DE3023554A1 - Metal objects coated with cermet and then silicate glaze - where cement consists of vitreous enamel frits mixed with aluminium powder, and glaze forms outer sealed coating - Google Patents

Abstract

A metal substrate is coated with a cermet underlayer (I), and then a top layer of silicate glaze (II) resistant to chemicals and corrosion. Layer (II) pref. has min. thickness 5 microns, and average thickness 15-25 microns, with compsn. by wt. 40-65% SiO2, 10-35% alkali oxides, and, all maxima, 20% B2O3, 5% Al2O3, 20% alkaline earth oxides, 20% TiO2 and/or ZrO2, 2% P2O5, 5% F, and 3% V2O5 and/or MoO3. Layer (II) is pref. formed at least partly by a spodumene or beta-eucryptite frit, whereas cermet (I) is pref. obtd. by electrophoretic coating using an aq. slurry, which may contain an organic, water-soluble cpd. providing electric insulation, e.g. an acrylic resin. The coating withstands thermal shock, vibration and corrosion.

Description

Coated metal object and method for it

Manufacture The invention relates to metal objects with high temperature, Resistant to temperature changes and vibration cracking, inorganic metal powder containing Protective layers that protect metallic materials from corrosion.

The protection of metallic workpieces, the high tempera figures and rapid Exposed to temperature changes, from corrosive vapors and liquids so far technically unsatisfactory. Such problems occur, for example, in incineration plants if this is caused by acidic or salty aerosols falling below the dew point or condensates come into contact. Boilers, heat exchangers, Exhaust pipes and exhaust silencers called. An attempt was made to pass metals through to protect temperature and corrosion resistant enamel coatings.

However, these fail at continuous temperatures above 600 ° C and at rapid Temperature change. Corrosion then sets in at the resulting cracks.

So-called cermet coatings have also already been proposed to use. In particular, the high ductility of such systems is connected with the catalytic effect of the porous surface for oxidation and cracking processes exploited.

For example, U.S. Patent No. 3,203,815 suggests metal through a mixture of a leaded frit, aluminum powder and acrylic resins to protect, which melted at temperatures around 800 ° C on the metal substrate will. The resulting layer is temperature-resistant, but is affected by boiling diluted citric acid solution (DIN 51 151) is complete after a short time destroyed.

In GB-PS 1 498 810 a similar system is described which consists of a lead borate, aluminum powder and also an organic acrylic resin.

US Pat. No. 3,706,579 became protective metal-ceramic coating compositions known, in which an initially homogeneous glass mass is used, the renewed Burning forms 2 liquid phases.

Although with such systems the corrosion protection because of the better Resistance to cracking of the coating against enamel and glaze systems is improved, «Rrie the resistance of the enamels and / or glazes per se chemical attack and corrosion not yet calibrated.

The object of the present invention is now to paint coated metal objects to provide in which the coating has both the high vibration resistance and crack resistance of the cermets, as well as the resistance of glazes exhibit against chemical attack.

The present invention therefore relates to a coated one Metal object with a closed surface, characterized by a first layer from a cermet and a second, overlying chemical and corrosion resistance Constant silicate glaze layer.

Cermets are the well-known ceramic-metal coatings that by baking one mixed with metal particles, especially aluminum particles Ceramic, enamel and / or glaze frit are obtained, suitable.

The burned-in cermet layer is generally rich in pores Two-phase system, in which the metal phase and the inorganic oxide phase coexist. The inorganic oxide phase generally forms the disperse phase, in which discrete metallic particles are contained. Particularly Cermets according to European patent application No. 80100106 are preferred used.

According to the invention, the partially open-pored, rough surface is now the cermet coating through a corrosion-resistant silicate glaze layer "sealed". The surface glaze layer is equal to the surface roughness the cermet layer by terminating Pores or filling of Roughness depths Gersrt that a closed surface is created.

