Shot Blasting Machine is a surface preparation equipment that removes rust and oxide layer on the surface of the workpiece by steel shots or steel grits which thrown on the surface through high-speed rotating impellers. It is a machine for shot peening, cleaning metal parts such as forging, casting parts, steel surfaces, heavy metal structures, rusted metal parts, etc.
Shot blasting machines not only can clean off contaminants like dirt or oil, remove metal oxides like rust or mill scale, but also can remove deburr the surface to make it smooth. Which will not change the shape of the workpiece, will not reduce the strength of the workpiece. Meanwhile, shot blasting machine can prepare a metal surface before the painting or coatings process, enhances the adhesion of the paint film and the material surface, increases the lifespan and the endurance of coating.
The origin of shot blasting machine
In order to prevent steel from being corroded, people have made unremitting efforts and come up with many effective methods. The earliest and most common application is the use of coatings to protect steel components from damage by external substances. The coatings that protect steel construction are divided into two categories: metal and non-metal.
There are two basic conditions for a strong bond between the coating and the steel component. First, the gap between the coating and the substrate should be as small as possible. According to the data, when the gap between the coating and the substrate surface is within 0.5nm, it can be firmly bonded. Second, there must be a large enough contact surface between the coating and the surface of the substrate, which means that there is no better way except to increase the surface roughness. A conclusion can be drawn from this, in order for the coating to effectively protect the steel components, it is necessary to treat the surface of the steel components. This can not only clear the impurities on the surface of the workpiece as thoroughly as possible, but also expose the substrate of the workpiece as thoroughly as possible; the second is to generate a certain degree of roughness on the surface of the workpiece, expand the surface area of the workpiece surface, and increase the bonding force between the unit area of the workpiece surface and the coating.
To achieve the purpose of appeal, among all treatment methods, abrasives are the most effective cleaning method as a cleaning medium. There are two cleaning methods using abrasives as the cleaning medium. One is the method in which compressed air (or high-pressure water) accelerates abrasive particles to a high speed to clean the surface of the workpiece, that is, shot peening. The other is to push abrasive particles with a high-speed rotating impeller, so that they can hit the surface of the workpiece at a relatively high speed, this is usually called shot blasting. It is a highly efficient cleaning method that appeared in the 1930s.
The world’s first shot blasting equipment was born 100 years ago. In the beginning, it was applied to various metal or non-metal surfaces to remove impurities, oxide scale, and increase roughness, etc. After a century of development, shot blasting equipment and technology have become quite mature, and its application is not only in heavy industry plants anymore. With the birth of the world’s first horizontally mobile shot blasting equipment in Blastrac in the United States, it was rapidly expanded to be applied to concrete surface coating treatment and ship deck metal surface treatment, and directly led to the industry’s standard formulation and construction method specifications.
Working principle of shot blasting machine
Shot blasting machine is composed of blasting turbines, blasting chamber, workpiece transfer system, abrasive recycling system, dust collector system, electric control system and others.
Blast turbines are the heart of shot blasting machine, as they represent one of the most important elements for its efficient operation. Blast wheels are made up of blades, control cage, distributor, impeller and guard plates. The abrasive enters distributor from silo by self-weight, then rotates in the blast turbines. The abrasive rotates to the window of the control cage, then thrown onto the workpiece along with the high-speed rotating blades.
How to choose different types of blades?
The blades have two kinds of types. The one is the same as its name, straight blades. The other one is the curve. If viewed from the side, the blades have a certain angle.
Compared with the same size of the straight blades, the biggest advantage of the curved blades is the higher grinding speed. So the energy shock transferred to the workpiece is greater.
The curved blade can achieve abrasive exit speed, 27% to 30% higher than the straight blade. It is mainly used in the following situations:
When more particle energy is required and distance is greater
The workpiece with higher requirements for roughness
Where scale needs to be removed
Under the same motor power, the straight blade can achieve a lower outlet speed but a higher mass flow rate. Therefore, the choice of the blade depends on the specific situation.
