Water Tanks Manufacturing
Rotational moulding process is not a new technology; this process has been in use since the 1940s. This is one of the most popular manufacturing processes used in the plastic industry for making several plastic articles. This is a highly helpful in making hollow plastic articles such as household as well as commercial containers etc.
Rotational moulding process is also used in the manufacturing of Polyethylene tanks used for water storage. This method of manufacturing polyethylene tanks brings a lot of design advantages. Using this process results such as strong outside walls that are of uniform thickness and stress free corners.
Making water tanks using rotational moulding process involves four stages or steps.
As a first step, the polymer has to be loaded into the mould. The mould should be a closable unit, which is in the shape of the product that is being manufactured. Measured amount of polymer resin has to be loaded into the mould and the polymer resin can be either in the form of powder or liquid. The polymer used will vary depending on the product that is being manufactured and in the case of Polyethylene tanks, the most widely used polymer is plastisols and polyethylene. Required colouring agent is added along with the polymer. When the mould is loaded with the required amount of resin or polymer, it is sealed and moved into the oven. Before moving the mould into the oven, the oven should be prepared by preheating it to 260°C - 350°C based on the polymer used.
In the second stage involves heating and the fusion of resins. This is one of the most crucial stages of the rotational moulding process. The oven used for rotational moulding process has special equipment that is capable of rotating the mould in bi-axial directions. The mould is continuously rotated at a low speed and the ideal speed for rotations is 20 rotations per minute. The duration for which the mould is in the oven is very critical. If the mould is not in the oven for enough time, then the polymer will not melt fully to stick to the walls of the mould. It will also form air bubbles in the product affecting the strength of the product. The purpose of this second stage is to melt the polymer and make it fuse to the walls of the mould. The mould is rotated in biaxial directions to ensure uniform settling of the polymer to the walls of the mould. The rotation should not be should not be centrifugal motion because centrifugal rotation will make all the polymer settle in one end of the mould.
The mould cannot be in the oven for too long either and if it stays in the oven for too long then it will affect the quality of the product and the impact strength of the product will be undermined and the mechanical properties of the product will be highly compromised. This becomes all the more important in the manufacturing of water tanks used for storage purposes. Only when the temperature and the duration inside the oven are perfect we will be able to get good quality Polyethylene tanks.
The next step involves cooling of the mould. The cooling stage is as important as the fusion stage. This phase takes longer than the heating and fusion phase. The strength of the product will be established during the cooling process. Cooling has to take place in a gradual and natural fashion using fan. As the mould cools, the fused polymer inside the mould solidifies. The mould cannot be handled when it is still hot. Moreover, it the mould shall not be removed before it cools fully because the product solidifies and gains its strength only during this phase and if the mould is opened before proper cooling, then the shape of the product too can be affected. Once the mould cools completely, it will shrink and the opening of the mould will be lot easier. Rapid cooling of the mould is not advisable. Rapid cooling can result in products that have poor mechanical strength and warped parts.
The final phase in the manufacturing of polyethylene tanks using rotational moulding process is the unloading of the mould or demoulding. The mould is removed from the finished product once it is cooled down. The finished product is sent for quality checks while the empty mould is filled with the polymer for the next tank.
Today the rotational moulding process of polyethylene tanks has been perfected using the latest technology. The quality of the product is no more a question of trial and error. The success of the process does not depend on the judgement and experience of the operator. The modern process allows the air temperature to be monitored throughout the process ensuring perfection and uniform quality of each product subjected to the rotational moulding process.
As rotational moulding has many advantages in the manufacturing of polyethylene tanks, Many Australian water tank companies make use of rotational moulding in the manufacturing of all its tanks. The over all cost of rotational moulding is much cheaper when compared to the other moulding processes while the quality of the water tanks obtained through rotational moulding process is much superior to the other moulding processes. These advantages are passed on to the customers directly both in terms of the cost of the product and the quality of the product.
Rotational moulding process allows uniform thickness of the walls of the water tanks. This is one of the most important qualities of a water tank that is used for storage purposes. If the wall strength should vary from one spot to the other, the water contained in the tank can exert pressure on the weak spot and damage the take over a period of time.