Do you knowkey technology of hot runner application?

Time:2021-06-09 11:44:27 / Popularity: / Source:

A successful hot runner mold application project requires multiple links to be guaranteed. Among the most important are two technical factors: one is control of plastic temperature, and the other is control of plastic flow.
technology of hot runner application 

1. Control of plastic temperature is extremely important in application of hot runner molds.

Many processing and product quality problems that occur in production process directly stem from poor temperature control of hot runner system. For example, problem of poor quality of product gate when using hot pin gate method for injection molding, problem of valve pin closing difficulty when molding with valve gate method, inconsistent filling time and quality of parts in multi-cavity molds. If possible, you should choose a hot runner system with separate temperature control in multiple areas to increase flexibility and adaptability of use.

2. Control of plastic flow

Plastics must flow in balance in hot runner system. Gates should be opened at the same time so that plastic fills cavities simultaneously. For parts with large differences in weight, runner size design should be balanced. Otherwise, there will be problems such as insufficient filling and holding pressure for some parts, excessive filling and holding pressure for some parts, excessive flashing and poor quality. Size design of hot runner should be reasonable. If size is too small, mold filling pressure loss is too large. If size is too large, volume of hot runner is too large, plastic stays in hot runner system for too long, which damages material properties and causes parts to fail to meet requirements of use after molding.
Hot runner gating system can be understood as an extension of injection molding machinery. Function of hot runner system is to deliver thermoplastic melt to vicinity of molding die or directly into die adiabatically.
Hot runner can be heated independently, but thermally insulated in injection mold, so that it can individually compensate for heat loss caused by contact with "cold" mold. Hot runner molds have been successfully used to process various plastic materials, and almost all plastic materials that can be processed with cold runner molds can be processed with hot runner molds.
Problem: Cavity is not filled
Reasons: Melting temperature is too low; injection pressure is too small; gate is too small; hot nozzle is too small; mold temperature is too low; nozzle opening of melt cylinder is too small; hot nozzle is blocked.
Treatment: Increase temperature of hot nozzle and manifold, increase injection pressure, expand gate, increase mold temperature, install a large-size hot nozzle, increase discharge port of melt cylinder, and remove blockage.
Problem: Hot nozzle casting
Reason: Insufficient draw-back (reverse cable), too high melting temperature, too large gate, insufficient gate cooling, and incorrect hot nozzle type selected.
Treatment: Increase amount of draw-back (reverse cable), reduce temperature of hot nozzle or mold, select appropriate nozzle, and process correct gate size.
Problem: Hot nozzle does not work properly
Reason: There is a problem with heating wire or thermocouple, hot nozzle is blocked, and expansion of hot nozzle is calculated incorrectly.
Treatment: Check/replace heating wire, check/replace thermocouple, clean hot nozzle, recalculate and process expansion of hot nozzle.
Problem: Poor color change effect
Reason: Color operation procedure is incorrect, and hot nozzle type is incorrect.
Treatment: Refer to operation guide for color-changing operation procedure, and select type of hot nozzle correctly.
Problem: There are more flashes on product
Reasons: Injection pressure is too high, temperature is too high, flatness of sub-template is poor, and clamping force is insufficient.
Treatment: Reduce injection pressure, lower temperature of hot nozzle/sub-template/mold, and increase clamping force.
Problem: Scorch marks are produced on product or in gate area
Reasons: Insufficient air exhaust on mold, too fast injection speed, wrong gate size, and insufficient material drying.
Treatment: Increase exhaust, reduce injection speed, increase "J" size on mouth and socket size, dry material.
Problem: Gate cooled too early or solidified in the middle of processing cycle
Reason: Insufficient melt temperature, too small gate, excessive cooling of gate, too large direct contact area between hot nozzle and fixed mold, incorrect gate profile or incorrect type.
Treatment: Increase temperature of hot nozzle, increase temperature of mold in gate area, check  nozzle socket of hot nozzle to ensure that direct contact area is minimized, check gate contour processing, and correct gate contour if necessary.
Problem: Moire appears on corresponding part of product
Reason: Mold is too cold and melt temperature is not enough.
Treatment: Increase mold temperature and melt temperature.
Problem: Occasionally squeeze out cold spots from head of mouth core
Reason: Excessive heat loss from hot nozzle head
Treatment: Reduce direct contact area of head to a minimum.
Problem: There is plastic stuck to tip of bushing tip and direct mouth tip
Reason: Contact area between bushing tip and mold is not enough, heat dissipation is not enough.
Treatment: Increase contact area and enhance heat dissipation effect.
Problem: Thermal manifold cannot reach set temperature
Reason: Thermocouple has poor contact or failure, heating wire is open, and heating wire connection is too loose or too short.
Treatment: Check whether thermocouple contact is normal and wiring is correct. Check heating wire loop.
Problem: Heat manifold heats up too slowly
Cause: A heating wire is open or wiring is too loose, air gap of heat splitter is insufficient, heat insulation gasket is overcooled, and thermocouple is in poor contact.
Treatment: Check all heating wires, increase air gap, require at least 10mm, or use a heat shield, add a heat insulation board on fixed mold fixed plate (bottom plate) or reduce cooling of fixed mold fixed plate, check whether thermocouple is in good condition.
Problem: Temperature of heat manifold is unstable
Reason: Poor contact of thermocouple.
Treatment: Check thermocouple.
Problem: There are metal fragments in melt
Reason: Fragments on screw of injection molding machine, metal fragments in injection material
Treatment: Remove metal fragments and repair impurities in plastic filter of screw.
Problem: Leakage at the junction of hot manifold and hot nozzle
Reason: Expansion calculation is incorrect, W surface processing height is inconsistent, material of fixed mold fixing plate (bottom plate) is too soft, temperature of the heat splitter plate is too high for a short time, and there is a problem with installation of "O" sealing ring.
Treatment: Recalculate and check expansion, check and correct height of W surface, replace fixed mold fixing plate (bottom plate) with appropriate hardness, replace damaged parts and "O" seal ring.
Problem: Thermal splitter plate compensates for plug leakage glue
Reason: No spacer.
Treatment: Install spacers.
Problem: Oil (gas) cylinder does not work
Reason: No air/hydraulic oil enters cylinder, pneumatic/hydraulic cylinder system is stuck, and system pressure is insufficient.
Treatment: Check pipeline and pump for leakage or blockage, check cooperation of cylinder and piston, check whether feed pipeline is excessively bent, whether piston and valve needle are flexible.
Problem: Cylinder system is bitten to death
Reason: Cylinder block, heat splitter plate, hot nozzle, etc. are not concentric, fixed mold fixed plate (bottom plate) has too much heat.
Treatment: Adjust concentricity of cylinder block, splitter plate, and hot nozzle to increase cooling around cylinder block.
Problem: Cylinder block gets stuck after overheating
Reason: Cylinder block, heat distribution plate, hot nozzle, etc. are not concentric, and fixed mold fixing plate (bottom plate) has too much heat. Gasket and valve pin fixing nut are friction.
Treatment: Adjust concentricity of cylinder block, heat splitter plate, and hot nozzle, increase cooling around cylinder block, adjust gasket and valve pin fixing nut.
Problem: Glue is leaking around the valve needle bushing
Cause: Valve pin bushing on the heat manifold is too loose.
Treatment: Check diameter and height of heat distribution plate hole and valve pin bushing.
Problem: Sticky material on valve needle head
Reason: Valve needle does not emit too much heat.
Treatment: Reduce temperature of hot nozzle and gate, and increase cooling time.

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