US2775825A - Apparatus for treating a strip of metal - Google Patents

Description

Jan. 1, 1957 w. PHILLIPS APPARATUS FOR TREATING A STRIP 0F METAL Filed Feb. 1, 1954 2 Sheets-Shae INVENTOR W/LL MM A. PH/LL/PS A TOEN Y United States Patent APPARATUS FOR TREATING A STRIP OF METAL William A. Phillips, Toledo, Ohio, assignor to Surface Combustion Corporation, Toledo, Ohio, a corporation of Ohio Application February 1, 1954, Serial No. 407,289

12 Claims. (Cl. 34-242) This invention relates to apparatus for treating a strip of metal by passing the strip at an elevated temperature through successive chambers containing different atmospheres, and more particularly to a structure for providing a constant narrow opening between successive chambers.

United States Patent No. 2,625,495 discloses one process for passing a strip of metal at an elevated temperature through three successive chambers containing difierent atmospheres. The third paragraph in column 8 of that patent explains that it is desirable to avoid leakage of the atmosphere from the second or treating zone into the firstor preheating zone, or into the third or cooling zone. That paragraph suggests that the cooling and preheating zones be'operated at pressures slightly greater than the pressure of the treating zone, so that any flow of gas from one zone to another will be toward the treating zone.

Figure IV of the patent drawings shows a construction in yet must not be so Wide as to permit the atmosphere of the treating zone to contaminate the adjacent zone.

Even though the pressure in the treating zone is lower than the pressure in the adjacent zone, it is necessary to maintain a substantially constant opening between the two zones in order to prevent the atmosphere of the treating zone from entering the adjacent zone. In order to avoid wasteful operating conditions, it is necessary to maintain in the treating zone a pressure only slightly lower than the pressure in the adjacent zone so as to restrict the rate at which atmosphere is lost from the adjacent zone into the treating zone. It will be apparent that the use of a relatively narrow opening between the zones, operating under a relatively slight pressure difierential, which is necessary in order to restrict the loss of atmosphere from the adjacent zone into the treating zone, makes the dimensions of the opening between the Zones quite critical so that a substantial increase in the size of thatopening might permit the atmosphere of the treating zone to contaminate the adjacent zone.

In the process disclosed in that patent,"the atmosphere of the treating zone contains hydrogen chloride, which reacts with the surface of a ferrous metal strip to remove iro'n'oxides,,thus producing iron chlorides in vapor form. Iron chlorides are extremely corrosive, and it is very important to prevent the iron chloride vapors in the treatnovel and durable structure which aifords a constant narrow opening between two chambers containing different atmosphere under slightly different pressures, in order to prevent the atmosphere of the chamber that is under lower pressure from contaminating the atmosphere of the other chamber, while maintaining a constant restricted flow of the atmosphere from the latter chamber into the former chamber and permitting a strip of metal to pass from one chamber to the other. More specific objects and advantages are apparent from the following description, in which reference is made to the accompanying drawings illustrating preferred embodiments of the invention.

Figure I of the drawings is a diagrammatic viewishowing an apparatus of atype in which the present structure is useful. 7

Figure II is a fragmentary vertical longitudinal section of the apparatus illustrated in Figure I, showing a structure embodying the invention located between the first and second chambers of the apparatus.

Figure III is a vertical transverse section taken on line III-III of Figure II.

Figure IV is a fragmentary vertical longitudinal section illustrating a modification;

These specific drawings and the specific description that follows merely disclose and illustrate and are not intended -to limit the invention.

A structure embodying the present invention, which provides a constant narrow opening between two chambers, comprises as its essential parts a lower wail, an upper gate the bottom of which normally is parallel to and spaced from the top of said lower wall to provide a narrow opening therebetween, end members extending upward at each end of said wall, a lintel extending between said members and means for raising said gate .to permit a strip to be threaded through the apparatus. In order that the only appreciable openingbetween the chambers may be the narrow space between the gate and the lower wall, the gate in its normal position is closely adjacent to the end members and the lin'tel. A further important feature of the invention isthat the lower wall, gate, end members and lintel are made of a dense, thermally stable refractory and are carried upon stable supports located outside of the high temperature zone.