Abrasive Recycle System
Abrasive recycle system is composed of a screw conveyor, bucket elevator, separator and storage hopper.
Bucket elevator lower part feeding gate is connected with screw conveyor, its upper part discharging gate is connected with separator. So the abrasive from screw conveyor into the bucket elevator, then transported by the bucket elevator to the separator on the top, and then the cleaned abrasive get into the storage hopper to recycle, the residue will get out of the recycling system from the separator system.
The separator is the most important part of the blasting machine, that determines the steel shot recycling rate. After into the separator, the steel shot and contaminants are uniform distributed in the separation chamber, presenting a flowing curtain. At this time, the separator fan absorbs air through the exhaust opening and separates the contaminants and steel shot by using the principle of gravity winnowing.
In the shot blasting process of the shot blasting machine, the steel shot is projectile with a high speed, it will collide and friction with the workpiece. After passing through the recovery system, dust will be generated. The dust collector is to remove the dust in the blasting chamber and other devices to prevent air pollution.
The dust collector can be divided into three levels: coarse purification, medium purification, and fine purification according to the size of the collected dust particles. Coarse purification is to capture dust articles larger than 100 microns, medium purification is to capture dust particles of 10-100 microns, and fine purification is to capture dust particles of 10 microns.
The function of the dust collector is basically the same as that of the volumetric separator, but the structure is simpler. Its main function is to make the airflow to settle down the coarse particles in the airflow when it flows down in a roundabout way, so as to reduce the burden of the dust collector used in the second and third levels of dust removal and purification. The settling box is used for coarse purification, the second level dust collector is used for intermediate purification, and the third level dust collector is used for fine purification.
The second level of dust removal generally uses the CLT/A cyclone dust collector, and its dust removal efficiency can reach up to 70-90. When dealing with large air volume, a large-diameter cyclone dust collector is required, but the dust removal efficiency will be reduced at this time. In order to maintain high dust removal efficiency, a two-stage cyclone dust collector with a concentrator can be used to remove dust. The efficiency is 85-90. The third level dust collector generally adopts pulse jet type filter cartridge dust collector. When the dust on the filter cartridge is removed, this kind of dust collector can clean the dust without stopping the wind. Its dust removal efficiency is 90.
In ventilation and dust removal devices, high-pressure centrifugal fans are usually used. The exhaust noise and mechanical noise produced by high-pressure centrifugal fans will cause harsh working environments. For this reason, a silencer can be installed on the exhaust spring of the fan. To reduce exhaust noise. In order to reduce the mechanical noise, the ventilator can be placed in the ventilator room with sound insulation device, or the sound insulation material can be hidden outside the ventilator casing.
Test standard of shot blasting machine
Rust removal grade and surface roughness are the important standards for testing whether the shot blasting machine is qualified.
The removal grade that can be achieved by shot blasting machine is SA2.5-SA3, which means after the shot blasting, the surface of steel without oil, oxide scale, rust and other contaminants, and the surface show a uniform metallic luster.
The surface roughness that can be achieved by shot blasting machine is 25-75μm, the influencing factors including blasting speed, blasting time, type and size of steel shot, etc…
Application field of shot blasting machine
Shot blasting machine is widely used in steel industry, such as steel plate, H beams, steel structure, steel pipe, wire and other steel products to remove rust, scale and others.
Shot blasting machine can be applied to the surface sand and oxide scale removal of cast steel and cast iron in the casting industry. Almost all steel castings, gray castings, ductile iron, etc., should be shot blasted. This is not only to remove the casting surface scale and sand, but also an indispensable preparation process before casting quality inspection.
Machinery (motor) industry
According to the requirements of the automobile manufacturing industry, the steel plate and casting parts used need to be blasting, but the strength of the steel plate and the original appearance should not be damaged, and the appearance of the casting parts should be ensured to be clean and beautiful. Since the parts of machinery and motor are not very regular, it requires a different type of shot blasting machine to finish.
