AAA MOULD - Plastic Injection Mould Manufacturer for custom mold design, precision processing, and plastic molding solutions.

Solutions to Part and Gate Adhesion Problems in Injection Molding

2026-05-18

In the injection molding production process, part and gate adhesion is one of the common process defects. This problem not only leads to difficult demolding and reduced production efficiency, but also may cause surface scratches, gate residues, and even part damage, directly affecting product quality and production efficiency, and bringing unnecessary cost losses to enterprises. Combining years of practical experience in the injection molding industry, this article systematically analyzes the core causes of part and gate adhesion, and provides actionable and highly adaptable solutions to help enterprises efficiently solve production pain points and improve the stability of injection molding production.

I. Core Causes of Part and Gate Adhesion in Injection Molding

The essence of part and gate adhesion is that after the plastic melt at the gate cools and solidifies, the bonding force between the melt and the part, as well as the mold gate structure, is greater than the demolding force, resulting in failure to separate smoothly during demolding. Combined with actual production, the main causes can be divided into three categories: mold design, process parameters, and raw material characteristics, which are detailed as follows:

Solutions to Part and Gate Adhesion Problems in Injection Molding 1

(1) Unreasonable Mold Design

The mold is the foundation of injection molding, and improper design of gate-related structures is the primary cause of adhesion problems. Firstly, the gate size and shape are unreasonable. For example, an excessively thick or short gate, or an irregular cross-sectional shape of the gate, will cause the melt to bond too tightly with the mold wall after solidifying at the gate, increasing demolding resistance. Secondly, the gate position is improperly selected. If the gate is set at a position with uneven part wall thickness or a corner, it will lead to unsmooth melt flow and inconsistent cooling speed, resulting in insufficient solidification at the connection between the gate and the part and forming adhesion. Thirdly, poor mold ventilation. The residual gas at the gate cannot be discharged in time, which will cause insufficient melt filling, generate internal stress after cooling, and aggravate the adhesion phenomenon. In addition, the absence of a demolding slope and insufficient surface roughness at the mold gate will also increase the friction between the plastic and the mold, leading to adhesion.

(2) Improper Setting of Injection Molding Process Parameters

The rationality of injection molding process parameters directly affects the filling, cooling and solidification process of the melt, and parameter deviations are likely to cause adhesion problems. Firstly, the melt temperature is too high, which will prolong the cooling and solidification time of the plastic melt, make the melt bond more closely with the mold and the part at the gate, and at the same time, the excessively high temperature may cause plastic degradation, generate viscous substances, and aggravate adhesion. Secondly, the mold temperature is too high. The excessively high temperature of the mold cavity and the gate will slow down the cooling speed of the plastic melt, resulting in incomplete solidification at the gate and easy adhesion to the part during demolding. Thirdly, the holding pressure is too high and the holding time is too long, which will cause the melt to be overfilled into the gate, increase the bonding force between the gate and the part, and at the same time, excessive holding pressure will generate internal stress, leading to difficult demolding. Fourthly, the demolding speed is too fast or too slow. Too fast will cause uneven force at the gate, which is easy to cause adhesion and tearing; too slow will make the gate contact the mold for a long time, aggravating adhesion.

(3) Improper Raw Material Characteristics and Handling

The inherent characteristics of raw materials and the quality of pre-treatment also have an important impact on gate adhesion. Firstly, the addition of additives in raw materials is unreasonable. For example, insufficient addition of lubricants and mold release agents will reduce the demolding performance of plastics and increase the friction with the mold and gate; if the addition of lubricants is excessive, it may cause surface defects of the part and affect the bonding stability at the gate. Secondly, the water content of raw materials is too high and they are not fully dried. During the injection molding process, the water will vaporize when heated, generating bubbles, leading to insufficient filling at the gate and loose adhesion after cooling. Thirdly, the raw materials themselves are highly viscous. For example, engineering plastics such as PA and PC have large intermolecular forces. If the formula or process is not reasonably adjusted, adhesion is likely to occur at the gate.

II. Targeted Solutions to Part and Gate Adhesion Problems

In view of the above causes, combined with the actual production scenarios, actionable solutions are provided from three dimensions: mold optimization, process adjustment, and raw material handling, which are both practical and economical, helping enterprises quickly solve adhesion problems.

Solutions to Part and Gate Adhesion Problems in Injection Molding 2

(1) Optimize Mold Design to Reduce Adhesion Hidden Dangers

Mold optimization is the key to solving adhesion problems from the root, focusing on adjusting the gate structure, ventilation system, and surface treatment:

1.Adjust gate size and shape: According to the part size, wall thickness and raw material characteristics, reasonably design the gate size. Generally, the gate thickness is recommended to be 1/3-1/2 of the part wall thickness, and the length is controlled at 1-3mm to avoid being too thick or too short. Prioritize the use of regular cross-sectional gates such as circular and trapezoidal to reduce melt flow resistance and facilitate cooling and demolding. For easily adherent plastics (such as PA and PC), point gates and submarine gates can be used to shorten the contact area between the gate and the part and reduce the risk of adhesion.

2.Optimize gate position: Avoid positions with uneven part wall thickness and corners, and prioritize setting the gate at a position with a thicker part wall and a flat structure to ensure smooth melt filling and uniform cooling. If the part structure is special, a multi-gate design can be adopted to disperse the filling pressure and reduce the force and bonding force of a single gate.

