Master Metal Surface Treatment: Heat to Paint Expertise

Surface treatment
This process aims to create a surface layer on the surface of the base material that is different from the base material in terms of properties, so as to meet the corrosion resistance, wear resistance, decoration or other specific functional requirements of the product. In the field of metal castings, our commonly used surface treatment methods include mechanical grinding, chemical treatment, surface heat treatment and spraying. Among them, surface heat treatment, as a key technology, has received particular attention. It austenitizes the surface of the steel by rapid heating and then quenches it, thereby significantly enhancing the performance of the surface of the part without changing its core structure. This process can be achieved by flame quenching or induction heating heat treatment, and the heat source can be selected from flames such as oxyacetylene or oxypropane, induced current, as well as lasers and electron beams.

Induction heating technology
The principle is to use alternating current to induce strong eddy currents on the surface of the workpiece, thereby achieving rapid heating of the workpiece surface. This method has a wide range of applications in the field of metal castings and can effectively meet the product's requirements for corrosion resistance, wear resistance and other specific functions.

Induction heating technology
It can be further divided into the following types:

High frequency induction heating: Its operating frequency range is 250-300KHz. This heating method can produce a hardened layer with a depth of 5-2mm.

Medium frequency induction heating: The frequency of this heating method is 2500-8000Hz, and the hardened layer depth can reach 2-10mm.

Power frequency induction heating: With a frequency of 50Hz, the hardened layer depth can reach 10-15mm.

In addition, there is flame heating, which uses acetylene flame to directly heat the surface of the workpiece. This method is low in cost, but the heating quality is relatively difficult to control.

Laser heating technology
Laser heating is the use of high energy density laser beams to quickly and accurately heat the surface of the workpiece. This method has high efficiency and excellent quality and is widely used in various industrial fields.

Laser surface strengthening technology
Laser surface strengthening is an important application of laser heating technology in the industrial field. It mainly includes laser phase change strengthening treatment, laser surface alloying treatment and laser cladding treatment. These methods can significantly improve the performance of the workpiece surface and extend its service life, thus meeting the needs of various harsh working environments.
Laser surface strengthening technology plays a key role in many fields, especially for parts that require local strengthening, such as punching dies, crankshafts, cams, camshafts, spline shafts, etc. In addition, precision instrument guides, high-speed steel tools, gears, and internal combustion engine cylinder liners also benefit from the strengthening treatment of this technology.
On the other hand, bluing and phosphating are also important means of metal surface strengthening.
The bluing process is to heat steel or steel parts to an appropriate temperature to form a blue or black oxide film in air-water vapor or chemicals. It is often used in the manufacturing process of precision instruments, optical instruments, tools, etc. Phosphating treatment is to immerse the workpiece in a phosphating solution to form a layer of water-insoluble crystalline phosphate conversion film through deposition, which is widely used in the fields of corrosion protection technology and metal cold deformation processing.
Chemical surface heat treatment
is also an important metal surface strengthening technology. It involves heating and keeping the workpiece in a specific medium so that the active atoms in the medium penetrate into the surface of the workpiece, thereby changing the chemical composition and organizational properties of the surface. Unlike surface quenching, chemical heat treatment can not only change the surface organization of steel, but also adjust its chemical composition to achieve the performance requirements of hard surface and tough inside. According to the different elements infiltrated, chemical heat treatment can be divided into carburizing, nitriding, multi-element co-diffusion and other elements infiltration. The process includes three basic steps: decomposition, absorption and diffusion.
Common chemical heat treatment methods include carburizing, nitriding (commonly known as nitriding), carbonitriding (commonly known as cyaniding and soft nitriding), etc. In addition, there are sulfurizing, boronizing, aluminizing, vanadiumizing, chromizing, etc. However, bluing and phosphating do not belong to the category of chemical heat treatment, they are more inclined to surface treatment technology.

When comparing the two chemical heat treatment methods of carburizing and nitriding, we can find their respective purposes and characteristics. Carburizing aims to improve the hardness, wear resistance and fatigue strength of the workpiece surface while maintaining good toughness in its core. It is often used for workpieces made of low carbon steel. Nitriding has a similar purpose and can also enhance the corrosion resistance of the workpiece. It is suitable for medium carbon steel containing elements such as Cr, Mo, Al, Ti, and V.

The common methods and temperature ranges of carburizing and nitriding are also different. Carburizing can be done by gas carburizing, solid carburizing or vacuum carburizing, and the temperature is usually between 900 and 950°C. Nitriding mainly uses gas nitriding or ion nitriding, and the temperature range is 500 to 570°C. In addition, the surface thickness of the two treatments is also different. Carburizing can generally reach a thickness of 5 to 2 mm, while nitriding does not exceed 6 to 7 mm.

