US2357126A - Alloying and fusing process - Google Patents

Description

Aug. 29, 1944. J. s. NACHTMAN ALLOYING AND FUSING PROCESS Filed May 5, 1938 3 Sheets-Sheet l Aug. 29, 1944. J. s. NACHTMAN 2,357,126

ALLOYING AND FUSING PROCESS Filed May 5, 1938 5 Sheets-Sheet 2 I i w 1 9) k Jwmvtm:

1944- J. s. NACHTMAN ALLOYING AND FUSiNG PROCESS Filed May 5, 1938 5 Sheets-Sheet C5 Patented Aug. 29, 1944 UNITED STATES PATENT OFFICE ALLOYING AND FUSIN-G rnoouss John S. Nachtman, Beaver, Pa.

Application May 5, 1938, Serial No. 206,257

Claims.

The present invention relates to methods and apparatus for applying a finishing treatmentalthough not necessarily the final treatment-to coated strip metal such as a sheet metal base carrying a film or layer of metal, e. g., electrodeposited metal, on a surface thereof.

The common hot-dip method involving, for example, the application of tin to strip steel, produces a coating generally poor in quality both as to uniformity and appearance. Electrodeposiposition alone, particularly in continuous highspeed processes, tends to produce a coating which, while having a better appearance and an improved uniformity, has localized areas wherein the strength of union or adherence of coating to base metal is too low. This problem is increased where the union is between the deposited metal and steel of relatively low carbon content. Accordingly, it is the primary object of the present invention to devise and provide a method oi treatment, and apparatus therefor, resulting in the production of a surface coating which is uniform in thickness, smooth and bright in appearance, and firmly and uniformly united to the base metal.

More specifically, this invention contemplates the formation of a sub-surface alloy zone between the base metal and a previously applied surface coating of metal with substantially simultaneous fusing of the surface coating-followed, of course, by cooling the fused material to solidification. In its preferred form the method comprises the steps of preheating the coated strip to a temperature approaching but below the fusing point of the coating; increasing the temperature sufficiently, or subjecting the strip to an already existing higher temperature that is sufflcient to produce fusion of the coating; and quick-chilling the strip to cause a rapid solidification of the fused material.

In the first step, some alloy is formed between the base metal and the coating, and the use of a preheating chamber also affords increased efflciency and permits a shortening of the actual fusion chamber associated therewith. A minimum possible shortness of the fusion chamber is desirable where an elongated or continuous strip is conveyed therethrough, as such a strip cannot well be supported (e. g., cannot be physically contacted) while its coating is in a partially molten condition. Most of the total heat required is used to raise the temperature of the base metal, and hence the temperature for preheating is made as high in each case as can be without rendering the coating soft and sticky.

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During the carrying out of the fusing step, in the fusion chamber, there is a further alloying of the base metal and its coating, the degree or amount of which is determined by the temperature of the strip and the time period during which the strip is subjected to such temperature. When the coated strip being treated is subjected to the heating zones for only a few seconds the amount of alloy formed is difficult to detect: nevertheless, the coating is brightened and is united to the base metal more firmly than it was prior to the treatment.

In the following cooling step, in the cooling chamber, the temperature of the strip, or at least of the coating, is quickly reduced and held to a value below the solidification point of the coating material, thus stopping the alloying action and simultaneously solidifying or hardening the fusedmetal into a continuous coating of excellent uniformity and fine appearance.

The heat source or sources for the preheating and fusing steps may be of any suitable character and arrangement. For example, electrical heating elements may be disposed within the preheating and/or fusing chamber. In some instances a liquid or gaseous medium may be heated exteriorly of the chamber or chambers and circulated therethrough. Likewise the chilling means may be varied in form and arrangement.

