US1581803A - Method of controlling the moisture content of leather - Google Patents

Description

A ril 20, 1926.

E. F. HULBERT METHOD OF CONTROLLING THE MOISTURE CONTENT OF LEATHER Filed June 15. 1921 E dwm Iifiulh art; fryf Jame (EJ 55 01 may P l lH I I H IHI Milil II.

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Patented Apr. 20, 1926.

UNITED STATES.

. 1,581,803 PATENT OFFICE.

EDWIN F. HULBERT, OF MILWAUKEE, WISCONSIN, AOSIGNOR TO PFISTER &. VOGEL LEATHER COMPANY, OF MILWAUKEE, WISCONSIN, A CORPORATION OF WISCONSIN.

METHOD OF CONTROLLING THE MOISTURE CONTENT OF LEATHER.

Application filed June 15, 1921. Serial No. 477,846.

To all whom it may cmwem:

Be it known that I, EDWIN F. HULBERT, a citizen of the United States, residing in the city of Milwaukee, county of Milwaukee,

and State of Wisconsin, have invented a certain new and useful Method of Controlling the Moisture Content of Leather, .of which the following is a specification.

My invention relates primarily to a moisture adjusting treatment of animal fibres such as hides and leather in which during the various operations it is necessary to vary the moisture content through a wide range. It is of the utmost importance in doing this that the moisture distribution be uniform throughout the entire body of the material treated and not be confined to surface applications or be either greater 01 less at thesurface than in the interior of the material.

In the past it has been the practice to remove substantially all of the moisture in drying. This has been done by hanging the leather in open rooms, preferably with the windows open, and raising the temperature by means of steam coils or equivalent means. Occasionally an attempt has been made to force the air to circulate by means of fans either located in the room or behind the steam coils. After the leather has becomedry it is very hard and before it can be further worked must be partially moistened. This is done by dipping the leather in tanks of warm water, with or without other matters in solution therein, draining it, piling up the leather and perv mitting it to sweat in the moist pack so that some of the moisture is driven into the hides, This operation is generally called sammying. The leather then is in condition for further operations.

Such methods are crude and unsatisfactory in that there is no proper control over either the drying or the remoistening step.

The time required varies greatly dependingupon temperature and humidity conditions, and where the air is made to circulate by fans its drying efiect is very much limited in that the moisture taken up from the wet hides practically saturates the air after the first few feet of travel and for the balance of its travel it exercises no drying effect whatever. It is only after the first set of leather has been dried that it be '11s to dry the next setin rotation, etc. he result is that it is very expensive, wastes time, 1

and does not dry the leather evenly. The leather that is most advantageousl placed either with reference to the fans, .t e steam coils, or other drying means, is dried too rapidly and too hard, whereas the leather which is less advantageousl placed is dried too slowly and it is impossible to thoroughly control all of the leather and to dry it uniformly as a unit.

The method of moistening back the leather or sammying as practiced is even more unsatisfactory in that moisture is introduced by means of surface application of water in liquid form and the subsequent sweating process so-called does not serve to cause the water to thoroughly penetrate the leather and do it uniformly. The surface is always more moist than the interior, and the soft parts like the belly and the flanks, absorb the moisture more rapidly and retain it more readily than do the more dense parts of the hide such as the back and the butt. The result is that the leather is un-' evenly dried and unevenly moistened; and not only is there a great loss in time but the resulting product is inferior.

As at present practiced in the case of heavy leathers it isusual to take as much as 27 0 hours in drying, sammying, and finishing processes on the leather. Furthermore there is a good deal of non-productive handling and rehandling. The leather has to be hung and piled, dipped and piled, and moved, all of Wl'llCll is not only expensive but has a deleterious effect upon the leather.

Above all the final result is not satisfactory in'that the leather is not uniformly treated either as between different sides in the same pack or as between difierent parts of the same side. Completely dry leather is hard and horny. When dry fibers are exposed to a moist atmosphere theybegin to take up the water which they have lost, this water being held in or on the fiber in the obscure condition known as adsorbed. The changes produced are progressive. With a certa n proportion of moisture the fibers regain their pliability and with a somewhat larger proportion they begin to swell. The changes are progressive between the completely wet leather and completely dry leather. Air and other gases exposed to water at any given temperature takes up a certain amount of the water as vapor until a certain par- 4 tial pressure or concentration of water vapor in the air is attained. Water, however, held in a state. of adsorption by leather fiber does not come to the same balance with air as does free waterit resists drying ofi' with somewhat greater force. These principles I apply to the present method.

