How to avoid 10 errors of spray mold gate design

There may be conflicts when choosing a gate design.A comprehensive and flexible review should be based on conditions and practical experience.The location of the gate is one of the determinants of product quality.

Consider the shape and structure of the plastic part.

The gate is placed according to the shape and structure of the product.It should be placed in an understandable position and does not affect the form of the plastic part.
The gate must be placed on the assembly surface.Avoid higher surface requirements.The number of ports that require CAE flow analysis.

2. Avoid jet reaction.

The melt pumps directly into the core to bend the core.It also has an effect on the mold insertion department.Flow into the cavity or core curved flow.Avoid jet-offs.As illustrated:

3. Avoid the retention effect of melting.

When the molten material enters the area where the thickness of the wall changes greatly.The front edge of the thin-walled area will slow down, even stagnate.Until it’s full of thick walls.Such gate design can cause sunken marks on the surface of the plastic part.
As the picture shows.The gate is placed at the maximum wall thickness.

4. Avoid difficulties for plastic casting.

Take the 90° tube mold, for example.AS figure A. Place the gate inside the elbow.The aim is to make the gate position of the mold suitable to the center of the mold to avoid the deviant gate of the mold.But the test results show that.Since the curved core is subject to the effect of the injection force, the core is pushed to the opposite side, so it is impossible to mold the tube.Place the gate position on the back of the elbow.Like Figure B.

5. The location of the gate should avoid the rate of excessive flow.

The number and location of the doors must satisfy the maximum flow length/thickness ratio into the tube.Avoid filling the difficult cavity.The melting process should be minimized and minimized in the direction of the flow to reduce energy losses.
As pictured (a).The L5 process is long, the direction of the flow changes a lot and the filling conditions are poor.It’s not conducive to exhaustion.It often causes defects such as a lack of material or bubbles at the top of the product.
Figure (b) showing the direct port and the short L2 process.

This table is the permissible value of the common plastic flow rate for design reference.

Substance Injection Pressure / MPa Flow rate Substance Injection Pressure / MPa Flow rate
Polyethylene 150 250~280 Polyvinyl hard chloride 130 130~170
Polyethylene 60 100~140 Polyvinyl hard chloride 90 100~140
Polypropylene 120 280 Polyvinyl hard chloride 70 70~140
Polypropylene 70 200~240 Polyvinyl soft chloride 90 100~280
Polystyrene 90 280~300 Polyvinyl soft chloride 70 100~240
Polyamide 90 200~360 Polycarbonate 130 120~180
POM 100 110~210 Polycarbonate 90 90~130

6.Port installation requires injection pressure balance in the mold cavity.

Each corner of the cavity can be filled with molten material at the same time.The plastic is melted at an optimal temperature.

7. Avoid placing the gate on the thin wall of plastic parts.

The gate position must be placed at the thickest part of the wall thickness of the product to facilitate the loading of the melting substance.Micro-minimized by the product, shrinking the vulnerability.

8. Avoid placing the gate in a position that is not conducive to air drainage.

For example, the gating system of the department is designed as a secondary port.The product is retained with gas.The gating system should be changed to a point gate.Top-down feeding facilitates ventilation and feeding.Molds should not be half structured.It has to be the whole cavity.Three-hole mold or hot running mold for two-point gate.

9.Avoid violating the gate design of the one-way flow principle.

The gate design is based on the plastic part structure to determine the level direction of the gate.Consider resistance and emission conditions during casting.Avoid welding lines on plastic parts.

10. The installation of the gate must not affect the form and use of plastic parts.


These 10 small details can prevent errors from occurring.Useful for inexperienced designers.Placing the gate properly can improve the quality of the plastic part.Avoid welds, dents,… in plastic parts.
If you have questions about molding, 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


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