DE1669144A1 - Anti-scaling paint for application on metal surfaces - Google Patents

Description

Anti-scaling paint for application on metal surfaces The invention relates to coating compositions for application or use on metal surfaces are intended to reduce surface oxidation phenomena, such as loss of surface metal in the form of oxide scale or decarburization Lower the minimum. Such surface coating compositions are described below for the sake of brevity as "paints against scaling" (anti-scaling Paints). According to the invention is a paint Provided against scaling, the aluminum metal in powder form, one or more refractory oxides of divalent metals or a compound which these with Heating results, and optionally comprises a binder. The paint is located usually in liquid form, although not necessary, and can be a Suspending agents included in order to suspend the solids in the liquid medium to support, the divalent metal is preferably one of its Oxide is known to combine with aluminum to form a spinel, and can in particular consist of zinc or magnesium. 'The paints against Scaling according to the invention are of particular value in their application Objects made of iron and steel that are to be subjected to heat treatment. Vienna described below, they have a very valuable effect in terms of reducing the formation of scale to a minimum. The reasons for its effectiveness the paints are not known with certainty. It is to be assumed, however, that during heat treatment the aluminum is converted to aluminum oxide, this being is preferably oxidized on the base metal (e.g. iron or steel) and thereby the oxidation of the base metal is reduced to a minimum and the aluminum oxide then unites with the refractory oxide, a highly fireproof to produce brittle spinel. After using anti-scaling agents metal objects treated according to the invention are heat treated under conditions which usually cause severe scaling of the metal, the paint can be easily removed from the surface of the objects concerned and it’s been found that a comparatively very small loss is present on base metals as a result of scaling.

The compositions provided according to the invention can be applied to those to be protected Metal surfaces can be applied in various ways. For example, can a -dry powdery product by a heat source on the metal surface be sprayed on; such a mass is only required from the aluminum-oxide mixture with a suitable binder such as a thermosetting resin, e.g. a phenol-formaldehyde resin, to pass. Optionally, the anti-scaling paint can be in the form a suspension'in a liquid carrier, in which case a suitable suspending agent for the solid constituents of the mass is present can be. After applying the paint, e.g. by spraying, dipping or Brushing, the paint can be left to dry or dried before the metal object is placed in a furnace for the heat treatment process. In some cases it may be useful to - carry out a wet loading, i.e. the metal object of its heat treatment to subjugate, without first drying the applied protective coating. In such cases It may not be necessary to incorporate a binding agent into the anti-scaling compound. The thickness of the protective coating is generally 0.15 to 2 mm, preferably 0.7 to 0.9 mm.

The aluminum component of the paint has anti-scaling properties preferably a fine particle size, e.g., less than 0.15 mm, preferably im substantially less than 0.075 mm. The refractory oxide can be used as such arrive or. a compound of the appropriate divalent metal, e.g. Magnesium carbonate, which is converted into magnesium oxide during heat treatment is converted. The liquid medium of the paint is the most appropriate from water, but other media can also be used, e.g. technical Spirit, technical isopropanol or aqueous alcohol. When the liquid medium consists of water, preferably distilled or deionized water is used, any tendency towards harmful attack on the aluminum powder reduce to a minimum.

When using some of the liquid media outlined above there is sometimes a tendency that the paint is weakly alkaline in the reaction is, presumably, due to a low solubility of the refractory Oxide or, for example, the divalent metal carbonate serving as a precursor; under under these conditions there is a tendency that the powdered aluminum metal becomes reactive.

According to a further feature of the invention is therefore a paint against Scaling of the type indicated above is provided in which the aluminum metal particles or the particles of refractory divalent metal oxide or a result thereof Compound or both are provided with an inert coating to their mutual Reduce exposure to an aqueous medium to a minimum.

This measure can reduce the disadvantages of alkaline reactions minimized or avoided. 'The coating can consist of an inert Material such as a natural or synthetic resin or polymer or a Wax or a waxy substance, e.g. polyethylene, polytetrafluoroethylene, Rosin resin, phenol formaldehyde or urea-formaldehyde resin, stearic acid or amide wax.

It has been found particularly valuable to provide an aluminum oxide coating on the aluminum particles for this purpose at least 2 microns thick. A suitable method for producing this coating * is to treat the powdery aluminum with a hot aqueous solution. an oxidizing agent, e.g. Sodium chromate solution, to submit. If necessary, the aluminum particles in the masses can be protected by the use of pIi buffer solutions known per se or by the addition of any of the nitrogen-containing compounds which are known per se for use as corrosion inhibitors, such as those used as additives to detergent compositions come into use, Use in washing metal objects / can be achieved; Examples are thiourea, benzotriazole and imidazole derivatives.

The suspending agent can consist of any compound, their Ability to suspend solid particulate matter in an aqueous Medium is known and should either have refractory properties or completely burn off after ignition. Bentonite or other refractory clays of similar properties are on the one hand suitable, while organic colloidal materials, such as cellulose ethers and derivatives, on the other hand, are most convenient.

