US 2806801 A
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EXAMIN' Patented Sept. 17, 1957 PROTECTOR ENAMEL FOR HIGH TEMPERATURE METAL TREATING PROCESSES Theodore I. Leston, New York, N. Y., assignor to Eutectic Welding Alloys Corporation, Flushing, N. Y., a corporation of New York No Drawing. Application August 15, 1952, Serial No. 304,631
7 Claims. (Cl. 106-84) This invention relates to an important and desirable improvement in the formation of a protecive composition for use in high temperature metal treating processesr More particularly this invention relates to an improved heat resistant protective enamel for use in various high temperature treatments of high melting metals, such as lLhOSfi-SlidlHSCd in armor plating and containing high percentages of chromium, nickel, and/or cobalt as alloy metals. Non-ferrous metals melting above 1700 F. may also be protected. Specifically, this invention relates to a protective enamel-like glaze for use in high temperature metal fusion and metal treating processes wherein the temperature in the working area is above 1700 F.
It is a well known phenomenon that in treating metals during various high temperature processes, a scaling and rapid oxidation of the treated metal occurs, unless adequate precautions, such as maintenance of an inert ambient atmosphere, are taken. Up to the present time no satisfactory, simple and inexpensive remedy has been found, although various types of protective covering compositions have been proposed. One of the main disadvantages of these prior compositions is that they are only partially successful in protecting the metal from oxidation at temperatures abgye 1700 F. Another disadvantage is that the specific ingredients of such compositions produce a residue slag and scale that sticks to the base metal with a tightly adherent bond and necessitates expensive and laborious mechanical procedures in removing the same, as by grinding, sand blasting, and the like. A further disadvantage of such prior protective coatings has been an inability to protect the surfaces of the treated metals from blistering and discoloration at the high temperatures of the heat treating processes.
It is, therefore, an object of the invention to produce a protector composition for high temperature metal heat treating processes, which has sufficient adherent qualifies to bond to the surface of the metal being processed while in a cold state and upon fusion ag hgg fi tempeiafures to form a protective ena'fn l lilie glaze fwhiclfwiil' becomc Ween," faclte'd' and" dis-associated upon a' subsequent quick cooling, so as to be readily removable therefrom. A further object of the invention is to produce a protector enamel that is especially eflicient in the welding of heat resistant metals and alloys at high temperatures in a fusion welding process. Another object of the invention is to produce such a metal protector composition having deoxidizing properties. A still further object of the invention is to pr qgl ug e ahigh ternpergture metal prgtector glaze which may be easily and expedieiii'ly plied fo' a'met al surface in the form of a firmly a'dh'fentf paste or paint film. Other objects and advantages will become apparent from the detailed description that follows.
Extensive experimentation has resulted in the discovery that the disadvantages of the prior art protector compositions can be eliminated, or at least strongly reduced, by adding a predetermined amount of a metal chloride to a conventional high temperature fluxing composition.
For instance, a conventional flux composition much used in the heat treating of stainless steels, but being ineificient and expensive due to the high cost and trouble encountered in removing the residue thereof from the surface of the treated metal, may be rendered fully eflicient and inexpensive to use by the simple addition of 10% by weight of a metal chloride.
Such innovation results in a protective covering which adheres to and efficiently protects the base metal when in a fused state, but is easily removable therefrom by a simple quenching subsequent to the heat treating process. Further, such protective coating may be painted over or spread on the metal surface, on the front and/ or back sides, to produce an enamel-like covering thereover during the high temperature process with the complete elimination of blistering of the base metal, while at the same time forming a stressed, cracked and segmented crust on the surface of the metal upon a subsequent quick cooling thereof (as by quenching), so as to present a residue which is readily removed.
While it is well known in conventional metallurgical practice to use various metal chlorides in low temperature flux compositions for soldering and brazing applications, such have not been used in high temperature metal treating applications. An example of such prior use at relatively low temperatures has been that of zinc chloride in a flux composition for the soldering of zinc parts, wherein the zinc chloride has merely functioned as a convenient source for providing a necessary ingredient of the soldering alloy.
