2015年5月14日星期四

Analysis and solution of injection flow

Flow marks (Flow Lines) definition:
Linear traces of the molded article surface, this trace shows the direction of flow of melt glue. Injection molding machine

1. Injection pressure and dwell inadequate
Injection pressure and holding pressure is insufficient condensed skin pressed against the mold surface, leaving in the direction of flow of melt glue sink marks. Increase injection pressure and holding pressure, condensate layer can be pressed against the mold surface until the product setting, free from the generated flow marks.

2. The residence time (Residence Time) improper
Plastic tube inside the residence time is too short, melt glue temperature is low, even if we manage to fill the mold cavity, when packing or plastic can not be compacted, leaving in the direction of flow of melt glue sink marks. Plunger tube material for the ratio (Shot-to-Barrel Ratio), should be 1 / 1.5 and 1/4 between.

3. Cycle time (Cycle Time) improper
When the cycle time is too short, plastic tube inside the heating less, melt glue temperature is low, even if we manage to fill the mold cavity, holding pressure still can not leave the plastic melt adhesive pressure to stay in the flow direction of sink marks, cycle time fully extended to plastic melting temperature high enough to melt glue so that the flow direction generated by the appropriate without sink marks.

4. Tube temperature is too low
When the tube temperature is too low, melt glue temperature is low, injection pressure and holding pressure is insufficient condensed skin pressed against the mold surface, leaving in the direction of flow of melt glue sink marks. Improve the material temperature, injection pressure and holding pressure condensate layer is pressed against the mold surface until the products stereotypes, not by the generated flow marks. Material temperature setting can refer to the material manufacturer's recommendations. After the feeding tube, middle and front nozzle (Rear, Center, Front and Nozzle) in four districts, later setting forth the material temperature should gradually improve, every forward one area, increased 6C. If necessary, sometimes the material temperature of the nozzle area and / or the front region of the set and in the same area.

5. Nozzle temperature is too low
 Plastic absorption heating zone (Heating Bands) in the feed tube heat release caused by rotation of the screw and the plastic molecules frictional heat generated by the relative motion, the temperature is gradually increased. Feed tube in a heating zone of the last nozzle, this should melt adhesive material to achieve the desired temperature, subject to moderate heating, in order to maintain the best condition. If the nozzle temperature is set high enough, because the nozzle and mold exposure, taking too much heat, melt temperature will drop, injection pressure and holding pressure is insufficient condensed die face pressed against the skin, leaving the melt glue in the flow direction of sink marks. Increase the nozzle temperature. Usually the nozzle zone temperature set lower than the front region of high temperature 6C °

Mold

1. Mold temperature is too low
Mold temperature is too low will cause the material temperature drops too fast, injection pressure and holding pressure is insufficient condensed skin pressed against the mold surface, leaving in the direction of flow of melt glue sink marks. Increase mold temperature, maintain a high melt temperature, injection pressure and holding pressure condensate layer is pressed against the mold surface until the products stereotypes, not by the generated flow marks. Mold temperature can be set from the proposed value starting material manufacturers. Every incremental adjustments may be 6C, plastic injection 10 times, after forming in stable condition, according to the results and decide whether further adjustments.

2. Gate (Sprue), runner (Runner), or / and gate (Gate) small gate (Sprue), runner (Runner), or / and gate (Gate) is too small, the flow resistance to improve , if the injection pressure is insufficient, advance melt glue wavefront will become increasingly slow, plastics will become increasingly cold, injection pressure and holding pressure is insufficient condensed die face pressed against the skin, leaving the melt glue in the flow direction The sink marks. In CAE (such as C-MOLD) on your computer to different melt adhesive delivery system (including the sprue, runners and gates) filling simulation analysis to identify the ideal sprue, runner and gate size ( including the length and cross section of dimensions such as diameter, etc.), it is feasible way.

2. Venting inadequate
inadequate venting will make melt glue filling blocked, before melt glue wave can not be condensed in the mold is pressed against the skin surface, leaving in the direction of flow of melt glue sink marks. Each section of the flow channel at the end began to exhaust, so you can exclude a large number of air before pouring into the mold cavity. Cavity exhaust but can not be overlooked. Parting surface opposite the gate, consider adding vents, corresponding to the product at the end of the blind hole, consider adding exhaust ejector pin. CAE (such as C-MOLD) simulation melt glue filling, can help us quickly find all possible at the end of the filling (Last Filled Area), which is required to increase the vent areas. Figure claims vary, foolproof. Installation of a vacuum system, was evacuated before filling and when filling, it is an effective method of exhaust. For some bite flower decoration products face words, this may be the only exhaust recipe.

Plastic

1. Illiquid
Flow length of the wall thickness ratio (Flow Length to Thickness Ratio) large cavity, shall be easily flowing plastic filling. If the plastic flow is not good enough, moving further and further slow melt glue, the more slowly the more cold, injection pressure and holding pressure is insufficient condensed skin pressed against the mold surface, leaving in the direction of flow of melt glue sink marks. Materials manufacturers depending on the particular design, can provide professional advice: In principle no burrs, selection of the most free-flowing plastic. 2. Using forming lubricant (Molding Lubricant) improper lubricant content is generally less than 1%. When the flow length to thickness ratio, the lubricant content must be appropriate to improve to ensure that the condensate is pressed against the mold surface until the products stereotypes, not by the generated flow marks. Increase the content of the lubricant, and shall be agreed upon after the material manufacturer.

Operator

1. Bad habits

Operators too early or too late switch forming machine door, will make molded inconsistent results. When the feeding tube heater due to heat loss irregular attempt to replenish calories, plastics uniform temperature easily, and have cold spots (Cold Spot) produced, injection pressure and holding pressure is not easy to cold near the surface of the skin is pressed against the mold on the left in the direction of flow of melt glue sink marks. Usually it should continue to educate the operator, so that we understand the trouble forming cycle inconsistency may bring, and understand the importance of maintaining good habit forming operation. Proper rest shifts, the operator can be prevented due to not following the physical, mental concentration, and cause errors. Using robots (Robots) and other automated molding cycle is to keep a consistent road.

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