Finishing Treatment for Filtration

09TT27 Industrial TextilesPresentation I

S.Dhandapani – 11MT62

Finishing treatment

• Fabric stability

• Filtration collection efficiency

• Dust release

• Resistance to damage from moisture and chemical agents

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.

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.

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.

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.

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.

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.

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.

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

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

Chemical Treatments - AntistaticHow 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

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.

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

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.

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.

Chemical Treatments – Fire RetardantHow 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 )

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.

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.

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 temperature4.Crushing the foam to produce an open cell structure5.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.

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.