US1965579A - Method of and apparatus for preparing pulp stock for delivery to a paper-making machine - Google Patents

Description

July 10, 1934-. P. DENNETT 1,965,579

METHOD OF AND APPARATUS FOR PREPARING PULP STOCK FOR DELIVERY TO A PAPER MAKING MACHINE Filed Aug. 19, 1932 2 Sheets-Sheet 1 July 10, 1934. P. BENNETT A 1,965,579

METHOD OF AND APPARATUS FOR PREPARING PULP STOCK FOR DELIVERY TO A PAPER MAKING MACHINE Filed Aug. 19, 1952 2 Shets-Sheet 2 Patented July 10, 1934 UNITED STATES lVIETHOD OF- AND APPARATUS FOR PRE- PARING PULP STOCK FOR DELIVERY TO A PAPER-MAKING MACHINE Phillips Dennett, Medfield, Mass., assignor to Bird Machine 00., South Walpole, Mass" a corporation of Massachusetts Application August 19,

4 Claims.

This invention relates to a method of and apparatus for preparing an aqueous suspension of pulp stock for use on a Fourdrinier paper-making machine and for delivering the stream of this 5 prepared stock on to such a machine in a condition which will be substantially uniform both as to the homogeneous nature of the mixture of water and fibre and most especially as to the hydraulic smoothness in the flow of the prepared stock both in the direction of the travel of the paper-making wire and across its width. A particular purpose is to eliminate the currents and eddies in the stream of pulp stock asit is ordinarily delivered on to a paper-machine wire by known methods and by accomplishing this to improve what is known in paper-making language as the formation of the paper, at any speed, and more particularly to enable paper of any given grade to be made with satisfactory formation at higher speeds than are now possible. As a practical matter it is exceedingly difficult to obtain a high degree of uniformity in the formation of a pulp web because of the constant tendency on the part of pulp fibres which are in suspension to collect in bunches instead of remaining uniformly distributed throughout the aqueous vehicle, due particularly to the currents and eddies mentioned above which are caused or not controlled by previously known methods of delivering the stream of pulp on to the wire. If ideal conditions for the furnish could be realized the pulp would be put-on to thewire with all individual fibres uniformly distributed through the water, every square inch of the-mixture at the 3 thickness required by the paper-making machine containing the same number of fibres and blending perfectly with each other and with no currents or eddies across the width of the paper machine, the stream of stock simply moving as a smooth-flowing, composite mass like a liquid ribbon of absolutely uniform texture, -every portion having movement in only one direction, forward, at the required and the same speed. It is the object of this invention to approach this ideal as closely as possible, particularly in supplying stock to a modern high-speed paper-making machine on which wide sheets of paper are made.

One obstacle to the attainment of the ideal condition of stock described is the presence of impurities therein, that is, things other than individual fibres, like foreign matter commonly called dirt or unreduced portions of the raw material from which the fibres are prepared or bunches of the fibres themselves which are called lumps or knots. In the production of good paper 1932, Serial No. 629,469

purity of stock is essential and a further object of this invention is to improve the method of removing impurities from the pulp stock, particularly as regards the use of such well known medium as paper-machine screens or centrifuges. In order to make what is called a cleansheet of paper of good appearance and also to permit continuous operation of the modern paper machines at the desired speed it is necessary to remove impurities efiiciently from relatively large volumes of stock. The common methods are to pass them through plates containing fine slots assembled on units of machinery called screens or through centrifugal machines or a combination of both. When screens are used, which is almost universal practice, the slots must be very fine in order to retain the impurities which are small in size. For modern requirements of large capacity paper machines operating at high speed this results in the necessity of supplying a number of screens for most paper machines and the small size of the slot necessary involves this further difficulty; that the fibres can in many cases be passed through only with serious difiiculty and often with considerable loss of efficiency as far as the screens are concerned because the mixture required by the paper machine, which obviously must determine, the consistency of the stock supplied thereto, is too thick for the screens.

