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The plastic wash basin mould determines the geometry of the basin, including its base profile, wall thickness, rim and handle details. Because the product has a broad, relatively shallow shape, uneven cooling can lead to distortion that becomes noticeable when the basin is placed on a flat surface. Even a small difference in shrinkage across the bottom may cause rocking or an uneven appearance.

Material behaviour is one factor behind these changes. Polypropylene and polyethylene are widely used for household plastic products, but their shrinkage characteristics differ according to resin grade, additives, processing conditions and part geometry. The mould dimensions must account for expected shrinkage, while trial moulding helps reveal whether the actual result matches the intended measurements. Compensation cannot be based on a single percentage alone, especially when the base and rim cool at different rates.

Cooling layout also affects dimensional consistency. If one area remains hot while another solidifies earlier, the resulting shrinkage may pull the base or side walls out of shape. Cooling channels therefore need to be considered in relation to the basin's depth, diameter and wall thickness. A balanced arrangement can help reduce temperature differences, although the final result also depends on the resin and production settings.

The base profile presents another design consideration. A completely flat surface and a gently shaped bottom behave differently during cooling and everyday use. Depending on the basin's intended function, a slight slope may help water drain toward a designated point, while the surrounding geometry provides stiffness. The required shape should be defined in the product drawing rather than left to adjustment after moulding.

Handles and thick rim sections introduce additional challenges. Material tends to cool more slowly in thicker areas, which can contribute to sink marks or pull adjacent walls inward. Core features and carefully arranged ribs can reduce unnecessary material thickness while maintaining the intended structure. Gate location also influences how melt travels through the cavity, particularly around handle connections where flow fronts may meet.

Recycled resin blends can add variation because their composition and processing behaviour may differ between batches. When a material change is planned, trial runs can help determine whether the existing mould settings still produce consistent dimensions and surface quality.

A plastic wash basin mould must therefore account for more than the basin's outer shape. Material characteristics, cooling balance, wall transitions and the intended base profile work together to determine how consistently the finished product can be produced.