US1159748A - Method of preventing the rusting of iron and steel. - Google Patents

Description

U IT D STATES- PATENT OFFICE.

DANIEL F. COMSTOGK, OF BROOKLINE MASSACHUSETTS, ASSIGNOR TO COMSTOCK &

WESCOTT, INCORPORATED, OF BOSTON, MASSACHUSETTS, CORPORATION OF MAS- SACHUSETTS.

No Drawing.

To all whom it may mm Be it known that I, DANIEL F. CoMs'rooK,

. a citizen of the United States, residing at Brookline, in the county of Norfolk and State of Massachusetts, have invented cer- It is well known that iron or steel will be attacked by rust if exposed to Watenor a moist atmosphere. Such rusting is particularly destructive to structural iron work so that to preserve it various methods have been proposed to prevent the attacks of rust. The usual method of protecting iron and steel is to coat them with various kinds of paint.- Theaim of'painting in all cases has been to exclude moisture from the metal surface.

When the rolled iron and steel comes from the rolling mill, its surface is covered with a black oxid known as ,mill bloom which does not rust. The usual method of protecting the iron or steel is to paint it at-the mill with the common red lead linseed-oil paints. Usually the paint is spread over the surface which is more or less covered with the bloom from the rolling'mill. This bloom, because of its different coefficient of expansion, in time becomes loosened from the underlying metal and opens upminute cracks so that moisture is able to penetrate through the cracks in the paint beneath the edges of the bloom scales and attack the metal beneathl The resultant rust working beneath the scales of bloom loosens them so that in time they peel off and. expose the naked metal. On account of the peeling of the bloom scales, it is considered the better, although the much more expensive, practice to remove the bloom from the iron or steel before painting at the mill. This is done mechanically by means of a sand blast, brush, hammer, or chisel, or chemically by means of acid baths. After the surfaces have been cleaned, they are painted at the mill before the iron or steel is shipped. The amount ,of protection against rust obtained Specificationof Letters Patent.

Application filed June 2, 1911. Serial No. 630.879.

METHOD OF PREVENTING THE RUSTING IRON AND STEEL.

' Patented Nov. 9, 1915.

by-such treatment depends upon the clearness and dryness of the surface and the imperviousness of the paint films applied.

Aside from the objection of expense 'in-. volvedin such treatment, it is found almost. imposslble, except by the exercise of the highest degree of care, to free the iron or steel surface from oxid or moisture and to,

keep it free before the paint is applied. The paint film is relied on to prevent the access of moisture to the underlying metal. It is well known that paint films seldommeasure more than a fewthousandths of an inch in thickness and that even the best paint film is not entirely impervious --to moisture. Whether this is because the paint, while drying, contracts and the contraction opens up 7 little pores or cracks in the film, or because the dried film, when subjected to moisture,

forms a semi-solid solution through which the moisture' 'penetrates by diffusion to the surface of the metal, is not known, but it is known thatunless the surfaceof the metal was free from oxid and moisture before the paint was applied,-tha-t'in time rustingwill take. place beneath'the paintfilm.

Afterthe metal sheets or'beams have been assembled in the: building, bridge, or ship, a

second coatof paint is usually applied to all of the exposed surfaces. Where the surfaces are left permanently exposed, as on the exposed parts of bridges or the outside of ship plates, new coats of paint are applied from time to time where the original paint has flaked oil and thus the life of the structure is prolonged. This cannot be done when the metal is inclosed in the building materials as, for instance, by being boxed in by a stone, brick, terra-cotta, or concrete sheath, so that the original paint coats are the only protection the iron or steel has against moisture coming through itsinclosing sheath.

' All iron or steel structures are made up of a number of members riveted or bolted together which are in turn often compound pieces themselves. The units making up the members are so riveted together that a considerable part of the surface of one is 0pposed to that of another. The integrity of the members depends on the bond'between the units effected by the contraction of the rivets oncooling. Since the riveted or bolted joints are generally made before the second coating of paint, their inner opposed sur- .rust.

. of the oxid over the original volume of iron from which it is formed. The pressure, due to the swelling or chemical increase inthe volume of the rust between the members, has been known to have become great enough to shear off the heads of the rivets and'destroy the joint. This rusting on the inaccessible surfaces of riveted joints is particularly destructive in its operation on marine structures such as steel ships. Here the constant vibration and the presence of a large amount'of moisture, whichinevitably is diffused through the riveted joints, tends to destroy them very rapidly.

