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High-wear parts of machinery such as shafts and gears need shot peening to ensure they have additional fatigue and wear properties. In this process, the metal surface is blasted with shots of ceramic, metallic, or glass material to form dents. Continuous blasting creates numerous overlapping dents where dislocation and cold work is done to increase the hardness scale of the metal.
Shot Peening Techniques, Technology, and Equipment
When trying to understand how shot peeners work, you must understand the various types of shot peening processes as well as the technology used. Shot peeners use rounded media to deform the metal surface of any equipment. As mentioned before, the target metal is compressed or stretched to form the dents. Special technology is applied to propel the peening media.
Shot Peening Process
The peening process involves different techniques that are all dependent on the amount of energy involved. Here are different types of shot peening processes:
- Air shot peening
- Water/wet shot peening
- Pressure shot peening
- Wheel shot peening
Common mechanical peening processes include water, air, and wheel shot peening. Some shot peening types of equipment for the same include:
Dry/Air Shot peening machine: It uses compressed air to move the peening media. This machine can either use a suction or direct pressure peening system.
Suction shot peening machine: suction peeners apply venturi siphoning to convert abrasives into high-pressure streams of air, water, or fluid. Venturi devices typically constrict moving fluid or abrasives to produce pressure. The peening media is absorbed into the water or fluid.
Pressure shot peening machine: Also known as direct pressure shot peening, this involves using pressure equipment to put energy into the abrasive media. A meter valve in the pressure equipment is opened to let out the peening media and pressurized fluid into the peening hose. The media moves through the hose to the pressure chamber and peening gun.
Direct pressure equipment is much stronger than suction machines as they can easily run heavy media like steel shot and steel grit.
Wet shot peening machine: This equipment uses water instead of air to run the shot peening media. It significantly reduces the dust produced in this process by close to 90 %. In most cases, water additives are added to prevent rust or increase its ability to remove grease.
This technique also keeps the metallic surfaces cooler than any other shot peening technique. It also suppresses static charges produced by dust from explosive materials like aluminum.
Wheel shot peening machine: This equipment applies centrifugal pressure technology. The media is usually placed at the center of a high-speeding wheel. The rotation of the wheel blades mixes the abrasive media in the machine. This technique is best for propelling heavy peening media like cast steel.
Alternative Peening Processes
Technology has given rise to new peening technologies that will soon take the industry by storm. These methods apply ultrasonic and laser energy to run the same shot peening media instead of air pressure. Let’s look at a few examples and how they work.
Cavitation peening: Applies an ultra-high pressure to produce cavitation bubbles that generate pressure for shot peening.
Ultra-sonic shot peening: It uses ultrasonic energy to peen different parts of machines.
Laser peening: This applies pressure to the surface from the water or tape layer. It doesn’t require peening media, making it easy to peen sharp corners and complex shapes.
Hammer peening: It uses air hammers or ball pen hammers to manually peen the desired metal surface. It is not an accurate method and is highly discouraged as it can damage the parts.
Strain peening: The target part is exposed to stress to expand it to its highest level before peening is done.
General Equipment Used in Shot Peening
For a successful application, you will need a machine for shot peening that meets your specific needs. In any peening technique mentioned above, you will need the following equipment for shot peening:
1. Blast Machine
It is the most important machine for shot peening you will need. They come in various types, and they all use high-quality pressure to clean and prepare the surface. You need to do a little research to help you choose a blast Machine that covers all your application needs.
2. Media Valves
These are usually placed in the blast machine and are used to control the amount of abrasive material that flows from the blast spot. Media valves come in two types: automatic and manual. Automatic valves have a shutoff that stops the abrasive flow, while manual valves do not have this feature.
3. Inlet/Outlet Valves
Inlet and outlet valves make an important component of any machine for shot peening. Valves come in different sizes depending on the piping of the machine. They are used to regulate pressure inside a shot peening machine.
4. Nozzles
Nozzles are responsible for accelerating the air and abrasive as the mixture leaves the machine. The length and width of the nozzle dictate the speed and pattern of the abrasion, while the makeup of the inner lining will determine its resistance to wear and tear.
5. Supplied-air Respirator
Operators of shot peening machines need to wear safety gear such as ears and eye protection, leather gloves, and air respirators. This ensures they have safe breathing air.
Conclusion
Shot peening is a tested and proven method to extend the lifespan of metal. A good machine for shot peening should meet the hardest performance requirements. Take note that the shape and properties of the media used can greatly influence the peening process.
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