DE1621405C3 - Process for two-layer enamelling in one fire - Google Patents

Description

be burned and with the basic enamel ζ. Β. Water glass or an organic substance as cold-curing Binder is added. However, these methods have not proven successful because the The quality of the enamelling obtained is completely inadequate.

A process for two-layer enamelling in a fire has now been found, whereby one on the object to be enamelled a self-hardening by an additive on an inorganic basis Basic enamel slip applies, and the slip dries before the application of the top enamel, which is characterized in that a basic enamel slip is applied, the one-piece f Basic enamel frit and 1 to 4 percent by weight alkali aluminates, aluminum hydroxide for self-hardening and / or aluminum oxide hydrates or reactive aluminum oxides and 2 to 15 percent by weight Contains phosphates, based on solids.

Surprisingly, it has been found that you can do without laborious pickling preparations and without the use of nickel or other deposits, one for all types of sheet metal and cast iron suitable thin-layer enamelling with a layer thickness of less than 0.15 mm in a fire can perform. With the new thin-layer process, a base enamel layer is applied conventionally pretreated sheet applied so thinly that after drying also by flowing Water cannot be detached again and in which the injection of a white enamel slip is possible without difficulty. After the top enamel has dried, the base and top enamel can be burned in together. After this Process you get flawless, thin-layer enamelling as with single-layer enamelling, however, if the basic enamel is known per se in a new slip composition applies.

A base enamel slip that self-sets on the sheet metal can be produced according to the invention, if the basic enamel is 2 to 15 percent by weight, based on the solid substance, of the phosphates used by alkali metals, alkaline earth metals, zinc, aluminum, iron, cobalt and nickel. Likewise, polyphosphates and metaphosphates, such as. B. sodium hexametaphosphate, suitable. It is advantageous to use a mixture of several phosphates. One can adhere to the basic enamel Even better if you add oxides or hydroxides of metals in the base enamel to the slip are responsible for the formation of the adhesive layer, adds, e.g. B. cobalt, nickel oxides or hydroxides. The adhesive oxide content of the base enamel can be up to about 5%, in extreme cases it can however, they are also higher.

Furthermore, the base enamel layer should be in amounts of about 2 to 4 percent by weight, based on solid substance, alkali aluminates, aluminum hydroxides, aluminum oxide hydrates and / or active aluminum oxides, such as. B. 7-Al ₂ O ₃ included. The layer thickness of the basic enamel used in this new process should preferably be around 0.025 mm. Base enamels for such a thin application preferably contain a high adhesive oxide content so that they are resistant to wear. Preference is given to using base enamel slips which are free from conventional mill additives such as quartz, clay, setting salts, etc., or at least have a significantly lower content of these additives.
The process is suitable for enamelling metallic objects of any kind that are enamelled using the two-layer process. The basic enamel only has to be matched to the top enamel in a known manner. Depending on the material to be enamelled and the frits used, the stoving temperatures range from about 720 to 880 ° C.

The new process can be carried out at the temperatures at which one would use the conventional one Working with basic enamels can achieve perfect adhesion. In addition to white enamel enamels and transparent enamels colored in the melt can also be used for top enamelling will. With this method you can increase the thickness of the enamel by about 50% compared to the conventional way of working. You have the same advantages of the thin layer thickness as with single-layer enamelling. Compared to this, the new process brings about a significantly simpler pretreatment of the objects to be enamelled and greater security in terms of adhesion.

example 1

A basic enamel of the composition (oxidic) 30

is used together with 2% sodium aluminate, 2% tripotassium phosphate, 2% iron phosphate, 2% zinc phosphate, 2% magnesium hydrogen phosphate and 0.5% lithium phosphate and 55% water, based on on frit substance, finely ground. The suspension is ground so finely that the residue on a 16900-mesh sieve is below 10%>. The finely ground A thin layer of suspension is sprayed onto the object to be enamelled and dried. After drying, a white enamel is applied to the hardened base enamel, which is suitable for the baking temperature of 820 ° C is suitable, sprayed on wet. After the cover enamel slip has dried The base and top enamel are burned in at 820 ° C.

Example 2

SiO, 42 0/0, F. 2%, A1, Ö, 50/0, CaO 6%, B, Ö, ' 190/0, NOK 3 ⁰ Zo, Well, 0 19 », Ό, CoO l, 5o / o, K ₂ O 4%>, P <A l ° / o,

A basic enamel of the composition (oxidic)

SiO ₂

Al ₂ O ₃

B ₂ O ₃

Na ₂ O

KO

450/0,

6 0/0,

Ho / o,

I90 / 0

CaO
NOK
CoO

2 0/0,
6 "/ ο,
30/0,
1%,

is used together with 1% sodium aluminate, 1% tripotassium phosphate, 1% iron phosphate, 1% lithium phosphate and 55% water in turn finely ground and on the object to be enamelled sprayed on. An 820 ° C white enamel is sprayed thinly onto the dried covering, dried and Burned in together with the basic enamel to a total layer thickness of about 0.15 mm.