There are many parts in the construction industry can be used for shot blasting machine, such as scaffolding, tower crane, aluminum formwork, steel structure, screws and bolts, etc
The steel plate used in the shipyard has rust will affect the quality of shipbuilding.
It takes a long time to use artificial derusting, so it is necessary to choose the shot blasting machine for derusting cleaning. Generally, the shot blasting and painting line is used more in shipyards, which can not only remove rust from steel plates, but also spray paint to ensure the quality of shipbuilding.
The aerospace industry has high requirements for its parts, not only requiring them to be light in material, but also requiring them to be able to withstand extreme loads in extremely harsh environments. By protecting the surface of the parts from external damage and extending the fatigue life, the shot blasting machine can improve the overall performance of the parts.Most parts used in the aviation industry, from aircraft frames to engines, landing gear, drives, and transmission parts (gears/bearings), shot blasting to meet the performance requirements of their materials.
The type of shot blasting machine
Shot blasting machine is the non-standard machine, also called customized blasting equipment, that can according to the shape, size and cleaning requirements of the different workpiece to choose different types shot blasting machine.
Roller conveyor shot blasting machine
Roller conveyor shot blasting machine is the most common and environmentally friendly shot blasting machine. The machine is mainly used to clean steel plates, H beams, steel structures, steel pipes, steel channels, steel scaffoldings and other steel profiles. Through the pretreatment of the steel profiles, to achieve the smooth surface. So as to enhance the adhesion of the paint film and the steel surface, thereby ensuring the quality of the steel anticorrosive coating.
Roller conveyor shot blasting machine can used in many industries, such as aerospace, automotive, construction, foundry, shipbuilding and other industries.
Hanger type shot blasting machine
Hanger type shot blasting machine is the most flexible and high-efficiency shot blasting machine. The machine operation easily, loading the workpiece on the hook then into blasting chamber to work. After a few times, all progress are completed. Hook type blasting machine is divided into single hook and double hook, hook type blast machine by two hook loading workpieces alternately into the blasting chamber.
Hanger type shot blasting machine mainly used in foundry, mechanism, chemical, motor, and other industries, to clean various of medium or large casting, forging, welding workpiece, including some fragile and irregularly shaped workpieces.
Tumble belt shot blasting machine
Tumble belt shot blasting machine usually clean some small or medium workpiece. The belt is made of a circular space to let the workpiece roll in it and to achieve the purpose of cleaning. The machine suitable for sand removal, rust removal, descaling and appearance strengthening of small castings, forgings, stamping parts, gears, springs, etc. It is especially suitable for cleaning and strengthening parts that are not afraid of collision and irregular shape workpiece. Tumble belt shot blasting machine is generally used in hardware manufacturing, die casting, precision casting and forging industries, etc.
Rotary table shot blasting machine
Rotary table shot blasting machine is suitable for the cleaning of flat, thin-walled, sand-sticky oxide scale on the surface of parts that are afraid of collision in the casting and forging and heat treatment workshops. It not only can remove the rust on the surface of the workpiece, but rust and dirt on various workpieces can also be cleaned, and the surface quality of the workpiece can be improved. This machine is widely used in steel, metallurgy, rolling stock, construction machinery, heavy mining machinery and other manufacturing industries.
Mesh belt shot blasting machine
Mesh belt shot blasting machine used the mesh belt as the conveyor device. The machine can work continuously and in the progress of working have no collision. It suitable for small or medium workpiece and the production with large quantities. The machine is a multi-functional shot blasting machine for cleaning dishes, flakes, castings, machine bodies, and structural parts, and it mainly used in automobile, aerospace, aluminum alloy industry and machinery manufacturing industries.
