US1751179A - Moisture-content tester for paper-making machines - Google Patents

Description

C. A. UPSON March 18, 1930.

MOISTURE CONTENT TESTER FOR PAPER MAKING MACHINES Filed Aug. 26. 1926 Patented Mar. 18, 1930 cit-earns A. user, or LOCKPQR'L NEW YoBKfass-Isuoa or ONE-HALF To w-..'n.eIi-- RISQN U s N, QF'LOGKPOR N W ORK MOISTURE-CONTENT, TESTER FOR PAPER-MAKING llllZACHIN'ES Application fi'ied' August 26, 1926.

My present invention relates to the art of paper making, and more particularly to meansfor testing the moisture content of the-paper as it progresses through or emerges from the making machines, and it has for its object to provide a simple and efiicient device of this nature that will accurately reflect the moisture content of the entire web, and from which the tender may frequently and accurately determine the condition of the'issuing'web of paper and correct factors in the general operation of the machine which maybe responsible for imperfections in the paper arising from imperfect moisture elimination. To these and other ends theinvention resides in certain improvements and combinations of parts, all= as will be hereinafter more fully described, the novel features being pointed out in the claims at the end of the specification.

In the drawings: 5 V

Figure 1 is a side elevation ofthe dry end of a paper making-machinefitted with a mois-. ture content testing apparatusconstructed in accordance with and illustrating one embodiment of my invention;

Figure 2 is a transverse sectional view through the roll: and hood shown in Fig ure 1 Similar reference numerals throughout-the several views indicate the same parts.

There are twov parts to a paper machine, one usually called the wet end, where the fibers are formed into. a web of paper by screening them out of the water with which thepulp or stock is mixed and fed tothe machine. This web is-weak and flabby. and containsa large percentage of water even. after the greater portion has been expressed by means of squeeze rolls. The other part of the machine is called the dry end toward which the web progressively proceeds: and which receives the very wet web and dries it. The process of drying on all types of paper machines is about thesame, consisting of a few or a large number of dryers which are revolving steam heatedcylind'ers. The paper coming from the wet end. passes over the surfacesof the drying-cylind'erswhich drives out the water inthei form; of vapor... The

Serial No. 131,773.

cylinders are so arranged that both surfacesi the felted pulp, first bymechanical means of.

squeeze rolls and then by the use of heated rolls, drawing out the water Icy-evaporation. About two tonsof water to one ton of-paper is evaporated.

The finished paper web as ijt issues from the machine still contains some moisture which is desirable to a certain extent and the proportion of which is varied according to the kind of paper being made. and the uses for which it is intended. To properly proportion this moisture contentis very important.

For example, in making newsprint paper, it is important to have thispaper dried at about theaverage humidity of the air. 12f the-newsprint. is overdried, it is very unsatisfactory, causing breaks, delaysin production and large waste in operatingthe'modern high speed newspaper printing machines Onthe other hand, it must be noted if newsprint paper is too moist, calendering cannot be accomplished satisfactorily. These same faults are true of many other kinds and grades of printing paper. In the making of wrapping paper for illustration, i f it is made too dry it lacks strength, folding qualities and it'is stiff: and brittle. In the makingof paper board productslike boxboard and container stock if the material is too dry: it Will not bend without breaking, and in an automatic box making machine causes reduced output and loss. Again, in themaking: of pasted or laminatedboard as used for containers, if the stock is over dried the strength is: re-

duced and board actually-damaged. On. the other hand, if theproduct istoo wet (JD-COIL tains wet streaks, the adhesive does not make a good bond of the plies: causing a tot-alt loss or a weakened stock.

The vapor or moisture in the sheet'oftp aper we speak of as'relative humidity, therela: tivity beingthat between the moisturescontent of the paper and the moisturev content of'the surrounding air when completely saturated. Such relative humidity. is thematic between the quantity of vapor actually present and that which would be present if the air were saturated at the temperature of observation. Such relative humidity is usually expressed in percentage at seventy-five per cent which denotes that the air contains three-fourths of the water vapor required to saturate it at a given temperature. t is the existence of this relative humidity or plainly speaking, humidity of the air which makes 7 it possible for us to utilize it in determining threads of lamp 'wicking from a very small reservoir of water. Thus the dry bulb indicates the temperature of the air itself, while the wet bulb cooled by evaporation shows usually a little lower temperature according to the amount and rapidity of evaporation. "Hence th'ewdilference' in temperatures of the two bulbs is the greatest.

when the ,air is driest. 7 By experimenting, it

has been ascertained the relative humidity corresponds to the degrees difference between the two thermometers for any given temperature of air. In other words, an observer reads the difference of temperatures in the two bulbs and from these two determinesthe relative humidity of the air." Knowing, the relative humidity of the air and carrying out laboratory tests in obtaining the moisture content of a sheet, it is possible to establish a chart showing the moisture content of the sheet for all the variations in the relative humidity indicated by the instrument. If a definite relative humidity canfbe standardized on the machine for various grades of paper at a given caliper speed, it is possible for the machine operator to watch his recording'chart attached to the psychrometer and know whether or not paper is being dried to the moisture content that is specified.

