US2288803A - Metal treating - Google Patents

Description

Patented July 7, 1942 UNITED STATES PATENT OFFICER METAL TREATING John Happel, Brooklyn, and Wayne A. Howard, Manhasset, N. Y., assignors to Socony-Vacuum Oil Company, Incorporated,New York, N. Y., a corporation of New York No Drawing. Application October 10, 1941, Serial No. 414,452

8 Claims.

result. At the high temperatures employed;

metals tend to oxidize in the presence of air and other oxygen containing mixtures and compounds wherein the oxygen is available for reaction with the metala This problem is found in connection with all heat treating operations wherein a bright surface is desirable and is particularly acute in connection with continuous bright annealing of strip metals.

Water and mineral oils have been used for quenching, but in many instances, as in handling strip metals, both are unsatisfactory. Water is highly objectionable because it tends to cause formation of an oxide film, while oils normally used are of such characteristics that obiectionably heavy deposits thereof are left on the metal and such oils have a tendency to decompose and deposit carbonaceous matter difficult to remove on metal being treated. The oils are also ineilicient because of their low capacityto take up heat and they therefore do not permit rapid operation.

The present invention contemplates overcoming these diiliculties by provision of a quenching method involving spraying onto the surface of the metal a liquid hydrocarbon or other inert liquid, preferably organic, which is substantially inert to the metal and which will evaporate at a temperature below that to which the metal'is to be quenched; The liquid to be sprayed should ment of, metals on which a bright finish is desired.

These quenching media furnish another important advantage in that they may be utilized as vehicles for carrying to and depositing on the metal any desired protective material such as mineral oil, pine oil or a slushingcompound to provide a residual film protecting the metal against rusting or discoloration or to assist in further processing such as drawing stamping and the like.

The preferred quenching media according to this invention are low boiling saturated hydrocarbons. Among these, pentane is an excellent agent because of several factors. It has a very\ low boiling point, resulting in rapid evaporation and immediate cooling whereforethe calculated cooling effect is promptly achieved and the process is therefore very responsive to control. This compound is readily available at oil refineries as a by-product of relatively small utility and low cost.

In applying the invention to quenching of three-foot wide tin-plated steel strip according to one embodiment of the invention, the strip is continuously passed at the rate of one thousand feet per minute through a chamber fifteen feet in length. Entry temperature of the strip is about 450 F. and the metal is to be cooled to 200 F. before leaving the treating zone. For that purpose, liquid pentane at 100 F. is sprayed on the metal at the rate of 19,000 pounds per hour and pentane vapors at approximately 100 Fi'are withdrawn. The hydrocarbon quenching medium in this case absorbs 2,900,000 B. t. u.

, per hour, providing adequate cooling of the also be refractory, that is, highly resistant to decomposition at the temperatures prevailing in the treating zone. In this manner advantage is taken of the latent heat of vaporization of the quenching medium. which is much greater than the specific heat. Further, very accurate control of the quenching operation is possible by regulation of the quantity of quenching medium supplied. Preferably the quenching liquid is supplied at such rate as to vaporize to a sub-- stantially complete extent in 'performing the desired cooling. The vapors of the quenching medium, because of their inert character provide an atmosphere peculiarly suited to treatmetal almost wholly by taking up latent heat of vaporization.

Other light hydrocarbons and the like may be utilized, the system being adjusted to the properties of the quenching medium employed. For example, liquid propane is also useful. It is easily liquefied and expands to 37 cubic feet of gas at standard conditions per gallon of liquid, insuring an adequate blanket of a reducing atmosphere about the metal under treatment. The latent heat of vaporization of propane is B. t. u. per pound, providing adequate capacity for cooling in a relatively small treating zone at a rapid rate. The commercial grades of pentane, butane, propane and other similar light hydrocarbons, are iree of materials such as sulphur which are capable of discoloring' or otherwise impairing the appearance of the metal surface and are readily available in adequate quantities.

The quenching medium should be of such properties that it will not recondense in the treating zone, but it is contemplated that the same may be withdrawn from that zone, cooled and compressed to liquefy it and recycled to the treating zone, with addition of such surface protective agents as may be desired.

One important advantage of light aliphatic hydrocarbons is that they are excellent solvents for the mineral lubricating oils which may be desirably left on the surface of the metal as protective agents or aids in further processing. Slushing compounds or other agents not soluble in the quenching medium may be suspended in th quenching medium without substantial difficulty. These aliphatic compounds are very refractory and are thermally decomposed only at extremely high temperatures on the order of those greatly above temperatures at which quenching is employed.

We claim:

1. A process of quenching hot metal to a desired temperature which comprises spraying liquid pentane on said metal within a treating zone, and effecting exclusion from said treating zone of gaseous material other than that from evaporation of said pentane.

2. A process of quenching hot metal to a desired temperature which comprises spraying on said metal within a treating zone liquid pentane containing a protective agent for said metal, and efiecting exclusion from said treating zone of gaseous material other than that from evaporation of said pentane.

3. A process of quenching hot metal. to' a desired temperature which comprises spraying liquid propane on said metal within a treating zone, and effecting exclusion from said treating zone of gaseous material other than that from evaporation of said propane.

4. A process of quenching hot metal. to a defaaeaeos sired temperature which comprises spraying on said metal within a treating zone liquid propane containing a protective agent for said metal, and effecting exclusion from saidtreating zone of gaseous material other than that from evaporation of said propane. v

5. A process of quenching hot metal to a desired temperature which comprises spraying on said metal within a treating zone a hydrocarbon liquid inert thereto and having a boiling point below said desired temperature, and effecting exclusion from said treating zone of gaseous material other than that from evaporation of said liquid.

6. A process of quenching hot metal to a desired temperature which comprises spraying on said metal within a treating zone a quenching liquid inert thereto and having a boiling point below said desired temperature, and effecting exclusion from said treating zone of gaseous material other than that from evaporation of said liquid.

l. A process of quenching hot metal toa desired temperature which comprises applying to said metal within a treating zone a liquid hydrocarbon inert thereto and having a boiling point below said desired temperature and efiecting exclusion from said treating zone of gaseous material other than that from evaporation of said liquid hydrocarbon.

8. A process of quenching hot metal to a desired temperature which comprises applying to said metal within a treating zone a quenching liquid inert thereto and having a boiling point below said desired temperature, efiecting exclusion from said treating zone of gaseous material other than that from evaporation of said liquid, withdrawing vapors of said liquid from said zone, condensing the withdrawn vapors and recycling the condensate to said zone and again applying it to said metal.

JOHN HAPPEL. WAYNE A. HOWARD.