Shot Blasting Machine for Forging Oxide Scale Removal

Forging is an important metal processing method that improves the internal structure of metals, enhances mechanical properties, and shapes metal workpieces through plastic deformation under high temperature and pressure. However, during the forging process, the surface of the metal workpiece is in contact with oxygen in the air, resulting in oxidation reactions and the formation of oxide scale (also known as scale). Oxide scale is mainly composed of metal oxides such as iron oxide (for ferrous metals) and aluminum oxide (for non-ferrous metals). It has a loose structure, poor adhesion to the metal matrix, and low hardness. If oxide scale is not removed before subsequent processing (such as machining, heat treatment, or surface coating), it will cause serious adverse effects. For example, during machining, oxide scale will accelerate the wear of cutting tools, reduce the machining accuracy and surface quality of workpieces; during heat treatment, oxide scale will affect the uniformity of heating and cooling, leading to uneven microstructure and mechanical properties of workpieces; during surface coating, oxide scale will prevent the coating from adhering to the workpiece surface, reducing the corrosion resistance and service life of the coating. Therefore, oxide scale removal is a vital post-forging processing step, and shot blasting machines have become the most widely used equipment for this purpose due to their high efficiency, thoroughness, and cost-effectiveness.

The shot blasting machine for forging oxide scale removal operates on the principle of using high-velocity abrasive particles (shot) to impact the surface of the forged workpiece, breaking and stripping the oxide scale from the metal matrix. The impact process is mainly based on the difference in physical properties between the oxide scale and the metal matrix: the oxide scale is brittle and has low tensile strength, while the metal matrix is tough and has high tensile strength. When the shot impacts the oxide scale, the oxide scale is subjected to a strong impact force and breaks into small pieces, which are then stripped from the workpiece surface. At the same time, the impact of the shot also causes a certain degree of plastic deformation on the surface of the metal matrix, forming a compressive stress layer, which can improve the surface hardness, wear resistance, and fatigue resistance of the workpiece. Compared with traditional oxide scale removal methods such as pickling, grinding, and wire brushing, shot blasting has obvious advantages in terms of environmental protection, efficiency, and surface quality.

The structural composition of a shot blasting machine for forging oxide scale removal is similar to that of the casting sand removal shot blasting machine, but there are some differences in the design of key components to adapt to the characteristics of forged workpieces (such as high temperature, large size, and high surface hardness). The core components include the blast wheel, blast chamber, feeding and conveying system, shot recovery and separation system, dust removal system, and electrical control system.

The blast wheel is the core power component of the machine, responsible for accelerating the shot to a high speed. Due to the high hardness of oxide scale and the large size of some forged workpieces, the blast wheel for forging oxide scale removal usually has a higher rotating speed and a larger diameter than that for casting sand removal. The rotating speed can reach 2000-3600 rpm, and the diameter can be 600-1200 mm. This ensures that the shot can obtain a higher projection speed (up to 100-120 m/s) and a larger impact force, which is sufficient to break and strip the tough oxide scale. The blades of the blast wheel are usually made of high-chromium alloy steel or wear-resistant ceramic materials to withstand the strong impact of the shot and the oxide scale, reducing wear and extending the service life.

The blast chamber is the enclosed space where the oxide scale removal operation is carried out. Due to the large size and heavy weight of some forged workpieces, the blast chamber is usually designed to be larger in volume. The inner wall of the blast chamber is lined with high-wear-resistant materials such as manganese steel plates, polyurethane plates, or rubber plates to withstand the continuous impact of the shot and the oxide scale. In addition, the blast chamber is equipped with multiple blast wheels arranged in different directions (such as top, bottom, left, and right) to ensure that the shot can fully cover the surface of the forged workpiece, including the sides, corners, and other difficult-to-reach areas. This ensures thorough oxide scale removal.

The feeding and conveying system is responsible for transporting the forged workpieces to be processed into the blast chamber and conveying the processed workpieces out of the machine. Forged workpieces have the characteristics of large size, heavy weight, and high temperature (some workpieces are still at a high temperature of 500-800°C after forging), so the feeding and conveying system must have high load-bearing capacity, high temperature resistance, and stability. Common conveying methods include roller conveyor, chain plate conveyor, and hanger conveyor. Roller conveyors are suitable for flat and heavy forged workpieces, such as forged steel plates, shafts, and discs. The rollers are usually made of heat-resistant steel and are equipped with heat insulation sleeves to prevent deformation due to high temperature. Chain plate conveyors are suitable for irregularly shaped forged workpieces, such as forks, connecting rods, and brackets. The chain plates are made of high-strength steel and have good wear resistance and high temperature resistance. Hanger conveyors are suitable for large and complex-shaped forged workpieces, such as large gears, crankshafts, and machine tool beds. They can lift the workpieces and rotate them during the conveying process, ensuring that all surfaces of the workpieces are exposed to the shot impact.

