GB2367227A

GB2367227A - Method of producing electrical resistors and resistors produced thereby

Info

Publication number: GB2367227A
Application number: GB0023228A
Authority: GB
Inventors: Franco Gianoglio
Original assignee: HT SpA
Current assignee: HT SpA
Priority date: 2000-09-21
Filing date: 2000-09-21
Publication date: 2002-03-27
Anticipated expiration: 2020-09-21
Also published as: GB0023228D0; GB2367227B

Abstract

An electrical resistor is provided with an outer housing (10) consisting of a substantially cylindrical element inside which a blind hole (11) is provided having a substantially elliptical cross-section which is flattened adjacent to the minor diagonal, thus substantially appearing 8-shaped. The blind hole (11), which provides two elongated parallel seats joined by a central narrow portion, receives conductor (12) which consists substantially of a U-shaped thread-like element which is frontally fitted in the two elongated seats. The conductor projects outwards with the two ends or connectors (13) which permits connection of the resistor to an electric plant or system. The single piece housing of the resistor achieves improvements in assembly. Moreover, the resistor can be of higher quality by having a single-piece housing which is aesthetically preferable and also provides improved resistance to the mechanical and thermal stresses imparted on heating.

Description

METHOD OF PRODUCING ELECTRICAL RESISTORS AND ELECTRICAL RESISTORS PRODUCED THEREBY The present invention relates to a method of producing electrical resistors, for example armoured electric resistors, with a single-piece frontally fitted housing. The preferred method can make the assembly operations of electrical resistors easier and can provide a single-piece housing having a blind hole in which the resistor is fitted, the resistor then being locked by means of a suitable resin-based or cement-based sealant or the like.

Electrical resistors generally consist of a substantially cylindrical ceramic housing in which the resistive coil forming the heating means is fitted, the heating means being fed by an electrical current supplied through connectors and/or thimbles and/or electric cables welded to the resistor ends.

More precisely, with reference to Figures I to 3, prior art electrical resistors comprise a cylindrical housing 1 having several holes 2 being parallel to one another and longitudinally arranged relative to the body 1. The resistive coil 3 is fitted into these holes, and generally consists of a spiral-wound wire, made of a suitable material, which is folded and fitted into the body 1, by inserting the wire end into the holes 2, so that the two ends extend out of the opposite side with the connectors or cables or thimbles, which are placed outside the casing to be connected to the current supply. On the side of the housing 1 from which the resistor has been inserted it is necessary to attach a locking member consisting of a cap 5 which is sealed by means of sealing resin or cement or the like, while the conductor 3 remains inside the hole 2, which then can be filled with magnesium oxide to help the heat transmission.

These resistors, which are largely used with good results in all electric heating apparatus, are quite complex to manufacture, since to assemble them it is necessary to provide a housing comprising a plurality of pieces which then have to be joined together after the insertion of the conductor and the resistive coil. Consequently, higher expenditure of time and labour is necessary to provide the end product, although this is a very simple and little expensive device. Furthermore, the achieved result is not satisfactory because assembling a housing comprising a plurality of pieces on one hand negatively affects the aesthetic features of the product and on the other hand it involves the need of additional operations in the production stage, with the consequent cost increase.

The present invention seeks to provide an improved electrical resistor and method of making an electrical resistor.

According to an aspect of the present invention, there is provided a method of producing an electrical resistor, wherein a blind hole is provided in a single-piece body, said blind hole receiving a heating member including a substantially U-folded thread-like wire, said wire being inserted through its central portion with the wire ends projecting outside said hole.

Compared to known assembly procedures, the preferred method can make assembly stages easier and it can also provide both an aesthetically and a qualitatively better end product with greater size control, since a single-piece housing is used instead of two-piece or multipiece housings, with all the economic and practical advantages resulting therefrom.

According to another aspect of the present invention, there is provided a resistor comprising an elongated body including a seat receiving a resistor wire, said body being of a single piece.

The invention encompasses the field of armoured electric resistors, such as those used to heat several devices, for example water or oil heaters, heating plates, irons and many other different types of apparatus, electro-domestic appliances and devices.

The preferred embodiment provides an electrical resistor the housing of which is made of a single piece and no longer of two or more parts as in prior art resistors, thus achieving a first advantageous result with regard to assembly, which can be completed in a considerably shorter time than commonly necessary to assemble known resistors, thus substantially lowering the production costs.

