Foaming principle


Discovered by Otto Bayer in 1937, polyurethane was soon used in a wide range of applications, either in everyday life or in the industrial field..
Polyurethanes are synthetic polymers generally obtained by a reaction between di-isocyanates and polyols.

ISOCYANATES :
Tere are 3 families :

  • MDI :
    Biisocyanatodiphenylmethane
  • TDI :
    Toluene di-isocyanate
  • HDI :
    Hexamethylene di-isocyanate
 POLYOLS :
These determine the type of foam (flexible or rigid).
Ex : Sexol 6 functions OH rigid foams
Diol 2 functions OH flexible foams

There are 2 main polyol families :
  • Hydroxylated polyethers
  • Hydroxylated polyethers

 

FOAM :
To obtain quality foam, several parameters have to be controlled:

  • Dosage (or mixing ratio)
  • Product temperature
  • Injection pressures ( for HP machines)
  • Flows
  • Injection time
   
Foams are obtained using various processes : spread, injection or casting.

  • High-pressure injection is the most widespread method :

    • Advantages :
    • Precise dosage
    • Better foam quality
    • No solvent use
    Disadvantages :
    • Increased levels of qualified maintenance required
    • Limited flow rates

  • Low-pressure injection is the oldest method  :

    • Advantages :
    • High outputs (for continuous casting, filling)
    • Little maintenance required

    Disadvantages :
    • Often requires use of solvents
    • Less precise mixing
    • Expensive
Examples of foam parts :
  • Rigid foams: from 10 to 1100 kg/cu. m3
    Mixing ratio 1:1 to 1:2


  • Semi-rigid foams: from 100 to 1100 kg/ cu. m3
    Mixing ratio 1:1 to 2:1


  • Flexible foams: from 20 to 70 kg/ cu. m3
    Mixing ratio 3 :1