US2893241A - Wet strength tester - Google Patents

Description

July 7, 1959 H. T. FISHER Erm. 2,893,241

vWET* STRENGTH TESTER Filed sept. 5o, 1955 BSheQtS-sheet 1 `luly 7, 1959 H. T. FISHER ET AL WET STRENGTH TESTER 5 sheetssheet 2 Filed Sept. 30, 1955 HEM/ey THOMAS F/.sf/f/e F IG IA JAW/E5 Mae/w NToR PATENT AGENT July 7, 1959 H. T. FISHERI ET AL. 2,893,241

WET STRENGTH TESTER Filedept. so, y1955 5 sheets-sheet s Tra/@Mey July 7, 1959 H. T. FISHERv ET Al.

WET STRENGTH TESTER 5 Sheets-Sheet 4 Filed Sept. 30, 1955 @n 2 .1M L

United States Patent O WET STRENGTH TESTER Henry Thomas Fisher, St. Catharines, Ontario, and James Moran, Baie Comeau, Quebec, Canada, assgnors to The Ontario Paper Company Limited, Thorold, ntario, Canada Application September 30, 1955, Serial No. 537,864

' 4 clams. (c1. 13-159) 'This invention relates to the paper making art, and more particularly to a means and method of determining the strength of a wet paper web.

In the course of manufacture of paper from pulp it is often desirable to estimate in advance the probable tensile strength of the paper web at various stages of its manufacture on the paper machine and thus of the strength of such web at varying moisture contents. In particular the strength of such sheet at the end of the Fourdrinier wire when the said sheet is of the order of 18% dry and also throughout the press section where additional water is removed up to about 33% dry is critical to satisfactory machine operation. The adequacy of strength of pulp in paper furnish is determined by preparing a test sheet of paper from such pulp by well known methods, eg. Oiiicial Standard Method No. T-205- m53 of the Technical Association of the Pulp and Paper lndustry, but tests on such test sheets correlate to the properties of iinished paper, e.g. in the case of newsprint to a sheet about 92% dry and do not provide pertinent data as to the papermaking characteristics of such pulp in the wet state as above described. The present invention provides a means of preparing and testing similar test sheets of pulp in a manner which does provide, the required information as to the character of the paper web at the wet end of the paper machine. Such testing becomes of particular importance in high speed papermaking machines where breaks in the paper web can cause costly delays.

In the past, methods devisedfor the testing of the wet paper web have been unsatisfactory. It will be appreciated that the wet sheet is extremely weak and easily damaged in handling, for example the handling required to transfer the wet sheet to a tensile tester, and clamping in such tester. Such a method has frequently damaged or weakened the sheet to a degree that the results of the testing have been substantially meaningless.

It is an object of this invention, therefore, to provide a means and method of testing the wet strength of a paper web which will give more accurate and significant results than has heretofore been possible.

It is another object of this invention to provide a wet web strength tester in which the possibility of damage to the web prior to making the desired strength measurement is practically eliminated.

These and other advantageous objects will become apparent through a consideration of the following detailed description taken in conjunction with the attached drawings in which Figure l is a vertical cross-section through the paper forming portion of a tester constructed so as to embody features of this invention. i

Figure 1A is a drawing similar to Figure 1 showing the suction apparatus attached to the drain and also showing the components more specically illustrated in Figures 1- 70 and 6.

'2,893,241v Fatented July 7, 1959 Figure 2 is an elevational view of the apparatus shown in Figure l.

Figure 3 is a front elevation, partly in section of tensile tester constructed so as to embody features of this invention.

Figure 4 is an exploded perspective view of the grid and supporting wire forming part of the apparatus illustrated in Figure 1.

Figure 5 is a perspective view of the split forming wire, and

Figure 6 is a detailed view similar to Figure 1 of a portion of the apparatus shown in Figure 1.

