US2992131A - Treatment of metal surfaces - Google Patents

Description

United States Patent 2,992,131 TREATMENT OF METAL SURFACES Frank Stubbs Bricknell, West Croydon, and Harry Augustus Cork, Ewell, England, assignors to Jenolite Limited, London, England, a British company No Drawing. Filed Mar. 11, 1958, Ser. No. 720,546

Claims priority, application Great Britain Mar. 21, 1957 6 Claims. (Cl. 117-70) A simplified flow diagram of the method 1s as follows:

Ferrous metal reinforcement member Removal of scale and oxide Deposition of a water-soluble, non-conducting coating of a heavy metal phosphate Covering phosphatecoated ferrous metal with a non-saponlfiable organic film former Encasting the coated ferrous metal in concrete Hitherto, steel reinforcement bars and the like for strengthening concrete have been embedded in the latter in the scaled or rusted form, or after sand blasting. It frequently happens that in the course of time such steel rusts so that, on the one hand, the joint between the metal and the concrete is weakened and, on the other hand, corrosion products accumulate at the junction of the metal and concrete, eventually causing cracks in the latter and spalling thereof, sometimes with serious consequences, the corrosion products, especially rust oxides, having a bulk several times that of the metal from which they are formed. In any case, there is frequent discoloration of the concrete due to rust or iron compounds being conveyed from the metal to the concrete surface.

Attempts have been made to mitigate corrosion of the steel by painting the latter before embedding it in concrete. However, since most commonly used priming paints are made from oleaginous vehicles, the latter tend to weaken the bond between the steel and the concrete and, in some cases, permit the steel to move Within the latter when loads are applied to such composite structures. In addition, alkalies, e.g. lime, liberated from cement mixes as they set, tend to destroy such paint type coatings, particularly by saponification of the oleaginous Patented July 11, 1961 r ICE vehicles to produce compounds which further weaken the cement bond and may indeed have some lubricating efiect facilitating movement of the concrete relatively to the steel.

Attempts have also been made to prevent the abovementioned difliculties by a preliminary grouting of the new steel bars, joists or the like with a view. to scaling them against the effects in question. These attempts, however, were also unsuccessful as the grouting was found to come away from the steel with the scale thereon so leaving the metal unprotected.

In view of this, further attempts were made in which the steel members were allowedto rust on site whereby the scale was loosened and flaked off, the members then.

being encased in concrete in the rusted state. These at-.

tempts appeared to give success, an excellent metal to concrete adhesion being obtained, possibly due to the eifect of the rust on the surface of the former. However, it was later found that the apparently satisfactory results did not remain satisfactory over the course ofv time; it appeared that strong lime and other salt solutions leaching from the concrete mix led to the setting.

of treating the surface of ferrous metal to be encased. in concrete or like cementitious material which comprises freeing the surface of any scale and oxide and depositing an insoluble amorphous or crystalline heavy metal phophate coating on the surface, and thereafter covering the surface with a coating composition comprising an organic film-forming medium, the coating composition being resistant to attack in contact with the concrete or like cementitious composition and having high bond. strength both to the latter and to the said surface.

The invention also includes buildings, articles and other structures, including roadways, airfield runways and the like, and parts of any of the foregoing compris' ing ferrous metal reinforcements, supports, stress members or skeletons thereof, the or a part of the surface of which has been treated as aforesaid and which is wholly or in part encased in concrete or like cementi ti-ous material.

The removal of scale and oxide from the metal surface may advantageously be effected by a conventional acid pickling treatment using for example dilute hydrochloric acid at room temperature or dilute sulphuric acid at a temperature of approximately F. After removal from the descaling tank, wherein the steelwork or the like should be completely denuded of all mill scale, heat scale and rust oxides, thorough water rinsing should be applied.

In the alternative, descaling may conveniently be effected by the application to the surface in question of a descaling jelly or paste, preferably such as is described in United States application Ser. No. 700,956, filed' December 6, 1957, now abandoned, by Frank Stubbs Bricknell.

However, in the case of steel members immersion or in the event that it may not be desired to use a descaling jelly or paste, the rust oxides and loose scale may be removed mechanically, as by wirebnushing.

