It is known from US Patent No. 4,551,159 to produce ice crystals in brine by: * passing the brine into a cooled ice generation cylinder, scraping away from the cooled wall of the cylinder both any ice crystals formed on the wall and the brine cooled against the wall by means of a scrapper continuously rotated around the wall, allowing ice crystals to form in the cylinder and * removing the brine and ice from the cylinder.

Other aqueous solutions than brine can be used. Normally, the brine will be pre- cooled below O°C prior to passing to the ice generation cylinder.

Production of ice by this method is limited by the rate of heat transfer from the brine via the cooled cylinder. Conventionally, stainless steel cylinders have been used. However, stainless steel is a relatively poor thermal conductor, with the result that for a given heat flux, the external wall of the cylinder must be cooled to a lower temperature than would otherwise be necessary for a metal having a higher conductivity. Nevertheless, the aggressively corrosive nature of brine has appeared to render use of other metals highly undesirable. The problem of corrosion is alluded to in US Patent No 5,383, 342, where a magnet at the inlet to the ice generation cylinder is said to reduce corrosion. Further it is known that aluminium should not be used for sea water heat exchangers on board ship.

However, we have experimented with aluminium ice generation cylinders and surprisingly found that corrosion can be avoided. Since the conductivity of aluminium is an order of magnitude higher than that of stainless steel, we are anticipating substantial improvements in thermal efficiency. In particular since we expect to be able to cool the outside of the cylinder with refrigerant at a higher temperature than previously, we expect to be able to use smaller refrigeration equipment for the same ice output. This is a further surprising advantage.

According to the invention there is provided a flowable ice producing machine, the machine comprising : a refrigeration unit for supplying cold refrigerant ; an ice generation cylinder having: an inner cylinder having an internal bore for ice generation, the outer surface of the inner cylinder being arranged for cooling thereof by the cold refrigerant, scraping means for scraping ice formed in the internal bore and * a pump for pumping aqueous solution to the cylinder and ice from the cylinder; wherein the cylinder is of aluminium or light alloy.

Preferably, the ice generation cylinder includes an outer cylinder and end plates welded to the inner cylinder to provide an outer cooling space for receiving the refrigerant to cool the cylinder In order to avoid electrolytic corrosion of the cylinder, it is preferably isolated, by use of plastics material end caps and one or more plastics material scrappers in contact with the bore.

Preferably, the internal bore is treated to provide a surface layer isolating the aqueous solution. This can enhance the isolation of the corrosion prone metal of the cylinder from the aqueous solution. Further it can enhance the hardness and lower the surface coefficient of friction, both of which are advantageous as regards the scraper in contact with the bore.

The preferred surface treatment is hard anodising. Preferably this is augmented by deposition of a friction reducing substance, in particular PTFE.

Alternatively, the friction reducing substance can be used without initial hard anodising.

The cylinder is preferably honed prior to hard anodising and subsequently polished again in a honing machine.

To enhance heat transfer between the inner cylinder and the refrigerant, the outer surface of the cylinder can be provided with surface undulations, such as ribs or fins. Alternatively, a similar effect can be achieved that the outer surface has shallow porosity.

To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a block diagram of an ice producing machine of the invention ; Figure 2 is a cross-sectional view of an ice generator of the machine of Figure 1; and Figure 3 is a cross-sectional end view on the line III-III in Figure 2 of a finned variant.

The ice producing machine shown in the drawings is arranged for use on board ship, as will be apparent from the use of sea water. However, its adaptation for use on land will be apparent to the man skilled in the art. It has a refrigeration unit 1, including: a compressor 11 for compressing evaporated refrigerant 10; a a condenser 13 for condensing the compressed gaseous refrigerant 3 to liquid 4, the condenser being cooled by sea water 5; * a refrigerant heat exchanger 15 for further cooling the liquid refrigerant with spent gaseous refrigerant 6 ; evaporation valves 17,18 downstream of both an ice generator 2 and a sea water pre-cooler 21, the spent refrigerant 6 from the ice generator and the evaporation valve 17 passing to the refrigerant heat exchanger 15 to cool the liquefied refrigerant below the sea water temperature to which it was cooled in the condenser and thence back to the compressor, whilst the spent refrigerant 7 from the sea water pre-cooler 21 passes directly back to the compressor.

The man skilled in the art will appreciate that control of the refrigerant unit will require a number of conventional components, which have not been further described since they are essentially conventional.

The ice generator 2 includes an inner aluminium cylinder 22, having an outer cooling space provided around it by an outer cylinder 23 and end plates 24, all these parts being of aluminium and welded together. The internal bore 25 is hard anodised and PTFE treated. Its production will be described in more detail below. The cylinder has upper and lower, plastics material end caps 26,27, each including a brine passage 28 and a bearing 29 sealed 30 from the interior of the generator and supporting a shaft 31 passing therethrough. This shaft supports a pair of upper and lower scrapers 32, which are driven in rotation around the internal bore 25 of the cylinder 22. The scrapers are pivotally supported on and extend forwards in the direction of rotation from radial studs 33 fast with the shaft in such a way that water pressure on them due to rotation urges their edges into scrapping contact with the internal bore 25. A motor 34 is provided on the upper cap 26 for driving the scrapper shaft. The latter and the studs 33 are of stainless steel, but the scrapers 32 are of plastics material. Thus it can be seen that the aluminium of the ice generating cylinder is not in electrolytic contact with any other metallic component in contact with brine within the cylinder.

In use, brine 8-in fact sea water-is pumped 35 through the pre-cooler 21, where it is cooled to below 0°C by the refrigerant. The brine is passed into the ice generation cylinder 22, where it is cooled further in contact with the interior 25 of the cylinder. The brine and any ice crystals forming are continuously scraped from the interior bore by the scrappers, which traverse the entire inside surface of the cylinder between the end caps. Ice crystals form and grow in the body of the brine in the cylinder. The crystals and remaining brine 9 is driven from the generator by the action of the pump 35.

The refrigerant 8 fed to the aluminium ice generator 2 can be at-10&C, which compares with-19&C as would be required for an equivalent stainless steel ice generator. This enables the machine to utilise a small, more economic refrigeration

unit. Alternatively, an increase of the order of 40% more ice output can be achieved for the same refrigeration energy input.

The aluminium cylinder 22 is of AlMg3 SiO. 5 and was honed truly parallel to a surface roughness of Rz < 0. 31lm. Then it was hard anodised, with PTFE treatment, to a thickness of 50 u. m. Again it was polished to a surface roughness of Rz= 0. 6pLm.

The scrappers are of polyamide and set up with their pivot axes and the central axis of the shaft 31 truly parallel with the central axis of the cylinder. With this treatment, no corrosion of the cylinder is experienced and good ice production is achieved.

The variant shown in Figure 3 has longitudinally extending fins 50, which increase the outer surface area of the inner cylinder and enhance its heat transfer properties. This is further enhanced by rendering the outer surface porous to a depth of Imm The invention is not intended to be restricted to the details of the above described embodiment. For instance where the bore of the inner cylinder is not to be hard anodised, a different aluminium alloy which is suitable for direct deposition of PTFE can be used.