US2079494A - Continuous annealing process - Google Patents

Description

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l M w Christian Dantsizen, by 77! n 9 H Attorney.

C. DANTSIZEN CONTINUOUS ANNEALING PROCESS Filed Feb. 20, 1935 ASW ma l r q ma atented ay 4, i937 ATEs PATENT OFFICE Christian Dantsizen, Schenectady, N. Y., assigner to General Electric Company, a corporation of New York Application February 20, 1935, Serial No. 7,370

2 Claims.

The present invention relates to a continuous annealing process, and more particularly to a method for bright annealing a ferrous metal strip in a hydrogen atmosphere.

It is very desirable to obtain a bright clean surface prior to tinning iron or steel. Heretofore, however, considerable diiculty has been encountered in obtaining a bright surface on iron or steel which has been annealed in a hydrogen 10 furnace. Attempts have been made to anneal iron or steel in hydrogen with the idea of producing a silver bright surface which might be tinned directly after the anneal thereby avoiding the necessity of subjecting the ferrous metal to it a pickling process. So far as I am aware, however, in practically all prior attempts to obtain a silver bright annealed ferrous metal in the commercial grade of hydrogen, the annealed metal always has come out of lche hydrogen furnace in an oxidized condition.

It is one of the objects of the present invention to provide an emclent relatively simple process whereby a ferrous metal strip may be annealed silver bright in a hydrogen atmosphere containing the usual water and oxygen impurities.

The novel features which are believed to be characteristic of my invention are set forth with particularity in the appended claims. The invention itself however will best be understood from reference to the following specification when considered in connection with the accompanying drawing in which Fig. l is a view partly in section and elevation of a furnace and rolls with which my'invention may be carried into effect; Fig. 2 is a cross sectional view taken on lines 2 2 of Fig. l; and Fig. 3 is a cross sectional view taken on lines 3-3 of Fig. I.

Referring lmore particularly to the drawing, I represents an ordinary, small hydrogen furnace provided with a chamber 2 which is heated by means of an electric heater wire 3 connected to a suitable source of electric power, and supplied with hydrogen through a pipe 4. At one end of the furnace, I provide a cooling chamber 5. A T-shaped member 6 is supported within the heating chamber 2. The upper or horizontal part of the T-shaped member is provided with an opening or passageway 'l extending longitudid l0 extends Within the cooling chamber and 1S nally therethrough, as clearly indicated in Figs.l

provided with a series of openings in one end thereof, as indicated in Figs. 1 and 3, so that, water in the form of a spray may be directed against the under side of the cover plate 8. The water which collects in the bottom of the coolingI chamber is drawn off through a pipe I2. The metal strip to be annealed is drawn through the opening 'l in the T-shaped member 6 and between the water cooled block 9 and cover 8 of the cooling chamber by means of the motor driven rollers Ii.

'I'he hydrogen gas within the furnace preferably should be substantially pure but usually contains a certain amount of moisture. The amount of water vapor in a water vapor hydrogen atmosphere in equilibrium with iron oxide varies with the temperature of the atmosphere. For example, at a temperature .of about 1050 C. if the hydrogen atmosphere contains about 50% water vapor it will be in equilibrium with iron oxide. Likewise, at '700 C. if the hydrogen atmosphere contains about 37% water vapor, it will be in equilibrium with iron oxide. If the hydrogen atmosphere contains less than 1% water vapor, it will be in equilibrium with iron oxide at about 400 C. The above data shows clearly the tendency for water vapor to become more and more active towards oxidation of iron as the temperature is lowered. For these reasons it is substantially impossible to permit a metal strip to cool down in a hydrogen atmosphere and obtain a bright surface. If the hydrogen furnace atmosphere contains less than 1% moisture and is heated to about 700 C. while the ferrous mtal strip is drawn through the furnace, any oxide coating on the steel will be completely removed in the furnace. However, if the strip, while still in the furnace atmosphere, is cooled down slowly to say about 400 C., it would be oxidized quickly as hereinbefore pointed out.

In the present case however the above dimculty is overcome by drawing the metal strip while it is still in the furnace atmosphere and at a temperature of about 700 C. into the cooling chamber 5 of the furnace where it passes between the water cooled block 9 and the spray cooled cover 8 and is cooled quickly or quenched to a temperature well below 400 C. and evento room temperature or lower. The annealed metal strip is cooled through the critical temperature zone (about 400 C.)' so quickly that it has no opportunity whatever to oxidize and as a result the annealed metal is left in a silver bright condition.

What I claim as new and desire to secure by 55 Letters Patent of the United States is:

1. 'Ihe method of continuously bright annealing a ferrous metal strip which comprises drawing the strip while heated at a temperature of about '700 C. through a hydrogen atmosphere containing water vapor and thereafter while stili in said hydrogen atmosphere suddenly quenching the strip to a. temperature below 400 C.

2. The method of continuously bright annealing ferrous metal strip in a reducing atmosphere containing water vapor, which comprises drawing the strip through said atmosphere while heated at a temperature sulciently high to reduce any. oxide on said strip and thereafter while in said atmosphere suddenly quenching the strip to a temperature below about 400sC.

CHRISTIAN DANTSIZEN.

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