If the nature of the coating metal is such that a damaging oxidation takes place in the presence of air in any of the chambers, e. g., wherein the strip and/or coating is maintained at elevated temperature, provision will be made for supplying a reducing atmosphere, or non-oxidizing atmosphere, in one or more of the chambers. This can be done in various suitable ways, including sim ply the injection of reducing gases into such chambers in sufi cient volume to displace all or most of the air. In the heating chambers the result is obtainable in desirable manner either by employing, as a heat source, gas jets burning with reducing fiame, or by utilizing a heat-transmitting medium such as oil so that use can be made of the reducing vapors or gases given off by the hot medium,

The major objects of the present invention will be apparent from the preceding discussion. Further important objects reside in the provision of novel and useful apparatus in several forms for effectively treating a strip of coated material in the manner set forth, and other objects will appear as the description proceeds. The drawings accompanying this specification consist of the following illustrations;

i Fig. 1 is a side elevational view, with portions of the supporting structure in section, of a preferred form of apparatus constituting a part of this invention;

Fig. 2 represents a vertical section taken substantially on the plane of line 2--2, Fig. 1, looking in the direction of the arrows;

Fig. 3 represents a further vertical section taken. on a plane normal to that of Fig. 2, substantially on the plane of line 33 of Fig. 2, looking in the direction of the arrows;

Fig. 4 is a view similar to Fig. 3, but showing a somewhat modified form of apparatus;

Fig. 5 represents, in section on the order of Figs. 3 and 4, a still further modified form of apparatus.

With continued reference to the drawings, wherein like characters are employed to designate like parts, and with particular reference for the moment to Figs. 1 to 3, the numeral l designates, let us say, a very long, i. e., continuous strip of sheet steel that has passed continuously through a series of treating apparatus and has just come through a plating bath where it received, by electrodeposition, a surface coating of metal, e. g., of tin. It is shown entering into, passing through and emerging from the apparatus of the present invention, indicated generally and in its entirety by the numeral 3.

The apparatus 8 has a shaping and supporting framework including vertical corner stanchions ll intertied by cross members ill, the stanchions projecting downwardly into a pit 52 below a floor l3. This framework carries four vertical walls l -l, properly joined and sealed at their edges to form a rectangular tank closed at the bottom by a plate IS. The tank is substantially filled with liquid as indicated, and by means of a horizontal baffle plate l6 and a vertical partition H the tank is divided into a pair of chambers l8 and IQ, hereafter referred to respectively as the fusing and chilling chambers. The partition I! is a hollow double-walled structure filled with a heat-insulating material 26.

The chambers 18 and i9 open upwardly into a hood 22 and have individual stack vents 23 and 24, separated by the upper part of the partition 17. The vent 23 preferably is provided with a damper 25. Two of the hood walls, as shown (Fig. 3), are inclined to overhang two of the walls I4 and form therewith and with a pair of added vertical walls 26 and 27, a pair of chambers 28 and 29 hereafter referred to respectively as the pre-heating and exit chambers. The walls 26 and 21 are approximately U-shaped in cross section, and the former is covered with heat-insulating material 39.

The bottom of chamber 28 is formed by a platform 3| upon which is mounted a pair of entrance rolls 32 which pinch and feed the strip l into said chamber. One of these rolls is driven by a motor 33 (Fig. 2). The strip passes upwardly, centrally of the chamber 28, to a driven guide roll 34, the latter being disposed within hood 22 and having a shaft 35 driven by a motor 36 and mounted in bearings 31. This guide roll is so located that the strip then passes downwardly centraveling strip. The strip preferably is then drawn downwardly toward floor level to leave the apparatus by way of a delivery roll 44 and thence either to be reeled or to be passed on for further treatment. A platform 45 carries the roll 44, and a shielding wall 21 preferably is provided to protect the strip in its passage to said roll.

One of the .walls M has a removable cover 41 for facilitating assembly, adjustment and repair of some of the parts.

As previously stated, the preheating and fusing may be done in any manner suitable for obtaining the requisite temperatures. The illustrated embodiment of preheating means comprises two banks of electrical heating elements 48 arranged in the chamber 28 on opposite sides of the strip I and controlled by a thermostat 49 which is adjusted to afford a chamber temperature that will cause some alloying between the coating metal and the steel without actually fusing the coating metal. If the coating material happens to be such as will oxidize readily, reducing gas may be injected into the preheating chamber or may be caused to pass from the hood above the fusion chamber 58 into the chamber 28 by closing the damper 25. In some cases, sufficient preheating temperatures are obtainable by conduction through and radiation from the wall between the fusing and preheating chambers.

