US3231708A

US3231708A - Heating means and method for continuous galvanizing process

Info

Publication number: US3231708A
Authority: US
Publication date: 1966-01-25
Anticipated expiration: 1983-01-25

Description

Jan. 25, 1 R. M. BEAUDOIN ETAL HEATING MEANS AND METHOD FOR CONTINUOUS GALVANIZING PROCESS Filed Dec. 26, 1962 m w. ON 6 T mww T R A W NE. .5 M w R B L| l Nu L 4 I H.

8K owigw United States Patent Ofiice 3,231,708 HEATING MEANS AND METHOD FOR CON- TINUOUS GALVANIZING PROCESS Reno M. Beaudoin, Winfield, and Theodor-old. Krengel,

Chicago, Ill., assignors, by mesne assignments, to Allied Tube & Conduit Corporation, Harvey, 111., a corporation of Illinois Filed Dec. 26, 1962, Ser. No. 247,104 6 Claims. (Cl. 219-10.61)

Thisinvention relates to a continuous galvanizing process, and, in particular, relates to an improved heating means and method responsible for producing high quality galvanized products.

The heating means of this invention is particularly suitable for use in the continuous galvanizing of elongated metal products. Reference will be made to the process of galvanizing tubing to provide'an illustration of the inventive concepts.

In the galvanizing of tubing, it is desirable to provide means whereby the tubing can be conveyed in a continuous manner through a galvanizing vat. It is also desirable to provide all necessary preparatory steps as continuous phases of the operation. In a copending application, Ser. No. 106,699, filed May 1, 1961, and entitled Continuous Tube Forming and Galvanizing, now Patent No. 3,122,114, there is disclosed a completely continuous operation including the phase of forming metal strip and tubing, and including all necessary preparatory and finishing steps incident to galvanizing.

In galvanizing operations of the type described in this copending application and in other continuous galvanizing processes, it has been found that the galvanizing reactions can be carried out more rapidly and with greater uniformity when the material to be galvanized is preheated to an elevated temperature above the melting temperature for the zinc such as about 850 F. This preheating takes place immediately prior to entry of the material into the galvanizing vat. It is important to achieve the desired preheating without exposure of the metal surface to oxidizing conditions, otherwise, the metal oxides that would form at an accelerated rate while the tubing is heated to an elevated temperature wouldinterfere with the formation of a suitable galvanized surface.

It has also been found desirable to effect the removal of moisture from the surface of the tubing prior to entry into the preheated furnace. Moisture which is left on the surface from preceding cleaning and rinsing operations makes oxygen available to the surface when the surface is raised to the galvanizing temperatures. Such oxygen will cause oxidation of the surface and, as noted, 1

the presence of oxides on the surface interferes with the application of uniform zinc coatings during the galvanizing steps. Furthermore, even if oxidation does not take place, moisture trapped in the surface of the metal will evaporate and result in bubbles which ultimately cause discontinuities in the zinc coating.

Prior systems for effecting removal of moisture and for preheating have not performed entirely satisfactorily. It has been found that all of the moisture could not be 're moved unless relatively expensive and time consuming operations were carried out;' Difiiculties'have also been recognized in the preheating operation particularly because of the inability of the heating fixtures to stand up during the process. Thus, the nature of the operation requires the continuous passage of tubing and other metal through the heating means. Ifthe continuous lengths of material were for some reason displaced from their normal line of travel, the heating means could be physically damaged by the work. Furthermore, induction coils are often used for these purposes, and, therefore, any shutdowns in the operation tend to damage the heating means since the coils will rapidly cool and thermal stresses will result.

It is an object of this invention to provide an improved heating means and method adapted to provide for high quality galvanized products in a highly eflicient continuous process.

It is an additional object of this invention to provide a heating means capable of providing for virtually complete removal of moisture and capable of preheating the work in a continuous galvanizing operation.- I

It is a further object of this invention to provide a heating means and method capable of achieving the foregoing objects in a highly reliable manner whereby the possibility of damage to the heating structures during continuous operationor asa result'of shutdowns is greatly diminished.

These. and other objects of this invention will appear hereinafter and for purposes of illustration but not of limitation, specific embodiments of this invention are shown in the accompanying drawings in which:

FIGURE 1 is a detailed elevational' view, partly cut away, 'of heating means characterized by the features of this invention;

FIGURE 2 is a detailed perspective view of the housing for the heating means;

FIGURE 3 is a cross-sectional view taken about the line 3'3 of FIGURE 2;

FIGURE 4 is a detailed view of an insulating sleeve employed in the construction of the heating means; and

FIGURE 5 is a plan view taken about the line 5+5 of FIGURE 2 illustrating the arrangement of the heating coils-in the structure.