My method of obtaining an immediate and continuous record of the moisture content of 'a sheet of paperas it is drying or about to leavethe machine in a finished condition is accomplished by placing one or'more hoods over one or more of the drying rolls. If only one hood is'used (and in many cases this is sufiicient) it is important that such hood be placedover or around one of the last'drying rolls to fit as closely to the paper as possible so that the machine operator-is not incon- Venienced and the threading of the sheet around the dryer is not obstructed. Re ferring more particularly to the drawings, 1 indicates the frame of the dry end of a paper making machine upon which are mounted drying rolls 2, 3, 4, 5, 6 and 7 in the order named, thelast mentioned roll being the issuing roll. In the present'instance, I have shown my hood indicated at 8, surrounding the upper portion of the roll 5 being the third from the last. It is preferably a metal hood closely encompassing the roll down to or below the shaft 9 thereof. The front or end of the hood'or cover is fitted with a door 10 which may be raised while threading in the sheet of paper or for inspection, purposes. Thehood fits so closely that only a small amount of outsideaircan come under it though it is necessary that a little air be allowed to pass over the sheet as it traverses the drying roll in order to supply a current to the psychrometer.

A pipe 11 is connected to the center of the hood 8 and leads therefrom to a housing 12 from which the air and vapor drawn from the hood, is discharged as indicated by the arrows under the influenceof a fan or blower located at 13, the'function of which latter is merely to cause a circulation and draw off. the accumulation within the hood. The psychrometer beforementioned is arranged in the casing 12 and is affected by the aircand the vapor from the hood 8 which rises from the web of paper passing thereover said web being indicated at 14;. Inasmuch as the hood covers the entire roll and the entire web passing over the same, it accumulates the evaporation of the paper along its entire width and over a considerable surface thereof that is in contact with the drying'roll so thatanaccw rate average vaporization of the particular temperature at which that drying T01]. is running is accumulated and recorded. The hood may be placed on any one of the rolls but one of the last ones, such as the roll 5, is preferable. I

A psychrometer such as that referred to is well known in the art, and for this reason has not been shown in detail. Itis shown in a general way in Figure'l, and consists ofla' wet bulb and ardry bulb arranged side by side. The wet bulb, indicated at 14, is covered by a wick 15 extending into a reser voir 16 supplied by a pipe 17. Tubes 18 and 19 run therefrom to a recording device 20 having arms or pencils 21 and 22 connected respectively to'the two bulbs to show the ratio between the temperature and the humidity.

In Figure 2 is shown a modification of the hood 8 which is marked 8 and is shown to entirely surround the drying roll 5. The roll being thereby made more or less inaccessible, feed rolls 23 are provided to carry the paper into the hood, these feed rolls being driven by a sprocket 24 from the shaft 9. At the point at which the web emerges a doctor blade 26 is provided to insure the passage of the web out through an opening 27.

The difference between these wet and dry bulbs in temperature gives at once the approximate moisture content of the air in the hood. Now it has been found by experimenting that if the sheet running over the dryers is kept at approximately the same caliper, furnish, speed and all other factors are as efficient as possible, the amount of water in the sheet will vary directly as the difference between the wet and dry bulb temperatures. Of course, this difference in temperature of the two thermometers is found to be characteristic for different classes ofpaper also. Hence if the relative humidity can be established for a given caliper and furnish, the moisture content of the sheet can be established so that the relative humidity indicates the exact moisture content of the sheetas it passes over that particular dryer or set of dryers. These recording thermometers, are, of course, purchasable in the market and are easily attached to the machine and the motor and fan are added in order to direct the air from within the hood or surrounding drum over the two temperature bulbs.

Referring again to the embodiment of th invention shown in Figure 1, a feed roller 30 is preferably mounted in the hood to rest on top of the drying roll 5 This is to facilitate threading the paper through the roll as the door that gives access to the interior of the hood is relatively small and it is advantageous to have a positive feed roll to which the paper can be threaded through the door and thence be sure of passing around the dry roll and emerging at the bottom of the hood on the other side.

This equipment can be attached to a ma chine at a very low cost and for economy of operation and in savings it cannot be equalled by any other machine known to me for obtaining the moisture content of the paper as it is being made. With its use the operator is given information on such factors in producing a good sheet of fibre consistency, correct freeness of the stock, condition of the belts, the eficiency of the press rolls, the proper Working of dryers and ventilation systems and other important things that may make or unmake a good sheet of paper, and all of which are reflected in the moisture content at the delivery end of the machine. Such information hitherto has been obtainable only by carefully watching each.

I claim as my invention:

1. In a paper making machine, the combination with a heated drier over which the paper web continuously travels, of a hood eX- tending transversely widthwise of the web from side to side and adapted to trap the vapor issuing from a complete section of the web while on the roll, and a psychrometer embodying wet and dry bulbs exposed to the action of such vapor.

2. In a paper making machine, the combination with a heated drier over which the paper web continuously travels, of a hood extendin transversely widthwise of the web from side to side and adapted to trap the moisture issuing from a complete section of the web, while on the roll, a psychrometer embodying wet and dry bulbs and means for driving a current of air through the hood and into contact with the wet and dry bulbs of the psychrometer.

3. In a paper making machine, the combination with a plurality of drying rolls, of means for trapping the vapor issuing from the paper web as it passes over a given one of said rolls, a psychrometer embodying wet and dry bulbs, and means for conducting the vapor arising from said roll into contact wit-h the wet and dry bulbs of the psychrometer.

4. In a paper making machine, the combination with a plurality of drying rolls,of a

CHARLES A. UPsoN.

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