Automobile using double-walled heat shrinkable pipe is a new material which comes into being with the improvement of the anticorrosion requirement of automobile brake tubing, which entered our country in the early 90, and has only been widely used in recent years. Especially in the current small car plus high-power engine and the increase of ABS and booster steering, is the arrangement of brake tubing more and more complex, often appear between the tubing and between the tubing and related parts interference problem, double-walled heat shrinkable pipe for the tubing provides a reliable protection. Below we discuss the protective effect of double-walled heat shrinkable tube in automobile braking system and fuel system. And the quality requirements of the Heat shrinkable pipe are analyzed.

In the past, automobile braking system and fuel system were often protected by the impact site of sandstone and the friction parts of related parts, generally using rubber sheath or spring protection and anticorrosion, but the drawbacks between the two methods are very large.

Rubber sheath protection, due to the rubber sheath and tubing between the existence of about 0.5mm gap, muddy water is easy to penetrate the gap between this, and infiltration between this mud water is not easy to dry, which in turn exacerbates the corrosion of the tubing surface, especially in the northern winter when the frequent spraying of salt water to make this problem more prominent.

Although spring operation protection can prevent the impact of gravel, but can cause spring friction on the surface of the tubing, there have been problems before the tubing is worn. Many tubing are now made of organic coatings (PVC/PVF/epoxy resins, etc.) and are not allowed to be fitted with protective springs at all.

Therefore, the appeal of two kinds of tubing surface protection measures in foreign countries has long been eliminated. Thermal shrinkage pipe processing is simple, can be through ordinary heating boiler or industrial hair dryer, such as heating shrinkage. And the price of heat shrinkable pipe is relatively low, will not increase the cost of products too much.

Performance of double-walled heat shrinkable tubes:

The characteristics of automobile special heat shrinkable pipe are: thermal shrinkage, double-layer wall, double-layer plastic tube with hot melt adhesive inside.

This double-walled heat shrinkable tube is divided into internal and external two layers, the outer layer is a mixture of low density high pressure polyethylene and ethylene-vinyl acetate co-polymer (EVA), the inner layer is very thin adhesive viscous strong hot-melt sealing resin. When the double-walled heat shrinkable tube is larger than the diameter of the tubing into the tubing surface, positioned and then heated, the double-walled heat shrinkable tube will shrink to a predetermined size, through the inner layer of hot melt glue, the heat shrinkable pipe and tubing tightly connected together, there is no gap between. This tubing protection method can greatly improve the service life of the tubing.

Use of double-walled heat shrinkable tubes:

Initially, the heat shrinkable tube is only a single-walled heat shrinkable tube, mainly used in electrical equipment and refrigeration equipment as the protection of electrical joints. Later, the United States Raychem (Rui Kan) company, the production office dedicated to the automotive industry double-walled heat shrinkable tube. Not only does it provide excellent antiseptic properties, but it also provides protection against the friction parts of the relevant parts, so it is especially suitable for compact small cars, so it is used in a large number of Japanese models in Japan and Korea. In particular, double-walled heat shrinkable tubes have been installed in the chassis of the vehicle, effectively preventing the corrosion of the brake tubing by gravel and muddy water.

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 to avoid direct friction between the steel pipe and other parts, so many foreign car companies stipulate that the interference between parts is allowed in the part where the double-layer heat shrinkable tube is added. Now the market on the small installation of high-power engines and "ABS" and booster steering more and more, is the small space is also more crowded, brake tubing layout has become more and more complex, often between the tubing and between the tubing and related parts interference problems, especially the addition of "ABS" The area of 6 tubing bundled together is difficult to ensure that there is enough clearance between the tubing, resulting in bumps and frictions between the tubing, is indeed a great safety hazard, the application of double-walled heat shrinkable tube so that this problem is solved accordingly.

Quality of double-walled heat shrinkable tubes:

Because double-walled heat shrinkable tubes play Such an important role, the quality of double-walled heat shrinkable tubes is crucial, and the use of shoddy heat shrinkable tubes will have fatal consequences. For example, there is a temperature interval between the heating shrinkage temperature of a high-quality heat shrinkable tube and the softening melting temperature of the heat shrinkable tube, so that the heat shrinkable tube remains in a good shape during the heating shrinkage process, and the air inside the heat shrinkable tube can be emptied as the heating area moves. But the inferior heat shrinkable tube has softened and melted while heating to the shrinkage temperature, so there is often air enclosed in the heat shrinkable tube, manifested as the bumpy on the surface of the heat shrinkable tube, in order to eliminate the bubbles need to be in the hot shrinkage tube in a softening state when the steel needle eye release gas, because of the shrinkage of the heat shrinkable tube during cooling, These needles form many scars and voids on the surface of the heat shrinkable tube, so the inferior heat shrinkable tube does not reach the protective effect on the tubing.

In addition, qualified heat shrinkable pipe in the heating shrinkage is only in the radial shrinkage, axial basic does not shrink, after processing the finished product consistency is very good, and poor quality heat shrinkable pipe not only axial shrinkage is very large, and even axial elongation, after processing the finished product heat shrinkage tube level is not aligned. In the assembly line often occurs when the tubing clip is not loaded with the phenomenon is often the use of inferior heat shrinkable pipe reasons. In this case, often take the blade elongation out of the heat shrinkable pipe cut off the measures, the surface of the problem solved, in fact, the damage to the tubing is greater, because in the course of operation there will be tubing organic coating scratches, resulting in complete damage to the tubing coating. Therefore, the quality of the heat shrinkable tube is very important.

