Shot peening of steel belts
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Shot peening is a surface treatment process that improves the durability and mechanical properties of materials by bombarding them with small spherical media. It is commonly used to recondition distorted steel conveyor belts, restoring their structural integrity and extending their lifespan.
The shot peening process
[edit]Shot peening is a restoration process for flattening a deformed steel belt in which the surface of the belt is impacted by small stainless steel or carbon steel balls, called peening shot. Each ball that strikes the belt acts like a peening hammer, creating a small indentation, or dimple, on the surface.
For the indentation to be formed, the steel belt surface layer must be in tension.[1][clarification needed] The compressed grains[clarification needed] contribute to restore the surface to its original shape by producing a hemisphere[clarification needed] of cold-worked metal, highly stressed in compression. Overlapping indentations create a continuous layer of residual compressive stress. Cracks do not propagate in a compressively stressed zone. Because most fatigue and stress corrosion failures originate at the surface, the compressive stresses from shot peening can extend the belt's lifespan.[2] Note that:
- Although it is possible to peen while the belt is in production, care must be taken to ensure that there is no loss of shot which would contaminate the finished product or the press system.
- The belt is run at a speed of 15 to 20 ft/min to start with, but this may be increased if the levelling function is satisfactory. The faster the belt runs, the less effective the peening process becomes.[3]
- The process starts with a low pressure (20 PSI), and work up in steps of 10 PSI until a noticeable effect is seen in the belt curve. For a precipitation-hardened stainless steel belt, the required pressure could be as high as 90 PSI.[4]
- If the shot becomes contaminated with oil from the belt, it becomes less effective as a blasting medium, and the oil also clogs the air blast system. If oil pickup is unavoidable, then frequent cleaning of the equipment and washing of the shot will be required.
- Peening must be done over a flat surface for results to be visible.[clarification needed]
- Peening starts from the center of a section and progresses towards the edge. Several light passes across the belt are less likely to over-compress the surface than one heavy pass which could distort the belt in the opposite direction.
- Peening must be applied to the concave side of a curve to stretch the metal on the "short" side.
Portable shot blasting unit
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Press belts may become deformed and worn over time. The portable shot blasting unit is primarily used to flatten deformed press belts and prepare the belt material for reuse. The unit is designed for field use and is portable, allowing for efficient operation. All necessary equipment (excluding the carriage frame and air compressor) fits into a box with dimensions of approximately 350 × 350 × 320 mm. The combined weight of the blaster, valve, air hose, and other components is about 25 kg, with the blasting machine itself weighing 9 kg.
A pair of universal channels (38 mm × 76 mm), typically 500 mm longer than the belt width, must be provided on-site. These channels are welded together to allow the blaster to move smoothly across the belt's surface. The total installation time, including assembling the carriage frame, generally takes only a few hours, after which the peening process can begin.[5]
An electric shut-off valve is mounted on the inlet air hose to protect the belt from over-blasting should it suddenly stop during the blasting operation. The valve solenoid must be connected (interlocked) to the press machine's power supply to be effective. For best blasting results, an air supply of 4,200 liters per minute is required at a pressure of 6 bar.[6] The unit is supplied with a flexible air hose that connects it to the local air supply. All local supply pipes should have a minimum bore diameter of 1 inch. The recommended shot blasting medium is tungsten shot (beads) with a diameter ranging from 0.2 to 0.4 mm and a hardness exceeding 40 HRC.[7]
The machine operates by drawing a quantity of tungsten shot from the bottom of the scroll case into the high-velocity nozzles. The shot is blasted onto the surface of the belt, and most of the shot bounces back into the scroll case. The air is vented through the filter socks, and any shot carried with the air is filtered out and dropped back into the scroll case.
Flattening out deformed belts
[edit]Since the 1980s, the standard procedure for addressing the issue of deformed belts has been to turn the belt over, using what was previously the back side to form the new product side.[8] This method flattens the belt by equalizing stresses on both sides. However, over time, the belt typically reverts to its original shape, albeit in the opposite direction. As a result, it often becomes necessary to turn the belt again after approximately one year.[9]
This process is time-consuming and expensive, requiring cutting the belt, dismantling it from the press, turning it, and then reinstalling it. The reinstallation involves various belt joining operations such as welding and grinding of the joint, as well as running-in procedures.[10] Additionally, this process demands specialized equipment for handling the belt, welding jigs, and skilled personnel for joint welding. Compounding the issue, production must be halted during these operations, with stoppages lasting up to a week not being uncommon.
