DE1771759A1 - Process for the surface treatment of objects made of ferrous metals - Google Patents

Description

Crane Co., Chicago, 111. / USA

Process for the surface treatment of objects made of ferrous metals

(Addition to patent (patent application P 16 21 401.0)).

The invention relates to a method for the surface treatment of objects made of ferrous metals, in which

a) the surface of the object is wetted on the surface to be coated,

b) on the wetted surface to form an enamel application a powdery mixture, which contains hot melt components, is applied,

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c) the body containing the order fired and

d) the object is allowed to cool,

according to patent (patent application P 16 21 401.0).

A commonly used process for producing objects with porcelain ^{enamel is 11} NaS enameling. Wet enameling is mainly used for sheet metal and pressed metal goods, for example in the manufacture of ovens and other devices This slurry is then fired in a furnace, the ware is removed from the furnace, cooled, a second coating is applied by a generally sprayed-on slurry, and the article is then fired again.

In the manufacture of enamelled cast iron objects, such as bath pipes, various have already been used Attempts carried out to apply the enameling mixture in the form of an aqueous slurry. One of the main ones Problems encountered when using an aqueous slurry are characteristic of cast iron rough surface, the pinholes, stamps and others

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Having irregular celestial For better handling one keeps the viscosity of the sludge sufficiently low, but this has the disadvantage that the sludge the irregularities of the GuSelsenoberflache follows, whereby in the end product the defective cast iron surface is reproduced and in some cases even reinforced. However, the aim is to cover the superficial irregularities, which has been the case with Gußelsen up to now by using the dry process, in which the final coating is dusted onto the hot goods, happens. In the dry process, the glass powder or the frosted glass can be dusted with a sufficient thickness, to hide the imperfections of the surface and keep graphite and garbide away from the top layer.

In the process according to patent (patent application

P 16 21 401.0) the surface of the goods is first wetted with water. Then on the moistened surface the enamel mixture applied to form an enamel application. The object is then dried and the Mixture baked in an oven.

In technical operations, after the enamel job has been formed, the objects with the email job often have to be be moved. If the email job is not stuck, it can be hit by bumps or suddenly stopping

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shaken off herds.

For example, in this method, in the production of the to form an enamel coating Enamel application, the iron objects moistened with water, whereupon the moistened surface Enamel mixture is dusted on. The items then pass through an oven for baking and firing. In the oven "The objects can be moved through different temperature zones. In the course of this movement, the objects Exposed to influences that may remove the order from the objects. In the production On enamels on steel by this method, the enamel coating obtained is in some cases not as good adheres like cast iron.

The invention therefore relates to an improved V _e r-. drive to apply the order to the surfaces of objects made of ferrous metals, in particular to a method for applying such an order in the surface treatment of iron objects, for example made of cast iron or steel.

It is therefore the aim of the invention to provide an improved method for producing an enamel application, for example in the To provide enamelling of Elsen objects, e.g. made of cast iron or steel. It's another one

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The aim of the invention is to provide an email job with structural advantages and possible uses. It is another object of the invention to provide an enamel application of increased thickness. It is a Another object of the invention is to provide a self-limiting enamel application. It is another The aim of the invention is to create an enamel application suitable for decorative purposes. It's another goal of the Invention, the work involved in enamelling iron objects and the costs involved to reduce. It is, after all, another goal ^. the Invention to provide a method in which certain stages can be performed automatically.

The invention is directed to the formation of an adhesive enamel application on metallic surfaces. Of the Enamel application is used to coat or treat the metallic surface, for example when enamelling, the application being heated to a temperature such that it melts. The job is thereby formed that the surface is first wetted with an aqueous solution containing metal salts. then a dust-like muddle is created on the moistened surface upset. The order thus obtained can then be dried. Those contained in the aqueous solution Metal salts improve the adhesion of the application

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at the surface of the object. According to a modified procedure, the aqueous salt solution can initially also be used be dried, whereupon the surface is wetted again and with a powder to form the order is pollinated.

Referring to the accompanying flow sheet, the main steps in the application of the Email order. The objects to be coated are made of iron-based metals, e.g. cast iron or steel.

