Window sill extrusion mould

Common Problems and Solutions in Window Sill Extrusion Mould Production

Shrinkage marks at the intersection of the outer wall and inner ribs are the most common and troublesome quality defect in the Window Sill Extrusion Mould production process. This problem not only affects the flatness of the product appearance, but in severe cases, it can also lead to surface depressions, uneven stress, and bending deformation of the finished product, directly reducing the product qualification rate and market grade. Based on 27 years of experience in extrusion mold R&D and on-site debugging, this paper systematically analyzes the causes of the high incidence of shrinkage marks in window sills and provides corresponding solutions, offering professional technical support for stable mass production.

1. Mismatch between the designed wall thickness and the actual production wall thickness of the window sill extrusion mold, resulting in excessive stretching and surface shrinkage.

Standard Window Sill Extrusion Mould are designed according to a standard 2.0mm finished wall thickness, with a preset die head discharge gap of 1.8mm. Utilizing the normal Balas expansion effect of the material, the billet naturally expands after exiting the mold, and after shaping and calibration, it is formed to a standard 2.0mm wall thickness, with stable material flow, no stretching, and no depressions. Some manufacturers, in order to reduce raw material costs and product weight per meter, have arbitrarily reduced the finished product wall thickness to around 1.5mm, far less than the mold design benchmark thickness. After the material is extruded through a 1.8mm die head gap, it must be forcibly stretched to thinner, easily causing shrinkage marks at the junction of the inner ribs and the plate surface.

Solution: Prioritize restoring the standard 2.0mm wall thickness for production; shrinkage marks will naturally disappear. For long-term lightweight and cost-reducing production, a 0.3mm thick stainless steel sheet can be welded within a 40mm range of the die head outlet to precisely reduce the die head outlet gap to 1.5mm, matching the actual production wall thickness and preventing surface shrinkage defects caused by forced stretching from the source.

2. The material flow rate of the inner ribs lags behind the plate surface, and uneven material flow causes shrinkage marks.

The Window Sill Extrusion Mould structure consists of a large thin plate with dense inner ribs. If the flow channel and feed channel design of the window sill extrusion mold are unreasonable, the plate surface will expel material quickly, while the inner ribs will expel material slowly. Insufficient inner rib material supply and delayed filling cause the sheet surface to be stretched during molding, resulting in obvious shrinkage marks at the inner and outer joints. To address this issue, professional mold repair and adjustment can be used to optimize the independent material flow channel for the inner ribs, increasing the material flow rate and ensuring synchronized and balanced material flow between the inner ribs and the outer wall, effectively improving surface shrinkage marks.

3. The length of the fusion section of the Window Sill Extrusion Mould head is mismatched with the calcium powder ratio in the formula.

The fusion opening length between the inner ribs and the sheet surface directly determines the flatness of the sheet surface. The shorter the fusion section, the flatter the sheet surface and the lower the probability of shrinkage marks. This parameter must match the calcium powder filling ratio. For low-calcium powder formulas (100 parts PVC to 60 parts calcium powder), which have good fluidity, a fusion opening of approximately 8mm is optimal. For high-calcium powder formulas (100 parts PVC to 150 parts calcium powder), the melt fluidity deteriorates and filling resistance increases, requiring a fusion opening enlarged to 15mm to ensure sufficient material fusion and filling. Parameter mismatch can lead to incomplete fusion, localized material shortages, and persistent surface shrinkage marks.

4. Inappropriate magnification ratio between the Window Sill Extrusion Mould head and calibrator.

The forming of the upper and lower wall thicknesses of the window sill has a fixed magnification process standard: the forming magnification ratio of the mold head is typically set at 3%. Taking a 20mm wall thickness product as an example, the output size of the mold head is 20.6mm; the shaping magnification ratio of the calibrator is set at 1%, and the shaping size is 20.2mm. The output size of the mold head is always slightly larger than the shaping size, and the material enters the shaping section under slight pressure, resulting in full filling and dense molding without shrinkage or depressions. If the mold magnification ratio is incorrect, the material will relax and rebound unevenly, leading to frequent shrinkage marks. This can be resolved by precisely adjusting the dimensions of the mold head and calibrator.

5. Inappropriate height difference in the multi-segment calibrator of the Window Sill Extrusion Mould easily causes shrinkage marks during high-speed production.

The window sill shaping calibrator adopts a three-segment structure, and the height difference between the three segments directly determines the shaping shrinkage rhythm. Defects are not obvious at low production speeds, but surface shrinkage marks are easily exposed when production speeds are increased. The industry-optimal process standard is: the height difference between the first, second, and third sections of the calibrator should be controlled within 0.06–0.1 mm to ensure uniform segmented shrinkage and gradual shaping. Disordered height differences can lead to stress concentration and uneven localized shrinkage, requiring engineers to specifically adjust the calibrator dimensions.

6. Bending and residual stress during the splitting of wide sheet metal can cause secondary defects.

600mm wide Window Sill Extrusion Mould are often split online into two 300mm finished pieces. If the finished pieces bend outwards to both sides, it indicates excessive resistance on both sides of the calibrator. The sheet metal is forcibly stretched in the middle, and shaping is hindered on both sides, preventing the release of internal stress. This not only causes bending deformation but also results in hidden shrinkage marks. Professional engineers must adjust the calibrator resistance and eliminate production stress.

Our company has been deeply involved in the extrusion mold industry for 27 years, focusing on the R&D and manufacturing of various PVC profiles and Window Sill Extrusion Mould. We have an experienced engineering team that can accurately solve various mass production defects, mold compatibility issues, and process debugging problems. Customers can contact AONA EXTRUSION TOOLING at any time for any difficulties encountered during production, and we will provide professional technical support throughout the process.