Paper machine headbox having convergent throat portion
United States Patent [1 1 Descary et all.  
 1 1 PAPER MACHINE HEADBOX HAVING CONVERGENT THROAT PORTION [75] Inventors: John Gilbert Descary, Lachine;  
 Ramamurthy Gopal Krishnan, Montreal, both of Quebec, Canada [73] Assignee: Dominion Engineering Works,  
 Limited, Quebec, Canada [22] Filed: May 21,1973  
 [21] Appl. No: 362,082  
 [30] Foreign Application Priority Data June 20, 1972 Canada 145134 [52] U.S. Cl. 162/336; 162/343; 162/344 [51] int. Cl. D21f 1/06 [58] Field of Search 162/336, 343, 344, 216  
 [56] References Cited UNITED STATES PATENTS 3,065,788 11/1962 Bcachler ct a1 162/336 3,298,905 l/l967 Spengos et a1 162/343 51 Apr. 15, 1975 Primary ExaminerSv Leon Bashore Assistant ExaminerRichard V. Fisher Attorney, Agent, or Firm-R. A. Eckersley [57] ABSTRACT A headbox is provided of slender profile having a shallow mixing chamber with a length to height ratio equal to or greater than 6. The headbox has a series of pipes connecting the header with the expansion chamber, and a preferred diffusion ratio in the range 1.9 to 3.5. A load bearing structure extending in the cross machine direction is located on one side of the headbox rectifier section, with load transfer partitions reaching across the depth of the rectifier section, to transfer pressure loading there-across so as to maintain the headbox in substantially undeformed condition during operation.  
 6 Claims, 4 Drawing Figures PILTENTEE 1 51975 3.878.039  
 &#39; SHEEH Z HIM/ll PAPER MACHINE HEADBOX HAVING CONVERGENT THROAT PORTION This invention is directed to a headbox for use with a web forming machine and to a method of fabricating a portion of the box.  
  Paper making and allied web forming machines utilize head boxes extending across the width of the machine in order to transform a flow of stock conveyed in a pipe by a fan pump into a uniform broad flat stream of controlled turbulence characteristic moving at a substantially uniform velocity for deposition onto a moving wire or between a pair of such wires.  
  Of the many forms of headbox previously developed. that shown in US. Pat. No. 3.298.905. June 13. 1967. resembles the arrangement of the present invention in certain aspects.  
  In view of the large width ofpaper machine for which such head boxes may be used. it is important to ensure dimensional stability of the box so as to provide consistently uniform flow characteristics for a reasonable range of box operation. One object of the present invention is to provide a form of head box suitable for web forming machines extending up to considerable widths.  
  A further object of the present invention is to provide controlled micro-turbulence in the issuing stock.  
  A further object ofthe present invention is to provide a head box of straightforward design suitable for low cost manufacture.  
  A further object is the provision of a head box providing satisfactory operation over a wide flow range and capable of operating with a number of different stock furnishes.  
  A further object of the present invention is to provide a head box possessing structural integrity and suited to the limited space available in twin wire forming machines.  
  A further object of this invention is the provision of a method of fabricating a slender approach section having great structural strength in a light structure. to provide predetermined flow characteristic at relatively low cost.  
  Thus. there is provided in a head box for supplying a stock suspension to a machine slice of a web forming machine at substantially uniform velocity profile. a distributor section having an elongated tapered header extending in a cross-machine direction to receive stock from a stock supply. a mixing chamber of shallow depth A extending across the machine and connected to the header by a plurality of substantially uniformly spaced flow connections. the flow connections entering one face of the mixing chamber adjacent the chamber back wall to produce impingement of stock against the opposing chamber face spaced the distance A therefrom. before flowing to an exit throat of depth E&#34; spaced a distance L&#39; from the chamber back wall. the ratio of mixing chamber length to height. L/A being equal to or greater than 6.  
  The invention further provides a head box wherein the ratio of the mixing chamber depth to the throat depth A/E. is greater than 3.  
  There is further provided a head box wherein the flow connections comprise a plurality of connection pipes having an internal diameter D spaced from each other at centre distances C&#34; along the header. the diffusion ratio N&#39; of the stock flow entering the 2 mixing chamber being represented by the expression A X C/ /4 11&#39; D where N has a value in the range L9 to 3.5.  
