Bead blasting use high speed jetted sand and iron shots to hit the surface of the workpiece. it will change the surface of part and improve the mechanical properties of part.
Bead blasting can be used to improve the mechanical strength of parts as well as wear resistance, fatigue resistance and corrosion resistance. It can also be used for surface matting, removing scale and eliminating residual stress in castings, forgings and weldments.
How does Bead blasting work?
Bead blasting technology uses impact media (sand shot and iron shot) ejected at high speed to impact the surface of metal materials, producing a huge impact force on the surface of the metal material that is far greater than the dynamic yield strength of the material, thereby triggering severe plastic deformation on the surface of the material.
The microstructure of the surface layer of the material is greatly fragmented (up to the nanometer level) due to this severe plastic deformation, resulting in dense, uniform and stable dislocation proliferation. At the same time, a high-amplitude residual compressive stress distribution is induced inside the material. When the residual compressive stress accumulates to a certain extent, the sheet will undergo macroscopic bending deformation to rebalance the internal force system and form new internal stresses. distributed.
Mediums used for Bead blasting
The media used for bead blasting surface treatment mainly fall into the following four categories:
Cast steel shot
Its hardness is generally 40~50HRC. When processing hard metals, the hardness can be increased to 57~62HRC. Cast steel shot has better toughness and is widely used. Its service life is several times that of cast iron shot.
Cast iron shot
Its hardness is 58~65HRC, brittle and easy to break. It has a short life and is not widely used. Mainly used in situations where high shot peening intensity is required.
The hardness of glass shot is lower than the first two. It is mainly used for titanium, aluminum, magnesium and other materials that do not allow iron contamination. It can also be used for secondary processing after steel shot peening to remove iron. Contaminate and reduce the surface roughness of parts.
The chemical composition of ceramic shots is roughly 67% ZrO2, 31% SiO2 and 2% Al2O3-based inclusions. It is made by melting, atomizing, drying, rounding and screening. The hardness is equivalent to HRC57~ 63. Its outstanding properties are higher density and higher hardness than glass.
Advantages of Bead Blasting
- 1. Enhance the hardness and strength of the workpiece surface.
- 2. Improve the ability of fasteners to resist stress corrosion and hydrogen embrittlement fracture due to fatigue fracture. After bead blasting strengthening, the reliability and durability of the workpiece can be significantly improved and improved.
- 3. Improve the bending fatigue strength and contact fatigue strength of gear teeth, improve gear anti-biting ability and increase gear lifespan.
- 4. Metal or non-metallic shot can be used to adapt to different requirements for cleaning the workpiece surface.
- 5. The cleaning flexibility is great, and it is easy to clean the inner and outer surfaces of complex workpieces and the inner walls of pipe fittings, and it is not subject to site restrictions.
Disadvantages of Bead Blasting
- A high-power air compressor station must be equipped, which consumes a lot of energy under the same cleaning effect.
- The cleaned surface is prone to moisture and rust.
- The cleaning efficiency is low, the labor intensity is high and it produces noise and dust.
Applications of Bead blasting
Improve fatigue life and surface compressive stress. Commonly used parts include: various forged leaf spring main reeds
Bead blasting will Increase the surface dislocation density, cold work hardening at the crankshaft fillet, can increase the compressive stress at the fillet. Bead blasting after carburizing and quenching of the gear transforms the retained austenite into martensite and improves the contact fatigue strength.
Improve surface roughness
Improve the surface roughness of the cast aluminum body. Commonly used parts include: aluminum cylinder block, cylinder head, supercharger impeller
Prevent surface fracture stress
- Used for Pre-treatment of chrome plating and nickel plating, commonly used parts: piston rings before and after chrome plating
- Eliminate lines after grinding. Commonly used parts include: high-speed gears
- Pre-treatment of anodizing, common parts include: aluminum wheel hub before anodizing
Tips for Bead Blasting Operation
- Select the appropriate bead blasting medium according to the work requirements and material characteristics.
- too high pressure and flow may damage the material surface, while too low pressure and flow may not achieve the cleaning effect.
- The angle and distance of blasting will affect the result of cleaning.
- When operating the bead spray machine, maintain uniform bead spraying.
- Wear appropriate protective equipment when operating the machine.
- Regulay maintain the nozzles and pipes of the bead blasting machines.
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