In blow molding production, product deformation is a common problem, especially when manufacturing large products such as water tanks, chemical drums, pallets and road barriers.
Sometimes the product looks perfect when it comes out of the mold, but several minutes later, it starts to bend, sink or lose its original shape.
From our experience, this is usually not caused by one single problem. Cooling, wall thickness, mold temperature, material distribution and demolding time all need to be considered.
5 Common Reasons for Product Deformation
1. Insufficient Cooling
Large blow molded products contain a lot of heat after molding. If the product is removed too early, the outside may look hard while the inside is still soft. Continued cooling after demolding can then cause shrinkage and deformation.
2. Uneven Wall Thickness
If some areas are too thick while others are too thin, different sections cool and shrink at different speeds. This can lead to warping, weak areas or dimensional changes.
For large hollow products, accurate parison control is therefore very important. Our machines can be equipped with a MOOG 200-point parison control system to help control wall thickness in different areas of the product.
3. Uneven Mold Temperature
A mold does not always cool evenly. Poor water flow or differences in cooling efficiency can make one part of the product solidify faster than another, resulting in uneven shrinkage.
4. Poor Material Distribution
Product weight is not the only thing that matters. A 1,000L water tank, for example, may need more material around the bottom, corners and stress-bearing areas. Proper material distribution is important for both strength and shape stability.
5. Demolding Too Early
Reducing cooling time can increase production speed, but if the product has not reached sufficient rigidity, deformation may occur after demolding.
What Do We Check First?
| Problem | Possible Result |
| Insufficient cooling | Deformation after cooling |
| Uneven wall thickness | Warping or weak points |
| Uneven mold temperature | Uneven shrinkage |
| Poor material distribution | Structural deformation |
| Early demolding | Shape changes |
Our Approach at SHANDONG GREAT MACHINERY
When we design large blow molding machines, we do not focus only on machine capacity or production speed.
We pay attention to the complete molding process, including stable extrusion, wall thickness control, cooling, mold matching and machine stability. (https://www.blowingmachinery.com/about-us/)
For us, producing one good sample is not enough. The real test is whether the machine can continuously produce consistent products over hundreds or thousands of cycles.
If your blow molded products are deforming after demolding, don’t immediately blame the material. Check the entire molding process first.
At SHANDONG GREAT MACHINERY, we provide large and customized blow molding solutions for water tanks, chemical containers, pallets, road barriers and other large hollow products.