The automobile body is welded by several steel plates. The existence of welds is inevitable. The sealability of the welds is directly related to the quality of the automobile body and the corrosion resistance. It is an important indicator of the technical performance of the vehicle. In automobile manufacturing, if the gap at the joint of sheet metal parts is not sealed by effective measures, water leakage, ventilation and dust leakage will occur in the running of automobiles, which may cause serious corrosion of the steel plate at the weld seam, make the steel plate perforate prematurely and accelerate the scrapping of vehicles. Spot welding sealant is a common sealant used in automobile industry.

 

Spot welding sealant used in automobile body-in-white production requires good construction technicality and thixotropy, which can ensure sealing performance. After pre-treatment of post-sequence painting process, it can not be washed out and electrophoretic solution can not be polluted. Spot welding sealant can not contain silicone substances. Trace silicone resin may cause harm to the quality of electrophoretic paint and topcoat. It can not affect the strength of spot welding. The spot welding glue does not decompose into toxic gases or can cause metal corrosion during welding.

 

In the manufacturing process of automobile body-in-white, the combination of the outer panel of automobile body-in-white and the reinforcing beam is usually assembled by welding method. The combination of the outer panel of automobile door and the reinforcing beam, the reinforcing beam of cab roof, the reinforcing beam of engine cover and the reinforcing beam of luggage box cover adopts welding method. Because there is a certain gap between the cover plate and the reinforcing beam, vibration may occur during driving. Noise is generated dynamically, and the solder joints on the cover plate seriously destroy the appearance smoothness. In order to overcome the above shortcomings, the anti-vibration adhesive can be coated on the stamping sheet and the reinforced beam structure before welding. After heating and curing by the paint drying equipment, the adhesive layer has a high bonding strength. After thermal expansion, the reinforced beam and the cover plate will be closely integrated to reduce or completely take. By eliminating the combined solder joints, the aesthetics of the body appearance can be improved, and the vibration and noise in driving can be reduced.

 

Vibration Absorbing Adhesive

 

Vibration-absorbing adhesives are usually liquid paste, and some are tape-like. In the process of body welding, the adhesive (or tape) is applied to the reinforced beam, and then combined welding. Similar to spot welding sealant, the expandable anti-vibration adhesive does not need to be adjusted by heating and solidification alone. It usually expands and solidifies in the drying oven of electrophoretic coating, so its application conditions and requirements are the same as spot welding sealant.

 

Body creeping process

 

There are few kinds of adhesive sealants used in the painting process, but they are the largest type used in automobiles. There are mainly sealants for welding seams and stone-resistant coatings (chassis protective glue). The base materials are PVC plastic sol. Although they have different emphasis on performance, both require mechanical coating or spraying through high-pressure glue-coating equipment.

 

Weld sealant

 

Weld sealant is mainly used for sealant coated on welding seam after body welding. It plays the role of sealing leak-proof, enhancing rust-proof ability and filling welding seam, and increasing the aesthetics of car body. Generally, weld sealant is required to have outstanding thixotropy. It can keep edges and corners when stacking a certain thickness without flowing. After heating and plasticizing, the sealant layer is elastic, non-cracking and smooth in appearance. It can not produce discoloration phenomenon in middle coating and top paint. Weld sealant plays a vital role in automobile sealing, leak-proof and rust-proof.

 

Stone-proof coating

 

Stone-proof coating is a kind of sealant sprayed on automobile chassis to improve its corrosion resistance and prolong its service life. In the painting process, a kind of PVC plastic sol with high adhesion and elasticity is sprayed on the automobile chassis several times to form a protective layer about 2 mm thick, which can be used to cushion the strong impact of various objects such as sand and stone on the chassis during the high-speed driving process of automobiles. It can also achieve the functions of anti-corrosion, anti-rust and stone-strike, especially the strong corrosion of rainwater, snow water and snow melting agent. Corrosion, stone-proof coating is indispensable. In addition, it can also help to reduce the noise in the car and improve the comfort of passengers, which has been widely used by automobile manufacturers.

 

Now some cars have been sprayed with PVC plastic sol before they leave the factory. The sprayed chassis has a layer of plastic sticking to the bottom of the car. It feels flexible by hand. Vehicles that have not been sprayed can be considered for chassis sealing. That is to say, PVC plastic sol is sprayed on the bottoms of the vehicles that have been manufactured, and the same effect can be achieved when the process and materials meet the requirements.

 

Finger pressure sealant

 

In the painting process, finger pressure sealant is used in addition to the bonding sealant mentioned above. It is used for finger daubing and compaction, mainly used for the sealing of large gap, process hole and the modification of bump and uneven place after body welding and assembling.

 

Finger pressure sealant requires non-toxic, odorless, non-sticky construction process, good adhesion with steel plate, curing together in the paint drying process, no flow and shrinkage in the drying process, and good adhesion with seals. This material is widely used in buses, off-road vehicles and heavy trucks.

 

The adhesives and sealants used in the automotive body-in-white manufacturing industry are quite different from those used in other fields, mainly in terms of the conditions and characteristics of use in the process of automotive body-in-white manufacturing.

 

The performance requirements for adhesives and sealants are as follows:

 

A. Fully meet the requirements of automotive materials. Maintain the work undertaken throughout the maintenance and overhaul mileage or expected service life.

 

B. It has good cold resistance and heat resistance. In order to meet the needs of the vehicle in different climatic conditions and the use of parts of the test.