GB1563891A - Production of material in web form - Google Patents

Description

(54) IMPROVEMENTS IN AND RELATING TO THE PRODUCTION OF MATERIAL IN WEB FORM (71) We, ESCHER WYSS G. m. b. H., a Company organised under the laws of Ger- many, of Ravensburg Wurttemberg, Fed eral Republic of Germanv, do hereby declare this invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement :- This invention relates to a process for producing material in web form, particu- larly but not exclusively paper, from a suspension of fibres in water, the suspension being fed to a breast box at the outlet from which the suspension is distributed over an element permeable to water. The inven- tion also relates to a machine suitable for performing the process.

In British Patent Specifications I, 129, 757 and 1,329,409 it has been proposed, for example in a paper machine, to feed to the stock suspension air or a gas which with the suspension forms a foam containing finely distributed air bubbles. On the onc hand this improves the quality of the resulting paper while on the other hand there is a considerable energy saving, since smaller quantities of water are circulated in the paper machine. To form the foam special mixing devices are provided in the feed line at a relatively considerablc dis. ailce from the breast box. Since there is risk of the air bubbles separating out in the feed line and in the breast box, special stabilizers and emuls-fiers have to be added to the water used for forming the stock suspension.

According to one aspect of the present invention, a process of producing a material in web form from a suspension of fibres in water comprises feeding the suspension to a breast box at an outlet from which the suspension is distributed over an element t permeable to water, the breast box containing a turbulence producing means comprising a plurality of suspension ducts each having at least one widening, gas being introduced to the suspension at a point within each of the parallel suspension ducts, the introduced gas producing fine gas bubbles in the suspension leaving the breast box. In this way it is possible to ensure that as the stock suspension leaves the breast box it contains the required content of gas bubbles with the requirement for stabilizers and emulsifiers eliminated or at least sub stantiallv reduced.

According to a second aspect of the inention, a machine for producing material in web form from a suspension of fibres in water comprises a suspension tank, a breast box, a suspension line leading from the tank to the breast box, a water-permeable ele- ment positioned to receive suspension from the breast box, a turbulence producing means contained in the breast box and comprising a plurality of parallel suspension ducts each having at least one step-like widening, and at least one duct for the supply of gas leading into each of the parallel suspension ducts.

It has been found that such an arrangement is particularly suitable for the present purpose because, on the one hand, it is possible to ensure intensive turbulence and uniform distribution of the jas in the form of small bubbles in the suspension while on the other hand there is a uniform distri brution of the fibres in the suspension flow.

Suspension ducts of this kind having step Hke widenings are known per se, for example from German Auslegeschrift 1, 220, 247 and United States Patent Specifiction 3,725,197. In both cases these suspension ducts are intended for intensive turbulence and hence to render the stock now in the breast box uniform and give a uniform distribution of the fibres for paper production in the entire flow.

The gas duct may be connected to that section of the suspension duct which has the sma11est cross-section. This produces a good distribution of the gas in the suspension flow before ; t reaches the first step-likc widening, while in addition the negative pressure formed by the flow of suspension in the suspension duct can be used to supply the gas.

The gas duct may alternatively lead into the suspension duct at the location of one of the step-like widcnings. It may in some cases be advantageous to introduce the gas directly into the turbulent zone where mix ing takes place.

In one possibfe arrangement, at) cast two gas ducts are connected to each suspension duct, the two gas ducts being aligned with one another and diametrically opposite onc another. Air flows directed in opposition to one another in this way may improve the mixing of the gas with the suspension.

The invention may be carried into practice in various ways but two paper machines and their method of operation in accordance with the invention will now be described by way of example with refcrence to the accompanying drawings, in which :- Figure I is a section of part of a paper machine showing the breast box and part of the water-permeable element on the line T-I in Figure 2; Figure 2 is a plan view of the machine shown in Figure 1 ; Figure 3 is a control diagram of the paper machine with the parts shown in Figures t and 2 ; Figure 4 is a partial section similar to part of Figure I and showing another breast box and mixing device ; and Figure 5 is a section on the line V-V in Figure 4.

Figures I and 2 show the breast box) of a paper machine which is not shown in detail. The breast box 1 is used to form a paper fleece on a machine wire 2 extending over a cylinder 3. The wire 2 may extend past various dewatering devices to a point where the web of paper formed from the neece is lifted off and passed on for subse- quent processing.

The breast box 1 is connected via a stock line 4 to a device for forcing and storing the stock suspension, which contains fibres finely and uniformly distributed in water.

The stock suspension may also contain other materials, e. g. fillers and dves.

The stock suspension flows from the stock line 4 to a distribution duct 5 from which it Dasses to individual stock ducts 6 in a turbulence producing device 7. The stock ducts 6 contain sections 8,9.10 between which there are steo- ! ike widening 11, 12. Each duct 6 terminates iust upstream of an out ! et gap 13 forming the slice of the breast box 1, the gap width being ajustable by means of a slide nlate 14.

Air ducts 15 leading from a common air conduit 16 are connected to the narrowest sections 8 of the stock ducts 6.

During operation, the stock suspension is fed to the distribution duct 5 via the stock line 4 and flows in equal flows therefrom through the stock ducts 4 to the outlet gap 13 of the breast box and from the latter on to the wire 2. At the same time, air is fed via the air conduit 16 and is intensively mixed with the suspension in the duct sections 8,9 and 10 and is uniformly distributed in the form of fine bubbles. Mixing is effected by the intensive turbulence in the vicinity of the step-like widenings l l and 12. Intensive eddies form in the flow downstream of each widening and remain in the flow even at some distance from the stcp in question.

