What is shot peening ?
Shot peening is a process that improves the mechanical properties and surface condition of workpieces by using high-speed sand shot or iron shot to impact the surface. This process can increase the mechanical strength, wear resistance, fatigue resistance and corrosion resistance of parts.
In addition, shot peening can also be used for matting surfaces, descaling and eliminating residual stresses in processes such as casting, forging and welding.
Sandblasting to remove old paint and rust on the surface of steel wheels
T yes of shot peening
Shot peening is divided into shot peening and shot peening.
Shot peening
The surface blasting treatment has a significant impact force and provides an obvious cleaning effect.
However, the treatment of thin sheet parts by shot peening can easily cause deformation of the part, and the steel shot hits the surface of the part regardless of blasting or shot peening, leading to the deformation of the metal substrate. Fé 3 Ó 4 and Fé 2 Ó 3 have no plasticity and peel off after being broken. The oil film is also deformed together with the substrate, so blasting or air blasting for oil-contaminated parts cannot fully remove the oil.
Among the existing surface treatment methods for workpieces, sandblasting provides the best cleaning effect.
Socket exploding
Sandblasting is suitable for cleaning workpiece surfaces to high standards. However, the current general sand blasting equipment in China is mainly composed of basic and heavy sand transport machines such as articulated dragon, scraper, bucket and elevator.
Users need to build a deep well and create an impermeable layer to install machinery, leading to higher construction costs, greater maintenance workloads, and higher maintenance costs.
Furthermore, the significant amount of silica dust produced during the blasting process cannot be removed effectively, posing a serious threat to the health of operators and polluting the environment.
Shot peening is divided into general shot peening and tension shot peening .
In general, during processing, the steel plate is in a free state, and high-speed steel shot is used to hit the surface to induce pre-compression stresses, reducing the tensile stress on the surface during work and increasing its service life .
Tension shot peening involves pre-bending the steel plate under a certain force, followed by shot peening.
Types of shot peening equipment
There are two main types of shot peening equipment:
1. Mechanical centrifugal engraving machine
Suitable for parts requiring high shot peening resistance, small variety, large batch, simple shape and large size.
2. Pneumatic blasting machine (compressed air type)
Suitable for parts requiring moderate resistance to shot peening, complex shapes and small sizes.
Projectile introduction
1. Cast steel shot
Typically, metal hardness is in the range of 40-50 HRC.
During the processing of hard metals, the hardness can be increased to 57-62 HRC.
Cast steel shot is highly valued for its good toughness and is widely used. It also has a longer service life compared to cast iron shot, often several times longer.
2. Cast iron shot
The hardness of this material is typically 58-65 HRC, making it brittle and prone to breaking, resulting in a short service life. As a result, it is not widely used.
However, it is mainly used in situations where high intensity shot peening is required.
3. Glass counts
Compared to the two previous materials, this one has a lower hardness. It is mainly used to process titanium, aluminum, magnesium and other materials that do not tolerate iron contamination.
In addition, it can also be used for secondary processing after steel shotpeening to remove iron pollution and reduce the surface roughness of parts.
4. Ceramic bead
The ceramic bead has a chemical composition of approximately 67% ZrO 2 31% SiO 2 and 2% Al 2 Ó 3 as main components. It is made through a process that involves melting, atomization, drying, rounding and screening.
The hardness of the ceramic bead is similar to that of HRC57-63.
One of its main advantages is that it has greater density and hardness compared to glass.
In the early 1980s, ceramic beads were first used to increase the strength of aircraft parts.
Compared with glass beads, ceramic beads have higher strength, longer service life and more affordable price.
Its use has now been extended to the surface reinforcement of non-ferrous metals such as titanium alloys and aluminum alloys.
Introduction to shot blasting machine nozzles
1 . Straight pipe nozzle
The straight pipe nozzle has a simple structure, its internal structure has only two parts: contraction and flat section.
2. Venturi nozzle
The venturi nozzle is divided into three parts: contraction section, straight section and diffusion section, which is more difficult to make.
3. Double venturi nozzle
Double Venturi nozzles are front and back, with spacing between the two, and several small holes around the spacing.
4. Mouthpiece with square hole
Abroad, a nozzle with square inlet and outlet ends was developed.
According to various tests, this nozzle has proven to be more efficient and economical compared to the Venturi nozzle.
Parameters that affect shot peening quality
Shot peening intensity
The process parameters that affect shot peening resistance mainly include: projectile diameter, projectile velocity, projectile flow rate and projectile time, etc.
Coverage rate
Factors that influence the coverage rate: hardness of the material of the parts, diameter of the projectile, spray angle and distance and projectile time, etc.
Surface stiffness
Factors that influence roughness: the strength and hardness of the part material, the diameter of the projectile, the angle and speed of spraying, and the roughness of the original surface of the part.
Characteristics of the parts after shot peening
The residual compressive stress on the part surface after shot peening, as well as the depth of the compressive stress layer, depend on the material properties and peening resistance.
Materials with greater strength and hardness result in greater compressive stress and shallower depth of the compressive stress layer.
Furthermore, the greater the resistance to shot peening, the deeper the compressive stress layer.
Changes in the material organization of the blasted surface layer
Surface roughness after shot blasting: Surface roughness after shot blasting worsens with increasing shot peening resistance, decreasing surface hardness and decreasing shot size.
Size increase: The metal on the sprayed surface is pushed outward, forming small wavy ridges of metal, resulting in an increase in size.
Shot peening application range
Shot peening can prevent bending fatigue in automobile parts.
It can also improve the flexural fatigue properties of the tooth profile roots.
Shot peening improves fatigue resistance and extends the safe service life of crankshafts.
Furthermore, shot peening increases the strength and rigidity of the connecting rods.
The robust shot peening process can increase the bending fatigue resistance and contact fatigue resistance of gear teeth, making it a crucial method for improving gear anti-seizing ability and prolonging gear life.
Surface shot peening is an effective surface strengthening process that improves stress corrosion resistance and hydrogen embrittlement fracture resistance in fasteners.
Shot peening leads to a significant improvement in part reliability and durability.
By altering the structure of the material, surface shot peening achieves the objective of improving fatigue performance, including stress corrosion performance, thereby improving the quality of fasteners.