In the specific apparatus illustrated in the drawings, a strip of sheet metal 10, such as cold rolled steel, is carried on rollers 11. The strip 10 first passes through a preheating chamber 12 in which the atmosphere temperature may be about 1700 F., causing the strip to leave the preheating chamber at a temperature of about 1350 F.

In the succeeding reaction chamber 13, the atmosphere temperature may be about 1400 F., so that the strip approaches equilibrium with .such atmosphere temperature ing chamber from contaminating the atmosphere of a suc- The principal objectof the invention is to provide a before leaving the reaction chamber.

In the third or cooling chamber 14, the atmosphere temperature maybe about 800 F. As the strip passes the last roller 15 in the cooling chamber, it descends through an extension 16 of thecooling chamber to enter a tank 17 containing a molten metal for coating the strip. The usual coating metal is Zinc, but other coating metals such as tin, aluminum and lead may be used. After entering the tank 17 the strip passes a roller 13 in the tank, and thereafter the coated strip may be handled in accordance with usual practice.

In order to protect molten zinc in the tank 17 against oxidation, there may 'be introduced, through an inlet 19 near 'the discharge end of the cooling chamber 14, an atmosphere consisting of approximately hydrogen and 25% nitrogen. A baflle 20 having a relatively wide opening for passage of the strip 10 may be used to partit-ion oit the discharge end of the cooling chamber so that a different atmosphere consisting of approximately nitrogen and 5% hydrogen may be supplied to the initial section of the cooling chamber through an inlet 21. Approximately 200 cubic feet of gas per hour may be supplied through the inlet 19 and approximately 1,000 cubic feet of gas per hour may be supplied through the inlet 21, so that 1,200 cubic feet of gas per hour flow from the cooling chamber 14 to the reaction chamber 13.

The ferrous metal strip may be protected against oxidation in the preheating chamber by introducing into that chamber through an inlet 22 approximately 3,000 cubic feet per hour of a gas having the same composition as the gas flowing into the cooling chamber 14 through the inlet 21. The structure :at the point where the strip enters the preheating chamber 12 may be such that approximately one-third of the gas entering the inlet 22 is discharged from the preheating chamber at the point where the strip enters. Itis estimated that an equal loss of this atmosphere may occur at other points, leaving about 1,000 cubic feet per hour of this atmosphere to be discharged from the preheating zone 12 to the reaction zone 13.

The gauge pressure in the reaction zone 13 may be maintained at about 0.36 inch of water in order to prevent air from entering the reaction zone, while the pressure in the preheating and cooling zones may be maintained at about 0.4 inch of water to cause gas to flow from these two zones into the reaction zone.

The gas supplied to the reaction zone 1-3, which for purposes of illustration is shown as entering through an inlet 23, may consist of 40 cubic feet per hour of chlorine. Thus the inlet 23 actually consists of a burner and the chlorine entering the reaction zone burns by combining with hydrogen in the reaction zone to form hydrogen chloride.

There is only one outlet 24 through which the gases may leave the reaction zone, and this outlet consist of a connection to an acid-resistant tile duct leading to a fume disposal system.

As hereinbefore explained, an apparatus of this type presents the difficult problem of maintaining a constant narrow opening at the two points 25 and 26v where the gases from the preheating chamber andthe cooling chamber enter the reaction chamber. The structure at these two points must be such that the size of the opening, which is determined when the apparatus is assembled at ordinary temperatures, will remain the same while the apparatus is in operation Theproblem is rendered more difficult by the fact that the temperature of the atmosphere in the preheating zone is 1700, whereas the temperature of the atmosphere in thereaction zone i 1400 and the temperature. of the atmosphere in the cooling zone is only 800. The structure must be such that there is no change in the width of the opening through warpage under these extreme variations. in temperature.

