PVC Injection Molding
The basic principle of PVC injection molding is to inject melted PVC material into a mold, cool it down and demold it to obtain the product. During the injection molding process, it is necessary to control important parameters such as temperature, pressure, and time of the product.
Injection Molding Manufacturers | Defect Analysis of PVC Plastic Parts
Injection Molding Manufacturers | Defect Analysis of PVC Plastic Parts
When injection molding manufacturers use PVC materials for injection molding production, plastic parts are prone to a series of problems and defects. The so-called PVC injection molding material (fully known as polyvinyl chloride) is a polymer produced by the reaction of vinyl chloride under the action of oxides or other initiators.
Characteristics of PVC Materials
Before plasticizing PVC materials, injection molding manufacturers need to fully understand their characteristics to conduct a targeted analysis of the problems that may arise during subsequent production.
- PVC material has good heat resistance and can remain stable at high temperatures, with a melting temperature of up to 160 ℃. Therefore, it is widely used in fields such as automobiles, wires and cables, and construction.
- PVC has excellent corrosion resistance and can resist the erosion of most acids, alkalis, inorganic salts, and various organic solvents. Therefore, it is widely used in fields such as chemical engineering and environmental protection.
- Polyvinyl Chloride has good electrical insulation performance, but by adding other agents, its insulation performance can be transformed into a conductive material.
- PVC has excellent physical properties and can maintain strength and toughness even in extremely low-temperature conditions, making it widely used in the manufacturing of products with longer service life requirements such as pipes, panels, and window frames.
- Material has good environmental friendliness and can be recycled and reused.
- PVC has good plasticity and flexibility, with various processing methods. It can be molded into products with certain shapes through hot processing, injection molding, etc.
- Polyvinyl Chloride itself has good flame retardancy and is not easily flammable, but this also depends on its softness and hardness. Therefore, PVC material can be widely used in fields such as wires and cables, construction, aerospace, etc.
Application of PVC Materials
Injection molding manufacturers can manufacture PVC products in many fields, such as:
- Pipe Material: PVC material has good compression resistance, chemical resistance, and low friction. In addition, it has a fast flow rate and low viscosity in a molten state and can be used to make inlet pipes, drainage pipes, electrical wiring pipes, etc.
- Hard Materials And Plates: PVC material can not only be used to make pipes such as hard pipes and corrugated pipes but also to make hard plates. The material can be cut and welded to make various storage tanks, containers, etc., with good corrosion resistance.
- Film: Manufacturers can use PVC film to make raincoats, tablecloths, packaging bags, etc. It can also be used for the production of advertising stickers, luggage adhesive tapes, etc.
- Foam Products: injection molding manufacturers add the appropriate amount of foaming agent when mixing PVC, which can be used to produce foam plastic products, such as foam slippers, insoles, and shockproof packaging materials.
- PVC Packaging Material: Injection molding manufacturers can mix PVC material with other polymers to make laminated or transparent products, which have good airtightness and barrier properties, such as mineral water bottles, beverage bottles, cosmetic bottles, etc.
- Other Products: PVC involves a wide range of injection molded products, such as credit cards, badges, badges, personalized keychains, mobile phone chains, bookmarks, membership cards, entry permits, business cards, product accessories, promotional materials, exhibition gifts, interior decorations, first aid information cards, product nameplates, refrigerator stickers, etc.
The Causes of Water Ripple and Fusion Marks in PVC Plastic Parts
When injection molding manufacturers use PVC materials for production, large-capacity plastic parts are prone to defects such as water ripples and fusion marks. The main reasons for these problems are:
- Due to the large internal space in the cavity of high-capacity plastic parts, when the melt is injected from the gate, it will be injected into the cavity in a folded wave or spiral shape under the influence of compressed air. Once these molten states converge, water ripples will be left at the gate position of the injection molded part, while fusion marks will be left at other positions.
- At the same time, injection molding manufacturers should pay attention to the fact that in a wide cavity, the flow rate of the melt in the middle part will be faster than that in the surrounding area. This is mainly because the melt-around is easily affected by the cooling and friction of the cavity wall, reducing the speed to a certain extent. This speed difference will cause the melt to split and merge again, resulting in weld marks. Various inserts in the cavity can also lead to the formation of fusion marks.
- According to the formation principle of water ripples and weld marks, injection molding manufacturers can understand that the larger the cavity, the larger the product volume, the faster the injection molding speed, and the more severe the water ripples and weld marks are. This is also the reason why water ripples and weld marks are difficult to eliminate.
- To solve these two problems, injection molding manufacturers must first reduce the injection speed so that the melt no longer folds or spirals into the cavity. At the same time, it is necessary to ensure the smooth flow of the melt, reduce the speed difference of flow, and prevent it from splitting.
Manufacturer's Solution to Water Ripple Defects in PVC Plastic Parts
Injection molding manufacturers can use various methods to solve the problem of water ripples in plastic parts, but the most effective method is still from the perspective of mold gating and machine adjustment, which can fundamentally solve such problems.
-Mold Gate Angle
- Injection molding manufacturers can choose to set gates at positions with various coarse needles or board surfaces as barriers in the mold cavity, and the distance from the gate to the blocking position is preferably within 4mm.
- Injection molding manufacturers will try to choose to set gates at positions where the thickness of the injection molded parts is less than 4mm. Although in principle, the smaller the thickness of the injection molded part, the better, it is best not to be less than 1mm, otherwise it will increase the difficulty of injection molding.
- If the actual situation allows, injection molding manufacturers can introduce a column with a diameter of 4mm or more from the injection molded part as a transition, and then set a gate at the end of the column.
- If the injection molding manufacturer is unable to find a suitable location to set the gate, a small injection molded part can be placed in the mold cavity to block and reduce the space of the mold cavity if the actual situation allows. This not only solves the problem of water ripple but also solves the problem of welding marks by reducing the volume of the cavity. Therefore, this method is particularly suitable for injection molded parts with large volumes.
-Adjustment Angle
- To solve this problem, injection molding manufacturers can use slow first-stage injection, sometimes even adjusting the screw to be almost immovable to eliminate water ripples. However, if the slow first-stage injection is continuously used, it will make it difficult for the injection-molded part to fill the cavity, and there is also a possibility of top whitening in the latter half of the injection-molded part. So, when performing a first-stage slow injection, the injection molding manufacturer should pay attention to observation and immediately switch to a second-stage injection with a faster injection speed after confirming that the water ripple has been eliminated, to ensure that the mold cavity can be filled.
- However, if manufacturers set the secondary speed too fast, it may lead to product defects such as overflow or whitening. At this point, injection molding manufacturers can switch to the third stage of slow and low pressure when the cavity is about to fill, for the final filling and holding stage. For the speed and pressure parameters of the third stage, injection molding manufacturers can determine based on the degree of defects in the injection molded parts, or use the “positioning injection” method to solve problems such as overflow and whitening. Of course, the speed of the second level injection does not need to be too fast, just slightly faster than the speed of the first level injection, and the specific situation also depends on the actual operation.
- When injection molding manufacturers start filling, there is a small portion of the molten material that enters the mold cavity at a slow speed around the gate. Therefore, when performing the secondary fast injection, this small portion of the molten material acts as a barrier, preventing the molten material in the middle from spraying too quickly, thereby reducing the difference in filling speed and allowing for smooth filling without diversion. The problem of fusion marks can also be solved together.
When injection molding manufacturers use PVC materials during the injection molding process, they encounter far more problems than these. Regardless of the material chosen and the process used, the first thing to understand is the characteristics and applications of the material, to produce high-quality and high-precision products.
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