Iron and steel are extensively used as reinforcing material for concrete. When so em.- ployed, the metal bars are generally cleaned to a more or less extent with a sand blast or wire brush and the concrete mixture poured and tam ped about them. The best Portland cement concrete is at most but a more or less porous sheath for the embedded iron or steel bars. It is well known that it is exceedingly difficult to make concrete even approximately water tight. It is found that in old rein forced concrete work, particularly if it has been exposed to water or a humid atmosphere, the bars have been more or less attacked by rust. This rust destroys the bond between the concrete and the bars and so lessens the strength of the structure. More over the phenomenon of swelling of rusted bars may be'particularly destructive. In certain instances this swelling of the iron bars by rust has become so great that the concrete has actually. been burst or disrupted by the rusting of the embedded iron bars. It is at present the general custom to embed the iron bars directly in the concrete without any special protection and trust that the preliminary cleaning of the bars and the conditions under which the concrete is used maybe favorable enough to keep the bars from any very rapid deterioration. by rustmg.

It is well known that if the surfaces of the iron or steel are kept absolutely; dry, no rusting will occur. The presence of moisture is one of the essential conditions for the chemical phenomenon known asrusting. Of the various theories which seek to explain the chemical action, the so-called electrolytic theory is the most generally accepted and is believed to ofier the correct explanation.

rium, the hydrogen ions of the solution migrate to the surface of the iron and give up their positive charges. Thus, according to the electrolytic theory, it is necessary that moisture be present to allow the iron to pass into solution and that the water or moisture must be sufficiently impure so that it will act as an electric conductor and must also be in such condition that hydrogen ions are pres cut. This electric local battery action is greatly assisted by the presence of impurities, such as rust, at the surface of the iron, because the impurities or rust are of a different potential with respect to the solution than the pure iron, so that a localbattery circuit is set up through the solution between the pure iron surface and the rust or impurities. This assistance to electric action given by the rust probably explains why the surfaces, which are somewhat rusted before paint is applied, rust more rapidly than surfaces which are absolutely clean before the paint is applied, because the rust tends to set up a local battery action through the moisture which has penetrated through the paint to the iron surface or which is diffused in the paint in a sort of semi-solid so lution. Theoretically, therefore, there are two ways in which to prevent rusting. First, by absolutely excluding moisture from the surface and, second, by rendering the'water or moisture incapable of acting as an electrolyte to support the local battery action at the iron surface. While iron will rust in im-" pure water, particularly if the. water contains acid and if there are already incipient rust spots on the surface, yetif a certain amount of alkali be present in the water abs solutely no rusting will take place even though the iron surface has been rusted before being placed in the alkaline solution.

The probable explanation of the inhibitire effect of the alkali on rusting is that the presence of the alkali prevents such a concentration. of the free hydrogen ions in the solution as to allow it to act as an electrolyte to decompose the iron.

The action of the alkali in preventing a. concentration of free hydrogen ions in solution. is the same chemical action which causes the alkali to neutralize an acid, therefore the alkaline carbonates, as well as the mains and has been proved by many experiments that iron which is in intimate contact with an alkali will not rust.-

The essential condition in preventing rust is that the alkali must be intimately associated with the entire surface to be preserved from rusting. Thus, a piece of iron tion which is the cause of the rusting. If,

on the other hand, the entire surface is not impregnated with the'alkali, rusting may occur at portions of the surface where for some reasonthe alkali is prevented from impregnating the metal surface. It is believed that the well known phenomenon of the rusting of iron containers of alkali after they are opened to the air and moisture, is

due to the fact that. there are present on the container surface places where, due to the presence of organic matter, scale or the like, the surface is not in intimate contact with the alkali. At such places rusting may occur, giving rise to the characteristic mottled appearance of the container surface when the rusting first occurs, and these rust centers may eat into the metal until the container is rendered useless. As above stated, this action is believed to be due to the rusting first set up at portions of the surface which are not alkali-impregnated and at which free hydrogen ions can and do exist to formv local rust centers which spread into the metal. This condition of local uniinpregnated rust centers is to be contrasted with a condition in which the entire surface is so treated with alkali that it is completely and thoroughly impregnated and no unimpregnated places exist to later form local rust centers. \Vit'h the object, therefore, of preventing iron and steel from rusting, the present invention consists in a method of preventing rust by the means of an alkali, and particularly by so treating the iron or steel that the alkali is maintained in intimate contact with the entire surface to be preserved. The present invention contemplates utilizing the rust preventing and arresting qualities of an alkalion a commercial basis for preserving iron and steel.

