US1740639A - Coating and heat treating - Google Patents

Description

A. O. AUSTIN COATING AND HEAT TREATING Dec. 24, 1929.

2 Sheets-Sheet Filled May 25, 1925 Alilllllll INVENTOR ATTORNEYS Dgg. 24, 1929. A. o. AUSTIN COATING AND HEAT TREATING Filed May 1925 2 Sheets-Sheet R O m m N I A TTORNEYS Patented Dec. 24, 1929 UNI-TED STATEISTPATENT OFFICE ARTHUR O. AUSTIN,

0F NEAR BARBERTON, OHIO, ASSIGI IOB, BY MESNE ASSIGNMENTS,

TO THE OHIO BRASS COMPANY, OF MANSFIELD, OHIO, A OOBPORATION OF OHIO COATING AND HEAT TREATING Application filed May 25,

This invention relates to a method and apparatus for coating and heat treating metal articles andhas for its object the provision of a method and apparatus in which a uniform coating may be economically applied to the articles and in'which difiiculties that heretofore have been experienced are largely avoided.

.The invention also, includes heat treatment of articles simultaneously with the coating operation. In the accompanying drawings there is illustrated, apparatus by means of which the present invention may be performed. This apparatus together with the process comprised in the invention is described in the following specification, the invention being more-particularly pointed out in the appended claims.

In the drawings- 1 is a vertical section view showing F1 one erm of apparatus for practicing the present invention.

Fig. 2 is a view similar to Fig. 1 showing a difi'erent'form of apparatus.

This invention deals with proved methods treating articles.

new and imof galvanizing and heat In galvanizing, tinning or coating articles with lead or other material, it

' zinc chloride is generally desirable to form a uniform coat which amalgamates with the material covered and acts as a water protection.

While the invention applies particularly to galvanizing or the process of coating steel, grey iron an mallea such as tin. In the process of galvanizing it is customary to clean the article by sand or shot blast or by pickling in acid. In the pickling tgieration, a coating as a vanized or tinned is placed in the bath, an amalgamation takes place. Where articles are simply clean iand bright, it is generally dip the articles in a flux such as or sprinkle the articles with necessary to 4 tion will le castings with zinc,v it applies to coating with some other metals may exist which acts ux so'that when the article to be'gal- 1925. Serial No. 82,109.

ammonium chloride commonly known as salammoniac. If. the galvanizing or tinnin bath is not very hot, an amalgamation usua ly takes place without much difiiculty, providing the usual amount of material galvanized is large, however, the bath is cooled. This makes it necessary to keep the articles tOybQ galvanized or tinned in the bath long enough so that they can allbecome heated up, otherwise, if they are taken out of the bath they will have too thick a'coat and there may be no amalgama tion owing to the chilling of the coating material in contact with the pieces.

One method of correcting thisdifliculty is l I but in many cases'it is 0 en to serious difficulties. Where a bath-o high temperature is used, there is a tendency to oxidize the surface of the article to be galvanized or tinned if amalgamation does not take place in a very short time such as may happen if there is a small amount of air or gas entrapped. This makes it exceedingly difiicult to use a high temperature bath on many classes of .ware which are galvanized or tinned. If the hot bath comes in contact on one side of the metal to be coated and an air or gas pocket exists on the opposite sides of:-

a thin section, the surface may-become oxidized or the'fiux driven off so that amalgamais allowed. Where the surface becomes 0x1- not take place readil unless more flux isappliedor considerable ength of time 7 dized or the'fiux is driven off before amalgamation takes place,, a,-bare spot or pinhole in -the' galvanizing ortinn'ing usually results.

One object of the present invention is to get away from this'difiiculty. This is accomplishedby placing the article to be coated in which has a relatively low a molten bath temperature. Where the bath is at lowtemperature, the tendency to drive ofi the flux before amalgamation takes place is not so at this end.

necessary 'finally raised to the is dropped great and the tendency to oxidize the surface is also reduced so that amalgamation takes place with a minimum amount of fiuxing and without the formation of bare spots or pinholes. After amalgamation takes place, the surface of the article to be galvanized or tinned will not be affected. by an increase in temperature and oxidization or the driving 01f of flux will not matter. The next step is to transfer the articles galvanized to a bath which is much hotter. This is frequently quite important when a thin uniform coat is desired orwhere large production is desirable. steps may be taken so that temperature is desired value. This can be readily done in one of several ways, depending upon the conditions. i

