Extrusion means the process of forming something by forcing or pushing it out, especially through a small opening.
Moulding means converting a raw product to a required shape or form.
So, extrusion moulding is the process of forming or shaping by forcing or pushing out the raw material through a die.
Extrusion Moulding is used to make pipes, hoses, drinking straws, rods, curtain tracks, and fibre. Extrusion Moulding is done using a Extrusion Machine.
Parts Of Extrusion Moulding:
1) Die opening:
It is present on the front side. It can be of any shape either square, circular, or triangular, or any shape as per requirement.
The shape of the extrusion moulding machine is like a toothpaste tube.
In the toothpaste tube, there is a circular hole from which the paste comes out in a cylindrical form.
The extrusion moulding process is very similar to extrusion moulding. In this, we have:
A tube is present on the back side of the machine.
1) Die Opening:
A die opening is present on the front side through which the raw material comes out.
The main function of the heater is to heat and melt the raw material. The raw material is generally metal or thermoplastic.
The heater makes this raw material much softer than before.
Thermocouples are used to measure the temperature. The temperature measurement given by the thermocouple is used to operate the machine properly.
Hopper is the opening on the top through which the raw material is inserted into the machine.
4) Rotating Screw:
Inside the extrusion moulding machine there is a screw-type mechanism. which has threads in it and when the screw is rotated, it pushes the raw material toward the heater and further out from the die opening.
5) Air or Water Blower:
An air or water blower is placed near the exit of the extrusion moulding machine It is used to cool down the final hot product obtained from the extrusion moulding machine.
Mostly air blower is used in extrusion moulding.
6) Thrust Bearing:
Thrust Bearing is present on the back side of the extrusion moulding machine. It is used to take up the backup pressure.
A gearbox is used as high torque is used to rotate the rotation screw.
A powerful motor is used to rotate the rotating screw. The motor alongside with a gearbox is used to produce the torque required to rotate the rotating screw.
Working Of Extrusion Moulding:
* At first, the raw material which is either thermoplastic or metal in inserted into the extrusion moulding machine through the hopper.
Materials that are generally used in extrusion moulding are thermoplastic materials like- Vinyl Resins, Cellulose Derivatives, Nylon Polypropylene, and polyethylene.
The materials can be in either powder or pallet form.
Some additives are also mixed with materials that are in granular form.
The feed hopper is cooled using circulating water so that premature softening of the feed is avoided and to prevent any type of blockage.
* Then a motor is used to rotate the rotating screw. A powerful motor is used to do this.
* Then rotating screw is used to mix the raw material and additive properly and carry the mixture to the die opening.
* When the rotating screw is rotated using a powerful motor then the screw pushes the raw material forward toward the die opening through the cylinder and mix the raw materials with additive properly.
* The cylinder or barrel is heated. Heating of the cylinder is done either using a heating coil or electricity or steam or oil. Heating is done along the length of the cylinder.
Some heat is also produced due to the friction between the rotating screw and the inner surface of the cylinder.
There are three sections of the cylinder or barrel:
i) Feed Section:
After entering from the hopper, the material reaches this section of the cylinder. Here it is pushed forward by the rotation of the rotating screw towards the melt section.
ii) Melt Section:
It is also known as a compression section or transition zone. In this section the diameter of the screw core increases gradually and the screw pitch decrease. In this section, heat is generated and the melting is started in this section.
iii) Melt Pumping Section:
Further melting is done in this section and pumping of the molten material is done towards the die in this section by rotation of the rotating screw.
* When the material is in a liquid state it will be pushed forward to exit from the machine through the die opening and takes shape according to the shape of the die opening.
* At starting the material is inserted in powder or pallets form and then it starts melting inside the cylinder and when the material completely transforms to a liquid state then it is extruded through the die present on the front side of the machine
* After that the final product that we get from the extrusion moulding machine is cooled down using an air or water blower placed outside the machine near the die opening.
* This extruded material can be cut according to requirements.
The length of each section of the cylinder can be modified according to requirements. The length of the sections is adjusted on the basis of the characteristics of the raw material to be moulded.
The shape of the extruded product will depend on the shape of the die.
* After the extrusion the extruded part is cooled using different mediums like exposing it to air and cooling at room temperature.
* The extruded shape is cooled by the liquid bath at a controlled temperature and it can be cooled with a jet of compressed air.
* Using the extrusion moulding process different shapes can be created like tubes, pipes, sheets, films, or customized structural parts.
* One thing should be kept in mind rapid cooling should not be done after extrusion because if rapid cooling is done, then the final or finished product will have internal strain.
Advantages Of Extrusion Moulding:
1) Low initial cost as compared to the injection moulding process.
2) It is a continuous production process.
3) The extrusion moulding machine has high uniaxial strength.
4) It has good dimensional control.
5) It can be used to make complex and intricate shapes.
6) It has a high production rate.
Disadvantages Of Extrusion Moulding:
1) If rapid cooling is done then internal strain is caused.
2) In metal casting, the casted product shrinks but the thermal co-efficient of plastic is more than that of metal.
Applications Of Extrusion Moulding:
1) It can be used to make the following:
* Long Tubes
The raw material that is put inside the hopper should have uniform particle size and must have controlled moisture content so that the close dimensional tolerance can be maintained.
If the above condition is met, then the final finished extruded product is obtained with a smooth surface finish.