Polyethylene (PE) raw materials

PE is widely used in rotational molding processes for a reason:

, PE has a wide processing window and is suitable for long-term high-temperature environments, which reduces the requirements for rotational molding machinery;

Second, at room temperature, PE does not react with water, most greases, acids and alkaline substances, and has a wide range of applications;

Third, PE raw materials are low in cost and easy to promote.

Polypropylene (PP) raw materials

In the consumption structure of synthetic resins, polypropylene is the most common raw material after polyethylene. Compared with polyethylene, polypropylene has the following characteristics:

Low density: The density of PP is roughly between 0.85-0.93, while that of ordinary polyethylene is between 0.91-0.98. One of the reasons is that the crystallinity of PP is lower than that of PE;

Good mechanical properties: The tensile strength and elastic modulus of PP are generally higher than that of PE. At present, the mechanical properties of modified PP can even be comparable to that of PS (polystyrene), and it is widely used in electronic appliances and automobile fields;Good optical properties: Compared with PE, PP has much higher transparency;

1. Application of innovative technology in rotational molding equipment

Intelligent technology

Internet of things technology

New heating technology

Environmental protection technology

2. Future development trends of rotational molding equipment

Personalization and customization

Efficiency and energy saving

Intelligence and automation

Environmental protection and sustainable development

Advantages and disadvantages of rotational molding aluminum molds:

1. Price advantage: Except for small rotational molds, if medium-sized molds are made with steel plate molds, the mold cost can be saved by at least one-third.

2. Compared with aluminum moulds, steel plate formwork is easier to modify, repair and maintain.

3. Use steel plate mold. Since the wall thickness of the steel plate mold is only 2.5 or 3.0mm, the powder melting time will be shortened during the rotational molding process, which reduces energy consumption to a certain extent.

4. By combining traditional technology with CNC technology, precise rotational molds can be made. In the rotational molding industry, steel plate molds are still widely used.

1.This innovative technology is based on the basic rotational molding technology of "polyethylene integrated molding, completely seamless". Through secondary proportioning of raw materials and innovative adjustments to the production process, it achieves the perfect combination of product flexibility and rigidity.

2. Innovative adjustment of the production process to achieve perfect combination In the rotational molding process, the adjustment of the production process is crucial. This innovative technology achieves the perfect combination of product flexibility and rigidity through the optimization of the production process. While ensuring the strength of the product, it also improves the impact resistance of the product so that it can remain stable in complex environments.

3. New concave and convex process design to optimize the box structure In product design, the optimization of the box structure is crucial. This innovative technology uses a new concave and convex process design to make all parts of the box more reasonable and effectively improve the product's pressure resistance. At the same time, the concave and convex design also enhances the sealing performance of the product, ensuring that the product can still maintain excellent performance without leakage even if it sinks 150mm to the bottom of the water.

4. Advanced silicone sealing technology to ensure product sealing In the rotational molding process, sealing technology is the key to ensuring product performance. This innovative technology uses advanced silicone sealing technology, which effectively solves the shortcomings of traditional sealing technology. Even when the product sinks 150mm into the water, the silicone sealing technology can still maintain good sealing performance and ensure no leakage of the product.

1. Selection of rotomolding mold. On the same rotational molding machine, if conditions permit, choose the same type of mold. If you want to produce other products of different categories at the same time, when selecting the rotational molding mold, strive to install the molds that are similar in size and the weight difference should not be too great. The thickness requirements are basically the same. This is to avoid product aging and degradation or residual plastic powder, because different rotational molding molds require different processing cycles.

2. The installation distance of rotational molding molds. How many molds should be installed on a mold bracket should be calculated well. There should be enough distance between the molds to avoid blocking each other, which is conducive to the conduction of hot air and also facilitates mold opening and closing.

3. The balance of the mold bracket. This point must be noted. If the bracket is heavy on one side and light on the other, the rotation of the rotomolding machine will be affected. At least it will cause uneven thickness of the product. In serious cases, it will damage the rotomolding machine.

4. Pay attention to the diameter of the oven of the rotational molding machine, and calculate the rotation range when installing the mold, otherwise it will bring adverse consequences.

5. When installing the rotomolding mold, you must consider both the firmness and the speed of installation and disassembly.

