This document discusses various finishing treatments for industrial textile fabrics used in filtration applications. It describes mechanical treatments like heat setting, singeing, raising and calendaring which improve fabric stability, filtration efficiency and dust release. It also discusses chemical treatments like antistatic, water and oil repellent, PTFE and fire retardant treatments which assist with dust release and protect from chemicals. Special surface treatments like PTFE membrane lamination and low density foam coating are also outlined which restrict dust to the fabric surface and reduce blinding.

1. Finishing Treatment for
Filtration
09TT27 Industrial Textiles
Presentation I
S.Dhandapani – 11MT62

2. Finishing treatment
• Fabric stability
• Filtration collection efficiency
• Dust release
• Resistance to damage from moisture and
chemical agents

4. Mechanical Treatments – Heat setting
 Improved Stability is essential in order to prevent shrinkage
during use.
 Such shrinkage may be caused by the relaxation to tension
imposed on fiber and yarns during manufacture,or be due to
the inherent shrinkage properties of the raw material
themselves.
 The thermal conditions that are found in a dust collector,will
conducive to fabric relaxation and if not effectively addressed
during manufacture, could lead to serious shrinkage problems
during use.

6. Mechanical Treatments – Heat setting
 As heat is the primary cause of shrinkage, it is logical that
fabric stability should be achieved by thermal means.
 In addition to stabilising the fabric, the heat setting process
will also effect an increase in the density of the structure
through increased fiber consolidation.
 This in turn will further assist in achieving a higher level
filtration efficiency.

7. Mechanical Treatments – Singeing
 Filter fabrics produced from short staple fibers, invariably
possess surfaces with protruding fiber ends.
 Such protrusions may inhibit cake release by clinging to
the dust,it is common practice to remove them, this is
achieved by singeing.
 He process which the fabric passed at relatively high
speed ,over a naked gas flame or over heated copper
plate.

9. Mechanical Treatments – Singeing
 The heat of the flame causes the fibers to contact to the
surface of the fabric where, in the case of thermoplastic
fibers.
 Singing conditions will normally be adjusted according to
polymer type and the intensity required by either the
end-use application of the individual manufacture’s
preference.
 Application with slight moisture &/or agglomeration are
present, where the smooth singed surface promotes
ideal dust release.

10. Mechanical Treatments – Raising
 Singeing process is designed to denude the fabric of its
protruding fibers.
 He raising process is designed actually to create a
fibrous surface, normally on the outlet side of the filter
sleeve.
 To enhance the fabric’s dust collection capability.
 This process is designed essentially for woven fabrics
comprising staple fiber yarns at least in the weft
direction.

13. Mechanical Treatments – Raising
 In this operation the fabric is pulled over a series of
rotating rollers termed ‘pile’ and ‘counter pile ‘
 The cylinder rotates the pile rollers raise the fiber proud
of the surface whereas the counter oile roller stroke them
into a more orderly fashion.
 Raised fabrics may comprise 100% staple fiber yarn
 Smooth surface provided by the multifilaments will aid
cake release whilst the raised staple yarns on the
reverse side will enhance particle collection efficiency.

14. Mechanical Treatments – Calendaring
 Calendaring operation fulfils two objectives
1.Improve the fabric surface smoothness and hence aid dust
release.
2.To increase the fabric’s filtration efficiency by regulation of its
density and permeability.
 The yarns and fibers become more tightly packed,
making it more difficult for particles to pass through or
even in to the body of the fabric.
 In calaenders in the industry consists of at least two
bowls,one manufacture from chrome plated steel,and
other from a more resilient material such as nylon or
highly compressed cotton or wool fibres.