The conditions of the breast box are so selected that the turbulence at step 12 remains substantially unreduced as far as the exit aperture 13, so that in this zone the air bubbles are prevented from separating out of the water of the stock suspension. It will be seen from Figure I that to achieve this the exit apcature l3 is at a distance A from the step-like widening) 2, this distance being less than ten times the vertical dimen- sion D of the duct section 10. This condition approximately defines the critical zone where the turbulence in the How is main taxi, substantially unweakened.

Figure 3 is a control diagram for the machine shown in Figures 1 and 2. Referring to Figure 3, the stock is drawn from a chest ~'0 having an overflow 21 and is fed by a pump 22 to the stock line 4. The latter contains a pressure controller 23 with a throttle device 24. The stock passes from the stock line 4, as already stated, to the distribution duct 5 of the breast box 1.

From the duct 5 a return line 5' (see also Figure 2) leads back to the chest 20. Air is fed to the air conduit 16 by a blower 25, the delivery line 26 of which contains a throttle clevice 28 adjusted by a pressure controller 27.

The control system shown in Figure 3, by which the stock and the air can be fed to the turbulence device 7 with accurately maintained pressures, ensures that constant relative proportions are maintained for the air and stock mixture.

It should particu'arly be noted that in some cases it may be possible to dispense with the supply of additional water otherwise necessary in paper machines and its addition to the stock taken from the chest 20, for the stock can be fed to the turbulence device 7 with the same densitv as in the chest 20. The uniform distribution of the fibres in the stock, which was hitherto obtained by adding large quantities of addi tional water, can be obtained in this case by the addition of air.

As a result, the energy consumption is greatly reduced while in addition dewater ing of the fleece on the permeable element 2 is facilitated. Given suitable stock den- sities it may even be possible to dispense with the wire otherwise required for fleece forming, and place the fleece directly on a fclt, e. g. the felt of a felt press. The machine, e. g. a paper machine, can be greatly simplified in this way.

Figures 4 and 5 show another breast box in which a distribution duct 5 is followed by two superposed rows of stock ducts 6 provided with step-like widenings 1 l and 12.

An air conduit 40 is provided, from which air ducts 41 lead to the individual stock ducts 6. Connecting ducts 42 branch from the air ducts 41 and each discharges into the respective stock duct 6 adjacent the step-like widening 11. The ducts 42 are so constructed that each is aligned with another opening into the stock duct 6 diametrically opposite.

Of course the breast boxes described can be modified in various ways. For example, a blower for feeding air to the conduit 16 may be dispensed with, since the suction effect of the flow of stock may be sufficient to draw in the required air.

The turbulence device 7 may have a dif- ferent number of steps and sections than the two steps and three sections 8,9 and 10 shown. More stock ducts 6 than shown may be superposed. A different number of air ducts may be provided to feed air to the stock ducts, and in some cases an annular duct may be provided which surrounds a suitable section of the associated stock duct 6.

As already stated, the wire 2 shown in the drawings may be replace by another permeable element, e. g. a felt. The machine may be a double wire machine in which the fibre fleece is placed between two wires or permeable elements running together.

Finally, in the arrangement shown in Figure 3, wire water may be added to the line 4 upstream or downstream of the pump 22 for the purpose of diluting the stock fed from the chest.

The throttle device 24 provided to control the stock supply need not be disposed in the stock line 4 as shown, but may be provided in a bypass conduit extending parallel to the pump 22. Also, the pump 22 may be provided with a speed control, by means of which the stock supply to the breast box 1 can be controlled.

Claims (9)

1. WHAT WE CLAIM IS :- 1. A process of producing a material in web form from a suspension of fibres in water, the process comprising feeding the suspension to a breast box at an outlet from which the suspension is distributed over an element permeable to water, the breast box containing a turbulence producing means comprising a plurality of suspension ducts each having at least one widening, gas being introduced to the suspension at a point within each of the parallel suspension ducts, the introduced gas producing fine gas bub blcs in the suspension leaving the breast box.
2. 2. A process as claimed in Claim 1 in which the gas is introduced into the suspen- sion upstream of a device which produces turbulence which breaks up the gas into fine bubbles.
3. 3. A process as claimed in Claim I or C'laim 2 in which the web is paper.
4. 4. A process of producing a material in web form substantially as described herein with reference to Figures I to 3 or Figures 4 and 5 of the accompanving drawings.
5. 5. A machine for producing material in web form from a suspension of fibres in water, the machine comprising a suspension tank, a breast box, a suspension line leading from the tank to the breast box, a waterpermeable element positioned to receive suspension from the breast box, a turbulence producing means contained in the breast box and comprising a plurality of parallel suspcnsion ducts each having at least one step-like widening, and at least one duct for the supply of gas leading into each of the parallel suspension ducts.
6. 6. A machine as claimed in Claim 5 in which each gas duct is connected to that section of the respective suspension duct which has the smallest cross-section.
7. 7. A machine as claimed in Claim 5 in which each gas duct leads into the respective suspension duct at the location of one of the step-like widenings.
8. 8. A machine as claimed in Claim 5 or Claim 6 or Claim 7 in which at least two gas ducts are connected to each suspension duct, the two gas ducts being aligned with one another and diametrically opposite to one another.
9. 9. A machine for producing material in web form from a suspension of fibres in water, the machine being constructed and arranged to operate substantially as described herein with reference to the accom panying drawings.