Overhead rail shot blasting machine
Overhead rail shot blasting machine is suitable for shot blasting large quantities of small and medium workpieces. The workpiece can run continuously or step by step along with the overhead rail conveyor system, so that the workpiece can be stopped in the loading and unloading area and the shot blasting area. Compared with hanger type shot blasting machine, that with high production efficiency. The machine is the most ideal choice for automobiles, tractors, diesel engines, motors, valves and other industries.
Stone shot blasting machine
Stone shot blasting machine is a machine that is mainly for cleaning stone. The main stone materials include : marble, artificial stone, granite, curbstones, floor tiles, cement tiles, pavement tiles and so on. The treated stone surface has high anti-skid performance, good flatness and a strong three-dimensional effect. The pavers shot blasting machine is a newly developed new type shot blasting machine with high work efficiency, low use cost and good dust removal effect.
Pipe shot blasting machine
Pipe shot blasting machine is suitable for continuous shot blasting of the outer and inlet surface of batches of steel pipes before welding or painting to thoroughly remove rust, oxide scale and other dirt. After shot blasting, it can obtain a smooth surface with a certain roughness, increase spray adhesion, improve surface quality and anti-corrosion effect. The machine mainly used in some gas and oil industry, cylinder industry, shipbuilding and some other heavy industry.
Barrel type shot blasting machine
Barrel type shot blasting machine is used to clean small and medium iron parts, steel parts, alloy and non-metal castings, forgings, heat-treated parts, stamping parts and assembly parts. The machine can achieve high-efficiency and uniform cleaning effect. In shot blasting machine, the barrel not only rotates but also shake up and down. Therefore, the workpiece in the barrel can be completed stirred. The barrel type shot blasting machine used in the automotive, iron, steel and metal industry, heat treat operations, forging operations and small stamping parts industries.
Wire rod coil shot blasting machine
Wire rod coil shot blasting machine is the most suitable machine to clean the wire rod coil surface oxide scale in the manufacturing industry. It is suitable for clean the outer surface of continuous batches to remove the oxide layer and stains, replace the pickling and phosphating process, reduce the investment cost, and present a metallic luster to facilitate the painting and coating of the workpiece.
Preservation line is the machine that combined the shot blasting system, painting system, drying system and paint mist treatment system in a whole machine and inform a continuous automatic working shot blasting and painting line, suitable for blast steel plate, h beam and other raw material. The machine mainly used in steel industry, aerospace, automotive, shipbuilding and other industries.
Floor shot blaster
Floor shot blaster is used to remove the coating on the floor, decontamination of nuclear power buildings; small-area steel surface cleaning; cross-street overpass coating cleaning; airport demarcation project; railway bridge deck waterproofing construction; highway bridge-tunnel pavement roughening. The machine can make the concrete surface uniform and rough, which greatly improves the adhesive strength of the waterproof layer and the concrete base layer.
Continuous rocker barrel shot blasting machine
The continuous rocker barrel shot blasting machine is an automatic, continuous, and dust-free shot blasting equipment. It has a high degree of flexibility, can respond to changing production requirements, and can quickly adapt to changes in production efficiency, processing technology and market demand. The machine is used to the shot blasting the castings and forgings rust removal. The machine is suitable for the hardware industry, electroplating industry, automobile industry, bearing industry and some small and medium foundry industries.
Continuous tumble pass-thru shot blasting machine
Continuous tumble pass-thru shot blasting machine is mainly used for surface derusting and burr removal of small and medium- size castings that are not afraid of corrosion. It is suitable for shot blasting of runners and risers during the production of large-volume castings.
Shot peening machine
Shot peening machine is mainly suitable for mass production of surface cleaning of small and medium-sized workpieces, such as engine connecting rods, gears, diaphragm springs, etc. It is widely used in casting and automobile manufacturing. It has high production efficiency, good sealing effect, compact structure, convenient loading and unloading, high technical content and other features.
