METHOD AND DEVICE ACHIEVING A FLOW OF STOCK IN A FORMING TANK

Abstract: The invention relates to a method and an arrangement for producing a flow of stock in a moulding tank (1). In this, stock is pumped into the moulding tank (1) at the bottom (1a) and allowed to flow up over the brim (1b) thereof. During its rise in the moulding tank (1), the flow of stock pumped in is distributed by at least one grating placed essentially horizontally and provided with flow openings. An arrangement for performing the said method comprises a line (2a, 2b), connected to the moulding tank (1) and a machine vat for ready prepared stock, for delivering fresh stock to the moulding tank (1) by means of a pump (5) connecting with the line (2a, 2b). The line (2b) opens out in an area close to the bottom (1a) of the moulding tank (1) in such a way that an upwardly directed flow of stock is obtained. The pump (5) is adapted to deliver excess stock so that excess stock is allowed to flow over the brim (1b) of the moulding tank (1). At least one essentially horizontal grating (6, 7) provided with flow openings is arranged in the moulding tank (1).

Description: Method and device achieveing a flow of stock in a forming tank The present invention relates to a method of producing a flow of stock in a moulding tank. The invention also relates to an arrangement in a moulding tank for producing a flow of stock therein, comprising a line, connected to the moulding tank and a machine vat for ready prepared stock, for delivering a fresh stock to the moulding tank by means of a pump which connects with the line Moulding tanks of this type are used to produce a fibre product, for example an egg carton or some other packaging product, from the fibres in the stock by means of a male tool with permeable walls and with the aid of a vacuum v. hich sucks the water out of the stock so that the fibres remain on the outside of the tool In order that the thickness of the fibre layer on the tool and hence the thickness of the product will be as uniform as possible it is essential that the fibre concentration of the flow of stock be as even as possible, at least in the upper areas of the tank. In a known moulding tank the flow of stock is directed essentially horizontally Two serious disadvantages arise as a consequence of this direction of flow, on the one hand most of the fibres in the fibre product become oriented in the direction of flow of the stock, which gives the product anisotropic characteristics, on the other the thickness of the fibre layer tends to become greatest where the flow ot stock first encounters the tool Anisotropy in the product means, for example, that it tends to become warped as the product dries out. The underlying reasons loi this aie well known to the person skilled in the art. The object of the present invention is to achieve a method of the said type which eliminates the above-mentioned disadvantages This is achieved according to the invention in that stock is pumped into the bottom of the moulding tank and allowed to flow up over its brim and that the flow of stock pumped in is distributed during its rise in the moulding tank by at least one grating, provided with flow openings and positioned essentially horizontally Accordmg to a special characteristic of the method according to the invention, a simplified handling of the ovei llow quantity of stock is achieved in that the overflowed stock is collected and together with fresh stock is pumped back into the moulding tank An arrangement of the type described in the preamble, by means of which the method according to the invention can be performed, is characteπsed in that the line opens in an area close to the bottom of the moulding tank in such a way that an upwardly directed flow of stock is obtained, that the pump is adapted to deliver excess stock so that excess stock can flow over the brim of the moulding tank and that at least one essentially horizontal grating, provided with flow openings, is arranged in the moulding tank According to a special characteristic of the invention the arrangement comprises a collecting tank for the excess stock and the pump is adapted to pump the excess stock from the collecting tank together with the fresh stock to the moulding tank, thereby achieving especially advantageous flow paths for the stock In order to obtain an optimum dispersal of fibres in the stock the arrangement, as will be apparent from another special characteristic of the invention, comprises two gratings positioned approximately symmetrically in relation to the half-height of the moulding tank, the lower grating having larger through-flow openings than the upper grating but the total through-flow area of both gratings being approximately equal The invention will be further explained below with reference to the enclosed drawing in which Fig 1 shows an embodiment of an arrangement according to the invention in plan view from the side and Fig 2 the arrangement in a plan view from above In the drawing 1 denotes a moulding tank foi stock intended to be used as descnbed in the preamble The tank 1 is connected by way of a line 2a to a machine vat, not shown in the drawing, for ready prepared stock In the embodiment shown in the drawing the tank 1 is surrounded by a collecting tank 3 A pump 5, driven by an electric motor 4 and adapted to pump excess stock to the moulding tank, is connected into the line 2a so that excess stock can flow over the brim of the moulding tank and down into the collecting tank 3 A line 2b connects the collecting tank 3 to the moulding tank by way of the pump 5 The mouth 2b 1 oi the line 2b in the tank is situated in an area close to the bottom l a of the tank, one side l c of the said tank being specifically penetrated at a point situated approximately midway between the edges of this side By means of this location of the mouth 2b 1 an upwardly directed flow of stock is obtained in the moulding tank 1 The bottom la of the moulding tank is inclined so that the tank can be drained by way of a line 2c It is known that fibres tend to flocculate In oidcr to prevent the occurrence of such flocks two horizontal gratings 6,7 are arranged in the moulding tank 1 The said gratings are preferably made of perforated plate, the lower grating 7 having a larger hole diameter than the uppei grating 6, but the perforation being executed so that the total through-flow areas of the two gratings are essentially equal In operation the arrangement according to the invention functions as follows Fresh stock is fed into the moulding tank 1 from the machine vat not shown in the drawing, by way of the line 2a Fresh stock, together with stock which has flowed over the brim lb, is pumped by means of the pump 5 by way of line 2b to the moulding tank 1, specifically to the bottom la thereof In this way an upwardly directed flow of stock is achieved which is homogenised by the gratings 6,7 The fact that the flow is directed upwards is important in achieving a fibre layer of even thickness on the male tool described in the preamble That is to say the fibres in the upwardly directed flow are oriented in random directions at least at the instant the fibres reach the male tool, as a result of which the anisotropy in the product referred to earlier is virtually zero It will be evident to the person skilled in the art that means of control are required for controlling valves which are not shown or described, so that a suitable flow is obtained with respect to the stock level sensed by means of level sensors It is further obvious that the embodiment of the arrangement according to the invention can be modified in many ways within the framework of the invention