Fig. 1 shows one form of the invention which is suitable for carrying on work where large production is involved. A suitable metal tank 10 containing a molten bath 11 and heated by hot gases in a flue 12 is provided for melting the spe'lter or tin. In this arrangement, it is desirable to have a tank which is rather long compared to the crosssection so that a material different in temperature in the bath may be obtained at the two ends of the tank. In operation, an ordinary galvanizing basket or container 13 down through a trap 14 to the position 15. Suitable means is provided for moving the basket containing the material to be galvanized to positions 16, 17 and 18. This may be done gradually or in ste s. Since the fire enters through the flue or die box 12 adjacent to the discharge end, this end of the bath will be considerably hotter as the heating gases and cool down as they travel along the tank. Another factor which tends to cause a difference in temperature between the entering and discharge end of the tank is that the material to be galvanized requires considerable heat upon entering which tends to cool off the bath This makes it comparatively easy to maintain a considerable difference in tlfmperature between the two ends of the Where the galvanizing tank is relatively long compared to'the cross-section, it is not to have the baskets or containers such size that they will prevent convection currents in the molten bath which will tend to cause a uniform temperature throughout nor is it necessary to provide means to prevent convection currents which, of course, is necessary where the cross-section of the tank is rather large compared to the length. Where the baskets travel at some distance below the surface, there is a tendency for the molten bath to travel with the baskets to some extent. This causes a flow in the opposite direction near the top. By properly proportioning the parts, this flow may be molten bath at the surface,

In order to insure uniformity,

are hotter at this point' controlled so that the flux and accumulation of dirt on the top of the bath may be kept at the enterin side. In this case, the bafiies 19 are partialfy or entirely removed. Where the motion of the baskets through the galvanizing bath is not too rapid, most of the flux will rise to the surface at the entering end where it will remain due to being held back by the bafiies 19 or the flow of the as previously described. When the basket reaches the end position 18 it is lifted either by hand or automatically and the contents emptied into the quenching tank 20 which is filled with water, oil or other suitable material. It is generally advisable to allow the material being emptied to strike bafiies 22 before it enters the quenching tank. This tends to separate the pieces so that when they are quenched, there will be no difliculty in the pieces being stuck together by the galvanize or tin. Where the latter takes place, a bare or rough spot usually results. By using the baffles 22 or other retarding device, the articles are separated as they enter the quenching bath so that they do not freeze together.

With the improved method, smaller batches may be sent through at a time. In addition to the improved condition for ordinary galvanizing and tinning operations, the improved method has a further advantage of great importance. With the method as shown, it is possible to use much higher temperatures in the bath without serious consequences. This forms an opportunity to heat treat articles during the galvanizing or tinning operation. By raising the temperature high enough, it is possible to materially improve the qualities of malleable iron which may otherwise be embrittled by the galvanizing operation. It is also possible to change the structure of steel pieces in order to increase their toughness. and control the elastic limit, resiliency or temper of the piece. This may be controlled in the usual way of the temperature of the piece and the nature of the quenching bath. Conditions are greatly facilitated in some cases by carrying out the operations, particularly at high temperatures, in a neutral or practically non-oxidizing atmosphere. This may be readily accomplished by causing the flue gases to fill the space above the tank and around the basket and articles before they enter the quenching tank. Not only does the neutral reducing air of the flue gases protect the bath from oxidation, but the articles are kept hot until they'enter the quenching bath. This is important in small high temperature of the molten bath permits a control of the thickness of the coating.

The method is particularly applicable for galvanizing or tinning baths which are electrically heated as the amount of material required is exceedingly small.

One form of a paratus for accomplishing the desired resu ts is shown in Fig. 2. In this case a tube 50 is filled with a molten bath and the articles 51 are put in at the charging end 52 and discharged at the end 53. The tubular member 50 containing the molten material ma be of metal or a suitable refractory.

The heating may be accomplished by any suitable fuel or by electrical energy as shown. Since the incoming material enters the end 52, it will tend to lower the temperature of the bath at this point. As the material traverses toward the end 53 it will be heated up. This movement may be provided by magnetic apparatus in the case that a refractory or nonmagnetic tube is used or by a mechanical feeder 53 which periodically shoves the pieces 51 forward. It the heating turns are concentrated at the discharge end a higher temperature will be provided at that end which with the cooling action at the entering end will tend to maintain a temperature d'iflerence with its advantages as previously explained. With this system an enclosed tube may be used which will prevent the bath from coming into contact with the air or gases except at the entering and discharging ends, so that there will be little oxidation.

Where the refractory tube is used, the amount of dross will be reduced to a minimum and under favorable conditions no dross will be formed. This is a very material advantage in that one of the principal objections to high temperature is the amount of dross formed. As the piece is discharged from the I end 53 it may be allowed to fall a considerable distance and strike several bafiles 54 and 55 before falling into the quench tank 56. Striking several bafiies tends to knock off any superfluous material and if time suflicient is allowed before striking the cooling bath, the surface tension will tend to form a very uniform coat. Instead of striking baflles it is possible to allow the article to fall thru a passage into which air is forced at a considerable velocity. This tends to blow ofi any superfluous material and the direction of the air may be used to retard the fall giving ample time to remove the superfluous material. With the methods shown, it is possible to raise the material to the desired temperature so that the article may be tinned or galvanized and at the same time given a heattreatment to increasethe mechanical strength, hardness or reliability. This method is applicable to the heating of articles for heat treatment as well as for the galvanizing or tinning operation.

I claim- 1. The method of imparting a protective coating to articles, comprising the steps of subjecting the articles to melted coating material, the temperature of the melted coating material to which the articles are initially subjected, being only slightly above the melting point of said coating material, and subsequently subjecting the articles to a bath of the same coating material at a temperature much higher than the temperature of the melted coating material to which the article are initially subjected.

