Nowadays, no matter in daily life or in fields of production and circulation, injection molded products can be seen everywhere. Injection molded products refer to plastics that are heated, plasticized and melted by an injection molding machine, then injected into cavity of a molding mold for molding. After cooling and cooling, melt is solidified and then demolded, product is injected by injection molding machine. These plastic products are inseparable from injection molding. As a branch of plastic processing industry, injection molding technology is fastest-growing production technology of all plastics processing technologies because it can quickly, batch, and low-cost products with complex shapes. For relevant knowledge of injection molding, many people may not know too much, following is a detailed introduction for everyone.

 

In many plastics, especially in plastics such as polyvinyl chloride, styrene, polyethyl acetate, and acrylic esters, residual trace monomers can produce unpleasant odors. Resins with very little monomer residues can eliminate those odor. If you use a resin that is odorless, it will also have a good effect. For example, DuPont plastic parts processing plant has developed a new grade of acetal copolymer, which releases a very small amount of odor during injection processing.

(1) Tertiary amine catalyst used in polyurethane foam production process often brings strong odors, and at the same time it also fogs up on interior windows of cars. Solution to this problem is to find substitutes for these amines. One of measures is to use polyhydroxy compounds. Polyhydroxy compounds are not only components of polyurethane molecular chain, but also have catalytic activity. Some polyhydroxy compounds can even replace half of tertiary amine catalyst, so that resulting product emits a much weaker odor.
(2) Phenolic stabilizers used in process of PVC extrusion or calendering are often replaced by low-odor zinc stabilizers. Heat stabilizer tin octoate is also commonly used in automotive PVC products due to its low odor and low fogging characteristics. Plant-derived oils such as erucic acid and oleic acid have much less odor than amine lubricants made from animal-derived oils (used in polyolefin and styrene food packaging materials).

If a small amount of zeolite (an aluminosilicate adsorbent) is filled in polymer, it can play a role in removing odor of material. Zeolite has a large number of crystalline cavities, these cavities can capture those small gas molecules with odor. Molecular adsorbents have been successfully applied to polyolefin extrusion pipes, injection and extrusion blow molding containers, isolation packaging materials, extrusion molding outer packaging materials and sealing polymers. Molecular adsorption powders can also be added to plastics as moisture absorbers to remove water vapor, which will also help plastic products produce odor.

For an injection molding factory, energy consumption of injection molding process accounts for about 60%. Therefore, effectively reducing energy consumption of injection molding machine is an important way to save energy in injection molding factory. With continuous improvement of energy-saving technology of injection molding machine itself, reducing overall energy consumption of injection molding plant requires a comprehensive consideration from aspects of production management, processing technology and materials, and production workshop matching.

Layout of production workshop focuses on two considerations: Under conditions of meeting production requirements, while optimizing layout according to production process, it also meets requirements of flexible application under specific production conditions.
1. Power supply, while meeting power required for stable production, there is a proper margin, so that excessive power consumption will not cause excessive functional consumption.
2. Build efficient cooling water circulation facilities, equip cooling water system with effective insulation and heat preservation systems.
3. Optimize overall production layout of workshop. Many productions have sequential process coordination, reasonable work position coordination can reduce time required for turnover and energy consumption, improve production efficiency.
4. Try to consider the most effective small units for separate control of lighting and other plant equipment.
5. Perform regular maintenance on workshop equipment to avoid damage to public facilities that affects normal production operations and increases energy consumption.
6. It is recommended to use a dust-free workshop if possible, do a good job of 5S work in workshop to prevent dust from harming precision parts of machinery.

