the spring compressed to open the valve, and the high-pressure air enters between the product and the male mold core. Make the product demould. But for box-shaped products, the side wall will be stretched horizontally due to the gas entering, and the air will leak out. At this time, it should be used in conjunction with a push plate.
8. Composite ejection
Affected by the shape of the product, most molds use more than two ejection methods in order to achieve the ideal ejection effect. The specific form must be determined according to the product and mold structure, and will not be described in detail here.
9. Other ejection methods
The dot-like sprue automatically falls off
The point gate is on the side of the master mold, and a parting surface must be added to take out the rubber channel. After the mold is opened, the rubber channel is generally taken out manually, which causes troublesome operation and lower productivity. In order to adapt to automatic production, it is best to design an automatic shedding device so that the rubber channel will automatically fall off when it is ejected.
- Side concave pull off Drill a slanted hole at the end of the runner, pull out the rubber channel after mold opening, and eject it from the center ejector rod
- Pull rod pull out Pull out the rubber channel from the pull rod, and open the mold for a certain stroke The rear limit rod drives the push plate to push down the glue channel
- The push plate of the mother mold is pushed away. When the mold is opened, the mother template and the push plate of the mother mold are separated first. The position rod restricts the movement of the push plate, the push plate is separated from the template, and the glue channel is pulled off and falls off automatically
- The thimble is broken. For the mold with a long and narrow deep cavity, an ejector system can be installed on the mother mold. After the mold is opened, the ejector pin can be pushed out of the rubber channel in the reverse direction with the stroke of the limit lever. The product is pushed out by the push plate. This method is the same as the mold opening It is related to the itinerary and the application is more special.
Master mold side ejection method
General products will be ejected from the side of the male mold, but for some products due to their special shape or special product requirements, the ejector device must be installed on the female mold. Because the master mold is a fixed machine, the ejector pin cannot act on the top plate, and it must be completed by mold opening force or external force. The common ones are oil cylinder, electric, pull hook, etc.
Due to the special shape of the thread and the general product, it must be ejected by rotation or sideways demoulding. According to the complexity and output of the product, there are generally two methods: manual and motorized.
1) Forced unthreading
- For plastics (PP, PE) with strong elasticity, their elasticity can be used for forced demoulding without damaging the thread
- The threaded core is made of elastic silicone rubber. When the mold is opened, the spring is used to withdraw the ejector pin from the core, so that the rubber core shrinks inward, and then the ejector pin is used to release the product. This method can simplify the mold structure, but the life of the rubber core is short, and it is only suitable for small batch production
- Some threads can be formed by semi-circular sliders or rings, and two halves of sliders can be combined to form a complete thread or the product can be ejected by hand.
2) When the motor unscrews the thread and the thread comes out, it must rotate relative to each other, and there must be a rotation stop device on the mold to ensure it.
- External stop, the female mold of the mold is equipped with anti-rotation patterns, and the product can automatically fall off when the male mold core rotates
- Internal stop. For products with internal threads, set the anti-rotation form on the top surface of the male mold core. When demolding, the stop mold core rotates and the thread can be ejected axially. Note that the pitch of the stop mold core must be consistent with the product pitch
- The end surface of the product is stopped, and a small stop bump is set on the end surface of the product. When the core rotates, the push plate pushes the product out.
When a small product has a side gate, the product can be brought out only by ejecting the rubber channel, but it should not be used for soft plastics.
Core rotation driving methods: Commonly used are manual, electric, oil cylinder, air cylinder, hydraulic motor and large pitch screw nut drive. Generally speaking, when the rotating mechanism is designed, the product has several threads, and the threaded core must be Take a few turns.
The role of the cooling system is to shorten the molding cycle and improve production efficiency. In the entire molding cycle, the cooling and solidification time reaches 60%~80%, so it is very important to design a reasonable cooling system. Improve product quality. not only cool the mold, but also try to keep the mold at a constant temperature, and control the cooling speed of the melt. If the cooling speed is too fast, it will affect the filling, and if the cooling speed is too slow, it will cause defects in the product and prolong the molding cycle due to excessive temperature.
The purpose of designing the cooling system is to maintain proper and efficient cooling of the mold. Cooling channels should use standard sizes to facilitate processing and assembly. When designing the cooling system, the mold designer must determine the following design parameters according to the thickness and volume of the plastic part: the location and size of the cooling channel, the length of the channel, the type of channel, the configuration of the channel and the design rules of the cooling system. Cooling systems are designed to maintain proper and efficient cooling. Cooling channels should use standard sizes to facilitate processing and assembly. When designing the cooling system, the mold designer must determine the following design parameters according to the thickness and volume of the plastic part: the location and size of the cooling channel, the length of the channel, the type of the channel, the configuration and connection of the channel, and the flow rate and flow rate of the coolant. heat transfer properties.