2. The method of imparting a protective coating toarticles, comprising the steps of immersing the articles in a bath of melted coating material, the temperature of the melted coating material to which the articles are initially subjected, being slightly above the melting point of said coating material, and thereafter moving the articles to a bath of said material at a temperature much higher than the melting point of said coating material and much higher than the temperature of the coating material to which said articles were initially subjected.

3. The method .of coating metal articles, comprising the steps of maintaining a bath of coating material at different temperatures in different portions of said bath, subjecting the articles firstto a portion of the bath at a lower temperature, and thereafter moving the articles to a portion of the bath composed of like material as said first portion but at a temperature muchhigher than the temperature of that portion of the bath to which the article was first subjected and suiiicicntly above the melting point of said material that only a thin coating of said material will adhere to said article.

4. The method of coating metal articles comprising the steps of providing a bath 0 coating material having one portion thereof at a lower temperature than another portion the material of the bath 'being the same throughout, subjecting the articles first to the portion at a lower temperature, then to, the portion at a higher temperature, and then removing the articles from the high tempera;

ture portion and agitating them to remove excess material, the portion of the bath from which the articles are removed being maintained at a temperature well above the melt ing point to permit all of the coatin metal but a thin layer thereof to be removed hy said agitation, the temperature of said last named portion being so high as to interfere with the modify the physical characteristics of the metal of which the bodies of'said articles are and a cooler portion. thetemperature of the hot portion being sufliciently above the melting point of the coating metal to interfere with the application of an initial coat of said metal to articles to be coated, subjecting the articles to the cooler portion first and there- -after to the hot portion, and then removing the articles from the bath at the hot portion [thereof into a substantially nonoxidizing atmosphere. v

' 7. The method of coating metal articles,

25 comprising the steps'of providing a bath of coating metal having one portion at a higher temperature than another maintaining a covering of nert gas over th of excess coating material but which would.

I interfere with the application of an initial coating of said material to said articles, then removing the articles from the bath into the quenching the articles.

8. The method of treating prising the steps of sub ecting the articles a to a bath of coating metal at a temperature but slightly above the melting point of said out serious oxidation or-lnterferenceiwith the action of the flux used, then to abath of the same metal at a temperature much higher than that -of the coating metal to which 'the article is initially subjected and suificient to composed, and then removin the articles from the bath and quenching te' articles.

9.- The method of treating articles, comprising the ste s of maintaining different portions of abat of coating material at differt temperatures' in angatmosphere of subataiitially non-oxidizing s, subje cti ng the articles w the cooler portion of the bath in e surface of the bath, subjectin the articles first to the cooler ac portion of the ath in the presence of a flux articles, com

coating metal and suitable for applying an initial coat of said metal to said artic as with the presence of a flux to impart a coating to the articles, then subjecting the articles to a portion of the bath having a temperature sufficiently above the melting point of said coating material to heat treat the articles and modify the characteristics of the metal of the articles but also hot enough to render it un- 7 suitable for the application of an initial coating of said material, then removin the articles from the bath into said atmosp ere, then agitating the articles while still hot to remove excess coating material, and then quenching the articles in a cooling medium.

10. The method of treating metal articles,

comprising the steps of maintaining one portion of a bath of coating metal at a temperature sufiiciently high to afiect permanently the physical characteristics of the metal of the articles and to interfere with the application of aninitial coating to said articles and another portion of said bath at a lower-temperature ut slightly above the meltin point of said coating material, subjecting t e articles first to the portion of the bath at the lower temperature to impart a coating thereto, and then transferring the articles to the hotter portion. of the bath for heat treating the articles.

- 11, The method of treating metal articles,

comprising the steps of causing products of combustion to travel along'a receptacle to impart difierent degrees of heat -to different" portions -of the receptacle, permitting the products of combustion to cover the surface of a bath of coating metal in said receptacle, introducing articles to he treated into the cooler portion of said bath in the presence said bath to heat treat the articles and insure inert gas, then agitating the articles while still hot to remove excess materiah andthen.

uniformity of said coating and facilitate removal of excess material therefrom, then removing the articles into said products of combustion, agitating said articles while still heated and while surrounded by said combustion products, and then quenching said articles in a cooling medium.

' 12. The method of treating metal articles,

comprising the steps of subjecting the articles to a bath of coating material having a relatively low temperature where the articles 1 are introduced into the bath and a higher temperature where the articles are removed therefrom, and permitting the articles to fall.

upon 'baflies and into a quenching bath as they are discharged from said bath.

. 13. The method of coating articles com! prising the steps of subjecting the articles to a' bath of coating metal at a temperature but slightly above the melting point of said coating metal and suitable for applying an initial cpat of said metal to'said articles without serious oxidation or interference with the action of the: flux used, then subjecting the articles to a bath of the same metal at a temperature much higher than that of the coating metal to which the articles were initially subjected and so high as to interfere with the coating operation if the articles were 5 subjected thereto prior to receiving an initial coating and then removing the articles from the bath at the hotter portion thereof.

In testimony whereof I have slgned my 4 name to this specification on this 19th day 10 of May A. D. 1925. ARTHUR O. AUSTIN.

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