The prior art practices, however, have no application to high temperature fusion and metal treating processes and should not be confused with the instant invention. In fact, a preferred form of the invention is not a welding flux composition as such term is ordinarily understood, although it has manifold applications in the high temperature welding art, due to the fact that it has an unusually high melting point and does not normally function to deoxidize the treated metal surfaces as do conventional fluxes. Such preferred form may be broadly described as consisting of a mixture of single or plural metal fluorides, metal silicates, alkaline earth metal fluorides, and selected metal chlorides, in predetermined. proportions, and is more aptly described as an enamel-like, protector composition for preventing metal scaling and oxidation. The composition functions by fusing at the high temperatures produced in the heat treating process to form a glaze or enamel-like coating overlying the metal surface and insulating it against the effects of the atmosphere at the high temperatures employed.
On the other hand, the instant invention also contemplates a composition in which a metal chloride is mixed with conventional high temperature welding flux ingredients and applied to a welding rod or on the base metal to be welded in the form of a paste or paint to render such composition useful as a surface protector for the metals being welded.
It is postulated that the important advantages accruing to the instant composition and its nature of application, as distinguished from those noted previously, arise because the content of the metal chloride forms a fused coating in the nature of a multi-phase solid solution at the high temperatures of the treatment, which upon cooling solidifies into separate phases in a pre-stressed and loosely bonded state. The removal of the ensuing slag is facilitated by the fact that it becomes cracked, flaked and chipped due to internal stresses arising from contraction, particularly away from the surface of the treated metal.
Broadly, the compositions of this invention include selected metal silicates and fluorides to provide temperature resistance and a metal cleansing action. Fused borax, clay and the like high temperature slag formers may also be present. To these ingredients there is added one or more metal chlorides as described above. These are preferably selected from the group comprising the chlorides of tin, cadmium, magnesium, lithium, zinc, copper and aluminum. The metal fluorides are preferably selected from both the alkali metal and the alkaline earth metal groups, while the preferred metal silicates are of aluminum or magnesium.
It has also been discovered that the efiicacy of the new high temperature protector enamels can be greatly increased, particularly with respect to their functioning as a deoxidizer at such high temperatures, by the addition thereto of liberal quantities of a metallic powder. Such addition is of special advantage in welding heavy surfaces, such as armor plate, wherein the heat resistance of the protector coating must necessarily be increased many fold to withstand the longer operating periods and higher temperatures of the treating processes. The greater heat resistance thus imparted to the protector enamel was quite unexpected, and no satisfactory explanation is available. This addition has also resulted in a further unexpected advantage in that a mixture or composition containing such metallic powder forms a paste or paint of a much better consistency than any heretofore known, which greatly enhances its ability to function as a backup material with fluxing properties. Preferably, the metallic powders are added in relatively large proportions. The metallic powder additive may be iron, chromeiron, stainless steel alloy, copper, nickel or any other metal or alloy which is compatible with the base metals.
To demonstrate the efficacy of the invention, a relatively small amount of a metal chloride (zinc chloride) was added to a conventional high temperature welding flux containing fused borax, sodium fluoride, magnesium silicate, and clay, and compounded together with an alcohol carrier to form a paste. The paste was spread on the back sides of a plurality of metallic test plates severally composed of iron, stainless steel, chrome-nickel alloy and copper, which were then subjected to a conventional heat treating process, at a temperature in excess of 1700" F., and subsequently quick quenched in cool water. In each instance the protective paste coating solidified in a cracked and flaked condition with the major portion of the coating being contracted away from the surface of the plate. Complete removal of the coatings was easily accomplished by scavenging the surface of the plates several times with a putty knife, and in at least one instance by lightly tapping the plate several times with a hammer.
The individual plates were then examined and found to be completely free of surface blistering, scale or other oxidation residue, and to present a clean, smooth surface which was free of the grime normally encountered in metal working processes. Metallurgical examination showed no ill effects except that the ferrous metal plates had assimilated some of the zinc chloride with usual deleterious effects.
The above tests were repeated after substituting different metal chlorides, listed previously, for the zinc chloride. In each case the same beneficial results were obtained. However, some of the tin chloride was absorbed by the ferrous metals. Because of this and other observed data it has been concluded that the metal chloride should be selected with reference to the base metal to be treated, as for example when treating aluminum I bronze, the tin chloride is preferred, but when treating ferrous metals, tin chloride should be avoided.
In the examples above mentioned, the relative percentage by weight of the metal chloride to the dry mixture was varied between 0.25 and 25%, with the most ef- F ficient proportion being in the range of 8 to 12%. It should be noted, however, that the additive was effective at both ends of the range, although percentages below 3% produced a residue that tended to cling together and resisted flaking. But even then it did not adhere to the metal surface with the tenacity of conventional high temperature compositions.