This invention consists broadly in a method of forming a wet paper test sheet upon a forming wire which is split on a centre line and subsequently placing the forming wire with the test sheet intact thereon in a device by which the two portions are displaced from each other so as to cause rupture of the sheet, the force required to effect such displacement and rupture giving a measure of the zero-span tensile strength of the wet paper test sheet formed thereon. This invention also provides means whereby the moisture content at the time of testing of such wet paper test sheet may be substantially predetermined.

The drawings illustrate a specific apparatus for forming a wet test sheet upon the split wire, and an auxiliary apparatus for applying the force to separate the portions of the wire and thus break the test sheet, both of these being designed to effect the purpose of this invention.

Referring firstly to the sheet forming portion of the apparatus illustrated in Figures 1 and 2, a reservoir 1, here shown as cylindrical in form, having suitably arranged mounting means at its lower end (indicated generally as at la), is secured as by hinges 2 to base member 8. An O-ring seal 3 located in a suitable channel provides a water-tight seal when the apparatus is in closed position as shown in Figure l. Two clamps 4 are adapted to retain the cylinder tightly in closed position against the O-ring seal 3, the clamps being rotatably affixed to the cylinder mounting la and cooperating with a projection 8a in the base member 8 when in closed position. The mounting 1a of cylinder 1 bears n closed position against carrying ring 6 of the forming wire cloth 5 through the O-ring 3, the carrying ring 6 being adapted to be inserted in a seat formed in the base member 8 and on a fixed ring 7 in which is mounted a supporting grid 7a and a supporting wire 7b. (See Figure 4.) A further O- ring seal 11 mounted in a suitable channel completes the water tight seal between the carrying ring 6 and the base member 8.

Thus, as is shown, the removable carrying ring 6 is mounted upon the base member 8 with O-ring seal 11 completing the seal. The carrying ring also ts on top of the supporting wire 7b and grid 7a, this grid 7a consisting of parallel stainless steel strips fitting loosely into slots in the supporting ring 10 and supporting a coarse wire 7b which is fastened to the supporting ring by a bezel ring 16. The forming wire cloth 5 thus rests upon and is supported by the grid 7a and the coarse wire 7b mounted upon the grid.

The lower portion of base member 8 is inwardly tapered as shown and terminates in a drain pipe 13. The drain pipe may conveniently be attached to a source of vacuum as applied from the vacuum pump 13f, the line 13e, the reservoir 13d, the line 13C and the valve 13b. The water supply may also be conveniently connected to said drain pipe controlled through the Valve 13g to.

the pipe 13h. The forming wire consists of a diametrically split wire of proper mesh to form a paper sheet. Although the split wire 5 rests upon the supporting wire, the split wire must itself possess rigidity and strength to fied long crimp twill weave wire 64 x 48 mesh has been employed by `us and is satisfactory for this purpose. The wire is soldered or otherwise securely affixed to the underside of the wire ring 5a which is similarly split.. The wire ring portions 5a are located by a keyway (not shown) into the carrying ring 6 with the two portions of the wire ring contiguous and so that the inside of the wire forms a continuous plane surface transversely across the cylinder bore.

' It will be appreciated that the splitting of the forming. wire cloth and the mounting thereof on corresponding sections of the wire ring must be carried out carefully and accurately to achieve continuity in wire pattern over the meeting line. Generally, it is believed that best results will be achieved if the wire is cut into half prior to mounting in the wire ring. During the operation of joining the split wire to the corresponding wire ring section, a continuous stress should be maintained parallel to the split and close to the meeting line. The completed wires will then be stressed throughout and when the wire rings are placed together in the carrying ring, the wire will form a taut, uninterrupted surface. If this splitting and mounting operation is carried out with care and precision, the wires in the two halves will meet continuously across the gap, and the split will be virtually undetectable in the formed sheet. Tests on paper formed on this split wire and subsequently dried have shown no significant difference in strength properties between the region over the meeting line and the remainder of the sheet.

