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Optimization of injection molding of large-scale plastic products: overcoming the problem of bubbles
2025-01-08
In the injection molding production of plastic products, when manufacturing large-scale products with demanding requirements for strength and toughness, the internal air bubble problem is like a “time bomb”, which may detonate quality hazards at any time.In order to ensure that the products meet the standards, precise investigation and adjustment of the key parameters of the injection molding machine-injection pressure, speed, holding time and cooling parameters-are the only way to eliminate air bubbles and improve quality.
1. Injection pressure: accurately explore the best value
The injection pressure is the key driving force for whether the plastic melt body fills the mold cavity smoothly.At first, it is necessary to examine whether the current set pressure can push the viscous melt to spread quickly and evenly to all corners of the large product.If the pressure is low, the melt flow is blocked and the flow rate slows down, which can easily involve air in the flow process, thereby forming air bubbles inside the product.At this time, the injection pressure can be cautiously and gradually increased, each increase should be 3-8Mpa, and at the same time, pay close attention to the appearance of the product for defects and the increase or decrease of internal air bubbles.However, the higher the pressure, the better. Excessive pressure will cause the mold to withstand a huge impact force, which may cause mold deformation, product flying edges and other undesirable consequences.Through repeated mold testing, for large-scale plastic products, a suitable injection pressure range of about 70-110MPa can usually be worked out to ensure smooth filling of the melt and prevent the source of air bubbles.
2. Injection speed: segmented regulation for optimal
The injection speed is closely related to the injection pressure, which synergistically affects the filling state of the melt.Although too fast injection speed seems to shorten the molding cycle, it is actually a hidden crisis, which can easily cause the melt to form turbulence in the cavity, just like a turbulent river stirring up sediment, trapping a large amount of air in it; and if the speed is too slow, the melt will cool prematurely and the viscosity will increase sharply, making it difficult to discharge the gas.For large plastic products, a fine segmented injection speed strategy is recommended.When the melt first touches the mold gate, gently “enter” at a lower speed of 15-25mm/s to ensure a smooth start and avoid jet chaos; when the melt is filled to about 30%-40% of the cavity, steadily increase the speed to 40-60mm/s to speed up the filling rhythm; near the end of the cavity, slow down the speed again to 20-30mm/s to ensure that the melt evenly and meticulously fills every fine space, preventing bubbles from forming at the end due to pressure mutations.After each adjustment of the injection speed, the dynamic changes in the bubble distribution of the product must be rigorously compared, and fine-tuned accordingly to achieve the best filling effect.
3. Holding time: weighing the length and confidentiality
The holding stage plays an important role in eliminating air bubbles and strengthening the compactness of the product.The holding time is too short, and the plastic melt does not receive sufficient pressure supply during the cooling and shrinking process, and the interior can easily produce vacuum bubbles, just like a house collapses due to lack of support.In the initial stage, it is advisable to moderately extend the holding time, gradually expand from the conventional 4-8s to 12-18s, and simultaneously observe whether the weight of the product tends to stabilize and whether the air bubbles decrease.However, it should be noted that if the holding time is too long, it will not only lengthen the molding cycle for no reason and increase production costs, but may also cause internal stress to accumulate inside the product due to excessive pressure, causing damage to strength and toughness.At the same time, it is necessary to adjust the holding pressure in combination with the holding pressure. Generally, the holding pressure is set to 60%-75% of the injection pressure. A two-pronged approach ensures that the melt continues to be compacted during the cooling and solidification process, fills the tiny voids due to shrinkage, and completely “squeezes out” the air bubbles.
Fourth, the cooling parameters: fine layout, temperature difference control
The cooling parameters are like a "double-edged sword", which directly affects the curing rate and gas solubility of the melt.First of all, we must comprehensively verify the rationality of the layout of the cooling water channel, and strive for balanced cooling of all parts of the mold.For large-scale plastic product molds, in view of their complex structure and uneven wall thickness, it is particularly wise to use zoning cooling methods. The flow rate and temperature of cooling water are accurately adjusted for thick-walled and thin-walled areas to prevent local shrinkage due to cooling imbalances. Too fast, which in turn spawns bubbles.The cooling water temperature can be set at 18℃-28℃ at the beginning, and then flexibly fine-tuned according to the molding condition of the product.The water temperature is too low, the melt solidifies instantly, the gas is trapped in it, and there is no way to escape; the water temperature is too high, the cooling efficiency is greatly reduced, slowing down the pace of production.In addition, the control of the cooling time must be precise. It is necessary to ensure that the product is fully cooled for smooth release, but also not to extend it arbitrarily, so as not to cause soaring costs and lengthy production cycles. It is usually based on the thickness of the product, estimated according to the rule of thumb of 12-18s per millimeter, and then calibrated repeatedly in combination with the actual mold test effect.