The present invention in* one of its broader aspects contemplates treating the surface to be preserved with an alkali in such a manner that the alkali is etained at the surface after the treating operation is completed.

The present invention contemplates as another featurefthe treating of the surface with an alkali and the subsequent sealing in,

or coating of, the surface to exclude moisture as much as possible, the exclusion of moisture being to exclude water as one of the rust contributing agents and also, what is fully as important, the exclusion of the water to prevent its washing the alkali from the treated surface.

The present invention is susceptible of being practised in a number of specific modes of procedure since the essentials of the invention consist in applying the alkali to the surface of the iron or steel and in the employment of a; suitable retaining agent or means to keep it there to inhibit rusting.

For convenience in disclosing various ways in which the present invention may be practised, the. preferred methods of preventing rust on such surfaces as are exposed in the structure after the iron Work is assembled and which are usually covered with the second coating of paint, such surfaces as are covered over with an embedding sheath likeconcrete, and such surfaces as lie between theriveted and bolted joints of the iron structure, which cannot be reached by the usual second coat of paint,

will be discussed.

Surfaces which may be painted after the iron or steel structure 2's aesembled.After the iron pieces come from the rolling mill, it is preferable not to give them the usual coat of' red lead linseed-oil paint, but to erect the iron posts, girders or plates without any treatment. The action of moisture and gases will tend to loosen the mill bloom from the iron surface so that by brushing most of the scale may be taken off. The exposed surfaces will then be clear from scale and although rusted somewhat most of the loose rust will be brushed off. The surfaces are then to be painted over with an alkali dissolved in a suitable solvent. A microscopic examination of any iron or steel surface will "reveal the fact that the surface is not continuous or solidbut is literally honeycombed with minute pores and crevices. The solvent acts to carry the alkali into the minutest pores and crevices of the surface so that not only is the surface covered with alkali but the surface layer of the iron itself is thoroughly impregnated by the alkali. The surfaces are exposed until the solvent is evaporated, and, in case the alkaliis applied as a hydrate, until the carbon, dioxid in the air changes the hydrate into a carbonate, and the alkali is left as a carbonate. Then the iron is painted over with a coating which is not prejudicially affected by the alkali and which will act' both as an inert holder to keep the chemically active alkali on the surface, and in the pores of the iron to prevent future rusting and as a protecting those at present in vogue.

To insure a better mechanical protectionagainst abrasion or weather, subsequent coatings of paints or varnishes may be applied. It is obvious, however, that these may be of any kind since the inner alkali resisting coating acts to seal the alkali in the porous surface of the metal and the outer coatings are merely for better mechanical protection to preserve the inner coating intact and exclude moisture as far as possible from it. It is obvious that this method of protecting the surfaces is much cheaper than The great item ofexpense has been to thoroughly clean and dry the iron surfaces before the paint is applied, because if any minute spots of rust or of moisture remain they will set up rusting beneath the paint. In the present method the iron surface need be cleaned of scale and rust only sufiiciently to allowthe coating, which is put on subsequently to the alkali, to have a good mechanical grip on the surface. Thus after the rust which would hinder a good mechanical bond between the coating and iron, has been brushed off, the remaining rust may be allowed to remain since it is thoroughly impregnated with the alkali and is thus rendered absolutely incapable of setting up any further rusting.

While any solvent which will take up the alkali may be employed, it is found that alcohol possesses particularly desirable qualities. The alcohol, on account of its" low surface tension, very easily permeates the surface of the metal and impregnatesit with the alkali, and alcohol, evaporates very rapidly and frees the surface of fluid. A solvent is used' which will entirely evaporate and leave only the alkali. While alcohol is preferred because it evaporates very readily,

