Calendering Presentation
Calendering Presentation
Calendering Presentation
ON
CALENDERING
PRESENTED BY
MARIA IMMANUEL RICHARD L
II ND SEM M.Tech TOOL ENGINEERING
R V COLLEGE OF ENGINEERING
Calendering
In the calendering process melted
plastic is passed through heated rolls to
form a sheet, and continues down a
series of rollers with gaps of decreasing
size until the required thickness is
achieved. Afterwards the film is cooled
on a chill roller.
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The equipment for calendering cost
more than the equipment for extrusion.
However, the process involves far less
cleaning than the extruder, which must
be flushed and cleaned post use.
The Machine
Typical Calender Line
Calender Roll Arrangements
I F
Z
Calendering Sheet Defects
Dimensional Non-uniformities
Thickness variations in the sheets due to roll bending with large separation forces.
Compensated with crowned rolls – larger diameter in center than at ends.
Structural Anomalies
Particulate and crystalline structure changes under the influence of high temperature
and stress
Mattness
Micro-irregularity or loss of surface gloss on the surface not in contact with the roll
when leaving the calender gap. Onsets at a wall shear stress value of 5x10 8 Pa.
V-shapes
Surface thickness variations with vertex of v-shape at center of sheet. Due to
undulating motions in the melt bank from the center to edges.
Air Bubbles
Captured in the melt bank. Can be prevented from passing through the calender rolls
through high pressure.
Uses
Industrial process
used to produce:
Car tires
Conveyer belts
Inflatable rafts
Waterproof cloth
tents
Rain coats
Limitations
Thickness
Generate film or sheet with a uniform thickness
distribution
Precise dimensions of the rolls
Cost
Installation requires large capital investment
Extruder is fraction of cost of calender
Superior for product production due to high
quality and volume capabilities