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Gear strengthening of numerical control sand blasting equipment

Author: admin Source: This station Time: 10:29, April 20, 2019

Shot peening is a process of cold treatment, that is, countless small round steel balls continuously hammer the surface of the parts, and each steel shot impacts on the metal parts, such as a micro stick hammering the surface, hammering out small indentation or depression. In order to form a depression, the surface of the metal must be stretched. Below the surface, the compressed grains attempt to restore the surface to its original shape, resulting in a hemisphere under high compression. Numerous depressions overlap to form a uniform residual compressive stress layer.
 

Shot peening process started from 1920s to 1930s, which uses the impact of high-speed projectile flow on metal surface to produce plastic cyclic strain layer on the surface, which leads to favorable changes in the microstructure of the layer and introduces residual compressive stress field into the surface layer. The microstructure and residual compressive stress field of the surface layer are to improve the fatigue fracture and stress corrosion (hydrogen containing) of metal parts The results show that the reliability and durability of the parts are improved.

Wear, corrosion and fracture are the three main failure modes of engineering metal parts. Among them, fracture failure brings the greatest harm, and fatigue fracture accounts for the largest proportion of fracture failure. Civil machine parts account for 40% - 50%, and military and aviation aircraft parts account for 90%. Shot peening process is not limited by material type, static strength, geometry and size of parts, and it is incomparable with any other strengthening process in terms of strengthening effect. Therefore, compared with the existing processing technology, shot peening strengthening technology has become an outstanding one, which has caused industrial developed countries' machinery immediately since it came into being Great attention has been paid to the device manufacturing industry and has been widely used.

It is conceivable that cracks are difficult to form or propagate in a compressive stress region. Since almost all fatigue and stress corrosion failures occur on or near the surface of parts, the introduction of compressive stress through shot peening can significantly prolong the life of parts. The residual compressive stress strength produced by strengthening must reach half of the tensile strength of the part material.

Tensile stress is the main cause of fatigue failure of many metals. These tensile stresses are caused by external alternating loads or residual stresses in production processes such as welding, grinding and machining. Tensile stress tries to stretch or pull the surface of the part, and eventually leads to cracks. The compressive stress extrudes the grains in the surface layer, which makes the grain structure in this area compact and tightly combined, thus greatly delaying the formation of fatigue cracks. Therefore, increasing the depth of compressive stress layer can effectively inhibit the occurrence and development of cracks.

application area

aviation industry
Aviation industry has a high demand for its parts, which not only requires light materials, but also requires them to be able to withstand extreme loads in extremely harsh environments. By protecting the surface from external damage and prolonging fatigue life, our surface treatment can improve the overall performance of parts.
Most parts used in aviation industry, including aircraft frame, wing, engine, landing gear, driving device, or transmission parts (gears), adopt shot peening / shot blasting technology to meet the material performance index.

 

automotive industry
The requirement of automobile industry is low cost and good performance under high alternating load. Surface treatment can improve the performance of parts by protecting the surface from the damage of cyclic load during operation.
Most of the metal materials used in automobile industry, including engine (crankshaft / connecting rod), suspension mechanism, automobile A / B pillar, transmission parts (gear / connecting rod), adopt shot peening / shot blasting technology to meet the performance index of materials.

 

Locomotive industry
High speed rail industry also requires high hardness, wear resistance and fatigue resistance of materials, and can maintain good performance under high alternating load. Surface treatment can improve the performance of parts by protecting the surface from the damage of cyclic load during operation.
Most of the metal materials used in locomotive industry, including engine (crankshaft / connecting rod), suspension and traction mechanism, transmission parts (gear / gear shaft), adopt shot peening / shot blasting technology to meet the performance index of materials.

 

Power energy industry
In the power industry, shot peening technology can improve the performance of steam and gas turbine, such as wheel disc, last stage blade, auxiliary parts and equipment. It can also reduce the fatigue failure of parts such as erosion, fretting wear, fretting wear fatigue, fatigue and stress corrosion cracking.
Shot peening technology is widely used to prevent parts from failure on transmission components, gears and shafts. However, recently, shot peening has been used more and more to increase the load resistance of key structures, such as shot peening on the inner wall of small diameter stainless steel pipe in supercritical power station, and the overload bench test of spiral active and passive bevel gears in automobile axle has also been proved.

