Textile Finishing

In textile finishing, often also referred to as finishing, the textile raw material is made ready for use by means of various processes so that it can be further processed as a textile surface. For example, a preparation or sizing applied during the manufacturing process must be removed, as well as defects and dirt. Furthermore, finishing is used to give textiles properties that they do not naturally possess. Particularly in textile finishing, great importance must be attached to environmental protection, both in terms of waste water and exhaust air. Finishing is always a combination of different operations using chemical, mechanical or chemical-mechanical processes. These can be independent of the raw material, but are often based on the chemical composition and surface properties of the fibers used.

In singeing, protruding fiber ends are burned away by gas flames or other heating elements, resulting in a smooth surface.

Washing processes are necessary both in the pretreatment and in the intermediate and posttreatment stages to remove impurities, preparations, sizing residues, etc. This is done with appropriate washing machines, also called jiggers. After such a wet treatment and before further thermal treatments, the fabric must be dewatered, which is done by spinning, suction or squeezing. It is then dried on the stenter frame. Any warping of the fabric caused by previous operations can be compensated for during the corresponding fabric infeed. For this purpose, the fabric is gripped on both sides with needles or clips and guided through the drying chamber to the desired width.

For synthetic fibers, heat-set is one of the most important finishing processes. Fixing compensates for tensions in the interior of the fiber that have arisen during fiber extraction and processing down to the surface. By heat-treating the thermoplastic synthetic fibers and then cooling them in a controlled manner, the fibers are fixed in a state of least stress. This makes them stable in shape and size.

The calendar plays a special role as a final treatment in textile finishing. It has the task of smoothing textile surfaces, compressing them by pressure and producing a shiny surface. For this purpose, the textile material is passed between rollers that are under pressure and temperature controlled. Depending on the desired effect, the roller properties, temperature, arrangement and speed play an important role. With regard to the use of calendared fabrics for filter cloths, calendering influences the air and particle permeability, improves cake detachment and cleaning. The mechanical resistance, on the other hand, can be negatively influenced under certain circumstances.

While the task of dry finishing is essentially to change the surface, in wet finishing textiles are given new properties that represent an improvement over the properties of the individual fiber materials. In impregnation, for example, textiles are impregnated or sprayed with water-repellent chemicals. Coating, on the other hand, is the application of synthetic substances to a textile surface with subsequent consolidation, for example on a stenter frame. Coating also creates a textile surface with new properties resulting from the properties of the carrier material and the coating compound. Here, it is important that the plastic surface is porous enough to ensure air and moisture transport. In laminating, two or more textile surfaces can be joined together. This is done by thermal lamination or by an adhesive. The latter also ensures a porous surface.

The following points must be taken into account when developing filter cloths with optimal properties:

  • The filtration efficiency or separation efficiency of particles – this can be influenced by the type of weave (choice of weave), the weave density and the type of finishing.
  • Size, shape and chemical composition of the particles to be separated.
  • Removability of the filter cake – quick and optimal cake removal is achieved through the choice of weave, the yarns used (in addition to multifilaments, monofilaments are best suited here) and a smooth surface by means of calendering.
  • Density and viscosity of the mass to be filtered.
  • Mechanical, chemical and thermal resistance – the right choice of yarn and its polymer composition is crucial here.
Polymer Operating Temperature °C Peak Temperature °C Resistance against acids Resistance against alkalis Resistance against oxidizing agents Resistance against hydrolysis
Polypropylene 90 100 ++++ ++++ +++
Polyester 100 120 +++ ++
Polyamide 6.6 110 110 +++ ++
Polyamide 12 130 130 +++ ++
Polyvinylidenfluoride 140 140 ++++ ++++ +++ ++++</td

A filter cloth should usually be replaced if it shows any visible amount of abrasion, holes, wrinkles, or loss of dimensional stability. In addition, if the process contains impurities in the filtrate, an insufficiently compressed filter cake and deteriorated cake detachment, the cloth must also be changed urgently.

When it comes to filter cloths, a distinction is made between the following variants, depending on the use:

  • Single filter cloths (in and outlet cloths)
  • Push-through or double filter cloths with hose connection
  • Drape-over cloths
  • Pan filter cloths
  • Backing cloths for improved drainage of sludge and extension of the service life of a filter cloth

They are used on frame, chamber or membrane filter presses in the following industrial sectors:

  • Food industry for the filtration of sugar and fruit juices, edible oils and fats as well as dairy products. For the production of starch and wine as well as in the brewing industry and much more.
  • Mining industry and its raw material extraction for the removal of sludge from mine water. For draining sand, clay and kaolin suspensions and much more.
  • Chemical industry for the production and purification of oxides and pigments. For the production of salts and their solutions, as well as acids and their salts as well as for the production of soda, fertilizers and much more.
  • Mechanical engineering for the filtration and separation of emulsions and degreasing agents in surface finishing such as electroplating and painting and much more.
  • Glass and ceramics industry
  • Wood, pulp and paper industry
  • Wastewater treatment and (drinking) water treatment
  • And many more…