Basic principles of mold runner design

The basic principle of mold runner design is also called main runner, injection runner (Sprue) or vertical runner. It refers to the runner from the part where the nozzle of injection machine contacts the bushing of mold main runner to the end of the shunting channel. This part is the first part that the molten plastic flows through after entering the mold.

Design consists of

Runner: Also known as Runner or Secondary Runner, depending on mold design can be divided into First Runner and second Runner. The shunting channel is the transition area between the main channel and the gate, which can make the flow direction of molten plastic smooth transformation; It has the function of distributing plastic evenly to each hole at the same time for multi-hole mold.

Gate: Also called feed port. It is the narrow opening between the shunting channel and the die hole, and it is also the shortest and thinnest part. The effect is to use the compressed flow surface to accelerate the effect of plastic, high shear rate can make plastic good liquidity (due to the shear thinning characteristics of plastic); The heating effect of viscous heating also has the effect of raising material temperature and reducing viscosity. After molding, the gate is first solidified and sealed, which can prevent plastic backflow and prevent mold pressure from falling too fast to produce shrinkage depression. After molding, it is easy to cut off to separate the runner system and plastic parts.

Coolant well: Also known as coolant hole. The purpose is to store and collect the cold plastic wave front in the initial filling stage, so as to prevent the cold material from directly entering the cavity to affect the filling quality or blocking the gate. The cold material well is usually set at the end of the main passage. When the shunt passage is long, the cold material well should also be set at the end.

The basic principle of

Consideration of Cavity Layout

Balances Layout can be used if possible.

The layout of die hole and the opening of gate should be symmetrical so as to prevent the problem of overflow of supporting die caused by uneven force on the die. Symmetrical designs are better.

The cavity arrangement is as compact as possible to reduce the mold size. Flow guidance considerations

Can smoothly guide the molten plastic to fill the cavity, no eddy current, and smooth exhaust.

To prevent Core Shift or deformation, try to avoid plastic melt from impacting the Core and metal insert with small diameter.

Heat loss and pressure drop considerations

The less heat loss and pressure drop, the better.

Keep the process short.

The cross-sectional area of the runner should be large enough.

As far as possible to avoid flow channel bending and sudden change of direction (arc Angle change direction). The surface roughness of the runner should be low.

Multipoint pouring can reduce pressure drop and required injection pressure, but there are suture problems.

Flow balance considerations

In the case of multi-cavity filling, the flow channel should be balanced and plastic should be filled in each Cavity at the same time as possible to ensure the quality consistency of molded products in each Cavity.

Shunting channel as far as possible using Naturally Balanced Layout.

When the natural balance is not possible, the artificial balance method is used to balance the flow channel.

Waste considerations

On the premise of smooth filling without affecting flow and pressure loss, the volume (length or cross-sectional area) of the runner is reduced to reduce the waste generation and recovery costs of the runner.

Consideration of cold materials

Appropriate Cold Slug Well and overflow groove are designed on the flow passage system to collect the Cold plastic wave front at the initial stage of filling, so as to prevent Cold material directly entering the cavity from affecting the filling quality.

Exhaust considerations

The plastic should be successfully guided to fill the cavity, and the air in the cavity can be successfully escaped to avoid the problem of sealing and burning.

Quality consideration of forming products

Avoid short shot, burr, sealing, suture, flow mark, jet flow, residual stress, warping deformation, die offset and other problems.

Coil coil During long or Multiple Gating due to flow imbalance, inadequate pressure holding, or uneven shrinkage

Flexural deformation should be prevented.

The product has good appearance and properties, it is convenient to remove and repair the Gate Mark, and the Gate Mark is not harmful to the appearance and application of plastic parts.

Production efficiency considerations

As far as possible to reduce the need for post-processing, so as to shorten the forming cycle, improve production efficiency.

The point of ejection

Proper ejection position should be considered to avoid demoulding deformation.

Plastic considerations

Avoid using too long or too small runner for plastics with high viscosity or short L/ T.