Calendering
is a finishing process applied to textiles and plastic. During calendering
rolls of the material are
passed between several pairs of heated
rollers, to give a shiny surface. Calendering is a process where rubber
compound is formed to a continuous sheet or
coated on a fabric. This is done by feeding the rubber compound to
one or several on each other following roll
gaps.
Two rolls built together in a frame, forms one gap and is
called a two-roll calendar.
Three rolls forms two gaps and is called
three-roll calendar.
Four rolls forms three gaps and is called
four-roll calendar.
The figures show different configurations
of the rolls in a calender and also gives examples of the use of respective
machine.
Calender Process for PlasticsThe molten material is fed
tothe calender rolls from a Banbury mixer and two-roll
mill system, or from a large extruder.The
major plastic material that is calendered is PVC. Products range from
wall covering andupholstery fabrics to
reservoir linings and agricultural mulching materials.Owing to the large
separating forces developed in the calender
gap, the rolls tend tobend. This may result in undesirable thickness
variations in the finished
product.Compensations for roll deflections are provided by using crowned rolls
having
a largerdiameter in the middle than at the
ends or by roll bending or roll skewing.
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