The liquid in the fusion chamber l8 may likewise be heated by banks of electrical units, 50, under the control of one or more thermostats 2 that are adjusted to afford a temperature that will cause the coating to fuse and flow sufficiently to spread uniformly and smoothly over the surface of the base metal; at the temperature of the fusion chamber the coating further alloys itself simultaneously with the base metal of the strip. The liquid heat-transmitting medium may consist of oil or oily medium with a sufficiently high flash point and no appreciable tendency to attack the metal coating.

The baiile plat 16 tends to prevent liquid circulation and heat exchange between the chilling and fusion chambers. It minimizes the formation of eddy currents by the moving strip.

Almost immediately after passing the baffle the strip 1 has its coating chilled and hardened by the impingement thereon of jets of cooling liquid which come from opposed sets of immersed pipes 53 designed to spray the cold liquid toward the two surfaces of the strip. These pipes connect to manifolds or headers 54 externally of the chamber and the manifolds in turn connect by way of a pipe 55 to the discharge side of a liquid cooling and circulating unit that comprises a pump 56 and a heat exchanger 51 (Fig. 1). The exchanger has the usual connections 58, 59 for circulation therethrough of a separate heat removing liquid.

The intake side of the pump 56 is designed to withdraw the heat-transmitting oil or other liquid from the chilling chamber I9, and, to effectively accomplish this, the withdrawal is effected at three points by means of a pipe 60 having branches 62, 63, the branch 83 in turn having a branch 64. Each branch is equipped with a valve, as shown, for manually regulating the flow through each and thus controlling the chamber temperatures at and adjacent the points where the branches enter the chamber.

The branch 62 enters the bottom of the chilling chamber and is regulated to draw 011 just enough liquid to ensure constant mixture or internal circulation of the liquid. Branch' 63 is connected to a manifold 65 from which a pair of pipes 68 project into the chamber immediately adjacent the baille It. Best temperature conditions are obtained by removing most of the total withdrawn liquid through these pipes 66. The third branch, 64, terminates in a pipe section 81 that is disposed in the extreme upper part of the chilling chamber (Fig. 3). In some instances, where the heat-transmitting or chilling liquid is viscous it will be desirable to use this pipe section, or added heating elements adjacent thereto, to heat th surface portion of the liquid and render it readily removable by the squeegee assembly 42,

As shown in Fig. 2, a chamber 88 containing a float 69 may be provided in communication with the upper part of the liquid body, with the derstood, and a detailed summary therefore is believed unnecessary. The preheating step has several functions as above set forth, but its primary purpose is to bring the entire strip to a temperature approaching but short of the fusion temperature of the coating, thus permitting the fusion chamber to be of a desirably short length. The vertical stretch of the strip is preferable for passage through the fusion chamber as it aids in producing a rapid and uniform spreading of the fused metal, and supports the strip without tendency to distort or to deflect. Henc the slot 38 in the baffle may be of a desirable minimum width. During the interval between contacting driven guide roll 34 and contacting roll 39 the coated strip does not contact any solid object: in that interval the already preheated coating is brought to fusion temperature and then is solidified, solidification being complete before the coated strip reaches roll 39. Preferably, the procedure is so effected that actual melting of the coating occurs by the time the strip approaches the bottom of chamber l8, thereby making the interval of actual molten condition of the coating an'extremely brief one. This is desirable because if the coating is maintained at or above melting temperature too long there is a tendency for the depth of coating to become less uniform than otherwise.

The heating and cooling arrangements of the Figs. 1 to 3 are important, but may be modified somewhat within the scope of this invention. For example, the liquid medium may be omitted partially or entirely. Fig. 4 illustrates a modification where it may be completely eliminated. In describing this form no specific reference will be made to those parts which are duplicates of some of those in Fig. 3.

The major change in Fig. 4 consists in removal of the upper section of the chilling chamber and its squeegee assembly and in withdrawal of the strip directly from the top of the shortened chamber. In doing this, the hood is narrowed to afford a suitable hood 2241 having an intake pipe 23a, and a shortened wall structure Ma is substituted for three of the walls ll of Figs. 1 to 3. The partition Ila and its insulating material 20a are brought downwardly into proximity to the lower guide roll 39, for efllciency in chilling by gas in the chamber l9a. The delivery roll 44 is mounted on the wall structure to receive the-strip direct from th roll 38 since the squeegee action is unnecessary where gas is used for the chilling pu pose.