  Certain advantages of the present invention over head boxes of similar general arrangement have been found in tests to be the achievement of uniform flow distribution in the cross-machine direction. the achievement of flow stability both in the direction of flow and in the cross-machine direction; the achievement of consistent mixing with avoidance of flocking: operation of the mixing chamber in a sufficiently stable manner to permit the use therein of pressure sensors for the determination of flow rates.  
  Certain embodiments of the present invention are described. reference being made to the accompanying drawing wherein.  
  FIG. 1 is a view from the back of the machine showing the flow header connection;  
  FIG. 2 is a section of the head box in conjunction with a portion of a twin-wire web forming machine. looking in the cross-machine direction;  
  FIG. 3 is a similar view of an alternative arrangement of the head box used in conjunction with a single wire wet end; and  
 FIG. 4 is a section at 44 of FIG. 2.  
  Referring first to FIG. I, the headbox arrangement comprises a tapered header 12 extending in the cross-machine direction having a plurality of connection pipes 14 extending upwardly in the present instance to the mixing chamber I6.  
  The mixing chamber 16 has a back wall 18. a chantber top face 20 and a bottom face 22 spaced therefrom. Reference characters relating to relative dimension proportions will be found in FIGS. 1 and 3.  
  The depth of the mixing chamber A. across which the inflowing stock from the connection pipes 14 must flow is related to the length of the mixing chamber L. being in the ratio of 6:1 or greater.  
  The exit from the mixing chamber 16 is by way of a restriction throat 24 having a depth E which is less than one-third of the depth A of the chamber. The convergent portion 26 of the chamber top face 20 which defines the throat 24 is inclined at an angle 6 preferably between and 55. A value of inclination of about has been found particularly effective.  
  The stock flow path diverges from the throat 24 into diffuser 30., which joins an approach section 40 having a constant depth F and a plurality of transversely extending divider walls 42 joining the top plate 44 to the bottom plate 46 thereof in load transfer relation. The diffusion in the approach section 40 is at a slow rate. the diffuser angle being of the order of 7 or less.  
  The stiffness of the approach or transfer section 40 is provided by an underlying beam structure 50 of considerable depth and great stiffness considered in the cross-machine direction.  
  The beam structure 50 comprises a bottom plate 62 having a plurality of web plates 64, 66, 68. A front extension 69 carries a lower slice plate 54. while a rear extension 70 carries the inlet header 12. Adjustable front mounts 72 and rear mounts 74 permit the inclination of the head box to be varied as required.  
  The rigidity of the beam structure 50 is transferred across the approach section 40 by the welded plates 43 that comprise a part of the divider walls 42, see FIG. 4. so as to maintain the section dimensionally stable through the full range of working loads.  
  With reference to the structure illustrated in FIG. 4. the approach section 40 has a plurality of steel divider plates 43 extending vertically between the upper and lower faces 44. 46 of the approach section. to provide an adjoining series of rectangular flow paths of great rigidity. The walls 48 of these flow paths are formed by cast epoxy. having suitable streamline fairings at the upstream and at the downstream ends. to promote smooth flow together with the avoidance of hang-up of the stock at the ends of the dividers 42. lt is contemplated that in addition to providing a stiff structure of substantially non-varying cross-section. the epoxy liners 48 generate a controlled degree of microturbulence due to the shearing action of the stock flowing therepast. The depth F of approach section 40 lies between the values A and E of mixing chamber 16.  
  One of the structure side walls 39 is shown. serving to enclose the approach section.  
  The approach section 40 is provided with a superstructure comprising a flange plate 43 and end plates 45, 47 forming with the upper face 44 a box structure to provide additional stiffness to the approach section.  
  In fabricating the approach section 40. the plate members of the structure are assembled and welded together. including the associated portions 64, 66 of the beam structure. Suitable cores (not shown) are then positioned in spaced relation between adjacent ones of the steel divider plates 43. and a metal filled epoxy resin is poured around the cores. to completely line the flow passages of the section 40. Adoption of this method of fabrication permits the use of a standard section structure. with control over the passage size in accordance with the size of core members used.  
