Text|Meite Polymer Nova
Those who are a little familiar with injection molding should know that when there is not enough material in injection molding, it means that material is not filled and, as a rule, there will be no flash (overflow, drape) or very little flash. , while injection molding has a flash (overflow) glue, Phi Feng), it means that material is sufficiently filled, and there will basically be no shortage of materials.
However, author faced such a situation. The structure of product is simple. As shown in figure, in process of product debugging, if pressure is insufficient, there will be a shortage of materials. When pressure gradually increases, shortage of materials will gradually improve, but pressure increases to When it is large enough, shortage of material still exists, but at same time, serious outbreaks (glue overflow, leading edge) are observed.
Before parsing, briefly explain reasons for lack of material and a flash drive. Reason for lack of material:
1. Insufficient injection molding pressure,
2. Insufficient barrel storage,
3. Not enough fluidity of material,
4. Bad exhaust in mold cavity.
Reason for flashing:
1. The injection pressure is too high,
2. Too much glue,
3. Insufficient clamping force,
4. The insertion and holding time is too long,
5. There are mold defects at parting line,
6. There is a deflection of clamping slide, which causes mold clamp to move.
Based on results of injection molding products, there is a material deficiency in middle of upper part of material A, and surrounding flashes (overflow, burrs) are serious, while situation of same material deficiency, material B has no material, and with flash material B (glue overflow, Phi Feng) situation is much better. The result of judgment is that product from material B is good and product from material A is bad.
Because product made from material B is fine, mold and equipment problems are basically excluded, so following analysis is carried out in terms of materials and processes.
The raw material is first analyzed in terms of fluidity. The melt index of two materials (230° C., 5 kg) is respectively: material A is 25 g/10 min, material B is 3 g/10 min, material A has better fluidity. , and theoretically suitable for injection molding. More favorable, so liquidity is not cause of defect. Further analysis shows that material A is fully vulcanized TPV, material B is semi-vulcanized TPV, fully vulcanized TPV is a pure sea island structure, and semi-vulcanized TPV is a two-phase mixture structure, so although fluidity of material B is only 3g/ 10 min. But due to its two-phase structure, uniformity of system is better, so corresponding products can be injection molded.
From technological point of view, two-material injection molding process is a single-stage injection molding. Theoretically, multi-stage injection molding will be used for large-scale injection molding to produce more advanced products. However, material B can produce quality products mainly because reason for its semi-fluid TPV system is that material flows more smoothly in cavity, so quality products can be produced while material A does not meet requirements. The author believes that injection pressure should be high enough for single-stage injection molding, and state of island structure of material is not enough. The stability of melt flow at high injection pressure is insufficient, and it is easy to create air traps. Therefore, for injection molding of material A, multi-stage injection molding, for example, fast-slow, should be used.
Some people here might think it's not enough to directly select material B, but material B is semi-vulcanized TPV and its physical properties are worse than fully vulcanized TPV, especially in terms of aging resistance, so final choice depends on perception buyer of commodity in demand.
Strength note. This article has a good idea and basically explains problem. Because response speedThe birth rate of a fully cured TPV is relatively high, requirements for a runner are relatively high. If it is small, it is easy to cause TPV to freeze, making it difficult to fill out form. Therefore, we also suggest that customers consider modifying mold guide to solve problem.
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