10 Hot Running Mold Design Flaws to Avoid

What is a hot running mold?

Use heating or insulation for runners.To keep the plastic from the nozzle of the injection molder to the molten cavity door.In each spray cycle, only the plastic parts are ejected and no debris runs.


Hot running mold has many advantages.But its cost is also expensive.Therefore, we should be more cautious in the process of designing and manufacturing molds.Avoiding mistakes is the best cost savings.
There are 10 flaws in the design.This will be helpful, get it quickly.

1. The design has been verified by mold flow analysis.

The molten material is molded into the respective compartments and reaches a pressure equilibrium.The number of hot leads is usually a multiple of 2 or 3. Then determine the location of the gate and the number of nozzles.To make the quality of the product meet the requirements of customers.

2. Correct selection of the nozzle for hot runners.

There are many types of nozzles in the hot tread kit.Type selection is based on the actual conditions of plastic parts and molds.

Cylindrical Faucet

Lower cost.Feed directly on the surface of the product.Suitable for plastic parts with textured surfaces.

Open type

When the plastic part is the technical plastic part.It is recommended to use an open nozzle.Prevent blockage of nozzles.

1. Circle 2. Main hot hose 3. Hot joining tube
4. Insulation Ring 5. Fireplace 6. High Temperature Insulation Plate
7. Dashboard 8. Support Plate 9. Support cushions
10. Secondary hot hose 11. Fix a plate 12. Insert a fixed mold
13. Lock pin  

Needle or point valve

This type of hot running system has an additional cylinder mechanism.Under the effect of the cylinder, the valve needle is raised during spraying.Close the glue gate at the end of the filling process.It can effectively stop the bleeding.


1 . . Cylinder Line 2. Hole circle 3. Top lid
4. OE Seal 5. Cylinder Block 6. Pistons
7. O-ring seal 8. Navigation belt 9. Riser Pad
10. Split runner 11. Manifold Positioning Pin 12. Valve Guide Bushing
13. Nozzle Locator Latch 14. Proboscis body 15. Core Heating Kit
16. Valve Gate 17. Tap head 18. Axis circle
19. Central positioning pin 20. Central support cushion 21. Stamped runner
22. Heating Main Nozzle 23. Main Nozzle Heating Kit 24. Axis circle

3. Hot tubs are not well insulated.

The hot running system comes into contact with the mold plate on a large area and needs a good insulation effect.The insulation of hot running plates, nozzles and mold plates is mainly air-insulated.Structural parts should reduce the area of contact with the plate.And there has to be enough space.

As structured A program:

If the hot running plate is designed overall with the pressure ring.It will make the hot runner’s insulation efficiency worse and increase costs.

As structure B shows:

The nozzle size of the faucet is easy to adjust. Place enough cooling water lines near the nozzle.Avoid hot runners near the gate aura.

4. The runner-up of the runner-up has a dead corner.

If there is a dead corner in the runner.This will make the remaining material accumulate in the runner.There will be color aberrations in plastic parts.

5.The faucet of the hot treadhip is leaking or clogged.

The hot nozzle will extend due to the size of expansion after heating.So in the design to calculate the expansion size of the nozzle.The size of the length stretch after the nozzle is heated.Otherwise, it will damage the cavity and the hot running unit.The tolerance required for assembly must be marked in the assembly drawing.

The center of the nozzle must be aligned with the central hole of the cavity.

The hot running plate temperature is 200°C.The cavity temperature is 60°C.There is a difference in heat dilation between the two types.

As in Figure A:

There must be enough space between the nozzle and the standard.Correct the position of the hot runner touching the mouth.The calibrated amount is the amount of thermal expansion of the current plate.Make sure that the center of the nozzle hole and the center of the gate hole are not deflected.

As in Figure B:

Nozzles are made of highly elastic steel or nickel copper or highly elastic berili copper.

7.Hot Running Mold Plate And Cavity Plate Fix

No. 1

It is not possible to use the screw structure between these two types.
As follows.If it is fixed directly with screws.The thermal expansion direction of the running plate is limited.It will make the plate tilt up.
As shown by Illustration B. Use screws with tiers.L1 is 0.05 mm higher than L. The running plate has enough space to expand and shrink.

8. Hot running mold design should consider plasticity.

The mold uses a hot runner structure and is selected according to the characteristics of the plastic.See Table for details.

Efficiency Plastic

9. The hot running mold of the hot running plate has a rough surface.

The roughness of the surface of the running holes matches the surface of the cavity.Avoid the rough runner’s holes as much as possible.

10.Hot running mold design electrical component misunderstanding.

1) The hot running system is not suitable for the power source.

Calculating the power capacity is calculated by the volume of 1 kg corresponding to 1-1.2 kw.Currently, hot running systems are standard or custom made.It was offered by the hot runner manufacturer.

2) The wire must enter and exit the head of the mold.

Cooling water compartment wets the conductor.Caused a leak accident.

3) The thermostat pair is not installed properly.

Flow plates and 2-storey nozzles are temperature-controlled separately.Minimize the temperature difference between the running disc and the level 2 nozzle.Thermoelectric pairs are usually placed in the places with the highest temperatures.Between the runner and the hottest part of the fireplace.

4) Pay attention to the electrical safety of hot runners.

The power cord must be fixed and protected from friction with parts.At the same time, it has used wax pipes to protect the wires.

5) Hot running components are not numbered accordingly.

Make sure the wire controls the temperature of the heater and the power supply corresponds to each other when wiring.The nozzle point of the plate runs hot and the compartment is numbered accordingly.The central feed is 1 and the rest is from the top right. Clockwise numbered from the y-axis. As the picture shows.


Here’s a basic 10 point suggestion.Maybe it will help you remember more details.If you still have questions, please contact us.

Vietnam Capacity Precision Mold Joint Stock Company

Address: Lot B2-3-3b, Nam Thang Long Industrial Park, Thu Phuong, Bac Tu Liem, Bac Tu Liem, Hanoi

Phone: (+84)24 6687 8283

Email: contact@vcc-group.vn

Hotline/Zalo: 0934683166

Website: www.vcc-mold.vn

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