  In the arrangements illustrated in FlGS. 2 and 3, the length G (see FIG. 3) of the flow channel is such that the turbulence imparted to the stock by the divider walls 42 of the approach section 40 can decay at least partially before the lips of the slice are reached.  
  In one arrangement embodying an approach section 40. in which the approach section had an internal height of 1.75 inches. the channel length G was made about 25 inches long. in order to provide a desired extent of turbulence decay. ln instances where an approach section is dispensed with, the dimension G may be correspondingly diminished.  
  Referring to the embodiment illustrated in FIG. 3. this shows a head box according to the present invention used in conjunction with a non-submerged cylinder former 80 suitable for making multi-ply board. A similar configuration might also be used in a tissue former. the embodiment illustrated being shown as having a multi-vacuum forming roll.  
  The slice 50 comprises an upper plate 52 and a lower plate 54. the plates 52. 54 being attached to the approach section 40 to maintain constant the inlet spacing therebetween for all operational flow conditions. The slice 50 has external stiffening members 56. 58 and an adjustable lip 60 to permit control over slice opening. by overall slice adjustment, and by localized control of the slice opening. as is well known in the art. Thus the slice upper wall 52 can be pivotted about the point of attachment 53, by actuation of actuators 55.  
  What l claim as new and desired to secure by Letters Patent of the United States is:  
  1. In a headbox for supplying a stock suspension to a machine slice of a web forming machine at substantially uniform velocity profile. a distributor section having an elongated tapered header extending in a cross machine direction to receive stock from a stock supply. a mixing chamber of substantially uniform shallow depth A throughout the length thereof. extending across the machine and connected to the header by a plurality of substantially uniformly spaced flow connection pipes of small diameter directly entering one face of the mixing chamber adjacent the chamber back wall to provide in operation a zone of sudden flow expansion with succeeding impingement of stock against the opposing chamber face spaced said distance A therefrom. with consequent increase in macro turbulence. said mixing chamber faces converging to a throat portion of depth E spaced a distance L from the chamber back wall and diverging in a downstream direction at an angle of divergence of not more than 7 to provide diffusion of the suspension. the ratio of mixing chamber length to depth, L/A, being equal to or greater than 6 and the ratio of mixing chamber depth to throat depth. A/E. being greater than 3.  
  2. In a headbox for supplying a stock suspension to a machine slice of a web forming machine at substantially uniform velocity profile. a distributor section having an elongated tapered header extending in a cross machine direction to receive stock from a stock supply. a mixing chamber of substantially uniform shallow depth A throughout the length thereof. extending across the machine and connected to the header by a plurality of flow connection pipes of diameter D sub stantially uniformly spaced at centre distances C directly entering one face of the mixing chamber adjacent the chamber back wall to provide in operation a zone of sudden flow expansion with succeeding impingement of stock against the opposing chamber face spaced said distance A therefrom, with consequent increase in macro turbulence before flowing to a convergent exit throat portion of depth E spaced a distance L from the chamber back wall havig a portion of a said chamber face inclined convergingly in the direction of flow towards the chamber other face at an angle in the range 35 to 55. the ratio of mixing chamber length to depth. L/A. being equal to or greater than 6, the ratio of mixing chamber depth to throat depth, A/E being greater than 3, and the diffusion ratio N of stock flow entering the mixing chamber, where N =A C/ /41rD is from about 1.9 to 3.5.  
 3. The head box as claimed in claim 2 having transfer.  
 passage means positioned in flow rectifying relation between said exit throat and an outlet slice, having a load.  
 bearing structural means located external thereto to substantially resist bending forces in the cross-machine direction. and maintain an adjacent wall of the transfer passage means substantiallly undeformed in operation. and a plurality of load transfer partition means in spaced relation across the width of the headbox. extending longitudinally in the direction of stock flow and securing said adjacent wall to the passage wall opposite thereto in load transfer relation. to maintain the transfer passage means substantially undeformed during operation under hydraulic pressure forces of stock flowing therethrough.  
  4. The headbox as claimed in claim 3 having a pair of lips defining said slice attached to said rectifier means. in load transfer relation therewith. to maintain the inlet flow area to the slice substantially constant for all working conditions of the box.  
  6. The headbox as claimed in claim 5, including a second slice adjustment means including a lip extension portion slid-ably attached to a said slice lip and slidably movable in closing relation.