US3242315A - Heater and contact structure therefor - Google Patents

Description

Mam}! 1966 J. J. FANNON, JR

HEATER AND CQNTACT STRUCTURE THEREFOR Filed Dec. 29, 1961 ATTORNEYS nected to a copper or copper alloy contact.

United States Patent 3,242,315 HEATER AND CONTACT STRUCTURE THEREFOR John J. Fannon, Jr., Grosse Pointe Park, M1ch., assignor to Hupp Corporation, Cleveland, Ohio, a corporation of Virginia Filed Dec. 29, 1961, Ser. No. 163,144 6 Claims. (Cl. 219356) The present invention relates to improvements in electrically powered radiant heaters and contact structures therefor and more particularly to improvements in the structure of electrical contacts intended for high temperature operation.

The specific present commercial application of the present invention is in the contact structures for the radiants or heating elements of infra-red generating electrically powered heaters. Such heaters customarily utilize heating elements of the quartz type. These heating elements, when utilized in groups and arranged for cross-irradiation, have a surface temperature in the order of 1600 F. at their radiant portions, typically have 1000 or 1500 watt power input requirements and may be utilized singly or in groups of two, four or more.

Such heating elements, at their opposite ends, have electrical contact ferrules or caps made of a heat resistant electrically conductive alloy to resist deterioration under the high operating temperatures involved. The alloy used is a stainless steel containing nickel, chromium and iron. In operation, the ends of the heating elements operate at temperatures in the order of 800 F. to 1000 F. In the heater assembly, the ferrules or end caps are pressed between the arms of housing mounted contact clips to form an electrically conductive pressure contact and a support for the heating element. customarily, these contact clips are made of a copper alloy such as beryllium copper or brass to provide the good electrical conductivity and resilience required in spring biased pressure contacts such as this.

It has been found, however, that with the stainless steel of the ferrules or caps in pressure contact with copper alloy contact clips and operating at a temperature in the order of 800 F. to 1000 F., the copper alloy will rapidly deteriorate. Similar deterioration in copper alloy contact elements results when a Nichrome wire is con- Nichrome is also an alloy containing nickel, chromium and iron. The exact nature of this deterioration is not fully understood. It seems to be either an oxidation or electrolytic reaction stimulated by high temperature and high electrical current flow dependent upon the relative positions of the metals involved in the electromotive series. The result is that the deterioration of the copper alloy rapidly produces a powder, greatly increases the resistance of the contact between the connected parts, rapidly reduces the operating efficiency of the heating unit and results, in many instances, in damage to the component parts.

The primary object of the present invention is, therefore, to provide an improved electrical infra-red heater and contact structure therefor in which a contact element formed of a nickel-chromium-iron alloy is in pressure contact with a copper alloy contact element but in which the copper alloy contact element will not deteriorate under elevated operating temperatures.

More specifically, it is an object of this invention to provide an improved electrical contact which is com patible with complementary electrical contacts formed of a nickel-chromium-iron alloy such as stainless steel or Nichrome, particularly one which is in the form of a spring element which can be biased against the nickelchromium-iron alloy contact element and which will not deteriorate under temperatures in the order of 800 F. to 1000 F.

Still more specifically, it is an object of this invention to provide an improved copper alloy contact clip which may be utilized with stainless steel or other nickel-chromium-iron alloy contact ferrules or caps without deterioration of the copper alloy at elevated temperatures.

A further specific object of this invention is to provide a nickel-plated copper alloy contact clip.

These and other objects of the present invention will become more fully apparent by reference to the appended claims and as the following detailed description proceeds in reference to the accompanying drawings wherein:

FIGURE 1 is a perspective view from beneath of a typical space heater utilizing quartz heating elements and embodying the contact structure of the present invention;

FIGURE 2 is a perspective view from above of the space heater of FIGURE 1;

FIGURE 3 is a fragmentary longitudinal sectional view through one end of the heater of FIGURE 1 illustrating in elevation the heating element mounting and contact structures; and

FIGURE 4 is a fragmentary sectional view taken substantially along the line 44 of FIGURE 3.

As is shown in FIGURES 1 and 2, the space heater there illustrated comprises a housing 10 having a downwardly facing opening 12 within which is located a plurality of heating elements or radiants of the quartz type designated 14, 16, 18 and 20 backed by a reflector 22 and having a blower 24 on the top thereof. Blower 24 supplies air to cool the reflector 22 by forced distribution of air through the chamber defined between the upper surface of the reflector 22 and the top wall of the housing 10. The detailed structure of the heater 10 forms no part of the present invention but, if further details are found to be necessary to an understanding of the present invention, reference is made to co-pending application Serial No. 163,256, filed on Dec. 29, 1961, by John I. Fannon, Jr., Robert J. Fannon and Gordon B. Moody for Space Heater.

