https://www.bronzecast.net/product/bushings-series/
In the production process of casting companies, casting defects such as shrinkage, bubbles, and segregation are unavoidable, which results in low yield of castings. Re-production is faced with a lot of manpower and electrical energy consumption. How to reduce casting defects is a problem that founders have always been concerned about. 1. Good casting starts with high-quality smelting. Once the casting is started, the smelting process must be prepared, inspected and handled. If required, the lowest acceptable standard may be used. machining bushing However, a better option is to prepare and adopt a smelting scheme that is close to zero defects. 2. Avoid turbulent inclusions on the free liquid surface.
This requires avoiding excessively high velocity on the front free liquid surface (meniscus). For most metals, the maximum flow rate is controlled at 0.5m/s. For closed pouring systems or thin-walled parts, the maximum flow rate will be increased appropriately. This requirement also means that the drop height of the molten metal cannot exceed the critical value of the "static drop" height. 3. Avoid laminar flow inclusions on the surface of the molten metal crust. This requires that during the entire filling process, the front end of any liquid metal flow does not stop early. The liquid metal meniscus in the early stage of filling must be kept in a movable state and not affected by the thickening of the surface shells, which will become part of the casting. To achieve this effect, the front end of the molten metal can be designed to expand continuously. In practice, only the bottom up "uphill" can achieve a continuous ascent. (For example, in gravity casting, flow upwards from the bottom of the sprue). This means: Bottom-injection pouring system; Do not have "downhill" form of liquid metal falling or slipping; Do not have a large area of horizontal flow; Do not cause the front end flow of liquid metal due to dumping or waterfall flow. 4. Avoid air entrapment (produce air bubbles) Avoid air bubbles generated by air entrapment in the pouring system from entering the cavity. This can be achieved by: Designing a stepped gate cup reasonably; Designing a sprue reasonably and filling it quickly; Using a "dam" reasonably;
Avoiding a "well" or other open gating system; Using a small cross-section runner or Straight runners use ceramic filters near the junction of the runners; use degassing devices; the pouring process is uninterrupted. 5. Avoid air holes in the sand core. Avoid air bubbles generated by the sand core or sand mold entering the metal liquid in the cavity. The sand core must ensure a very low gas content, or use appropriate exhaust to prevent the sand core porosity. Unless it is guaranteed to be completely dry, the clay-based sand core or mold repair glue cannot be used. 6. Avoid shrinkage holes Due to the influence of convection and unstable pressure gradients, castings with large cross-sections cannot achieve upward shrinkage. So follow all the packing rules to ensure a good packing design, use computer simulation technology to verify, and actually cast the sample. Control the flash level at the connection between the sand mold and the sand core; control the thickness of the mold coating (if any); and control the alloy and mold temperature. 7. Avoid convection Convection hazards are related to solidification time. Both thin-walled and thick-walled castings are not affected by convection hazards. For medium-thickness castings: reduce the convection hazard by casting structure or process; avoid upward shrinkage; turn over after pouring. 8. Reducing segregation Prevent segregation and control within the standard range, or the area where the composition allowed by the customer exceeds the limit.
If possible, try to avoid channel segregation. 9. Reduce residual stress Do not quench water (cold or hot water) medium after solution treatment of light alloy. If the casting stress does not seem to be large, polymer quenching media or forced air quenching can be used. 10. Given reference points All castings must be given positioning reference points for dimensional inspection and processing.
In the production process of casting companies, casting defects such as shrinkage, bubbles, and segregation are unavoidable, which results in low yield of castings. Re-production is faced with a lot of manpower and electrical energy consumption. How to reduce casting defects is a problem that founders have always been concerned about. 1. Good casting starts with high-quality smelting. Once the casting is started, the smelting process must be prepared, inspected and handled. If required, the lowest acceptable standard may be used. machining bushing However, a better option is to prepare and adopt a smelting scheme that is close to zero defects. 2. Avoid turbulent inclusions on the free liquid surface.
This requires avoiding excessively high velocity on the front free liquid surface (meniscus). For most metals, the maximum flow rate is controlled at 0.5m/s. For closed pouring systems or thin-walled parts, the maximum flow rate will be increased appropriately. This requirement also means that the drop height of the molten metal cannot exceed the critical value of the "static drop" height. 3. Avoid laminar flow inclusions on the surface of the molten metal crust. This requires that during the entire filling process, the front end of any liquid metal flow does not stop early. The liquid metal meniscus in the early stage of filling must be kept in a movable state and not affected by the thickening of the surface shells, which will become part of the casting. To achieve this effect, the front end of the molten metal can be designed to expand continuously. In practice, only the bottom up "uphill" can achieve a continuous ascent. (For example, in gravity casting, flow upwards from the bottom of the sprue). This means: Bottom-injection pouring system; Do not have "downhill" form of liquid metal falling or slipping; Do not have a large area of horizontal flow; Do not cause the front end flow of liquid metal due to dumping or waterfall flow. 4. Avoid air entrapment (produce air bubbles) Avoid air bubbles generated by air entrapment in the pouring system from entering the cavity. This can be achieved by: Designing a stepped gate cup reasonably; Designing a sprue reasonably and filling it quickly; Using a "dam" reasonably;
Avoiding a "well" or other open gating system; Using a small cross-section runner or Straight runners use ceramic filters near the junction of the runners; use degassing devices; the pouring process is uninterrupted. 5. Avoid air holes in the sand core. Avoid air bubbles generated by the sand core or sand mold entering the metal liquid in the cavity. The sand core must ensure a very low gas content, or use appropriate exhaust to prevent the sand core porosity. Unless it is guaranteed to be completely dry, the clay-based sand core or mold repair glue cannot be used. 6. Avoid shrinkage holes Due to the influence of convection and unstable pressure gradients, castings with large cross-sections cannot achieve upward shrinkage. So follow all the packing rules to ensure a good packing design, use computer simulation technology to verify, and actually cast the sample. Control the flash level at the connection between the sand mold and the sand core; control the thickness of the mold coating (if any); and control the alloy and mold temperature. 7. Avoid convection Convection hazards are related to solidification time. Both thin-walled and thick-walled castings are not affected by convection hazards. For medium-thickness castings: reduce the convection hazard by casting structure or process; avoid upward shrinkage; turn over after pouring. 8. Reducing segregation Prevent segregation and control within the standard range, or the area where the composition allowed by the customer exceeds the limit.
If possible, try to avoid channel segregation. 9. Reduce residual stress Do not quench water (cold or hot water) medium after solution treatment of light alloy. If the casting stress does not seem to be large, polymer quenching media or forced air quenching can be used. 10. Given reference points All castings must be given positioning reference points for dimensional inspection and processing.
