Runner and gate design are critical to injection molding, influencing how molten plastic flows into the mold cavities, impacting product quality and production efficiency.

Optimal runner and gate design in molds ensures efficient molten plastic flow, enhancing cycle times and product quality by minimizing defects. Crucial factors include runner type, size, and gate location.

Understanding runner and gate design is essential for optimizing injection molding processes. Learn more about how tailored designs can improve efficiency and product quality in your manufacturing operations.

What are the Components of a Sprue System?

Sprue systems are crucial in the injection molding process, facilitating the efficient transfer of molten plastic into the mold cavities.

Sprue systems channel molten plastic into mold cavities, comprising the sprue, runner, and gate. They solidify material and shape products, crucial in automotive and consumer goods manufacturing.

A koşucu sistemi¹, also called a sprue system or pouring system, is the necessary passage for molten plastic from the injection nozzle of an injection molding machine to the cavity of the mold. A runner system consists of a main runner, a manifold, and a gate.

Ana Koşucu

Also known as the main runner, injection runner, or vertical runner, it is the runner that starts from the part of the ejector nozzle that comes in contact with the main runner bushing of the mold, and ends at the manifold. This part is the first part that the molten plastic flows through after entering the mold.

Separate Runner

Also known as a split runner or secondary runner. Depending on the mold design, it can be further divided into a first runner and a second runner. The manifold is the transition area between the main runner and the sprue, which allows a smooth transition of the molten plastic flow; for multi-cavity molds, it also serves the function of distributing the plastic evenly to the various cavities.

Kapı

Also known as the sprue, it is the narrow opening between the runner and the mold cavity, and is also the shortest and thinnest part. Its function is to accelerate the plastic by tightening the flow surface. The high shear rate can make the plastic flow well (due to the shear thinning property of plastic); the warming effect of viscous heating also has the effect of raising the material temperature and lowering the viscosity.

After molding, the gate is the first to cure and seal, which prevents the plastic from flowing back and the pressure in the mold cavity from dropping too fast, resulting in the shrinkage of the molded product. After molding, it is easy to cut off to separate the runner system and the molded part.

Cold Feed Wells

Also called a cold slug well. It is used to store and replenish the cold plastic wavefront at the beginning of the fill, preventing the cold material from going directly into the mold cavity and affecting the fill quality or blocking the gate. Cold slug wells are usually placed at the end of the main runner, but when the runner is long, cold slug wells should also be placed at the end.

What are the Basic Principles of Sprue System Design?

Sprue system design is a fundamental aspect of injection molding, affecting efficiency and quality in manufacturing processes.

Sprue system design optimizes flow paths for smooth material distribution, minimizing waste and reducing cycle times. Key considerations include sprue size, angle, and material to enhance mold performance and product integrity..

Principles of Gate Design

Choose the gate location² on a non-critical surface or feature of the part to minimize witness marks and blemishes on the part. Keep the gate shape as simple as possible to help the plastic flow during injection molding and to avoid defects like bubbles and short shots. Size the gate according to the needs of the part.

If the gate is too big, the pouring time will be too long. If the gate is too small, the pressure will be too high. The connection between the gate and the product should be as smooth as possible to reduce the trace and loss during the removal. The number of gates should be as small as possible. Multiple gates will cause the enjeksiyon kalıplama³ to be unbalanced, resulting in inconsistent product size.

Put the gate at the thickest part of the molded part. This makes sure that the melt fills the thick part first, which gives you better filling and pressure holding. When you design the gate, think about the venting inside the mold so you don’t get air bubbles or wind buildup. Don’t put the gate at the weak point or embedded position of the molded part. That will concentrate stresses and cause defects in the molded part.

Koşucu Tasarım İlkeleri

The runner shape should be simple, with few turns or sharp corners, to minimize flow resistance and defects caused by uneven plastic flow. The runner length should be as short as possible to reduce the injection cycle and the plastic’s condensation time.

The cross-sectional area of the runner should be gradually reduced to ensure that the plastic flows evenly in the runner and to avoid air bubbles. The joints between the runners and the mold cavities should be as smooth as possible to avoid impact and extrusion when the plastic flows to reduce traces and defects on the product.

