Flake ice is made in this sheets approximately 1.5-6.0 mm thick. The sheets may be curved or flat and the thin ice is generally broken into random-sized flakes when harvested.
Flake ice is particularly suitable for packing products such as fish or frozen foods as the ice flakes can be packed close to the products. In other applications such as chemical processing and concrete cooling, where rapid cooling is important, flake ice is ideal because the flakes present the maximum amount of cooling surface for a given amount of ice.
Flake ice is commonly produced by the application of water to the inside or outside of a refrigerated cylindrical drum. The water is applied at a first angular location on the datum and adheres thereto in a thin layer by surface tension. As the drum rotates, the water freezes into a thin layer of ice, which is fractured by an ice removal device at a second angular location downstream from the first angular location in the direction of rotation.
The thickness of the flake ice can be varied by adjusting the speed of the rotating drum, varying the evaporator temperature, and regulating the water flow on to the freezing surface. Since flake ice can be made in a continuous operation without being interrupted for a harvest cycle, less refrigeration tonnage is required to produce a tonne of ice than any other type of manufactured ice when similar make up water and evaporating temperatures are compared.
In known machines, water is applied to only one side of the drum, i.e. either the outside or inside, but not both. As a result, the refrigerated surface on the other side of the drum is unused, and the ice making operation represents an inefficient use of the refrigeration capacity of the machine.
Furthermore, as the ice removal device is located only on the side of the drum on which ice is formed, the continual unbalanced force applied to that side of the drum to fracture the ice from the freezing surface accelerates the wear on the drum bearings.
A further disadvantage of known ice making machines of the drum type is that their capacity cannot be readily increased. If increased capacity is desired, it is usually necessary to install a whole new machine. That is, in addition to installing an extra refrigerated drum, it is also necessary to install another refrigeration unit including motor, compressor and condensor, and a new drive unit. Any upgrading in capacity will therefore involve considerable expense.
With a view to overcoming the above described problems and increasing the production capacity of ice making machines, it has been proposed to use refrigerated discs. U.S. Pat. No. 3,863,462 describes a large scale flake ice producing machine which comprises one or more upright refrigerated discs rotatable on a horizontal shaft. Water or other congealable liquid is applied to both surfaces of the disc and frozen into sheets of ice as the disc rotates. Thereafter, the sheets are removed from disc in ice flakes. Each disc is approximately 1.8 m in diameter and comprises a pair of large round aluminium plates spaced apart about 20 mm and sealed at their periphery to form an enclosed space. Baffles are placed within the interior of the space to form rudimentary passages through which a coolant is pumped in order to refrigerate the disc surfaces.
However, the flake ice producing machine of U.S. Pat. No. 3,863,462 possesses several inherent disadvantages, including:
(a) Due to the large flow passages inside the disc, it is necessary to use a non-evaporative coolant such as brine or glycol. That is, a "boiling" or evaporative refrigerant which cools by direct expansion is not suitable for use in the disc of U.S. Pat. No. 3,863,462. Brine and glycol have low cooling capacity and large amounts of such coolants must be pumped through the disc in order to achieve the required cooling. PA1 (b) Since a coolant such as brine or glycol must be used, a separate refrigeration plant is required in order to chill the brine or glycol. PA1 (c) The discs are difficult to manufacture according to the tolerances required. The 1.8 m diameter discs must be cast and machined, and welded at their periphery, yet the flat outer surfaces of the discs must not vary from the plane in which they rotate by more than 1/8 mm.
For the foregoing reasons, the ice making machine of U.S. Pat. No. 3,863,462 is not considered to be commercially acceptable.
It is an object of the present invention to overcome or ameliorate at least some of the abovedescribed disadvantages of the prior art by providing an improved ice making machine.
It is another object of the present invention to provide an improved refrigerated disc for use with the ice making machine.