Figure II of the drawings shows a structure located at the point 25 between the preheating zone and the reaction zone. However, an identical structure embodying the invention may be located at the point 26 between the reaction zone and the cooling zone. The novel structure illustrated in Figure II is adapted to. maintain a constant narrow opening so. as to maintain a constant restricted flow of gas into the reaction chamber and to prevent the atmosphere of the reaetion chamber from contaminating the atmosphere of the adjacent chamber, even though the pressure diiferential from one chamber to the other is only 0.04 inch of water.

Another important requirement ofthe structure at the point 25 or 26 is that provision be made for enlarging the normally narrow opening to a much greater width at the time when the leading end. of astrip is threaded through the apparatus. That is necessary because a relatively thick threader bar is attached to the leading end of the strip during the threading operation.

Another serious problem that must be met by this. structure arises from the. faet that thestruetnremnst be p ed o p weld nd qmssss w is ap ear. rom.

time to time in the strip, without any manual manipulation. Because of such irregularities, and also because of the random lateral movements that are executed by the strip, the structure forming the opening through which the strip passes must be extremely durable.

In the construction shown in Figure II, the chambers 12 and 13 are provided with an outer casing 27 of mild steel that is supported by a suitable external framework (not shown) and is lined with insulating fire brick 28. A layer of expanded metal 29 may be provided between the casing 27 and the fire brick, and a protective atmosphere may be supplied under pressure, through a connection not shown, to the space formed by the layer of expanded metal 29. This protective atmosphere may be the same atmosphere that is supplied by the inlets 21 and '22.

The chambers 12 and 13 may beheatcd by means of internally fired combustion tubes 30, only one of which is shown in Figure II. These combustion tubes may be of the return bend type described in. U. S, Patent No. 2,048,644. An outlet 24 leads, from the bottom of the reaction chamber 13 to an acid-proof tile 3 1,

The portion of the structure shown in Figure II, that embodies the present invention comprises first a lower wall 32 composed of a base 33 and a cap 34. Also forming part of the structure of the present invention are end members 35 and 36 (see Figure III) extending upward at each end of the lower wall 32,. Extending between end members 35 and 36 are a pair of lintels 37 and 38. A gate 39, when in its normal position, rest upon the lintels 37 and 38 so as to provide a narrow opening between the bottom of the gate 39 and the cap piece 34 of the lower wall 32. In the normal position of the gate, clearance of about nd inch may exist between the gate and each of the end members 35 and 36.

As shown in Figure III, the gate 39 -is composed of five intermediate sections 40, separated by four metal wear plates 41, and two end sections 42 and 43 that are separated from the intermediate sections by two Wear plates 44 and 45.

These sections and wear plates in the gate are provided with aligned openings 46 through which is threaded a tubular member 47 for lifting the gate. The lifting of the gate by means ofthe tubular member 47 is performed through the wear plates 44 and 45, which are connected through links 48 to lifting rods 49 and 50. The lifting rods 49 and 50 in turn are hung from cranks 51 and 52 that are mounted on a shaft 53 carriedin bearings 54, 55 and 56. The. end of a cable 57 is wrapped around the shaft 53 so that the shaft can be rotated through the cable by means of a winch 58, for lifting the gate 39.

In order to provide an effective seal between the chambers 12 and 13, the lower wall.32, end members 35 and 36, lintel 38 and gate 39, which constitute the structure separating the two chambers, should be made of a dense, thermally stable refractory, and should be carried upon stable supports located outside of the high temperature zone. When one of the chambers contains an acidic atmosphere, such as the hydrogen chloride-containing atmosphere hereinbefore described, the refractory. should be an acid-resistant material. Although any refractory having the characteristics that have been described, such as a thermally stable form of silica, may be. employed, the preferred refractory is carbon. Although carbon could not be used as a, refractory in an oxidizing atmosphere, in which it would be rapidly consumed, carbon may be classed as a refractory when it is usedin nonoxidizing atmospheres such as those present in the chambers 12 and 13.