• Cavity arrangement:When arranging the cavity, try to use a balanced layout. The layout of the cavity should be symmetrical with the gate position, which can prevent the mold from being unevenly stressed and the molten plastic from overflowing.The cavity arrangement⁴ should be as compact as possible, and the size of the mold should be reduced so that the molten plastic can be guided to fill the cavity and vent smoothly. Attention should be paid to the cross-sectional area of the runner should be large, the flow should be short, the heat loss and pressure drop is as small as possible, in the runner processing should ensure that the roughness of the surface.Using multi-point pouring can help lower the pressure drop and injection pressure needed, but it can also cause weld lines.

• Runner balance⁵: When you’re filling multiple cavities in one mold, you need to think about balancing the runners so that the molten plastic fills each cavity at the same time as much as possible. This way, you can make sure that the plastic in each cavity is molded consistently. You can balance the runners by arranging the manifolds in a naturally balanced way. If you can’t get a natural balance, you can use an artificial balance method to balance the runners.

• Scrap: In the design of plastic runners, flow and pressure loss are not a concern. You can reduce the volume or cross-sectional area of the runner to save material, reduce waste, and save on recycling costs.The size of the runner cross-section should change gradually, not suddenly, to match the flow characteristics of the material. Increasing productivity and reducing molding cycle times can improve the economic efficiency of plastics processors.

• Air venting⁶:If you guide the plastic to fill the cavity, the air inside the cavity can escape smoothly, so you won’t have the problem of encapsulation scorching. You want to avoid short shots, burrs, flow marks, and residual stress because they’ll affect the quality of your molded products. You also want to avoid curved deformation because it’ll affect the appearance of your plastic parts.

Consideration of mold Cavity Arrangement

Try to make the layout as balanced as possible, and try to make the layout of the kalıp boşluğu⁷ and the gate opening symmetrical as much as possible to avoid the problem of mold overflow caused by uneven stress on the mold and uneven loading; try to make the layout of the mold cavity as compact as possible to reduce the size of the mold.

Consideration of Flow Guide

Gently guide the molten plastic to fill the mold cavities without causing swirls and smooth out the exhaust;Try to avoid the molten plastic from pushing the smaller diameter core and metal inserts too much to prevent the core from moving or deforming.

Consideration of Heat Loss and Pressure Drop

The smaller the heat loss and pressure drop, the better. The flow should be short. The cross-sectional area of the runner should be large enough.

Avoid sharp bends and abrupt changes in flow direction (change direction with a curved angle); the surface roughness of the runner should be low; multi-gate pouring can reduce the pressure drop and the required injection pressure, but there will be a problem with the weld line.

Akış Dengesinin Dikkate Alınması

When you fill multiple cavities in one mold, you need to balance the flow channel⁸. Try to make the plastic fill each mold cavity at the same time to ensure the consistency of the quality of the molded products in each mold cavity. Try to adopt the natural balanced arrangement for the manifold. When it can’t be balanced naturally, use the artificial balancing method to balance the flow channel.

Consideration of Waste Material

To make sure the filling is smooth and doesn’t cause any flow or pressure loss, you should reduce the size of the runner (either the length or the cross-sectional area) as much as possible. This will help you minimize the amount of runner waste⁹ you generate and the cost of recycling it.

Cold Material Considerations

Design suitable cold material wells¹⁰ and overflow tanks on the runner system to collect the cold plastic wavefront at the beginning of filling and prevent the cold material from going directly into the mold cavity, which will affect the filling quality.

Consideration of Air Venting

The plastic should be guided smoothly to fill the mold cavity, and the air inside the cavity should be able to escape smoothly, so as to avoid the problem of encapsulation scorching.

Kalıplanmış Ürün Kalitesinin Dikkate Alınması

Don’t use short shots, flash, sink marks, weld lines, flow marks, jets, residual stresses, warpage, mold shift, etc. When the flow path system is long or multi-point injection, it is necessary to prevent warpage and deformation of the product caused by flow imbalance, insufficient pressure holding, or uneven shrinkage. The product has good appearance, easy to remove and trim the gate, and the gate mark does not affect the appearance and application of the molded part.

Consideration of Production Efficiency

Minimize the post-processing needed to shorten the molding cycle and improve productivity.