 

Injection molding machine is a big energy consumer in injection workshop, energy consumption is mainly motor and heating.
1. Choose appropriate injection molding machine according to characteristics of product. "Big horse-drawn cart" injection molding process often means a lot of energy waste.
2. All-electric injection molding machines and hybrid injection molding machines are selected, which have excellent energy-saving effects and can save energy by 20-80%.
3. Adopting new heating technology, such as electromagnetic induction heating, infrared heating, etc., can achieve 20-70% heating energy saving.
4. Adopt effective insulation measures for heating and cooling systems to reduce heat and cold losses.
5. Keep transmission parts of equipment well lubricated, reduce increase in energy consumption caused by increased friction or unstable equipment operation.
6. Use low-compression hydraulic oil to reduce waste of working energy in hydraulic system.
7. Use of parallel action, multi-cavity injection, multi-component injection and other processing technologies can significantly save energy.
8. Traditional mechanical hydraulic injection molding machine also has a variety of energy-saving drive systems, which replace traditional quantitative pump mechanical hydraulic injection molding machine with significant energy-saving effect.
9. Regularly maintain heating and cooling pipelines to ensure that there are no impurities and scale blockages in pipelines, to achieve designed heating and cooling efficiency.
10. Ensure that injection molding machine is in good working condition. Unstable processing may lead to defective products and increase energy consumption.
11. Make sure that equipment used is suitable for products being processed. For example, special screws are often used for PVC processing.

Mold structure and mold conditions often have a significant impact on injection molding cycle and processing energy consumption.
1. Reasonable mold design, including runner design, gate type, number of cavities, heating and cooling water channels, etc., all help reduce energy consumption.
2. Use of hot runner molds can not only save materials and reduce energy consumption of material recovery, but molding process itself also has a significant energy saving effect.
3. Profiling fast cooling and fast heating mold can significantly save processing energy consumption and achieve better surface quality.
4. Ensure balanced filling of all cavities, help shorten the molding cycle, ensure product quality stability, and have excellent energy-saving effects.
5. Use of CAE-aided design technology for mold design, mold flow analysis and simulation can reduce energy consumption of mold debugging and multiple mold repairs.
6. Under premise of ensuring product quality, using a lower clamping force for molding can help extend life of mold, quickly fill mold, and help save energy.
7. Do a good job in mold maintenance to ensure effective heating and cooling water channels.

1. Choose auxiliary equipment suitable for ability, which not only meets work requirements, but also does not have too much margin.
2. Do a good job in equipment maintenance to ensure that equipment is in normal working condition. Auxiliary equipment that does not work properly can cause unstable production and even poor quality parts, resulting in increased energy consumption.
3. Optimize cooperation and operation procedures of host and peripheral equipment.
4. Optimize mutual position of peripheral equipment and production equipment, keep peripheral equipment as close to host as possible without affecting operating conditions.
5. Many auxiliary equipment manufacturers provide systems that provide energy on demand, which can achieve significant energy savings.
6. Use quick mold change equipment to reduce waiting time required to switch products in production.

Different material processing consumes different energy. At the same time, poor management of materials or improper management of recycled materials will increase production energy consumption.
1. On the premise of meeting product performance, materials with lower processing energy consumption should be selected first.
2. Under condition of satisfying performance and cost optimization, preferentially select high-fluidity materials.
3. Note that materials from different suppliers may have different process conditions.
4. Material is dried, it is best to use it as it is dried, to avoid material returning to moisture after drying and wasting energy.
5. Do a good job of material storage to prevent materials from being mixed with impurities or foreign bodies, which will eventually cause defective products.
6. Some products are allowed to add a certain amount of recycled materials, but attention should be paid to preservation and cleanliness of recycled materials to avoid defective parts due to unclean materials.

1. On the premise of satisfying product performance, use the shortest molding cycle.
2. If there are no special factors, use processing technology recommend supplier for processing as much as possible.
3. For specific products and molds, all stable equipment and process parameters are saved to shorten time for adjusting time for next production replacement.
4. Optimize process, adopt lower clamping force, shorter cooling time and pressure holding time.

