Support Apparatus for a Dewatering Unit in the Web Forming Section of a Paper Machine

The present invention relates to support apparatus for a dewatering unit in the web-forming section of a paper machine and especially to the supporting of a dewatering unit below a bottom wire, said unit being used in connection with a twin wire former. This supporting method allows a wide range of adjustments to be made.

There are several known shoe constructions for the forming section of a twin wire former, most of which are stationary and quite stiff. Some vertically adjustable constructions have, however, been disclosed, for example in U.S. Pat. No. 3,994,774, FI Pat. No. 69885 and DE Pat. No. 3406217.

U.S. Pat. No. 3,994,774, although it relates to a so-called gap former, discloses vertical adjustment of the lower dewatering unit by means of pressure-medium filled cylinders disposed in the corners of said lower unit. Such arrangement enables stepless adjustment of the inclination of the lower dewatering unit.

FI Pat. No. 69885 discloses a forming shoe for a twin wire forming section in a paper machine, said shoe comprising a number of pivoted blade rows disposed transversely with respect to the forming shoe. The height of each forming shoe is separately adjustable in order to provide a leading surface of a desired form. Articulation of the blade rows allows forming of a curved leading surface comprising several partial plane-like surfaces.

In DE Pat. No. 3406217, the cover of a dewatering unit below a bottom wire is formed of lists, each of which is adjustable to compress the web against the dewatering unit above the bottom wire at pressure unequal to that of other rows. In the embodiment disclosed in said patent, the rows are attached to a flexible membrane, below which a desired pressure prevails. Dividing the pressurized space below the membrane into separate chambers makes it possible to change the state of pressure in the chambers, which enables the comprssive effect on the web to be adjusted. The more chambers the pressurized space is divided into, the greater the number of unequal compressive pressures that can be used.

The above described, relatively advanced arrangements have some disadvantages that cannot be eliminated because of their constructions. Neither is it possible to apply the newst technique in them such as, for example, provision of dewatering elements, disposed on different side of the web, that are adjustable with respect to one another in the longitudinal direction of the web.

Although the arrangement as disclosed in U.S. Pat. No. 3,994,774 allows vertical adjustment in the lower dewatering unit, such arrangement is not readily applicable to said unit. Disposition of pressure-medium filled cylinders in the corners of the lower unit also sets too high demands on the stiffness of said unit, at least if the width of the unit exceeds five meters.

Although every blade can be vertically adjusted independently of each other if FI Pat. No. 69885, it seems unlikely that such an adjustment could be made during operation or that such a unit would be adjustable in the direction of the web. Furthermore, in view of a wide paper machine, lack of stiffness constitutes a problem also in this arrangement if said type of shoe is used as a counterpart of the upper dewatering unit.

Thirdly, the apparatus as disclosed in DE Pat. No. 34062127 has some disadvantages even though it is highly developed. Due to a complicated pressure-medium chamber and especially due to its adjustment and feed equipment, it is hard to imagine said apparatus being transferable in the direction of the web. It is also highly probable that if said arrangement were applied as a counterunit of a suction box, the cover of which is formed of foils, it would not function reliably because of a flexible attachment of the foils to the membrane covering the pressure-medium filled chamber. In that case, the foil/foils would most probably vibrate due to pressure pulses, thus not achieving the advantages that can be reached by means of stationary, fixed lists.

It is an object of the present invention to provide a dewatering unit and means of supporting thereof, which together eliminate or minimize the defects discovered in known arrangements. The result of the invention is a dewatering unit with means of support, which unit is readily and in a diversified manner adjustable, and is simple and reliable in operation, characterized in that the dewatering unit below the bottom wire is supported by hose-like pressure elements on beams disposed transversely with respect to the machine direction, said pressure elements enabling the dewatering unit to be adjusted both vertically and horizontally. Other characteristics of the apparatus are disclosed in the accompanying claims.

The apparatus will be further described, by way of example, with reference to the accompanying drawings, in which

FIG. 1 is an overall schematic elevational view of the wet end of a paper machine to which the support apparatus according to the invention is applied; and

FIG. 2 is a detailed side view of the apparatus in accordance with the invention which may be regarded as an enlarged fragmentary detail of FIG. 1.