The screens or centrifuges, while performing their functions of removing impurities, except for the limitations imposed by a consistency which is too thick, as mentioned above, have in part caused, or at least have not prevented, the existence of eddies and currents which interfere with smooth formation when the stock is put on to the paper-making wire, this because the usual installation consists of a number of units individually discharging ordinarily at different pressures with the result that the stock in the spout or pipe which conveys them to the paper. machine is never quite homogenously mixed or made uniform as regards the relation of one portion to another. It is therefore the first part of this invention to collect the stock from the various 100 purifying units, whether screens or centrifuges, and pass it through a single evening device which will make the stock homogeneous as to mixture and will deliver it on to the paper-making wire according to the ideal condition expressed above. 105 According to this invention, the combination of apparatus for preparing pulp stock for delivery to a paper-making machine may include a thickening apparatus which can be placed between the screening and the evening units so that, as will 110 be described hereafter, the screening of the stock may be handled at that consistency which will produce the maximum efficiency in screening, after which as much water is removed from the stock before it goes to the paper machine as will give it the proper consistency for the paper-machine wire, all without affecting the homogeneous nature of the mixture and the proper delivery of stock on the wire for accomplishing formation in in an ideal way.

In paper-making practice in the past, cylindrical screens of the outflow type have been used for purifying stock for slow-speed paper-making machines. To such a machine the stock was supplied in a slow stream which involved no problem ofturbulence or eddies. The stock stream was introduced into the interior of a cylinder screen arranged for convenience transversely with reference to the paper-making machine and adjacent to the head box thereof. The slots in the cylinder were necessarily narrow enough to retain the impurities present in the stock, and owing to the small requirements of a slow-speed paper-making machine an outflow screen could supply its needs. With the development of highspeed paper machines, the use of outflow screens had to be abandoned owing to their small capacity in proportion to the floor space they occupied, batteries of screens of the more efficient inflow type or of centrifuges taking their place, the inflow screens being for convenience arranged with their axes in the direction of the paper machine.

According to the present invention, apparatus is provided for supplying an adequate stream of purified pulp stock to satisfy the demands of a high-speed paper-making machine of any width, the stock being delivered in a stream which is substantially free from eddies and in which the fibres are distributed with a high degree of uniformity. To this end, I provide a suitable number of individual purifying devices for removing objectionable particles from the stock. These devicesmay be rotary screens, centrifuges, or any other suitable apparatus. The streams of pulp stock discharged from these purifying devices are collected' preferably into a single stream which is subsequently distributed and delivered to the paper-making machine through a distributing cylinder. Since purifying devices often operate most efficiently on pulp stock having a thirmer consistency than that which is desired for the paper-making machine, I may employ between the purifying devices and the distributing device a means for partially dewatering the stock so as to thicken the purified stock to a suitable consistency for the paper-making machine.

For a more complete understanding of the invention, reference may be had to the description thereof which follows, and to the illustration of embodiments thereof on the drawings, of which,-

Figure 1 is a plan view of apparatus embodying the invention.

Figure 2 is a sectional view of the same on the line 22 of Figure 1.

Figure 3 is a plan view of another embodiment of the invention.

Figure 4 illustrates mechanism for vibrating the stock-evening cylinder.

As shown in Figures 1 and 2, the apparatus may include a trough 10 to which dilute stock is supplied from the stuff chest or any other suitable source. The stock from the trough 10 flows through pipes 11 into a series of vats 12 in which are rotatably mounted cylindrical screens 13. These screens are preferably made of sheet metal having narrow slots therethrough, usually of the order of .010 to .018 inch in width. This size permits the passage of fine stock through the screen but retains coarser particles. 'Screens of this type are known as inward flow screens (as the stock flows through the screen from outside of the cylinder into the interior of the cylinder) and are well known in the art. These screens are preferably rotated by any suitable means (not shown), and each discharges through an open end 14 into a suitable trough 15, which may be provided with a baflie 16 therein. As shown the stock entering the trough 15 flows thence into a receptacle 20 in which is rotatably mounted a transverse foraminous cylinder 21. This cylinder is covered with wire screen or the like so as to permit a portion of the water in the stock stream to filter into the interior of the cylinder, keeping the pulp on the outside thereof. The cylinder may be driven by a suitable motor 22 through reduction gearing 23. By such means the stock may be thickened to a consistency suitable for delivery to the paper-making machine. As the stock flows past the submerged surface portion of the thickening cylinder, the water which filters into the cylinder will come chiefly from the stock nearest to the cylinder so that this stratum of stock in the stream leaving the receptacle 20 is of thicker-consistency than that stock which did not pass so close to the cylinder. Hence the stock leaving the receptacle 20 tends to be of uneven consistency. In order to separate thoroughly the fibres in the thickened furnish, to restore a substantially homogeneous consistency, and to deliver the pulp stock in a stream substantially free from eddies and uniform in consistency, the stock from the receptacle 20 is collected in a trough 30 from which it flows through a delivery pipe or pipes 31 into one or both ends of a rotatable distributing cylinder 35. This cylinder is arranged to rotate in a vat 36 on an axis which is transverse to the paper-making machine, the cylinder itself being substantially as long as the paper-making machine is wide. A suitable motor or driving belt 37 may be provided to engage a reduced end projection 38 of the cylinder for the rotation thereof.