When wet leather fiber is dried by 3. current of dry air, the evaporation is at first rapid; this representing the evaporation of what may be called the free water; the water which is present as actual liquid. Later drying becomes slower as the free Water goes off and the removal is of absorbed moisture.

In drying leather I have found that, strangely enough, the removal of the total quantity of water which I wish to remove goes much more quickly if the initial drying stages be not too rapid; that is, I can get ofi a greater proportion of water in ten hours of total drying if I do not attempt to remove too much in the first half hour or other period. Wet leather rapidly dried behaves as if the surface pores were closed and water sealed in, while with slower drying in the first stages, while the leather is still wet, it behaves as if the pores were left open permitting circulation of air through the leather. I find that it is wholly inadvisable to dry a number of the sides of leather in series so that the air passes first over one and then over another; the best conditions are afforded when the air passes the sides of of air to a like moisture content, I establish What may be called a major flow of natural air which I warm to a desired degree and then admit a minor flow of similarly'warm air containing a relatively large amount of 7 water vapor. In practice, 'I simply deliver natural air through a fan to heating elements and then admix it with a smaller proportion of hot air coming from the fan and bypassing through a suitable moistening device. 7

Gontrol v of the process then simply means control of' the minor flow of air.

By my method I am enabled to control the moisture content of leather uniformly not only as regards each individual hide or side 80 of leather but as regards all the sides in the pack that are undergoing treatment at the same time. Further, I am enabled to very .power, do away with a large part of the 85 mechanism I am enabled to take a heavy leather side and condition it so that it is in the best condition for working within a period of 50 to 60 hours, and in the case of light leathers, very much less.

l. I have found thatgood results cannot be obtained by using raw unconditioned air 95 nor by using water for moistening, that uniform accurate results can only be obtained in controlling the moisture content of leather by use of air at fixed predetermined temperleather, so to speak, in parallel; and .that atures and containing constant predeterquick drying is effected by performing the first stages of drying with a1r already containing considerable proportions of moisture.

The leather should be so hung or arranged as to give the air what may be termed a washing efiect over the entire surface.

Operating in the described manner, that is drying with currents of air containing moisture, it is practicable by suitable adjustment of conditions either to dry the leather down to the point where the exact amount of moisture wanted is left, or to over-step this point and then. bring back the moisture tothe desired point by exposure to a moist atmosphere. By observing these conditions the conversion of wet leather to leather having the right amount of moisture for convenient working is muchshorter. Heavy leather can be gotten into good condition for working within a period of 50 to 60 hours as compared with the usual 270 hours and in case of lightleathers, the time re-. quired is very much less.

emoval of moisture is, of course, much accelerated by heat; but as warming air decreases the relative humidity, it is necessary, for my purposes, to add somewhat more water vaporwhen warmed air is used. In the most convenient application of my process instead of endeavoring to bring a large body gently downward through a grating, and no discharged at the bottom. I have illustrated the apparatus for using my method in the accompanying drawings, in which Fig. 1 i's a view partly in section and partly diagram-x matic, taken on the plane of line ,11 of Fig. 2 and Fig. 2 is a view similar to Fig. 1 and taken on the plane of line 22 thereof.

I have discovered that the ability of the air to extract or deposit moisture in leather is de endent not alone on the temperature or re ative humidity but on the combination of the two, and that where I desireto 'd1- minish the moisture content of leather the best results are obtained if the air has a temperature varying from 80 to 95 degrees F. and a moisture content from 35 to 45 per cent relative humidity. Where. it is desired to have the leather take up moisture from the air I find best results are obtained by having temperatures of 80 to 85 degrees F.

for a period suflicient to dry the leather to the degree desired, varying from 18 to 24 hours or thereabouts, depending upon the weight of the leather and the amount of the moisture. Where the leather comes from the previous operations and it is'de- I sired to dry it before stuffing, I continue this process until it is in the state generally designated as bone dry. By my method I am enabled to extract practically every particle of moisture throughout the entire thickness of theleather, with the result that the leather will take up a much lar er amount of fats in the stuffing room an they will more thoroughly penetrate into the leather than is true with the processes heretofore practiced. After the leather has been stufledit is again placed in the chamber and the moisture content lowered. It is not necessary this time toextract so much of the moisture, but it is desired to bring the leather down to a mellow condition. In practicing my method I am enabled to do this in one process, i. e., by extracting only the surface moisture leaving a suflicient amount to make the leather mellow and easily worked. This has not been done in practice in the past. It has been dried bone dry and then dipped and sammied. In this treatment of leather I start in with higher temperatures and also relative humidity, watching the progress of the dehydration and then gradually lowering the temperatures and adding to the relative humidity until the leather is the exact degree of moisture content that I desire. If, for instance, I am working with heavy'leathers I would commence using temperatures of 80 to 95 degrees with a relative humidity of 30 to 35 per cent, subject it to this temperature for 12 to 14 hours. I would then gradually raise the relative humidity and slowly lower the temperature until I got a relative humidity of 93 to 97 per cent and temperatures,

