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Prezentace aplikace PowerPoint

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Wet laid nonwovens are made by a modified papermaking process. ... sheeting for roofs, shingling, separators, filters, reinforcement material ... – PowerPoint PPT presentation

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Title: Prezentace aplikace PowerPoint


1
Chapter IV.
Mechanical technology of nonwovens Department of
nonwovens
Wet laid, Air laid, and Random laid
2
Wet laid - Principle
Mechanical technology of nonwovens Department of
nonwovens
  • This topic is disskused in subject Thermal and
    chemical technology of nonwovens because wetlaid
    fabricks are usually chemical bonded.
  • Wet laid nonwovens are made by a modified
    papermaking process. That is, the fibers to be
    used are suspended in water, which is
    subsequently taken out.
  • In terms of wet laid technology compared with dry
    laid technology is possible to process short and
    smooth fibers (for example glass microfibers).
  • The typical features of airlaid and wetlaid
    fabrics are
  • Random orientation of fibers on the fabric
    surface
  • Wider range of area density compared with dry
    laid technology

3
Wetlaid used material
Mechanical technology of nonwovens Department of
nonwovens
  • The wet laid fibers must be miscible in water so
    their main feature are
  • low surface tension (which is possible to adjust
    by surfactants
  • small lenght or low ratio between the fiber
    length and diameter it is possible to process
    short fibers (2-50 mm)
  • low crimpiness it is possible to proces smooth
    fibers

A major objective of wetlaid nonwovens is to
produce structures with textile properties
(flexibility, strenght etc...) at speeds similar
to papermaking process. Textile fibers tend to be
longer, stronger and relatively inert when
compared to papermaking fibers, which are short,
fine and are able to pack together into a dense
structure. The structure, which contains textile
fibers, is more open and extensible but preserves
the basic strenght and stability of the fabric.
Thus wet laid textile is stronger, softer,
bulkier, more drapeable, less smooth and more
porous than paper.
4
Wet laid principle of technology
Mechanical technology of nonwovens Department of
nonwovens
  • There are three characteristic stages in the
    manufacture of nonwoven bonded fabrics by the
    wet-laid method .
  • Swelling and dispersion of the fiber in water
    transport of the suspension on a continuous
    traveling screen
  • Continuous web formation on the screen as a
    result of filtration
  • Drying and bonding of the web

Fiber swelling and dispersion
Suspension transport
Web formation
Water recycling
5
Wet laid examples of end uses of wet laids
Mechanical technology of nonwovens Department of
nonwovens
  • Special papers
  • synthetic fiber paper, dust filters, liquid
    filters, overlay paper, stencil paper, tea bag
    paper, paper for wrapping susage and cooked meats
  • Industrial nonwovens for
  • waterproof sheeting for roofs, shingling,
    separators, filters, reinforcement material for
    plastics, backing material, shoe uppers,
    decoration, interlinings, insulation
  • Nonwovens similar to textiles
  • surgical clothing, bed-linen, table cloths,
    servittes, towes, household cloths, face cloths,
    nappy, sanitary articles

6
Air laid - principle
Mechanical technology of nonwovens Department of
nonwovens
The fiber material is at first opened by rotating
cylinder named lickerin. Then single fibers are
dispersed into the air stream and condensed on
the perforated cylinder or belt.
  • Air laid fabric compared with carding technology
    has these features
  • The fibers are oriented randomly on the fabric
    surface isotropic structure.
  • Voluminious webs can be produced
  • The range of the area weight is wider (15 250
    g/m2) but the mass uniformity of light air laid
    (up to 30 g/m2) is bad.
  • Wide variety of processable fibers

7
Air laid production problems
Mechanical technology of nonwovens Department of
nonwovens
  • Low level of opening fiber material by lickerin
    roller
  • Thus is suitable to use pre-opened fibers or
    combine air laid with card machine Random card
    machine
  • Various structures of web in width of layer due
    to irregular air flow close to walls of duct
  • This problem requires high quality design of
    duct.
  • Possible entangling of fibers in air stream
  • This problem can be reduced by increasing the
    ratio air/fibers which nevertheless means
    decrease in performance and increase of energy
    consumption due to high volume of flowing air.
    The relation between air flow and performance of
    device shows the importance of fiber lenght and
    fiber diameter. QA is air flow, K is device
    constant, P is performance of device (kg/hour), L
    is lenght of fiber staple (m) and D is fiber
    fineness (dtex).

Thus is suitable to use short fibers for this
technology.
8
Example of air laid machine
Mechanical technology of nonwovens Department of
nonwovens
Production up to 3 000 kg/hour
9
Scheme of airlaid line dust controll
10
Random cards combination of air laid and
carding technology
Mechanical technology of nonwovens Department of
nonwovens
A major objective of this combination is
isotropic textile fabric (random orientation of
fibers) with good mass uniformity of light
fabrics and with high production speed.
  • The first part card machine opens perfectly
    fibrous material so single fibers are as a
    output.
  • The second part air laid system uses the
    centrifugal force to strip the fibers off a
    roller and. put them down on an air controlled
    scrim belt.

11
Main variations of random cards I.
Mechanical technology of nonwovens Department of
nonwovens
Airlaid function of random card 1) Random
roller between main cylinder and doffer, which
rotate in the opposite direction of the main
cylinder.
12
Main variations of random cards II.
Mechanical technology of nonwovens Department of
nonwovens
2) Centrifugal force of mean cylinder strips the
fibers off
Random card Fehrer K12
13
Example of random card lineFehrer
Mechanical technology of nonwovens Department of
nonwovens
14
Air laid and random cards used fibers
Mechanical technology of nonwovens Department of
nonwovens
synthetic fibres, viscose, cotton and blends
thereof natural fibres such as flax, hemp, sisal
etc. reclaimed textile waste and shoddy,1.7 -
2000dtexmax. 120 mm staple length
Air laid and random cards end products
interlinings, shoe linings, high loft" products
for the garment and furniture industries base
material for coating substrates and synthetic
leather waddingsgeotextiles, filter materials
needle blankets carpets and wall coverings
technical felts insulation felts mattress felts,
waddings for the upholstery and automotive
industry undercarpets
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