US2196232A - Protective paint - Google Patents

Description

Patented Apr- 9, 1940 I PROTECTIVE PAINT .Harry A. Sweeney, Chicago,

111., assign to Na- 4 tional Copper Paint Corporation, Chicago, 111.,

a corporation of Illinois No Drawing. Application April 22.1938,

I Serial-No. 203,613

' '3 Claims. (01. 148-27) This invention relates toimprovements in protective-paint used inconnection with carburizing and similar metallurgical processes.

It has long been common practice in the metallurgical arts to treat metal objects by heat. in the presence of gases,- liquids orsolids for the purpose of changing theircharacteristics. When'this is done, it is some times desirable to protect some part orparts of the object being treated so that'while onepart of the object will have its characteristics changed, another part or parts will remain unchanged;

For instance, in the well known carburizing process, it has in the past been proposed rowan some part of ametal object as for instance the teeth of a gear or the blank in which gear teeth are to be cut or the threaded end of a shaft by some protective coating which when theobject was placed in a carburizing pot will protect part of the object from contact with the gas 0r:solids or liquids used in the heater so that the protected, part will remain in its original condition, whereas the other parts will be changed.

It has been proposed to use certain'clays or clay-like materials as a protective coating or paint. The difficulty with these is that clays lack flexibilityor elasticity and tend as the metal expands orcontracts with temperature variation to crack and scale and so permit ingress to the metal through the protective coating of the vapor or liquid.

It has also been proposed to coat the metal metal asfor instance surface with some other by copper plating. The difiiculty here is that copper plating is exceedingly expensive and unless the utmost care and skill is employed, porosity and unevenness of the electro-deposited coating may permit the treating material to reach the surface and'so change the character of the parts which it was intended to protect.

I have produced a new and hitherto unknown coating material, the use of which permits application by hitherto unknown methods and which gives a continuous protective coating which will not crack or spoil or break and which can be applied without special skill or apparatus and which is to all intents and purposes fool proof.

I propose to dip or if desired paint with a brush or sprayor otherwise suitably apply tothe metal to be treated a plastic paint-like protective coating which comprises generally a mix-- ture of clay and amorphous copper, and which is adhesive to the material to be coated so that this paint or protective compound when it dries or chemical and physical and 13 pounds amorphous copper.

' of sodium chloride.

sets, adheres to the metal, provides a protective sheath and has the resistance to heat characteristic of clay or clay-like coatings and the power of expansion and contraction, flexibility and the like characteristic of a metal coating. j r In other words, I propose to use as a protective coating a material which has the resistance to heat characteristic of clay and clay-like protective coatingsand atthe same time has such a coeificient of. expansion and contraction that it 10 can expand and contract with temperature variation of the metal being protected so that the protectivecoating remains'intact throughout all stages of treatment and throughout all reasonable temperature variations and my coating is '1 further characterized by the fact thatit may be likened for illustration in a sense to concrete, theclay or clay-like material being the cement and'aggregate and the copper being metallic reinforcing though in another sense it may be said ,20 7

heat treatment flows .or travels-sufliciently and adheres sufliciently to the metal so as to provide at all times a continuous impregnable coating which protects the metal from the effect of the treatmentto which the unprotected part is subjected I.

, 'The coating material which takes the form of-a paint or. paint-like substance comprises certain mixed solids in solution or suspension or i at any rate, mixed with aliquid material and Y 5 the concentration of thev solids in the liquids may be varied within a rather wide range to suit the type of. Work to be done, the. thickness of the coating desired andthe like.

- If the material is to be coated by dipping, the 40 paint-like material will be thick; if it is to be sprayed relativelythin; if it is to be applied by a brush, somewhere in between and under some circumstances experience teaches that if 'it is to be applied by hand or with a spatulaas sometimes 45.

may be the case, the material may be almost put l ty-like in its' consistency. I

The solids part Of the material comprises prefof a'clay or clay-like material consisting of eight pounds kaolin and Z 'pounds C. F. celite;

The liquid comprises one gallon Silite; one gallon of water; 2 ounces of Emulzone B plus of one percent mercial market generally);

The above formulae give proportions for the solid and liquid components which I have found satisfactory. Some changes in proportions might under some circumstances be permissible, and it is noted that the liquid and solid as above indicated may be mixed together in any desired concentration to produce any desired thickness.