In the preferred structure embodying the invention, the lower wall 32 is supported directly upon the mild steel casing 27,- and such casing is not subjectedtohightem! peratures sothatit forms a stable support. for the lower. Wall. The base 33 and cap 34 of the lower wall preferably consis of relatively. h r morphous. carbpnblocks of the commercially available type, whereas the vertical pieces 59 that occur in the lower wallat each endmay consist of softer blocks of the commercially available type that is made of flake graphite. Blocks of the latter type can be shaped with woodworking tools, whereas special diamond tools are required for shaping blocks of the former type.

The end members 35 and 36 are supported directly upon the cap 34 and preferably are made of the hard type of material.

The lin-tels 37 and 38 also are carbon blocks of the hard type. The lintel 37 is supported at each end by a pillar 60, and the lintel 38 is supported at each end by a pillar 61. The pillars 60 and 61 are made of the same hard carbon refractory. Except for the presence of a fire brick orifice member 62, in which the outlet 24 is for-med, the portions of the casing 27 lying on both sides of the lower wall 32 are lined with two layers'of base blocks 63, made of the same hard carbon refractory, which support the pillars 60 and 61. Although .the pillars 60 and 61 support the lintels 37 and 38, respectively, the exposed corners of the lintels are protected by angle plates 64 and 65.

The pillars 60 and 61 abut against each side of the lower wall 32, and against the sides of the end members 35 and 36 (which appear only in Figure II=I). These end members, in longitudinal section, have substantially the same shape as the gate 39. Thus the end members 35 and 36 are supported by the pillars 60 and 61 as well as by the lower wall 32. From the foregoing it is apparent that the lower wall 32, the pillar 61 and the lintel 38 frame the opening which, except for a narrow slot, is closed by the gate 39.

The intermediate sections 40 of the gate 39 may be made of the soft type of carbon refractory, but the end sections 42 and 43 preferably are made of the hard type of refractory material.

In a structure embodying the invention, any metal parts that are exposed to an acid-containing atmosphere, such as the wear plates in the gate 39, should be made of an acid-resistant metal, such as type 309 heat resistant alloy, which is composed of 12% nickel, 25% chromium and 63% iron. In addition to hydrogen chloride, the atmosphere in the chamber 13, like the atmospheres in the chambers 12 and -14, contains hydrogen, so that the refractories used in all three chambers should be resistant to reduction.

The construction of the gate 39, as shown in Figure III, is such that each of the separate sections of the gate, when the gate is in normal position, is free to rise independently of the other sections, to accommodate a weld, torn edge, or other projection on the strip. The tubular lifting member 47 has a diameter substantially less than the diameter of the openings 46 through which it is threaded, so that when a projection on the strip strikes one of the sections 40, such projection can lift that section from its normal seat on the lintels 37 and 38, through a vertical distance equal to the difference between the diameter of the openings 46 and the outer diameter of the tubular lifting member 47, without lifting the other sections of the gate 39.

The freedom of the individual sections of the gate 39 to rise separately is an important factor in prolonging the life of the gate, because the force required to lift one of the sections is much less than the force that would be required to lift the entire gate if the gate were made all in one piece. Because of the small amount of force required to lift one section of the gate, each such section offers relatively little resistance to a projection on the strip and thus is lifted readily by such a projection without damage. The wear plates in the gate also are helpfiul in prolonging the life of the gate, since the wear plates are much more resistant to abrasion than the carbon blocks and tend to protect the carbon block-s against rap-id erosion.

The width of the gap bet-ween the lower wallv 32 and the gate 39 may be for A to inch to accommodate strips up to A; inch in thickness, traveling at speeds up to 250 feet per minute.

As shown in Figure 11, one of the rollers 11 is located so. as to support the strip just ahead of the lower wall 32. By means of such a roller, the strip may be maintained relatively high in the gap between the lower wall and the gate 39, whereby the cap piece 34 of the lower wall 32 suffers practically no abrasion. In view of the construction of the gate 39, hereinbefore described, the strip 10 may be permitted to run relatively close to the bottom of the gate without danger of damage to the gate.

Each of the rollers 11 is mounted in sealed bearings (not shown). These bearings are carried on relatively stable supports outside of the high temperature zone.