The shot recovery and separation system is used to recycle the used shot and separate it from the oxide scale and other impurities. Forging oxide scale has a higher density than casting sand, so the separator for forging oxide scale removal shot blasting machines usually has a more efficient separation structure. Common separators include air separator, centrifugal separator, and magnetic separator. Air separators use the difference in density between shot and oxide scale to separate them through wind force. Centrifugal separators use centrifugal force to separate the mixture of shot and oxide scale, which has higher separation efficiency. Magnetic separators are mainly used for separating ferrous oxide scale from steel shot, which has a good separation effect. The separated clean shot is sent to the storage silo for reuse, while the oxide scale is discharged to the waste bin for centralized treatment. Some enterprises can also recycle the oxide scale as raw material for steelmaking, realizing resource reuse.

The dust removal system is an important part of the shot blasting machine for forging oxide scale removal. During the oxide scale removal process, a large amount of dust and fine oxide scale particles are generated, which not only pollute the environment but also harm the health of operators. The dust removal system usually consists of a dust collector, a fan, a dust duct, and a dust hopper. For forging shot blasting machines, due to the large amount of dust generated, bag filters or electrostatic precipitators with high dust collection efficiency are usually used. Bag filters have the advantages of high dust collection efficiency (up to 99.9% for fine dust), stable performance, and easy maintenance. Electrostatic precipitators are suitable for large-scale shot blasting machines with high dust emission, which can collect dust efficiently and continuously. The fan generates negative pressure in the blast chamber, and the dust is sucked into the dust collector through the dust duct. The collected dust is discharged into the dust hopper for centralized treatment, and the clean air is discharged into the atmosphere after reaching the standard.

The electrical control system is the "brain" of the shot blasting machine, responsible for controlling the operation of each component. Modern shot blasting machines for forging oxide scale removal are usually equipped with PLC and HMI systems, which can realize automatic control of the entire process, including feeding, conveying, shot blasting, shot recovery, and dust removal. Operators can set parameters such as the rotating speed of the blast wheel, the feed rate of the shot, the conveying speed of the workpiece, and the shot blasting time on the HMI. The system can automatically adjust these parameters according to the type and size of the workpiece to ensure the oxide scale removal effect. In addition, the electrical control system is equipped with multiple safety protection devices, such as overload protection, overheating protection, emergency stop button, and safety door interlock. When the machine has an abnormal situation (such as overload of the motor, overheating of the bearing, or opening of the safety door), the system will automatically stop the machine and issue an alarm, ensuring the safety of operators and equipment.

The application of shot blasting machines for forging oxide scale removal is very extensive, covering almost all forging industries. In the automotive industry, forged workpieces such as crankshafts, connecting rods, gears, and half shafts all need to go through shot blasting to remove oxide scale before subsequent processing. This not only improves the machining accuracy and surface quality of the workpieces but also enhances their fatigue resistance. In the aerospace industry, forged workpieces such as turbine discs, blades, and landing gear components require shot blasting to remove oxide scale to ensure their high precision and high reliability. In the construction machinery industry, large forged workpieces such as excavator arms, bulldozer frames, and gearboxes rely on shot blasting to achieve efficient oxide scale removal. In addition, shot blasting machines for forging oxide scale removal are also used in the production of forged steel pipes, valves, flanges, and other products.

Compared with traditional oxide scale removal methods, shot blasting machines for forging oxide scale removal have many advantages. First, high efficiency. A single shot blasting machine can process dozens of large forged workpieces or hundreds of small and medium-sized forged workpieces per hour, which is much higher than manual grinding or pickling. This greatly shortens the production cycle and improves the production capacity of the enterprise. Second, thorough oxide scale removal. The high-velocity shot can penetrate into the gaps and corners of the forged workpieces, removing the oxide scale that is difficult to remove by other methods. This ensures the surface cleanliness of the workpieces and lays a good foundation for subsequent processing. Third, environmental protection. Traditional pickling methods use strong acids (such as hydrochloric acid, sulfuric acid) to remove oxide scale, which will generate a large amount of acid waste water and acid mist, causing serious pollution to the environment and corroding equipment. Shot blasting is a dry processing method that does not use any chemicals, and the generated dust and oxide scale can be collected and treated centrally, which is environmentally friendly. Fourth, surface strengthening. The impact of the shot on the workpiece surface forms a compressive stress layer, which improves the surface hardness, wear resistance, and fatigue resistance of the workpiece. This is particularly important for forged workpieces that work under dynamic loads, such as crankshafts and connecting rods. Fifth, stable processing quality. The automatic control system of the shot blasting machine ensures that the processing parameters are consistent, so the surface quality of the processed workpieces is stable and uniform, avoiding the quality fluctuation caused by manual operation.