The heating means of this invention generally include a housing open at both ends and supporting a plurality of hollow insulating means disposed in end-to-end relationship. The insulating means'define a passage through the housing and an induction'coil is wrapped around the insulating means in order to provide for heatingof the lengths passing therethrough. Means are also provided for directing coolant through the induction coils.

The invention also contemplates the use of second'hollow insulating means which define a passage in line with the above mentioned passage. Induction coils are also provided around this insulating means and, therefore, the continuous lengths to be galvanized are passed through a pair of heating means in succession.

In the use of the heating means, they are arranged adjacent each other and the lengths to be galvanized are passed through them immediately prior to entry into the zinc vat. The first heating means are adapted to drive off moisture and oil residue picked up by the lengths during the washing and rinsing operations. The second heating means then serve to preheat the continuous lengths and they are then movedinto the zinc vat. A hot inert aL-nosphere or dry air blast may be directed onto the materlal to be galvanized at a point intermediate the two heating means. This hot blast'cooperates with the first heating means to provide for removal of all detrimental moisture.

The accompanying drawings will provide a more detailed illustration of the inventive concepts. FIGURE 1 illustrates a continuous length of tubing 10 as it is being passed through a first heating means 12 and a second means'14. The heating means 1-2 comprises a hollow insulating sleeve 16 dimensioned to receive the tubing 10 a small clearance being provided for the tubing. An induction coil 18 is wound around the sleeve 16. The coil may be formed of copper tubing and is provided with an internal passageway for a cool-ant. Terminal 20 provides one electrical connection for this induction coil.

Intermediate the coil 18 and the sleeve 16, there is Patented Jan. 25-, 1966' provided a wrapping 22 of insulated material. The material for the wrapping must have insulating characteristics so that it will not short out the induction coil. In addition, the wrapping must be heat resistant and is also adapted to resist the passage of moisture into the passage. With this arrangement, the wrapping serves to protect the work while in the heating means so that there is no danger of moisture accumulating on the work during this time.

A conduit 24 extending from the terminal 20 carries the current as well as the coolant to an induction coil 26 associated with the heating means 14. This heating means also includes a plurality of sleeve means 28 arranged in end-to-end relationship, and extending along the entire length of the passage. As shown, these sleeves are slightly larger in diameter than the work so that a slight clearance is provided when the work passes through the heating means.

A wrapping 30 similar to the wrapping 22 of the heating means 12 is provided for protecting the work in the same manner as above described. The

wrappings

22 and 30 may be provided in several layers around the sleeve and a preferable material for the wrappings comprises silicone covered Fiberglas although other suitable materials will be obvious to those skilled in the art.

A housing 32 of a type suitable for mounting the heating coils is shown in FIGURES 2 and 3. This box-like structure includes front and

rear ends

34 and 36 which define openings leading to the passage 38 defined by the sleeves 28. The coil 26 which is disposed around the sleeves 28 is preferably provided with insulating strips 40 between the loops therein to void any danger of shorting out the coil.

Four oppositely disposed ribs 42 extend toward the center of the housing 32 and these ribs support the heating means 12 disposed therein. Extending through the housing, there are provided

conduits

44, 46, and 48 which provide for circulation of coolant through tthe induction coils. The conduit 46 comprises the passageway for entry of coolant and conduits 44 and 48 serve as the exit passageways. It will be noted that with this arrangement, the coolant will split into two paths as it enters at the juncture of the conduits 46 and the coil 26.

Disposed on the side wall 50 of the housing, there is provided a first terminal 52 and a larger terminal 54. The coil 26 is connected to the conduit 48 which extends into a portion 56 welded across the face of the terminal 54. The terminal 54 comprises a relatively great area in order to decrease the current density, and the provision of the conduit portion 56 across the face of this terminal further serves to eliminate the tendency toward overheating in this area.

FIGURE 1 illustrates the preferred form of the invention in which both of the heating means 12 and 14 can be connected in the same electrical and coolant circuits. FIGURE 1 also illustrate-s a hot blast outlet 58 interposed between the heating elements 12 and 14. This blast is preferably included in the system since it serves to remove any remnants of moisture or other undesirable substances which form on the surfaces of the work prior to preheating.

