Raw Material Pretreatment

The production of rotational molding starts with the scientific compounding of raw materials. Raw material particles, color masterbatches, anti – aging agents and other additives are accurately proportioned relying on a metering and weighing system. This step is of great significance. Accurate metering ensures that the proportion of each component meets the performance requirements of the product, and it is the basis for the uniformity of product color and the achievement of performance indicators such as anti – aging in the subsequent process. For example, in the production of outdoor water tanks, the accurate addition of anti – aging agents in strict accordance with the formula can delay the aging and embrittlement of the water tank under long – term sunlight and ensure its service life.

Thermoplastics: PE, PP, PVC , PA. Engineering Plastics: PC, ABS. Other Materials: TPE , biodegradable plastics

The metered materials are put into a color mixer, and with the help of equipment agitation, the uniform dispersion of additives is achieved. This link is directly related to the consistency of the appearance and performance of the product. Take outdoor floating balls as an example. Uneven dispersion of color masterbatches will lead to mottled color on the surface of the floating ball, which not only affects the appearance, but also may cause local premature aging and damage of the floating ball due to insufficient anti – aging additives in local areas, making it unable to serve stably in the outdoor environment.

The mixed materials enter the water ring pelletizing link and are granulated to form granular intermediates. The water ring pelletizing has significant advantages. On the one hand, it improves the dispersion uniformity of additives, making the distribution of additives in the particles more reasonable and avoiding performance fluctuations due to raw material dispersion problems during subsequent rotational molding; on the other hand, the water ring cooling is efficient, reducing material thermal degradation, which is friendly to heat – sensitive additives (such as anti – aging agents). For example, in the production of outdoor floating balls with high requirements for color consistency and anti – aging, water ring pelletizing can make the color masterbatch and anti – aging agent stably remain in the particles, safeguarding the quality of the floating balls.

The granular intermediates are then crushed by a mill to the target particle size. Powder with an appropriate particle size can be more uniformly melted and adhered to the inner wall of the mold during rotational molding heating and rotation. If the powder is too coarse, the melting is slow and easily leads to uneven wall thickness of the product; if it is too fine, impurities may be introduced during grinding, affecting the purity of the product. For example, in the production of large – scale water storage tanks, powder with a uniform particle size can ensure that the wall thickness of the water tank is consistent after molding and the pressure – bearing performance is stable.

Rotational Molding

The powder after pretreatment is put into the mold, starting a key step in rotational molding. The mold is heated while rotating on two axes, and the powder is heated and melted, gradually and uniformly coating the inner wall of the mold. Rotation ensures that the molten material covers all – around, avoiding uneven wall thickness; the precise control of heating temperature and duration determines the melting state of the material. Taking the outdoor water tank as an example, appropriate heating makes the polyethylene powder fully melted, and after cooling, a box body with no joints and high strength is formed, which can store liquid for a long time and withstand outdoor temperature differences and pressure changes.

In the cooling and solidification stage, the mold continues to rotate and cool. This “dynamic cooling” avoids the deformation of the product due to gravity and ensures a regular shape. For example, in the production of parts of outdoor amusement facilities with complex shapes, rotating cooling makes the molten plastic uniformly shaped, maintaining the designed curved surface and structure, and ensuring the installation adaptability and use safety of the parts.

After demolding, the product is trimmed to become a usable product. From the precise compounding, dispersion and color mixing in pretreatment to the melting and cooling solidification in rotational molding, each link is interlocked, jointly creating outdoor rotational molding products with anti – aging properties and uniform color, which can be used for a long time in scenarios such as water tanks and floating balls, demonstrating the unique advantages of the rotational molding process due to its fine procedures.

Advantages of Rotational Molding

1. Suitable for manufacturing large – sized and complex – shaped products

The rotational molding process enables materials to be evenly distributed on the inner wall of the mold through the rotation of the mold. It does not need to consider the problem of mold strength caused by pressure in processes such as injection molding. Therefore, it can easily produce large – volume and complex – structured products, such as large liquid storage tanks, yacht hulls, and children’s amusement facilities. Even if the products have complex structures such as depressions and hollows, they can be formed in one time without subsequent splicing.

2. Products have no internal stress and high strength

In the rotational molding process, plastic raw materials are gradually melted and formed under no pressure or low pressure, so there will be no internal stress in the products caused by pressure. This makes rotational molding products less likely to crack, deform, or have other problems due to the release of internal stress during use. The overall structural strength and toughness are better, which is especially suitable for scenarios with high requirements for mechanical properties, such as industrial heavy – duty containers and anti – collision facilities.

3. Low mold cost

Rotational molding molds are usually manufactured by means of steel plate welding, casting, etc. Compared with the high – precision processing requirements of injection molds, their manufacturing process is relatively simple, and the requirements for equipment and technology are lower. Therefore, the production cost of the molds is significantly reduced. For products produced in small batches, it can significantly reduce the overall production cost, and is suitable for the production of personalized and customized products.

4. High material utilization rate

In the rotational molding process, raw materials are added to the mold after being accurately measured according to the weight of the product, and almost no excess leftover materials are generated. The material utilization rate can be close to 100%. This not only reduces the waste of raw materials, lowers the production cost, but also conforms to the concept of environmental protection production.

5. Capable of realizing composite molding of multiple materials

The rotational molding process can add plastic raw materials with different properties (such as materials of different colors, densities, or functions) into the mold simultaneously or step by step, and realize multi – layer or composite structure products through rotational molding. For example, it can produce storage tanks with wear – resistant outer layers and anti – corrosion inner layers, or decorative products with color gradient effects, expanding the functions and application ranges of products.

6. Flexible production process, easy to change products

When replacing rotational molding products, it is mainly realized by replacing molds, and the installation and debugging of molds are relatively simple. For the production demand of multiple varieties and small batches, it can quickly switch production plans and adapt to the market’s demand for product diversification.