any other solvent which will evaporate and leave the, alkali maybe used. Ordinary caustic soda or potash, on account of their cheapness, are preferably used as the alkali. Moreover, both of these alkalis are readily soluble in alcohol. After the alcohol has evaporated, the action of the ca'rbondioxid in the air very soon chan es the sodium and potassium hydrateto sodlum and potassium carbonate which, on. account oftheir alkaline properties, prevent rust. The particu-. lar reason for applying the alkali as a hydrate and allowing it to change to a carbonate on the surface is that the hydrates are easily soluble whereas the carbonates are soluble with great dificulty, particularlyLin alcohol. While any coating may be applied over the alkaline treated surface, which is not prejudicially affectedby' the alkali, ordinary orange shellac is found to serve satisfactorily. The carbonate does not appear to materially afiectthe shellac but if the shellac is applied over the surface before the by drate is changed to the carbonate, the hydrate turns the shellac to a pinkish color and apparently causes it to be more brittle al-' though notcausing it to flake or peel. off.

Surfaces to be embedded in codcrcta- If the iron or steel is to be used in concrete, the concrete in which the iron or steel is embedded may act as the inclosing sheath or binder to prevent the alkali from leaving the surface. A convenient method of treat-' ing bars to be used in concrete reinforcing is to paint them over with a solution of an alkali. This impregnates the surface of the bar with the rust preventing alkali but does -not prevent the strong bond which takesmoisture does reach the iron surface the concrete acts to keep the alkali from being washed away so that the alkali is always present in the pores of the iron to absolutely prevent the action of rust. Moreover the alkali may be mixed with the concrete which immediately surrounds the iron bars if the conditions are such that the alkali, requisite to prevent rusting,will not weaken the con.- crete.

Opposed surfaces of riveted 'or bolted joints which cannot be reached after the iron or steel structure is asscmbZcd.-The compound pieces of structural iron or steel work, such as girders or posts, are usually assembled and riveted at the iron mills. The-opposing surfaces between the riveted pieces must, therefore, be treated before being sent out. The preferred method of treating such surfaces is to brush, mop, or otherwise apply directly to the-surfaces, just before the assemblage of such members, an alkaline bearing substance. A preferred alkaline coating is a modified form of sappo viridis or green soap which is modified by an addition of 1 to 2% of a saturated water solution of caustic soda or potash. The soap is readily soluble in water and is not prejudicially afiected by the ordinary temperature changes to which it is subjected in forming the joint. If the soap is heated, the oily constituents will either be melted'or carbonized, leaving the alkali. The. soap is not volatile or inflammable, is soft enough to be easily spreadand worked into the surfaces and is thick enoilgh so that it will not run off. In assembling the iron or steel in place, the surfaces of the joints, which care not be reached by the subsequent painting, are to be likewise treated with the alkaline soap. The edges of the cracks or crevices of the joint should be calked with shellac or paint so that the alkaline soap is held in place and cannot be washed out by moisture to which the structure may be subjected. This calking of the cracks may be done immediately after the joint is finished or may be delayed until the final painting of the structure, depending upon the conditions.

The present invention is also applicable to preventing the further attacks of rust on structures which have already been attacked. If the surfaces are exposed, they should be cleaned of paint, rust, or scale, and then treated with an alcoholic solution of alkali and painted over with an alkali resisting coating. If the surfaces'are such that it is impossible to reach and clean them mechanically as, for instance, the opposing surfaces of joints in bridge structures or the joints between the plates of ships, an alkaline solution, preferably of alcohol which, because of its low surface tension, will permeate the joint very readily, is injected or poured between the surfacesand the edges of the cracks, and the joint subsequently'hermetically sealed up to retain the alkali on the opposed surfaces where it will act to positively check any further inroads of rust.

While the preferred manner of treating the iron and steel surfaces has been specifically described, it is to be understood that consisting of an alkali and an evaporable solvent, in evaporating the solvent, and in protecting the treated surface with a coating not prejudicially affected by the alkali, sub stantially as described.

2. The method of preventing the rusting of iron and steel which consists in treating the surface to be preserved with an alcoholic solution of a caustic alkali, in evaporating the solvent, and in subsequently coating the alkali treated surface with shellac, substantially as described. g

3. The method of preventing the rusting of iron and steel Wl'llCll consists in treating the surface to be preserved with an alcoholic solution of an alkaline hydrate, in evaporating the solvent, in exposing the treated surface to the air to change the hydrate to a carbonate, and in protecting the treated surface with a coating not prejudicially affected by the alkaline carbonate, substantially as described.

DANIEL F. COMSTOCK.

Witnesses:

' HORACE VAN EVEREN,

W. BURTON Wnsco'rr.