FIG. 3 is an end elevational view of the support apparatus hereof.

The apparatus according to the invention is primarily intended to be used in a fourdrinier machine 1, as shown in FIG. 1. In its simplest form, the wet end of the fourdrinier machine 1 comprises a headbox 2 and a fourdrinier wire section 3, said wire section comprising and endless mesh loop or "wire" 4, breast rool 5, other rolls and rollers 6 and dewatering elements 7. The rear or downstream end of the fourdrinier wire section 3, i.e. a so-called web forming section 8, comprises an upper or "on-top" unit 9 above the web and a dewatering unit 30 below the fourdrinier wire or lower wire 3.

In the arrangement as shown in FIG. 2, the dewatering unit 30 of the web-forming section of the paper machine comprises two covers 34 and 35 formed by a row of rod-like elements 32 and 33 extending transversely of the wires, said covers being united by a joint 31. The covers 34 and 35 are supported on beams 36, said beams extending transversely with respect to the direction of extension of the machine and being attached to the machine frame through pressure-medium (compressed air, hydraulic fluid) filled expansible, flexible vessel means of hose-like elements 37 so as to enable longitudinal adjustment of the angular position of the covers 34 and 35 with respect to the machine. In other words, the pressure exerted by the covers 34 and 35 on the bottom wire 4 can be changed. The adjustability is achieved by the pressure adjustment of each hose-like pressure element 37 being independent of other elements 37. Furthermore, to improve the adjustability of the dewatering unit 30, the covers 34 and 35 are displaceably engaged or supported by an adjustable means of element 38 adjustable longitudinally with respect to the direction of extension of the machine, said element being attached to the machine frame at one end and to the cover 34 at its other end. Any other elements for the longitudinal adjustment are unnecessary because hose-like elements 37 provide a sufficient adjusting allowance both horizontally and vertically. if required, distances between various covers may be adjusted.

The advantage of hose-like elements 37 is that, even though the beams 36, disposed transversely with regard to the manchine, become bent due to the load on them, the hose-like elements 37 may be adjusted to keep the covers 34 and 35 in plane-like disposition. The hoses 37 also allow the covers 34 and 35 to be lowered to such an extent that, for example, changing of the rod-like elements 32 or 33 is facilitated. Furthermore, it is possible to make the hose-like elements 37 from a plurality of parts in the longitundinal direction of the beam 36, i.e. divide the hoses into a plurality of shorter parts, each of which can be independently pressure-adjusted. For example, as illustrated in FIG. 3, hose 37 is divided into a plurality of compartments 37a-37d in its longitudinal direction transverse to the direction of paper extension. Each compartment 37a-37d is a separate inlet pressurized fluid line under control of a discrete independently adjustable control valve 40a-40d. In this way, it is easier to adapt the form of the lower dewatering unit to that of the upper one.

If necessary, the pass of covers 34 and 35 can be limited by means of special limit plates 39 that prevent moving of the hose-like pressure element 37 from the top of the beam 36 during adjustments. Transverse movement of the covers 34 and 35 can be limited in many ways. It is possible, for example, to arrange slide surfaces on the side of the covers, said surfaces only allowing movement in the longitudinal direction with respect to the machine. Even though the above description illustrates a two-part cover of the dewatering unit 30, said cover can alternatively be made from one part or be assembled of several parts by joining them together. Also, even though the above description discloses the covers being composed of rod-like dewatering elements, they can be of any appropriate type. Furthermore, supporting of the sides adjacent to the covers 34 and 35 can be made so as to affect or achieve the joint between the covers.

Although in FIG. 2, the adjustable means 38 is illustrated as a pressure-medium filled cylinder, it may alternatively be a manual screw adjuster or any other appropriate adjusting device.

As can be seen from the above, by a simple construction and reliable operation the invention makes up a unit or whole, meeting all the objects required of. The above only discloses one preferred embodiment of the invention and is not intended to limit the invention from what is claimed in the accompanying claims.