Woven filters have open spaces around the fibers. The weave design used will depend on
the intended application of the woven filter. The simplest weave is the plain weave. The
yarn is woven over and under to form a checkerboard pattern (Figure 1). This weave is
usually the tightest, having the smallest pore openings in the fabric. Consequently, it
retains particles very quickly. This weave is not frequently used, because the bags tend to
have a high pressure drop (even without any dust cake).
Other weaves include the twill and sateen (satin). In the twill weave, yarn is woven over
two and under one for a 2/1 twill and over three and under one for a 3/1 twill weave (see
Figure 2).
The twill weave does not retain particles as well as the plain weave, but does not tend to
blind as fast. Bag blinding is a condition where the particles (dust) becomes embedded in
the filter over time and are not removed by the bag cleaning process. The twill weave
allows good flow rates through the filter and high resistance to abrasion. In the satin
weave, yarn is woven over one and under four in both directions. Satin weave does not
retain particles as well as the plain twill weave, but has the best (easiest) cake release
when the fabric is cleaned (Figure 3).
Different weaving patterns increase or decrease the open spaces between the fibers. This
will affect both fabric strength and permeability. Fabric permeability affects the amount
of air passing through the filter at a specified pressure drop. A tight weave, for instance,
has low permeability and is better for the capture of small particles at the cost of increased
pressure drop.
The true filtering surface for the woven filter is not the bag itself, but the dust layer or filter
cake. The bag simply provides the surface for capture of larger particles. Particles are
collected by impaction or interception as the open areas in the weave are closed. This process
is referred to as sieving (Figure 4). Some particles escape through the filter until the
cake is formed. Once the cake builds up, effective filtering will occur until the bag
becomes plugged and cleaning is required. At this point, the pressure drop will be exceedingly
high and filtering will no longer be cost effective. The effective filtering time will
vary from approximately 15 to 20 minutes to as long as a number of hours, depending on
the concentration of particulate matter in the gas stream.
the intended application of the woven filter. The simplest weave is the plain weave. The
yarn is woven over and under to form a checkerboard pattern (Figure 1). This weave is
usually the tightest, having the smallest pore openings in the fabric. Consequently, it
retains particles very quickly. This weave is not frequently used, because the bags tend to
have a high pressure drop (even without any dust cake).
Figure 1. Plain weave or checkerboard
Other weaves include the twill and sateen (satin). In the twill weave, yarn is woven over
two and under one for a 2/1 twill and over three and under one for a 3/1 twill weave (see
Figure 2).
Figure 2. Twill weave patterns (2/1 and 3/1)
The twill weave does not retain particles as well as the plain weave, but does not tend to
blind as fast. Bag blinding is a condition where the particles (dust) becomes embedded in
the filter over time and are not removed by the bag cleaning process. The twill weave
allows good flow rates through the filter and high resistance to abrasion. In the satin
weave, yarn is woven over one and under four in both directions. Satin weave does not
retain particles as well as the plain twill weave, but has the best (easiest) cake release
when the fabric is cleaned (Figure 3).
Figure 3. Sateen weave (satin weave)
Different weaving patterns increase or decrease the open spaces between the fibers. This
will affect both fabric strength and permeability. Fabric permeability affects the amount
of air passing through the filter at a specified pressure drop. A tight weave, for instance,
has low permeability and is better for the capture of small particles at the cost of increased
pressure drop.
The true filtering surface for the woven filter is not the bag itself, but the dust layer or filter
cake. The bag simply provides the surface for capture of larger particles. Particles are
collected by impaction or interception as the open areas in the weave are closed. This process
is referred to as sieving (Figure 4). Some particles escape through the filter until the
cake is formed. Once the cake builds up, effective filtering will occur until the bag
becomes plugged and cleaning is required. At this point, the pressure drop will be exceedingly
high and filtering will no longer be cost effective. The effective filtering time will
vary from approximately 15 to 20 minutes to as long as a number of hours, depending on
the concentration of particulate matter in the gas stream.
Figure 4. Sieving (on a woven filter)
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