US2144798A - Tinning compound - Google Patents

Description

Patented Jan. 24, 1939 UNITED STATES PATENT OFFICE TINNING COMPOUND No Drawing. Application March 22, 1937,

' Serial No. 132,300

'7 Claims.

This invention relates to a composition of matter to be used for coating metals, particularly ferrous metals. The principal contemplated use is, as preliminary treatment in connection with the application of further metallic coating thereto--as by spraying melted metal, such as tin, lead, solder, zinc and/or other metals, either for the purpose of protecting the surface against corrosion or to fill cavities or dents, as in making repairs to articles made from sheet steel. The

above indicates the general object.

A specific object is to provide an improved cold tinning compound, i. e. a compound for depositing a tin-like coating on metal without specific use of electrolysis or heat.

Another object is to provide a novel method of preparing a composition for cold tinning.

A further object is to provide an improved restorer for the compound, should the same become ineffective, for any reason, properly to tin the metal. I

The invention is on the order of that disclosed in the copending application of Carl G. Neldhardt, Serial No. 103,926, filed October 3, 1936.

Other objects and features of the invention will become apparent from the following description.

The expression cold tinning as used herein is not intended to signify that the film or coating produced on the surface of the work is wholly or principally tin. The metal to be coated is tinned, in the sense that metals such as ordinary solder will unite operatively with the base metal and remain thereon permanently without requiring roughening, kerfing, puncturing, etc., of the base metal as preparatory treatment. It might be mentioned that when metal, such as solder, is sprayed on tin, most copper alloys, nickel, silver, and various other metals, the sprayed-on metal will adhere tightly without special preparation, other than to clean the surface, but in general this is not true with respect to ferrous metals. The compound hereof was developed principally to provide an effective bonding between sprayed-. on metal and ferrous metals, such as sheet steel 45 and various other alloys, which are principally iron. This is not intended to limit the use of the present invention, but merely as indicating the principal problem.

The composition preferably comprises an amalgam of tin and mercury to which is added copper sulphate, corrosive sublimate, suitable abrasive such as carborundum and/or powdered glass, water and glycerine (the latter as a plasticizer and drying pre /enter); a relatively small proportion of zinc chloride being added to the above. ingredients after thorough mixing of the same.

Pure tin is suggested in lieu of a composition such as ordinary solder as a base, because pure tin goes into an amalgam with the mercury with less difiiculty. I do not, however, intend to indicate that ordinary solder may not be used in lieu of pure tin in the practice of the invention. A preferred procedure in mixing the various ingredients and the preferred proportions of the same will now be described in connection with making a batch of, roughly, 15 pounds.

Five ounces of pure tin is melted in an iron crucible, and just as soon as the tin is melted, approximately four pounds of mercury are added and the two metals thoroughly stirred together. The amalgam thus formed is now poured into a mortar or earthen vessel and the following ingredients are added: (proportions approximate).

. Pounds A Copper sulphate 2 To the above mixture, a suflicient quantity of distilled water (or water which contains substantially no iron) is added gradually, during very thorough mixing of the whole, until all the mercury is triturated into the compound. Only sufiicient water is added to bring the consistency to that of a thick paste. Afterward, approximately one and one-quarter pounds of zinc chloride is added and thoroughly mixed in.

The batch is then allowed to stand for about 72 hours in a temperature of about degrees F. until all chemical action has terminated (gassing stops). It may then be placed in small jars, which are preferably allowed to stand overnight, covered, but not sealed, further to insure that chemical action has stopped before sealing as with screw caps for storage and shipment.

It is to be understood that the various active ingredients, i. e. tin, the mercury, the copper sulphate, corrosive sublimate, zinc chloride and water, may be varied in proportion considerably. For instance, a larger percentage of tin may be used. If more than about twenty-five percent excess mercury is used, it is unlikely to stay in suspension, hence becomes wasted. The copper sulphate and corrosive sublimate may also be varied each way, say minus twenty-five percent and plus not much in excess of seventy-five percent. However, these two metallic salts should be kept in about the ratio given, namely, two to one.

It should be mentioned that some of the active ingredients can be used without others with fair results. Furthermore, mercury and copper may be used in the form of other salts than mentioned providing suitable precipitating agents are used to render the metals effective. Also, other sulphates can be used in place of the copper sulphate mentioned, and other copper salts can be used.