To reduce the water content of the formed sheet to the desirable moisture content, vacuum is applied. It has been found preferable (but not essential) to carry out this part of the procedure on a separate part of the apparatus. In Figure 6 base member 51 is identical with base member 8 of the sheet forming apparatus. It is fitted with a ring 52 identical in diameter with ring 10 on the sheet forming apparatus but resting on springs 53. A supporting wire and grid 54 (identical with 7) with its -bezel ring 55 (identical with 16) is fitted in base member 51. If it is desired to accomplish this part of the operation in the equipment of Figure 1 only, then the spring lifting mechanism shown as 52-53 of Figure 6 can replace element 10 of Figure l.

The procedure in forming the test sheet is as follows:

The wire rings 5a are fitted into their appropriate keyways in carrying ring 6, the split wire then presenting a plane continuous surface. The cylinder reservoir 1 is swung back on hinges 2 and the carrying ring placed in its seat and with the wire portion thus supported by and resting on the supporting wire 7b and grid 7a. The cylinder is then swung down and locked in place by clamps 4, the whole assembly by O-rings 3 and 11 forming a water tight seal. Suicient water is added to the cylinder to cover the wire. Such water may be added through a `valve connection in the drain pipe, the water supplied rising up through the grid and forming wire. A measured quantity of pulp stock is then added in the form of a dilute suspension and the water level raised to a predetermined standard level through the further addition of water. The diluted stock in the cylinder should then be stirred and the cylinder then drained through drain pipe 13 by opening aquick-opening drain valve (not shown). The cylinder reservoir 1 is then swung back on its hinges 2. The carrying ring 6 holding the forming wire with the formed sheet is transferred on to the vacuum drying arrangement as shown in Figure 6. Prior to inserting the carryingY ring a wetted blotter 30B is laid on to the supporting'wire and grid 54. The use of this blotter is toobtain uniform moisture distribution in the formed testv sheet. The carrying ring isV then pressed down and' vacuum applied for such a length of timey aste` give approximately a predetermined moistureAV cnntentirr the test: sheet; the 'required times have' been determined on the basis of previous experience with the equipment. When the vacuum is released the spring loaded ring 52 automatically lifts the forming wire from the supporting wire thus preventing reabsorption of moisture from the blotter. The test sheet is now ready for testing and is carried on the forming wire in the carrying ring to the tester'.

The tensile tester may be any apparatus designed to displace the two portions of the split wire with the test sheet intact thereon from each other and thus cause rupture of the sheet, and to record the force required to effect such rupture. y

Such a device may take the form shown in Figure 3.

This drawing shows` ai chain loaded balance type of tensile tester. In operation, the carrying ring with the forming wire and formed sheet are placed on a raised hydraulic jack. The jack now lowers automatically leaving the two halves of the forming wire on the movable -head 21 and the fixed head 22. The movable head is then pulled via a linkage system 30, 31, 32 and 33 by a chain balance. When the sheet breaks the balance loading is stopped' and the breaking load is noted on scale 34. The two heads 21 and 22 are provided with machined top surfaces onto which the wire ring is seated, and locating means such as pins 21a and 22a which serve to locate and hold the wire.

. The chain balance is driven by a constant speed motor 24 with speed reduction effected both in the motor ygear box. and in a further gearbox 27 at the top ofthe shaft.

The electric motor runs continuously during operation of the tester. The test is eected by engaging the motor clutch 26 and starting the loading' of the balance. When the sheet breaks or the indicator reaches the end of the scale 34' the clutch disengages.

After thesheet breaks the breaking forc'e is read from the' indicator 37 on scale 34. The two halves of the sheet are then' removed and weighed to determine the total weight and then dried and weighed to determine the percentage dry' solids.

We have' described: the above specic apparatus designed to carry outV our invention. It will be obvious that considerable variation is` permissible in the dimensions and minor detailsV of the apparatus and it is to be strictly understood that our invention isv not to be deemed limited to' such specific apparatus or to the construction of details thereof. Such embodiments of the invention as come within the scope and purview of the appended claims are to be considered as partof this invention. As an example of certain dimensions and apparatus details which we have found satisfactory, the following may be noted.

The cylinder 1V maybe 4" in diameter.

