Papermaking apparatus with variable pulse turbulation blades

#The present invention relates generally to papermaking apparatus having variable, or adjustable, dewatering elements, and more particularly to variable turbulation blades.

#In the manufacture of paper, paper stock is carried by a conveyor over dewatering elements. Some of the dewatering elements have a geometry or position which produces turbulence in the paper stock to produce selected action in the paper stock. In the past, such turbulence has been produced by providing various foils or turbo blades in selected positions over which the conveyor and the paper stock move. The angular positioning of the foils, or turbo blades is selected to produce the turbulation action desired.

#Prior turbo blades have been provided which have a fixed in-going angle between a flat leading portion of the blade and the conveyor to obtain a stock pulse of selected magnitude. However, such prior turbo blades generally have not been coupled with adjustment mechanism which allows the in-going angle for the blade to be varied, or adjusted, while the blade is adjacent the conveyor.

#FIG. 1 is a schematic view of a papermaking machine showing the location of variable dewatering devices and paper sheet characteristic sensors which are operated by a control system;

#FIG. 2 is a block diagram of the control system;

#FIGS. 3A and 3B show the flow chart of a computer program which can be employed to operate a computer control system of FIG. 2;

#As shown in FIG. 1, a papermaking machine includes a forming section 10 where the paper sheet is formed from a liquid slurry of paper pulp and water known as paper stock, a press section 12 where additional water is removed from the paper sheet by pressing it against a felt sheet which acts as a blotter to absorb moisture, and a dryer section 14 where the paper sheet is dried and finished. In addition, the forming section 10 may be provided with a top surface finishing section 16 where a special finish is provided on the top surface of the paper sheet. The forming section 10 includes a porous conveyor belt 18 in the form of a woven screen or “wire” which may be made of stainless steel, bronze, or other suitable metal, or of a woven fabric of synthetic plastic such as polyester. A liquid slurry of paper pulp and water referred to as “paper stock” is supplied from the output of a head box 20 onto the upper surface of the conveyor wire 18 driven over a breast roll 21 which transports it across the surface of a forming board 22 and a dewatering table 23. The paper sheet is formed on such forming board and dewatering table in a conventional manner and such paper sheet is then conveyed across the surface of a plurality of gravity boxes 24 having variable angle foils 26 provided on their upper surface. In addition, the gravity boxes of dewatering table 23 may be provided with variable turbulation blades 28, such as variable height turbo blades, which provide turbulence to the paper stock during formation of the paper sheet and are adjusted in height relative to the bottom surface of the conveyor wire. Both the variable angle foils 26 and the variable height blades 28 are dewatering devices which remove water from the paper sheet as it is formed and conveyed across these elements. The variable angle foils 26 each engage the bottom surface of the conveyor at a small foil angle preferably in the range of about zero to four degrees, which produces a vacuum below the conveyor belt that sucks water from the paper sheet. Adjustment of this foil angle controls the water removal rate of the foil and such removed water then drains through the gravity boxes 24 and is disposed of. The variable height blade 28 is spaced from blades on either side of such blade which are at different heights relative to the conveyor 18 in order to provide an undulation and turbulence of the paper stock to form the paper sheet and to assist in removing water therefrom.

#Next the paper sheet passes from the variable angle foils 26 across the upper surface of suction boxes 30 which have fixed blades that engage the conveyor wire and are spaced apart by slots to allow water to drain from the paper sheet as it is conveyed across the suction boxes 30. The vacuum of the suction boxes 30 may be changed to vary their water removal rate by adjusting vacuum control valves 32 on such suction boxes. The conveyor transports the paper sheet over a final suction box 34 and around a suction couch roll 36 at the output of conveyor 18 from which the paper sheet 38 is transferred into the press section 12.

#A conveyor felt 40 of an endless sheet of water absorbing blotter type woven felt material engages the upper surface of the paper sheet 38. The paper sheet is pressed between conveyor felt 40 and a press conveyor wire 42 of the same type material as conveyor wire 18, when the paper passes over a press roll 44. The water absorbed in the felt sheet 40 is removed by a Uhle tube vacuum box 46 which includes a pair of spaced blade elements that engage the felt and are separated by a variable slot which is adjusted by movement of one of the blades for controlling the water removal rate of such Uhle box. The paper sheet 38 is transferred from the press section 12 into the dryer section 14 where it is conveyed about dryer rolls 48 which are heated internally with steam to dry the paper sheet by evaporation due to thermal contact with such rolls. As a result, the dried paper sheet 38 is transmitted from the output of the dryer section across a transparency sensor 50 which includes a laser light source and photo detector on opposite sides of the sheet for testing the light transparency characteristic of the paper sheet. It should be noted that the transparency sensor 50 may be located alternatively at the output of the press section 12 at position 50′ instead of at the output of the dryer section.