The surface to be coated is first coated with a salt solution, for example by dipping or spraying moisturizes. The solution used should not contain any impurities that would cause defects in the finished coating would cause.

The invention is based on the knowledge that the adhesion of the enamel application can be improved by that salts are added to the solution. The preferred salts used should be in the solvent such as E.g. dissolve water without decomposition and crystallize after evaporation of the liquid. The preferred salts should not decompose or volatilize during the subsequent treatment either, i.e. they should with

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the formation of the enamel coating at the melting temperature of the enamel application, which is, for example, in the range of approx. ⁰ 87I ⁰ C, do not form any volatile substances. Suitable metal salts are inorganic metal salts including the alkali and alkaline earth metal chlorides, such as e.g. Sodium chloride, potassium chloride, calcium chloride, magnesium chloride of alkali chromates, such as sodium chromate; Sodium aluminate, the metal nitrates such as aluminum nitrate, chromium nitrate, nickel nitrate, cerium nitrate and the like. Although the nitrates decompose with the release of oxygen and nitrogen, their decomposition is completed sufficiently below the melting temperature of the application, so that in this way the risk of the formation of bubbles and pitting is reduced. The above-mentioned salts are effective in their

not

samiteness / uniform, so that is particularly suitable for special Applications may result in a preference for certain salts. There are also mixtures of several salts suitable. For the salts listed, water is the most suitable Solvent, so the use of aqueous salt solutions is preferred, although others are also used Solvents can work.

Cases

It may be necessary in many / with a colorless solution to work what, for example, through the use of sodium chloride, calcium chloride and magnesium chloride is achieved.

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In other cases it is desirable to add organic salts which color the water and thus act as a coloring agent. For example, a red colored solution may be useful in applying the powder mixture to displayed areas that have not been dusted enough to cover the aqueous solution. The metal salt can be used in a wide concentration range, from the presence of traces to the saturation of the aqueous solution * . The optimal concentration depends on the particular metal salt used and the other working conditions. After wetting the surface with the salt solution, the moistened surface can be dusted with a powder mixture to form an enamel application. On the other hand, the so-called “pre-coating method ¹¹ can also be used. In the pre-coating method, the salt solution is dried in order to deposit the salt uniformly on the surface to be treated. The surface r <

re-moistened with pure water and then with the powdery mixture covered.

The powder mixture is applied sufficiently strongly to the wetted surface that the desired area is covered. The dusting takes place at temperatures below the melting point of the mixture, before

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preferably at room temperature. The powder adheres to the moistened surface with the formation of an enamel coating at. Moistening can be used to increase the thickness of the enamel application. The mixture can be applied before application to be moistened on the moistened surface. It can also be used during pollination with the on the Goods to be deposited powder are moistened. Sufficient moisture is added to the enamel application that the particles adhere to the surface of the goods and stick together in the desired thickness. The moisture content However, it is kept below the value at which uj.e powdery Mixture as a liquid mass would flow.

Although in many cases it is advantageous to have surface wetting and dusting as separate process steps in other cases it is again expedient to carry out the moistening essentially at the same time with the application of the dry powder. The invention therefore prefers wetting the Surface of the article and the application of a moist powder in detail and in a separate procedure into consideration.

Mixtures suitable for application in powder form those that were previously considered for the production of enamel coatings on cast iron. Below

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some typical mixtures of this kind should be given »

Example 1

White coating borax Weight Silicon oxide 28.60 Cryolite 2 ^, 80 Sodium nitrate 20.30 anhydrous soda 2.30 Fluorspar 4.10 Black lead 2.30 Antimony oxide 11.30 Example 2 6.30

Acid-proof white coating

Weight %

Potassium feldspar 8.70

Borax 11.60

Silicon oxide 25.80 sodium nitrate 5 »10

anhydrous soda 1 ^, 30

Sodium Antimonate 10.10 Sodium Sodium Fluoride 1.70

Black lead 7.80

Zinc oxide 5.10

Chalk white 3.00

Titanium oxide 6.80

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The particle size of the mixture is not critical. Typical Mixtures comprise fine particles that pass through a 0.07 ^ 4- mm (200 mesh) screen to coarser particles that pass through a sieve with a clear mesh size of 0.250 mm (60 mesh).

