US1525131A

US1525131A - Process of drying articles

Info

Publication number: US1525131A
Application number: US454527A
Authority: US
Inventors: Halbert K Hitchcock
Original assignee: Pittsburgh Plate Glass Co
Current assignee: PPG Industries Inc
Priority date: 1921-03-22
Filing date: 1921-03-22
Publication date: 1925-02-03
Anticipated expiration: 1942-02-03

Description

Feb. 3', 1925. 1,525,131

H. K. HITCHCOCK PROCESS OF DRYING ARTICLES Filed March 22, 192.1

INVENTOR .M. JWM /Q,

Patented Feb. 3, i925.

STATES PAENT OFFICE.

HALBER-T K. HITCHCOCK, O'F PITTSBURGH, PENNSYLVANIA; ASSIGNOR TO PITTS- BUB-GE PLATE GLASS COMPANY, A CORPORATION OF PENNSYLVANIA.

PROCESS OF DRYING ARTICLES.

Application filed March 22, 1921.

T all whom it may concern:

Be it known that I, HALBERT K. HITCH- cocK, a citizen of the United States, and a resident of Pittsburgh, in the county of 6 Allegheny and State of Pennsylvania, have made a new and useful invention in Improvements in Processes of Drying Articles,

of whichthe following is a specification.

The invention relates to a drying process.

W It is illustrated as applied to the drying of clay articles, such as the pots employed in the manufacture of plate glass, which is probably'its largest field of use, but is not limited to use with clay articles, and may be employed in the drying of wood and other materials. The invention has for its princi al objects the provision of an improve process, (1') wherein a more rapid drying can be accomplished than is the case with the apparatus and processes now employed, which will secure a drying from the inside of the body subject to the drying action to the outside thereof, (3) in which the drying. action for each interval of time 95 can be accurately observed and easily regulated and controlled, (4) and which requires apparatus of very simple character requiring no complicated or expensive temperature or humidity controlling devices.

One embodiment of the invention is illustrated in the accompanying drawing, where- The figure is a vertical section through the apparatus preferably employed.

Briefly stated the apparatus comprises a drying compartment or chamber, circulating means whereby the air may be withdrawn from the chamber and returned thereto, means for reducing the humidity of the air as it is circulated; and means for gradually raising the temperature of the circulated air as the drying progresses. The means for removing the moisture from the circulating air and thus increasing its drylng capacity,

is preferably a condenser, although this function may be accomplished in part or m whole by withdrawing a portion of the moist air and supplying relatively dryer air to the system to take the place of the an withdrawn.

. In the practice of the process, the air is kept relatively moist, in fact just below the saturation point, for the ma or port on of the dryin operation, the purpose being to prevent t e too rapid drying of the ml- Serial No. 454,527.

terial at the surface and the formation of a dry crust. Such surface drying destroys the capillarity of the material, so that any vaporization of the liquid on the interior of the mass which occurs subsequently, must occur inside the mass rather than at its surface, rendering the drying out. of the interior slow and imperfect, and in the case of a clay article, tending to cause cracking during the subsequent firing operation. The necessary humidity is preferably supplied by the vapor from the drying articles themselves, which quickly brings the air u to the saturation point. The humidity o the air is reduced slightly below the saturation point and kept at such point by increasing the temperature of the air, thus increasing its capacity to hold moisture. This operation is continued at'a gradually increasing temperature, thus increasing the speed of drying of the articles. As the moisture taken from the pots would soon bring the air above saturation point and thus stop the dryin action, it is necessary that means. he provi ed for removing a portion of the moisture from the air. This means is supplied by the condensing coil, which condenses a portion of the moisture in the air, thus reducing the humidity of the air to the desired point. After the clay in the pots has been reduced to a condition of comparative dryness, the humidity of the air may be still further reduced, either by increasing the temperature of the air or by drying the air to a still greater degree by t e use of the condensing means.

Referring now to the drawing, 1 is the drying chamber, in which are placed the pots 2 to be dried; 3 is a heating chamber, located below the drying chamber, and 4: is an outlet chamber located above the heating chamber. A circulation of air is accomplished by means of the fan 5, driven by a motor (not shown), and having the connection 6 with the outlet chamber 4. The fan discharges air to the heating chamber 3, through the

pipes

7 and 8, the condensing chamber 9 also lyin in the line of connection. The condensmg chamber carries a coil 10, having an inlet i 11 and an outlet pipe 12, the inlet pipe mg provided with a valve 13 for governin the flow of cold water through the coil. ipes 14 for steam or other heating fluid are provided 1n the heating chamber 3, A pair of connection:

15 and 16 are provided in the

pipes

6 and 8, such connections leading to the atmosphere. These connections are provided with controlling valves 17 and 18. whereby the flow of air may be regulated or entirely cut off.

