Plastic Injection Molding
Plastic injection molding is the process of heating, plasticizing, and melting plastic using an injection molding machine, then injecting it into the cavity of a molding mold to form a product. After cooling and lowering the temperature, the molten material solidifies and is demolded to obtain the product. Plastic products are widely used in various industries, including textile equipment and automobile manufacturing.
Injection Moulding Manufacturers
Injection moulding manufacturers can achieve high automation in production by utilizing plastic injection molding, resulting in faster production speed, higher efficiency, and reduced manual errors. Injection molding production can implement small batch production for the development of new products, as well as large batch production for products with high demand. Its production method is relatively flexible, and the design is more personalized, with a wide variety of types.
Selection of Injection Moulding Materials
Before injection molding, injection moulding manufacturers should choose injection molding materials reasonably. The selection of injection molding materials will affect the performance and quality of plastic parts. The similarity of plastic properties also poses significant difficulties for this step. In addition, injection moulding manufacturers can also consider selecting plastic materials based on their service life and later maintenance. BOOLING has summarized the following principles for selecting plastic materials.
- Plastics used on parts that require good corrosion resistance should have outstanding corrosion resistance. The variety of plastics varies, and their corrosion resistance also varies. Most plastics are prone to chemical reactions with strong acids, bases, and oxidants, leading to changes in performance. At this time, various fluoroplastics stand out among various plastics, such as polytetrafluoroethylene, perfluoroethylene, polytetrafluoroethylene, and polyvinylidene fluoride. Some chemical pipelines, chemical experimental containers, and parts that are prone to wear and tear and require frequent lubrication need to be made of corrosion-resistant plastic materials.
- Generally, lightweight and high-density structural components, such as covers, brackets, connectors, handwheels, handles, etc., have lower requirements for strength, hardness, and heat resistance, but require good aesthetics. These products often require mass production, and plastics that can be selected include ABS, modified polypropylene (PP), low-priced polyethylene (PE), polystyrene (PS), etc. Among them, ABS has the strongest comprehensiveness and is the most commonly used; The processing of the other three materials can also improve their mechanical properties, rigidity, and heat resistance. Sometimes, plastics with better comprehensive properties such as polycarbonate are also used to produce certain more precise and demanding plastics.
- Most of the components in the mold and the plastic materials used in the braking system can only work at a temperature of 80-150 ℃ under normal stress conditions. When the stress suddenly increases, the normal working temperature range is only 60-80 ℃. However, some plastics that can work in high-temperature environments, such as polyphenylene oxide, polyimide, aromatic nylon, etc., can work at temperatures of 150 ℃ or even higher, and some can even work normally for a long time at temperatures close to 300 ℃.
- Some products are subjected to relatively low stress during normal work and often have lower requirements for mechanical strength. However, their movement speed is often faster, such as piston rings, mechanical motion seals, bearings, and loading and unloading box frames. Therefore, this requires them to choose materials with higher friction resistance. The materials used for such parts are often polytetrafluoroethylene and various fillers such as polytetrafluoroethylene, as well as polyoxymethylene and low-pressure polyethylene filled with polytetrafluoroethylene powder or fibers.
- The components of the transmission system have high mechanical properties and high-temperature resistance requirements, such as various rollers, cam bearings, racks, gears, worm gears, worms, couplings, etc. The plastic materials available for selection include MC nylon, polyoxymethylene, polycarbonate, etc. Under normal pressure, MC nylon can quickly polymerize and form in molds, usually used to manufacture large plastic parts. The small gears in the instrument can be made of polycarbonate; And some precision parts and structurally complex parts are suitable for manufacturing with polyphenolic oxide; Chlorinated polyethers are widely used in corrosive media, such as working bearings, gears, and friction transmission parts and coatings.
Management Measures for Condensed Materials in the Flow Channel of Injection Molding Machines
Injection moulding manufacturers usually need to set up some precautions to manage and improve injection molding efficiency to prevent damage or contamination of the runner material of the injection molding machine.