According to the invention, the thickness of the glaze layer should be such that that sufficient elasticity is retained to ensure adequate Vibration crack liability. The low thickness of the glaze layer should ensure the glaze layer did not peel off from the cermet. Preferably the average is Layer thickness of the glaze between 15 and 25 μm. A minimum thickness of D / um should be not be undercut.

In principle, all glaze frits are used to produce the silicate glaze can be used according to the invention that wet the underlying cermet layer and Form a closed layer when stoved. Through the special selection of a silicate glaze frit it is possible to improve the properties of the coating focus on influencing. Is used, for example, as a focus property in particular Requires good acid resistance, are preferably substantially according to the invention non-crystallizing silicate glazes selected. In particular, can also Combinations of several non-crystallizing frits to create the glaze can be used. On the other hand, it becomes a special mechanical property as a focal property Resistance required, are preferably crystallizing according to the invention Fries that have a glaze layer inside Generate compressive prestress, chosen. This particularly increases the resistance to Impact, impact and shear forces, as well as against thermal cycling. For such crystallizing glazes, in particular spodumene or B-eucryptite-precipitating ones are used Fries used. To ensure the wetting and training of closed Layers are such crystallizing frits preferably also in a mixture used with non-crystallizing silicate glaze frits. Here is it is then possible to vary the properties of the coating as desired within wide limits to vary.

Non-crystallizing silicate to be used according to the invention Glaze frits preferably have the following composition: SiO2 40 - 65% by weight B2O3 0-20% by weight Al203 0-5% by weight alkali metal oxides 1 0-35% by weight alkaline earth metal oxides 0-20% by weight TiO2 and / or ZrO2 0-20% by weight P205 0-2% by weight V2O5 and / or MoO3 0-3 wt% F O-5 wt%.

Crystallizing silicate glaze frits to be used according to the invention preferably have the following composition: SiO2 45 - 70 % By weight, preferably 50-65% by weight B203 0-10% by weight, preferably 0-8% by weight Al2O3 8-20% by weight, preferably 10-15% by weight, Li20 5-20% by weight, preferably 8-15% by weight Na2O + KO O-10% by weight, preferably 0-5% by weight alkaline earth oxides 3 - 20% by weight, preferably 5-15% by weight TiO2 and / or ZrO2 0-15% by weight, preferably 8-12% by weight P205 Q-7% by weight, preferably 2-5% by weight F O-5% by weight 7 preferably 1 - 5% by weight The silicate glazes can also contain coloring heavy metal oxides contained in amounts of 0 to 8 wt .-%. As coloring heavy metal oxides come in particular the oxides of iron, manganese, copper, cobalt, nickel and / or chromium in question.

For the production of the coated metal object, the usual two-layer enamelling techniques are used. Then it is on the metal object first a first system that generates the cermet is applied and, if necessary After the first system has been fired in, a second system, which produces the glaze, is applied and burned in.

The systems can be used as an aqueous slip consisting of the frit, usual slip additives and water, with the first system additionally the metal particles contains, are applied. When using the usual dipping or spraying technique the first system can be dried first and then the aqueous slip of the second system are applied and both systems are burned in together (2-layer i-fire).

However, the modern litrags procedures are preferred electric fields used. For example, the job can be done by electrophoresis take place. The aqueous systems then preferably contain to improve throwback additionally aluminate compounds (e.g. according to GB-PS 1 228 434). The cermet slip advantageously also contains 3 to 20% by weight, preferably 5 to 9% by weight, based on on the total solids content of the slurry of organic, water-soluble, according to the deposition of electrically insulating substances. Preferably a through Amine addition, neutralized water-soluble acrylic resin used.

In this application process, the metal object is initially in Pretreated pickling baths, then electrophoretically in a further bath with the the cermet-producing system coated, and optionally after intermediate drying Electrophoretically coated in a further bath with the system producing the glaze. Both systems can then be burned in together.