16. Mechanical Treatments – Calendaring
 The steel bowl is equipped with a heat source, for
gas,electic elements, superheated steam or circulating
hot oil.
 He process tempreature presure and speed,the desired
density and degree of surface polish can be achieved.
 In reality, rather than density, a more common control
parameter is measurement of the fabric's air permeability
 Aggressive conditions in the filter may well negate the
effect of the calendering operation before the fabric has
become fully’acclimatised’to the conditions

17. Chemical Treatments
 Chemical treatment are normally applied for one of two
reasons.
1.To assist in dust release, especially where moist sticky dusts,
possibly containing oil or water vapour or encountered.
2.To provide protection from chemically aggressive gases such as
So2 and So3
TYPE OF FINISHINGS
 Antistatic
 Water & oil Repellant
 PTFE Treatment
 Fire Retardant

18. Chemical Treatments - Antistatic
How it works
 Coats fiber with thin layer of material that will attract a
thick layer moisture.
 Fabric hold a charge opposite to that normally
accumulated to neutralize the static charge.
 Improves conductivity of fibers
 It is use for polyester fabrics
 Typical for light polymer powders

19. Chemical Treatments – Water & oil Repellant
How it works
 Provides s durable,clear protective barrier,characterized
by extremely low surface tension,which is lower than that
of oils
 Imparts hydrophobic and oleophobic properties.
 Main purpose is to prevent bags from blinding caused by
accumulation of wet, sticky or agglomerating dust.
 It is uses for all filtration systems where moisture in the
flue gas in present.

20. Chemical Treatments – Water & oil Repellant
 Drying processes, food processing and combustion
processes
 Industrial facilities which burn any type of a fossil fuel
 Cement plants, Refuse systems and incinerators

21. Chemical Treatments – PTFE Treatment
How it works
 Applied to high temperature filtration fabrics by full
impregnation of fabrics in PTFE dispersion.
 Imparts high level of oil & water repellency.
 Improves fabric clean-ability and lower operation
pressure drop.
 Improves abrasion resistance
 Prevent moisture and acids formed during dew point
transitions from being absorbed by the filtration fabric.

22. Chemical Treatments – PTFE Treatment
 It is uses for all types of high temperature filtration
applications where the possibility of an acid dew point
transition exists.
 Coal fired boilers, cement, asphalt and incineration.

23. Chemical Treatments – Fire Retardant
How it works
 Reduces flammability of fabrics
 Slows spread of fire in situations when flammable dust is
ignited inside the dust collector.
 It is uses where there is a possibility that the filter bags
may be ignited by sparks, smoldering dusts, tinder,
chemical reaction or during dust collector repair or
maintenance ( welding )

24. Special Surface treatment
 This category of treatments is devoted still further the
fabric’s filtration efficiency and cake release
characteristics.
1.Attachment of a more efficient membrane,for example biaxially
stretched PTFE in a lamination operation.
2.The application of a low density microporous foam.
 Both these treatments are designed to restrict the dust
particles, as far as possible. to the surface of the fabric,
thereby reducing the tendency for blinding.
 The PTFE membrane, comprising an extremely fine
structure, is particularly effective in this respect.

25. Special Surface treatment
 It may be laminated to the surface of the fabric either by
special adhesives or, where appropriate, by flame
bonding.
 Although highly efficient, the gossamer – like surface is
rather delicate and care must be exercised when
handling filter sleeves produced from such material.
 PTFE laminated fabrics are relatively expensive ,their
use in normally restricted to difficult applications.
 Where the particles are extremely fine or of a particularly
hazardous nature or where the interaction with a surface
of this type shows unique advantages in respect of cake
release.

26. Special Surface treatment
1.Mechanically generating a low density latex foam.
2.Applying this foam to the fabric by the knife over roller
technique.
3.Drying the foam at a modest temperature
4.Crushing the foam to produce an open cell structure
5.Curing the foam at a higher temperature to crosslink the
chemical structure.
 The principle ingredient of the treatment is usually an aqueous
based acrylic latex, the precise formulation may comprise a
variety of chemical agents to ensure the production of a fine,
regular and stable pore structure perhaps also to provide
specific characteristics such as antistatic or hydrophobic
properties.

27. Special Surface treatment
Treatment for PP
 PP is a very interesting material for plasma treatment.
PP is a very hydrophobic material with extreme low
surface tension.
 On the other hand PP is used in a large number of
technical applications were an improved wet-ability or
adhesion properties are advantageous.
 This is also the case for PP technical textile applications
such as filters, medical or hygiene applications. By using
oxidative plasma important improvements in surface
tension can be obtained within a very short plasma
treatment.