- When the produced water outlet material and recyclable waste have been filled into the rubber bucket, a lid should be covered to cover the dust, and a label should be affixed, indicating the date of waste generation and the shift and machine of the production machine. When it cannot be recycled or other problems occur in the future, the cause can be identified promptly and solutions can be proposed.
- The glue bucket needs to be checked in advance for oil stains, dust, or foreign objects and should be cleaned promptly before use
- When the mold operator is not using the material barrel, they also need to regularly check for foreign objects in the barrel;
- The material barrel needs to be classified for use. Generally, newer material barrels can be used to hold white or transparent nozzle materials and waste products.
- The personnel in the water inlet room need to inspect the machine’s water inlet material during the production process, and if any problems are found, they should be reported and dealt with promptly.
- When crushing the water inlet material and waste, the crushing personnel should check for foreign objects. If there are any, they should be promptly eliminated and reported.
Solution to Color Difference on both Sides of Fusion Marks in Injection Molded Products
In fact, in the production process of injection moulding manufacturers, the appearance of fusion marks on products is not the most serious problem. What is serious is the color difference on both sides of the fusion marks, and the solution to this problem is relatively complex.
- The Flow Channel is too Narrow
When plastic in the liquid state flows in the mold cavity, due to the narrow flow space, the cooling degree of the melt passing through this part is higher, resulting in a significant temperature difference. When this part of the melt intersects and fuses with other melts, it will cause color differences and be more serious.
- The Color Difference on both Sides of The Fusion Mark Caused by Melt Shear is Large
In actual production, during the injection molding process, it is often found that if some elastic plastics are to be processed, one side of the fusion line will turn white while the other side is very bright, especially for some high-gloss plastic parts such as HIPS, PP, ABS, etc. Among them, high gloss ABS is the most obvious. If you want to analyze the causes of such phenomena, you can use the method of under-injection molding. During injection molding, let two molten streams with different temperatures separate and not intersect, which often leads to one side turning white and the other side turning bright after molding.
To achieve this, the following measures can be taken: increase the temperature of the dynamic mold to above 70 ℃; By adjusting the process, when the melt passes through the position of the corner, the speed is rapidly reduced, which can effectively eliminate the phenomenon of whitening on one side. The main reasons for this phenomenon are low mold temperature and a narrow flow channel, which leads to a rapid decrease in temperature at the front end of the melt, forming a thicker curing layer. Once this curing layer deviates in direction, it will be subjected to significant shear force, which then pulls the high-temperature curing layer, causing stress shear and whitening.
- Due to Poor Exhaust, There is a Large Color Difference in the Fusion Marks
Taking the interior panel of the car door as an example, the original design of the molded plastic part was to use three side gates, but this design resulted in two fusion marks on both sides of the frame, blocking the upper gate. However, the fusion marks in the circular area are still very clear. Later, when considering how to improve, injection moulding manufacturers achieved good results by adding exhaust and overflow grooves.
- Large Color Difference on Both Sides of The Fusion Mark Caused by Low Mold Temperature
During injection molding, due to the significant difference in the size of the area filled by different gates in the mold, there is a significant difference in the flow rate of molten materials from different gates when they meet. In addition, if the mold temperature is too low, it will cause the slow flow rate of the molten material to cool down too much at the front, resulting in too much cold glue in the curing layer at the front, and the curing layer will be accumulated or pushed and pulled to produce fog marks. Therefore, there will be a large color difference on both sides of the plastic part.
- Color Mixing Causes Significant Color Differences on Both Sides of The Fusion Mark
Taking the interior panel of the car door as an example, there is a serious color difference on both sides of the fusion mark. The main reason is that before this, the injection molding machine processed black material with a lower melt index (MI) and higher viscosity, and did not thoroughly clean the machine with plastic with good fluidity, which has been unable to eliminate the color difference on both sides of the fusion mark. This can consider using another material with higher viscosity for processing and cleaning first, and then replacing it with the formal material, and the color difference will disappear.
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