The space above the lintels 37 and 38 and the gate 39 may be supplied (through an inlet not shown) with the same gas that is supplied to the chamber 12, the lifting rods 49 and 50 being provided with adequate seals at the points where they pass through the casing 27, to prevent excessive loss of gas at such points. It will be observed that the lintel 37 is'not actually part of the sealing structure between the chambers 12 and 1-3. The function of the lintel 37 is to assist the lintel 38 in supporting the gate 39 in a fixed position.

Figure IV illustrates a structure in which a gate 66, which is generally rectangular in cross section, is supported mainly upon the lintel 38. In this structure the rearwardly inclined lintel 37 is replaced by a forwardly inclined lintel 67. In addition, guides 68 are provided at each end of the lintel 38 to assist in supporting the gate 66, and a stop 69 limits the extreme lower position of the gate 66 and thus determines the minimum gap that may be provided between the gate 66 and the cap 70 of the lower wall.

In the structure illustrated in Figure IV, since the lintel 67 does not support the gate 66, the lifting mechanism may be used not only to lift the gate during the operation of threading the strip, by sliding the gate up along the lintel 38, but also may be used to vary the position of the gate so as to vary the width of the opening between the gate 66 and the cap piece 70 to accommodate various thicknesses of strip.

Iclaim:

1. In an apparatus for passing a strip of metal at an elevated temperature through two successive chambers containing different atmospheres under slightly different pressures, a structure for providing a constant narrow opening between said chambers, in order to prevent the atmosphere of the chamber that is under lower pressure from contaminating the atmosphere of the other chamber, while maintaining a constant restricted flow of the at mosphere from the latter chamber into the former chamber and permitting the strip to pass from one chamber to the other, said structure comprising a lower wall, an upper gate the bottom of which is substantially parallel to and spaced from the top of said lower wall to provide a narrow opening therebetween, end members extending upward at each .end of said lower wall, a lintel extending between said end members, said gate being at least closely adjacent to said end members and said lintel and being adapted for movement between said end members, and means for raising said gate to permit a strip to be threaded through the apparatus, said lower Wall, gate, end members and lintel being made of a dense, thermally stable refractory and being carried upon stable supports located outside of the high temperature zone.

2. A structure as claimed in claim 1 wherein the gate is composed of separate sections each of which, when the gate is in normal position, is free to rise to accommodate a projection on the strip.

3. A structure as claimed in claim 2 wherein the sections of the gate are separated by metal wear plates.

4. A structure as claimed in claim 2 wherein the sections of the gate are provided with aligned openings through which is threaded a member for lifting the gate that is substantially smaller than said openings to permit relative vertical movement of said sections.

5. A structure as claimed in claim .4 wherein the sections of the gate are separated by metal wear plates having openings aligned with those in said sections, and the means for raising the gate is connected to at least one of said wear plates, which in turn can lift the member that is threaded through said sections.

6. A structure as claimed in claim 1 wherein the refractory is carbon.

7. A structure as claimed in claim 1 wherein the face of the lintel is inclined rearwardly and the opposed surface of the gate is correspondingly inclined, whereby the gate, in its normal position, rests upon the lintel.

8. A structure as claimed in claim 7 wherein a second lintel having a rearwardly inclined face is located on the opposite side of thegate, and. the surface of the gate opposed to said second lintel is correspondingly inclined; whereby the gate, in its normal position, rests upon both lintels.

9. A structure as claimed in claim 8 wherein the means for raising; the gate is adapted to slide the gate up and down upon the inclined face of the lintel, whereby said means may be used to adjust the width of the opening between the gate and the lower wall.

10. A structure as claimed in claim 1 wherein a roller for supporting the strip out of contact with the lower wall is located adjacent to said lower wall.

11. A structure according to claim 1 wherein the lower wall is composed of separate sections.

12. A structure according to claim 11 wherein the lower sections of the lower wall are separated by metal wear plates.

References Cited in the file of this patent UNITED STATES PATENTS 1,829,684 Stausel Oct. 27, 1931 1,872,434 Fahrenwald Aug. 16, 1932 2,278,275 McDonell Mar. 31, 1942 2,367,174 Renkin Jan. 9, 1945

Images