US2218177A - Wire treating furnace - Google Patents

Description

Oct. 15, 1940. E. B. POWELL WIRE TREATING FURNACE Filed Fb. 2a, 1939 2 Sheets-Shet 1 INVEN TOR. EVERTON B. POWELL 0% 5, 1940-. E. B. POWELL WIRE TREATING FURNACE Filed Feb. 28, 1939 2 Sheets-Sheet 2 m u m r E M w. w 0 m Q M .A 4 r W q H II I H Patented Oct. 15, 1940 WIRE TREATING FURNACE Everton B. Powell, Maplewood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application February 28, 1939, Serial N 0. 258,880

3 Claims.

My invention relates to furnaces, particularly to furnaces for heating, in an atmosphere of desired gases, a plurality of continuously moving wires or strips of metal,

Wire is commonly heat treated either by placing large spools of the wire in a closed oven or by slowly reeling the wire through a heated tube, the speed of reeling being proportional for given time and temperature to the length of the heated l0 tube.

be the speed of the wire through the furnace. Since wire of most metals must be heated in an atmosphere of reducing gas, such as hydrogen, to prevent excessive oxidation, and because a ll heating tube through which the wire is drawn must be open at its ends, a rather fast moving stream of gas through the tube must be'provided to completely envelope the wire; The gas escapes from the ends of the tube and, in furnaces of conventional construction, where the tubes are short and the wire speed is low, the gas wastage per foot of treated wires is considerable. It is difllcult, however, to make long furnaces. Either ceramic or refractory metal tubes must be used,

with exterior heating means, but the few refractory metals available for furnace tubes for continuous operation at high temperatures are difflcult'to work and expensive, and long straight tubes of ceramic material cannot be made because of brittleness, structural weakness, and a tendency to warp when heated.

An object of my invention is a furnace for continuously heating a moving wire in a gaseous atmosphere with means for reducing waste of gas.

'Another object of my invention is a furnace with heated ceramic tubes of any desired length for continuously heat treating: wire.

A more specific object jmy invention is a o furnace for heat treating a umber of wires, the furnaces being of any desired length with a straight ceramic tube for each wire treated and' so constructed and arranged that individual tubes may be easilyreplaced.

u; A further object of my invention is a furnace for simultaneously heat treating a plurality of continuously moving wires.

According to my invention, a relatively large number of wires reeled from their individual so spools are each drawn through a small ceramic heated tube. Each of the-small ceramic tubes, 24 in number and divided into three end-to-end sections, is, in the specific furnace hereinafter described, supported in a unitary ceramic casing 5 which is surrounded throughout the length of The shorter the furnace the slower must the furnace with an electric heating element. The sections of the tubes and casing are loosely fitted end-to-end and are supported on rollers to permit free longitudinal expansion, one end of the ceramic assembly being fixed and the other end being spring pressed to yieldingly hold the sections straight and together. The several tubes and their surrounding casing with the. heating element areembedded in a mass of powdery heat insulating material in a gas-tight metal housing. 1. Gas admitted to the housing is diffused through the ceramic walls of the casing and thence through the. tube walls where the gas pressure is low and uniform throughout the length of the tubes. The metal housing is a gas reservoir 1 about the casing and tubes from which a quiescent envelope of gas is obtained about the wiresin thetubes'.

The characteristic. features of my. invention are defined in the appended claims and one specific embodiment is described in the following specification and shown in the accompanying drawings in which Figures 1 and 1a are side elevations, partly in section, of my improved furnace in combination with wire reeling means at each end, the structure in the two figures being divided along line X X to facilitate'illustration on one sheet, Figure 2 is a longitudinal section view of my improved furnace showing the internal arrangement of parts and Figure 3 is a view of the .I left hand end of the furnace shown in Figure 2.

