Cooling System Design of Injection Mold for Thickened Plastic Stool
The overall wall thickness of thickened plastic stool is relatively large, with obvious plastic accumulation areas on the stool surface, supporting legs and reinforcing ribs. The heat dissipation speed of plastic solidification is much slower than ordinary thin-wall plastic parts. The cavity surface area of the mold is large. If the water channel arrangement is sparse or asymmetric, local rapid cooling and lag cooling of thick-wall positions will occur, further causing overall inward or outward warpage of the stool and excessive flatness deviation of the stool surface.
Meanwhile, the shrinkage volume of melt solidification in thick-wall areas is large, and uneven cooling is easy to produce surface shrinkage and internal micro-voids. Excessively high mold temperature during demolding will also lead to product sticking, whitening by ejection and deformation. In addition, stool is a mass-produced general product with high requirements on molding cycle. Natural cooling alone cannot meet the mass production rhythm, and forced circulating cooling water channels must be designed for efficient constant temperature heat dissipation.
2. Basic Design Principles of Cooling System
3. Cavity Cooling Water Channel Design
The cavity is dominated by the molding area of the upper surface of the stool, adopting a multi-layer series annular water channel layout arranged evenly along the outer contour of the stool surface. The water channel hole adopts standard specification with uniform spacing, surrounding the outer edge of the stool surface and the middle thick-wall area to form closed-loop circulating heat dissipation. Appropriately encrypt the water channel arrangement at the four corners and edge thick plastic positions of the stool, narrow the water channel spacing, speed up heat dissipation at corners, and prevent warpage and shrinkage caused by lag cooling at corners. The water inlet and outlet of the cavity water channel are arranged diagonally to avoid excessive local temperature difference caused by water flow retention, ensuring uniform molding temperature and synchronous solidification shrinkage of the entire stool surface, and guaranteeing flat and non-deformed stool surface.
The core corresponds to the inner supporting legs, reinforcing ribs and concave thick-wall areas of the stool with more concentrated heat accumulation, which is the key part of cooling design. The core adopts a combined structure of straight water channels and baffle plates. Independent vertical water channels are set for the four supporting legs, directly leading to the thick plastic heat accumulation area at the root of the legs to accurately take away local high temperature. Transverse water channels are interspersed at the inner longitudinal and transverse reinforcing ribs, connected with vertical water channels to form a three-dimensional heat dissipation network, solving the problems of slow cooling and easy shrinkage marks at thick ribs. The core water channel also maintains a fixed distance from the molding surface, balancing heat dissipation efficiency and mold structural strength. The water flow circulates from top to bottom to take away accumulated heat inside the core, making the internal and external cooling speed of the stool tend to be consistent.
5. Local Strengthened Cooling Design for Key Positions
The root of supporting legs, the thickened center of stool surface and the junction of strips are the positions with the most serious heat accumulation of thickened plastic stool. Conventional water channels are difficult to achieve ideal heat dissipation effect, so local strengthened cooling design is required. Inlaid cooling structures such as copper inserts or straight water wells are added at these concentrated plastic accumulation points to quickly export local heat by using high thermal conductivity of metal. For narrow rib positions where conventional water channels cannot be arranged due to limited mold space, water-stop columns and water-stop plates are adopted to force cooling water to form turbulent circulation locally, improving heat dissipation efficiency and avoiding shrinkage, deformation and prolonged molding cycle caused by lag local cooling.
6. Cooling System Parameters and Pipeline Layout Specifications
Unified standard aperture is adopted for mold water channels. The distance between water channels and cavity molding surface is kept at a fixed value, and the spacing between adjacent water channels is arranged evenly to avoid excessive density difference. All water channel interfaces adopt unified specifications, centrally arranged on the side of the mold to facilitate external connection of cooling water circulator with neat pipeline installation without interfering with the action of injection molding machine. Independent inlet and outlet water circuits are designed for zoned temperature control of cavity and core. The water flow and water temperature can be adjusted separately according to actual molding conditions to realize fine adjustment of local temperature difference. Normal temperature circulating water is adopted for cooling water. A water temperature machine can be equipped for constant temperature control in mass production to stabilize the mold temperature within a reasonable range, further reduce internal stress of products and stabilize dimensional accuracy.
7. Design Summary
The core of cooling system design for thickened plastic stool injection mold is to balance overall cooling and strengthen heat dissipation at thick positions. Through the annular water channel of cavity, three-dimensional through water channel of core, combined with local strengthened cooling structure of supporting legs and ribs, it can effectively solve common problems such as uneven cooling, warpage deformation, surface shrinkage and long production cycle of thick-wall products. Reasonable water channel layout not only optimizes the heat dissipation performance of the mold, but also makes the molding shrinkage of the stool more uniform and demolding more stable. While ensuring the appearance and dimensional quality of products, it greatly shortens the injection cooling time and improves the mass production stability and economic benefits of the mold.