of from 80 to 85, and continue in this manner for 6 to 10 hours to insure a uniform distribution of the moisture in the leather..

Whatever method of controlling moisture content is used the surfaces of the leather are and must be affected first, and I therefore necessarily have to extract slightly more moisture from the surfaces and then replace some in order to get a uniform distribution of moisture content in the final result. By using my moisture carried in a gas I am enabled to do this, which is not the case where it is used in liquid form. Occasionally I desire to use the air to deposit moisture on the surface of the leather or part thereof in finely divided liquid form for special, purposes and I then make a fog in the bottom of the tunnel of such a density and rising to such height as I may desire. As illustrated in the drawing, the leather is suspended in the chamber or tunnel 5 by a suitable conveyer 6, adjacent hides being spaced to provide vertical air spaces through which the air from a duct 7 passes downwardly to outlets 8 located at or near the bottom of the chamber. The exhaust air is drawn through the outlets by a suction fan 9 connected therewith by one or more return ducts 10. If desired for special effects, a fog can be made in the bottom of the chamher or tunnel by admission of cold air, in the desired volume, through inlets 11 connected by one or moreducts '12 with a cold air supply so as to cool the air below the dew point. 4

Having thus described my invention, I claim:

1. The method of conditioning leather which consists in subjecting it to a stream "of drying air of uniform temperature and moisture content until the leather begins to have a surface hardening and then subjecting the leather to washing by means of a flow of uniformly moistened air containing a relative humidity in excess of 85 per cent until the leather is mellow and of homogeneous moisture content throughout.

2. In the conditioning of leather to bring it to definite moisture content, the process which comprises subjecting it to a wash of.

drying air of uniform temperature and moisture content so regulated as to almost entirely remove the free water before re-' moving the adsorbed water.

3. In the conditioning of leather to bring it to definite moisture content, the process which comprises subjecting it to a wash of drying air of uniform temperature andmoisture content so regulated'as to almost entirely remove the free water before remov-,

ing the adsorbed water and then washing the leather by a stream of uniformly moistened air of the temperature and moisture content within the limitations of the leathers homogeneous absorption and adsorption limits until the leather is of homogeneous moisture content.

4. In the conditioning of leather to bring it to definite moisture content, the process surface thereof by subjecting the same to an artificially produced fog.

6. In the conditioning of leather to bring it to definite moisture content, the process which comprises subjecting both sides of moist leather to a flow of drying air at a temperature of 80 to 85 degrees F. and to ifi per cent relative humidity until its moisture content is less than that ultimately desired and then subjecting both sides thereof to a flow of air at a temperature of 80 to 85 degrees F. and 93 to 97 per cent relative humidity till its moisture content is at the desired point.

7. In the conditioning oi leather to bring it to definite moisture content, the process which comprises subjecting both sides of the leather to a flow of drying air at a temperature of 80 to 85 degrees F. and 30 to per cent relative humidity for a period sufficient to dry the leather to the degree desired.

8. In the conditioning of leather to bring it to definite moisture content, the process which comprises subjecting both sides thereof to a flow of air at a temperature of to degrees F. and 93 to 97 per cent relative humidity for a period sutficient to bring the leather to the desired moistened condition.

9. In the conditioning of heavy leathers to bring them toa' definite moisture content, the process which comprises subjectin both sides of the hide to a flow of drying air at a temperature of 80 to degrees F. With a relative humidity of 30 to 35 per cent for twelve to fourteen hours and then gradually raising the relative humidity of the drying air to 93 to 97 per cent and lowering the temperature of this drying air to 80 to 85 degrees F. andcontinuing to subject the hide to air in the last-named state for six to ten hours to insure uniform distribution of the moisture in the leather.

EDIVIN F. HULBERT.

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