3.Improve the mold ventilation system: Set ventilation grooves near the gate and at the end of melt flow. The width of the ventilation groove is recommended to be 0.02-0.05mm, and the depth is 0.01-0.03mm to ensure that the gas is discharged in time during the injection molding process, avoid the generation of bubbles, and improve the filling density at the gate. At the same time, clean the sundries and accumulated materials in the mold cavity and gate to avoid adhesion caused by foreign objects.

4.Optimize mold surface treatment: Set a reasonable demolding slope (generally 1°-3°) at the gate to facilitate demolding. Polish the mold cavity and gate to reduce surface roughness and the friction between plastic and mold. If necessary, spray a special mold release agent at the mold gate to improve demolding performance, but the spray amount must be controlled to avoid affecting the surface quality of the part.

(2) Adjust Injection Molding Process Parameters to Optimize the Molding Process

By adjusting the process parameters, optimize the filling, cooling and solidification process of the melt, and reduce the bonding force between the gate and the part. The specific adjustment directions are as follows:

1.Control melt temperature: According to the raw material characteristics, appropriately reduce the melt temperature, generally by 5-10℃, to shorten the cooling and solidification time of the melt and reduce the bonding time between the melt and the mold and part. At the same time, avoid the melt temperature being too low to prevent insufficient melt fluidity, which may lead to new defects due to insufficient filling.

2.Adjust mold temperature: Appropriately reduce the mold temperature, especially the mold temperature at the gate, it is recommended to reduce by 10-15℃ to accelerate the cooling and solidification speed of the melt at the gate and reduce adhesion. For crystalline plastics (such as PP and PA), the mold temperature can be reasonably controlled to avoid adhesion caused by incomplete crystallization.

3.Optimize holding pressure parameters: Reduce the holding pressure (generally by 10%-20%) and shorten the holding time (by 2-5s) to avoid overfilling of the melt into the gate and reduce the bonding force between the gate and the part. At the same time, adjust the holding pressure switching time to avoid excessive extrusion on the gate during the holding stage.

4.Adjust demolding parameters: Control the demolding speed to maintain stable and uniform demolding, avoiding being too fast or too slow. For large parts or easily adherent parts, a segmented demolding method can be adopted to gradually separate the gate and the part, reducing adhesion and tearing caused by uneven force. At the same time, check the demolding mechanism to ensure that the ejector pins and ejector sleeves move flexibly and are evenly stressed, avoiding adhesion caused by jamming of the demolding mechanism.

(3) Standardize Raw Material Handling to Improve Demolding Performance

Do a good job in the pre-treatment and formula adjustment of raw materials to improve the demolding performance of plastics and reduce adhesion problems from the root:

1.Standardize raw material pre-treatment: For raw materials with high water content (such as PA and PET), dry them in advance. The drying temperature is controlled at 80-120℃, and the drying time is 2-4h to ensure that the water content of raw materials is less than 0.2%, avoiding the generation of bubbles during injection molding and leading to gate adhesion. For moisture-absorbing raw materials, they should be sealed and stored after drying to prevent re-absorption of moisture.

2.Adjust raw material formula: Reasonably add lubricants and mold release agents to raw materials, with the addition amount controlled at 0.5%-2%, to improve the demolding performance of plastics and reduce the friction with the mold and gate. Select raw materials with moderate viscosity. If it is necessary to use highly viscous engineering plastics, an appropriate amount of modifier can be added to reduce their viscosity. At the same time, avoid using degraded and deteriorated raw materials to prevent the generation of viscous substances.

3.Optimize raw material mixing: Fully mix raw materials with lubricants and mold release agents to ensure uniform dispersion of additives, avoiding adhesion problems caused by insufficient local additives. Avoid mixing impurities and foreign objects during the mixing process to prevent affecting the molding quality of the part.

III. Preventive Measures for Adhesion Problems

The core of solving adhesion problems is "prevention first, treatment second". By establishing a sound production control system, potential adhesion hazards are avoided in advance, and production stability is improved:

1.Daily mold maintenance: Regularly inspect and clean the mold, clean the accumulated materials and sundries at the gate, check whether the demolding mechanism and ventilation system are normal, timely repair mold wear and scratches, and keep the mold surface smooth. Regularly perform anti-rust and lubrication treatment on the mold to extend the service life of the mold and reduce potential adhesion hazards.

2.Standardization of process parameters: According to the part model and raw material characteristics, formulate standardized injection molding process parameters, clarify the melt temperature, mold temperature, holding pressure parameters, demolding parameters, etc., to avoid random adjustment of parameters. Regularly verify and optimize the process parameters, and fine-tune them according to the actual production situation to ensure parameter adaptability.

3.Raw material quality control: Establish a raw material incoming inspection system, strictly inspect indicators such as water content, purity, and additive content of raw materials, and eliminate the use of unqualified raw materials. Standardize the storage, drying and mixing processes of raw materials to ensure stable performance of raw materials.

4.Operator training: Strengthen professional training for operators to make them familiar with the mold structure and process parameter adjustment methods, master the emergency handling skills of adhesion problems, and be able to timely find and handle abnormal situations in the production process to avoid the expansion of problems.

IV. Conclusion

The problem of part and gate adhesion in injection molding is the result of the combined action of multiple factors such as mold design, process parameters, and raw material characteristics. In the production process, enterprises should first find the core causes of adhesion through investigation, then take targeted measures such as mold optimization, process adjustment, and standardized raw material handling, and establish a sound preventive control system to avoid potential adhesion hazards from the root.

Analysis of Causes and Solutions to Blooming Problems in Injection Molding