Shot Blast Leakage Mapping
Preventing Efficiency Loss in Machines
Shot blasting is a widely used process in industrial applications to achieve a smooth and polished surface finish for workpieces. During the shot blasting process, shots of small size with high velocity are propelled onto the surface of the workpiece. However, this process can result in the loss of efficiency of the machine due to the critical issue of shot leakage.
Shot blast leakage occurs when shots escape the chamber through various points, leading to increased waste, potential safety hazards, and decreased efficiency of the machine. To prevent these issues, it is important to map the critical points of leakage in the shot blasting machine and take remedial measures to prevent further loss of efficiency.
OBSERVATIONS
One of the main causes of leaks in machine cabins is worn out rubber padding along the sides of the doors and walls of the cabin. This rubber padding can deteriorate over time, potentially allowing water or other substances to enter or exit the cabin. If not addressed, this issue can lead to damage or malfunction of the equipment housed within the cabin, as well as potential safety hazards for operators and nearby personnel.
Another critical point where leaks can occur in machine cabins is at the upper side of the cabin where the chain hook is attached. This area can be susceptible to wear and tear, which can cause cracks or gaps that allow water or other substances to enter or exit the cabin. Depending on the specific design of the cabin, there may be different methods for managing this issue, such as adding additional sealing materials or replacing worn components.
Hard metal plates that are welded inside machine cabins can erode over time, potentially leading to leaks if not addressed. These plates are typically used to reinforce the structure of the cabin or provide additional protection for sensitive equipment. However, if they become corroded or damaged, they can create gaps or cracks that allow water or other substances to enter or exit the cabin.
This study involves an investigation into the surface topography of aluminium after undergoing the shot blasting process. The Alicona “InfiniteFocus” microscope (IFM) G4 was utilized to obtain the surface topography data from all surfaces of the standard comparators and the castings. The objective used in the microscope was 5×, providing a vertical resolution of 410 nm. The XY range for this objective was 2.84 mm × 2.15 mm, with a light beam spot diameter of 6 mm and a cut-off length of 800 m.
For the tactile standard roughness comparators A1 and A2, 20 areal scans were conducted on each surface, while six areal scans were performed on each surface of the six Swecast standards (S25, S40, S63, S100, S160, and S250). Each areal scan had five corresponding profile scans. To compare the roughness values obtained with the Alicona “InfiniteFocus” microscope (IFM) G4, the Taylor Hobson Form TalySurf stylus instrument was used to measure the roughness of the Swecast comparators.
The casting geometry utilized for the production of the castings examined is described in below figure for the vertically-parted molds. Prints 2 and 4 were spray-coated, while prints 1 and 3 were uncoated. For each print in a mold, the top and down arms of the front face and reverse face were scanned for roughness measurement. Six measurements were taken on each face and then averaged.
Fig. Surface topography of comparators from measuring system (a) A1 and (b) A2
Fractography was used to study fracture surfaces of tested samples, revealing that cracks always originated at the corners of the samples. Figure below exhibits secondary electron images at the casting skin, crack propagation zone, and sudden rupture zone. The images show that a cleavage fracture is seen in the casting skin and crack propagation zone, while a ductile-dimple fracture is seen in the sudden rupture zone. The study identified the different fracture mechanisms and also revealed a layer of graphite depletion/degradation at the top surface of the casting skin. The use of fractography provided important insights into the materials’ properties and behavior under stress.
Fig. Three secondary electron images of an as- cast sample (a) at the casting skin (b) cleavage fracture in crack propagation zone and (c) ductile-dimple fracture in a sudden rupture zone.
The study investigates the effect of nodularity on casting skin thickness and the pearlitic rim thickness in CG iron plates. Higher nodularity leads to a decrease in casting skin and pearlitic rim thickness. The study also found that lower nodularity CG iron had better fatigue properties due to lesser casting skin. Shot blasting was found to effectively eliminate casting skin and improve the fatigue limit of the plates by up to 43.5%. The improvement was attributed to work hardening on the surface of the samples. The study provides insights for improving the quality of CG iron castings and designing shot blasting processes for their surface treatment.