It wil be obvious that several different metal chlorides may be employed together whenever desired to match the composition of the base metal that is to be treated. Thus, in the case of aluminum-bronze, tin and aluminum chlorides may be combined. In such cases the proportion of metal chloride to the mixture may be increased above the preferred range, and yet retain the same beneficial qualities.
Reference will now be made to a preferred form of the invention in which a mixture of selected, relatively high melting-point, inorganic metal cleansing ingredients, such as alkali metal fluorides, aluminum silicates and alkaline earth metal fluorides are compounded together with any of the metallic chlorides previously mentioned to form a paste or paint that may be spread on the surface of metal parts to protect them from damage during high temperature heat treating processes. The specific range of this preferred high temperature protector composition may be listed as follows:
Parts by weight Alkali metal fluorides 3 to 20 Alkali metal silicates 1 to 20 Alkaline earth metal fluorides 5 to 50 Chloride of a metal (or mixtures thereof) 0.25 to 25 The chloride of metal should be selected, as noted previously, so as not to be incompatible with the metallurgy characteristics of the base metal to be treated. For example, in treating ferrous metals, tin and zinc ch10- rides should be avoided.
The results of this protector composition are surprising. It completely eliminates blistering or surface oxidation of the base metal, and, to date has not resulted in even one discolored finished part. It can be used as an anti-splatter, anti-blistering and scaling compound as well as a back-up material for a conventional high temperature welding'flux. The great versatility of this composition makes it a worthwhile tool for anyone who works metals in a high temperature, heat treating process.
The following composition is given as a specific example of the above protector composition and in which the relative ingredient ranges are listed in parts by weight as follows:
Preferred Acceptable Ingredient Proportion, Range,
parts parts Sodium fluoride 15 3 to 20 Sodium silicate 5 1 to 20 Fluorspar 40 5 to 50 Aluminum sodium fluoride 20 2 to Z) Aluminum silicate l0 1 to 10 Cadmium chloride 10 0.5 to 25 The above composition may be compounded in the same manner as that previously described, preferably in conjunction with an alcohol carrier of sufiicient quantity to form a paste-like substance, which may be readily spread over the surface of the metal to be treated, but which will not run off readily.
In another preferred embodiment of the invention it has been found desirable to add a relatively large percentage of a owder, chrme-nickel u". r, copper power wh ieh additive great- Broadly, this type of protector composition may be described as having the following range of ingredients, the parts being by weight:
In general, the purpose of the added metallic powder is to enable the protector composition to function as a better deoxidizer and protector for the metal surfaces which are kept at fusion temperatures for extended periods. The metal powder seems to absorb the major quantity of the heat generated adjacent such surfaces and to thereby enable the other ingredients of the protector composition to function for their intended purpose without oxidation or volatilization for long periods of time.
One of the advantages of the addition of the metallic powder is that it provides a medium for accommodating rapid radiation of heat from the treated surfaces and an eventual absorption of precipitated carbon by such medium (powder).
As a specific example of this type of protector composition, the following details are given, the parts being parts by weight:
This composition was compounded together as a dry mixture and thereafter combined with an alcohol carrier to form a paste of relatively thick consistency. This paste was then applied to several test armor plate pieces which were thereafter subjected to a heat treating process at temperatures between 2300 and 2700" F. fora period of 1 hours. During this treatment the composition fused to form an enamel-like film completely covering the surface of the plates as an immobilized glaze. Subsequently, the pieces were quick quenched in cool water and the protector composition immediately solidified. Ilpon examination it was noted that the surface of the residue was covered with interlocking crevices which divided such into a multitude of separated islands. It is assumed that the sudden cooling of the protector composition sets up inherent stresses due to the fine and uniform dispersion of the metallic powder with the other composition mgre dients which results in their being solidified in more or less independent or separated phases. This condition renders the removal step a simple one, since all that is necessary is to scrape the surface of the plate several times with a sharp blade or a wire brush.
