In the rotational molding process, there are often some quality problems. So today I would like to share with you the quality of plastic rotational molding products quality.
Many factors affect the quality of plastic rotational molding products. Among them the more important are the mold shape, the mold rotation speed, mold heating temperature, heating time, the physical characteristics of plastic powder, and so on.
Next, we will analyze the factors that affect the quality of plastic rotational molding products one by one.
- Mould for plastic rotational molding products
The mold used for rotomoulding is a single-wall closed mould. It gives only the outline of the product and cannot be accurate to the details of the internal outline. Common carbon steel plate welding is usually used for the rotational mould. The cost of welding die is low, especially suitable for large plastic rolling products.
The rolling process has the following basic requirements for the mold:
①Die in the process of repeated heating and cooling is not easy to deformation and deflection.
②The mold should be attached to the easy release of the clamping mechanism, to make the mold in the heating and cooling process can be closed tightly, and in the need to unload products and loading can be easily opened.
③The design and installation of the mold should be conducive to the airflow around the surface of the mold for relative movement, to make the mold get uniform heating and cooling.
④The mold should be set up to ventilate the pipe, to prevent the heating process in the mold gas heat expansion and melt the plastic along the joint extrusion, and to prevent the mold in the cooling process produced negative pressure and lead to deformation of the mold and products.
⑤When designing the local structure of the mold, a deep cavity and hole should be avoided as far as possible, as well as the structure of reinforcing rib and solid bulge. Because the powdered material is difficult to cover the surface of the structure.
⑥The sum of the weight of the mold and the weight of the material shall not exceed the maximum bearing capacity of the rolling molding machine.
- The rotation speed of the plastic rotation mold
Generally, the rotational molding machine uses two adjustable motors to provide power for the rotation and swing motion of the mold around the spindle and the secondary axis, so that the rotation speed and swing of the mold around the spindle and the secondary axis can be adjusted. By adjusting the speed of the two speed regulating motors, the operator can obtain a relatively uniform product wall thickness in any product shape. The basic function of the rotation and swing of the mold is to evenly mix the powdery material and spread it all over the surface of the mold.
- The particle size of polyethylene powder
The size of polyethylene powder has an important effect on the melting process. The smaller the particle, the larger the ratio of surface area to volume, and the higher the melting rate. Normally the rolled powder particles should be no less than 30 mesh. However, the particle size of the powder should not be too small, because the powder is too fine easily moisture absorption, caking, it is difficult to dry, increasing the difficulty in the process. Too fine powdery material will agglomerate as it rolls in the mold, resulting in uneven heating of the powder, resulting in uneven product wall thickness or an inadequately molten plastic in the product.
- Heating time and cooling time
If the heating time is too short, the powder will not melt completely. Too long heating time will lead to the oxidation of plastics, thereby damaging the molecular structure of plastics, easy aging, brittle effect the quality of plastic rolling products. And cooling time is also very critical, cooling too fast, easy to make products out of shape, affect the usability and beauty of products.
The above are several common factors that affect plastic rotomoulding products.
Blow molding, like rotational molding, is a common form of plastic molding.
Compared with rotational molding, blow molding products have more advantages.
- Environmental stress cracking resistance: as a container, it can prevent cracking when in contact with surfactant;
- Airtightness (permeability): the property of preventing the outward diffusion of oxygen, carbon dioxide, nitrogen, and water vapor.
- Impact resistance: to protect the articles in the container, the products should have the impact resistance of falling from a height of one meter.
- Besides, there are drug resistance, antistatic, toughness, and extrusion resistance.
If you want to learn more about the blow molding process, please continue to follow our blow molding blog.