In Figures 1 and 1a. are'shown a plurality of reels I from which are drawn wires 2 through treating baths and into the right hand end of my improved furnace 3. Each wire passes through E an individual heating tube and through aligned cooling tubes in cooling chamber 4 on to reels 5 at the left end of the furnace assembly. While my improved furnace is shown in Figures 1 and 1a in combination with wire plating mechanism, it may be used for annealing purposes only, where the wire passes directly from the. unloading reels into the inlet end of the furnace. For nickel plating iron wire, for example, the particular baths shown in Figure 1 may for purposes of illustration comprise first a caustic cleaner in tank 6, a 20% solution of nitric acid for etching the wire'in tank I and a nickel electrolytic plat-, ing bath in-tank 8. Between each emersion tank may be various water rinse sprays. preferably tensioned on'the reels to hold the wire centrally in the tubes and prevent drag in the heating zone.

The furnace proper shown indetail in Figure 2 comprises a large metal tank 9, gas-tight for g The wire is 0 low pressure gas, closed at each end with cast iron headers. Extending inwardly from the inlet header [0 is an integral flange Ii rectangular in cross section with a flange collar l2 telescoped over the end of the first section of the ceramic casing l3. Two additional sections of the casing are fitted end-to-end with the first, and are supported on rollers l4, preferably one roller being under each section, to relieve the butt joints of the casing from strains. The header l5 at the other end of the furnace is movable and has an integral inwardly extending flange l6 and flange collar IT for engaging the left hand end of the ceramic casing. This header flange slides in close fitted engagement with the inner surface of the hood or cast iron extension l8 bolted gastight to the outer end of the housing, and is spring pressed against the end of the casing by springs l9 compressed between adjustable stud bolts in the end of the spring housing 2| and guide posts 22 on the outer face of the movable header. To maintain uniform pressure against the end of the ceramic casing one spring is preferred at each corner of the header.

Transverse ceramic spacers or partitions 23 held preferably at the junctions of the casing sections support the wire heating tubes 24. The tubes are in end-to-end sections, adjacent ends of the sections resting in the spacers, and are free to move independently of the spacers. The tubes are held against longitudinal displacement by a removable plate 25 fitted over the inlet header at one end and by countersunk shoulders in the movable header at the other end. A cracked tube may be easily replaced by remov ing the plate and sliding the damaged tube out the inlet end without disturbing the other tubes. While the spring pressed ceramic casing and tube assembly is long and the sections sumciently rigid to remain straight, the assembly is strong and will not warp when heated. Distinguished from furnaces of the usual construction, there is no practical limit to the length of the ceramic wire heat treating tubes or to the number of parallel tubes that may be placed side-by-side within one heating element.

A commercial reducing gas, such as hydrogen, may be employed to prevent oxidation of the wires as they are heated. The gas in my improved furnace is admitted under low pressure at three spaced points in the bottom of the furnace through gas pipes 26. The gas fills the entire space in the housing and filters through the pores of the ceramic casing to the interior of the casing where it then passes through the pores of the ceramic tubes into their interior. An unglazed ceramic is quite pervious to hydrogen. The open space in the casing about the tubes permits the gas pressure to become uniform throughout the length of the casing and permits uniform and low pressure distribution of the gas throughout the interior of the tubes. There is substantially no gas flow along the interior of the tubes and although the gas pressure is nearly atmospheric, each wire is effectively enveloped in gas throughout its heated length. If gas leakage about the edges of the spacers is insufficient to permit even gas pressure throughout the casing, holes may be provided through the spacers.

There is no gas pressure gradient between the ends of the tubes and the gas leakage from either end of the tubes is slight so that the consumption is small and efiiciency is high.

Heat from the heating element 21 surrounding the ceramic casing, preferably in the form of a continuous heating ribbon wound from one end of the casing to the other and connected to insulating lead-in bushing, is emciently transferred through the quiescent mass of gas to the wires to be treated. Heat flows readily from the heating ribbon inwardly through the ceramic walls of the casing and the hydrogen atmosphere transfers the heat with only slight temperature drop to the several tubes, whereas outward heat flow is reduced to a minimum by the powderedinsulating material 28 which fills the casing. One furnace with ceramic tubes 90 inches long for simultaneously annealing twentyfour nickel plated iron wires has produced good results with the wires travelling at the rate of thirty feet per minute with the heating tubes maintained at a temperatureof 850 C. This furnace whose housing is only about 15 inches by 25 inches in cross section had an outside housing temperature comfortable to the hand although consuming about forty kilowatts of heating power.