The anti-scaling paint can also be a binder include, which serves to create a matrix for the solid components in the dried To produce paint films. It can be any common paint binder or paints are used. However, it has been found that due to the high degree of resistance to impact and mechanical abrasion makes it especially is valuable to use an aqueous polyvinyl acetate emulsion and thereby that Manufacture product in the form of a so-called emulsion paint. Through suitable Choice of the material used can give the paint thixotropic gel properties be granted.

While the relative proportions of aluminum and refractory oxide in Can be varied widely, it has become general as expediently found that the aluminum 3o to 7o wt.; ö the total amount of Aluminum and refractory oxide represents a proportion of aluminum over 7o%, although it is still effective, in some cases lead to disadvantages, e.g. because aluminum penetrates the surface of the base metal.

The amount of binder used, if any, is chosen to provide the required binding properties and resistance to abrasion. In the case of polyvinyl acetate emulsion binders, the optimum level of polyvinyl acetate is usually within the range of 1 to 15; ö, preferably @, based on the weight of the total mass. The temperature at which the mass becomes effective seems to depend on the spinel formation reaction between aluminum, the oxide of the divalent rivet and the atmospheric chemical. The oxide used therefore has an effect on determining this temperature level. If magnesium oxide is used, the reaction appears to take place only after a temperature of 100 ° C has been exceeded, while in the case of zinc oxide the reaction occurs at about 20 ° to 95 ° C. It has been found, however, that the effective temperature can be artificially lowered * by incorporating a small proportion of a fluoride of an alkali or alkaline earth metal or of magnesium into the masses. When such fluoride is incorporated, it is preferably used in an amount up to 10% by weight by weight, with about 3% by weight magnesium fluoride being most preferred. It can be seen that the invention comprises new antioxidant preparations as described above, through the use of which the oxidation phenomena, for example scale formation and decarburization, are reduced to a minimum in the heat treatment of metal objects, in particular objects made of iron or steel. . The invention is explained in more detail below with the aid of examples. In the examples, the parts and percentages are. Sentences on weight. based. In these examples tests were carried out with steel. of type * EN8 of the British Standard Specification No: 97o / 1955.

In each of Examples 1 to 3, the aluminum powder was pretreated with sodium chromate and sodium silicate solution ox d create an aluminum coating on the particles. example 1 An anti-scaling paint was as follows: composed: Aluminum powder - 35.1 parts . Magnesia (calcined) 23.4 ° @@ Bentonite - '.. 196 aqueous polyvinyl acetate emulsion (Polimul 1015) 890 Weiser 31L #r loo; o parts The product "Polimul 1015" is an aqueous polyvinyl acetate emulsion with a pesticide content of about 55% by weight, manufactured by vunlop Chemicals Limited. This paint * was applied as a coating to steel billets or blocks at room temperature. The paint could be dried prior to any oven treatment, or the painted billets could be put into the oven while the paint was still wet. In the oven, the effect of the paint was to protect the surface metal of the steel billets against oxidation. When the steel billets cool down, the paint residue can, to a certain extent, crack and fall off; however, it is in any event removable by any conventional scale removal procedure.

The paint stays for up to 5 hours at temperatures of around 115o effective up to 135o ° .0.

In a test applied to EN8 steel blocks heated to 125oodi hour, it was found that the metal loss due to scaling in comparison between unpainted blocks and blocks painted with the anti-scaling paint of this example was as follows: Uncoated blocks metal loss 180 mg / cm2 painted blocks metal loss 2o, mgfcm2. . ' Example 2 Another composition that is used for dry Bring is suitable and protection at temperatures'above 11500C granted is the following: Aluminum powder 31.9 Magnesium Oxide .. 21.25 w Quaint Polyvinylace * l # breathing emulsion a - (Polimul 10l5) 8.0_ Sodium carboxymethyl llulose o, 54. ' . Sodium orthouhenylphenolate _ (Preservative) 0.01 j - - water 38.3 This mass was applied to an EN8 steel specimen by spraying, so that a coating 0.9 mm thick resulted. After allowing to dry, the specimen was kept in a muffle furnace at 125 ° 0 for 1 hour. As a result of this treatment, the loss in the form of oxide was 21 mg / cm2, while an untreated sample lost 2oo mg / cm2. . Example 3 A: Preventing scaling a: Means for introducing wet was suitable was composed as follows: Aluminum powder 31.9 Magnesia 21.25p. Sodium carbonomethyl cellulose 0.54% . Water 46.3 Preservative 0901 ö Further EN8 steel samples were sprayed with this mass, so that a 99 mm thick coating was created, before they were then subjected to a four-hour heat treatment cycle in which the temperature was gradually increased from 40 ° to 120 °.

Metal loss of the coated samples 119.mg/em2 Metal loss of the uncoated samples 29o mg / cm 2 Example _4 The following is a spirit-based paint for dry use that is effective above 115o ° 0: Aluminum powder, 33, oj Magnesia 22.25 Wood resin '3.5 ö Crosslinking agent (for alcohol soluble gelulose derivatives), 1.0 hydroxypropyl cellulose o, 25 Isopropanol - 40, o '., The crosslinking agent used is sold under the tradename MANAZOX EP3ol by Hardman and Holdman, and the hydroxypropyl cellulose is sold under the tradename KLÜGEL HA by Hercules Powder Co.