Example 3

A base enamel of the composition according to Example 1 is used together with 2.5% sodium aluminate, 2.5% tripotassium phosphate, 2.5% iron phosphate, 2.5% zinc phosphate, 2.5% magnesium hydrogen phosphate, Finely ground 0.5% clay and 0.5% bentonite as well as 55% water on a steel sheet the type USt 12 sprayed on and dried. A titanium white enamel is placed on this solid surface applied at a baking temperature of 820 ° C, dried and baked together with the base enamel.

Claims (5)

1 2 dries, and melted in a second firing. F "The total layer thickness of this conventional enamelling is relatively large. In recent times one is 1. Process for two-layer enamelling in 5 endeavors to reduce the thickness of the enamel layers, a fire, where you have to enamel because the physical properties are thinner rend object are cheaper by adding an enamel coating. So show this inorganic based self-hardening base enamel layers z. B. a reduced tendency to flake. Daschlicker applies, dries, a cover enamel is susceptible to assembly and and reduces both layers in the usual way, one-way transport damage. burns, characterized in that thinner layers are obtained by a base enamel slip is applied that dispenses with the use of base enamel applies a finely divided basic enamel frit as well as the self and the white enamel directly to the steel, Hardening 1 to 4 percent by weight of alkali aluminates. Two direct enamelling processes are known today, the Aluminum hydroxide and / or aluminum oxide 15 can be carried out industrially. In one proceeding Hydrate or reactive aluminum oxides are enamelled directly in a layer on sheet steel and 2 to 15 percent by weight of phosphates with normal carbon content. Before the enamel pulled on solid substance, contains. Adhesion layers must be applied to the sheet metal surface 2. The method according to claim 1, thereby generating the arsenic, antimony, copper or nickel indicates that one contains a basic enamel 20. This requires a large number of applies slip, which has up to 5% of adhesive oxides in pretreatment baths. Contains white enamel on one side. Sufficiently good surfaces are obtained. 3. The method according to claim 1 and 2, characterized in the case of direct enameling of carbon on both sides, that the sheet additionally containing the slip, the surfaces are highly porous and Adhesive layer-promoting compounds such as nickel-25 show many dark spots. The quality of the and / or cobalt oxides or hydroxides, tensile enamelling does not meet today's requirements will. changes. 4. The method according to claim 1 to 3, characterized in the direct white process on decarburized steel characterized in that a base enamel slip with a C content of about 0.005% gets is applied without added clay. 30 you get much better enamel surfaces. For this 5. The method according to claim 1 to 4, thereby enamelling process is again a complicated one marked that a basic enamel slip requires special treatment of the steel. As is well known is applied, the phosphates in the form of it comes with the conventional basic enamelling Ortho-, meta- or polyphosphates of lithium, to a roughening of the sheet metal surface as well as a Sodium, potassium, magnesium, calcium, cobalt and nickel enrichment at the interface Strontiums, bariums, zinc, aluminum, iron, enamel metal. Both of these operations must be performed with Contains cobalt and / or nickel. the direct enamelling before the enamel application the sheet metal pretreatment run. Therefore you have to the sheets more carefully than after degreasing 40 pretreat with conventional enamelling. You have to achieve a certain stain removal and nickel plating, the amount of applied Nickel depends on the amount of iron pickled. Tartaric acid, glycolic acid, 45 phosphoric acid, nitric acid or citric acid used. On the specially pre-treated sheet metal In the conventional enamelling of steel, the white enamel is applied by spraying and sheet metal, base and top enamels are used. baked in after drying. While the cover enamel protects against corrosion and the direct enamelling has at the same time should have an aesthetic effect, conventional enamelling is qualitative and economical the adhesion of the enamels to the steel sheet through borrowed advantages. The email consumption is lower and Basic emails conveyed. 5 to 7% of these are baked in only once. The benefits will be Clay and 0.2% Na nitrite as well as with water partly due to the complicated pretreatment of the grind, applied, dried and baked. Balanced again on sheet metal. These basic enamels can be effective adhesives. 55 In the ceramics industry, it is known to contain acidic nickel, cobalt, antimony, cerium, molybdenum and aluminum phosphate or mixtures of phosphorus-copper oxide. The oxides result in the adhesive acid and aluminum oxide hydrate as cold-setting strength. B. to use the following binding agent (see, for example, "Glas-Enaildem scheme: Fe + NiO -> FeO + Ni. Keramo-Technik" 1962, issue 1, pp. 12 and 13). These reactions also produce iron oxide, which is known to dissolve aluminates and Al (OH) ₃ as well as phossich in the base enamel. At the same time, phates are created as mill additives for enamels to be used for enamel firing, gases such as CO and H ₂ . This (cf. "Glas-Email-Keramo-Technik" 1966, No. 10, gases form a bubble structure in the base enamel, pp. 390 and 391). For a two-layer enamelling that does not interfere with the basic enamelling, as they were not used in a fire, however, after the top enamelling, such additives have not yet been used with success,
tion occurs. Furthermore, from DT-PS 662 727 and US-PS. On the baked base enamel then wet 1,875 721 processes become known in which ground white or colored enamel is applied, the base and top enamel layers are applied at the same time.