To address the belt cross-curvature problem, the steel belt shot peening process was introduced as a potential solution.
References
[edit]- ^ Wu, Junnan; Liu, Daoxin; Guan, Yanying; Shi, Hailan; Cheng, Shumin; Shi, Jianmeng; He, Xueting; Fu, Xiaoqiang (December 2023). "Effect of shot peening forming and shot peening strengthening post-treatment on the fatigue behavior of bolt-connected 2024HDT alloy". Engineering Fracture Mechanics. 293: 109690. doi:10.1016/j.engfracmech.2023.109690.
- ^ Cheng, Yongjie; Wang, Yanshuang; Lin, Jianghai; Xu, Shuhui; Zhang, Pu (April 2023). "Research status of the influence of machining processes and surface modification technology on the surface integrity of bearing steel materials". The International Journal of Advanced Manufacturing Technology. 125 (7–8): 2897–2923. doi:10.1007/s00170-023-10960-x. ISSN 0268-3768.
- ^ Xiao, Guijian; Gao, Hui; Zhang, Youdong; Zhu, Bao; Huang, Yun (March 2023). "An intelligent parameters optimization method of titanium alloy belt grinding considering machining efficiency and surface quality". The International Journal of Advanced Manufacturing Technology. 125 (1–2): 513–527. doi:10.1007/s00170-022-10723-0. ISSN 0268-3768.
- ^ Beck, Tilmann; Smaga, Marek; Antonyuk, Sergiy; Eifler, Dietmar; Müller, Ralf; Urbassek, Herbert M.; Zhu, Tong (2024), Aurich, Jan C.; Hasse, Hans (eds.), "Influence of Manufacturing and Load Conditions on the Phase Transformation and Fatigue of Austenitic Stainless Steels", Component Surfaces, Cham: Springer International Publishing, pp. 257–288, doi:10.1007/978-3-031-35575-2_11, ISBN 978-3-031-35574-5, retrieved 2025-02-02
- ^ Heggade, V.N. (2023-04-03). "Engineering of the National Namaste Signature Bridge Pylon". Structural Engineering International. 33 (2): 291–301. doi:10.1080/10168664.2023.2174476. ISSN 1016-8664.
- ^ Wei, Xin'ao; Li, Qiyue; Ma, Chunde; Dong, Longjun; Zheng, Jing; Huang, Xing (2022-02-01). "Experimental investigations of direct measurement of borehole wall pressure under decoupling charge". Tunnelling and Underground Space Technology. 120: 104280. doi:10.1016/j.tust.2021.104280. ISSN 0886-7798.
- ^ Maleki, Erfan; Shamsaei, Nima (2024-04-25). "A comprehensive study on the effects of surface post-processing on fatigue performance of additively manufactured AlSi10Mg: An augmented machine learning perspective on experimental observations". Additive Manufacturing. 86: 104179. doi:10.1016/j.addma.2024.104179. ISSN 2214-8604.
- ^ Mingshan, Fang (2024), Kuangdi, Xu (ed.), "Block Preparation", The ECPH Encyclopedia of Mining and Metallurgy, Singapore: Springer Nature Singapore, pp. 174–174, doi:10.1007/978-981-99-2086-0_570, ISBN 978-981-99-2085-3, retrieved 2025-02-02
- ^ Shiqi, Li (2024), Kuangdi, Xu (ed.), "Secondary Remelting Refining", The ECPH Encyclopedia of Mining and Metallurgy, Singapore: Springer Nature Singapore, pp. 1886–1888, doi:10.1007/978-981-99-2086-0_988, ISBN 978-981-99-2085-3, retrieved 2025-02-02
- ^ Oravecz, Éva; Benkó, Zsolt; Arató, Róbert; Dunkl, István; Héja, Gábor; Kövér, Szilvia; Németh, Tibor; Fodor, László (2024). "Age, Kinematic and Thermal Constraints of Syn-Orogenic Low-Temperature Deformation Events: Insights From Thermochronology and Structural Data of the Nekézseny Thrust (Alpine-Carpathian-Dinaric Area)". Tectonics. 43 (4): e2023TC008189. doi:10.1029/2023TC008189. ISSN 1944-9194.