The housing may be of sheet metal and the ceramic casing and tubes may be of commercial aluminum oxide or alundum" made with wall thicknesses sufllcient for good mechanical strength and the ceramics should be unglazed. The housing around the ceramic casing is filled with a powdery insulating material to a level near the top of'the housing. Good results have been obtained with highly calcined magnesium oxide powder. Good results, with high thermal efficiency, low ceramic breakage and high speed wire annealing, has been obtained with tubes about 90 inches long, .740 inch outside diameter, .100 inch wall thickness and a casing with the same length, 12 inches by 2.75 inches and .375 inch wall thickness.

To cool the wires, before removal from the hydrogen atmosphere, to a temperature below oxidation temperature, I have found that a cooling chamber 4 may conveniently be mounted directly on the outlet end of the furnace. In this chamber is a plurality of metal pipes 29 aligned with the heating tubes and joined water-tight with the end plates of the chamber. Water admitted to the inlet pipe fills the chamber, cools the pipes and effectively chills the wires before their exit to the reels. Thecooling chamber 4 is preferably fastened gas-tight to the hood ll so that gas which leaks into the hood from the ends of tubes and around the edges of the header I5 can escape only by passing through the constriction of the small relatively long cooling pipes.

A furnace for continuously heating moving wires in a gas atmosphere constructedaccording to my invention is easy to erect, inexpensive to maintain and is eflicient in operation. A furnace constructed according to my invention may be of any desired length and provision may be made for simultaneously heat treatinggany desired number of continuously moving wires.

I claim:

1. A plurality of gas pervious refractory tubes arranged side-by-side, a cooling pipe coaxial with each of said tubes, a gas pervious refractory casing surrounding said tubes and a heating element surrounding said casing, a gas reservoir comprising a gas tight housing surrounding said casing for supplying a quiescent gaseous atmosphere'to the interior of said tubes, said housing having a fixed header on one end with openings fitted around one end of each of said tubes, one

end of said casing abutting said fixed header, a

movable header inside said housingat the other end of the housing and being spring pressed against the other end of said casing, the other end of said tubes abutting said movable header and being Iree to move longitudinally, said other end of said housing being joined gas-tight to the ends of saidcooling pipes, and a cooling compartment surrounding said pipes.

2. In combination in a wire treating apparatus, an elongated metal housing, a fixed metal header closing and joined gas tight to one end of said housing, a metal hood closing and joined gas tight to the other end of said housing, a siidable header in said hood with spring biasing means to press s'aid movable header toward said fixed header, a tubular casing of gas pervious refractory material extending the length of said metal housing with its ends abutting the opposed faces of the fixed and movable headers, a heating element surrounding said casing, and means for admitting gas to said casing, a plurality of open ended ceramic tubes extending side-by-side through said casing with their ends supported in openings in said headers, a plurality of cooling pipes joined gas tight at their rims in openings in said hood, said pipes being in axial alignment with said tubes.

3. A refractory wire heating assembly comprising a gas-tight housing, a straight elongated ceramic casing in said housing, said casing comprising a plurality of butted end-to-end sections, a heating element surrounding said casing, a. plurality of side-by-side tubes extending longitudinally through said casing, each tube comprising a plurality of end-to-end sections, a transverse partition in said casing supporting adjacent ends of the tube sections, the casing and tubes being fixed at one. end to one end of said housing, a slidable header, the other end of said casing and said tubes abutting said slidable header, means to press said header against the ends of the tube and casing sections to hold the casing and tubes straight and structurally rigid yet free to expand lengthwise, and a gas inlet to said housing.

EVERTON B. POWELL.

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