The present invention relates to automatic ice making machinery, and particularly to an improved, combined evaporator/ice forming assembly made from integral refrigeration tubing sections and ice forming pocket elements.
Automatic ice making machinery is commonplace. Ice machines are found in food service establishments, hotels and other places where large quantities of ice are needed on a continuing basis. Some ice machines produce flaked ice, while others produce ice cubes of a variety of shapes. The present invention relates to ice machines that make cubed ice.
Automatic cube ice machines generally comprise a refrigeration system (compressor, condenser and evaporator), a plurality of ice formation pockets (usually in the form of a grid of cells) and a water supply system. A typical ice machine has the evaporator section of the refrigeration system connected to the ice formation pockets so that the pockets are directly cooled by the refrigeration system. Water may either be supplied to fill the pockets in a static relationship, or may be trickled over or sprayed into the pockets, with the run-off being recirculated. When clear ice cubes are desired, the spray or trickle methods are used, since static freezing produces white ice.
In a typical cube ice machine, when the supply of previously created ice is insufficient, automatic controls cycle the machine through ice production and harvest modes. In the production mode, the refrigeration system operates in a normal manner, and expanding refrigerant in the evaporator section removes heat from the ice forming pockets, freezing the water to form an ever growing layer of ice. When the ice thickness reaches a preset condition, such as contacting an ice sensor, the machine goes into a harvest mode. Typically this involves a valve change so that hot refrigerant gases are directed to the evaporator section. The ice forming pockets are thus heated until the ice next to the pocket surfaces thaws. Weep holes are provided in each ice pocket (or cell) so that air is allowed to enter the back of the cell, preventing a vacuum from forming, allowing the ice to fall out the front of the cell. The valving in the refrigeration system is then changed back to its original configuration and the cycle repeats.
In some prior art cube ice machines, such as those disclosed in U.S. Pat. No. 3,280,588 to Brindley, the ice forming pockets are created by bonding evaporator tubes and partitions to a base wall. Such a structure, even if welded together, will not have a homogeneous cross section. The metal making up the original parts will have grain boundaries at the edges of the original parts. Even if disrupted during a welding process, the grain structure will evidence a welding of various parts.
Nickel- or tin-plated copper is most commonly used for the ice forming pockets in cube ice machines today. Such pockets may be formed by fitting notched strips of copper together in an "egg crate" relationship to form a grid of four sided pockets. The strips are then soldered to a backing pan. At the same time a serpentine piece of copper tubing (forming the evaporator section of the refrigeration system) can be soldered to the back of the pan. The entire evaporator/ice forming assembly is then nickel or tin plated. The plating is required by National Sanitation Foundation (NSF) codes, which prohibit the use of copper parts in contact with food products.
While plated copper assemblies work well in cube ice machines, they have several drawbacks. One of the primary problems is that the plating operation itself is costly, and typically produces sludge that is costly to dispose of in an environmentally safe manner. Also, copper is relatively expensive. Further, though it has very good heat conduction properties, copper is dense, so that it has a high heat capacity per unit volume. The duration of the production/harvest cycle is thus longer than desired because, at each change in the cycle, the copper ice forming pockets have to be either heated or cooled.
Another disadvantage of assemblies made from bonded parts, including plated copper assemblies, is that structures made from bonding different parts together usually suffer a heat transfer impediment. Usually, two elements may not be perfectly joined because the elements are not perfectly flat or otherwise matched in profile, and the presence of dust particles or oxides may cause surface irregularities decreasing thermal conduction at those locations. Further, because air has poor conducting properties, the presence of air pockets in two bonded elements may also reduce thermal conduction.
In attempting to overcome these disadvantages, a cast aluminum grid was experimented with. Cast aluminum was found to present several drawbacks. Primarily, even though the ice cube pockets could easily be formed in the casting, the evaporator system tubing had to be attached after the casting operation. This proved to be unworkable because the cast aluminum was so porous that the tubing could not suitably be brazed to the casting.