The coated metal objects are advantageously produced also by applying the glaze system as a dry powder electrostatically to the damp or dry layer of the system producing the cermet is applied. The electric one The resistance of the frit powder is set according to DE-OS 27 41 971. Both Systems can then be burned in together. The powder electrostatic application The glaze system can also be applied to the cermet that has already been cured.

It has also been found that the coatings according to the invention in an excellent way for enameling castings by using conventional spraying and immersion methods, as well as the methods using electric fields are. Because of the high carbon content of cast iron and the associated poor wettability and blistering during firing are these after state of the art only by powdering the enamel frit to the firing temperature heated cast body can be enamelled. The intermediate layer applied to the cast body, partly

open-pore cermet system apparently allows the passage of the Burning-in gases without the formation of bubbles. So by the cermet intermediate layer is used according to the invention in the cast enamel as a base enamel layer, is with it also the casting the modern enamelling process using electric fields accessible. Instead of those described here, you can use the cermet intermediate layer Silicate glaze systems can also be used to apply any enamel layers. condition The only thing is that the enamel frit touches the underlying cermet coating during firing wetted and forms a closed layer.

The invention is explained in more detail using the following examples: Examples 1 to 6 a) Cermet system Made from commercially available raw materials such as those used for enamel production are used, a matrix of steps I of the following oxidic composition was used at 12500C melted: SiO2 51.0 B203 16.5 A1203 1.0 Na20 12.0 NaF 1.0 K20 1.0 Li20 2.0 CaO 2.0 BaO 4.0 Ti02 5.0 CoO 2.0 NiO 2.0 CuO 0.5 100.0 The melt was in water quenched and dried.

They were also made from commercially available raw materials, such as those used for enamel production are used, at 1350 to 140000 the low-melting frit II following Composition melted: SiO2 46.0 Na2O 9.0 K20 2.0 CaO 5.0 Fe2O3 7.0 MnO 1.0 CuO 19.0 TiO2 6.0 ZrO2 5.0 After quenching the melt in Water and drying the granules thus obtained, these were placed in a porcelain ball mill Grind together with the matrix frit I according to the following mill offset as long as until the residue on a sieve with a mesh size of 100 µm is less than 3% on the solids was: Matrix frit 1 50.0 parts of frit II 50.0 enameled clay 2.0 Bentonite 1.0 Boric acid 4.0 Sodium nitrite 0.2 Water 65.0 In this so obtained Suspension were 40 parts of aluminum powder with a particle size distribution maximum between 20 and 60 / um introduced.

Six 100 x 100 mm steel sheets were made with this slip with a thickness of 1 mm, which is prepared in a known manner for enamelling had been coated on both sides by spray application and dried. The layer thickness was chosen in such a way that this should be approx. 150 μm after firing.

b) Glaze system The raw materials in the table were made from commercially available raw materials I specified glaze frits for those specified in the previous line of the table Temperatures melted, quenched and dried.

Table I% by weight of glaze frit 1 2 3 4 5 6 SiO2 53 63 41 61 55 51 B2O3 18 4 - 10 6 -Al2O3 1 1 3 - 11 14 Na2O 12 15 19 13 5 2 K2O 1 2 12 - - -Li2O 2 3 2 - 10 9 CaO 2 - - - - -BaO 4 - - - 10 TiO2 6 7 20 9 9 8 ZrO2 - 4 - - - -P2O5 - - 1 - - 4 V2O5 - - 2 - - -MoO3 - - - 1 - -NaF 1 1 - - - -CaF2 - - - 6 4 2 Melting temperature 1250 ° C 1300 ° C 1150 ° C 1300 ° C 1150 ° C 1250 ° C Firing temperature 820 ° C 860 ° C 790 ° C 840 ° C 820 ° C 840 ° C The glaze frits were made with the one given below Grind the mill offset until the residue is on a sieve the mesh size 40 / by less than 2% of the solids content: frit 100 parts by weight of enameled clay 4 parts by weight bentonite 0.2 parts by weight boric acid 0.2 parts by weight sodium nitrite 0.1 Parts by weight of water 60 parts by weight of the six steel sheets obtained according to a), which were coated with the dried, the cermet-forming slip, was a slip containing the glaze frit each so thin by spraying or dipping plotted that after firing at the temperature given in Table I during 5 minutes each a closed glassy top layer of an average A thickness of 15 to 25 µm resulted. The coating showed a closed, chemically well-resistant surface that is closely connected to the underlying cermet layer was.

