Repair plastic parts broken by cracks or ruptures by welding instead of throwing away the pieces.

Resin parts used in various parts of the car body, including exterior parts, are not easily damaged by slight impacts or bending, but cracks or ruptures can occur if force beyond the elastic deformation range is applied. Replacing expensive parts is a pain in the wallet, but in the case of out-of-print cars, replacement parts are sometimes no longer available. In such cases, try welding with heat. Even if it is difficult to get the same look as a new one, it is possible to use it again if the function can be restored.

Resin parts that can be broken even by a light force of pushing and pulling

Resin parts are widely used not only on scooters, which are covered entirely with plastic, but also on the exterior of sport bikes, such as cowls and tank covers. These parts are cleverly designed to improve design and texture, and often require careful work to avoid breaking nails and pins when disassembling. When new, these resin parts can be bent and twisted slightly, but their flexibility decreases over time. The pins that are inserted into rubber grommets, which are often used to secure sight covers and other components, can also break off during removal over time. One of the causes is the hardening of the rubber of the grommet, but it is an unavoidable problem that resin parts for motorcycles, which are often exposed to ultraviolet rays outdoors, become vulnerable to deformation and impact.

For a successful weld repair, it is important not to discard even the dislodged pieces

Typical examples of reduced flexibility and brittleness are broken or cracked nails at panel joints of cowls and screw hole flange areas. Both are difficult to strengthen due to the fine shape and thin thickness of the material, and are more likely to break due to the addition of aging factors. Even if excessive force is not applied, cracks and breaks can occur. ABS, PE, and PP resins, which are often used for motorcycles, can be melted by applying heat, and welding can be used to melt and join the damaged area. In such cases, welding, which melts the base material, is more advantageous. There are two types of welding repairs for plastic parts. One is to butt-weld the damaged pieces together, and the other is to fabricate a new part using the same resin material and welding rod. If the shape of the part is complex, such as a cowl or side cover, the former method is recommended because it is easier to reproduce the shape. In the case of the air cleaner case cover fixing part presented here, the flange part of the screw hole is slender to begin with, and considering the fact that it has been manufactured for more than 30 years, it is no wonder it is damaged. The air cleaner case cover is located under the seat and is not usually visible to the public, so as long as the cover does not float when the screws are tightened, it does not matter much what shape it is. Fortunately, however, in this case, a torn piece was pressed against the washer, so we reused it to make the repair. The reason why we decided to reuse even a small piece is that the same material can be welded more reliably.

Add reinforcement to areas of low strength.

If the welded area is large or the volume is large, deformation due to heat applied during welding is acceptable, but if the joint surface is small, the heating during welding may change the shape of the part. Also, even though there is an advantage over bonding, if the area of the welding part is small, it will be difficult to ensure strength. In such cases, it is recommended to use a reinforcing material in conjunction with the joint. Specifically, by melting a heated metal pin into the joint, physical strength is increased compared to welding by melting with a soldering iron or the like. Stainless steel pins included in resin part repair kits are available as reinforcement materials, but depending on the repaired part, heating stainless steel wire or mesh with an outdoor gas torch or similar tool and melting it into the joint may also be effective. In either case, the joint has the advantage of being stronger and more durable than welding, which only melts the adhesive or base material.

The right amount of welding is important to achieve strength without deformation.

Welding plastic parts is quite effective as a repair method and can be used to securely join cracked or broken parts. However, there are several key points to maximize the effectiveness of welding. The most important is to "apply sufficient heat to the welded area while not deforming the resin. When welding instead of bonding, the joint must be melted. This is because the strength of the welded area is only achieved by melting and integrating the cracked or fractured surface. However, if the welding is done too carefully so that the effect of the heat does not show on the surface, the heat will not be transferred sufficiently, the weld will not be strong enough, and the weld may be damaged again with the slightest force. The same applies to the use of stainless steel pins, which can easily peel off from the weld if they are visible. However, be careful not to be too greedy, as the resin can be deformed by heat and the pins can poke through or the pin shape can become visible through the resin. When repairing a scratch caused by a fall and assuming repainting, it is best to weld from both the front and back sides and correct with putty. However, if there are no abrasions and the original paint is utilized to repair the crack, the key to the finished product is to weld so that the surface is not affected by heat distortion or deformation. Ideally, tests should be conducted to establish conditions, as the degree of melting of the material due to heating depends on the thickness of the part and the heat source. In reality, however, the location of damage and repair conditions will vary from case to case, and in most cases, the welding process will be performed on a one-shot basis without testing. To reduce the risk of failure in such a situation, it is essential to work while carefully observing the melting process of the welding part. Neither a soldering iron nor a resin repair kit will immediately start melting as soon as it is applied to the resin at room temperature. On the other hand, once the melting point is reached by heating, the heat spreads widely and melting begins. Especially for small parts, it is important to determine when melting begins, as the heat can build up and cause the part to turn into a sludge at once. The same is true for pins and mesh reinforcement. If a pin you press against begins to melt, the area around the pin will begin to melt as well.

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