Means may be provided for vibrating or shaking the cylinder 35, either by mechanical or electrical means. As shown in Figures 1, 3 and 4, the reduced ends of the cylinder, which serve as bearings, are supported by arms 45 hinged to the main frame at one end as at 46. The opposite end 48 of each arm 45 rests on a polygonal cam 50, these cams being mounted on a shaft 51. Any desired means, such as a pulley 52 and belt 53, may be employed to rotate the shaft 51. The cylinder 35 may be made with a foraminous sheet metal surface having apertures therein larger than the apertures in the screen 13 so as to permit the free passage of pulp therethrough. The rotation and vibration of this cylinder tend to agitate the pulp stock therein so that it is uniform in consistency and the individual fibres are separated. A spray 55 may be mounted above the cylinder 35 to wash the same and to keep the slots thereof clear. This Wash water may be carried off by a convenient trough 56. Thus an adequate supply of uniform homogeneous stock escapes from-the cylinder 35 into the vat 36 for delivery to the paper-making machine. To this end an apron 60 may lead onto the Fourdrinier wire 61 of a paper-making machine, a flexible connection 62 being provided between the apron and thevat 36 to permit vertical adjustment of the vat and cylinder by well known means such as threaded shafts 65 which may be turned by a motor 66 through suitable connections.

The flow of stock over the apron may be regulated not only by the vertical adjustment of the vat 36 but also by a pair of adjustable slices 6'7, 68. Thus the stock which flows through the distributing roll 35 into the vat 36 is delivered to the Fourdrinier wire in a stream which is uniform and substantially free from eddies.

The screening devices 13 illustrated in Figure 1 operate on the principle of separating from a stream of pulp stock particles of larger than a predetermined size. Figure 3 illustrates apparatus for separating particles from a stream of pulp stock on the basis not only of size but also of relative gravity. As shown in the figure, stock from a supply trough 10 is delivered through suitable channels 70 to -centrifuging units 71. Within each of these units the stock stream is subjected to a high centrifugal force and is caused to pass over the surface of one or more mats of pulp which tend to remove from the stream particles which have a greater density than that of the pulp stock, and also particles which are of greater mass than the fibres in the stock. Provision is also made for the separation of particies of lesser specific gravitythan that of the pulp stock. Centrifugal purifiers of this type are not per se a part of this invention but are described and claimed in Patent No. 1,599,502, granted to Thomassen Sept. 14, 1926. Purified stock from these centrifuges is delivered through discharge pipes '12 to a collecting trough 15, the subsequent treatment of the purified stock being as hereinbefore described in connection with Figures 1 and 2.

It is evident that many modifications and changes may be made in the particular embodiments of the inventioii herein described and illustrated without departing from the spirit or scope of the invention as defined by the following claims.-

I claim:

1. The method of preparing pulp stock for delivery directly to a paper-making machine, which comprises purifying a thin aqueous suspension of the stock, removing a portion of the water from the purified stock to thicken it, evening the thickened stock, and delivering the evened stock directly to a paper-making machine.

2. Apparatus for preparing pulp stock for delivery to a paper-making machine, comprising a plurality of rotary foraminous screens having fine apertures for screening impurities and lumps from the stock, a rotary foraminous evening and distributing cylinder adjacent to the supply end of a paper-making machine and transverse thereto, said distributing cylinder having apertures larger than those of the screens, means for vibrating said distributing cylinder as it rotates, and means for collecting pulp stock from said screens and delivering it to said distributing cylinder.

3. Apparatus for preparing pulp stock for delivery to a paper-making machine, comprising means .for separating from a stream of dilute pulp stock particles larger than a predetermined size, means for removing a portion of the water from the stream of stock to thicken its consistency, and means for evening the thickened stock and delivering the evened stock directly to a paper-making machine.

. 4. Apparatus for preparing paper pulp stock for delivery to a paper-making machine, which comprises means for purifying pulp stock, a rotatable distributing cylinder adjacent to the supply end of a paper-making machine, said cylinder having apertures through the wall thereof of greater diameter than those of a screening cylinder, means for feeding a stream of purified stock into said cylinder, and means for vibrating said cylinder during rotation thereof.

PHILLIPS DENNETT.

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