First of all, from the overall scope of plastic processing, rotational molding is only a smaller branch, and its output value and scale only account for a very small part of the entire plastic processing industry. Rotational molding, a non-mainstream processing method, is inherently determined to not be the focus of the plastics processing industry.

Secondly, the rotational molding industry lacks large and influential companies, and rotational molding products have not been widely popularized and applied in our country, which makes people's awareness of the rotational molding industry low.

Furthermore, the lack of industry information, the scarcity of research talents, and the lack of publicity are also one of the reasons why rotational molding has not attracted enough attention.

However, compared with other mainstream plastic processing methods, rotational molding has its unique advantages, especially in agriculture (such as drone plant protection machines) and intelligent fields (such as smart robots, smart lifebuoys, etc.), and is increasingly favored by brands. It is favored by finished product manufacturers because rotational molding has great cost advantages under the demand of small batch manufacturing and can leave customers with several times the money.

We will see that more and more rotomolded products have replaced or are replacing products previously made of metal, wood, glass, ceramics, fiberglass and other materials. Originally, they were mostly made of wood, iron and other materials, but boxes of these materials are easy to store. It has shortcomings such as corrosion, easy damage or rust, heavy weight, and inconvenient loading, unloading and transportation. Therefore, after the rotational molding box is produced, it is quickly accepted by users and used more and more.

1. Main materials

Rotational molding toner: usually made of polyethylene (PE), polypropylene (PP) and other materials.

Other process toners (such as injection toners): may be made of PVC, ABS and other plastics.

2. Production process

Rotational molding toner: Its production usually involves mixing the pigment and resin through physical friction, high-speed rotation, etc., so that the pigment is evenly dispersed in the resin.

Other process toners (such as injection molding toners): usually made by dissolving the pigment in a solvent, mixing it evenly with the resin and then drying it to form a powder.

3. Performance characteristics

Rotational molding toner: It has good weather resistance, gloss and waterproofness. These characteristics make rotational molding toner widely used in the manufacturing of outdoor products and daily necessities.

Other process toners (such as injection molding toners): Their performance characteristics may be more focused on internal product applications, such as electronics, electrical appliances, toys and other industries.

4. Scope of use

Rotational molding toner: Due to its good weather resistance and waterproof properties, it is suitable for the manufacture of outdoor products such as furniture, trash cans, water tanks, etc.

Other process toners (such as injection molding toners): are more suitable for coloring internal products.

5. Price

Rotational molding toner: Since the raw materials are relatively cheap and the production cost is low, the price is more favorable than other process toners (such as injection molding toner).

6. How to use

Rotational molding toner: usually painted or mixed on the surface of plastic products for color mixing.

Other process toners (such as injection molding toners) are directly injected through an injection molding machine to color the inside of plastic products.

The perfect result of rotational molding is to produce high-quality rotational molded products. However, due to factors such as raw materials, equipment, molds, processes, and product structures, various problems often occur during or after the processing of rotational molded products. Most of these problems are problems with the products, some are equipment and mold problems, and some are process problems.

To sum up, the more common problems in rotational molding processing are:

The product has bubbles and pinholes;

The surface and inner wall of the product are uneven and frizzy;

The wall thickness of the product is uneven, with some parts thick and some parts thin;

The corners of the product have chipping and bridging phenomena;

Products are prone to shrinkage, warping, and deformation after being demoulded;

Product color solution;

The product has low strength and poor rigidity;

The product cannot be released from the mold;

The bonding fastness between inlays and products is low;

Molding heating time is too short or too long;

Flash appears on the product;

Blockage of ventilation tube;

The mold deforms or even explodes;

…

These problems that occur during the rotational molding process not only affect the appearance of the product, but also damage the mechanical properties of the product, affect the use efficiency of the product, and even lead to the scrapping of the product. Therefore, it is necessary to fully understand the importance of solving the above problems and find out the causes of the problems, thereby improving the efficiency of rotational molding processing and the quality of products.

1. In terms of raw materials and additives, choose raw materials with better toughness and impact resistance. Raw materials with low density or low melt flow rate generally have better toughness than raw materials with high density or high melt flow rate; try to use special rotomolding materials; Increase the amount of raw materials; the raw materials should be kept dry and not expired; it should be clear whether the colorants or additives used are suitable for the rotational molding process and whether they can withstand the long-term high temperature of rotational molding without decomposing. Do not use them blindly. Add Just the right amount, not too much.