Through systematic investigation and fine adjustment of the above-mentioned key parameters of the injection molding machine, the air bubbles and haze inside large-scale plastic products are gradually dispelled, and the strength and toughness of the products are improved in all directions, so that their quality is excellent, and they can help enterprises move forward steadily in the turbulent market wave and gain a competitive advantage.
1. Injection pressure: accurately explore the best value
The injection pressure is the key driving force for whether the plastic melt body fills the mold cavity smoothly.At first, it is necessary to examine whether the current set pressure can push the viscous melt to spread quickly and evenly to all corners of the large product.If the pressure is low, the melt flow is blocked and the flow rate slows down, which can easily involve air in the flow process, thereby forming air bubbles inside the product.At this time, the injection pressure can be cautiously and gradually increased, each increase should be 3-8Mpa, and at the same time, pay close attention to the appearance of the product for defects and the increase or decrease of internal air bubbles.However, the higher the pressure, the better. Excessive pressure will cause the mold to withstand a huge impact force, which may cause mold deformation, product flying edges and other undesirable consequences.Through repeated mold testing, for large-scale plastic products, a suitable injection pressure range of about 70-110MPa can usually be worked out to ensure smooth filling of the melt and prevent the source of air bubbles.
2. Injection speed: segmented regulation for optimal
The injection speed is closely related to the injection pressure, which synergistically affects the filling state of the melt.Although too fast injection speed seems to shorten the molding cycle, it is actually a hidden crisis, which can easily cause the melt to form turbulence in the cavity, just like a turbulent river stirring up sediment, trapping a large amount of air in it; and if the speed is too slow, the melt will cool prematurely and the viscosity will increase sharply, making it difficult to discharge the gas.For large plastic products, a fine segmented injection speed strategy is recommended.When the melt first touches the mold gate, gently “enter” at a lower speed of 15-25mm/s to ensure a smooth start and avoid jet chaos; when the melt is filled to about 30%-40% of the cavity, steadily increase the speed to 40-60mm/s to speed up the filling rhythm; near the end of the cavity, slow down the speed again to 20-30mm/s to ensure that the melt evenly and meticulously fills every fine space, preventing bubbles from forming at the end due to pressure mutations.After each adjustment of the injection speed, the dynamic changes in the bubble distribution of the product must be rigorously compared, and fine-tuned accordingly to achieve the best filling effect.
3. Holding time: weighing the length and confidentiality
The holding stage plays an important role in eliminating air bubbles and strengthening the compactness of the product.The holding time is too short, and the plastic melt does not receive sufficient pressure supply during the cooling and shrinking process, and the interior can easily produce vacuum bubbles, just like a house collapses due to lack of support.In the initial stage, it is advisable to moderately extend the holding time, gradually expand from the conventional 4-8s to 12-18s, and simultaneously observe whether the weight of the product tends to stabilize and whether the air bubbles decrease.However, it should be noted that if the holding time is too long, it will not only lengthen the molding cycle for no reason and increase production costs, but may also cause internal stress to accumulate inside the product due to excessive pressure, causing damage to strength and toughness.At the same time, it is necessary to adjust the holding pressure in combination with the holding pressure. Generally, the holding pressure is set to 60%-75% of the injection pressure. A two-pronged approach ensures that the melt continues to be compacted during the cooling and solidification process, fills the tiny voids due to shrinkage, and completely “squeezes out” the air bubbles.
Fourth, the cooling parameters: fine layout, temperature difference control
The cooling parameters are like a "double-edged sword", which directly affects the curing rate and gas solubility of the melt.First of all, we must comprehensively verify the rationality of the layout of the cooling water channel, and strive for balanced cooling of all parts of the mold.For large-scale plastic product molds, in view of their complex structure and uneven wall thickness, it is particularly wise to use zoning cooling methods. The flow rate and temperature of cooling water are accurately adjusted for thick-walled and thin-walled areas to prevent local shrinkage due to cooling imbalances. Too fast, which in turn spawns bubbles.The cooling water temperature can be set at 18℃-28℃ at the beginning, and then flexibly fine-tuned according to the molding condition of the product.The water temperature is too low, the melt solidifies instantly, the gas is trapped in it, and there is no way to escape; the water temperature is too high, the cooling efficiency is greatly reduced, slowing down the pace of production.In addition, the control of the cooling time must be precise. It is necessary to ensure that the product is fully cooled for smooth release, but also not to extend it arbitrarily, so as not to cause soaring costs and lengthy production cycles. It is usually based on the thickness of the product, estimated according to the rule of thumb of 12-18s per millimeter, and then calibrated repeatedly in combination with the actual mold test effect.
Through systematic investigation and fine adjustment of the above-mentioned key parameters of the injection molding machine, the air bubbles and haze inside large-scale plastic products are gradually dispelled, and the strength and toughness of the products are improved in all directions, so that their quality is excellent, and they can help enterprises move forward steadily in the turbulent market wave and gain a competitive advantage.
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