1.Induction region

•*Cross linking starts at this stage * Scorch time is taken as two units above minimum viscosity

•* All processing and shaping operations are done before scorch time

•2.Curing region

•* Permanent cross links are formed, Dependent upon-Amount of vulcanizing agent,Activity,Reaction time,

•Temperature,Nature of rubber,Presence of other ingredients

•* Optimum cure time – is the time for attaining 90% torque

•* Amount of cross links formed decide the physical properties of the vulcanizate

•*3. Overcure region – Desides the stability of the network towards heat

Vulcanization of thick articles

* Upto 6 mm thickness cure time from Rheometer is sufficient

*For thick articles 5 min extra is added for every additional 6mm

*For industrial products cure input requirement for vulcanization is obtained using programmed

temperature – profile curometer

Vulcanization – Different methods

• Moulding( Shaping and curing

within the mould)* Compression

moulding* Transfer moulding* Injection moulding* Blow moulding* Vacuum moulding

Methods other than moulding(Curing of previously shaped compound/composites)

Batch curing Continuous curing•Autoclave or steam pan • High pressure steam tube

•Hot air oven • Hot air tunnel

•Water curing • Fluidized bed

•Lead curing • Liquid curing method

• Continuous drum cure

• Microwave vulcanization

Batch curing methods1.Autoclave or steam pan

cylindrical pressure vesselUsed for curing 1.Extrusions, sheeting and other items which are

unsuitable for mould curing

• Unjaketed Autoclave• Admits steam directly

• Chance of partial degradation

• Imparts condensation markings

• Jacketed Autoclave• Curing in inert atmosphere

• Produces bright coloured items

• Advantages• Large number of components can be cured at a time• Improves press and mould utilization by using it for the

secondary vulcanization of large mouldings

2.Hot air ovenMainly used for post curing of heat resistant polymers like silicone and

fluorocarbonAdvantages of post curing

1.Improves the state of cure of the product, there by the physical properties2. Drives off volatile materials from components intended to serve at high

temperatures

3.Water curing

Uses autoclaves as pressure vessels— heating by steam jacket or steam injection

Load the vessel—— fill water——apply heat for the prescribed periodApplications

vulcanization of very large hand built rubber lined machinery such as pump, pipes and chemical tanks

4.Lead curing

Used for the vulcanization of hoses. Cover hose with lead using T-head extruder or press——wound on large drum——fill the hose with water, seal the ends——place the

assembly in autoclave and cure. Super heated warer exert presdsure on the inner side against the outer cover.

5.Sulphur chloride curing

Thin walled rubber articles can be cured by dipping in the solution of sulphur chloride in carbon di sulphide or

exposure to its vapours

Continuous vulcanization shaping, curing and finishing are continuous

Major componets are EXTRUDER /CALLENDER VULCANIZER

DOWN STREAM EQUIPMENTS

1. High pressure steam vulcanization

Major applications:- Reinforced hoses, wires and cablesThe extrudate is un supported and is subjected to tension. So that this

technique is suitable only for composite products having continuous non – rubber reinforcement

Vulcanization is carried out in steel tubes of long length(75 m), sealed one end to the extruder and the other end with rubber/water seals. Steam at 15 kg/cm2

( 216 kg/cm2 )is used for heating

2.Hot air tunnel

For the vulcanization of cellular and carpet underlay which do not have to meet tight dimensional

tolerences

*Conveyor belts are used to carry the extrudate* Gas heated or electrically heated

Temperature at the exit point is 250 – 300oC

Drawbaks: Poor heat transfer Very long line(360 m)

3.Liquid Curing Method

Thermally isolated metal chamber contains a heatingmedium * eutectic salt

*glycol *silicone oil

eg:- NaNO2-40%,KNO3 -53%, and NaNO3-7%

Operating temperature – 120 – 280oC

Advantages:- 1.Excellent heat transfer 2.High line speed

4.Fluidized bed*A metal chamber containing glass beads(0.1-0.2mm) with perforation at the bottom

*Steam from the bottom initially

*compressed air replaces steam once the temperature is attained

* glass beads behaves just like a fluid and the rubber section is drawn through the medium

o Good heat transfero Chemically inerto Non wettingo Requires no guides or supporting rollers

5.Continuous drum cure

For vulcanization of * Sheet materials

* flooring

* belting Important parts-heating drum,reversing rolls and pressure belt

Drum dia-600 –3000mm, pressure 4.6 – 15.3 kg/cm2

(155 – 216 oC )

Emerging Methods of Vulcanization

Conventional methods Heat is supplied from out side

* Steam * Electrical heating

* Gas heating * Oil heating

Modern Methods * Heat is generated within the bulk of the polymer by irradiating with microwaves or ultrasonic waves

* No need of curing agents for high energy radiating systems like Co60

& Electron beam

Microwave curing*Electromagnetic radiations of

Freq. 915-2450 MHz for domestic and industrial purposes

* Heat is generated in the bulk of the polymer

* The poloymer should be polar or other wise made polar by incorporation with polar polymer/ingredients

The Unit consists of

1.Microwave section2.High temperature heating section

3. Conveyor belt

Applications

* Production of Automobile profiles(water strips, tubing,seals,sponge etc)

* Construction profiles(Highway seals, gaskets expansion joints foe bridges

etc)

Ultrasonic Vulcanization

Elastic waves produced by cyclic vibrating movement of ultrasonic transmitter when

come in contact with viscoelastic material, the ultrasonic energy is converted into heat

High energy radiation system

• Co60 or Electron beams of 1021-1018Hz is used

• High penetrating power (fast curing of thick articles)

• No need of conventional curing agents

• Free radicals are formed by high energy radiation – which joins at reactive sites to form the cross linking

Thank you