The pots 2 in the drying chamber 1 are seated upon boards 19, which in turn are supported upon a plurality of blocks 20, the boards being-preferably arranged so that they come over openings 21, leading from the heating chamber to the drying chamber. Communication between the drying chamber 1 and the outlet chamber 4 is provided by means ofthe vertically n'iovable pipes 22, which are counter- Weighted by means of the cables 23 passing over the pulleys 24- and attached to the weights 25.

Pipes 22 extend down into the pots, as illustrated, in order to promote a flow of air through the interior of the potand secure a proper drying thereof. The vertical adjustment of the tubes 22 permits of a convenient positioning or removing of the pots.

The lower end of the condensing chamber 9 is provided with av collecting compartment 26, a valve 27 being located at the bottom of the compartment and a gage '28 at the side thereof for indicating the height of the water.

' In operation, the green pots are placed in the drying chamber, as indicated in the drawing, and the fan started, the temperature in the chambers 1 and 3 being at such time about the same as the outside air. The circulation of the air about the pots soon causes saturation of such air, as the pots are relatively damp and give off sufficient moisture to accomplish this result. In order to reduce the air below the saturation point, heating fluid is applied to the coils 14;thus raising the temperature of the circulated air and increasing its capacity for moisture. The air is in this manner reduced slightly below the saturation point so that a drying effectis secured upon the pots. As the drying progresses the temperature is gradually raised, such increase in temperature being just sufficient to keep the air below the saturation point, moisture being continually added to the body of air by reason of the evaporation from the clay. In case the air becomes too moist, it may be dried by the use of the condensing coil 10, or by the use of the valves 17 and 18. In the latter case the valves are opened to a certain extent, depending upon the conditions. This permits some of the moist air to be forced out past the valve 18 and drier air from the atmosphere to be sucked in past the valve 17, thus reducing the percentage of moisture in the circulated air. Preferably, however, the control is secured by means of the condensing coil 10, as this is more economical and can be more accurately regulated by means of the valve 13. After the temperature of the body of air hasreached a certain maximum temperature, preferably near 150 F., any further increase in temperature is stopped and the body of air is circulated at this temperature until the pots are substantially dry, the air during all this period being kept just below the saturation point, so that the capillarity of the material is not destroyed, thus promoting a drying of the mass of clay from the inside out and preventing the formation of a dry crust on the surface of the clay, which would tend to hold the moisture on the interior of the clay. During the circulation of the air at the maximum temperature, the moisture is continuallyfwithdrawn from the air by means of the condensing coil 10, thus preventing the vaporization from the clay bringing the air up to the saturation point. After the pots have been substantially dried out, the

final drying may be accomplished with much drier air, and to this end the condensing coil is employed to take out of the air as much moisture as possible, the controlling valve 13 being at this time opened full.

The foregoing operation or process can be accurately controlled. The amount of condensation is easily regulated from the condensing coil by means of the valve 13, which controls the flow of cooling liquid through the coil. The rapidity of the condensation can also be easily noted for each interval of time by means of the gage 28 or by withdrawing the water collected from time to time through the valve 27. When a satisfactory dryin cycle has once been determined by experiment and by observation as to the amount of condensation for each period of time, such cycle can be easily and accurately followed in subsequent drying operations. The necessity for expensive and complicated humidifying and temperature controlling means is avoided, and the relatively simple apparatus shown provides for a wide range of control, which can be regulated to a nicety. A range of control in addition to that of the condenser is afforded by means of the valves 17 and 18, whereby the humidity of the air may be reduced by exhausting moist air from the system and supplying drier air to take the place thereof. Under certain conditions this control can be made to advantageously supplement that of the condenser or entirely take its place, although there is a loss advantages incident to the process will be readily apparent to those skilled in the art.

lVhat I claim is:

1. The process of drying articles which consists in subjecting the same to the drying action of a moving body of air at a degree of humidity slightly under the saturation point and at a relatively low temperature, and gradually increasing the temperature of the air as the drying progresses while maintaining such air at a degree of humidity which departs farther and farther from the saturation point as the drying progresses.

2. The process of drying articles which consists in subjecting the same to the drying action of a moving body of air maintained at a degree of humidity slightly under the saturation point and having a gradually increasing temperature until the material of the articles is relatively dry and then decreasing the humidity of the drying air to complete the drying.

3. The process of drying articles which consists in subjecting the same to the dry? ing action of a moving body of air maintained at a degree of humidity slightly under the saturation point and having a gradu-. ally increasing temperature until the material of the articles is relatively dry and then decreasing the humidity ofthe drying air and still further increasing its temperature to complete the drying.

4. The process of drying clay pots which consist in supporting the pots in an upright position in a drying chamber, withdrawing air from the chamber from outlets leading from the interior of the pots, circulating the air so withdrawn past a condenser, heating such air, and supplying it to said chamber beneath the pots whereby a circulation of drying air is secured upward along the sides of the pots and then downward into the interior thereof.

In testimony whereof, I have hereunto subscribed my name this 21st day of March,

-HALBERT K. HITCHCOQK.