Optimization of Parting Surface of Injection Mold to Reduce Flash of Threaded Cap in China
The parting surface of threaded cap products is mostly at the end of thread or product end face. Annular flash easily appears during mass production. It not only increases manual trimming cost, but also affects thread screwing assembly. Targeted optimization of mold parting surface structure, lapping process and supporting structure can reduce melt overflow risk and stably control flash problem.
Structure Optimization of Sealing Area on Parting Surface
Set sealing land width reasonably according to outer diameter of threaded cap product and injection pressure. Too narrow sealing land is easy to be crushed by high-pressure melt, while too wide sealing land increases lapping workload. Change flat parting surface into stepped sealing structure, sink sealing surface at outer edge of product by a certain height, disperse mold clamping force and resist radial impact of melt. Make arc transition at thread corner to avoid stress concentration at sharp corners and repeated compression collapse of parting surface. Carry out relief treatment on parting surface outside sealing area, only retain annular sealing contact band, reduce lapping difficulty brought by large-area fitting and lower mold clamping load.
Flatness Correction and Red Lead Lapping of Parting Surface
After long-term production of mold, template thermal deformation and repeated mold closing impact cause local depression of parting surface and form tiny gaps inducing flash. Disassemble mold and grind parting surface of plate A and plate B with surface grinder to eliminate template warpage and surface pressure injury. Carry out comprehensive red lead coloring lapping after grinding. Focus on checking annular sealing band outside thread to guarantee uniform contact of coloring and eliminate local virtual gap. Control contact ratio during lapping, keep non-sealing area relieved, avoid uneven stress caused by overall fitting of template and unilateral opening overflow.
Optimization of Mold Stiffness and Balanced Mold Clamping Force
Multi-cavity molds for threaded cap are prone to eccentric cavity layout and unbalanced mold clamping force. Unilateral opening of parting surface generates annular flash. Adjust cavity arrangement and adopt symmetric layout as far as possible to ensure uniform mold clamping force acting on each cavity. Add support pillars below high-pressure area of thread cavity. Support pillars cling to template to share pressure generated by injection packing and reduce elastic bending deformation of template. Check fit clearance of guide pin and guide sleeve. Replace guide parts timely when clearance is too large due to wear to guarantee mold closing positioning accuracy and prevent unilateral gap of parting surface caused by mold closing offset.
Layout Optimization of Vent Slots on Parting Surface
Trapped gas causes sudden local pressure rise in cavity, and melt breaks through parting seal to generate flash. Open vent slots at melt convergence position at thread end, process along annular parting surface in sections, reserve sealing partition between each section of vent and cannot process continuous full-circle long vent slots. The depth of vent slots strictly matches flash threshold of raw materials. Excessive depth directly leads to material overflow, while insufficient depth cannot discharge gas. Extend vent channel outward to guide gas to outside of mold, make smooth transition at channel corner to reduce carbon accumulation and blockage. Vent position should avoid thread molding working surface to prevent vent marks left on product surface.
Cooling System Optimization to Reduce Thermal Deformation of Parting Surface
Uneven mold temperature leads to different thermal expansion amount in different areas, slight warpage of parting surface and overflow gap. Add cooling water channels near outer ring of thread cavity and parting sealing band, shorten distance between cooling water and parting surface and reduce temperature difference of template. Control temperature difference between inlet and outlet of cooling water to reduce deformation caused by alternating cold and heat of template. Clean scale of water pipeline regularly to prevent local mold temperature rise caused by pipeline blockage, reduced steel rigidity and increased template compression deformation. Stable mold temperature can control shrinkage of plastic parts, reduce fluctuation of molding pressure and indirectly lower generation probability of flash.
Sealing Control of Insert Parting Joint
Thread cap molds adopt a large number of thread insert structures. Splicing gap between insert and template is invisible material overflow channel. When splitting inserts, move splicing seam out of parting line of product sealing, do not make seam at end face sealing position of threaded cap. Use positioning pin for insert assembly, finely grind insert mating surface and reserve reasonable thermal expansion gap. After mold heating, seam will not expand and become larger. If overflow trace appears at insert seam, carry out local welding repair and regrinding to eliminate tiny gaps. Check fitting state between insert and template with red lead after assembly.
Supporting Optimization of Gate and Runner to Reduce Local High Pressure
Gate position should be far away from parting sealing area at end face of threaded cap as far as possible to prevent direct impact of melt on parting surface and instantaneous high-pressure overflow. Optimize runner cross-section to reduce filling pressure and peak cavity pressure. Balance filling of each cavity in multi-cavity molds to avoid continuous flash at corresponding position caused by excessive pressure of individual cavity. Optimize mold structure corresponding to packing parameters, shorten packing transmission path, reduce continuous pressure borne by parting surface and reduce possibility of melt overflow from parting gap.
Daily Maintenance and Inspection Control of Parting Surface
Carry out nitriding surface strengthening treatment on sealing area to improve surface hardness and resist wear from long-term mold closing impact. Clean glue debris and hard particles on parting surface before each production. Foreign matter clamped between mold halves will press sealing surface and form permanent gaps. Control mold opening stroke to prevent ejection mechanism from impacting parting cutting edge and edge chipping of sealing edge. Establish regular inspection process, use red lead to check fitting condition of annular sealing band, detect tiny wear and pressure injury in advance and complete mold repair before mass flash appears.
