Structural Design Key Points of Plastic Injection Molds for Oil Seals and Gaskets
Oil seals and sealing gaskets demand strict dimensional tolerance, concentricity and sealing surface quality. Most products are thin-walled circular components prone to flash, eccentricity, uneven shrinkage and ejection scratches. Mold structural design must focus on sealing surface precision, venting, ejection and cavity positioning to reduce common molding defects.
1. Cavity Layout and Concentric Positioning Design
Sealing rings belong to rotary circular parts. Symmetrical center gating layouts are preferred to reduce eccentricity caused by uneven melt pressure. Multi-cavity arrangements adopt uniform circular distribution to prevent wall thickness deviation triggered by unilateral pressure. Cavities and cores must adopt precision spigot positioning. Circular spigots assist centering during mold closing instead of relying merely on guide pins to guarantee coaxiality. Thin-wall oil seal molds control core floating clearance and adopt wear-resistant locating rings. Wear on positioning structures during continuous production leads to inconsistent wall thickness on sealing surfaces and weakens sealing performance of finished parts.
2. Gating System Selection and Gate Location Control
Small-sized sealing rings often use pinpoint gates or submarine gates. Large oil seals can adopt circular film gates. Gates should be placed on non-sealing surfaces. Gate marks on sealing lips cause burrs and weld lines that trigger liquid leakage. Circular film gates enable uniform circumferential melt flow, reduce weld line visibility and improve concentricity, yet operators must plan gate trimming procedures accordingly. Side gates on one side should be avoided, as unilateral filling easily creates weld marks and core offset. Runner systems must maintain symmetrical balance. For multi-cavity molds, each runner maintains equal length and cross-section to achieve synchronized filling of all cavities.
3. Targeted Optimization of Venting Systems
Closed circular cavities easily trap air where melt converges, leading to burning marks and bubbles that damage sealing performance. Circular vent grooves are arranged at weld line positions and core roots. Vent groove depth requires strict control to avoid thin flash difficult to remove. Combine circular parting line venting. Vent depth for miniature oil seal molds is recommended between 0.01mm and 0.02mm. For large skeleton oil seals, additional vent gaps at core fitting sections facilitate air removal during filling and lower bubble defects on sealing lips.
4. Ejection Structure to Prevent Deformation and Scratches on Seals
Rubber and soft elastomer gaskets are flexible. Single-point ejection with rigid ejector pins easily twists components and creates scratches on sealing lips. Combined ejection using circular ejector rings and evenly distributed ejector pins ensures uniform circumferential ejection force. Core surfaces should achieve low surface roughness with fine polishing. Wear-resistant and anti-corrosion mold steel reduces material adhesion. Appropriate draft angles must be designed for sealing lips. For internal undercut sealing lips, simplified core pulling mechanisms should be evaluated. Forced ejection will tear lip structures. Negative pressure auxiliary ejection can be adopted for soft elastomer products to improve surface integrity.
5. Cooling Channel Layout for Stable Shrinkage and Dimensions
Uniform shrinkage around circular gaskets determines dimensional accuracy. Cooling channels follow circular cavity contours, and internal cores contain central cooling lines to achieve balanced internal and external cooling. Avoid uneven distance between cooling lines and mold cavities. Uneven temperature distribution creates inconsistent shrinkage, oval shape and variable wall thickness. Precision oil seal molds reduce local overheating near gate regions. Uniform spacing between cooling channels and cavities stabilizes molding cycles and minimizes dimensional variation in mass production.
6. Parting Line and Flash Prevention for Sealing Surfaces
No flash is allowed on oil seal sealing lips. Parting surfaces require precision machining with sufficient hardness to resist deformation after repeated mold closing. Continuous circular parting surfaces are recommended, and extra pressure-bearing surfaces can be added in critical sealing zones. Tight control over parting line clearance is required, with stricter standards for soft elastomer molding. For composite oil seals with metal skeletons, precision locating seats fix skeletons to avoid material overflow caused by offset skeletons. Sufficient space should be reserved for manual or robotic skeleton loading operations.
Conclusion
The core goals of oil seal and gasket mold design are maintaining concentricity, eliminating sealing surface defects and realizing stable ejection without deformation. Design priorities include symmetrical filling, precision centering, sufficient uniform venting, balanced circular ejection and synchronized circular cooling. Gates must stay away from functional sealing surfaces, and parting line gaps are controlled to limit flash. Clearance and ejection structures should be adjusted according to material hardness. Proper structural design supports consistent production of gaskets meeting sealing specifications over long production runs.