Ejection Point Consideration

Make sure to choose the right ejector position to prevent any deformation of the molded parts.

Consideration of Plastics to be Used

Don’t use too long or too small runners for plastics with high viscosity or short L/t.

How to Design the Gate of the Injection Mold is Reasonable?

Designing a reasonable injection mold gate enhances product quality and production efficiency, crucial for successful manufacturing processes in various industries.

When designing an injection mold gate, consider material flow, part geometry, and gate location to minimize weld lines and ensure a good surface finish. Choose from edge, pin, or diaphragm gates based on specific application needs.

Selection of Gate Location

Put the gate at the thickest part of the part. Gating from the thickest part gives better filling and pressure retention. If you don’t have good pressure retention, the thinner areas will freeze off before the thicker areas. Don’t put the gate at a sudden change in thickness because you’ll get hysteresis or short shots.

If possible, pour from the center of the product. Placing the gate in the center of the product gives you equal flow lengths, which affects the shot pressure you need, and the center feed makes the holding pressure uniform in all directions and avoids uneven volume shrinkage.

As the plastic flows into the runner, the plastic is first cooled and solidified near the mold surface. When the plastic flows forward again, only the solidified plastic layer flows through. And because the plastic is a poor conductor of heat, the solid plastic forms an adiabatic layer and keeps the layer flowing.

So, ideally, the gate should be located at the cross runner layer to get the best plastic flow effect. This is usually the case for round and hexagonal cross runners. But trapezoidal cross runners can’t do this because the gate can’t be in the middle of the runner.

Choose the gate location¹¹ on the parting surface as much as possible, so that the gate can be easily cleaned during mold processing and use; the distance between the gate and each part of the cavity should be as equal as possible, and as short as possible; the gate location should ensure that the plastic flows into the cavity,

The gate location should be such that the plastic does not flow into the cavity when the cavity wall, core or insert, so that the plastic can flow into the cavity parts as soon as possible.

And avoid the deformation of the core or insert; the location of the gate should try to avoid products produce fusion marks, or make its fusion marks produced in the unimportant parts of the product; the location of the gate should be located in the most easy to remove the parts of the mouth of the system, and at the same time as far as possible not to affect the appearance of the product; the location of the gate should be prevented from generating the gate at the injection in the filling process to produce serpentine flow.

Size of Gate Cross-Section

Generally, the gate size should be small, not large. First, set a smaller size. Then, adjust the size according to the filling condition of the cavities in the test mold. Especially in the case of a multi-cavity mold, the adjusted gate size can achieve the uniformity of glue feeding into the cavities at the same time. At the same time, the small gate can increase the melt speed. Increasing the melt temperature is good for filling, and small gates are also good for removing.

But for those products that are very thick, if the gate is too small, the gate will cure prematurely, resulting in product defects due to insufficient replenishment. Therefore, the specific size of the gate should be determined according to the specific shape of the gate.

Gate Shape

• Direct Gating: Direct gating is the simplest type of gating, and the gate size design refers to the design of the vertical main runner. The main advantages are easy filling, low pressure loss, and fast filling speed. The disadvantage is that it is easy to generate a lot of stress at the gate, which makes the product easy to be deformed, and at the same time, the size of the gate is large. Removal is not convenient. It affects the appearance of the product. Direct gating is mainly used for large and deep barrel-shaped products.

• Side gate: Side gate, also known as common gate, has the following main features: simple shape, easy to process, easy to repair the gate, can be used for products of various shapes, but PC material or transparent parts should not be used, and other thin and long barrel-shaped products should not be used.

• Fan-shaped gate: Fan gate, also called fishtail gate, is a type of gate that opens up from the runner to the cavity in the shape of a fan. It can reduce the internal stress of the part during injection and is mainly used for flat parts and shallow shell or box-shaped parts.

• Thin-sheet gate: Thin-sheet gate is mainly suitable for large flat products, which makes the products less prone to deformation, flow marks, bubbles, etc. The disadvantage is that the gate is not easy to cut out. Its disadvantage is that the gate is not easy to cut off.

How to Calculate the Runner Design of Injection Mold?

Calculating runner design in injection molds involves optimizing flow paths to ensure balanced and efficient filling, reducing defects and cycle times in production.

