This invention relates to the preparation of ice pellets. More particularly, the invention is concerned with a method for manufacturing ice pellets which comprises allowing water to fall or contact a silver iodide surface which is maintained at a temperature of at least -10° C. or colder.
In the preparation of ice cubes or ice pellets it has been the practice to either prepare the ice cubes or pellets by freezing water in molds or else to place the water on a cold surface maintained at temperatures low enough to effect the conversion of the water to the solid ice state.
These methods, although commonly employed for making ice cubes and ice pellets, have disadvantages in that the time required for making the ice, in whatever shape it may be, is quite long.
We have now discovered that ice pellets of different sizes can be made inexpensively and quickly by allowing drops (either large or small) of water to fall upon a silver iodide surface which has been cooled to a temperature of at least -10° C., or lower, for example, from -10° to -70* C., or even lower.
A silver iodide surface at normal temperatures (about 25° C.) is very hydrophilic and water will spread readily on such a surface. We have now discovered that drops of water, when allowed to fall on a silver iodide surface, will not spread if the later surface is maintained at a temperature of about -10' C. or colder. This is due to the fact that as the drops of water fall on the cooled silver iodide surface, they freeze so quickly that they have relatively little time to spread and they are transformed into ice pellets with contact angles of about 90°. Because of the quick initial freeze, the adhesion of the ice pellets to the silver iodide surface is very low. Thus, the ice pellets can be easily removed from the silver iodide surface by only a slight pressure.
In practicing our invention, any suitable method for preparing a silver iodide surface may be employed. Thus, a metallic surface having good heat-transfer properties, for example, steel, copper, etc., is coated with a solution of silver iodide, and the solvent allowed to evaporate to leave a thin residue of silver iodide. Thereafter, small portions of cold water of any desired size, e. g., drops, or globules, or pools of water, are placed on the silver iodide surface which has previously been cooled to a temperature at least as low as -10* C. to yield ice pellets.
Another suitable method, which we have found preferable, is to electroplate or coat by other puitable means a metal base plate, for instance, iron, steel, copper, etc., with elementary silver so that an essentially smooth surface of silver is obtained. The silver surface of the coated metal plate is thereafter exposed to iodine vapors, for example, in an oven filled with the aforementioned iodine vapors, thereby to give a silver iodide surface. Instead of using vaporous iodine to form the silver iodide, it may be desirable to use, for instance, an alcohol solution of iodine and paint the silver surface with the said solution permitting the alcohol to evaporate leaving behind a silver iodide surface. The thickness of the silver iodide layer is not critical. It is preferred, however, that the silver iodide layer should not be any thicker than necessary, e. g., about 2 to 40 mils, in order to have the best heat-transfer properties. As described above, water drops are placed on the silver iodide surface of the plate automatically while maintaining the temperature of the silver iodide surface at a temperature of at least -10° C. At definite intervals a rider may be pushed across the plate knocking the ice pellets off and into a collecting trap maintained at a temperature below 0° C.
It will of course be apparent to those skilled in the art that solid silver sheets or plates may also be employed which can then be treated with the iodine vapors prior to cooling and application of the cold water for producing the ice pellets. Still another method for making the ice pellets involves coating (for instance, by electroplating) an endless belt of thin gauge, cold-rolled stainless steel with a film of silver and exposing the silver film to iodine vapors. By allowing this belt to travel between two pulleys in a cold chamber maintained at a temperature of -10* C. or lower, ice pellets can be made continuously by dropping water on the belt surface at definite time intervals. Due to the low adhesion of the ice to the silver iodide surfaces by mere bending of the belt around the pulley, the ice pellets; will fall off into a receptacle.
The accompanying drawing discloses an 1llustrative, though not limiting, embodiment of the means whereby our claimed invention may be practiced.
In said drawing, Fig. 1 is a perspective view of an apparatus for manufacturing ice pellets; Fig. 2 is a cross-sectional view of the surface on which the ice pellets form.
Referring to Fig. 1, water is led in through a pipe I which is connected to another pipe 2 containing spouts 3 through which the incoming water is allowed to fall. The rate of flow of the water is regulated by a valve 4. The pipe arrangement 2 is mounted on riders 5 positioned to slide along at a regular speed on bearing members 6. As the water impinges on the cooled silver iodide surface 7, the total pipe assembly is moved along the bearing members 6. A rider I is used S to push off the formed ice pellets into a receptable I maintained at a temperature below the freezing point of water. The metal plate II on which the silver iodide surface is formed is cooled to at least as low as -10* C. by means of a cooling fluid circulating through the said metal plate, entering in pipe I and coming out of pipe 12.
Fig. 2 comprises a metal plate 10 cooled by suitable means, a layer of silver 13 suitably disposed thereon, and a thin layer of silver iodide 14. An ice pellet 15 with the typical peaked center caused by the rapid freezing due to the silver iodide surface is also shown.
The thickness of the ice pellets as well as the size may be varied within wide limits depending, of course, upon the portion of water allowed to fall on the silver iodide surface. In addition, lower temperatures will cause quicker freezing of the water whereas temperatures closer to -10" C. will permit larger size pellets to be formed, due to the lower rate of reezing of the water.
The water, which is preferably though not essentially cooled, may be applied to the silver iodide surface by allowing it to drop onto the surface from a nozzle, or it may be allowed to flow in a continuous stream onto the cooled surface. It is desired to point out that, for optimum results, the amount of water added to a given area of the cooled silver iodide surface should not be so large as to cause the surface temperature'to rise above -10* C.
By means of our invention it is possible to make ice pellets of varying sizes and shapes which can be employed for use in applications requiring such frozen materials. It will, of course, be apparent to those skilled in the art that modifications of the abovedescribed invention may be made without departing from the scope of the invention and that all the matter set forth above is merely ilustrative and not limiting of the manner in which this invention may be practiced.
What we claim as new and desire to secure by Letters Patent of the United States is: 1. The process for making ice pellets which comprises placing water on a silver iodide surface maintained at a temperature at least as low as -100 C.
2. The process for making ice pellets which comprises placing water on a silver surface previously exposed to iodine vapors, the said surface being maintained at a temperature of at least as low as -10* C.
3. The process for manufacturing ice pellets which comprises (1) exposing the silver surface of a silver-plated metal to the vapors of iodine, (2) cooling the said silver-plated metal surface to a temperature of at least -10* C., and (3) allowing water to fall on the said cooled silver iodide surface.
4. In the process for manufacturing ice pellets by allowing water to impinge on a cold metal surface, the improvement which comprises permitting the water to fall on a silver iodide surface maintained at a temperature of from -10° to -70° C.
5. A composite surface adapted for making ice pellets, said surface comprising (1) a metallic member having good heat-transfer properties and containing cooling means therein, (2) a layer of metallic silver on the aforesaid surface (1), and (3) a thin layer of silver iodide positioned on the silver surface.
REFERENCES CITED The following references are of record in the file of this patent: UNITED STATES PATENTS Number 1,528,043 2,057,762 2,128,550 2,368,675 2,431,278 Name Date Bennett --_-------- Mar. 3, 1925 Boone et al. -------_ Jan. 25, 1935 Ford --.---------- Aug. 30, 1938 Mufly ---------____ _ Feb. 6, 1945 Raver ------------_ Nov. 18, 1947