 

1. Adopt auxiliary molding technology, such as gas-assisted, liquid-assisted, steam-assisted, micro-foam injection molding technology, etc.
2. Adopt a unitized molding scheme to reduce intermediate links.
3. Adopt new technologies such as in-mold welding, in-mold spraying, in-mold assembly, and in-mold decoration.
4. Use of new low-pressure molding technology shortens molding cycle and reduces melt temperature.
5. Adopt energy regeneration system.

1. To produce high-quality products at one time, reducing defect rate is the greatest energy saving.
2. Maintenance of entire production system is closely related to energy consumption. This involves not only host, but also peripheral and factory equipment. For example, if mold changing crane in workshop fails, manual mold replacement is required, which will inevitably extend waiting time of equipment and increase energy consumption of equipment.
3. Equipped with workshop energy consumption monitoring system, which is convenient for enterprises to implement energy analysis and improvement purposefully.
4. When equipment is shut down for maintenance, not only check maintenance content and items of equipment itself, but also pay attention to condition of connection between equipment and other systems, whether working performance is reliable.
5. Regularly compare with industry benchmarks to see if there is room for further improvement.
6. Establish reliable contracts and cooperative relationships with suppliers, which are beneficial and harmless to enterprise energy conservation management.

1. Operators must conduct systematic operation training.
2. Machine personnel should carry out simple equipment maintenance training.
3. Close cooperation with front-line production personnel of various departments.

Processing of injection molded products is an extremely complex process, a little carelessness will cause errors and lead to product scrapping. Complete injection molding process includes stages of feeding, plasticizing, filling, holding pressure, backflow, cooling, and demolding. Each stage must be strictly monitored and controlled.
First, feeding: Adding granular or powdered plastic into hopper of injection molding machine, which is brought into barrel by plunger and screw for heating.
Second: Plasticization: After heating, compacting and mixing molded plastic in barrel of injection molding machine, it is a process in which loose powdery particles or granular solids become continuous homogenized melt.
Third, filling: Plasticized plastic melt is pushed by plunger or screw of injection molding machine to enter and fill mold cavity through nozzle and gating system of mold at a certain pressure and speed. This stage is called mold filling.
Fourth, pressure retention: After mold filling is completed, under push of plunger or screw, melt still maintains pressure for feeding, so that melt in barrel continues to enter cavity to supplement shrinkage of plastic in cavity. Pressure holding time should be appropriate. Long holding time will easily cause internal stress in plastic part, causing warpage or cracking of injection part.

 

Fifth, reverse flow: After pressure holding is over, melt pressure in plunger or screw backstage and cavity is released. At this time, melt pressure in cavity will be higher than pressure in front of gate. If opening is not frozen at this time, melt in cavity will flow backwards through gating system, causing injection molded parts to shrink, deform, and loose texture. If gate is frozen when injection pressure is withdrawn, backflow phenomenon will not occur. It can be seen that whether backflow occurs is related to pressure holding time.
Sixth, cooling: Cooling process of plastic injection molded part in mold refers to entire process from when plastic melt at gate is completely frozen to injection molded part being pushed out of mold cavity. At this stage, neither feeding nor reverse flow continues, plastic in cavity continues to cool, harden and shape.
Seventh, demoulding: Mould can be opened after plastic part is cooled, and plastic injection part is pushed out of mould under action of ejection mechanism.

1. Different raw materials require different temperatures during injection molding. Too high or too low temperature will have a bad effect on processing of raw materials and adversely affect production of final product. For example, if temperature is too low, there will be some abnormalities in color of liquid raw materials; if it is too high, product will have burrs after production, and product quality will not meet requirements.
2. It is necessary to pay attention to controlling cooling time during injection molding process, specific time required needs to be determined according to specific conditions of processed product. Injection mold processing has a greater impact on brightness of product, so more attention must be paid.
3. It is necessary to pay attention to controlling speed in pouring channel during injection molding. If it is too fast, there will be burrs, it will also lead to overfilling and burning. If it is too slow, it will shrink and break easily. Therefore, when pouring, we must pay attention to control of its processing speed, so that quality of products produced can meet required requirements.