Plastic Injection Molding
One of the biggest advantages of plastic injection molding is the wide range of material selection, which can be selected according to different products and usage environments. Plastics can be mainly divided into general plastics, engineering plastics, and special plastics according to their uses.
Injection Molding｜Inspection of Plastic Molds
Injection molding plastic molds generally put granular or powdery materials into the hopper of the injection molding machine. By heating, the materials are completely melted and in a flowing state. And driven by the screw or piston, they can pass through the nozzle. The pouring system of the mold smoothly enters the mold cavity, where it can harden and form, ultimately forming the desired thermoplastic injection molding product.
During this custom injection molding process, injection molding factories generally need to perform various processes on materials and final molded products to meet customer needs, such as material inspection, color matching, mold testing, cleaning, and other steps.
Inspection of Raw Materials
Whether it is thermosetting or thermoplastic injection molding, the factory must inspect the materials used before molding begins:
- Engineers need to observe the outer packaging of plastic raw materials and judge whether the selected content is consistent with the model, color, material, etc. required for production according to its particle shape, particle size, appearance, color, etc., to prevent usage errors, which will cause time and material losses. of waste.
- The factory also needs to check whether the packaging is damaged and whether the raw materials show signs of contamination. Especially transparent raw materials.
Coloring and Ingredients of Plastic Raw Materials
When plastic raw materials leave the factory, their colors are mostly primary colors (natural colors), white, milky white, light yellow, and transparent, rather than the colorful colors displayed in our finished products. However, to meet the color needs of the product, the injection molding factory will add color masterbatch, color powder, and other auxiliary materials before use to configure the color to the required state in advance.
After the toner and masterbatch ratios of the materials are prepared, the factory will also produce some color control samples. During the mass production stage, users only need to strictly follow the material requirement list and compare the ingredients with the work instructions.
- Key points of ingredients operation
Before the user makes ingredients, the mixer must use an air gun and a soft cloth to clean the inner wall of the hopper. The location where the toner material has been mixed needs to be cleaned with mold-washing water or kerosene. The filling bag can be selected to maintain the original filling bag. Under normal circumstances, the original material bag is very clean.
- Drying of raw materials
Since many raw materials are highly hygroscopic, when the moisture in the raw materials exceeds a certain amount, undesirable problems such as material flakes (silver streaks), bubbles, shrinkage cavities, etc. will appear on the surface of the products being produced. This phenomenon In severe cases, plastic degradation is easy to occur and affects the appearance and internal quality of the product. Therefore, the factory must dry the plastic raw materials before molding the product.
It should be noted that different types of plastic raw materials have different hygroscopicity, so generally, injection molding factories will classify and process them according to the characteristics of the materials. Usually, such materials can be divided into two categories: easy-to-absorb moisture and easy-to-absorb moisture. Those that are easy to absorb moisture include ABS, PA, PC, PMMA, etc.; those that are not easy to absorb moisture are PE, PP, PS, PVC, POM, etc.
It can be understood that the factors that affect the drying of materials mainly come from drying temperature, drying time, and material layer wall thickness. When the dried raw materials leave the dryer, they will absorb moisture again, or the materials will not be used for a long time. It can also cause this problem, so remember to dry it again under the same conditions before use.
Equipment Cleaning
Generally, for different molds, products, or orders, the factory will use different types of plastic raw materials or prepare plastic raw materials of different colors. However, full mixing cannot be achieved through the plasticization of the plastic tube of the injection molding machine. Even if it can be mixed, the production The finished products may also have deviations, such as: easy to break, no elasticity, large overall or partial color deviation, black spots and black lines, etc.
In addition, the molding process may be unstable, and some may even be unable to produce (such as plugging mouthpieces, etc.). Therefore, when transferring molds for production, engineers need to clean up the previous mold or product. During production, the different colors or plastic materials remaining in the machine will be removed.
Mold Cleaning
Before injection molding, the injection molding factory must clean the mold surface, cavity, gaps, spouts, runners, and other parts around the insert to prevent oil from sticking to the product or blocking the exhaust of the mold, thereby affecting the mold. Stability after molding. If it is a mirror product, electroformed shell, or post-processing mold that has strict appearance requirements, it is strictly forbidden to wipe it with cotton wool, rags, or old gloves to prevent damage to the mold surface during operation and lead to scratches on the surface of the product. For this type of product, it is best to rinse it with mold-washing water or blow it with an air gun.
Due to the needs of product appearance and production capacity, during production, the factory needs to control the water supply to the mold, the mold temperature controller, the water chiller, and the temperature of the mold within a reasonable range. Generally, after the water supply is connected to the machine, the process of starting the mold temperature controller again takes a while to heat up, usually 15 to 30 minutes. Some molds will also use a hot runner. After putting on the machine, you need to turn on the power of the hot runner. After preheating for 15 to 30 minutes, observe that the display value of the hot runner electrical box reaches the set value before you can try injection molding plastic molds.
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