US3842181A

US3842181A - Furnace

Info

Publication number: US3842181A
Application number: US00384569A
Authority: US
Inventors: F Dijkstra; T Groothuizen; H Pasman; De Putte T Van
Original assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Current assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Priority date: 1972-08-02
Filing date: 1973-08-01
Publication date: 1974-10-15
Anticipated expiration: 1991-10-15
Also published as: FR2194925B1; FR2194925A1; NL7210578A; DE2338039A1; GB1389157A; CH567704A5

Abstract

A furnace provided with three heating mantles mounted around each other and separated by insulating layers, wherein the innermost, i.e., the first mantle is connected to a first supply voltage source, and the second and the third mantles are connected in series to a second supply voltage source, which second source is controlled by heat flow in the insulating layer located between the first and second mantles, the second and third mantles being constructed such that the power excitable per unit of surface in the mantles are substantially equal.

Description

United States Patent Dijkstra et al.

FURNACE lnventors: Fokke Cornelius Dijkstra,

Maastricht; Theodorus Maria Groothuizen, Schipluizen; Hermanus Johannes Pasman, Wassenaar; Tonny Van de Putte, De Lier, all of Netherlands Nederlandse Organisatie Voor Togepast-Natuurweten-Schappelijk Onderzoek Ten Behoeve Van De Rijksverdediging, The Hague, Netherlands Filed: Aug. 1, 1973 Appl. No.: 384,569

Assignee:

Foreign Application Priority Data [56] References Cited UNlTED STATES PATENTS 3,112,919 12/1963 Gunow 13/20 X 3,427,011 2/1969 Boyer et a1. 13/31 X Primary ExaminerR. N. Envall, Jr. Attorney, Agent, or FirmWatson, Cole, Grindle & Watson 5 7 ABSTRACT A furnace provided with three heating mantles mounted around each other and separated by insulating layers, wherein the innermost, i.e., the first mantle is connected to a first supply voltage source, and the second and the third mantles are connected in series to a second supply voltage source, which second source is controlled by heat flow in the insulating layer Aug. 2, 1972 Netherlands 7210578 located between the first and Second mantles the ond and third mantles being constructed such that the US. Cl 13/22, 13/24, 13/31 power excitable per unit of surface in the mantles are Int. Cl. F27b 5/08, F27d. 1 1/02 substantially equal Field of Search 13/20, 22, 25, 31;

219 209 2 0 5 39 1 Claim, 1 Drawing Figure HQ 2 we A n W v L 3 J mmcmoit 4 "1O 1 1Q K 15 4 RELAY 1: CONTROLLER gggggg FURNACE The invention relates to a furnace, comprising a hollow metal housing for containing a sample in its cavity and provided with a first electric heating mantle, a second electric heating mantle around the first mantle, a heat-insulating intermediate layer between the two mantles and means for regulating the flow of heat in the intermediate layer. Such a furnace is generally known in the art.

The second electric heating mantle about the first mantle, the heat-insulating intermediate layer between the two mantles and the means for controlling the flow of heat in the intermediate layer in this known furnace are provided to render the furnace adiabatic, i.e., the frequency of the impulses of current through the second mantle is controlled in such a way that the flow of heat through the intermediate layer becomes practically zero.

A slight modification in the temperature of the first mantle is then followed by a slight modification in the temperature of the second mantle. If the housing is to pass linearly through a temperature trajectory however, then it should be sufficient to provide the first mantle with a constant current. In practice it has been found, however, that then the impulses of current as a result of readjusting the second mantle are highly perceptible with respect to the temperature of the metal housing.

It is the object of the invention to improve such an arrangement. Therefore, a third electric heating mantle is mounted about the second mantle. This third mantle is provided with an external heat-insulating layer, and a heat-insulating layer is disposed between these two mantles. The second and third mantles are electrically connected in series, and the power excitable per unit of surface in the second and the third mantles are practically equal. They are controlled as a whole by the means for controlling the flow of heat in the intermediate layer, and the supply voltage of the first mantle is independent of the supply voltage control of the series connection.

With such an arrangement, the third mantle is found to be always lower in temperature than the second mantle, and the impulses of current in these mantles do not or hardly interfere with respect to the temperature of the housing.

The invention will be further described with reference to the drawing, showing an embodiment of a furnace according to the invention.

In the FIGURE furnace space 1 is surrounded by a metal housing 2 and a lid 20. Housing 2 is provided with a first heating mantle 3, connected to a stabilized current source 4. ln furnace space 1 a temperature probe 5 is mounted, connected to a registrating and/or indicating device 6.

A heat-insulating intermediate layer 7 is mounted between heating mantle 4 and a second heating mantle 8.

A third heating mantle 9 is connected in series with mantle 8, which mantle 8 is mounted on a heatinsulating intermediate layer 10. Probes l1 and 12, inserted in first and second heating mantles 3, 8, respectively, control the series connection of mantles 8 and 9 with the aid of a controller 13 and a relay 14. A heatinsulating layer 15 is mounted.

Layers

7, 10 and 15 are provided with

lids

70, 10a and 15a.

The device operates as follows:

Controller 13 will operate relay 14, when the temperature difference between probe 11 and probe 12 adopts a certain value. In the process, probes 11 and 12 are inserted in the input circuit of controller 13. Current I, which is switched by relay l4 and which passes through the windings of mantles 8 and 9 connected in series, excites per unit of surface a power equal to that as in mantle 7 by applying such a construction that the number of windings per unit of surface is practically equal. Accordingly the temperature in mantle 9 is always lower than that in mantle 8 and the fluctuations in temperature in housing 2 resulting from switching of current I by relay 14 are absorbed for the greater part.

Further data of the embodiment.

volume of space 1 housing 2 thickness of layer 7 We claim:

I. A furnace, comprising, a hollow metal housing for containing a sample in its cavity, a first electric heating mantle surrounding said housing, a second electric heating mantle surrounding said first mantle, a heatinsulating intermediate layer disposed between said mantles, means for regulating flow of heat in said layer, a third electric heating mantle having an external heat insulating layer thereon surrounding said second mantle, another heat-insulating layer disposed between said second and third mantles, said second and third mantles being electrically connected in series, wherein the power excitable per unit of surface in said second mantle and in said third mantle is substantially equal, means for controlling the flow of heat in said intermediate layer, each such power being controlled by said control means, and the supply voltage of said first mantle being independent of the supply voltage of the series connectron.

Claims

1. A furnace, comprising, a hollow metal housing for containing a sample in its cavity, a first electric heating mantle surrounding said housing, a second electric heating mantle surrounding said first mantle, a heat-insulating intermediate layer disposed between said mantles, means for regulating flow of heat in said layer, a third electric heating mantle having an external heat insulating layer thereon surrounding said second mantle, another heat-insulating layer disposed between said second and third mantles, said second and third mantles being electrically connected in series, wherein the power excitable per unit of surface in said second mantle and in said third mantle is substantially equal, means for controlling the flow of heat in said intermediate layer, each such power being controlled by said control means, and the supply voltage of said first mantle being independent of the supply voltage of the series connection.