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Prefabricated Plastic Steel Directly Buried Insulation Pipes Common Problems and Solutions
Plastic-steel thermal insulation pipes have been widely used in many developed countries for several decades, delivering excellent energy-saving performance. In recent years, Chinese heating engineers have significantly advanced domestic pipeline technology by adopting and improving this cutting-edge method. The directly buried insulation pipe is created by tightly bonding a steel pipe for medium transmission, a high-density polyethylene outer sleeve, and a rigid polyurethane foam insulation layer located between the steel pipe and the outer sheath.
However, when using field foaming spray polyurethane, some common issues may arise. For instance:
One problem is that the polyurethane insulation pipe starts slowly, often occurring during colder months like autumn or winter, or in the early morning due to sudden temperature drops. To address this, it's recommended to raise both the ambient temperature and the temperature of the black material. Typically, the black material should be warmed up to 30–60°C, while the surrounding environment should reach 20–30°C.
On the other hand, if the polyurethane insulation pipe rises too quickly, this usually happens during warmer seasons such as spring or summer, or during midday construction when temperatures are high. To prevent this, the black material can be cooled with cold water or left to cool naturally at night, away from direct sunlight.
Another issue is that the foam inside the polyurethane insulation pipe may have low strength and soft bubbles. This typically results from an imbalance between the black and white materials. To fix this, the proportion of the black material can be slightly increased, ideally between 1:1 and 1:1.05. However, care must be taken not to increase it too much, as this can lead to brittle bubbles and negatively affect the overall performance of the foam.
To avoid these problems and ensure better quality, it’s advisable to use the factory-preset method when producing insulation pipes. This involves using a high-pressure foaming machine to inject rigid polyurethane foam liquid into the cavity formed between the outer sheaths in one go. This method is not only simpler to implement but also more efficient, easier to transport, and provides superior insulation performance.