Runner design in injection molding ensures even plastic flow, reducing waste and defects. Key steps include sizing based on part geometry, optimizing layout for balanced filling, and considering material properties, enhancing efficiency and quality..

Boşluk Sayısı

When we set up the runner of a plastic mold, we need to take into account the number of cavities. The number of cavities depends on the quality of the raw materials, the geometric structure characteristics of the plastic parts, the dimensional accuracy requirements, the batch size, the difficulty of maintenance and repair, and the processability of molding manufacturing, etc. We calculate the number of cavities by considering various factors. The formula for calculating the number of cavities is as follows: Number of cavities = L x k x tc/tm.

L the number of products per batch; tm unit production time required; tc a mold production cycle; K elimination factor.

• Injection volume:The injection mold cavity may or may not be filled with the maximum injection volume of the injection machine. When designing the mold cavity, you need to consider the maximum injection volume range of the injection machine. The maximum injection volume of the injection machine should be greater than the volume of the plastic part. The injection volume needs to meet the requirements of the plastic part. The general common injection formula is: NM1 + M2 =

M is the maximum injection volume of the injection machine. M1 is the mass or volume of the big plastic part. M2 is the plastic mass of the pouring system that you need.

• Plasticizing capacity:The number of cavities is determined by the plasticizing capacity of the injection machine. The formula for calculating the number of cavities based on the plasticizing capacity of the injection machine is: P/(X×W).

P plasticizing capacity of the injection machine; X number of injections per minute; W weight of the plastic part.

Cavity Arrangement

Once you know how many cavities you need, you have to look at the layout of the cavities. You have to think about where each cavity is in relation to the main runner. You have to make sure that the distance from the main runner to each cavity is short so you don’t have a lot of pressure drop. You have to make sure that the temperature of the melt going into each cavity is the same so that the internal stress in the molded part is the same.

If you can, make the distance between the holes as big as possible so it’s easy to connect the top bar to the water channel.

Rod and cooling waterway. Cavities in the injection of reaction force should act in the center of the template, so that it can correspond to the center of the barrel, to ensure the balance of stress. The arrangement of the cavities in the mold can be divided into balanced and non-balanced according to the balance, in the selection of cavities in plastic molds try to adopt the balanced arrangement.

Calculation of Runner Size

The length and diameter of the runner will affect the flow resistance of the molten material. The greater the flow resistance, the greater the pressure drop required to fill the cavity. Increasing the diameter of the runner will reduce the flow resistance, but it will also increase the amount of raw material and slow down the cooling rate. Therefore, when designing the size of the runner, it is necessary to use mold flow analysis to adjust the diameter of the runner reasonably. The initial estimated formula for the diameter of the runner is:

D=W1/2×L1/4/3.7 D is the runner diameter (mm); W is the weight of the molded part (g); L is the runner length (mm).

Selection of Runner Cross-Section

There are a few different types of runner cross-sections that are commonly used in injection molding. These include the modified trapezoidal runner cross-section, the circular runner, the trapezoidal runner cross-section, the semi-circular runner cross-section, and the rectangular runner. When designing the runner cross-section, it is important to minimize the pressure drop in the runner. This can be achieved by making the runner cross-section as large as possible.

To reduce heat loss, you need to reduce the runner’s cross-sectional area. The runner’s efficiency is the ratio of the runner’s cross-sectional area to the perimeter of the runner’s cross-section. A circular runner has the highest runner efficiency and the lowest pressure drop and heat loss. However, you need to machine the circular runner’s movable and fixed mold plates, which is expensive. So, you need to align the movable and fixed mold runners and improve the machining accuracy when you close the mold.

Sonuç

This article is mainly about the design principles and principles of runners and gates in enjeksi̇yon kaliplari¹². It introduces the components of the runner system, including the main runner, manifold, gate, and cold material well, and discusses the factors that affect the gate position, shape, size, and runner design.

When designing a mold, you need to think about a lot of things. You need to think about how the product looks, how it fills, how the runners balance, how you control waste, and how the pressure drops. All of these things affect the quality of the molding and how productive you are. If you design the mold right, you’ll get good flow, fewer defects, and a better process.