Sample * of EN8 steel used to create a 0.76 mm thick coating Sprayed were allowed to dry before being used in an electric Muffle furnace took place for 1 hour at 12,000.

Metal loss of the coated sample 26 mg / CM 2 Metal loss of the uncoated sample 200 mg / cm 2 Example 5 . Another spirit-based paint for dry use, but containing a fluoride additive to be effective at lower temperatures, is similar to that of Example 4, except that 3% magnesium fluoride replaced a similar amount of the isopropanol carrier. EN8-14 samples were re-sprayed to produce a coating 0.76 mm thick, which was allowed to dry before subjecting the samples to a heating cycle of 800 to 1200oC-in.4 hours followed by an additional heating at 1200o0 for one hour followed.

w Metal loss from the coated sample 7o mg / cm2 Metal loss from the uncoated sample 21o.mg/cm2 In the following two examples use is made of an addition of Ohromat to the compound itself, in which it inhibits attack on the aluminum. If this method is used, an addition of 0.1 to 15%, preferably about 50%, of a water-soluble chromate, for example sodium or potassium chromate, is used. Example 6 - Aluminum powder 3o, 4 Magnesium Oxide 2o, 25 aqueous polyvinyl acetate emulsion (Polimul 1015) 7'6. @ Potassium Ehromat 498 Sodium arboxymethyl cellulose o, 54 Water . 36.4 All of the constituent parts, with the exception of the magnesium oxide, were mixed together thoroughly, after which the latter was added. The shelf life of the whole mixture was found to be at least 3 pounds. - EN8 steel samples covered with a coating with a thickness of 0.76 mm '. were allowed to dry and placed in a muffle furnace at 125ooC 'for 1 hour.

Metal loss of the coated pattern .42 mg / em2 Metal loss of the. uncoated specimen " 310 mg / cm2 - Example 7 Another mass was prepared exactly as for Example 6 except that zinc oxide was used instead of magnesium oxide. This mass was used to make-EN8 specimen with a coating with a thickness The dried samples were subjected to a heating cycle from 600 to 120000 in 3 hours, followed by heating for a further hour at 1200C.

Metal loss of the coated;: n sample 60 mg / em2 Metal loss of the-uncoated sample 43o mg / cm2. Example 8 This example describes a method by which a long shelf life can be obtained for aqueous anti-scaling paints. According to this example the formation of a two part composition is envisaged, the two parts being stored separately and mixed together when required for use. The following two compositions can be produced in this way: Pack A. Powdered aluminum 6o, 25 buffer solution. 32940 ö aqueous Polyvinylacetat®_mulsion '' (13olimul 1175) 6.75 sodium carbozymethyloellulose 0.60; Ä. The buffer solution consists of an aqueous solution containing 3.63 g / l potassium dihydrogen phosphate, 5.68 g / l disodium hydrogen phosphate and 20 g / l thiourea as an inhibitor. Pack B Calcined Magnesium Carbonate .37966 - aqueous polyvinyl acetate emulsion (Polimul 1175). 7, o9 sodium carboxymethyl cellulose 1908 water 54.7 The two compositions are mixed together in equal parts if necessary for use. In tests, such bulk goods gave protection at temperatures from 115o to 13500C.

Claims (5)

1. A paint versus Yerzunderung for application to metal surfaces, characterized in that it contains aluminum metal in powder form and at least one refractory oxide of a divalent metal or a eerbindung, 'the egibt this upon heating. 2. Paint according to claim 1, characterized characterized in that the refractory oxide consists of one that deals with Aluminum combined to form spinels when heated. 3. Paints -according to claim 1 or 2, characterized in that the divalent metal consists of zinc or magnesium consists. . 4. Coating material according to one of claims 1 to 3, characterized in that that it is in the form of a suspension in a liquid carrier. 5. Paints according to claim 4, characterized in that it contains a suspending agent. ' 6th Paint according to one of Claims 1 to 5, characterized in that it contains a binder. 7. Paint according to one of claims 1 to 6, characterized characterized in that it contains magnesium and / or zinc carbonate. 8. Paints according to one of claims 1 to 7, characterized in that the aluminum is a Has particle size of less than 0.15 mm. .. 9. Paints according to any one of claims 1 to 8, characterized in that the aluminum metal particles or the particles of refractory divalent metal oxide or a compound, which results in this, or both are provided with an inert coating to a mutual Reduce exposure to an aqueous medium to a minimum. 1o. Paints according to claim 9, characterized in that the coating is made of a natural or synthetic resin or polymers or a wax or a waxy substance is. _ -11. Coating material according to Claim 9, characterized in that the coating consists of aluminum oxide at least 2 microns thick. 12. Paints according to one of claims' l to 11, characterized in that there is a small proportion an alkali or alkaline earth fluoride or magnesium fluoride.