Plastic corner molding is an extensively used technique to form a great variety of complicated and straightforward products. It requires raw material that is mostly plastic and molds it into the desired size and shape. It can manufacture open containers like buckets and everyday items such as combs, medical products, and toothbrushes. The molding process forms unique finished products as plastic housings and corners. Moreover, it can fabricate small toys and medical devices also.
Several factors impact the corner molding process and can affect the quality of the finished product. This article discusses the plastic corner molding process, its steps, and the factors that impact it.
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Plastic corner molding is a unique and widely used technique to mold various materials in different shapes and sizes. These materials can be metals, glass, and mostly thermosetting and thermoplastics. The raw material gets into the molding machine, where it gets heated and melts. There is a screw that ensures perfect mixing of the molten material and other utilities like-colored resins. The screw thus injects the perfectly mixed material through a nozzle into the mold cavity where it gets solidify, and there is an ejector that ejects the finished product.
The corner molding technology extensively produces a large variety of products. The corner molding process is an all-rounder in creating great finished products from aircraft and airplane parts to the mobile casing and hair combs.
The molding process involves several processes that include clamping, injection, solidifying, and ejection.
The clamping unit holds the mold together to give the molten material the desired shape and size. The process can produce a colossal amount of finished products in one cycle.
The screw injects the molten material into the mold cavity. The material inside the mold experiences shrinkage, which can affect the size of the product. More molten material should be injected immediately after the product gets shrink to compensate for the loss of escaped gases.
The molten material solidifies inside the cavity and attains the shape of the mold.
Finally, the ejector ejects the finished product. The molding process produces a large number of products in one cycle. Once the ejector ejects one part, the cycle repeats the same process once again.
Several factors affect the plastic corner molding process, like the temperature, pressure, and time associated with different steps.
The different temperatures involved in the injection molding are the barrel, nozzle, and mold temperatures. These temperatures have a significant impact on the plastic corner molding process.
The barrel supports a rotating screw that is responsible for melting the plastic. It takes heat from an electrical source. Its temperature needs serious consideration. From melting the plastic to injecting it into the mold, the temperature needs careful consideration. The temperature should not be higher than the decomposition temperature of the plastic. It should also not be lower than the optimum melting temperature to prevent the nonuniform melting and lump formation.
The nozzle in plastic corner molding is responsible for letting the flow of molten plastic into the molds. The temperature in this zone is lower than the barrel temperature. The high-temperature molten plastic cools slightly before going to the solidifying area. However, the temperature should not be too low to prevent molten plastic condensation as it can block the flow and cause cavitation, i.e., vacuum formation.
Mold temperature has a significant impact on the properties of the finished product. The solidification of the product depends on the mold temperature. The lower the temperature, the more quickly the product cools down. The optimum mold temperature depends on the product's size and structure, barrel or the melt temperature, injection pressure, and speed.
Pressure significantly impacts the plastic corner molding process as it controls the key processes from injection to extrusion.
Injection pressure is responsible for forcing the molten plastic into the mold cavity. Its value is not constant and varies with the size and shape of the finished product. It must be capable enough to push 95% of the molten plastic into the cavity. The optimum value of injection pressure varies from 70 to 112 MPa. High injection pressure helps to minimize the shrinkage of the product.
The holding pressure is responsible for filling the remaining 5% of the mold cavity. Once the injection pressure fills the mold cavity, trapped gases find the vents to escape the cavity, and the remaining resins start acquiring shape. So the holding pressure then pushes the molten plastic to compensate for the shrinkage that can affect the final product's size. Moreover, holding pressure must fill the cavity before the product freezes off. However, high holding pressure can result in product deformation.
As the reciprocating screw moves the molten product in a forward direction, back pressure plays its role to resist the movement of the screw. Backpressure maintains the speed of the screw, thus enhancing the melting of plastic and enhanced mixing in case of colored resins. This pressure also ensures the escape of trapped gases and helps in achieving excellent product density. However, back pressure increases stress on the system, so it must be much lower than the injection pressure.
Injection speed is the speed with which the screw moves to push the molten plastic into the cavity. It affects the heating of the plastic. The plastic corner molding requires an optimum injection rate to enhance the melting, mixing, and escape of any trapped gas.
The cooling rate is the last factor involved in the plastic corner molding process. It is the speed with which the temperature of the product drops in the mold. Once the temperature drop becomes constant, the extruder allows the product to leave the mold. The injection pressure and temperature significantly impact the cooling rate. The shrinkage can cause contraction, thus affect the size of the product. So to avoid shrinkage, the cooling rate needs to be controlled.
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To sum up the discussion, the plastic corner molding process is unique as it can manufacture several products simultaneously. The addition of colored resins and molten raw plastic aids the production of a finished product.
There are almost four steps involved in the corner molding process. These four steps work based on temperature, pressure, cooling rate, and injection speed. These factors, if not controlled carefully, can impact the process. So the need for serious consideration and optimum values of these factors can help enhance the quality of the finished product.
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