 

Other areas
Shot peening technology is also used in construction machinery (piston / drill bit), mining machinery, petrochemical natural gas, urban gas supply and heating, medical equipment, offshore engineering and offshore oil exploitation, large and special performance ships and ships, power station equipment, energy conservation and environmental protection and other fields.

 

Three elements of shot peening

 

The three elements of shot peening are as follows: 1. Shot peening equipment and its accessories; 2. Medium: various types of projectiles; 3. Process: shot peening parameters and the relationship with fatigue strength;

1、 Shot peening strengthening equipment: (1) pneumatic shot peening machine is suitable for a wide variety of parts and each product has a low output and a few parts but complex shapes;

(2) The mechanical centrifugal force shot peening machine is suitable for a small number of parts with large output, large size and simple shape.

 

2、 Shot peening medium: the shot used for shot peening is usually as follows: cast iron shot, cast steel shot, stainless steel shot, steel wire cut shot, glass shot, ceramic shot, nickel base alloy shot, etc.

Projectile quality requirements

1. The geometrical shape of the shot for shot peening shall be spherical, and sharp edges and corners shall not be allowed. In addition, in order to avoid a large amount of fragmentation in the process of impact, the projectile must have a certain impact toughness.

2. In the total amount of shot recycled in the shot peening machine, the weight of the shot that conforms to the actual size should account for more than 80%.

Projectile selection principle

1. Any kind of projectile can be selected for ferrous metal parts.

2. Glass shot or stainless steel shot is recommended for nonferrous metal and stainless steel parts. If cast iron, cast steel or steel shot is used, it shall be cleaned immediately after shot peening to prevent chemical corrosion on the surface of parts.

3. For large parts with strict requirements of surface luminosity and shape and position tolerance (or non matching surface), larger size shot can be used to obtain higher shot peening strength; for parts with higher surface photometric requirements (including mating surface), smaller size shot should be used. In this way, the specified intensity of shot peening can be obtained, and the specified photometric requirements can also be met. For parts with inner and outer fillet and groove, the shot diameter should be less than half of the radius of inner and outer fillet and groove width.

 

3、 Shot peening process parameters:

 

The parameters affecting shot peening strengthening process include shot material, shot size, shot hardness, shot velocity, shot flow rate, injection angle, injection time, distance between centrifugal wheel and part surface.

Intensity control

Shot peening intensity represents the energy produced by shot flow. It is a very important parameter index in strengthening process and a key factor to ensure the repeatability of enhanced production. The energy produced by shot jet on the surface of parts is directly related to the compressive stress level. The shot peening strength will be increased by using larger shot size and / or increasing shot flow velocity. In addition, the angle of injection and the shot used also affect the strengthening strength.

The residual stress of the test piece sa070 can be measured by shot peening on one side of the test piece. The arc height (i.e. arc height value) of Almen test piece represents shot flow intensity, and the arc height value is repeatable.

Coverage

In order to obtain high-quality reinforcement results, it is necessary to ensure that the requirements of complete reinforcement coverage are met. Coverage measures the area covered by small dents formed by shot peening on the surface of parts. The coverage rate should not be lower than 98%, because if it does not reach 100%, the stress corrosion and fatigue cracks will occur and develop in the places that are not strengthened to or introduced into the residual compressive stress, and finally may lead to the fracture failure of the parts.

If the required coverage is more than 100% (e.g., 150%, 200%), then the enhancement time should be proportionally increased. For example, to achieve 200% coverage, the strengthening time will be twice that of 100% coverage.


Form of work Four position turntable
Spray gun 4 / 8mm Venturi nozzles It can be designed according to the requirements
Shot peening flow 0-15kg / min (each spray gun) Electromagnetic flow control system
Shot peening pressure 0-6bar Closed loop control system of compressed air
Mechanical arm Z axis / maximum stroke 600mm Up and down movement
Compressed air consumption Max.20Nm³/min When the number of spray guns is 2
Total power Approx.6kw
Suitable medium 0.2-1.6mm steel wire cutting shot Or cast steel shot
Maximum diameter / height / weight of parts 600mm/500mm/50kg

 Numerical control sand blasting strengthening equipment

 Numerical control sand blasting strengthening equipment