One of the surprising advantages of the above noted compositions containing the metallic powder additive is the fact that the protector composition acquires some features of a welding flux, at least to the extent of deoxidizing the metal surface to which it is applied throughout the entire period of the heat treating process. As will be readily understood, this has been hitherto unobtainable due to the fact that most conventional protector compositions and high temperature welding fluxes are unable to withstand extended periods of exposure to high temperatures, such as are encountered in the heat treating of armor plating. Another surprising factor in the use of the metallic powder additive is the fact that it does not adhere to or fuse with the surface of, the metal being treated, even though it may itself be in a molten state and the surface of the treated metal may be at fusion temperature. This surprising result appears to be due to the fact that the additional ingredients present in the composition prevent the segregation of the metallic powder as a fluid strata adjacent the metal surface being treated. it is apparent that the metallic powder simply functions as a heat absorbing and conducting medium and to prevent oxidation and volatilization of the other ingredients present in the composition. In some applications where extremely high temperatures are encountered for abnormally long periods of time, the metallic powder may melt and resolidify as a heterogeneous mass requiring a light grinding operation to remove it from the treated surfaces.
Another feature of the invention is the fact that various and different chlorides of metals, as for example cadmium and lithium chlorides, may be used together with an end result of an enhanced cleaning action for the surface of the metal being treated.
It will be understood that while the instant invention has particular efiicacy in metal treating processes, such as annealing, bending or straightening, etc., it is alsoapplicable to metal joining processes. As for example, it has een found to be extremely advantageous for welding metal parts without the benefit of a filler metal. In such cases, the protectorenamel coating of the invention-is applied to the surfaces (or at least one surface) of the metal parts to be joined prior to heating such parts. Thereafter, the metal parts are heated till their mating portions are at fusion temperature, and then mated together under pressure. Subsequently the mated and welded parts are quick quenched to stress, crack and disassociate the applied enamel coating so as to render it easily removable therefrom. The application of the protectorenamel coating has been found to be completely effective in preventing any scaling, blistering or discoloration of the parts so joined.
As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope hereof, it is to be understood that the above invention is not limited except as defined in the appended claims.
What is claimed is:
1. A high melting point protector composition capable of fusing to an enamel-like glaze for preventing scaling, blistering and oxidation of metal surfaces during high temperature heat treating processes, consisting essentially of 1 to 20 parts by weight of metal silicates selected from the group consisting of alkali metal, aluminum and magnesium silicate and between 5 and 50 parts by weight of alkaline earth metal fluorides and 3 and 20 parts by weight of alkali metal fluorides, and between 0.5 and 25 parts by weight of a chloride of a metal that is compatible with the metal being protected.
2. A protect-or composition capable of fusing to an enamel-like glaze for protecting the surfaces of metal articles during high temperature heat treating processes, consisting essentially of between 3 and 20 parts by weight of alkali metal fluorides, between 1 and 20 parts by weight of alkali metal silicates, between 5 and 50 parts by weight of alkaline earth metal fluorides, and less than 25 parts by weight of aluminum chloride.
3. A protector composition capable of fusing to an enamel-like glaze for protecting the surface of metal articles from scaling, blistering and oxidation during extended exposure to high temperature heat treating processes, consisting essentially of between 1 and 20 parts by weight of alkali metal silicates, between 5 and 50 parts by weight of alkaline earth metal fluorides, between 3 and 20 parts by weight of alkali metal fluorides, and between 0.25 and 25.0 parts by weight of chlorides of metals that are compatible with the metal being protected compounded together with between 5 and 60 parts by weight of a metal powder.
4. The combination set forth in claim 3 in which said protector composition is made up in paste form by addition of an alcohol carrier.
5. A protector composition according to claim 3 wherein said metal chlorides are present in a proportional amount of between 0.5 and 12.5 parts by weight from the group consisting of tin, cadmium, magnesium, lithium, zinc, copper and aluminum chloride.
6. An anti-scaling, anti-blistering, oxidation preventing protector composition for metal surfaces and capable of fusing at temperatures above 1700 F. to form an enamellike glaze, consisting essentially of 1% to 20 parts by weight of sodium fluoride, l to 20 parts by weight of sodium silicate, 5 to 50 parts by weight of fluorspar, 2 to 20 parts by weight of aluminum sodium fluoride, 1 to 10 parts by weight of aluminum silicate,
References Cited in the file of this patent UNITED STATES PATENTS Brown Feb. 9, 1869 Thompson et al Feb. 3, 1914 Caugherty et al. Jan. 4, 1944 Gayley July 11, 1950