rotational molding

Rotational molding machines are used in most manufacturing companies in the world. This process helps to manufacture stress-free, seamless hollow products. Let’s understand the different steps involved in the process of rotational molding.

Step 1- Mold Preparation

For creating hollow products, the mold needs to be filled with the required mix of material like resin or polymer powder. Some of the raw materials used in mold preparation are nylon, polyvinyl chloride, or polyethylene.

The manufacturer also adds some compounds for hardness properties and color. The mold is then heated as per the features of the material used. The next step involves loading of the powder in the mold and moving the mold to the oven.

Step 2 – Mold Heating

In the rotational molding process, rotating the mold on two axes is an essential factor in allowing adequate material spreading and coverage. If the mold is rotated on a single axis, there is no guarantee the material is dispersed evenly, and it would be hard to achieve consistent wall thickness in the end product.

The speed of rotations needs to maintain below 20 rotations per minute that ensures the molten material spreading is not affected by the centrifugal forces, and you can get excellent coverage. Timing is also an essential factor in the 2nd stage of the manufacturing process.

Insufficient rotation time will affect the melting and adherence of the polymer to the wall of the mold. Too much rotation time will degrade the mechanical properties of the end product. It will not only impact its final form but will also make the product less resistant to wear.

Step 3 – Mold Cooling

It is a common misconception that mold cooling should be accelerated to get the molded parts to the room temperature. However, mold cooling is a critical parameter in the blow molding process.  The cooling process should be carefully controlled, like the heating rate.

You can spray water or air on the outside of the mold, which will cool the polymer inside the mold. Maintaining the right rate of cooling will help prevent problems related to warping or shrinkage.

If the mold cooling is accelerated or reduced beyond the cooling rate, there can be problems like inconsistent thickness and undesired flow of polymer in the mold. Manufacturers use advanced software programs to predict the solidification pattern of the compounds in the mold and maintain the cooling rate for a superior quality product.

Step 4 – Mold Unloading

The last stage is undoubtedly an important one, and you need to ensure the final product leaves the mold undamaged. Mold release needs a great deal of attention.  The role of mold design is vital in mold release. The mold design should allow parts to freely separate from the mold cavities.

The use of modern material and polymers in the manufacturing process can offer tight tolerances, paintable surfaces, and excellent surface finishes. However, proper demolding is vital to guarantee high-quality parts. After the parts are removed, they go through different processes like finishing, inspection, assembly, and packaging.

These are four stages of the rotational molding process in a variety of industries that includes the manufacturing of medical devices and toys manufacturing.


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