A common design for a cube ice-making machine includes a vertical ice-forming mold. The mold has dividers that create individual pockets. When the pockets are sufficiently filled with ice, the control system for the machine switches into a harvest cycle. The ice cubes are released from the mold. The dividers may be sloped downward toward the open front so that the ice cubes slide out of the ice-forming mold under the influence of gravity, and into the ice collection bin.
The ice-making machine also includes a sump located beneath the ice-forming mold, a water distributor above the ice-forming mold, and a pump to transfer water from the sump up to the distributor. The water cascades down over the surface of the ice-forming mold. A part of the water freezes into the pockets and the rest runs off the surface of the ice-forming mold. A water curtain is placed adjacent to the ice-forming mold so that any splashing water is directed back into the sump. The bottom edge of the water curtain is bent to reach back under the ice-forming mold. This allows the front edge of the sump to be spaced behind the front of the ice-forming mold. With this design, the unfrozen water can return to the sump, but ice can fall straight down out of the ice-forming mold and into the collection bin.
The water curtain is typically suspended from pivots or hinges located near the top of the water curtain. The shape of the water curtain and location of the pivots are such that the center of gravity of the water curtain causes the sides of the water curtain to stay closed against the ice-forming mold frame while the machine is making ice. However, during the harvest cycle the water curtain can swing away as the ice is released from the ice-forming mold.
A common technique for shutting down the ice-making machines when the bin is full is to place a sensor, such as a magnetic reed switch, near the water curtain, and put a magnet on the water curtain. The reed switch can then determine whether the water curtain is closed. This reed switch has two uses. First, when the water curtain closes, the machine can automatically switch back into an ice-making mode from a harvesting mode. Second, if ice has built up in the bin such that the slab of ice being harvested does not fall all of the way past the bottom edge of the water curtain, the water curtain will remain open, and the reed switch will not close. If the water curtain stays open for a sufficient amount of time, the ice machine shuts down and the “bin full” condition starts.
During a freeze cycle, a thin bridge of ice forms over the dividers and between the individual cubes of ice. Most automatic ice-making machines allow for adjustment of the duration of the freeze cycle, which thus controls how thick this ice bridge becomes. A common control technique is to mount an ice thickness sensor so that as the ice bridge gets thicker, water running over the surface of it will contact a probe, directing the machine to automatically go into a harvest cycle. A thick ice bridge has the benefit that it helps in the harvest cycle, when water stops cascading over the front of the ice and the ice-forming mold is heated. A thick ice bridge allows the entire slab of interconnected ice cubes to be released at once. On the other hand, with a thin ice bridge, individual cubes have to each melt and drop out of their pockets, and adjoining cubes cannot help pull all of the ice out at once.
While thicker ice bridges have some benefits, there are also some drawbacks. Because ice is an insulator, the efficiency of the freezing operation decreases as the ice bridge builds, since the heat is commonly transferred out of the back of the ice-forming mold by serpentine refrigerant coils forming the evaporator section of a refrigeration system. Most importantly, many end users do not want thick ice bridges, because the slabs of ice cubes do not break into individual cubes as easily, and chunks of ice cubes frozen together are hard to dispense, scoop or fit into a cup.
Accurate control of ice bridging can be effective in providing properly sized ice cubes for the user. Care must be taken, however, to avoid the inadvertent freezing together of the ice cubes once they are delivered to the ice bin. Water going down the face of the ice-forming mold may fall into the ice bin rather than being directed by the bottom of the water curtain back into the sump. The leakage of water into the ice bin can cause the ice cubes in the ice bin to freeze together, or create wet ice in the ice bin. Also, for those machines that do not add water during the freeze cycle, and go into harvest when the water level drops to a predetermined point, the loss of water from the water recirculation system will result in less ice being made in each cycle. Accordingly, a need existed for an improved water curtain and ice machine that minimizes the leakage of water into the ice bin of an ice machine.