US2131645A

US2131645A - Method of drying

Info

Publication number: US2131645A
Application number: US37936A
Authority: US
Inventors: Thomas K Sherwood; Louis E Garono
Original assignee: Research Corp
Current assignee: Research Corp
Priority date: 1935-08-26
Filing date: 1935-08-26
Publication date: 1938-09-27
Anticipated expiration: 1955-09-27

Description

Patented Sept. 27, 1938 UNITED STATES PATENT OFFICE E. Garono, Buffalo, N. Corporation, New York, N. Y.,

New York Y., assignors to Research a corporation of No Drawing. Application August 26, 1935, Serial No. 37,936

'1 Claims.

This invention relates to the drying of wet porous insoluble solids and particularly of those which contain non-volatile solutes which, in localized high concentration, are undesirable,

When porous materials dry, solutes are carried by the solvent along the capillary channels in the mass and congregate near the surface in increasing concentrations. Although the original concentration of solutes may be so low as to have no harmful effect, yet the high concentration built up in the surface layer frequently is destructive.

If the tanning of leather be taken by way of example, the tanned hide is uniformly saturated with tanning liquor and then dried. As water evaporates from the surface, the tanning substances, whether they be true solutes or colloidal particles, are carried by the liquor through the capillary channels between the hide fibers until the surface is reached. There they remain while the water evaporates. If the drying of a hide is carried on much above 80 to 90 F. the surface is discolored and badly scorched. This condition is evidenced by discoloration and by brittleness. Deep cracks form whenever the leather is flexed.

We have discovered that one may prevent all harmful concentration of dissolved substances at the surface and consequently, may dry such substances as leather at high temperatures and at higher evaporation rates than heretofore has been possible.

The objects of our invention, therefore, are to avoid the concentration of deleterious substances adjacent the surface of a drying mass; to avoid harmful concentrations of tanning substances at the surface of the leather; to secure a more uniform distribution of the substances within the dried hide; to dry at temperatures and at rates which heretofore have been destructive; to secure good color without the necessity of a bleaching operation; and generally, to secure more uniform distribution of dried solutes in a dried-out mass. These and other objects will become apparent from the specification. h

According to our invention, and again taking leather as an example, we coat the wet hide with a porous mass possessing a multiplicity of capillary channels and through these channels and from the temporary, removable surface so pro- 5 duced, evaporate the water. The tanning substances contained in the wet leather, instead of concentrating at the leather-air interface as previously, cross the boundary of the leather,

enter the porous mass and now concentrate at 55 the new air-porous mass interface.

Thus, there is no high concentration of tanning substances anywhere in the hide and, consequently, it may be dried at a temperature as high as 180 F. with no discoloration or embrittlement of the surface. Unbleached leather 5 when dried by the same method is practically identical in apearance to leather which previously has been bleached.

A great variety of coating materials are suitable since it is only necessary that they be capill0 lary active substances and form a coat thick enough to hold the whole layer of concentrated tanning agents. A coating of plaster of Paris may be cast against the leather, or a clay slip poured thereover, or a sheet of fibrous material such as a paper felt or even newspaper stock (for thinner leathers) may be rolled into contact with the hide, but we have found coatings of finely divided mineral substances are the cheapest and the easiest both to apply and to 20 remove. We prefer to daub a thick slurry of kieselguhr over the liquor-soaked hide. Fine sand, slate flour, fullers earth and other clays may be used in place of kieselguhr with practically equal effect.

Although we prefer such inorganic coatings, organic coatings are also suitable, cotton flock, wood flour held in starch or flour paste or even starch or flour pastes alone form satisfactory absorptive coatings.

Essentially, therefore, our invention may be practiced by applying a temporary coat of a capillary active substance to the material to be dried and allowing the deleterious substances to con centrate therein throughout the drying process. 35 When the drying is complete the capillary active substance is stripped or dusted off from the dried material.

Many of the coating substances, but particularly kieselguhr, may be recovered for reuse by 40 dumping whatever material is dusted off from the dried hide into water and allowing the tanning substances to leach out. When the sludge has settled, the water plus the tannin may be run off. The sludge is then mixed with fresh water to 45 give it the proper consistency for reuse.

As a specific example of our invention, 85 parts of kieselguhr and 15 parts of fine sand are mixed with a sufficient amount of water to form a. stiff paste. This is painted over the wet hide. The hide is immediately placed in a drying shed and the temperature maintained at about 180 F. The time required for drying is, of course, dependent upon the water content, the thickness of the hide, and the humidity in the shed and,

consequently, we give no time therefor, but it has been our experience that large, thick parts may be thoroughly dried in this manner in from six to eighteen hours.

According to the statutory requirement, we have set forth the preferred example of our process as applied to the drying of leather, but we intend no limitation thereby. It is evident that the process is applicable to the drying of any substance wherein a concentration of solutes is undesirable at the surface.

What we claim therefore is:

l. The process of drying wet porous masses having solutes therein which comprises covering a surface of the mass with a water slurry of a capillary-active substance which is insoluble in water, thereby depositing a relatively thin adherent coating of said substance on the surface of said mass. maintaining the substances and the mass in close contact, and drying both the mass and the substance by evaporation of water from the surface of the coating of substance, whereby excess solutes leave the mass and concentrate in the coating of substance.

2. The process of drying leather which comprises coating the wet hide with a water slurry of a finely powdered material capable of forming a capillary-active layer, evoporating water from the surface of said layer, and thereby causing the excess tanning substances present in the hide to concentrate in said layer and removing the finely powdered material from the hide.

3. The process of drying leather which comprises coating the drying surface of a wet hide with a relatively thin layer of a water slurry of a comminuted material capable of forming a capillary active layer, subjecting the layer to drying conditions and thereby drying the hide and removing the comminuted material from the hide.

4. The process of tanning which comprises submitting the hides to a. tanning bath, coating the wet hides taken from said bath with a water slurry of finely powdered material capable of forming a capillary-active layer, evaporating water from the surface of the layer, to thereby cause the excess tanning substances present in the hide to concentrate in the capillary-active layer, and removing the finely powdered material from the hides.

5. The process of drying wet hides containing a tanning solution and preventing concentration of solutes at the surface of said hides, said process comprising covering the surface of said hides with a water slurry of a finely powdered material which is insoluble in said tanning solution, thereby depositing a relatively thin adherent coating of said substance on the surface of said hides which has a capillary action sufficient to draw the tanning solutes from the surface of said hides, drying said layer by evaporation while allowing the excess tanning solutes to concentrate in said layer of capillary active material, and removing said layer from said hides.

6. Process of drying leather as defined in claim 3 in which the finely powdered material is kieselguhr.

7. Process of drying leather as defined in claim 3 in which the finely powdered material is fuller's earth.

THOMAS K. SHERWOOD. LOUIS E. GARONO.

CERTIFICATE OF CORRECTION Patent No. 2,131, 614.5.

September 27, 1958.

THOMAS K. SHERWOOD, ET AL.

It is hereby certified that error a ppears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 28,

claim 2, for "evoporating' read evaporating; and second column, lines 29 and 52, claims 6and7 respectively, for the claim refer ence numeral "3" read 2; and that the said Letters Patent should be read with this correction therein that the samemay conform to the record of the case in the Patent Office.

Signed and sealed this 1st day of November,

(Seal) Henry Van Arsdale Acting Commissioner of Patents.