16-01-2013, 12:09 PM
CALENDERING
[attachment=47122]
INTRODUCTION
CALENDERING : A process of converting a polymer material or compound with or without support of fiber to continuous sheets of uniform thickness by pressing the molten polymer between the two or more counter rotating rollers.
It has its origin in paper industry where entire production activities are done through moving rollers.
In 1835 Edwin Chaffee developed the first calendering machine which consisted of a series of heated roll for continuous coating of cloth and leather by rubber.
It is nowadays used for both rigid and plasticized compounds.
MATERIAL SPECIFICATIONS
The best polymers for calendering are thermoplastics. They soften at a temperatures much lower than their melting temperature.
They also adhere well to the rollers, allowing them to continue through the chain well.
The thermoplastic melts have a fairly low viscosity.
TYPES OF CALENDERS
I – Type
It is used with 3-roll calender system for frictioning.
Have feeding problem.
L – Type
These are mostly used in research laboratories.
More ease of operation due to lower forward roll arrangement as compare to F-type.
CALENDERING DEFECTS
Blisters
Holes
Nibs (mostly in thermoplastic compounds)
Fish eyes
Scorching (only rubber based compounds)
Peeling of coating
Cold checks
Crow’s feet
Chatter marks
ADVANTAGES AND DISADVANTAGES
Advantages :
The best quality sheets of plastic today are produced by calenders.
It is very good at handling polymers that are heat sensitive as it causes very little thermal degradation.
It is good at mixing polymers that contain high amounts of solid additives that don't get blended or fluxed in very well.
Save money on raw materials.
Disadvantages :
Installation require huge investment.
If the thickness is below 0.006 inches then there is a tendency for pinholes and voids to appear in the sheets.
If the thickness is greater than about 0.06 inches though there is a risk of air entrapment in the sheet.
[attachment=47122]
INTRODUCTION
CALENDERING : A process of converting a polymer material or compound with or without support of fiber to continuous sheets of uniform thickness by pressing the molten polymer between the two or more counter rotating rollers.
It has its origin in paper industry where entire production activities are done through moving rollers.
In 1835 Edwin Chaffee developed the first calendering machine which consisted of a series of heated roll for continuous coating of cloth and leather by rubber.
It is nowadays used for both rigid and plasticized compounds.
MATERIAL SPECIFICATIONS
The best polymers for calendering are thermoplastics. They soften at a temperatures much lower than their melting temperature.
They also adhere well to the rollers, allowing them to continue through the chain well.
The thermoplastic melts have a fairly low viscosity.
TYPES OF CALENDERS
I – Type
It is used with 3-roll calender system for frictioning.
Have feeding problem.
L – Type
These are mostly used in research laboratories.
More ease of operation due to lower forward roll arrangement as compare to F-type.
CALENDERING DEFECTS
Blisters
Holes
Nibs (mostly in thermoplastic compounds)
Fish eyes
Scorching (only rubber based compounds)
Peeling of coating
Cold checks
Crow’s feet
Chatter marks
ADVANTAGES AND DISADVANTAGES
Advantages :
The best quality sheets of plastic today are produced by calenders.
It is very good at handling polymers that are heat sensitive as it causes very little thermal degradation.
It is good at mixing polymers that contain high amounts of solid additives that don't get blended or fluxed in very well.
Save money on raw materials.
Disadvantages :
Installation require huge investment.
If the thickness is below 0.006 inches then there is a tendency for pinholes and voids to appear in the sheets.
If the thickness is greater than about 0.06 inches though there is a risk of air entrapment in the sheet.