Shrinkage cavities often form during the production of textile machinery die castings due to solidification shrinkage. These defects not only affect the appearance of the parts but also reduce their mechanical properties and service life. To address this problem, optimizing the gating system requires comprehensive improvements in three aspects: structural design, process parameter control, and material property matching. The following analysis focuses on key technological pathways.
The core function of the gating system is to guide the molten metal to fill the cavity in an orderly manner and provide continuous feeding pressure during solidification. Traditional straight-sprue designs tend to result in excessively high molten metal flow rates, creating vortices at cavity corners and entraining gas, leading to shrinkage cavities. An improved solution is to use an arc-shaped runner, which reduces the flow rate by extending the molten metal's flow path and simultaneously utilizes centrifugal force to push the gas towards the overflow channel. For example, after optimizing the gating system, the diameter of a shrinkage cavity originally located at the root of the reinforcing rib in a textile machinery die casting decreased from 3mm to less than 0.5mm, improving the product yield by 25%.
The location and size of the ingate directly affect the feeding effect. If the ingate is too far from the hot spot area, the molten metal will solidify before completely filling the cavity, causing the feeding channel to be interrupted. For thick-walled gearboxes commonly found in textile machinery parts, a multi-point ingate design can be used to introduce molten metal into the cavity from multiple directions, ensuring that the hot spot area is always surrounded by molten metal. One company reduced the volume of shrinkage cavities inside the gearbox by 60% and essentially eliminated surface shrinkage defects by increasing the number of ingates and adjusting their cross-sectional area ratio.
The layout of the overflow system is crucial for venting gases from the cavity. Textile machinery die castings often contain complex oil passages and mounting grooves, which are prone to forming gas stagnation zones. By setting an annular overflow groove on the mold core, gas can be guided to accumulate in specific areas. For example, in the die casting of a certain type of spinning machine bearing housing, after adding a trapezoidal overflow groove to the parting surface, the shrinkage cavity originally located at the root of the threaded hole was transferred to the overflow groove, and after subsequent processing, the product performance met the standards. In addition, the coordinated design of the overflow groove and the venting groove needs to control the cross-sectional area ratio to avoid premature blockage of the venting channel by the molten metal. Matching the pouring temperature with the mold temperature is crucial for controlling the solidification sequence. Textile machinery parts often use aluminum alloys, which have a high liquid shrinkage rate. Uneven mold temperature distribution can lead to premature solidification in localized areas. By embedding copper alloy cooling rods in the hot spot zone of the mold, the solidification of the molten metal in that area can be accelerated, creating a sequential solidification pattern from thin-walled to thick-walled sections. One company optimized the mold temperature field, shifting the location of shrinkage cavities in the die-cast cradle of a textile machinery from the center of the casting to the residual section of the ingate. After removal, the internal quality of the product was significantly improved.
Adjustments to the injection process parameters must be synchronized with improvements to the gating system. If the low-speed injection stage is too fast, the molten metal fills the cavity in a jet-like manner, easily entraining gas; conversely, if the high-speed injection starts too late, the molten metal at the front of the cavity will solidify prematurely. By employing multi-stage injection speed control, the flow rate can be reduced before the molten metal reaches the hot spot zone, minimizing gas entrainment. During the die casting of a textile machinery part, adjusting the injection speed from 0.5 m/s to a segmented variable speed (0.3 m/s → 0.8 m/s → 0.5 m/s) reduced the shrinkage cavity rate by 40%.
Fine-tuning the material composition can further improve shrinkage cavity tendency. Adding 0.15% titanium to the aluminum alloy refines the grain structure and reduces solidification shrinkage stress; while controlling the silicon content within the range of 7%-9% ensures fluidity and reduces the tendency for hot cracking. One company reduced the shrinkage cavity depth of a textile machinery pulley die casting from 2 mm to 0.3 mm by adjusting the alloy composition, while simultaneously increasing the tensile strength by 15%.
The shrinkage cavity problem in textile machinery die castings requires systematic optimization of the gating system and process parameters. From the design of the curved runner to the layout of multi-point ingates, from the coordination of the overflow system to temperature field control, and then to the precise matching of the injection process and material composition, improvements in each link must be based on actual defect analysis. By comprehensively applying the above technical approaches, the internal quality of textile machinery die castings can be significantly improved, meeting the manufacturing requirements of high-precision and high-reliability equipment.
