METHOD AND APPARATUS FOR DE-ICING A FAN

Abstract: The invention relates to a method for de-icing a fan (41) mounted in a freezer and comprising a fan motor and a fan housing (44) supporting the fan motor. The method comprises the step of mounting at least part of the fan (41) in a yieldable manner. An ice-cover formed on fan blades (40, 42) shakes loose during operation of the fan owing to the unbalance that arises. Moreover, there is provided an apparatus for de-icing a fan (41) mounted in a freezer and comprising a fan motor and a fan housing (41) supporting the fan motor. The apparatus comprises members (46) of the fan which are arranged yieldably to support at least part of the fan (41). An ice-cover formed on fan blades (40, 42) is shaken loose during operation of the fan owing to the arising unbalance.

Description: METHOD AND APPARATUS FOR DE-ICING A FAN The present invention relates generally to de-icing of machine parts, and more particularly to a method and an apparatus for de-icing a fan mounted in a freezer. Ice-formation and frost deposits on machine parts are in many fields a problem which is difficult to solve. Especially in refrigeration technology, frost deposits constitute a problem which owing to the continuous forma- tion thereof requires constant attention and a specific measures for checking the growth of frost and for removing ice from machine parts. For maintaining a satisfactory effect and availability of the freezer it is desirable that the number of stoppages for de-icing cooling-coil batteries, fans etc per unit of time be reduced. No con¬ tinuous defrosting of the entire freezer is available. Continuous de-icing of the cooling-coil batteries of a freezer, however, is prior art. The cooling-coil batteries are kept free from frost by blastwise injection of compressed air. Injection nozzles are mounted on a holder moving slowly back and forth along the cooling-coil bat¬ tery while the freezer is in operation. Since the cooling- coil batteries are kept almost free from ice, the time between planned service intervals can be extended signi- ficantly. Still longer service intervals could be obtain¬ ed, if the fans of the freezer were also de-iced continu¬ ously. Owing to ice-formation on the fan blades, the flow of air inside the freezer decreases as the degree of frost increases. In other fields, such as in aircraft engineering, there are problems with ice-formation on aircraft wings, propellers etc. Besides using de-icing agents, EP 224,941 discloses the supplying of pulses to the interior of a wing, whereby any ice that is present on the wing cracks and slides off. Mechanical actuation for removing ice coatings is also known from cableways whose track ropes must be kept free from ice. In freezers, it is known, in addition to the above technique comprising pulsating blasts of air, from US-A- 4,585,849 to dehydrate the return air in the freezer so as to reduce the ice-forming tendency. However, this solution does not deal with the problem directly but merely reduces the effects. Since the problem with defrosting of cooling-coil batteries must be considered to be solved, there remains but the problem with de-icing of fans. One object of the present invention therefore is to suggest a method for de-icing a fan mounted in a freezer. A further object of the present invention is to pro¬ vide an apparatus for automatically de-icing a fan mounted in a freezer. Moreover, it should be possible to mount the appar¬ atus according to the present invention in an existing freezer. According to the invention, these and other objects are achieved by a method of de-icing a fan mounted in a freezer and comprising a fan motor and a fan housing supporting the fan motor, said method being characterised by the step of mounting at least part of the fan in a yieldable manner, an ice-cover formed on fan blades shak¬ ing loose during operation of the fan, owing to the aris¬ ing unbalance and vibrations resulting therefrom. For achieving the above-mentioned objects and for carrying out the method according to the invention, there is also provided an apparatus for de-icing a fan mounted in a freezer and comprising a fan motor and a fan housing supporting the fan motor, said apparatus being charac¬ terised by members of said fan which are arranged yield- ably to support at least part of the fan, an ice-cover formed on fan blades shaking loose during operation of the fan, owing to the arising unbalance and vibrations result¬ ing therefrom. In a preferred embodiment of the present invention, the members are made of a cold-resistant rubber mixture and are connected by fastening means on the one hand to the fan body and, on the other hand, to the fan attach¬ ment, and a fan blade has a local increase in weight for producing unbalance in the fan, thereby immediately pre¬ venting ice-formation. The present invention will now be described in more detail, with reference to the accompanying drawings in which: Fig. 1 is a schematic cross-sectional view of a freezer, Fig. 2 is a cross-sectional view of a fan for the freezer illustrated in Fig. 1, and of a first embodiment of the present invention, Fig. 3 is a view, corresponding to Fig. 2, of a second embodiment of the present invention, and Fig. 4 illustrates a fan having a means according to the invention, which produces unbalance. Fig. 1 is a schematic cross-sectional view of a freezer 2. The freezer 2 comprises a first compartment 4, the top face of which is formed with an inlet 6. Further there are a first freezing chamber 8 and a second freezing chamber 10. Finally, a second compartment 14 having in its top face an outlet 12 is arranged in the freezer 2. The first compartment 4 communicates via an opening 16 in a side wall 18 with the first freezing chamber 8. This communicates, via an opening 20 in a side wall 22 facing away from the opening 16, with the second freezing chamber 10 which, in turn, communicates with the second compart¬ ment 14 via an opening 24 in a side wall 26 facing away from the opening 20. For conveying products from the inlet 6 of the first compartment to the outlet 12 of the second compartment, there are arranged a plurality of conveyors 28, 30, 32 and 34. In the first and second freezing cham- ber 8, 10, the products are frozen. Fans 36 in each of the freezing chambers cause a refrigerant to circulate which passes a cooling-coil battery 38 for absorbing the heat of the products while contacting them. Owing to a number of factors, such as different products qualities, frost is formed on the cooling-coil battery and the fans. Fig. 2 illustrates a first embodiment of the present invention. For automatic de-icing of fan blades 40, 42 of a fan 41, a fan housing 44 of the fan 41 is yieldably attached to the freezer 2. As is evident from Fig. 2, this is accomplished by a spacing piece 46 preferably made of a yieldable material and supporting the fan housing 44 spac¬ ed from the freezer 2. The spacing piece 46 is attached by bolts 43A, 43B and 47A, 47B, respectively, to the freezer 2 and the fan body 45. The same technical effect is provided by the embodi¬ ment shown in Fig. 3. Here, too, a differently designed fan housing 50 of a fan 51 is supported by spacing pieces 52 spaced from the freezer or an attachment 48. The spacing piece 46 illustrated in Fig. 2 preferably is a single piece and is shaped so as to follow the outer contour of a fan body 45 which is used to mount the fan 41. This embodiment is particularly useful when the fan housing 44 which accommodates a fan motor (not shown) is mounted outside the freezing chamber so that a fan shaft 60 extends through a freezing chamber wall 3 of the freezer 2, the spacing piece 46 establishing a yieldable seal between the freezing chamber and the surroundings. When supplementing existing freezers with the de- icing apparatus according to the present invention, the embodiment shown in Fig. 3 is particularly useful, since existing fastening points can be used. The spacing piece 52 is then introduced in the form of a yieldable insert between a fan body 55 of the fan housing 50 and the attachment 48 of the freezer and is attached by bolts 54A, 54B and 56A, 56B, respectively. During operation of the freezer, the ice-cover formed on the fan blades 40, 42 produces unbalance which results in vibrations of the entire fan. Through these vibrations, the ice-cover is shaken loose from the fan blades, and the freezer operating time between service intervals can thus be extended. Owing to the spacing piece 46 and 52, respec¬ tively, the vibrations of the fan are not transmitted to the freezer 2 or the attachment 48. Fig. 4 shows two fan blades 58, 59 of a fan which have the same contour and the same cross-sectional shape. One fan blade, however, has an area 62 of higher density, which preferably is spaced from the fan shaft 60. In this area, an increase in weight thus is produced, which when putting the fan into operation results in unbalance and, consequently, causes the fan to vibrate. Those skilled in the art will appreciate that the yieldable spacing pieces may be designed in a different manner and may comprise, for example, springs which like the spacing pieces described above are positioned between the fan housing or the fan body and the freezer or the attachment. It is further possible to mount the fan motor resiliently in the fan housing, whereby no spacing piece is required between the fan housing and the freezer or the attachment. Also the above-mentioned, artificially produced unbalance in the form of an increase in weight in a restricted area of a fan blade can be accomplished in some other way. Thus, it is possible to bend the fan shaft in such a manner that, during operation of the fan, it follows the circumferential surface of a cone. All these variants and changes which fall within this scope of the inventive concept are thus intended to be covered by the accompanying claims.

