Random web cards
- the opportunities provided by aerodynamic web forming

by Dipl. Ing. (FH) Michael Marr, FEHRER AG, Linz/Austria

Since the introduction of the K 12 random card to the market some 30 years ago, more than 300 machines have been sold worldwide. Moreover, during this long and successful history, FEHRER has contuinually upgraded the original system.


V21/R + K12 web forming production line

' The V21/R + K12 web forming line, which is available in working widths of up to 5.4m, consists of a feeding tower and a hopper feeder, which transforms the fibre material fed in from the opening and blending system into a mat of the required width. The installation of a weighing station immediately downstream of the hopper feeder controls the accuracy of the web weight at the beginning of the web forming process and thus ensures an immediate reaction to weight changes.

A weighing belt is used to deliver the web to the V21/R pre-web former, which consists of a smooth pressure roller, an inlet roller, a nose bar, a picker and a perforated drum with a suction device inside. The V21/R is employed to transform the fibre flocks coming from the hopper feeder with 1000 - 1500 g/mē into a pre-web of approximately 300 - 500 g/mē and to guarantee the correct fibre orientation. This is needed in order to fully utilise the high throughput and quality performance levels of the K12.

The "heart" of the web forming line is the K12 random card. An inlet design consisting of a nose bar and an inlet roller provides excellent fibre opening by the tambour, which is then improved still further by two pairs of worker and turner rollers. At the fibre delivery point of the tambour, the fibres are emitted from the surface due to centrifugal forces and a laminar air flow generated by a transversal blower, which also supports the fibre flow to a sieve conveyor at the outlet.

At the outlet, a suction device is installed underneath the sieve conveyor, which in conjunction with a pressure roller, serves to stabilize the web in the web forming zone.

The V21/R + K12 nonwoven line offers a wide spectrum of possible applications for an approximate weight range of 50 - 3000 g/mē. Moreover, depending on the type of fibres used, this range actually extends up to 6000 g/mē. All types of synthetic fibres can be processed, and the system is also suitable for natural cotton, bleached cotton, flax, jute, hemp, regenerated textile fibres and recycled fibres. Furthermore, it is possible to form webs from special fibres, such as P84, Kevlar, glass and many other sophisticated materials. With this line, nonwovens can be produced at a capacity of up to 500 kg/m/h.


The HIGH-LOFT device

The production of high volume webs for furniture and similar products has always been an important K12 random card application because of the huge benefits of product isotropy. Accordingly, in response to the market demand for machines, which would facilitate the production of webs with a higher volume-per-weight, FEHRER modified the web forming zone of the K12. The plain pressure roller was replaced by a perforated drum, which contains a suction device and is driven at the same speed as the sieve conveyor. The result is a web forming zone with suction from both sides, i.e. from above the web, via the perforated HIGH-LOFT drum, and from underneath, through the sieve conveyor. The position of the HIGH LOFT device in relation to the tambour and exit conveyor at the K12 and also the angle of the suction device inside the drum is adjustable, allowing the height of the web to be increased by up to 80% during forming between the two suction zones.

The V21/R - K12 (with or without HIGH LOFT) nonwoven line offers the market the following advantages:
   - Increased finished web uniformity by means of the electronic weighing of the pre-web and
     control of the feeding speed.
   - High production speeds and throughput levels.
   - Limited space requirement.
   - Simple access for maintenance.
   - Working width adjustment.
   - Uniform MD:CD ratio.
   - No folding marks.


Fibre orientation

While webs from a conventional card are longitudinally oriented and cross-laid webs clearly show an orientation that is transverse to the production flow, K12 webs are completely randomised, or isotropic.

Isotropic characteristics, i.e. the same physical properties in every direction, are very important to the production of high quality products.

In order to prove this fact and to underline its significance, we completed a series of trials in co-operation with a German university, in the course of which we compared K12 HIGH -LOFT products with randomised webs produced on a random card with crosslapper.

The results provide impressive evidence of the fact that FEHRER air-laid products offer some incomparable product advantages, i.e. an increase in compression resistance of more than 200% and very high delamination resistance.


Recent V12/R developments

The need for the market to produce economic webs with high weights and throughput for, e.g. insulation felts, waddings for the upholstery and automotive industry, induced FEHRER to develop a new, modified machine, the V12/R, which can be delivered in working widths of up to 5.4m.

The V12/R consists of a smooth pressure roller, inlet roller, nose bar, picker and a perforated drum with a suction device inside. The perforated drum can be adjusted both horizontally and vertically, and there is also a suction device underneath the sieve conveyor. This results in a web forming zone with suction from both sides, which provides all the benefits derived from isotropy.

Textile waste fibres, synthetic fibres, all natural fibres (e.g. coir, sisal, jute hemp, flax, cotton) and animal fibres, as well as fibre blends can be run on this machine.

With the V12/R, FEHRER offers an economic machine to the market which, depending on type of the fibre used, has a weight range of 300 - 6000 g/m2 and a throughput of up to 1500 kg/m/h.

In addition to these production specifications, the V12/R provides further advantages such as:
  - Space saving design
  - Low investment costs
  - Economic production


Summary

The V21 / R + K12 nonwoven production line is extremely versatile due to its ability to process different raw materials in combination with high productivity, good delamination and compression resistance, an excellent MD:CD ratio, dimensional stability, tensile strength, etc.

The HIGHLOFT - device meets the demand of the industry for extra voluminous products with the same advantageous features.

The V12/R is an excellent choice for costumers wishing to produce nonwovens with high weights, exceptional throughput speeds and low costs.

February 2002