The coarse wire 7b supporting the wire on which thev wet sheet is formed may be ZOmesh.

A groove maybe engraved on'the inside of the cylinder I at a distancev ofv 13'^%1"`abovel the surface of the wire to indicate the maximum level during filling of the cylinder with water prior toV drainage in sheet formation.

The effective hydraulic legpr'oviding drainage may be 31.5, this being the distance from the forming wire to the out-flow levelof a water seal.

The vacuum applied t'o the web for adjustment of moisture content may be 20 of mercury. With the apparatusv which wey have constructed the application of such vacuum permits'adjustment ofthe solids content of a pulp sheetof newsprint furnish substantially as follows:

Time of vacuum: Solids content, percent of 0.416r0-004 gram equivalent dry weight. Such a weight lof sheet corresponds closely to a basis weight of 32 1b. per 3,000 sq. ft. and is a suitable weight of sheet for investigation of the wet strength of newsprint furnishes. A trial sheet is normally made and its weight used to calculate the exact volume required to give a sheet weight as above for any given stock.

The pertinent information to be derived from our invention is a measure of the substantial zero-span tensile strength of a wet pulp sheet correlated to the moisture content of such sheet. It is convenient to record the tensile strength in terms lof grams per millimetre of web at the break, and the scale of the tensile strength tester chain balance as previously described may be calibrated directly in such units. We have found that in general for a given pulp the relation of the above zero-span Weight tensile strength expressed in grams per centimetre of web at the break is linear with respect to moisture content over the 7%-22% solids range. A graph may therefore be plotted from a series of tests on individual sheets of a given pulp and we have found the above tensile strength at 20% equivalent dry solids obtained from such a graph together with an indication of the slope of the tensile strength-moisture relationship on such graph to be an overall and comprehensive measure of the strength of a wet sheet of a given pulp which measure is the specic object of this invention.

The above information, relative to details of apparatus land procedure of using it, has reference to a preferred method of applying our invention to determine the wet strength of pulp and is given by way of example only and it is obvious that anyone skilled in the art may introduce modifications therein without departing from the spirit and intent of our invention.

What we claim as our invention is:

l. Apparatus for forming a paper test sheet comprising a reservoir for paper stock, said reservoir having an outlet, a removeable forming wire cloth located at the outlet of said reservoir, said forming wire cloth being formed in two separable sections located so as to form a substantially continuous paper forming surface, a source of vacuum beneath said forming wire cloth, and means for preventing the reabsorpton of water withdrawn through said source of vacuum by the formed paper test sheet.

2. Apparatus as claimed in claim l wherein said means comprises a spring loaded retaining means for both sections of said forming wire cloth, said spring load being such as to be overcome by the force exerted on the test sheet by said vacuum, but such as, when such vacuum is released, to raise both sections of said forming wire cloth free of said vacuum source.

3. The method of determining the substantially zero span wet tensile strength of a paper sheet which consists in forming a test sheet yof substantially predetermined solids content on two separable sections of forming wire cloth, the wire cloth sections being positioned adjacent each other to provide a continuous forming surface, applying a force to the test sheet to cause its failure in tension substantially at the meeting line of the wire cloth sections while it is still positioned on the said sections and indicating the force required to effect such failure in tension.

4. The method of determining the substantially zero span wet tensile strength of a paper sheet which consists in forming a test sheet of substantially predetermined solids content on two separable sections of forming wire cloth, the wire cloth sections being positioned adjacent each other to provide a continuous forming surface, applying a force to the test sheet to cause its failure in tension substantially at the meeting line of the wire cloth sections while it is still positioned on the said sections, indicating the force required to effect such failure in tension and measuring the moisture content of said sheet.

References Cited in the ile of this patent UNITED STATES PATENTS 1,193,613 Riegler Aug. 8, 1916 1,514,236 Smith Nov. 4, 1924 2,469,013 Sobota May 3, 1949 FOREIGN PATENTS 24,891 Finland Sept. 26, 1951

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