Referring now to FIGURES 3 and 4, each of the quartz radiants or heating elements such as 14 has at each of its ends a metal cap or ferrule 26 which, in order to withstand the heat involved (800 F. to 10'00 F.), is formed of a suitable nickel-chromium-iron alloy material such as stainless steel. When the radiant 14 is installed, cap 26 is pressed upwardly between the depending arms 28 and 30 of the contact clip 32. Contact clip 32 is mounted by a suitable terminal assembly 34 comprising, in the illustrated structure, complementary and interfitting ceramic insulators 36 and 38 and a bolt 40 mounted upon a suitable support plate 42 fixed relative to the housing 10. The diameter of cap 26 is slightly larger than the normal spacing between arms 28 and 30 so that the arms 28 and 30 are in pressure contact with the exterior surface of the cap 26 due to the resilience of arms 28 and 30 and of the interconnecting portions of the clip 32. The form of the clip 32, as illustrated, is conventional. Such clips are customarily formed of a copper alloy such as brass, beryllium copper and the like. While such contacts are satisfactory for use at low temperatures, when placed in contact with a complementary contact element formed of a nickel-chromiumiron alloy such as stainless steel or Nichrome and subjected to elevated temperatures, a powder will rapidly develop between the engaged surfaces of the contact elements which increases the electrical resistance therebetween to unacceptably high levels.

I have found that by interposing between the copper alloy and the nickel-chromium-iron alloy a layer of nickel thereon. V by the nickel plating from contaminants and atmosphere,

in the form of a plating upon the copper alloy contact no such distintegration of the contacting surfaces occurs. For this reason, the clip 32 is plated, at least on the \surfaces of its arms 28 and 30 which contact the ferrule or cap 26, with a layer of substantially pure nickel. This layer of nickel eliminates deterioration of the contact clips 32. The reason it does is not clear. It does form a layer on the copper alloy element of a metal which is a constitutent of the alloy of which the other contact is for-med.

Also, as is apparent from reference to the electropotential series of metals, in a normal ionic solution at 25 C., chromium has a potential of +.557 volt, iron +.441 volt, nickel +231 volt, and copper -.344 volt. Thus, the potential difference across the surfaces in pressure engagement in the prior art contact structure is .901 volt between copper and chromium, .785 volt between copper and iron and .575 volt between copper and nickel. With the contact structure constructed in accord with the present invention, the potential difierence across the surfaces in pressure engagement is only .326 volt between nickel and chromium and only .210 volt between nickel and iron. The .575 volt potential difference between copper and nickel exists at the boundary surfaces between the copper alloy clip and the nickel plating Since this boundary surface is fully shielded no material current flow results.

While at low temperatures these factors are not significant, at elevated temperatures in the order of 800 F. to 1000 F., they apparently become quite important.

Whether these factors are the controlling factors involved or the fact that the melting point of nickel is substantially higher than that of copper and its alloys is an involved factor is not presently known. It is clear, however, that nickel plating of the copper alloy contact does prevent its deterioration at elevated temperatures and high current flow when in pressure contact with a nickel-chromium-iron alloy. From the foregoing it should be apparent that other metals similar to nickel in that they do not melt at temperatures below 1000 F. and are at least as high in the electromotive series as nickel may be used in the place of nickel and are within the scope of this invention;

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. An air exposed pressure contact structure comprising a first electrical contact in pressure engagement with a second electrical contact wherein said first electrical contact is a nickel-chromium-iron alloy and said second s s ita smt q a copper base alloy ving a. la er 9t substantially pure nickel on at least the portion of said copper base alloy contact in pressure engagement with said first contact to prevent deterioration of the copper base alloy at temperatures in the order of 800 F. to 5 1000 F.

2. In an air exposed electric radiant heating unit having an electrical radiant heating element and a power supply means including a pressure contact structure, the improvement wherein said pressure contact structure comprises a first electrical contact in pressure engagement with a second electrical contact wherein said first electrical contact is a nickel-chromium-iron alloy and said second electrical contact is a copper base alloy having on at least the portion of said opper base alloy contact in pressure engagement with said first contact a layer of metal having a melting point greater than 1000" F. and an electromotive potential at least as high as nickel to prevent deterioration of the copper base alloy at temperatures in the order of 800 F. to 100'0 F.

3. The heating unit of claim 2 wherein said metal is nickel.

4. An electrically powered infra-red radiant heater comprising:

(a) a reflector equipped housing,

(b) a heating element,

(c) air exposed means mounting said heating element upon said housing including a pair of heating element supporting contact structures each embodying a copper base alloy contact element fixed to said housing and a nickel-chromium-iron alloy contact element fixed to said heating element, and

(d) a substantially pure layer of nickel on at least the portion of said copper base alloy contact in pressure engagement with said first contact for preventing deterioration of said copper alloy contact element under the influence of heat generated by said heating element.

5. The heater defined in claim 4 wherein said nickelchromium-iron alloy is a stainless steel.

6. The heater defined in claim 4 wherein said copper base alloy is brass.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS 3/1937 France.

REST-1A5]; M, WOOD, Primary Examiner.

Claims (1)

1. AN AIR EXPOSED PRESSURE CONTACT STRUCTURE COMPRISING A FIRST ELECTRICAL CONTACT IN PRESSURE ENGAGEMENT WITH A SECOND ELECTRICAL CONTACT WHEREIN SAID FIRST ELECTRICAL CONTACT IS A NICKEL-CHROMIUM-IRON ALLOY AND SAID SECOND ELECTRICAL CONTACT A COPPER BASE ALLOY HAVING A LAYER OF SUBSTANTIALLY PURE NICKEL ON AT LEAST THE PORTION OF SAID COPPER BASE ALLOY CONTACT IN PRESSURE ENGAGEMENT WITH SAID FIRST CONTACT TO PREVENT DETERIORATION OF THE COPPER BASE ALLOY AT TEMPERATURES IN THE ORDER OF 800*F. TO 1000*F.

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