One of the post-weaving processes available in fabric production is calendering. Let’s take a closer look at calendering, what it does, and some examples of when it’s used.
What is Calendering?
Calendering is a process that involves running fabric through two large heated rollers. The rollers are closely spaced so that there is significant pressure on the fabric as it passes through them. For those of you old enough to know about (or remember, for real “oldsters”) think of it like the wringer on an old washing machine – just with heat added.
This process alters the physical characteristics of the fabric. Typically, the individual yarns are flattened and the inter-yarn gaps are reduced because as the yarns flatten, they become wider.
Obviously, this will affect the amount of air and light allowed through the fabric, so air and water flow rates and shade factor change once calendering is complete. The fabric is also smoother if standard flat drums are used. (In some clothing fabric applications, a calender is used to imprint or emboss a pattern on the fabric).
In addition to these obvious fabric changes, calendering can also affect other fabric specifications such as tear and burst strength. These changes relate to the effects on the yarns and how they move or don’t move during some of these tests (such as the tear tests). Since calendering can flatten and widen the yarns, the space between the yarns decreases, reducing the yarns’ abilities to move. When yarns move, they can “bunch” and essentially form a composite yarn comprised of multiple yarns. This can increase the tear resistance of the fabric.
The changes to tear strength and burst strength due to calendering can vary from one fabric to another, and it is always prudent to check the specs of a fabric both before and after calendering to see the measured changes. Calendering also adds additional cost to the fabric.
Calendering serves a useful purpose for many types of fabric. One example Acadian has is our standard 10444 truck cover fabric (often referred to as “gorilla mesh”) and our trampoline fabric. Both are identically constructed fabrics with the same number and types of yarn. The overall weight is also the same, but the trampoline fabric is calendered after weaving. In this particular case, the trampoline fabric is smoother, with increased tear strength and increased burst strength. Specifications for both of these fabrics are available here.
Please contact us if you have any questions about calendering or fabric in general. We are always glad to help.