Discussion on Coating Technology of Truck Chassis Parts

Authors of this article: Zhou Quan, Yu Ruisheng, Meng Dongyang, Gong Jian

Source of this article: Issue 4 of "Coating Industry" in 2021

Recently, thanks to multiple favorable factors such as the upgrade of emission regulations, stricter overload management, and the pull of infrastructure investment, the domestic truck market has been booming both in production and sales

This article briefly analyzes the main chassis parts of trucks such as frame, wheels, axles and leaf springs from the aspects of product characteristics, coating quality requirements, coating technology, coating materials, etc.

1 Frame

The frame is the whole vehicle frame of a truck.

Domestic trucks generally adopt the overall coating process of the assembly after the frame is assembled, and basically use the cathodic electrophoresis single coating system

In recent years, with reference to the mature technology of foreign car companies, some domestic frame production lines have adopted the process of separately coating the parts and then proceeding to the frame assembly process, which can effectively solve the frame gaps, interlayers, and interlayers while ensuring the coating performance.

2 wheels

Truck wheels are important security components.

The "cathodic electrophoresis + topcoat" process is commonly used in the coating of steel wheels of domestic trucks

In order to reduce the cost of painting, many steel wheel painting lines have adopted the "underside-in-one" cathodic electrophoretic coating, and some of the topcoat process has been eliminated

3 axle

Truck axles are very important chassis parts, which are responsible for transmission and load-bearing functions.

The assembly painting process is generally used in the painting of domestic truck axle assemblies

In order to improve the spraying efficiency and ensure the spraying quality, the large-volume vehicle axle assembly coating line adopts a pile-type spraying robot, and a high-pressure airless or mixed-air spraying process

Due to the large variety of axle assembly parts, it is necessary to strengthen the quality control of the primers and parts, and choose primers with excellent anti-corrosion performance; after the axle assembly is assembled, the parts that are difficult to be painted or cannot be painted are required.

4 Leaf spring

Leaf springs are typical and special automobile chassis parts.
They are subjected to high-frequency reciprocating motion during vehicle driving, and play an important role in cushioning and damping.
They play an important role in the stability and safety of vehicles.
They are the suspension elasticity widely used in trucks.
The components are divided into multiple leaf springs and few leaf springs
.
Some data show that the early corrosion of the leaf spring caused by the coating defect, the rust point will become the new fatigue source of the leaf spring, thereby affecting the fatigue life of the leaf spring
.
The coating of leaf spring is required to have good anti-corrosion performance.
For example, some manufacturers require the coating to be resistant to neutral salt spray for ≥120 h, and some manufacturers require the coating to be resistant to neutral salt spray for ≥240 h
.

In order to improve strength and fatigue life, leaf springs require stress shot peening, but some domestic manufacturers only perform stress shot peening on one side (concave surface).
The other side (convex) of the leaf spring has oxide scale to varying degrees, which seriously affects Coating adhesion and corrosion resistance
.
It is recommended to adopt the "general shot peening + stress shot peening" process, which can not only remove the oxide scale, but also meet the product characteristics requirements
.
Since the leaf spring is a superimposed structure, the cracks are prone to early corrosion.
The leaf spring should be coated with a single piece (cathodic electrophoresis or painting), and the leaf spring assembly shall be painted or touched up after assembly
.
The leaf spring has a large heat capacity.
It is recommended to use low-temperature curing cathodic electrophoretic coatings.
Cathodic electrophoretic coatings with curing temperatures as low as 150 ℃ have been produced and applied.
The selection of blocked isocyanate crosslinkers that can be deblocked at low temperature and the introduction of composite catalytic systems are new The key technology of electrophoretic coating development
.
The leaf spring assembly that is assembled after the single leaf spring electrophoresis is painted with top coat.
It is recommended to use a coating with both anti-corrosion and weather resistance
.
The leaf spring monolithic spray paint should use anti-corrosion primer, and the assembled leaf spring assembly should be sprayed with the top coat, and the coating with both anti-corrosion and weather resistance should be used.
It is recommended to use low-temperature and quick-drying water-based anti-corrosion paint and "underside in one" "Type water-based anticorrosive coating
.

5 Conclusion

The coating of chassis parts is a relatively weak link in the coating of domestic trucks
.
The improvement of the coating quality of chassis parts has always been one of the main contents of the improvement of coating quality .
With the continuous progress of coating materials and processes, green coating technologies represented by water-based coatings, high-solid coatings and powder coatings are increasingly being applied to the coating production of various chassis parts
.
More attention needs to be paid to the surface quality and pre-treatment quality of various substrates of chassis parts
.
While the coating of chassis parts meets the requirements of corrosion resistance and weather resistance, it is also necessary to consider the improvement of the overall protection and decoration of the vehicle chassis
.
For some parts of chassis parts that are difficult to be coated and protected, such as cavity structure parts, assembly bonding surfaces, sports connection surfaces, etc.
, how to carry out effective surface protection still needs to be studied in depth
.