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  • The valve is only open for about seven seconds; it lets in just enough water to fill the ice mold. The ice mold is a plastic well, with several connected cavities. Typically, these cavities have a curved, half-circle shape. Each of the cavity walls has a small notch in it so each ice cube will be attached to the cube next to it.

  • Once the mold is filled, the machine waits for the water in the mold to freeze. The cooling unit in the refrigerator does the actual work of freezing the water, not the icemaker itself (see How Refrigerators Work for details). The icemaker has a built-in thermostat, which monitors the temperature level of the water in the molds. When the temperature dips to a particular level -- say, 9 degrees Fahrenheit (-13 degrees Celsius) -- the thermostat closes a switch in the electrical circuit (see How Home Thermostats Work for details on this operation).

  • Closing this switch lets electrical current flow through a heating coil underneath the icemaker. As the coil heats up, it warms the bottom of the ice mold, loosening the ice cubes from the mold surface.

  • The icemaker has a heating coil underneath the ice mold.

    • The electrical circuit then activates the icemaker's motor. The motor spins a gear, which rotates another gear attached to a long plastic shaft. The shaft has a series of ejector blades extending out from it. As the blades revolve, they scoop the ice cubes up out of the mold, pushing them to the front of the icemaker. Since the cubes are connected to one another, they move as a single unit.

    • At the front of the icemaker, there are plastic notches in the housing that match up with the ejector blades. The blades pass through these notches, and the cubes are pushed out to a collection bin underneath the icemaker.

    • The revolving shaft has a notched plastic cam at its base. Just before the cubes are pushed out of the icemaker, the cam catches hold of the shut-off arm, lifting it up. After the cubes are ejected, the arm falls down again. When the arm reaches its lowest resting position, it throws a switch in the circuit, which activates the water valve to begin another cycle. If the arm can't reach its lowest position, because there are stacked-up ice cubes in the way, the cycle is interrupted. This keeps the icemaker from filling your entire freezer with ice; it will only make more cubes when there is room in the collection bin.
    This system is effective for making ice at home, but it doesn't produce enough ice for commercial purposes, such as restaurants and self-service hotel ice machines. In the next section, we'll look at a larger, more powerful icemaker design.

    Commercial Icemakers
    There are any number of ways to configure a large, free-standing icemaker -- all you need is a refrigeration system, a water supply and some way of collecting the ice that forms.

    One of the simplest professional systems uses a large metal ice-cube tray, positioned vertically. You can see how this system works in the diagram below.

    In this system, the metal ice tray is connected to a set of coiled heat-exchanging pipes like the ones on the back of your refrigerator. If you've read How Refrigerators Work, then you know how these pipes work. A compressor drives a stream of refrigerant fluid in a continuous cycle of condensation and expansion. Basically, the compressor forces refrigerant through a narrow tube (called the condenser) to condense it, and then releases it into a wider tube (called the evaporator), where it can expand.

    Compressing the refrigerant raises its pressure, which increases its temperature. As the refrigerant passes through the narrow condenser coils, it loses heat to the cooler air outside, and it condenses into a liquid. When the compressed fluid passes through the expansion valve, it evaporates -- it expands to become a gas. This evaporation process draws in heat energy from the metal pipes and the air around the refrigerant. This cools the pipes and the attached metal ice tray.

    The icemaker has a water pump, which draws water from a collection sump and pours it over the chilled ice tray. As the water flows over the tray, it gradually freezes, building up ice cubes in the well of the tray. When you freeze water layer by layer this way, it forms clear ice. When you freeze it all at once, as in the home icemaker, you get cloudy ice (see this Question of the Day for more information).

    After a set amount of time, the icemaker triggers a solenoid valve connected to the heat-exchanging coils. Switching this valve changes the path of the refrigerant. The compressor stops forcing the heated gas from the compressor into the narrow condenser; instead, it forces the gas into a wide bypass tube. The hot gas is cycled back to the evaporator without condensing. When you force this hot gas through the evaporator pipes, the pipes and the ice tray heat up rapidly, which loosens the ice cubes.

    Typically, the individual cube cavities are slanted so the loosened ice will slide out on their own, into a collection bin below. Some systems have a cylinder piston that gives the tray a little shove, knocking the cubes loose.

    This sort of system is popular in restaurants and hotels because it makes ice cubes with a standard shape and size. Other businesses, such as grocery stores and scientific research firms, need smaller ice flakes for packing perishable items. In the next section, we'll look at a typical flake icemaker design.

    Flake Icemakers
    In the last section, we looked at a standard cube icemaker design. Flake icemakers work on the same basic principle as cube icemakers, but they have an additional component: the ice crusher. You can see how a typical flake system works in the diagram below.

    Like the cube icemaker design we examined in the last section, this machine uses a set of heat-exchanging coils and a stream of water to build up a layer of ice. But in this system, the coils are positioned inside a large metal cylinder. Water passes through the cylinder, as well as around its outer edges. The passing water gradually builds up a large column of ice surrounding the cylinder from the inside and outside.

    As with a cube icemaker, a solenoid valve releases hot gas into the cooling pipes after a set length of time. This loosens the ice column so it falls into the ice crusher below. The ice crusher breaks the ice cylinder into small pieces, which pass on to a collection bin.

    The size of the ice bits depends on the crusher mechanism. Some crushers grind the ice into fine flakes, while other crushers produce larger, irregularly shaped ice chunks.

    There are many variations on these designs, but the basic idea in all of them is the same. A refrigeration system builds up a layer of ice, and a harvesting system ejects the ice into a collection bin. At the most basic level, this is all there is to any icemaker.

    For more information on icemakers and related topics, check out the links on the next page.

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