US1283973A - Method of electroplating. - Google Patents

Description

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A GORIPO i'l [DION 015 NEW JERSEY.

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To all whom it may concern:

Be it known, that we, WILLIAM THUM and JoHN J. MULLIGAN citizens of the United States, residing at llammond and East Chicago, respectively, in the county of Lake and State of Indiana, have invented certain new and useful Improvements in Methods of Electroplatin'g; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The invention relates to electroplating the surfaces of steel, iron, ferrous alloys and kindred base metals belonging to the more electro-positive series of metals, with lead, copper or kindred metals belonging to the more electro-negative series.

The object/of the invention is to obtain a homogeneous and firmly adhering deposit of the plating metal directly on the steel, iron or kindred'metal surfaces.

To this end the contact reactions (some of which are of a purely chemical or catalytic action) which usually result from the contact of the base metal with the electrolyte containing-acids or producing'free acids in the process of electrolysis, and which cause such porosity in the shape of pin holes as to render a thin'plating useless as a protective covering for the baser metal, are prevented by the direct electroplating of the surfaces of the base metal with an initial thin, smooth, homogeneous and adhesive coating ofa plating metal such as lead which protects the base-metal from contactwith the electrolyte during the continued deposition of the plating metal.

ile the invention may be employed with advantage in the .electrodeposition of various. metals on iron, steel. and ferrous alloys, it is particularly adapted for the electro-de ositidn of lead, and its application to lead p ating will be specfically described.

The preferred procedure to obtain the desired electro-plated coating is as follows.

The surfaces of the articles to be plated are first cleansed of foreign adherences, such as oxide, grease and slags. This cleansing operation may beefi'ected in the usual way by acid and alkaline dips orpickles, but we have found that a sand blast applied 1n a i suitable manner is quite satisfactory for this purpose.

Specification of Letters Patent.

Application filed July 31, 19M. fierial No. MLIWTO.

Patented n w. a ft.

The next step in the process istowarm the thus prepared article to a desired temperatu e of to degrees Fahrenheit. This operation is preferably done immediately after the cleasing operation so as to avoid any possibility of oxidation or condensation of moisture on the surface to be plated.

The article may then be connected with the source of the de ositing current, either by a flexible or rigi conductor, and immediately dipped into a solution of animal gelatin and clean water, which solution is previously prepared by dissolving the gelatin in the water at a temperature of about degrees F. The percentage of gelatin in the solution can be varied to some extent, but is preferably approximately two per cent. When plating the interior of a container or other article, it is found to be more convening'steps in the process.

The next step, which, to secure the best results, should be performed immediately after the article has. been dipped, or after the solution has been emptied from themterior of the article, as the case may be, is totransfer the article to the plating bath or, if the sha e of the article permits, it may be filled with the electrolyte. As the article has previously been connected with the electric current, electrolytic action-takes place at the moment of contact of the article and electrolyte.

Tn the plating operation we have found that the use for a short space of time of an initial current of abnormally high density results in the deposit upon the base metal surface of a erfectly homogeneous covering which. will uild further without porosity after thec-urrent density has been lowered to normal. 4

As a normal current density with moderlib till

ate circulation of the electrolyte, we have 1 found that 10 to 15- amperes per square foot give satisfactory results. For the initial excessive current density, which need only be applied for a few seconds (less than a minute) we have found that 25 to 50 amperes solution is employed, a lead contents 11 per cent. and a total hydrofluosilicic acid contents of to 12 per cent. is recommended.

In explanatlon of the assumed reactions taking place during the several steps of the I process, it appears evident that the formation of minute gas globules which would otherwise be caused by chemical reaction at the moment of contact of the base metal to be plated and the acid onstituents of the electrolyte is 'prevented by the gelatin solution. It acts as a momentary protective coating against direct contact of the elec-. trolyte, and simultaneously the overpowering electric energy of the excessive current density deposits an initial homogeneous and protective metal coating in the shortest possible interval and before the protective'gelatin, coating has been fully difi'used with the electrolyte wherein it acts as an addition agent to promote a smooth electrodeposit.

When lead is used as the anode, it should preferabl be of the highest purity, and it can be cast into any convenient shape to suit the requirements; moving either one of the electrodes, a'much increased mixing or circulating of the electrolyte can be brought about, thereby permitting a relative increase inthe excessive and normal current densities and consein the rate of deposit. g n practlsing th s invention, other com pounds containing an addition agent acting similarly to animal gelatin can be-used as the initial protective and soluble coating but this will obviously in no way changethe principles of the invention.

at is claimed is v 1. The method of electroplating which By rotating or otherwise gelatin, connecting the article to be an Initial current of abnormally high density, reduced interval.

3. The method of electroplating which consists in covering the surface to be plated with a film of gelatin solution and then depositing'the plating metal thereon by electrolysis with an initial current of abnormally high density reduced to normal after a short interval.

4. The method of directly electroplating the surfaces of iron, steel and kindred base metals which consists in covering thesurface to be plated with a protective film soluble and difiu'sible in the electrolyte, subjecting the same to the action of a lating bath current having an abnormal y high current density for a short interval, and then reducing the current density to normal until the desired thickness of deposit has been obtained.

5. The method of directly electroplating the surfaces of iron, steel and kindred base to normal after a short metals which consists in covering the surface to be plated with a protective film of latcd to the source of electric current, and t en subjecting'the same to the action of a plating bath current having an abnormally high current density for a short interval, and then reducing the current density to normal until the desired thickness of deposit has been obtained.

WILLIAM THU'M. JOHN J. MULLIGAN.