The Hi I-Ieat Silica comprises preferably 52 parts feldspar (NaKAlSisOa) 3 parts borax (boron trioxide 36.6, soda 16.2, H2O 47.2. I have refrained from using the chemical formulae for the boron trioxide and soda because it is not necessary that they be chemically pure. They are merely approximate as found on the com- 10 parts zirconium parts Valendar clay, clay suitable for highsilicate (ZrSiOz) and which is merely a molding er temperatures.

The above mixture is heated to a high temperature until it flows and becomes a hardened mass. It is then allowed to cool. is broken up or ground in a ball mill or suitable apparatus until 90 percent will pass through a 180 mesh screen.

The kaolin above referred to is a clay usually used in the manufacture of porcelain china and the like. One suitable formula consists of silica 46.5 (SiOz); alumina 39.5 (A1203) Water 14 percent. This is a material which becomes dehydrated at a temperature above 330 C.

The C. F. 110 celite is a composition essentially silica S1051.) in a calcined and chemically treated amorphous diatomaceous condition. It is ground to a fineness such that approximately 99 percent will pass through the 150 mesh screen. The apparent density is nine pounds per cubic foot.

The amorphous copper is copper having no crystalline characteristic such for instance as may be produced by the process disclosed in my application Serial No. 38,216, filed August 28, 1935, for Process of producing amorphous copper and the like.

The Silite above referred to consists of 4.54 parts sodium oxide (NazO); 14.62 parts silicon dioxide (SiOz); .8 part sodium chloride (NaCl) and 80.4 parts water (H2O).

Emulzone B is a white vegetable gum powder, odorless, tasteless and edible. It tends to produce viscous emulsions that are stable in the presence of alkaline solutions, neutral in action, colloidally dispersable in liquids having a high water content. It tends to act as a plasticizer between the copper, clays and silicates and furnish greater adhesion to the mixture. Emulzone B may be classed as the oil in water type with Silite acting as the true emulsifying agent.

My paint or protective coating then is used in the following manner: The article to be heat treated or to be protected is dipped or brushed or sprayed with the protective coating. That part of the article which is to be subjected to treatment being left uncovered. If the article is of a type which is not convenient to coat in this way a thicker coat may be applied by hand or with a spatula. The article with its coating is then allowed to dry and after drying to hardness sufficient to permit handling has taken place, the article is introduced into the treating bath or the carburizing pot or the annealing furnace or the gas treating chamber as the case may be and the treatment proceeds in the usual manner. As the temperatures change the metal expands or contracts as the case may be and the coating first is baked to hardness and then if the temperature is high enough flows by melting or sintering if necessary or otherwise expands or contracts to conform to the expansion and contraction of the article upon which it is applied so as to maintainin a close integral continuous gas tight covering.

When the process of treatment is complete and the article is withdrawn from the furnace or similar place of treatment and cooled, then the protective coating may be knocked or chipped or ground or cut off as the case may be.

Experience teaches that while under some circumstances crystalline copper may be used with some measure of desirable result, nevertheless amorphous copper is very much more satisfactory and very much more effective.

Experience also teaches that other metals may be used but in connection with ordinary heat treatments or ordinary metallurgical treatments where ferrous or similar metals are being treated, it is necessary that such metal have a melting point in the order of the melting point of copper. For instance, gold or silver may under some circumstances be used. Zinc, lead, tin, antimony and the like are not satisfactory because their melting points are too low though under some circumstances as a protective coating where lower temperatures are used, it sometimes will happen that even other metals of lower melting point may be made use of.

I claim:

1. A protective paint for use in connection with carburizing and similar metallurgical processes comprising in combination Hi Heat Silica, clay, kaolin and celite and amorphous copper in a liquid carrier comprising Silite plus an emulsifying agent.

2. A paint-like material comprising a claylike mixture including feldspar, borax, soda, zirco-nium silicate, molding clay, kaolin, calcined diatomaceous silica and amorphous finely divided copper in suspension in a liquid including sodium oxide, silicon dioxide, sodium chloride, an emulsifierand water.

3. A plastic protective coating for use in connection with carburizing and similar metallurgical processes which comprises a clay-like nonmetallic material in intimate mixture with finely divided amorphous copper in the presence of a liquid carrier, there being substantially no crystalline copper present in the compound.

HARRY A. SWEENEY.