The sets of heating elements 48a, disposed in the preheating chamber and controlled by the thermostat 49a, preferably consist of gas jets which burn with reducing flames directed against the strip surfaces. This is true also of the heating elements 50a of the fusion chamber l8 under control of thermostats 52a. If a reducing atmosphere is desirable, and not sufficiently provided by the gas jets, reducing gases may be injected into the heating chambers through the hood pipe 23a. The injected gases may be sufllciently hot for preheating, and hence need to be augmented only by fusing elements in the chamber 18. It is of course to be understood that the temperatures and their relationship to each other and the fusion point of the strip coating must be maintained as previously set forth in the objects and in the description of Figs. 1 to 3.

Although liquid may be used for cooling in conjunction with gaseous heating, the chilling apparatus of Fig. 4 is designed to operate through a gaseous cooling medium, such as cold air, cold neutral gas or cold reducing atmosphere-preferably a cold reducing atmosphere, To this end the pipes 53a receive the cold gas under pressure and discharge it in jet form against the strip. Circulation is maintained by withdrawing the warmer gas through the pipe sections 66a, any suitable pumping and heat-exchanging apparatus being connected to pipes 53a and 66a externally of the chamber in obvious manner.

By filling the chilling chamber with liquid to a level just below the baiiie l6, and substituting a pair of squeegee rolls for the delivery roll 44, a liquid cooling medium such as cold oil, or cold waterpreferably cold water-may be circulated through the pipes 53a and 66a in lieu of the cold reducing atmosphere.

In Fig. 5 there is illustrated a further modification, having the same three major parts as the preceding forms but having said parts rearranged, and designed to operate with a liquid medium in both heating chambers and a gaseous medium in the chilling chamber. This entire apparatus may be above floor level, or its heating chambers may be disposed in a pit. In view of its close relationship to the previous forms, and

its three-step process, a very brief description will sufiice.

The heating chambers of Fig. 5 comprise a vertical preheating tank 12, and a fusion tank 13 substantially in the-shape of a triangular prism having one side inclined to the horizontal in a direction upwardly and away from the tank 12. An inclined tube 14 which is rectangular in cross section joins the two chambers, both of which are filled with liquid tothe indicated level, maintained'by the float-switch device 69, 10 in conjunction with any suitable supply means. The tanks have normally closed drain pipes 15, 16.

The upper end of the preheating tank has a slot ll for the entrance of the strip 1. from the feeding rolls 321). From these rolls the strip passes downwardly to the guide roll 34b and then is drawn off at an angle through the tube 14, the fusion tank and the baffle l 6b by a pair of squeegee rolls 42b, 43b. The latter are located adjacent the strip outlet side of a chilling tank 18,

which at said outlet side has a baflie 19 through which the treated strip is discharged.

The liquid is preheated in the tank 12 by elements 48b that may comprise hot pipes but which preferably consist of electrical units controlled by a thermostat 4%. Likewise the units 50b in the fusion tank may take various forms but preferably comprise electrical elements un der control of a thermostat 52b. A vent pipe 80 serves to remove hot vapors and gases adjacent the baflle I62), thus minimizing the heat transfer between the fusion and chilling chambers.

The strip is quickly chilled in the tank 18 by jets of cold air, cold neutral gas or cold reducing gas, preferably fed against it from pipes 531). A withdrawal pipe 82 at a higher point in the tank serves to return the warmer gas to the cooling system from which the pipes 531) receive their supply.

If desired, the direction of strip travel in Fig. may be reversed; and the chilling chamber may be removed and the preheating chamber converted into a cooling chamber; this would combine the preheating and fusion units, in effect, into one tank, but such an arrangement, is satisfactory in cases where the strip is permitted or caused to travel at slow speed.

While the process and apparatus above described were devised With particular reference to a treatment of strip steel carrying a coating of tin, they may, without the exercise of inventive genius, be employed for a like treatment of other metallic coatings and for combinations in which the base metal is other than steel. Thus, the process and apparatus are operable for like treatment of metallic strip material carrying a coating of copper, or zinc, or nickel, or lead, or bismuth, or other metal which has a melting point lower than the melting point of the base metal, or copper and zinc, or copper and tin, or nickel and copper, or lead and tin, or lead and bismuth, or any other combination of two coating metals the outermost of which shall have a melting point below the melting point of the base metal. Likewise, they are operable for treating metal-coated strips whose base metal is copper, aluminum, nickel, stainless steel, Monel metal or any other metal strip having a higher melting temperature than that of the exposed coating metal.

