Rotational Molding – Working Principle,Application , Advantages

 Rotational Molding – Working Principle , Application , Advantages, Disadvantages

Rotational Molding

The rotational molding is a high temperature and low pressure plastic forming process. The powder is inserted into the closed split mold and rotated in biaxial to produce a hollow part. The schematic of rotational molding process is shown in figure

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Working Principle

The plastic material in the form of powder is inserted into the mold. The mold is heated in an oven and rotated biaxial until the powder has melted. The molten powder is adhered to the mold wall and makes a thin layer. The mold is opened and finished part is removed.
The mold is rotated at different speeds in order to avoid the accumulation of molten powder. The amount of time required to heat the powder at molten temperature in to the oven is important. If the oven is heated for long time, powder will degrade and it will affect the mechanical properties. If the mold is heated short time, the powder may not be completely melted, resulting in large bubbles in the powder. The formed part must be cooled through the air so that it solidifies slowly. The formed part will shrink on cooling, and facilitating easy removal of part. The cooling rate must be kept within a certain range. The water cooling should be avoided, because formed part may shrink and warped after cooling.
Rotational Molding - Working Principle,Application , Advantages
Rotational Molding – Working Principle,Application , Advantages

A mold release agent should be used to quickly remove the formed part. Mold release can reduce cycle times and defects of finished product. Three different types of mold release agent may be used i.e. sacrificial coating (silicones), semi-permanent coating, (polysiloxane), and permanent coating (polytetrafluoroethylene).

Process Parameters

  1. The amount of powder
  2. Heating temperature and time
  3. Rotational speeds
  4. Cooling rates

Material Used

Thermosets and thermoplastic material can be used, for example: low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene, and polyvinyl chloride (PVC).


Additives for weather resistance, flame retardation can be incorporated. Products that can be manufactured include storage tanks, bins and refuse containers, airplane parts, road cones, footballs, helmets, and rowing boats.


  1. Allows complex mold split lines.
  2. Allows molded threads and mold-in inserts.
  3. Allows a wide range of surface finishes (textured, smooth, or polished).
  4. Very little waste.
  5. Low residual stresses
  6. Tooling is less expensive
  7. Suitable for both low-volume prototypes and high-volume production runs


  • Slow production speed. It usually takes about one hour to complete the process
  • Lower precision

Sachin Thorat

Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.

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