Surface deformation strengthening
is also an important metal surface strengthening technology. It increases the hardness of the surface and produces a favorable residual compressive stress distribution by causing the steel part to undergo plastic deformation at room temperature. This process is simple and low-cost, and is an effective measure to improve the fatigue resistance of steel parts and extend their service life. Among them, shot peening is a typical surface deformation strengthening technology. It impacts the metal surface by ejecting a large number of high-speed projectiles, thereby causing plastic deformation of the surface and sub-surface layers to achieve a strengthening effect.
Application: Commonly used for parts with complex shapes, after grinding, electroplating and other processes.
Rolling treatment: The machined surface of the steel part is rolled by a freely rotating hardened steel roller to cause plastic deformation. This process can flatten the rough raised parts on the surface of the steel part, while forming favorable residual compressive stress, thereby significantly improving the wear resistance and fatigue resistance of the workpiece.

Application: For parts with simpler shapes such as cylindrical surfaces, conical surfaces, and planes, surface expansion (extrusion or extrusion) process can be used for treatment. This process is to squeeze a steel ball or other expansion tool with a diameter slightly larger than the inner hole of the workpiece into the machined inner hole at room temperature to obtain a treatment effect with precise size, smooth surface and strengthening.

Surface coating strengthening
Surface coating strengthening is a strengthening process that covers the metal surface with one or more layers of other metal or non-metallic materials by physical or chemical means. Its purpose is to improve the wear resistance, corrosion resistance and heat resistance of steel parts, or to perform decorative surface treatment. Among them, metal spraying technology is an important method in this strengthening process. It involves heating metal powder to a molten or semi-molten state, and then using high-pressure airflow to atomize and spray the metal powder onto the surface of the workpiece to form the required coating.

Using thermal spraying technology, the wear resistance, corrosion resistance, heat resistance and insulation of the material can be effectively improved. This technology is widely used in many cutting-edge technology fields such as aerospace, atomic energy, and electronics. In addition, metal plating technology is also an important strengthening method. By covering the surface of the base material with one or more layers of metal plating, its wear resistance, corrosion resistance and heat resistance can be significantly improved, and even special functions can be given to it. This includes electroplating, chemical plating, composite plating, infiltration plating, hot dip plating, vacuum evaporation, spraying, ion plating and sputtering.

Metal carbide coating - vapor deposition method

Vapor deposition technology, an innovative coating method, involves depositing gaseous substances containing deposition elements on the surface of materials by physical or chemical means to form a thin film. This technology is widely used in many fields, including the preparation of metal carbide coatings.

According to the different principles of the deposition process, vapor deposition technology is mainly divided into two categories: physical vapor deposition (PVD) and chemical vapor deposition (CVD). Among them, physical vapor deposition is to convert materials into atoms, molecules or ions in a vacuum environment by physical means such as evaporation, sputtering or ionization, and deposit them layer by layer on the surface of the material to form the desired film. This technology mainly includes three basic methods: vacuum evaporation, sputtering and ion plating.
Physical vapor deposition technology has a wide range of applicability, and its selection range is quite wide, whether it is substrate material or film material. In addition, the technology is simple, material-saving, environmentally friendly and pollution-free. The film layer prepared by physical vapor deposition has strong adhesion to the substrate, uniform film thickness, dense film layer and few pinholes. For this reason, physical vapor deposition technology has a wide range of applications in many fields such as machinery, aerospace, electronics, optics, and light industry, such as the preparation of wear-resistant, corrosion-resistant, heat-resistant films with specific electrical, optical, magnetic and other properties.

Next, let's introduce chemical vapor deposition (CVD). This is a method of forming a metal or compound film on a substrate through the interaction of a mixed gas with the substrate surface at a specific temperature. Because the chemical vapor deposition film has excellent wear resistance, corrosion resistance, heat resistance, and various electrical and optical special properties, it has been widely used in many industrial fields such as machinery manufacturing, aerospace, transportation, and coal chemical industry.

Finally, let's talk about surface cleaning and decoration. Polishing is a commonly used surface modification method that obtains a smooth surface effect by finishing the surface of the part. Although polishing cannot improve the accuracy of pre-processing, it can improve the surface roughness and make the Ra value reach the range of 6 to 008 mm. Mechanical polishing includes wheel polishing, drum polishing, vibration polishing and other methods.
Chemical polishing is to immerse metal parts in a special chemical solution, taking advantage of the fact that the convex parts of the metal surface dissolve faster than the concave parts, to achieve the effect of polishing the surface of the parts. Electrochemical polishing adds a direct current to this, and the workpiece is connected to the anode to achieve polishing through anode dissolution. In addition, the coating process is also an important part of surface treatment, including brushing, automatic dipping, manual spraying and other methods.