1. The location and size of the cooling pipeline
To maintain an economical and effective cooling time, excessive thickness of plastic parts should be avoided. The cooling time required for plastic parts increases rapidly with the increase of its thickness. The thickness of plastic parts should be kept as uniform as possible. The cooling channels are preferably installed in the male module and the female module, and the cooling channels located outside the modules are not easy to cool the mold accurately. Usually, the distance between the cooling channel of the steel mold and the mold surface, mold cavity or mold core should be maintained at 1 to 2 times the diameter of the cooling channel. According to experience, the steel cooling channel should maintain a depth of 1 times the diameter, and the depth of the beryllium steel alloy should be 1.5 times. The depth of the diameter, aluminum should be twice the depth of the diameter. The spacing between the cooling channels should be maintained at 3 to 5 times the diameter. Cooling channel diameters are typically 10 to 14 mm (7/16 to 9/16 inches).
2. Flow rate and heat transfer
The temperature difference between the two sides of the plastic part should be kept at the minimum, and the temperature difference between the closely matched plastic parts should be kept within 10°C. When the flow of coolant changes from laminar flow to turbulent flow, the heat transfer effect becomes better. Laminar flow only transfers heat between layers by heat conduction. turbulent flow transfers heat in the radial direction, plus heat conduction and heat convection. As a result, the heat transfer efficiency is significantly increased. Care should be taken to ensure that the coolant flow in all parts of the cooling circuit is disturbed.
When the coolant reaches the turbulent flow state, the increase of the flow rate has a limited effect on the improvement of heat transfer. Therefore, when the Reynolds number exceeds 10,000, there is no need to increase the flow rate of the coolant, otherwise, the heat transfer will only be slightly improved. , but causes high pressure in the cooling pipeline, requiring higher pump costs. Coolant follows the path of least resistance. Sometimes you can try to use a restrictor plug to direct the coolant flow to the cooling channel with higher heat load. Air gaps reduce heat transfer efficiency, so try to eliminate air gaps between the insert and formwork, as well as air pockets in the cooling lines.
Mold Flow Analysis software's cooling analysis can assist in finding and correcting static cooling lines and shortcut cooling lines, as well as high pressure drop in cooling lines.
Exhaust of injection mold is an important issue in mold design, especially in rapid injection molding, the requirements for exhaust of injection mold are more stringent.
1. The source of gas in the injection mold
- Air in gating system and mold cavity.
- Some raw materials contain moisture that has not been removed by drying, and they are vaporized into water vapor at high temperature.
- Due to the high temperature during injection molding, the gas produced by the decomposition of some unstable plastics.
- Gas generated by volatilization of certain additives in plastic raw materials or chemical reactions with each other.
2. Poor exhaust of injection mold will bring a series of hazards to the quality of plastic parts and many other aspects. The main performance is as follows:
- During the injection molding process, the melt will replace the gas in the cavity. If the gas is not discharged in time, it will cause difficulty in filling the melt, resulting in insufficient injection volume to fill the cavity.
- The gas that is not removed smoothly will form a high pressure in the cavity, and penetrate into the interior of the plastic under a certain degree of compression, resulting in quality defects such as pores, loose tissue, voids, and silver streaks.
- Because the gas is highly compressed, the temperature in the mold cavity rises sharply, which in turn causes the surrounding melt to decompose, burn, and cause local carbonization and scorching of the plastic parts. It mainly appears at the confluence of two melts, dead corners and gate flanges.
- Poor removal of gas makes the speed of the melt entering each cavity different, therefore, it is easy to form flow marks and fusion marks, and reduce the mechanical properties of plastic parts.
- Due to the obstruction of the gas in the cavity, the filling speed will be reduced, the molding cycle will be affected, and the production efficiency will be reduced.
3. Key points of exhaust groove design
- The exhaust groove should be placed on the side of the die on the parting surface as much as possible to facilitate the manufacture and cleaning of the mold.
- Try to set it at the end of the material flow and at the thicker part of the plastic part.
- The exhaust direction should not face the operator, and should be processed into a curved or bent state, so as to avoid scalding workers when the gas is sprayed.
- The width of the exhaust groove is usually 1.5-6mm, and the groove depth is 0.02-0.05mm. It is advisable that the plastic does not enter the exhaust groove.
4. The way of the exhaust system
(1) Set up exhaust grooves
Vent grooves are usually set on one side of the cavity, around the cavity or at the last part of the melt.
(2) Vacuum exhaust
This method requires that the parting surface of the mold is warm and good, and the air in the mold cavity is pumped out through the air holes. However, it needs to be equipped with vacuum equipment, which increases the cost of the mold, and is generally not used.
(3) Use the gap to exhaust
- The gap between the mating surfaces of the mosaic parts, such as cavity and core insert
- Lateral core-pulling part clearance
- Ejection parts with clearance (push rod, block)
- Parting surface gap (roughness is average) When the gap is used for exhaust, the gap may be blocked after a long time of use, and it should be cleaned regularly to keep it unblocked.
