Rotational Molding Process for hollow in without weld line

Basic of Rotational Molding process (or) rotation molding:

The hollow part is made by rotational axis force, or bi-axial mold rotation, the material such as nylon, poly carbonate, High impact polystyrene, ABS and polypropylene can be molded using the rotational molding process. It is also called as rotomolding or rotation molding. The rotational molding technology is developed in 1940’s for use with vinyl plastisols in liquid. Air craft , tank, toy and more are the rotational molding products.

Step by step process for rotational molding technology:

Example of Rotational Molding Process
                                               Example of Rotational Molding Process

Step 1: Mold is opened and load the polymer (powder form)

Step 2: The mold is closed together and rotated with two axes, rotation speed range of slowly 4-20 rpm.

Step 3: The rotation of mold continuously with two axes, all polymers melted and adhered to wall. The mold is heated in temperature range of 250-450⁰c. The heating the molds come with good condition (or) approximate time range. Now the melting the polymer may be uncompleted because of large bubble in the polymer. That has adverse effect on mechanical properties of finish product.

Step 4: Now stop the heating the mould, and cooling the mold by using fan. The mold continuously rotated, during the period the require shape. Now the mold rotation is stopped and when the mold plastic is sufficiently rigidly. Now the part will be shrinking together on the cooling process remove from the mold.

In this construction the mold is rotational, it is most common mold, and materials are aluminum or steel sheet, with this process. They are having two halves from metal, the complex parts require mold to separate into two or three and more.


  • It method using to make hollow part without any weld lines or joints.
  • The mold part made with stress free.
  • Mold is inexpensive require low time spend.
  • Require low time spend.
  • Wall thickness can be altered without modify the mold.
  • Economically viable.


  • Molding time is more.
  • Particular material only manufactured.
  • The materials cost mostly high.
  • Geometrical of mold is difficult.

The Following rotational molding products can be manufactured:


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