The deposition of an insoluble amorphous or crystalline heavy metal phosphate coating may be eifected by. a conventional phosphating treatment. Such treatment.

too bulky forif properly applied should produce on the metal surface a phosphate coating which is rust-inhibiting and resistant to the alkaline conditions prevailing in contact with concrete, due particularly to the liberation of lime from wet concrete mixes as the latter set and mature. Such coatings may be formed by the use of solutions based on phosphoric acid which may be applied to the steel by dipping, brushing or spraying, as convenient, and allowed to dry on the surface in air to form a coating consisting principally of substantially amorphous iron phosphates. Alternatively the surface to be treated may be subjected to the action of a solution containing one or more heavy metal phosphates, for example iron and/or manganese phosphates, which is allowed to dry on the surface to produce thereon a coating of insoluble crystalline heavy metal phosphate.

These phosphate coatings, on the one hand, assist in keying the concrete to the metal surface, and on the other, inhibit a tendency for steel to be corroded by water or moisture penetrating through the concrete, as may happen in the course of time after soluble constituents of the latter have been leached out.

The steps of removing scale and oxide and of depositing a phosphate coating may in certain circumstances be effected simultaneously, as in the case in which the steelwork to be treated carried only remnants of mill scale but may nevertheless bear a considerable amount of rust oxides, by the use of a phosphating solution, preferably by immersion, of such a composition that it will itself regove from the surface the oxides and any residual sc e.

The coating composition comprising an organic filmforming medium is applied over the phosphated surface further to protect the metal from corrosion. The coating produced must be resistant to attack in contact with the concrete or the like; thus it should be non-saponifiable under the prevailing conditions, which may include the presence of strong solutions of lime and/or salts leaching from the concrete mix. The coating should further have high bond strength both to the phosphated surface and to the concrete so that the keying of the latter to the former is not substantially impaired.

Thus the coating composition may be an appropriate sealer coating in which the film-forming medium is an air-drying or curable resin satisfying the foregoing requirements, and containing a suitable pigment as an extender, to give the coating vehicle the necessary covering power to ensure the formation of a continuous film. The pigment itself must naturally not be affected adversely by the conditions to which the coating formed will be subject. Thus, for example, amongst other properties it should be non-reducible. Furthermore, the sealer coating must not yield any lubricating properties such as might detract from the strength of the concrete/metal bond as measured by, for example, either a draw test or a compression test.

We prefer to use as pigment one or a mixture of ferric oxide, ferrous phosphate, strontium chromate, strontium sulphate, barium chromate, calcium earth plumbate and metallic lead. The first two are protective against corrosion'whilst not actually inhibiting it, whereas the remainder are inhibitive of corrosion.

The film-forming medium may be a natural or synthetic resinous material satisfying the requirements set out above; thus for example it may be chlorinated rubber, rubber modified chlorinated rubber, an epoxy resin such as that sold under the trade name Epikote or Epon, of a vinyl resin, for example polyvinyl chloride, or polyvinyl acetate, plasticised or not, dissolved or dispersed in a suitable solvent or vehicle.

We prefer to incorporate in the coating composition a hydrogen acceptor, for example glyoxal.

In one embodiment of the process of our invention steelwork to be encased in concrete is first denuded of all mill-scale by immersion in a dilute solution of hydrochloric acid at room temperature, conveniently a solution of two parts by weight of tap water to one part by weight of the material known under the trade name Jenolite H.S.R./ l, which is a 32% w./w. solution of hydrochloric acid suitably inhibited with ferric chloride to prevent preferential attack on the substrate.

Alternatively, descaling may be effected by the use of' hot dilute sulphuric acid, conveniently a solution of two parts by weight of tap water and one part by weight of the material known under the trade name of Jenolite H.S.R./2, which is a 50% w./w. solution of sulphuric acid, heated to a temperature of F.

When descaling is complete the steelwork is removed from the descaling tank and thoroughly rinsed with water either by immersion in a rinse tank or by power hose.

Thereafter the surface of the steelwork is phosphated by immersion in a hot dilute solution of phosphoric acid containing manganese, iron or zinc salts to produce thereon a water-insoluble, non-conductive amorphous or crystalline phosphate coating. After extraction from the phosphating tank the steelwork is air-dried, force dried or rinsed in water, depending on the type of phosphate process applied. The phosphate coatings produced by some of the above mentioned treatments mature by oxidation in reasonably dry air.

