Rotational Moulding: Critical Design Issues You Should Know

water tank produced using rotational moulding

The material options for water tanks are currently vast. Plastic is one of the most popular materials owing to its durability, lightweight and low cost. There are different techniques used to moulding plastic water tanks. The most frequently used one is rotational moulding.

The technique involves moulding of melted plastic around a cylindrical item and then cooling the plastic to form the desired shape. Unlike other tanks, poly water tanks made through rotational moulding are more leak-proof, durable, weather-resistant and eco-friendly. Here are some of the design issues you should be on the lookout for when buying a rotationally moulded tank.

Flat Walls

Since the rotational moulding process forms hollow moulds, getting a flat tank wall might be hard. There are, however, times that a tank might have flat walls. The flat surface increases your tank’s susceptibility to damage from harsh environmental conditions. Crowns, kiss-offs and reinforcement ribs are used by most tank designers to minimise flat walls. For large flat surfaces, it is recommended that a crown measuring .015 inch-per-inch is added.

Sharp Corners

A sharp corner will affect the resin flow during manufacturing and hence create stress in different areas of the eventual tank. This is because the corners have thin resin and are thus at high risk of leaks with minimal strain. A sharp corner will also increase the chances of your tank collecting more heat, which can lead to thinner inside corners and thicker wall sections.

The minimum radii of your water tank’s walls should be 0.125 inches, as anything less than this is considered a weak wall. Also, the tank’s inside corners should not be less than the thickness of the nominal wall.

Narrow Wall Separation

water storage tanks

Failure to provide an adequate gap between a tank’s walls for proper material flow is a common design flaw. Narrow wall separation during manufacturing will cause webbing of materials in the tank’s walls and voids in others. The recommended minimum wall separation during fabrication is five times of the desired water tank walls’ thickness.

Draft Angles

Draft angles play an active role in ensuring the success of a rotationally moulded product. These are responsible for releasing the part from the mould. Deeply engraved textures need at least three degrees of draft. On the other hand, undercuts usually require five degrees.

Material Flow

Material flow issues should be avoided with your rotationally moulded tank. It is quite common, however, that the physical properties of the material bridge between wall surfaces. This prevents the material to flow through the mould, creating voids in some parts. It is recommended to have at least five times the thickness of the wall between the ribs and walls of the tank.

With careful consideration when picking your rotationally moulded tank, the above design flaws can be avoided. One method of minimising the risk of these flaws is to get your tank from an experienced manufacturer. This way, you can be sure that the plastic water tank you purchase is manufactured following only the highest standards.

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