With reference to the specific combination hereinbefore referred to, of strip steel of relatively low carbon content and of about 30 gauge, carrying on its surfaces electrodeposited coatings of tin, it is noted that the coated strip desirably is preheated to a temperature of about 400 F. in the preheating chamber; that it desirably is further heated to a temperature of about 460 F. in the fusing chamber and is held at the latter temperature for some seconds; and that it is cooled to about 150 F. or below before being contacted by any solid object.

While the invention has been specifically described hereinbefore with particular reference to the treatment of electrically deposited metallic coatings, it is to be appreciated that the process and apparatus of the invention are applicable, without inventive change, to the treatment of coatings which have been applied by the known hot dip method.

Obviously, many other alterations and rearrangements of parts in the several illustrated forms may be made without departing from the spirit and scope of the invention, which may be determined from the appended claims.

I claim: a

1. In a method of treating metal strip having a metal plating on surface portions thereof to provide a bright, uniform and adherent coating of improved characteristics, the steps of heating the strip to bring the entire strip to a temperature approaching but short of the melting point of the plating in one heating zone, then further heating the strip in a second heating zone communicating with the first zone 'to melt the plating, then cooling the strip in a cooling zone communicating with the second heating zone to solidify the plating, controlling the temperatures of the heating and cooling steps so that the plating is melted for only a relatively short period of time, and protecting the strip by non-oxidizing fluids during the heating and cooling steps and the passing betwee zones.

2. In a method of treating strip steel having a tin surface plating thereon to provide a bright,

tin plating, controlling the temperatures of the heating and cooling steps so that the tin plating is melted for only a relatively short period of time, and protecting the strip by non-oxidizing fluids during the heating and cooling steps and the passing between zones.

3. In a method of treating metal strip having a tin plating on surface portions thereof to provide a bright, uniform and adherent coating of improved characteristics, the steps of preliminarily subjecting the tin plating and adjacent surface portions of the strip to heat treatment at about 400 F. in a heating zone to bring the entire strip to a temperature approaching but short of the melting point of the tin plating, then subjecting the tin plating and adjacent portions of the strip to heat treatment at a temperature of about 460 F. to melt the tin plating in a second heating zone communicating with said first zone, then cooling the strip at a temperature of about F. to solidfy the tin plating in a cooling zone communicating with the second heating zone, controlling the temperatures of the heating and cooling steps so that the tin plating is melted for only a relatively short period of time, and protecting the strip by non oxidizing fluids during the heating and cooling steps and the passing between zones.

4. In a method of treating metal strip having a metal plating on surface portions thereof to provide a bright, uniform and adherent coating of improved characteristics, the steps of moving the strip in a preliminary heating zone to bring the entire strip to a temperature approaching but short of the melting point of the plating in said zone, then further moving the plated strip downwardly in a vertical path through a second heating zone communicating with the first zone and maintained at a temperature to melt the plating, then further moving said strip downwardly in said vertical path into a cooling zone communicating with the second heating zone and maintained at a temperature to solidify the plating, controlling the temperatures of the heating and cooling steps so that the plating is melted for only a relatively short period of time, and protecting the strip by non-oxidizing fluids during the heating and cooling steps and the passing between zones.

5. In a method of treating metal strip having a metal plating on surface portions thereof to provide a bright, uniform and adherent coating of improved characteristics, the steps of heatin the strip in a segregated heating zone to bring the entire strip to a temperature approaching but short of the melting point of the plating in said zone, then further moving the plated strip downwardly in a vertical path through a second segregated heating zone communicating with the first zone and maintained at a temperature to melt the plating, then further moving said strip downwardly in a vertical path through a segregated cooling zone communicating with the second heating zone and maintained at a temperature to solidify the plating, controlling the temperatures of the heating and cooling steps so that the plating is melted for only a relatively short period of time, protecting the strip by non-oxidizing fluids during the heating and cooling steps and the passing between zones and restricting substantial circulation between the fluids in adjacent zones.

- JOHN S. NACH'I'MAN.

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