Claims: CLAIMS 1. Method for de-icing a fan (36; 41; 51) mounted in a freezer (2) and comprising a fan motor and a fan housing (44; 50) supporting said fan motor, c h a r a c t e r i s e d by the step of mounting at least part of the fan (36; 41; 51) in a yieldable manner, an ice-cover formed on fan blades (40, 42; 58, 59) shaking loose during operation of the fan, owing to the arising unbalance and vibrations resulting therefrom. 2. Method as claimed in claim 1, c h a r a c ¬ t e r i s e d by the step of arranging in said fan a means (62) producing unbalance, thereby preventing immedi- ate ice-formation on the fan. 3. Method as claimed in claim 1, c h a r a c ¬ t e r i s e d by the step of connecting blades of the fan with a curved shaft whose longitudinal axis, when putting the fan into operation, performs a motion which follows the circumferential surface of a cone. 4. Apparatus for de-icing a fan (36; 41; 51) mounted in a freezer (2) and comprising a fan motor and a fan housing (44; 50) supporting said fan motor, c h a r a c ¬ t e r i s e d by members (46; 52) of said fan which are arranged yieldably to support at least part of said fan, an ice-cover formed on fan blades (40, 42; 58, 59) being shaken loose during operation of the fan, owing to the arising unbalance and vibrations resulting therefrom. 5. Apparatus as claimed in claim 4, c h a r a c - t e r i s e d in that said members (46; 52) preferably are made of a cold-resistant rubber mixture and are connected by fastening means (43A, 43B, 47A, 47B; 54A, 54B, 56A, 56B) on the one hand to the fan body (45; 55) and, on the other hand, to the fan attachment (3; 48) in said freezer, said members (46; 52) preventing direct contact between the fan (41; 51) and the freezer (2), thereby preventing the vibrations of the fan from being transmitted to the freezer. 6. Apparatus as claimed in claim 5, c h a r a c ¬ t e r i s e d in that said members (46) establish a yieldable seal between said fan body (45) and a casing (3) surrounding a freezing space. 7. Apparatus as claimed in claims 4-6, c h a r a c ¬ t e r i s e d in that the impeller is suspended from the fan body in an oscillating manner. 8. Apparatus as claimed in claim 4, c h a r a c ¬ t e r i s e d in that said members comprise spring ele¬ ments arranged between the fan motor and the fan housing (44; 50) and preventing transmission of vibrations to the fan housing fixedly mounted at the freezer. 9. Apparatus as claimed in any one of claims 4-8, c h a r a c t e r i s e d by a means (62) producing un¬ balance, which is a local increase in weight at the end of a fan blade (59) facing away from the fan shaft (60).

Inventors: LOEFKVIST CHRISTER, LUNDQVIST THOMAS, LOEFKVIST, CHRISTER, LUNDQVIST, THOMAS
Applicants: FRIGOSCANDIA CONTRACTING AB
Application year: 1990
Main classification: F04D29
IPC codes: F04D29, F25D17, F25D21, F28F17