Shell ice is formed on 6" diameter stainless steel tapered evaporators. Water cascades across both the inner and outer tube surfaces, which allows the machine to operate efficiently. Once the desired ice thickness has been reached (operator adjustable), the automatic controls will terminate the flow of liquid refrigerant to the evaporators and initiate the flow of hot gas refrigerant. The introduction of hot gas forms a thin layer of water between the ice and the tube surface allowing gravity to pull the ice easily off the evaporator tubes. As the ice slides off the tubes, the discharge auger (or beater bar depending on the style of icemaker) removes the ice from the machine. Once again, gravity or another mechanical delivery device will take the ice to storage. Any free water on the shell ice surface will quickly refreeze on the sub-cooled shell ice, leaving dry, hard ice fragments.
Unlike other types of icemakers, where cutters or scrapers are used to remove the ice, the shell ice machine uses the reverse refrigeration cycle and gravity (described above), so fewer mechanical parts are required. An auger or a beater bar assembly (depending on the machine style) is used to remove the fallen ice from the machine. The ice machine can produce a variety of ice types ranging from a hard, clear, pure-water ice to a soft, white, seawater ice, each of which has advantages for different applications. Due to the nature of the freezing surface on which the ice is formed, shell ice is easy to handle. The curvature of the ice prevents the formation of solid fusing or bonding while in storage, enabling the ice to be mobilized easily once disturbed.
*Note: This operating principle describes the Berg Shell Icemaker. Other shell ice machines might work differently and produce different results.