ADAMA SCIENCE AND TECHNOLOGY UNIVERSITY
SCHOOL OF MECHANICAL, CHEMICAL AND MATERIALS
ENGINEERING
DEPARTMENTS OF MATERIALS SCIENCE AND
ENGINEERING
Polymer Processing presentation on Calendering
Prepared by: Rahel Abera
Submitted to: Profe.Jung Yong Kim
November 13, 2021
Introduction
Working Principle
of calendering
CONTENTS
Uses and Types
Advantage and
Disadvantages
1. Introduction
Calendering is a process where materials
are squeezed between pairs of rollers. or is a
process of smoothing and compressing a
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material(notably paper) during production by
Materials
are
calendered
to
reduce
passing a single continuous sheet through a
thickness, to produce an even
number of pairs of heated rolls.The rolls in
thickness,
combination are called calenders. Calender
to produce a texture and to
laminate two
rolls are constructed of steel with a hardened
or more sheet materials.
surface, or steel covered with fibre.
1
History
 The PVC sheet was successfully calendered in GERMANY in the 1930s and after
a decade calendering was being used for both rigid and plasticised compounds of
PVC resin.
 In general extrusion film blowing and die casting methods are preferred for
materials such as PE, PP and PS, plastics but calendering has the major
advantage of causing less thermal degradation and so it is widely used for heat
sensitive material such as PVC.
 Both rigid and plasticized compounds of PVC resin can be used in calendaring
process.
 The sheet is formed in the range of 0.1 to 1.0 mm and above thickness. The sheet
can be transparent, colored, embossed, printed or laminated form.
2
Plastic material and its
Compound
• The PVC resin is generally processed in calendaring plant, and it needs
blending, mixing and compounding by addition of suitable chemicals called as
additives and fillers to make compound before processing in the calendering
plant.
• Other then PVC resin ABS, PE, PP and Styrene are also used for calendering
process.
3
Compound formulation
•
PVC resin for rigid compounds made either by the suspension or bulk
polymerization process is best in the 1. 7 to 2. 0 relative viscosity range.
• Homopolymer grades are used alone and in combination with 2 to 10 percent
acetate copolymer.
• Heat stabilizers are needed, when heated PVC naturally tends to degrade, first
by yellowing then by turning dark brown and losing its physical properties.
• Many types of stabilizers are used, Metallic salts, mixed metal salts, organotins
and tin mercaptides are the major categories.
4
Cont............
•Stabilizers
added to a formula between 0. 1 and 5. 0 percent to retard
degradation by tying up hydrochloric acid (HCL) generated by the heat of
processing.
• Plasticizers are used to make PVC soft and flexible but thereby lower melt
viscosity, modulus and transition temperature.
Work Report
•Two common plasticizer groups are in use such as Dioctyl
phthalate(DOP)
and
This PPT template
for the rice husk
Epoxidized soyabean oil.
designer pencil demo works, focusing
This PPT template for the rice husk
designer pencil demo works, focusing
5
Cont............
• Impact modifiers are used to absorb shock to improve impact resistance of
PVC compound. The selection of ABS, MBS, Chlorinated polyethylene( CPE) or
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acrylic polymer chosen on the basis of their impact efficiency, clarity, weather
ability and stress whitening, as well as their processing characteristics
• Process aids assist stabilization and increase the melt strength of the sheet
during calendering and post processes such as thermoforming.
6
Cont............
•
Lubricants are added to reduce the tendency of PVC to stick to the hot metal
rolls of Calender
• Lubricants are either external or internal depending on where they are most
effective. Stearic acid or zinc and inorganic stearates and soaps are classified as
internal lubricant. Paraffin and polyethylene
Thiswaxes
PPT templateare
for the external.
rice husk designer
pencil demo works, focusing on the production
of high-end design husk
7
2.How It Works
 The basic idea of the machine is that squishes a heat
softened polymer between two or more rollers (this area
is called a nip) to form a continous sheet.
 To begin this process the polymer must go through
blending and fluxing before it goes through the
calendar.
 It make it a consistency easier for the calendar to handle
8
How It Works Cont............
The thickness of the polymer sheet is dependent
mainly on the gap between the last two rollers.
The last set of rollers also dictate the surface finish,
Ad
d yofothe
u rsurface.
glossiness and
texture
t
i
t
l
e
 Polymer is ready for going through the rollers tends to
follow the faster moving roller of the two that it’s in contact
with and it also sticks more to the hotter rolls.