Claims: Claims Method of producing a flow of stock in a moulding tank ( 1 ), characterised in that stock is pumped into the moulding tank ( 1) at the bottom ( la) and allowed to flow upward over the brim ( lb) thereof, and that during its rise in the moulding tank ( 1 ) the flow of stock pumped in is distributed by at least one grating, placed essentially horizontally and provided with flow openings. Method according to claim 1 , characteπsed in that stock which has overflowed is collected and together with fresh stock is pumped back into the moulding tank. 3 Arrangement in a moulding tank in order to produce a flow of stock therein, comprising a line (2a, 2b),connected to the moulding tank ( 1 ) and a machine vat for ready prepared stock, for delivering fresh stock to the moulding tank ( 1 ) by means of a pump (5) connecting with the line (2a,2b), characterised in that the line (2a,2b) opens out in an area close to the bottom ( 1 a) of the moulding tank ( 1 ) in such a way that an upwardly directed flow of stock is obtained, that the pump (5) is adapted to deliver excess stock so that excess stock is allowed to flow over the brim ( lb) of the moulding tank ( 1 ), and that at least one essentially horizontal grating (6,7) provided with flow openings is arranged in the moulding tank (1) Arrangement according to claim 3, characterised in that the ai rangement comprises a collecting tank (3) for the excess stock and that the pump (5) is adapted to pump the excess stock from the collecting tank (3) together with the fresh stock to the moulding tank ( 1 ) Arrangement according to any of claims 3 or 4, characterised in that the arrangement comprises two giatings (6,7), placed approximately symmetrically in relation to the half-height of the moulding tank ( 1 ), the lower grating (7) having larger through-flow openings than the upper grating (6) but the total through-flow areas of the two gratings being appioximately equal

Inventors: LARSSON PETER, LARSSON, PETER
Applicants: CELTEC DEV AB, LARSSON PETER, CELTEC DEVELOPMENT AB, LARSSON, PETER
Application year: 1996
Main classification: D21J7
IPC codes: D21J7