The ingredient, zinc chloride, is of great importance to the compound, and subject to critical limits, i. e. maximum and minimum quantities that may be used with satisfactory results. In the batch given there should be used at least one-half pound and not over two and one-half pounds. The most important function of the zinc chloride is to liberate metallic copper from the copper sulphate, thereby to assist in depositing a more uniform and heavier deposit of copper on the surface to be tinned. This is probably due to the position of zinc with respect to copper in the electrochemical series. It is also possible that a reaction takes place between the zinc chloride and free iron on the surface to be tinned, causing acceleration of the iron in liberating copper from the sulphate. The zinc chloride also appears to assist the mercurous chloride in its function of holding the mercury against precipitating from the batch. Zinc chloride, as is well known, is highly hygroscopic, and it therefore has a desiccating effect in holding moisture distributed through the paste, if used in proper amounts. In this connection, it should be mentioned that if more than the prescribed quantity of zinc chloride is used, then apparently too much water is absorbed from the air since liquid accumulates on top of the batch. It has also been noted that when an excess of zinc chloride has been used, then a hard sediment of ingredients remains on the bottom of the mixing container, such sediment being too hard to be effectively used for cold tinning. The zinc chloride appears to form a better bond between the copper and ferrous metal being coated, also, better bonding of the mercury or amalgam and the copper, and a better bonding of the sprayed-0n metal, for instance, solder, to the amalgam. The above, I believe to be functions or properties of the zinc chloride alone, and not in combination with the other chemicals used, because if the zinc chloride is in proper proportion to the batch, then a great amount of variation as to the other chemicals is permissible.

The water content can, of course, be varied considerably, but the paste is less effectively applicable if either too thin or too hard.

If the compound becomes too dry, at any time, a 75%: 25% solution of glycerine and distilled water can be mixed in to soften it to the desired consistency.

The carborundum, powdered glass and glycerine are inert ingredients and these can, of course, be varied indefinitely.

Referring again to the matter of gassing off after mixing, the importance of maintaining a temperature of at least degrees F. during the chemical action of the compound is to save time. The process may take as much as a couple of weeks at lower temperatures. Under the temperature given, if left to stand for about seventytwo hours, all chemical action will be found to have ceased. A final test heating of about 200 degrees F. is given to the batch, to determine with certainty that no further action is likely to take place. The product may then be bottled or put in jars, as above mentioned. The importance of insuring that chemical action has terminated will be easily understood when it is considered that gassing off after bottling may cause leakage, disfigurement of labels, etc.

In use on say sheet steel, the paste is applied on the metal surface to be tinned, and the surface is then rubbed as in applying an abrasive paste or grinding compound. The first application is preferably rubbed with steel wool to assist the abrasive material in cleaning foreign matter off the surface. If the surface is not pitted or scored, one application of the paste is usually sufficient to deposit a continuous metal film, suitable for bonding sprayed-on metal, such as solder, to the work. The pits and scorings can usually be cleaned or removed in one or two applications with steel wool. The treated surface is then wiped off cleanly with cloth or paper. The deposited metal film from the paste can not be wiped off. Only one application to the work is usually necessary, if the metal is fairly clean to start with. Apparently, copper and tin are both deposited on the metal to be coated, and mercury, in the form of small globules .or particles, the nature of the coacting depending considerably upon the porosity of the metal surface being treated.

In the event the above described compound becomes weak, and will not tin iron or steel in one application, a restorer, the composition of which is given below, may be used to rejuvenate it. A highly satisfactory restorer may be made by mixing together thoroughly the following ingredients:

Distilled water gallons 3 Copper sulphate pounds 1 Zinc chloride do 1% Sulphuric acid c. c. 500

a The above mixture should stand for about one hour before bottling. The metallic salts given, completelydissolve. This may be added in small amounts from time to time to the paste, as required.

I claim:

1. A metal coating composition for use directly on ferrous metal, comprising an amalgam of mercury and a low melting point metal, copper sulphate, corrosive sublimate and zinc chloride thoroughly mixed with the amalgam.

2. A metal coating composition for ferrous metals, comprising an amalgam of mercury and tin, to which has been added and thoroughly mixed therewith, copper sulphate, corrosive sublimate, zinc chloride for releasing metallic copper from such salt,,and water.

3. A metal coating composition for ferrous metals, comprising the following ingredients and a proximate proportions: an amalgam of a low melting point metal and mercury (three to five parts); copper sulphate (one and one-half to three parts); corrosive sublimate (one-half to one and one-half parts); zinc chloride (onehalf to two and one-half parts) and water sufficient to produce a paste.

4. As a restorer for a cold-tinning composition for ferrous metals, the following ingredients and approximate proportions, namely: three gallons of water; one and one-half pounds of copper sulphatepone and one-quarter pounds zinc chlo-v ride; 500 cc. of sulphuric acid.

5. A restorer'for a cold-tinning composition for ferrous metals, comprising an aqueous soluof corrosive sublimate and copper sulphate, and tion containing copper sulphate, sulphuric acid then adding a small proportion of zinc chloride, and zinc chloride. and water.

6. The method of preparing a metal coating 7. A cold-tinning compound for ferrous metals, composition for ferrous metals, comprising meltsaid compound containing copper sulphate, cor- 5 ing a quantity of metal having a relatively low rosive sublimate, a tin-mercury amalgam, and melting point and mixing therewith mercury to zinc chloride. form an amalgam, mixing with the amalgam a NEWELL M. EPPERSON. metallic salt selected from the group consisting