Headbox

Abstract

 The head box of paper making machine has a tube bank comprising a flow straightener module (1) and a module of diffuser nozzle (2). The box is equipped with a system for diluting of supplied paper stock inside the outlet zone W from flow straightener (1) into a module of diffuser nozzle (2).

Description

[0001] The invention relates to a head box, particularly used in a paperindustry.

[0002] The raw material for the paper manufacturing ― most frequently it is a water solution of fiber suspension ― is supplied through a header into a head box mainly from a side. Then, a suspension is distributed onto a forming section of a paper machine by passing through elements equalizing a suspension flow and an outlet gap of a box.

[0003] It is essential to distribute a fiber suspension onto a wire of a paper machine as evenly as possible through an entire width of an outflow and with an equal velocity close to a paper machine velocity. A feed accuracy of a paper machine from a head box is a significant factor for a range of a basis weight tolerance of a produced paper both in the machine and cross direction of a paper web.

[0004] To get a product with as small as possible basis weight spread a feeding header is convergent in shape. Supplied paper stock changes the flow direction, flows through a stabilizing system said tube bank into an outlet chamber and from that chamber is distributed through the outlet gap onto the wire of a paper machine.

[0005] In practice a stock flow control causes a lot of difficulties. A change of outflow head is one of a method to control the flow from the headbox. The another method is zone dilution of a fibrous stock by an introducing of diluting medium into the high basis weight zones.

[0006] There is a known solution as described in an United States patent No 5196091 where the diluting medium is introduced into the individual zones of the supplying header in a direction reverse to the stock flow through the tube bank. The aforesaid method can cause turbulences inside the supplying header and disturbances of a stock flow into the tube unit of the headbox.

[0007] On the other hand the tube bank is a monolith and it does not allow to make a significant rebuilt of the head box. In this case if there is necessary to modify the paper machine because of change of its capacity or paper grade the whole head box must be replaced with new one.

[0008] To overcome the mentioned difficulties the new solution of the head box is presented. The new type of the head box comprises a tube bank of at least two modules: a flow straightener and a module of diffuser nozzle. In the basic configuration the module of flow straightener is a solid structure in the shape of a beam situated transversely to a main axis of a paper machine and the direction of paper web movement. The tubes of flow straightener are located inside the module and their direction correspond with the axis of the paper machine. The tubes of the straightener could be favourably round in shape along their entire length.

[0009] The module of flow straightener adjoins the module of diffuser nozzle which is also in shape of the cross beam containing inside the tubes of diffuser. These tubes are favourably round in shape from the stock inlet side and change smoothly toward the outlet to flattened oval resembling shape.

[0010] The diameter of diffuse tubes is bigger than the diameter of flow straightener.

[0011] The aforesaid described module arrangement of tube bank enables to introduce the diluting medium - favourably wire pit water or clarified water - into the adjoining zone of flow straightener and diffuser nozzle module. To accomplish it the holes supplying the diluting medium could be made in the plate located at the outlet of stock from the flow straightener to the diffuser nozzle module. The holes are favourably made in the center lines of straightener tubes rows and they are perpendicular to these tubes; moreover the end parts of the holes where the tubes of flow straightener come through are selectively enlarged so that the diluting medium together with the paper stock fed from the flow straightener could gain access into the appropriate tube of the diffuser nozzle module.

[0012] The next solution is a system of additional tubes connected to the same plate of the flow straightener. Appropriately selected holes in the plate are counterbored together with some holes of the tubes of flow straightener and as described previously it will allow the flow of stock together with the diluting medium into the appropriate tube of the diffuser nozzle module.

[0013] In both solutions the diluting medium is supplied into the that places of the head box where the diameter of the flow is enlarged substantially and due to that, the mass flow is moderated and the effect of pressure rise due to introducing of the diluting medium is reduced and the mass flow through the headbox is equalized.

[0014] The subject of the invention is presented in the drawings where Fig.1 presents the side view of the head box, Fig.2 presents the module of flow straightener with the holes pattern in the plate where diluting medium is introduced. It is the cross section and side view. Fig.3 presents the axial section of the connected modules of the tube bank and also detail X showing the junction point of a straightener tube and holes of diluting medium (example I). Fig.4 presents the axial section of the connected modules as an arrangement with the additional tubes supplying diluting medium and detail X showing the connections of stock outlets and diluting medium (example II). Fig.5 presents the main view and the side views of the tube of the diffuser nozzle.

[0015] The head box according to the invention has a tube bank comprising a flow straightener 1 and module of diffuser nozzle 2. The straightener is fed at least with one supplying header KZ. The box is equipped with set of holes 4 in a plate 3 to introduce the diluting medium into the zone W. Alternatively the box has additional set of tubes 6 and plate 3 has counterbores 7 connecting outlets of tubes of flow straightener and tubes 6 of diluting system.

[0016] An object of the invention is to provide a simplified modification of head boxes due to easy replacement of flow straightener with another one.

[0017] It allows to use the straighteners fed with two or more headers KZ and also to change the spacing of diluting holes. Whereas the application of paper stock diluting system in zone W as described in example I, when diluting medium is introduced near the walls of the hole significantly reduces the disadvantageous effect of paper fibers deposition inside the tubes of diffuser nozzle module.

Claims

1. A head box for for supplying of pulped paper stock onto a forming wire section of a paper making machine equipped with at least one supply header, tube bank and outlet nozzle and also with a system of basis weight control by zone dilution of supplied stock characterized in that the tube bank is modular in form and comprises a module of flow straightener (1) and module of diffuser nozzle (2) whereas a unit of introducing of medium diluting a paper stock is realized in an outlet zone W of paper stock from a module of flow straightener (1) into a module of diffuser nozzle (2).

2. A box according to claim 1, characterized in that the carrying plate (3) of flow straightener located at a side of paper stock outlet toward a module of diffuser nozzle (2) comprises holes (4) for introducing of diluting medium, made transversely to paper stock flow direction and that the plate comprises selectively chosen and enlarged holes (5) in a carrying plate (3) for some tubes of a flow straightener,

3. A box according to claim 1, characterized in that it comprises additional sets of tubes (6) of diluting medium connected to the carrying plate (3) and that it comprises zonal counterbores of holes (7) in the carrying plate (3) common for the outlets of straightener tubes and tubes of diluting medium (6).

4. A box according to claim 1, characterized in that the single tube of diffuser nozzle (8) is round in shape from the inlet side whereas from the outlet side the shape is flattened and resembling oval but transition from round to flattened part is realized smoothly without offsets and folds.

Drawing