The phosphated steelwork is thereafter coated with an organic coating designed to seal the phosphate coating completely and to resist underfilm corrosion which might develop from the free pore areas. The sealer coating is also designed to resist any attack by lime solutions liberated in the concrete mix and a suitable sealer coating has the following composition by weight:

Parts Strontium chromate 7 Strontium sulphate 43 Epoxy ester modified with linseed oil 33 White spirit 16 Cobalt naphthenate 1 In a second embodiment of the invention of particular application in cases in which immersion techniques are not practicable, millscale is removed from the steelwork by weathering on site or alternatively by the application of a descaling jelly, such as one of those described in said application Ser. No. 700,956, now abandoned. In the latter event, the steelwork is thereafter thoroughly washed with clean running water.

A thin application of one of the materials known under the trade name Jenolite R.R.N./B. or the trade name Jenolite Jenocote Solution (the latter material being the subject of our co-pending British application No. 1467/58) is then applied by brush to the steelwork to dissolve rust oxides and simultaneously deposit an amorphous water-insoluble iron phosphate coating which is allowed to mature by air-drying, whereafter a sealer coating composition such as that described above is applied to the steelwork. When this coating has dried, the steelwork is ready for encasement.

What we claim is:

1. The method of making a structural article composed of ferrous metal encased at least partially in concretetype cementitious material which comprises removing scale and oxide from the ferrous metal of such article, depositing a water-insoluble non-conductive coating of a heavy metal phosphate on the thus-treated ferrous metal, covering the phosphate-coated ferrous metal with a nonsaponifiable organic film-forming composition and then applying thereto at least partially a concrete-type cementitious casing to produce a structural article in which there is a high bond strength between said composition and said phosphated ferrous metal and between said composition and said casing and in which the composition is resistant to attack from cementitious casing in contact therewith.

2. The method of claim 1, in which the film-forming composition contains a hardenable organic resin and a pigment extender.

3. The method of claim 2, in which the pigment extender is at least one of the pigments selected from the group consisting of ferric oxide, ferric phosphate, strontium chromate, strontium sulfate, barium chromate, calcium earth plumbate and metallic lead.

4. The method of claim 2 in which the resin is at least one of the resins selected from the group consisting of chlorinated rubber, epoxy resins and vinyl resins.

5. The method of claim 1, in which glyoxal as a hydrogen acceptor is incorporated in the film-forming composition.

6. The method of claim 1, in which the heavy metal phosphate is a salt of phosphoric acid with a metal se- 6 lected from the group consisting of manganese, iron and zinc.

References Cited in the file of this patent UNITED STATES PATENTS 2,611,945 Simonsson et a1. Sept. 30, 1952 2,700,622 Burwell Jan. 25, 1955 2,725,310 McBride Nov. 29, 1955 2,774,701 Koryta Dec. 18, 1956 2,832,706 Toubes Apr. 29, 1958 2,854,370 Kronstein Sept. 30, 1958 2,887,404 Evans May 19, 1959 2,930,106 Wrotnowski Mar. 29, 1960

Claims (1)

1. THE METHOD OF MAKING A STRUCTURAL ARTICLE COMPOSED OF FERROUS METAL ENCASED AT LEAST PARTIALLY IN CONCRETETYPE CEMENTITIOUS MATERIAL WHICH COMPRISES REMOVING SCALE AND OXIDE FROM THE FERROUS METAL OF SUCH ARTICLE, DEPOSITING A WATER-INSOLUBLE NON-CONDUCTIVE COATING OF A HEAVY METAL PHOSPHATE ON THE THUS-TREATED FERROUS METAL, COVERING THE PHOSPHATE-COATED FERROUS METAL WITH A NONSAPONIFIABLE ORGANIC FILM-FORMING COMPOSITION AND THEN APPLYING THERETO AT LEAST PARTIALLY A CONCRETE-TYPE CEMENTITIOUS CASING TO PRODUCE A STRUCTURAL ARTICLE IN WHICH THERE IS A HIGH BOND STRENGTH BETWEEN SAID COMPOSITION AND SAID PHOSPHATED FERROUS METAL AND BETWEEN SAID COMPOSITION AND SAID CASING AND IN WHICH THE COMPOSITION IS RESISTANT TO ATTACK FROM CEMENTITIOUS CASING IN CONTACT THEREWITH.