During the operation of the shot blasting machine for forging oxide scale removal, operators need to pay attention to the following key points to ensure the processing effect and operational safety. First, the selection of shot. The type, size, and hardness of the shot should be selected according to the material, size, and surface requirements of the forged workpiece. For ferrous metal workpieces (such as carbon steel, alloy steel), steel shot or cast iron shot with high hardness is usually used; for non-ferrous metal workpieces (such as aluminum alloy, copper alloy), glass bead or aluminum oxide shot with low hardness is used to avoid damaging the workpiece surface. The size of the shot should be matched with the thickness of the oxide scale. Larger shot is suitable for thick oxide scale, and smaller shot is suitable for thin oxide scale or workpieces that require a smooth surface. Second, the adjustment of processing parameters. The rotating speed of the blast wheel, the feed rate of the shot, and the conveying speed of the workpiece are the key parameters affecting the oxide scale removal effect. Operators need to adjust these parameters according to the actual situation. For example, for workpieces with thick oxide scale, the rotating speed of the blast wheel and the feed rate of the shot should be increased, and the conveying speed should be reduced to ensure sufficient impact time. Third, the handling of high-temperature workpieces. Some forged workpieces are still at a high temperature after forging, and direct shot blasting can not only remove oxide scale but also take advantage of the high temperature to improve the surface strengthening effect. However, operators need to pay attention to the heat resistance of the machine components, such as the conveyor belt, liners, and seals, to avoid damage due to high temperature. Fourth, safety protection. Operators must wear protective equipment such as safety helmets, goggles, earplugs, and protective clothing when operating the machine to prevent injury from flying shot and dust. In addition, operators should not open the safety door of the blast chamber during the operation of the machine to avoid accidents.

The maintenance of the shot blasting machine for forging oxide scale removal is crucial to ensure its long-term stable operation. Daily maintenance work includes: checking the wear of the blast wheel blades, liners, and other components, and replacing them in time when the wear exceeds the limit; checking the tension and operation of the conveyor belt or chain, and adjusting and lubricating them in time; cleaning the shot recovery and separation system to prevent blockage of the hopper, screw conveyor, and separator; maintaining the dust removal system, such as cleaning the filter bag, checking the fan, and ensuring the smoothness of the dust duct; checking the electrical system, such as the wiring, connectors, and sensors, to ensure the safety and reliability of the electrical components. Regular maintenance work (such as monthly, quarterly, or annual maintenance) includes: disassembling and inspecting the blast wheel, cleaning the internal components, and replacing the worn parts; inspecting and repairing the reducer, motor, and other transmission components; checking the thickness of the liner in the blast chamber and replacing it if necessary; calibrating the sensors and instruments of the electrical control system to ensure the accuracy of the parameters.

With the continuous development of the forging industry, the requirements for the quality and efficiency of oxide scale removal are getting higher and higher, which promotes the continuous innovation and development of shot blasting machines for forging oxide scale removal. The future development trends of such machines are mainly reflected in the following aspects: first, intelligence and digitization. The integration of advanced technologies such as IIoT, AI, and machine vision makes the shot blasting machine capable of real-time monitoring of the oxide scale removal process, automatic identification of the workpiece type and oxide scale thickness, and automatic adjustment of processing parameters. For example, machine vision technology can detect the surface quality of the workpiece after shot blasting, and the system can automatically optimize the processing parameters according to the detection results to ensure the best oxide scale removal effect. Second, high efficiency and energy saving. The optimization of the blast wheel structure, the adoption of high-efficiency motors and frequency conversion technology, and the improvement of the shot recovery system can reduce the energy consumption of the machine while improving the processing efficiency. Third, environmental protection and green production. The development of more efficient dust removal and noise reduction technologies, the adoption of environmentally friendly materials, and the recycling of oxide scale can reduce the impact of the machine on the environment and realize green production. Fourth, customization and flexibility. Manufacturers can provide customized shot blasting machine solutions according to the specific needs of different users, such as the size, shape, and production capacity of the forged workpieces. At the same time, the development of flexible shot blasting machines that can process multiple types of workpieces can improve the utilization rate of the machine and reduce the production cost of enterprises. Fifth, high-temperature resistance. The development of shot blasting machines that can handle higher-temperature workpieces (such as workpieces at 800-1000°C) can realize online oxide scale removal after forging, avoiding the re-oxidation of workpieces due to cooling, and improving the production efficiency and quality.

In summary, the shot blasting machine for forging oxide scale removal is an important equipment in the forging industry, which plays a crucial role in improving the quality of forged workpieces, improving production efficiency, protecting the environment, and ensuring operational safety. With the continuous progress of technology, the performance and function of such machines will be further improved, and they will make greater contributions to the development of the forging industry. Enterprises engaged in forging production should choose suitable shot blasting machines according to their own production needs, strengthen the training of operators, do a good job in the operation and maintenance of the machines, and give full play to the role of shot blasting machines in improving product quality and enhancing market competitiveness.