Rubber injection moulding is one of the most widely used technologies for producing technical rubber components. This process makes it possible to achieve parts with good dimensional accuracy, fast production cycles, and consistent quality even in high-volume manufacturing. Despite the high efficiency of the process, certain issues may arise during production that can compromise the quality of the moulded parts. These defects are often linked to a combination of process parameters, compound characteristics, and mould conditions.
When a mould does not operate under optimal conditions, imperfections can appear on the parts, leading to production scrap and slowdowns in the manufacturing line. For this reason, it is essential to quickly identify the causes of defects and take prompt corrective action.
Let us look at three of the most common problems in rubber injection moulding and their possible solutions.
1- Incomplete filling of the mould cavities
This is one of the most common defects in injection moulding. It occurs when the mould cavities are not completely filled with material, resulting in an incomplete component or areas with missing material.
This issue can be caused by several factors, including:
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an insufficient amount of injected material
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excessively high compound viscosity
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unsuitable mould or material temperatures
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filling speed that is too low
In particular, in more complex cavities or those with thin walls, the material may encounter greater resistance during flow and fail to reach all areas of the mould.
How to solve the issue
To prevent incomplete filling, several process parameters can be adjusted:
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increase the volume of injected material
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use a compound with higher flowability
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raise the mould or compound temperature
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increase the filling speed or injection pressure
Mould design also plays a key role: the correct positioning of injection points and an optimised flow channel layout promote uniform cavity filling.
2- Material shrinkage
During the cooling and vulcanisation phase, rubber naturally undergoes dimensional contraction, known as shrinkage.
This phenomenon causes the moulded part to be slightly smaller than the cavity from which it was produced. If not properly managed, shrinkage can lead to dimensional tolerance issues or difficulties during assembly with other components.
How to control shrinkage
Shrinkage is a natural characteristic of elastomeric materials, but it can be managed through careful mould design and proper process parameter control.
Key actions include:
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maintaining adequate holding pressure
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extending holding time to compensate for contraction
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designing the cavity taking into account the compound’s shrinkage rate
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ensuring uniform pressure distribution within the cavity
Rubber shrinkage is a critical parameter in mould design: it is essential to predict how the material will behave during moulding in order to define the correct cavity and runner dimensions.
If shrinkage is estimated incorrectly, the finished part may fall outside tolerance.
3- Excess flashing
Flash occurs when material escapes between the mould’s closing surfaces along the parting line.
This defect can negatively affect both the appearance and functional performance of the part, especially in the case of seals or components designed for tightness.
The most common causes include:
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insufficient clamping force of the press
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excessively high injection pressure
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wear of the mould surfaces or cavity edges
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misalignment between the mould plates
When the issue occurs frequently, it may indicate that the mould requires maintenance or refurbishment.
How to prevent flash
To reduce flash formation, it is possible to:
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increase the clamping force of the press
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optimise the injection pressure
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check the condition of the mould’s closing surfaces
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verify proper alignment of the mould plates
Regular mould maintenance makes it possible to detect wear early and prevent production defects.
The quality of moulded components does not depend solely on process parameters, but also on the condition of the mould and its maintenance over time.
Material residues, deposits, or surface wear can compromise proper mould operation and lead to defects in the finished part. Regular cleaning and maintenance, on the other hand, help maintain high production performance and reduce scrap and machine downtime.
Careful mould management therefore improves production efficiency and ensures consistent quality of technical rubber components.
Moulding defects, mould maintenance, and process optimisation are key aspects in improving product quality and production stability.
