Blow Moulding Process | Rotational Moulding Process

Blow moulding

Working principle

In this process between the two parts of open moulds a hot extruded tube called parison is placed. The two valves of the moulds move close to each other so that the moulds closes over the tube.

01 - Blow moulding - Types of moulding process

The parison’s bottom end is sealed. The molten plastic is mould with the help of blowing compressed air and the tube gets pinched off and also gets welded at the bottom by closing the moulds. The air pressure is about 0.7 to 10kg/cm². This air pressure will force the tube against the walls of the mould. Then is component is cooled to room temperature, and the mould is opened to release the component. The bloe moulding method will vary from simple manual operation to complicated automatic ones. The different types of blow moulding process are

1. Injection blow moulding

2. Extrusion blow moulding

3. Multi blow moulding

In multilayer blow moulding, multi layer structure are generally used. Typical example for multilayer blow moulding are plastic packing for food and beverage.


It is used in making plastic bottles and toys.The hollow containers are produced by this process only. The multilayer blow moulding is used in cosmetics and pharmaceutical industries.

Rotational moulding

Working principle

Generally the thin walled hollow parts will be manufactured using rotational moulding process. In this method, a measured amount of polymer will be placed in a thin walled metal mould. Then the mould will be closed. And then it will be rotated about two mutually perpendicular axes as it is heated.

01 - Rotational moulding - TYPES OF MOULDING

The rotation will make the powder to settle upon the mould walls. After heating and sintering, the mould is cooled while it is still rotating. The cooling of the mould is generally done by spraying air and water. After this the rotation is stopped and the moulded component is removed.

In this type of moulding a thin walled metal mould is made of two pieces and is rotated in perpendicular axis. A measured quantity of powdered plastic material is placed inside the mould. Then the mould is heated and rotated. Most of the thermo plastics and some types of thermosets can be formed into large hollow parts by rotational moulding. Rotational moulding is also used for producing components with hollow shapes with a very less wall thickness of about 0.4mm. Larger parts in terms of 4m can also be produced using this process. The surface finish of the internal of the mould is the same as that of surface finish of the walls. In this process time and temperature plays a vital role.


It is generally used in making large containers of polyethylene. Manufacturing of buckets, housings, boat hulls are made easy by this process. It is used to produce tanks of various sizes. It is also used for making football bladder.

Heat Treatment | Purpose of Heat Treatment


The strength toughness of the base material are determined by its chemical composition and the heat treatment it undergoes. Low carbon steel is easily available and cheap having all material properties that are acceptable for many applications. Low carbon steel contains carbon contain of 0.15% to 0.45%.

Heat treatment on low carbon steel is to increase ductility, to improve toughness, strength, hardness and tensile strength and to relive stress developed in the material.

It is neither externally brittle nor ductile due to its lower carbon content. It has lesser tensile strength and malleable. The increase in carbon content makes the metal to becomes harder and strong but less ductile and more difficult and more difficult to weld. Here MS we use En353, a low carbon alloy steel which contains 0.18 %C, 0.99%Mn, 1.42%Ni, 1.12%Cr, 0.11%Mo, 0.28%Si.

The process that heat treatment is carried out first by heating the material and then cooling it in water, oil and brine water. The use of heat treatment is to soften or harden the material, to modify the size of the grain, to modify the structure of the material and relive the stress setup in the material.

The most important heat treatment process and purpose.



A low-temperature treatment, to reduce or relive internal stress remaining after casting or work hardening.


Annealing is a rather generalized term. Annealing consist of heating a metal to a specific temperature and then cooling at a rate that will produce a refined micro structure.

The rate of cooling is generally slow. Annealing is most frequently used to soften a metal for cold working, to increase machinability, or to improve properties like electrical conductivity.


Normalizing is technique used to provide uniformity in grain size and composition throughout alloy. The term is frequently used for ferrous alloys that have been austenitized and then cooled in open air.

Normally not only produce pearlier, but also binate and sometimes Mortem site, which gives harder and stronger steel, but with less ductility for some composition then full annealing.


Untemper martensitic steel, while very hard, is to brittle to be useful for most application. A method for alleviating this problem is called tempering.

Most application requires that quenched parts be tempered. Tempering contains heating steel below the lower critical temperature to import some touchiness. Higher tempering temperatures, are at times used to import further ductility, although some yield strength is lost.


To harden by quenching, a metal must essentially be heated beyond the upper critical temperature and then quickly cooled.

Depending on the alloy and other respects, cooling may be done with forced air or other gases, Liquids may be used, due to their better thermal conductivity, such as oil, water, a polymer dissolved in water, or a brine.

Upon being quickly cooled, a percentage of austenite will transform to martensitic, a hard, brittle crystalline structure.



Casehardening is a thermo chemical diffusion process in which an alloying element, most commonly carbon or nitrogen, diffuses into the surface of a monolithic metal.

The subsequent interstitial solid solution is harder than the base material, which improves wear resistance without sacrificing touchiness.


Carburizing is the heat treatment process in which iron or steel absorbs carbon liberated when metal is heated in the presence of a carbon bearing material, such as charcoal or carbon monoxide, with the intent of making the material harder.

Depending on the amount of time and temperature, the affected area can vary in carbon content. Extended carburizing times and higher temperatures lead to greater carbon diffusion into the part as well as increased depth of carbon diffusion.

As soon as the iron or steel is cooled quickly by quenching, the higher carbon content on the outer surface becomes hard via the transformation from austenite to martens tic, while the core remains soft and tough as a ferrite or pearlier microstructure.