Application of Double-wall Heat-shrinkable tube in Automotive Oil Pipe

- May 23, 2019-

The use of double-wall heat-shrinkable pipes in automobiles is a new material accompanied by the improvement of anti-corrosion requirements of automobile brake oil pipes. It has entered China in the early 1990s and has been widely used in recent years. Especially in the current small cars, with the increasing installation of high-power engines, ABS and power steering, the arrangement of brake tubing is becoming more and more complex. There are often interference problems between tubing and related parts. Double-wall heat-shrinkable tubing provides reliable protection for tubing. Next, we will discuss the protective effect of double-wall heat-shrinkable tube in automobile brake system and fuel system. The quality requirement of heat shrinkable tube is also analyzed.

Previously, automobile brake system and fuel system were often protected by sand and stone impact parts and easily rubbed parts. Generally, rubber sheath or spring were used to protect the automobile brake system from corrosion, but there are many disadvantages between the two methods.

Rubber sheath protection, because of the gap between rubber sheath and tubing of about 0.5mm, mud is easy to penetrate into the gap between them, and the mud penetrating between them is not easy to dry, which on the contrary exacerbates the corrosion of tubing surface, especially in the northern winter when salt water is often sprayed to make this problem more prominent.

Spring operation protection can prevent the impact of gravel, but it can cause spring friction on the surface of tubing, which has occurred before. Nowadays, many oil pipes are coated with organic coatings (PVC/PVF/epoxy resin, etc.) and no protective springs are allowed at all.

Therefore, the two kinds of surface protection measures for oil pipelines appealed have long been eliminated in foreign countries. The process of heat shrinkage pipe is simple, and it can be heated and contracted by ordinary heating boiler or industrial electric hair dryer. Moreover, the price of the heat shrinkable tube is relatively low, and it will not increase the cost of the product too much.

Performance of double-wall heat-shrinkable tubes:

The characteristics of automotive heat shrinkable pipe are: heat shrinkage, double wall, double plastic pipe with hot melt adhesive.

The double-walled heat-shrinkable tube is divided into two layers, the outer layer is a mixture of low density high pressure polyethylene and ethylene-vinyl acetate copolymer (EVA), and the inner layer is a very thin adhesive hot-melt sealing resin. When the double-wall heat-shrinkable tube is inserted into the surface of the tubing under the condition that the diameter of the tubing is larger than the diameter of the tubing, after positioning and reheating, the double-wall heat-shrinkable tube will shrink to the predetermined size. Through the hot melt glue of the inner layer, the heat-shrinkable tube and the tubing are closely connected without any gap in the middle. This tubing protection method can greatly improve the service life of tubing.

Use of double-wall heat-shrinkable tubes:

Initially, when there was only one kind of heat-shrinkable tube, it was mainly used in electrical equipment and refrigeration equipment as the protection of electrical joints. Later, Raychem (Rycan) Company of the United States, the production department dedicated to the automotive industry, double-walled heat shrinkable tubes. Because it not only provides excellent anti-corrosion performance, but also provides the protection of friction parts with related parts, it is especially suitable for compact small cars, so it is widely used in Japanese and Korean models. Especially in the chassis of vehicles, double-wall heat-shrinkable pipes are installed to effectively prevent the corrosion of brake oil pipes caused by sand and mud.

In addition, due to the high hardness and wear resistance of the double-layer heat shrinkable tube, a protective layer is formed outside the tubing, which avoids the direct friction between the tube and other parts. Therefore, many foreign automobile companies have stipulated that interference between parts is allowed at the position where the double-layer heat shrinkable tube is installed. Nowadays, there are more and more small and high-power engines, ABS and power steering on the market. The narrow space is also more crowded, and the arrangement of brake tubing is becoming more and more complex. There are often interference problems between tubing and related parts. Especially, it is difficult to ensure that there are enough tubing bundled together with six tubing in the "ABS" part. Clearance, resulting in collision and friction between oil pipes, is indeed a great potential safety hazard. The application of double-wall heat-shrinkable pipes makes this problem solved accordingly.

Quality of double-wall heat shrinkable tube:

Because the double-wall heat-shrinkable tube plays such an important role, the quality of the double-wall heat-shrinkable tube is very important. The use of fake and inferior heat-shrinkable tube will cause fatal consequences. For example, there is a temperature interval between the heating shrinkage temperature of high quality heat shrinkable tubes and the softening melting temperature of heat shrinkable tubes. Therefore, the heat shrinkable tubes can maintain a good shape during the heating and shrinkage process. With the movement of the heating area, the air inside the heat shrinkable tubes can be emptied. But the inferior heat shrinkage pipe has softened and melted at the same time of heating to the shrinkage temperature, so air is often enclosed in the heat shrinkage pipe, which is manifested as a lump on the surface of the heat shrinkage pipe. In order to eliminate bubbles, it is necessary to use steel needle to prick the eye when the heat shrinkage pipe is in the softening state, because the shrinkage of the heat shrinkage pipe during cooling process, these needle eyes form many scars and marks on the surface of the heat shrinkage pipe. Because of the void, the inferior heat-shrinkable pipe can not protect the oil pipe.

In addition, qualified heat-shrinkable pipes only shrink in the radial direction when they are heated and contracted, and the axial direction is basically not contracted. The consistency of processed products is very good, while inferior heat-shrinkable pipes not only shrink greatly in the axial direction, but also extend in the axial direction. The processed heat-shrinkable pipes have uneven layers. In assembly line, it often happens that the tubing clips can not be installed, which is often the reason for the use of inferior heat shrinkable tubes. In this case, the measures of cutting the heat-shrinkable pipe with the blade extension are often adopted. The surface problem is solved, but the damage to the oil pipe is more serious in fact, because the organic coating of the oil pipe will be scratched during the operation, which will cause the complete damage of the oil pipe coating. Therefore, the quality of heat shrinkable tube is very important.

Development of double-wall heat-shrinkable tubes:

Due to the wide application of double-wall heat-shrinkable tubes in automobile oil pipes, a new generation of heat-shrinkable pipes, PC pipes, has been developed. The polyolefin material is directly extruded outside the organic coating of the tubing to achieve the purpose of tight bonding, which reduces the cost and processing procedures. However, this kind of PC pipe has too many limitations. It is suitable for the tubing with open-body coated heat-shrinkable pipe and not suitable for the product with partial protective casing. Therefore, the double-wall heat-shrinkable pipe will continue with the development of automobile industry.