Plastic Rotational Moulding
The process of plastic rotomoldingBasically, the first step includes the use of a specific type of resins. They may be polyethylene, fluorocarbons, elastomers, plastisols, ethylene, acetate butyrate and when a more advanced base is needed, a cross-link of two resins is introduced. Rotational moulding is a very simple process which involves the introduction of a measured amount of plastic in powder or viscous form into a shell-like mold of a certain shape. This mold is then heated, rocked and rotated at an axis expertly so the enclosed plastic swirls to coat the mold cavity. With time, the rocking and rotating motions ensure that the plastic adheres to the shape of the mold. These motions are not stopped even when cooling to ensure that the plastic stays compressed and in form. After the plastic solidifies, the cooling and rocking processes may be stopped to allow for the removal of the plastic product from the mold.
The process can be simplified into three stepsCharging – This involves filling the mold with the polymer material in powder form. Heating- The mold is then placed in the oven to melt the polymer material. Rotation and rocking motions enable the material to take the shape of the mold. Cooling – The mold is put through a cooling process mostly by air or a thin mist. The rotation motion is not stopped to maintain shape until the plastic hardens. Demolding – Removing the finished product from the mold. The concept may sound simple but those who have been involved in the actual process would tell you that it can get a bit complicated. Due to the fact that there is no pressure involved, the material pretty much controls itself as opposed to the high pressure processes which allow you to control the material. Several conditions and variables affect the end product, such as the temperature, humidity, the type of mold used and the quality of the polymer material advantages of rotational moulding
Materials used97% of rotational moulded products are made from Polyethylene. This is because due to the fact that the process requires the use of powdered raw materials, there is need to use something that can be easily ground. Polyethylene is easy to grind, readily available and allows for easy moulding, thus makes the perfect polymer material for rotocasting. The use of other materials such as Polypropylene and Polyamide is limited by the fact that they cannot be easily ground. They require cryogenic grinding (freeze grinding) which is more expensive. There is however a much needed expansion in R&D to widen the range of materials that can be utilized in the industry..
The benefits of the plastic rotational moulding process.
# It is relatively inexpensive. # It is great for making complex shapes. # The process allows for consistent wall thickness, with the corners being thicker. The products therefore have strength and durability. # The price of rotomoulding machines is relatively low when compared to other plastic shaping machines. # There is room for production flexibility such as the creation of multilayered products. # There is absolutely no limitation to the size or shape of products that a designer may opt for. The process even allows for textured products.