In the aforementioned copending application, there is described a preheating means which is enclosed in a housing mounted in communication with the zinc vat. Furthermore, the housing in this application is provided with a source of inert gas which protects the work during preheating and which is passed into the zinc vat to form an inert atmosphere therein. The present invention contemplates the use of inert gas in the housing 32 and, furthermore, means providing communication with the Zinc vat in the manner described in the prior application are also envisioned. v

In the operation of the heating means of this invention, the respective heating coils are energized and the length of tubing is passed therethrough. It will be understood that the operation contemplates various preparatory steps by means of mechanisms not shown in the drawings, and, furthermore, the actual galvanizing operation will take place in a logical succession.

The tubing 10 will have substantial amounts of moisture thereon as a result of the previous washing and rinsing operations. The heating means 12 is adapted to drive out moisture and oil residue in the surface of the tubing, and these contaminants are thus effectively removed at this time. Where the hot blast means 58 is employed, a highly effective preparation of the surface is accomplished. Thus, this blast means serves as a further drying means and is also effective to remove mechanically any foreign material on the surface of the tubing.

Following the above steps, the tubing is conducted into the heating means 14 where it is preheated to the desired temperature for galvanizing. As previously indicated, the use of an inert atmosphere in the housing 32 containing the heating means 14 is contemplated. The tubing will, there-fore, be protected during its traverse through this heating means and will enter the galvanizing vat in an ideal state for this operation. The described system provides many advantages over systems previous-1y employed for similar purposes. With regard to the heating means 12, it has been found that the provision of this separate heating means of the specified design provides clear advantages. Thus, it has been recognized that the use of a relatively low capacity heating means for removing moisture prior to entry into the preheating housing produces unexpected results since the moisture is more effectively removed at this time. In other words, the simple application of heat from preheating coils has been ineffective to remove all detrimental moisture while the use of a separate low capacity heating means at a point preceding the preheater will remove the detrimental moisture.

It is believed that the specific design of this low capacity heating means is particularly important in providing the results described. Specifically, it is believed that the use of induction coils at this phase of the operation serves to drive out moisture in the surface of the tubing. It is well-known that the magnetic field setup in induction heaters will penetrate beneath the surface of the work being heated, and this is believed to result in a more thorough removal of moisture than would be possible if radiant heat were employed.

The structure of the heating means 12 and 14 is also highly important. Thus, the provision of

wrappings

22 and 30 is critical since these wrappings protect the passages which are defined by the insulating sleeves. The wrappings provide a continuous seal around the sleeves and, therefore, penetration of coolant or condensation from the coils into the passage is prevented. Furthermore, the sealing prevents passage of zinc through the sleeves into contact with the coils. The zinc is known to enter the passage on occasion as when it backs up from the galvanizing vat.

The use of a plurality of sleeves 28 in the heating means 14 also represents a critical feature of this invention. These sleeves, which may be formed of Transite asbestos or similar materials, will give if subjected to thermal stresses, and, therefore, the danger of cracking is greatly minimized. If cracking of any one sleeve should occur, it will be apparent that the damaged sleeve could be replaced without the necessity for replacing the entire passage. I

The mounting of the coils 26 of the heating means 14 provides an arrangement capable of resisting damage if for some reason the tubing 10 is moved out of line during the continuous operation. Thus, the rib supports 42 provide secure mounting for the coils and also serve to center the coils with respect to the housing. It will also be appreciated that if the operation is suddenly stopped, and the tubing 10 moves out of normal position, the ribs 42 will provide effective support for the heating means.

As previously indicated, the preheating is preferably carried to a temperature of about 850 F. or above. The coils 26 must, therefore, be connected across a source of power suflicient to achieve this end. The heating means 12 preferably raises the tubing to a temperature of about 200 F. and it is preferred to have the coils 18 of this heating means energized by the same source of power as the coils 26. It will be apparent that the terminals shown in the accompanying drawings will permit connection of each of the heating means in this manner.

The frequency of the power for energizing the coils is not critical and high or low frequency induction heating is, therefore, contemplated. This is particularly true in the case of thin walled tubing since virtually all induction heating means will serve to heat the relatively thin walls of the tubing. Any moisture which is to be driven out of walls of the tubing will extend, at the most, only a few ten-thousandths of an inch into the tubing and, therefore, induction means of any design will be effective to dispose of this moisture.