(4) Using porous metal to vent
In recent years, a newly developed metal material with a uniform interconnected pore structure-porous metal has a good effect on the exhaust of the mold cavity. When it is difficult to exhaust some parts of the cavity, porous metal can be used to make cavity inserts, and the exhaust effect is very obvious. Pay attention to maintenance and cleaning when using the mold to keep the pores unblocked.
(5) Mixed exhaust
Usually, it is a mixture of opening exhaust channels and gap exhaust. The overflow value of the plastic and the exhaust clearance, the exhaust system should ensure that the gas escapes smoothly, and the plastic melt cannot flow out. The overflow value of plastic materials can be divided into the following three types: low-viscosity materials do not produce medical clearance: 0.01~0.03mm. medium-viscosity materials do not produce medical clearance: 0.03-0.05mm. high-viscosity materials do not produce medical clearance The gap is: 0.05~0.08mm.
Core Pulling System
When the side wall of the plastic product has through-hole grooves and bosses, the plastic product cannot come out of the mold directly, and the molding parts of the forming holes, grooves and bosses must be made movable, which is called a movable core. The mechanism that completes the active extraction and reset is called the extraction mechanism.
1. Classification of core pulling mechanism
(1) Motorized core pulling
When opening the mold, rely on the mold opening action of the injection inspection, and use the core pulling machine to bring the movable core and pull the core out. Motorized core pulling has the advantages of large demoulding force, low labor intensity, high productivity and convenient operation, and is widely used in production. According to its transmission mechanism, it can be divided into the following types: inclined guide column core pulling, inclined slider core pulling, rack and pinion core pulling, etc.
(2) Manual core pulling
When opening the mold, rely on manpower to extract the active core directly or through the action of the transfer parts. The disadvantage is that the production is labor-intensive, and it is difficult to obtain a large core-pulling force due to restrictions. The advantage is that the mold structure is simple, easy to manufacture, and the mold manufacturing cycle is short. It is suitable for trial production of plastic products and small batch production. Due to the limitations of the characteristics of plastic products, manual core pulling must be used when motorized core pulling cannot be used. Manual core pulling can be divided into the following types according to its transmission mechanism: thread mechanism core pulling, rack and pinion core pulling, movable insert core, other core pulling, etc.
(3) Hydraulic core pulling
The movable core depends on the hydraulic cylinder. Its advantage is that the core hydraulic device can be replaced according to the size of the demoulding force and the length of the core-pulling distance, so it can get a larger demoulding force and a longer core-pulling distance. High-pressure liquid is the power, and the transmission is smooth. Its disadvantage is that the operation process is increased, and a complete set of core-pulling hydraulic device is required at the same time. Therefore, its application range is limited, and it is generally rarely used.
2. Design principle of inclined guide column core-pulling mechanism
- The movable core is generally small and should be firmly installed on the slider to prevent loosening and slipping during core pulling. The connection between the core and the slider has a certain strength and rigidity.
- The sliding block should slide smoothly in the guide chute, and no jamming, jumping and other phenomena should occur.
- The slider limit device must be reliable to ensure that the slider stops at a certain point and does not slide arbitrarily after the mold is opened.
- Prevent the slider from being set on the fixed mold, in order to ensure that the plastic product remains on the fixed mold, the lateral core must be pulled out before the mold is opened, and it is best to use a directional and fixed distance tensioning device.
3. Design of inclined slider core-pulling mechanism
The cavity or boss on the side of the plastic product is relatively shallow, and the required core-pulling distance is not large, but when the required demoulding force is large, the oblique slider core-pulling structure can be selected. The feature of this oblique slider core-pulling structure is that when the push rod pushes the oblique slider, the push rod and core-pulling (or parting) actions are performed simultaneously. Because the oblique slider has good rigidity and can withstand a large demoulding force, the oblique angle of the oblique slider is slightly larger than that of the oblique guide post. Generally, the oblique angle of the oblique block cannot be greater than 30°, otherwise it is prone to failure. The push-out length of the oblique slider generally does not exceed 2/3 of the guide length, if it is too long, it will affect the guide sliding of the oblique slider. Because the inclined block core-pulling structure is simple, safe and reliable, and it is relatively convenient to manufacture. Therefore, it is widely used in plastic injection molds.
- Guide sliding and combination form of inclined slider. According to the shape of the sliding part, it can be divided into rectangular, semicircular and dovetail.
- Combination of inclined sliders The combination of inclined sliders should consider the direction of core pulling, and try to keep the appearance of plastic products beautiful without leaving obvious marks on the surface of plastic products. At the same time, it is also necessary to consider that the combined part of the slider has sufficient strength. If the shape of the plastic product has a turning point, the stitching line of the inclined slider should coincide with the folding line of the plastic product.