The preferred resistor can also be of higher quality than conventional resistors, by achieving a single-piece housing which is aesthetically better and also provides some advantages with regard to the resistance to the mechanical and thermal stresses imparted by the heating means.

The preferred method provides a preferably cylindrical single-piece housing, inside which a blind hole is provided having a substantially elliptical cross-section which is flattened adjacent to the minor diagonal, thus substantially appearing 8-shaped. the blind hole, which provides two elongated parallel seats joined by a central narrow portion, advantageously receives the resistive coil which consists of a substantially inverted Ushaped thread-like element and fits in the two elongated seats, ending outside with the two ends or cables or connectors for the connection to the electric plant.

An embodiment of the present invention is described below, by way of example only, with reference to the accompanying drawings, in which : Figures I to 3 are schematic views of a prior art electrical resistor : Figure 4 shows a side schematic view of the outer housing containing a resistive coil of an embodiment of resistor ; Figure 5 is a horizontal sectional view of the housing taken along line A-A of Figure 4 ; Figure 6 is a schematic view of the electrical conductor of the resistor of Figure 4; and Figure 7 is a schematic side view of the assembled resistor of Figure 4.

With reference to the accompanying drawings, the outer housing 10 of the embodiment of electrical resistor shown consists of a substantially cylindrical element inside which a blind hole 11 is provided having a substantially elliptical cross-section which is flattened adjacent to the minor diagonal, thus substantially appearing 8-shaped, as clearly shown in Figure 5.

The blind hole 11, which provides two elongated parallel seats joined by a central narrow portion, receives conductor 12 which consists substantially of a U-shaped threadlike element which is frontally fitted in the two elongated seats.

The conductor projects outwards with the two ends or connectors 13 which permits connection of the resistor to an electrical plant or system.

The hole 11, which is partly occupied by the conductor, can be filled with a material such as magnesium oxide and the whole sealed by means of resin and/or cement or the like.

According to the preferred method of producing the electrical resistor, the conductor 12 is inserted into the seat 11 of the housing 10. The seat is possibly filled with a suitable material such as magnesium oxide, allowing the two ends of the conductor or connectors to project for the connection to the current supply. Then, the whole is sealed with resin, cement or the like.

The electrical resistor produced by this method is aesthetically better than known resistors and it has a higher quality than conventional resistors just because the housing consists of a single piece, with a great advantage with regard to the resistance to the thermal and mechanical stresses imparted by the heating means. Furthermore, the production time can be considerably lowered and, since the resistor is no longer inserted through its ends but directly through its central portion, it is also possible to provide the resistors with thimbles or connectors of any size, independently of the size of the hole in which the heating element has to be inserted.

Those skilled in the art can provide several modifications and variations, all of which fall within the scope of the claims.

Claims

CLAIMS 1 A method of producing an electrical resistor, wherein a blind hole is provided in a single-piece body, said blind hole receiving a heating member including a substantially U-folded thread-like wire, said wire being inserted through its central portion with the wire ends projecting outside said hole.
2. A method according to claim 1, including the step of filling said seat with a material helping heat conduction,
3. A method according to claim 2, wherein said material is magnesium oxide.
4 A method according to claim 1,2 or 3, including providing said blind hole with a substantially elliptical cross-section which is flattened adjacent to the minor diagonal, thus appearing substantially 8-shaped, said 8-shape providing two elongated substantially parallel seats joined by a central narrow portion.
5. A method according to any preceding claim, including the step of inserting the resistive coil in the seat of the housing, and then sealing the seat with a filling material to allow the two conductor ends or thimbles to project for the electrical connection.
6 A method according to claim 5, wherein the seat is sealed with magnesium oxide or the like.
7. A resistor comprising an elongated body including a seat receiving a resistor wire, said body being of a single piece.
8. A resistor according to claim 7, wherein said wire is located in a seat provided by a blind hole having a substantially elliptical cross-section which is flattened adjacent to the minor diagonal, thus appearing substantially 8-shaped, said 8-shape providing two elongated substantially parallel seats joined by a central narrow portion.
9 A method of producing an electrical resistor substantially as hereinbefore described with reference to and as illustrated in Figures 4 to 7 of the accompanying drawings.
10. An electrical resistor substantially as hereinbefore described with reference to and as illustrated in Figures 4 to 7 of the accompanying drawings.