Development of double-walled heat shrinkable tubes:

Because of the common application of double-walled heat shrinkable pipe in automobile tubing, a new generation of heat shrinkable pipe-PC tube has been developed. The polyolefin material will be squeezed directly outside the organic coating of the tubing, so that it can achieve the purpose of close bonding, which not only reduces the cost and reduces the processing process. However, the limitations of this PC tube are too many, is suitable for the full package of heat shrinkable pipe tubing, not suitable for local installation of protective casing products, so double-walled heat shrinkable pipe will continue to accompany the development of the automotive industry.

双壁热缩管在汽车油管上的应用

汽车使用双壁热缩管是伴随着汽车制动油管防腐要求的提高而产生的新材料，在90年代初就进入了我国，近几年才被普遍应用。特别在当前小型车加装大功率发动机以及ABS和助力转向的增多，是的制动油管的布置越来越复杂，常常出现油管之间以及油管与相关零件之间的干涉问题，双壁热缩管为油管提供了可靠的保护。下面我们就双壁热缩管在汽车制动系统和燃油系统的保护作用进行探讨。并且对热缩管的质量要求做出分析。

以前汽车制动系统和燃油系统经常受沙石冲击部位以及易与相关零件摩擦部位的防护，一般都是采用橡胶护套或者是弹簧保护防腐，但是在这两种方法之间的弊病很大。

橡胶护套保护，由于橡胶护套和油管之间存在的0.5mm左右的间隙，泥水很容易深入这之间的缝隙，而且渗入这之间的泥水不容易干燥，这反而加剧了对油管表面的腐蚀，特别是在北方的冬季经常喷洒盐水的情况下使这一问题更加突出。

   弹簧作业保护虽然可以防止碎石的冲击，但是可造成弹簧对油管表面的摩擦，以前就有发生过油管被磨穿的问题。现在许多油管都采用有机涂层（PVC/PVF/环氧树脂等），根本不允许加装保护弹簧。

所以上诉两种油管表面防护措施在国外早已被淘汰。热缩管的加工简单，可以通过普通加热锅炉或者工业电吹风机等加热收缩。而且热缩管的价格比较低，不会过多的增加产品成本。

双壁热缩管的性能：

   汽车专用热缩管的特性为：热收缩、双层壁、内有热熔型胶粘剂的双层塑料管。

这种双壁热缩管分为内外两层，外层为低密度高压聚乙烯和乙烯-醋酸乙烯共聚合物（EVA）的混合物，内层是很薄胶黏性很强的热熔型密封树脂。当这种双壁热缩管以大于油管直径状态下套入油管表面， 定位后再加热，双壁热缩管便会收缩到预定尺寸，通过内层的热熔胶，把热缩管和油管紧密的连接在一起，中间没有任何间隙。这种油管保护方法，可使油管的使用寿命大大提高。

双壁热缩管的使用：

   最初热缩管只有单壁热缩管这一种的时候，主要是应用在电器设备和制冷设备上作为电气接头的保护。后来美国Raychem（瑞侃）公司，生产处专用于汽车行业的双壁热缩管。由于不仅提供了优良的防腐性能，还提供了与相关零件摩擦部位的防护，因此特别适用于结构紧凑的小型汽车，所以在日本和韩国的日系车型中被大量使用。特别是在车辆底盘部位都加装了双壁热缩管，有效的防止了砂石及泥水对制动油管的腐蚀。

   另外由于双层热缩管有较高的硬度和耐磨性能，在油管外面形成一种保护层，避免了钢管与其他零件的直接摩擦，因此许多国外的汽车公司都规定：在加装了双层热缩管的部位允许零件之间的干涉。现在市场上的小型加装大功率发动机以及“ABS”和助力转向的越来越多，是的狭小的空间也更加拥挤，制动油管的布置也变得越来越复杂，经常出现油管之间以及油管与相关零件之间的干涉问题，特别是加装了“ABS”部位6支油管捆绑在一起很难保证油管间有足够的间隙，由此造成油管之间的磕碰和摩擦，确实是极大的安全隐患、双壁热缩管的应用使这一问题得到相应的解决。

双壁热缩管的质量：

   由于双壁热缩管起到如此重要的作用，因此双壁热缩管的质量就至关重要，伪劣热缩管的使用将造成致命的后果。例如：优质热缩管的加热收缩温度与热缩管软化熔融温度之间有一段温度的区间，因此热缩管在加热收缩过程中任然保持较好的形态，随着加温区域的移动就可以将热缩管内部的空气排空。但是劣质热缩管在加热到收缩温度的同时已经软化熔融，因此经常有空气被封闭在热缩管中，表现为热缩管表面的疙疙瘩瘩，为了消除气泡就需要在热缩管处于软化状态的时候用钢针扎眼放气，因为热缩管冷却过程中的收缩，这些针眼在热缩管表面形成许多疤痕和空洞，因此劣质热缩管达不到对油管的保护作用。

   另外合格的热缩管在加热收缩时只是在径向收缩，轴向基本不收缩，加工后成品一致性很好，而劣质热缩管不仅轴向收缩很大，甚至还有轴向伸长的，加工后的成品热缩管层次不齐。在装配线时经常发生油管卡子装不上的现象往往就是使用了劣质热缩管的原因。在这种情况下往往采取用刀片伸长出的热缩管切掉的措施，表面上问题解决了，实际上对油管的伤害更大，因为在操作过程中会有油管的有机涂层刮伤，造成油管涂层的完全破坏。因此热缩管的质量至关重要。

双壁热缩管的发展：

   由于双壁热缩管在汽车油管上的普遍应用，有发展出新一代热缩管—PC管。即将聚烯烃材料直接挤压在油管的有机涂层外面，使其达到紧密结合的目的，这样既降低了成本有减少了加工程序。但是这种PC管的局限性太多，是适用于通体包覆热缩管的油管，不适于局部加装保护套管的产品，因此双壁热缩管还将伴随着汽车工业发展继续下去。