The enamel application can be preheated long enough at a sufficient temperature before the mixture is fired to remove volatile substances such as water, carbon dioxide, organic substances and the like. For example, the email job can be done before burning about 5 minutes to a temperature from room temperature to about 538 ° ΰ. The burning of the object takes place at temperatures which are sufficiently high that the coating melts. The inventive method allows to work at lower firing temperatures with the associated advantages.

The temperatures can move from about 538 G to about 816 G, and are usually about 732 ° G - ⁰ G 788, wherein the treatment time is about 10 minutes. The firing temperature is expediently kept below the temperature at which brown spots appear due to the reaction of the iron with the enamel mixture. The values for the temperature and the time are expediently below the

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those held in which there is a noticeable increase in iron.

After firing, the goods are cooled in the usual way. On the other hand, the method according to the invention allows before cooling, also the achievement of special effects.

There are many unusual ones with the coating of cast iron articles by the method described above Advantages connected. The inorganic metal salts contained in the aqueous solution improve the adhesion of the enamel application on the ferrous metal surface. Through this Not only are the losses caused by the article peeling off due to the peeling off of the email order being reduced, but also a suitable substrate for further processing is formed. For example, the liability of the

Enamel application on the surface, the application of decals and other decorative materials before firing the Email order, eliminating the additional and laborious application the decoration fabrics are switched off after firing while the enamel application is still hot.

The addition of certain salts improves the acid resistance of the enamel application in some cases, for example the addition of sodium aluminate and calcium and magnesium salts to the saline solution. In the "pre-coating process" the enamel application has better flow properties in

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shorter time during the burning process. Furthermore, the finished object has fewer brown spots - a mistake which is conditioned by certain properties of the iron surface.

When applying an enamel application to a steel object, the salty solution has the beneficial effect, that a self-limiting thickness of the enamel application is achieved. This way it doesn't get too fat and therefore cannot peel off.

Presumably, the application of the saline solution causes a monomolecular layer of the metal salt between the surface of the object and the powdery mixture er-bugt. This molecular layer of the metal salt improves the chemo-absorptive properties of the material. The metal salts adhere better to the surface of the object than the enamel application, which means better adhesion for the application layer is achieved. The metal salts effect also a better binding of the individual particles of the enamel application than by sticking together. The better one Adhesion of the metal salts to the surface of the objects can lead to the formation of a complex of the oxidic surface of the object with the metal salt.

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Claims (1)

Patent claims •1. Method for the surface treatment of objects made of ferrous metals, in which a) the surface of the object is wetted on the surface to be coated, b) on the wetted surface to form an enamel application a powdery mixture, which contains hot melt components, is applied, c) the body containing the order fired and d) the object is allowed to cool according to patent (patent application P 16 21 401.0), characterized in that the surface of the object is wetted with a solution containing at least one metal salt and that after the application of the enamel at a sufficiently high temperature the water from the enamel application is evaporated. - 15 109853/0 550 - 15 - 2. The method according to claim 1, characterized in that the surface of the object with at least one a solution containing Kptallsalz is wetted that the solution is dried and that the surface of the object is applied before the application of the e-tail is wetted with water. 3. The method according to claim 1 or 2, characterized in that the metal salt is an inorganic metal salt is. 4. The method according to claim 1-3 »characterized in that the metal salt used is within the temperature range not decomposed when the email job is burned. 5. The method according to claim 1 or 2, characterized in that the Ketnllsalz is an alkali metal chloride. ο. Process according to Claim 1 or 2, characterized in that a «) s inorganic metal salt is an alkaline earth metal chloride is. ?. Method according to claim 1 or 2, characterized in that? the metal salt is a metal chroaate. 109853 / C550 BAD ORlGiNAU - Io - 8. The method according to claim 1 or 2, characterized in that the metal salt is a metal aluminate. 9. The method according to claim 1 or 2, characterized in that the metal salt is a metal nitrate. 10. The method according to any one of claims 1 to 9, characterized characterized in that the object is heated to a temperature of at most 538 ° G before the enamel application is fired
and at least 10O ⁰ C is heated. 109853/0 550