2.In terms of molding process, appropriately adjust the heating temperature and heating time, neither under-burning nor over-burning, to prevent decomposition and oxidation of raw materials or insufficient melting, which will lead to a significant decrease in the strength of the product; keep the vents open to balance the pressure inside and outside the mold. Avoid pinholes and pores in the product and improve the density of the rotomolded product; maintain an appropriate rotational speed ratio to make the wall thickness of the molded product uniform; appropriately increase the cooling intensity and cooling rate.

③In terms of rotomolding product design, rationally design the structure to avoid acute angles and planes where stress is concentrated, increase the arc transition angle of corners and grooves; increase the wall thickness of the product; add design reinforcement structures in areas where the product is subject to greater stress, etc.

The rotational molding process can produce many different types of hollow plastic products, but how to make the products more suitable for the rotational molding process requires designing rotational molding products that meet the requirements of the rotational molding process, so that the rotational molding products can give full play to their best qualities. As for the effect, the following is the experience accumulated by Dongguan Keshan Rotational Molding Equipment in the rotational molding industry for many years. I hope it will be helpful to the rotational molding colleagues.

How to solve the problem of poor coating of modified engineering plastics in rotational molded products?

1. Eliminate the factors that are unfavorable to the heat conduction of the insert, so that the embedded metal product has an excellent heat transfer structure.

2. Under the premise of considering the rotational molding conditions and the strength requirements of the insert, the insert should be as small as possible relative to the surface height and volume of the product.

3. The depth and width of the anti-rotation and anti-pull grooves on the insert must comply with the rotational molding requirements.

4. When rotomolding, preheat the inserts according to actual conditions, so as to achieve good results, which is more suitable for rotomolded products with large and medium-sized inserts.

At present, most orders for rotational molding products from overseas directly indicate the use of linear density low-pressure polyethylene (LLDPE) rotational molding profiles for rotational molding. The products are mostly different products with higher requirements for rotational molding technology. Specifications of cleaning equipment casings, lawn mower casings, shipping boxes, storage boxes, various mechanical automated packaging wooden boxes, two-layer insulated boxes with polyurethane foam layers inside, automobile parts, etc. my country's rotational molding technology and rotational mold manufacturing technology are rapidly improving, but there are still differences compared with European and American countries in the rotational molding product design stage.

The rotational molding process plays a very important role in product quality. After the product is designed and the stamping mold is manufactured, the mold design that is likely to cause product defects is generally not easy to change casually. It is more important to find ways to solve the defects of rotational molded products from the forming process.

1. Material issues: If the materials used contain a large amount of volatile substances or moisture, bubbles may easily occur during the heating process. Especially when manufacturing plastic products, toxic substances in the materials may also produce harmful gases. In addition, a melt index that is too low may also lead to the formation of bubbles.

2. Temperature problem: During the manufacturing process, if the heating temperature is insufficient or the heating time is not enough, the material may not be fully heated and it will be difficult to fully fit the mold, resulting in bubbles.

3. Pressure problem: Insufficient or uneven pressure during manufacturing can easily lead to the generation of bubbles. These bubbles may be caused by gas being indented into the material, or they may be caused by insufficient fit between the material and the mold.

4. Mold design: The design of the mold may also affect the generation of bubbles. For example, the diameter of the mold ventilation pipe is too small or blocked, the pressure inside and outside the mold is not balanced enough, the internal pressure increases, and the resistance increases when gas escapes, resulting in residual gas in the raw material, resulting in bubbles in the product. In addition, if the parting surface of the mold is not closed tightly or there are blisters and pores on the cavity surface of the mold, bubbles may appear on the rotomolded products during molding.

5. Gas in the raw material: The gas in the raw material cannot be completely eliminated. During the heating process, it gradually melts, flows and adheres to the mold cavity. During this process, the gas trapped in the raw material is gradually squeezed to the surface, but due to the melting process Due to the existence of body surface tension, if the force of gas pushing outward is insufficient, it will be unable to break away from the melt surface and can only nest in the raw material.