1. Reduces the height of the stack
2. Facilitates feeding Automatic strip feeds can be
used in place of “Piggy” or “Dolly”manual feeding
3. Independent nip control
4. Minimised exposure of the rolls and therefore
better temperature control
Sizes of Calenders
Diameter and length of Calender depend on the application
that the Calender is intended to be used. The ratio of the
length to the diameter is a major factor in determining the
stability of the equipment against deflection stresses caused by load
2. Facilitates feeding Automatic strip feeds can be
used in place of “Piggy” or “Dolly”manual feeding
3. Independent nip control
4. Minimised exposure of the rolls and therefore
better temperature control
Sizes of Calenders
Diameter and length of Calender depend on the application
that the Calender is intended to be used. The ratio of the
length to the diameter is a major factor in determining the
stability of the equipment against deflection stresses caused by load
Parts of Calender
Calenders are generally made of high quality close grained
cast iron, chilled on the surface to a depth of 0.75 inches,
and have surface hardness of 500-520°Brinell.
The working faces of the rolls are precisely finished and
ground for concentricity and “crown”. Also the rolls are
ground internally to ensure uniform wall thickness to ensure
uniform heating and cooling.
Calender Roll Types
1. Cored Rolls:
Mould cast with cores internally and is
machined on the outer surface only.
Will have variations in wall thickness due to
casting irregularities inherent in the process.
2. Centrally Bored Rolls:
Mould cast with cores internally and is machined
internally
Rolls are heavy - so the heat transfer will be slow
and uneven.
May develop “Hot Spots “ during processing
3. Peripherally drilled Rolls:
When line speed increases (above 30-40 mpm), the
fast heat transfer required will not be possible with
centrally bored holes
The peripherally drilled rolls are equipped with
channels close below the roll surface.
With the heat transfer media passing at a relatively high
speed through these channels, the roll surface
temperature can be adjusted to a tolerance range of
±1 °C
Maintaining the rolls at the correct temperature is most
critical to the right quality of the product. The decision of the
roll is therefore the next most important decision after
machine stability.
Calendering Operations
Skim coating or Topping
Rubber coating on both sides of the fabric--Sheeting is produced
in the first and third nips and are brought together and laid on
both sides of the fabric at the same time in second nip
The second and third rolls which apply coats on the fabric must
be even speed, where as first and fourth can be even or odd
speed
Frictioning
Rubber is forced in to the fabric weave. 3R calenders are mostly
used , where the top and bottom rolls going slowly and middle
roll fast. Normally used friction ratio is in between 1:1.5-2.0
4R Calenders cannot be used for frictioning ,because of the
problem of obtaining a speed difference between fabric and
compound.
Hence two 3R Calenders in tandem have to be used
Embossing
By pressing a heavy engraved roll against hot rubber compound,
so that the engraved design is transferred to the rubber
compound
Profile Calendering
Used to produce tread sections of cycle tires and hand
building of certain types of foot wear. Calender contains
pattern rolls to produce profiled treads or patterned sheets
Calenders are generally made of high quality close grained
cast iron, chilled on the surface to a depth of 0.75 inches,
and have surface hardness of 500-520°Brinell.
The working faces of the rolls are precisely finished and
ground for concentricity and “crown”. Also the rolls are
ground internally to ensure uniform wall thickness to ensure
uniform heating and cooling.
Calender Roll Types
1. Cored Rolls:
Mould cast with cores internally and is
machined on the outer surface only.
Will have variations in wall thickness due to
casting irregularities inherent in the process.
2. Centrally Bored Rolls:
Mould cast with cores internally and is machined
internally
Rolls are heavy - so the heat transfer will be slow
and uneven.
May develop “Hot Spots “ during processing
3. Peripherally drilled Rolls:
When line speed increases (above 30-40 mpm), the
fast heat transfer required will not be possible with
centrally bored holes
The peripherally drilled rolls are equipped with
channels close below the roll surface.
With the heat transfer media passing at a relatively high
speed through these channels, the roll surface
temperature can be adjusted to a tolerance range of
±1 °C
Maintaining the rolls at the correct temperature is most
critical to the right quality of the product. The decision of the
roll is therefore the next most important decision after
machine stability.
Calendering Operations
Skim coating or Topping
Rubber coating on both sides of the fabric--Sheeting is produced
in the first and third nips and are brought together and laid on
both sides of the fabric at the same time in second nip
The second and third rolls which apply coats on the fabric must
be even speed, where as first and fourth can be even or odd
speed
Frictioning
Rubber is forced in to the fabric weave. 3R calenders are mostly
used , where the top and bottom rolls going slowly and middle
roll fast. Normally used friction ratio is in between 1:1.5-2.0
4R Calenders cannot be used for frictioning ,because of the
problem of obtaining a speed difference between fabric and
compound.
Hence two 3R Calenders in tandem have to be used
Embossing
By pressing a heavy engraved roll against hot rubber compound,
so that the engraved design is transferred to the rubber
compound
Profile Calendering
Used to produce tread sections of cycle tires and hand
building of certain types of foot wear. Calender contains
pattern rolls to produce profiled treads or patterned sheets
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