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How It Works Cont............
That’s why calendar typically end with a smaller roller
at a higher speed to peel the sheet off
03
It is also why the middle roller is kept cooler so that the
sheet won’t stick to the other rollers nor will it split by
sticking to both rollers which can happen
10
Cont............
Schematic of a typical calendering
process (Berstorff GmbH, Germany).
11
Cont............
Schematic of a typical calendering
process (Berstorff GmbH, Germany).
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Precautions to be taken during
processing
•Preparation of stock for calendering, conditions on the
calender, the take off, thickness measurements, and
control to wind up.
• Other considerations include whether the plastic is
laminated to a fabric on the calender.
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3.Uses
Automobile
And Furniture
Upholstery
Wall Coverings
Continuous
Flooring
Pressure
Sensitive Tapes
Luminous
Ceilings
Rainwear
Shower
Curtains
Signs
Floor Tile
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Types of calendering
system
4.Types
‘I’ Type calendaring
(Superimposed)
‘L’ Type
calendaring
(offset)
‘Z’ Type calendaring
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Types Cont............
I Type (Superimposed)
•It can built with one more roller in the stack
•This design was not ideal though
because at each nip there is a an outward
force that pushes the rollers away from thenip
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Types Cont............
L Type (offset)
• L Type calendar are often used for processing
rigid vinyl’s and inverted L type calendar are
normally used for flexible vinyl’s
• These both setups have become popular and
because some rollers are at 90 degree angle to
other their roll separating forces have less effec
on subsequent rollers.
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Types Cont............
Z Type
•The Z type calendar places each pair of rollers
at a right angles to the next pair in the chain
•This means that the roll separating forces that are
on each roller individually will not effect any other
rollers
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HEATING AND COOLING OF CALENDER
Calendar rolls are normally made of chilled cast iron. Calendars are also
made with steel rolls which are more resistant and which exhibits less
deflection under the pressure of the material in the nip.
Heating system
• High pressure steam is used on calendaring plants. Working pressure range -
680- 1380 KN/m and a temperature range 120-185℃
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Cont............
• High pressure hot water (H. P. H. W. ), This is effective method to heat and cool the
calender rolls by circulating H. P. W. H. through each roll. The hot oil can be circulated
through the rolls to achieve the high operating temperature.
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Processing Parameters
The processing parameter needs to be set and control are
pressure and the nip gap.
Examples: Roll No. Roll Temp. (°C)
1st
165
2 nd
168
3 rd
171
4 th
174
Nip gap between rollers:
Roll No.
Nip Gap
1 st - 2 nd High
2 nd -3 rd Medium
3 rd -4 th
Low
temperature, speed,
Speed( m/min. )
80
82
85
88
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Mechanism against Roll bending
• The calender lines during operation generate very high forces exerted on the rolls
to squeeze the plastic melt into a thin web or sheet. High forces can bend the rolls.
• Crowned rolls, which have a greater diameter in the middle than at the edges
• Crossing the rolls slightly, thus increasing the nip of opening at either end of the
rolls.
• Roll bending, where the bending movement is applied to the end of each roll by
having a second bearing on each roll neck, which is then loaded by a hydraulic
cylinder.
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Troubleshooting in calendaring process
Faults
Causes
Compound formulation
The use of wrong ingredients
or wrong quantities
Poor gauges
Improper temperature
Improper compound
Improper flow
Streaks
Poor compounding
improper temperature
Contamination
Thickness variation
Bent / deflection in
rolls
Mis alignmentt
Film curling or side bending
Wrong roll design
Non uniform roll temperature
Discoloration
Regrind material Poor compound
Quality of Pigment
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5.Advantage and Disadvantages
Advantages
 The calendar is very good at handling
polymer that are heat sensitive as it causes
very little thermal degradation
 It is good at mixing polymers that contain
high amount of solid additives that don’t get
blended or fluxed in very well
 Due to this calendar is produce a large
amount of melt than extrusion
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Cont............
Disadvantages
 It is a very expansive process to perform
 If the tickness is below 0.006 inches then there
is tendency for pinholes and voids
to appear in the sheets
 If the thickness is greater than about 0.06
inches then there is risk of air entrapment in the
sheet
 So to achieve the desired thickness is also a
very difficult process
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MSE
THANKS