Working routine of shot blasting machine
- Dust collect system running
- Elevator running, separator running
- Screw conveyor running
- Workpiece transport system running, let the workpiece into blasting chamber.
- Blast wheels running
- Open abrasive supply valve, start work
- After the blast, close abrasive supply valve
- Blast wheel stop
- Workpiece transport system running, move out the chamber
- Continue to work, repeat step 4-9
- If stops working, please let the elevator stop, the separator stop, the dust collector stop, the whole machine stop.
How to maintenance the wear resistant parts of shot blasting turbines?
The shot blasting turbines mainly wear resistance parts including side guard plate, rear guard plate, top guard plate, blades, distributor, and control cage. If the wearing parts are severely worn and not replaced in time, the service life of the shot blasting machine will be affected. When the shot blasting machine vibrates too much or abnormal noise occurs, the machine must be shut down to check the use of the wearing parts and check whether foreign objects enter the shot blasting machine.
After each shift, check the wear of the wearing parts of the shot blasting turbines.
The blades are the wearing parts that rotate at high speed and are most easily worn out. The wear of the blades should be checked frequently. When the following situations occur, the blades should be replaced.
- The blade thickness is reduced by 4-5mm
- The blade length is reduced by 4-5mm
- The shot blaster vibrates severely
If the shot blasting turbines are installed in a shot blasting chamber that is easy for personnel to enter, the blade can be inspected in the shot blasting chamber; if it is difficult for maintenance personnel to enter the shot blasting chamber, the top plate of the shot blasting turbines must be opened outside the shot blasting chamber for inspection.
Note: When the blade is replaced, all the blades should be replaced; the weight difference between the replaced blades should not exceed 5g, otherwise there will be greater vibration when the shot blasting machine works.
The distributor is located in the control cage of the shot blasting turbine, which is usually inconvenient for inspection. You can check the wear of the distributor every day when the blade is replaced.
If the distributor continues to be used after it is worn out, the projectile diffusion angle will increase, which will accelerate the wear of the shot blasting turbine guard plate, and affect the cleaning effect and efficiency. If the outer diameter of the distributor wears 10-12mm, the distributor needs to be replaced.
The main function of the control cage is to adjust the spray angle of the shot blasting turbines, so the direction adjustment of the control cage is particularly important for the use of the shot blasting machine. Before the new shot blasting machine is used, the position of the control cage must be adjusted correctly, so that as many projectiles as possible are projected to the surface of the workpiece to ensure the cleaning effect and the service life of the wear protection plate of the shot blasting chamber.
- Paint black ink on the board or spread a piece of thick paper, and place it on the position of the workpiece to be cleaned.
- Turn on the shot blasting turbines, and manually add a small amount of steel shot into the quicksand tube of the shot blasting turbines.
- Turn off the shot blasting turbines. If the position of the ejection belt is advance, the position of the control cage will be adjusted in the opposite direction after the shot blasting turbines. After adjustment, go to the second step to continue to check whether the adjustment is in place.
- After reaching the satisfactory result, mark the position of the control cage window on the shell of the shot blasting turbine for reference when replacing the blades, distributor, and control cage later.
Control cage wear inspection
- If the window is worn within 10mm and the window is worn at 5mm, it is necessary to extend the position mark of the control cage to rotate the control cage against the impeller rotation by 5mm; the window is worn by 5mm, and the position mark of the control cage needs to be extended to rotate the control cage against the impeller by 5mm.
- The control cage needs to be replaced if the window is worn out by 10mm.
Choose the right abrasive
Abrasive is an important medium for shot blasting machine work, and it can affect the blasting effect. And correct choice of shot blasting media can mean great savings which most of users are not even aware of.
If the steel shot/ steel sand is too soft, it will slow down the cleaning speed and reduce the working efficiency. Hardness is too high, will produce unsatisfactory surface, increase the fragmentation rate of the projectile, consumption is too high, and the equipment wear is larger.