What is the difference between rotary molding and injection molding?

1, Principles and processes of craftsmanship
Rotational molding
Rotary molding, also known as rotational molding, rotary molding, rotational molding, etc., is a thermoplastic molding process. This process first adds the measured plastic (liquid or powder) into the mold, and after the mold is closed, it rotates along two vertical rotation axes while heating the mold. Under the action of gravity and thermal energy, plastic raw materials gradually and uniformly coat, melt, and adhere to the entire surface of the mold cavity, forming the same shape as the mold cavity. Finally, after cooling and shaping, demolding, the desired shape of the product can be obtained.
During the entire molding process, plastic is subjected to almost no external force except for gravity. Therefore, it is particularly suitable for manufacturing and processing medium, large, or ultra large hollow products such as handling boxes, dump truck skins, sailboat hulls, clothing models, industrial storage tanks, and storage tanks. The maximum container for processing can reach 100000 liters, which is difficult to achieve through injection molding and blow molding.
injection molding
Injection molding, also known as injection molding, is an intermittent plastic molding process. It uses an injection molding machine to inject molten plastic into a closed mold cavity under high pressure, and after cooling and solidification, opens the mold to remove the product. The process of injection molding mainly includes stages such as mold closing, injection, pressure holding, cooling, and mold opening.
The injection molding process has the characteristics of high efficiency, diversity, and precise control. It is suitable for almost all thermoplastic plastics and can also process certain thermosetting plastics. Injection molding can produce products with complex shapes and precise dimensions, and has a wide range of material choices to meet the performance requirements of different fields.
2, Product Features and Quality
Rotational molding
Rotating molding products have uniform wall thickness, stable dimensions, no molding seams, and no edge waste, making it an economical and effective molding method. Due to the fact that rotational molding does not require high injection pressures, high shear rates, or precise compound meters, molds and machines are relatively inexpensive and have a longer service life. In addition, products formed by rotary molding are easy to change colors. When it is necessary to change the color of the product, only the molding mold needs to be cleaned.
However, the dimensional accuracy of rotary molded products is relatively low, usually ± 5%. In addition, due to the fact that the rotary molding process mainly relies on static plastic to conduct heat, the heating time is long and the molding cycle is long. At the same time, energy consumption is also high because the mold and mold frame need to undergo repeated heating and cooling during each molding cycle.
injection molding
The structural dimensions of injection molded products are relatively accurate, the surface quality is good, and they can be standardized, normalized, and serialized. The injection molding operation is relatively simple, and the molding mold is easy to adjust and update. It can adopt fully automated production with high production efficiency. In addition, injection molding can also achieve high-precision and high-quality product production, meeting consumers' high requirements for product appearance and performance.
However, injection molding equipment requires significant investment and incurs high initial costs. At the same time, high precision is required for molds and equipment, and professional technicians are needed for operation and maintenance.
3, Material adaptability
Rotational molding
Rotary molding is mainly suitable for thermoplastic materials such as polyethylene, polypropylene, etc. These materials can flow and be evenly coated on the surface of the mold after heating. With the development of technology, rotational molding of thermosetting materials such as cross-linked polyethylene has also developed rapidly. However, due to the small shear force experienced by plastic during the rotational molding process, rotational molding may not be suitable for materials that require high shear force to plasticize, such as polyvinyl chloride.
injection molding
Injection molding is almost applicable to all thermoplastic materials, such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, etc. At the same time, it can also process certain thermosetting plastics, such as phenolic plastics. Injection molding requires high flowability of raw materials because the injection process is completed in a mold, and the geometric constraints of the mold composition do not require high melt strength, but have high requirements for the flowability and filling performance of the raw materials.
4, Production efficiency and application areas
Rotational molding
The production efficiency of rotary molding process is relatively low because each product needs to go through a complete heating, cooling, and demolding process. However, due to its ability to produce large, complex shaped hollow products, rotational molding plays an irreplaceable role in some specific fields. For example, in terms of container products, rotational molding products are widely used in water storage tanks, storage tanks for various liquid chemicals (such as acids, alkalis, salts, chemical fertilizers, pesticides, etc.), gasoline containers (gasoline storage tanks and fuel tanks for cars and airplanes), etc.
In addition, rotary molding is widely used in automotive products (such as air conditioning bends, backrests, armrests, etc.), sports equipment and various substitutes (such as water balloons, floats, bicycle cushions, etc.), toys, models, handicrafts and other fields.
injection molding
The injection molding process has the characteristics of high efficiency, diversity, and precise control, and is therefore widely used in various fields such as automotive parts, household appliances, daily necessities, medical equipment, toys, etc. Injection molding can produce products with complex shapes and precise dimensions, and has a wide range of material choices to meet the performance requirements of different fields.