It will be understood that various modificatiops can be made in the above described heating system which provide the characteristics of this invention without departing from the spirit thereof, particularly as defined in the following claims.

That which is claimed is:

1. A heating means for use on continuous lengths of metals comprising a housing open at both ends, a plurality of hollow insulating means disposed in end-to-end relationship and defining a passage through said housing, said hollow insulating means being disconnected with respect to each other whereby the insulating means are adapted to give relative to each other in response to thermal stresses and whereby individual damaged insulating means can be replaced, an induction coil wrapped around said insulating means and extending lengthwise of said passage whereby the lengths passing therethrough can be heated, and means for circulating coolant through said coils.

2. A heating means for use in the galvanizing of continuous lengths of metal tubing comprising a housing open at both ends, a plurality of insulating sleeves disposed in end-to-end relationship and defining a passage through said housing, said sleeves being disconnected with respect to each other whereby the sleeves are adapted to give relative to each other in response to thermal stresses and whereby individual damaged sleeves are adapted to be replaced, a conductive coil having an internal passageway wound around said insulating means and extending lengthwise of said passage whereby the tubing passing therethrough can be heated, and means for circulating coolant through said coils,

3. A heating means for use in the galvanizing of continuous lengths of metal tubing comprising a housing open at both ends, a plurality of insulating sleeves disposed in end-to-end relationship and defining a passage through said housing, a conductive induction coil having an internal passageway wrapped around said insulating means and extending lengthwise of said passage whereby the tubing passing therethrough can be heated, a second insulating sleeve means defining a passage preceding said first mentioned passage, a conductive induction coil having an internal passageway disposed around said second insulating means whereby moisture can be removed from said tubing prior to passage of the tubing through said first mentioned passage, means for passing coolant through the passageway of said coils and wrappings disposed around each of said sleeve means and beneath said coils, said wrappings being heat resistant and adapted to prevent passage of moisture to said sleeves from said coils and to prevent passage of zinc from said passages to said coils.

4. A heating means in accordance with claim 3 including means disposed between said passages in the path of movement of said tubing adapted to direct a hot inert atmosphere blast onto said tubing for removing any remnants of moisture or other foreign material on the surface of said tubing after passage from the preceding passage.

5. A heating means in accordance with claim 3 wherein said housing is provided with ribs extending inwardly from the side walls thereof, said ribs contacting the induction coil in said housing and holding the coil in the path of said tubing.

6. A heating means in accordance with claim 3 wherein said housing is provided with means for maintaining an inert atmosphere in its interior and around the tubing passing therethrough.

References Cited by the Examiner UNITED STATES PATENTS 1,691,349 11/1928 Harrington et al. 2l0-10.49 2,459,507 1/1949 Denham 219-1051 X 2,583,227 1/1952 Neidigh 21910.61

' 2,648,759 8/1953 Machian et al 219-10.69 2,661,386 12/1953 Lundgren 13-35 2,722,589 11/ 1955 Marquardt 219-1061 2,762,894 9/1956 Body et al. 219-10.61 3,010,844 11/1961 Klein et al. 11751 3,047,420 7/1962 Bernick et al. 117-51 3,117,209 1/1964 Peltier 21910.61

RICHARD M, WOOD, Primary Examiner.

Claims

1. A HEATING MEANS FOR USE ON CONTINUOUS LENGTHS OF METALS COMPRISING A HOUSING OPEN AT BOTH ENDS, A PLURALITY OF HOLLOW INSULATING MEANS DISPOSED IN END-TO-END RELATIONSHIP AND DEFINING A PASSAGE THROUGH SAID HOUSING, SAID HOLLOW INSULATING MEANS BEING DISCONNECTED WITH RESPECT TO EACH OTHER WHEREBY THE INSULTAING MEANS ARE ADAPTED TO GIVE RELATIVE TO EACH OTHER IN RESPONSE TO THERMAL STRESSES AND WHEREBY INDIVIDUAL DAMAGED INSULATING MEANS CAN BE REPLACED, AN INDUCTION COIL WRAPPED AROUND SAID INSULATING MEANS AND EXTENDING LENGTHWISE OF SAID PASSAGE WHEREBY THE LENGTHS PASSING THERETHROUGH CAN BE HEATED, AND MEANS FOR CIRCULATING COOLANT THROUGH SAID COILS.