2. Shaping of Rubber
Shaping processes for rubber products can be
divided into 4 basic categories:
1.Extrusion
2.Calendering
3.Coating
4.Molding and Casting
3. Extrusion
o Unvulcanized rubber compound is fed
into the screw extruder.
o Flutes of the revolving screw carry
the rubber into the die.
o Pressure forces the material through
the opening where it swells.
o Swelling occurs because the polymer
is in highly plastic condition and
exhibits the ‘memory’ property.
4. Extrusion Die
o Tool made by cutting an opening
shaped in the form of the finished
rubber cross-section.
o Rubber compounds tend to swell
passing through this die.
o Hence each die is made according
to each part to ensure all
tolerances are made.
5. Calendering
o Calender is a machine to form
rubber sheets into various
thickness, widths and lengths.
o It consists of rolls which are run at
various speeds and temperatures.
o It is applied when a smooth and
flat surface is desirable.
o It is used in manufacturing of
tires.
6. Roller Die Process
o Combination of extrusion and calendaring resulting in better
quality product than either extrusion or calendaring.
Rubber extrusion followed by rolling
7. Coating Fabrics with rubber
o An important industrial process for producing automobile
tires, conveyer belts, inflatable rafts, and waterproof cloth tents
and rain coats.
Coating of fabric with rubber
using calendaring process
8. Molding
o Principal rubber processes are :
1. Injection Molding
2. Compression Molding
3. Transfer Molding
o Molded rubber products include:
1. Shoe soles and heals
2. Gaskets and seals
3. Suction cups
4. Bottle stops
9. Injection Molding
oRubber is heated and placed
under high pressure per square
inch of cavity surface in
molding.
oMaterial is mixed in bulk and
then stripped immediately.
oStrips are fed into a
screw, which fills the barrel with
the rubber material.
10. Compression Molding
oRubber compound is taken
and ‘pre-form’ is created in
the shape of the end
product.
oMold is closed applying heat
and pressure to the pre-
form, allowing it to fill the
cavity.
11. Transfer Molding
oIt also requires preparation of
preforms.
oHowever pre-forms are
placed between top plate
and plunger.
oMold is closed, material is
compressed by the plunger
and transferred through
sprue’s into the cavity.
12. NOW A VIDEO COMPRISING ALL THE
METHOD
IN MAKING OF TYRE
