How to apply surface coating to round rods?

How to apply surface coating to round rods?

In the field of industrial production and machinery manufacturing, round bars are widely used as basic components. However, round bars often face problems such as wear, corrosion, and oxidation during use, which not only affect their appearance, but also reduce their performance and service life. Surface coating technology can effectively enhance the corrosion resistance, wear resistance, and oxidation resistance of round bars by covering the surface of the round bars with a layer of material with specific properties, becoming an important means to improve the comprehensive performance of round bars. From preliminary preparation to coating construction, and then to post-processing, each link has a key impact on the coating quality. The implementation process of round bar surface coating will be introduced in detail below.

1. Surface pretreatment: laying a solid foundation for coating

Surface pretreatment is the key first step for the successful coating of round rods. Its purpose is to remove surface impurities, oil stains, scale, etc., improve surface roughness and cleanliness, and enhance the bonding strength between the coating and the substrate. First, degreasing treatment is carried out, which can be done by organic solvent cleaning, alkaline degreasing or emulsified degreasing. For round rods with light oil stains, the oil stains can be removed by wiping the surface with organic solvents such as gasoline and alcohol; for those with heavy oil stains, alkaline degreasing agents are required to remove the oil by using the principle of saponification reaction between alkaline substances and oils. For example, before coating round rods of automobile engine shafts, alkaline degreasing processes are usually used to ensure that there is no oil residue on the surface.

After degreasing, rust and scale removal are required. Common methods include mechanical rust removal (such as sandblasting and shot blasting), chemical rust removal (pickling) and electrochemical rust removal. Sandblasting and shot blasting use high-speed sand or projectiles to hit the surface of the round bar to remove rust and scale, while also improving surface roughness and enhancing coating adhesion; pickling uses acid solution to react chemically with rust and scale to dissolve and remove them. For example, in the coating treatment of round steel for construction, sandblasting is more commonly used, which can not only effectively clean the surface, but also form a suitable surface roughness, creating good conditions for subsequent coating construction.

2. Coating material selection: matching usage requirements

According to the use environment and performance requirements of the round rod, it is very important to choose the coating material reasonably. If the round rod is used in a humid, acidic, alkaline and other corrosive environment, such as parts in marine engineering, epoxy resin coating, polyurethane coating or zinc-based coating can be selected. Epoxy resin coating has excellent chemical corrosion resistance and adhesion, and can effectively resist the erosion of various chemical media; polyurethane coating has good wear resistance and weather resistance, and is suitable for round rods used outdoors. Zinc-based coating uses the sacrificial anode protection principle. Even if the coating is partially damaged, the zinc layer can still protect the substrate from corrosion. It is widely used in the anti-corrosion of steel structure round rods.

For round bars that need to improve wear resistance, such as shaft parts in mechanical transmission, ceramic coatings, tungsten carbide coatings, etc. can be used. Ceramic coatings have high hardness and good wear resistance, which can significantly reduce the wear rate of the round bar surface; tungsten carbide coatings have good toughness while maintaining high hardness, and are suitable for working conditions with high loads and impacts. In addition, if the round bar needs to be used in a high temperature environment, such as parts in a boiler, high-temperature resistant alumina coatings, metal ceramic coatings, etc. can be selected. These coatings can maintain stable performance at high temperatures and prevent the round bar from being damaged by high-temperature oxidation.

3. Coating process implementation: precise control to ensure quality

There are many different processes for coating the surface of round bars, including spraying, electroplating, chemical plating, hot-dip plating, etc. Each process has its own characteristics and scope of application. Spraying processes include powder spraying and liquid spraying. The paint is evenly sprayed onto the surface of the round bar through a spray gun to form a coating. Powder spraying has the advantages of uniform coating thickness, strong adhesion, and environmental protection, and is suitable for round bars of various shapes; liquid spraying is flexible in operation and can adjust the coating thickness according to needs, but it is slightly inferior in coating uniformity. For example, in the surface treatment of furniture hardware round bars, powder spraying can quickly and efficiently form a colorful and wear-resistant coating.

Electroplating is the process of depositing a layer of metal or alloy coating on the surface of a round bar through the principle of electrolysis. Electroplating can improve the corrosion resistance, wear resistance and aesthetics of the round bar. Common methods include galvanizing, nickel plating, and chrome plating. Galvanizing can effectively prevent the round bar from rusting, while nickel plating and chrome plating can improve the surface hardness and finish. Chemical plating does not require an external power supply and uses a chemical reduction reaction to deposit a coating on the surface of the round bar. It has the advantages of uniform coating and the ability to plate complex shapes. It is often used for surface treatment of round bars with high precision requirements. Hot-dip plating is to immerse the round bar in molten metal to form a layer of metal coating on its surface. Hot-dip galvanizing is a common method and is widely used in the corrosion protection of round steel in the construction, power and other industries.

4. Post-processing and quality inspection: ensuring coating performance

After the coating is applied, necessary post-treatment is required to improve the performance and stability of the coating. For some organic coatings, such as epoxy resin coatings and polyurethane coatings, curing treatment is usually required. Through heating or natural drying, the resin in the coating undergoes a cross-linking reaction to form a dense polymer film, thereby improving the hardness, wear resistance and corrosion resistance of the coating. For metal coatings, such as electroplating and hot-dip coatings, passivation treatment can be performed to form a passivation film on the surface of the coating to further enhance its corrosion resistance.

Quality inspection is the key link to ensure the quality of round bar surface coating. Through appearance inspection, observe whether the coating surface is flat and uniform, and whether there are defects such as sagging, bubbles, and missing coating; use a thickness gauge to measure the coating thickness to ensure that it meets the design requirements; use the cross-cut test and pull-off method to test the adhesion of the coating and determine the bonding strength between the coating and the substrate; and simulate the actual use environment through salt spray test and wear resistance test to test the corrosion resistance and wear resistance of the coating. Only after strict inspection, the round bars with qualified quality can be put into use.

Round bar surface coating is a systematic and delicate work. From surface pretreatment, coating material selection, process implementation to post-processing and quality inspection, each link is closely linked and indispensable. Only by strictly controlling each link can we obtain a surface coating with excellent performance and meet the use requirements, providing a strong guarantee for the stable and reliable operation of round bars under different working conditions.