Electric heating – Heating devices – With heater-unit housing – casing – or support means
Patent
1989-05-17
1991-09-24
Evans, Geoffrey
Electric heating
Heating devices
With heater-unit housing, casing, or support means
219536, 219549, H05B 358
Patent
active
050515632
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a surface heating element having an electrical resistance heater for components of tools and machines and including an annular outer shell, an inner part and a heat conductor or heat conductors between the inner part and the outer shell.
Surface hearing elements which largely conform to the shape of the machine component to be heated are known.
An annular, known surface heating element has a thermal insulating jacket consisting of two shell segments which are articulated to one another. The heating element is equipped with a wave-shaped reflector at its inner side and, to the outside, covers heating bands drawn onto a ring which can be placed upon the machine component to be heated.
The overall structure of this surface heating element is very expensive and its life is short since the heated bands can come into contact with the oxygen in the air. This causes scaling which, in turn, results in wear of the heating bands.
It is an object of the invention to design a surface heating element of the above type in such a manner that the heat conductor is arranged in the heating element so as to be largely free of wear and attrition, and that the heating element achieves a high thermal output together with long life and can be easily adjusted to the tool and machine components to be heated.
According to the invention, this object is achieved in that each heat conductor, which is enclosed in a thin insulating layer, is arranged without play in a receptacle defined by two parts of the heating element and sealed so as to be gastight and liquidtight relative to the atmosphere.
In accordance with an embodiment of the invention, the receptacle for the heat conductor is defined by the outer shell and the inner part. This results in a surface heating element with small dimensions. In order that the heat conductor, which lies in the receptacle without play, remains firmly clamped between the outer shell and the inner part during operation also, a metal having an expansion coefficient less than or equal to the expansion coefficient of the inner part is selected for the outer shell.
The outer shell and the inner part can define a plurality of neighboring receptacles for the heat conductors. It is also possible to provide one or more annular intermediate parts between the outer shell and the inner part so that one or more neighboring receptacles for heat conductors are defined by the outer shell and the adjacent annular intermediate part and/or by two annular intermediate parts and/or by an annular intermediate part and the inner part.
The gastight and liquidtight sealing of the receptacles for the heat conductors with respect to the atmosphere can be achieved by welding the adjoining surfaces of the parts defining the receptacle externally of the heating element.
By firmly clamping the heat conductors in the receptacles defined by the parts of the heating element and preventing the penetration of atmospheric oxygen, in particular, into the receptacles, mechanical wear of the heat conductors and attrition due to corrosion are held to small amounts.
Exemplary embodiments of the invention are illustrated in the drawings and are described below. There is shown:
FIG. 1 a partly sectional view of an annular surface heating element with a current connection extending parallel to the longitudinal axis of the heating element,
FIG. 2 a sectional view of a heating element as in FIG. 1 with an inclined current connection,
FIG. 3 a sectional view of a machine nozzle with a heating element positioned on the same,
FIG. 4 a fragmentary sectional elevational view of an injection molding machine for plastic with a heated sieve carrier, and
FIG. 5 a partly sectional view of a nozzle of a zinc pressure casting machine with two surface heating elements.
The surface heating element 1 of FIG. 1 consists of an outer shell 2 and an annular inner part 3 which, by virtue of a stepped construction, interlock in a complementary fashion and define a receptacle 4 of circular cross section for a heat conductor 5 enclosed in an elec
REFERENCES:
patent: 2274839 (1942-03-01), Marizk
patent: 3110795 (1963-11-01), Bremer
patent: 3436816 (1969-04-01), Lemelson
patent: 3849630 (1974-11-01), Halliday
patent: 4008845 (1977-02-01), Bleckmann
patent: 4386262 (1983-05-01), Gellert
patent: 4574186 (1986-03-01), Sakai et al.
patent: 4778981 (1988-10-01), Ruede
Patent Abstracts of Japan, Feb. 18, 1986, vol. 10, No. 40, Japan, A, 60-193,625.
Evans Geoffrey
EWIKON Entwicklung und Konstruktion GmbH & Co. KG.
Kontler Peter K.
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