DAL COL IVANO (IT)
PEROZZO GIANANGELO (IT)
DAL COL IVANO (IT)
| US3099914A | 1963-08-06 | |||
| GB940499A | 1963-10-30 | |||
| EP0204850A1 | 1986-12-17 | |||
| US2758150A | 1956-08-07 | |||
| EP0456216A2 | 1991-11-13 | |||
| FR2754128A1 | 1998-04-03 | |||
| FR1094486A | 1955-05-20 | |||
| US4358667A | 1982-11-09 | |||
| EP0660644A2 | 1995-06-28 | |||
| US4112410A | 1978-09-05 | |||
| US4432211A | 1984-02-21 | |||
| DE9416355U1 | 1994-12-08 |
| 1. | A resistance element for evaporators in refrigeration units comprising a resistive wire (4) surrounded by a layer of dielectric materai and housed in a sheath (6) of heatconducting material, to the ends of the sheath there being applied at least one temperature limiting element (12) and one temperature regulating element (10), characterised in that said elements have their sensitive part in contact with the sheath and are surrounded by a block of heatinsulating material. |
| 2. | A resistance element as claimed in claim 1, characterised in that both elements consist of bimetallic thermostats with different operating temperatures. |
| 3. | A resistance element as claimed in claim 1, characterised in that the regulating element consists of a temperature sensor and the limiting element consists of a temperature fuse. |
Resistance elements used for this purpose are known.
The resistance elements are currently mounted on the finned pack after which, but not necessarily, a thermostat and/or a safety temperature fuse able to sense ambient temperature are mounted.
The purpose of the thermostat is to prevent current passage on attaining a predetermined temperature, the purpose of the temperature fuse being to intervene if the thermostat does not operate, in which case overheating of the resistance element couid occur with consequent damage.
These known resistance elements have however certain drawbacks, and in particular : -the appliance manufacturer has to assemble the thermostat and the temperature fuse, with consequent time loss, -temperature control is not reliable in that as the thermostat senses ambient temperature, which is less than the temperature of the resistance element, it may not intervene when the temperature of the resistance element reaches the limiting value, but later. Because of this, plastic parts and components cannot be reiiably used in contact with the heating element, because of safety problems related to high temperature.
An object of the invention is to eliminate these drawbacks by providing a resistance eiement for evaporators in refrigeration units which reliably intervenes when the limiting temperature is exceeded.
Another object of the invention is to provide a resistance element which improves the effectiveness of the defrosting process by being able to operate at the correct temperature.
A further object of the invention is to provide a combined resistance element and temperature controls which is of small overall size.
These and further objects are attained according to the invention by a resistance element for evaporators in refrigeration units comprising a resistive wire surrounded by a layer of dielectric material and housed in a sheath of heat-conducting material, to the ends of the sheath there being applied at least one temperature limiting element and one temperature regulating element, characterised in that said elements have their sensitive part in contact with the sheath and are surrounded by a block of heat-insulating material.
The invention is described in detail hereinafter with reference to the accompanying drawing, on which : Figure 1 is a schematic view of the resistance element applied to an evaporator ; Figure 2 is a perspective view of the resistance element ; Figure 3 is a longitudinal section through the part by which the thermostat is fixed to the resistance element.
As can be seen from the figures the resistance element of the invention is indicated overall by 2 and consists of a resistive wire 4 covered with a glass fibre core which itself is covered with a layer of silicone, all housed in a tubular aluminium sheath 6.
Said resistance element 2, which extends with such a configuration as to enable it to adapt to the finned pack 8 of the evaporator, comprises at its ends a thermostat 10 and a temperature fuse 12.
The thermostat 10, which is of the bimetallic strip type, rests directly on the tubular sheath 6, and is enclose by a resin block 14 obtained by injection in a mould formed from two half-moulds provided with the corresponding impressions.
The thermostat has a maximum operating temperature less than the activation temperature of the fuse.
The device operates in the following manner.
At normally predetermined intervals the timer activates the resistance element which however can only operate if the thermostat positioned inside the refrigeration unit senses a temperature less than the limiting temperature.
From the aforegoing it is apparent that the resistance element of the invention provides numerous advantages, and in particular : -a smaller overall size than known assemble devices available commercially, -improved efficiency of the defrosting process as the temperature sensor measures the real temperature of the resistance element sheath, it being in contact with it and thermally insulated towards the outside, hence preventing the resistance element and those evaporator regions in contact with it from reaching too high a temperature and limiting defrosting to the time necessary, -it ensures correct current passage interruption on exceeding the set temperature, hence if this value is of a suitable level it enables components with a lower temperature limit to be used.
The description refers to an aluminium resistance element, however the invention can be applied to armoured resistance elements of steel construction in which the resistive wire is surrounded by magnesium oxide.