Examples 7 to 12 a) Cermet system The matrix frit I and the frit II according to Examples 1a) to 6 a) is used in the following mill offset: Matrix frit I 50 parts by weight of frit II 50 parts by weight of carboxymethyl cellulose 0.5 part by weight of water 18 parts by weight The mixture is ground until the residue on a Sieve with a mesh size of 100 μm was less than 3%, based on the solids. 50 parts by weight of aluminum powder with a particle size distribution maximum were added to the suspension obtained in this way between 20 and 60 stirred in, as well as 12 parts by weight of a neutralized by adding amine water-soluble acrylic resin BAYCRYL L 461 W (commercial product of Bayer AG). Further 4 parts by weight of oleic acid and 25 parts by weight of water were added.

In the electrophoresis bath obtained in this way, 6 are added in the usual way pretreated steel sheets dipped and anodically connected. After reaching the desired Layer thickness, the steel sheets are removed from the bath and the knocked down Dried slip.

b) Glaze system The dried biscuit that produces the cermet containing steel sheets ground according to Example 1b) to 6b) each with a glaze slip coated and dried. Then both layers are baked in together.

EXAMPLES 13 to 18 Examples 7 to 12 were repeated with the deviation that the content of neutralized, water-soluble acrylic resin BAYCRYL L 461 W was 5 parts by weight and the oleic acid content was 3 parts by weight.

Examples 19 to 24 a) Cermet system According to Examples 7a) to 12a) the slurry producing the cermet is electrophoretically applied to six steel sheets upset. However, the applied slip does not need to be dried.

b) Glaze system One frit according to Table I is used with the following Mill offset up to a residue of less than 1% on a sieve of the mesh size 40 μm ground: frit 100 parts by weight bentonite 0.5 parts by weight sodium aluminate 0.2 part by weight of carboxymethyl cellulose 0.2 part by weight of water 50 parts by weight of each the one obtained according to a) provided with the still moist slip which produces the cermet Sheet steel is placed in one of the resulting slips producing the glaze system immersed, anodically connected and electrophoretically coated. The steel sheets are dried and both coatings are applied together. burns. The steel sheets then showed a closed, chemically well-resistant surface, wherein the upper glaze layer is intimately connected to the underlying cermet layer was.

Examples 25 to 30 a) Cermet System The matrix frit I and the glaze frit 5 according to Table I is used in the following mill offset: Matrix frit I 50 parts by weight of glaze frit 5 50 parts by weight of carboxymethyl cellulose 0.5 part by weight Water 18 parts by weight The mixture is ground until the residue on a sieve with a mesh size of 100 µm less than 3% - based on the solids - fraud. 50 parts by weight of aluminum powder were added to the suspension thus obtained a particle size distribution maximum between 20 and 60 μm, as well as 12 parts by weight a water-soluble acrylic resin BAYCRYL L 561 neutralized by adding amine W (commercial product of Bayer AG). In addition, 4 parts by weight of oleic acid and 25 parts by weight were added Water added.

In the electrophoresis bath obtained in this way, 6 are added in the usual way pre-treated steel sheets dipped and switched anodically. To When the desired layer thickness is reached, the steel sheets are removed from the bath and the precipitated slip dried.

b) Glaze system The dried biscuit that produces the cermet containing steel sheets are according to Example 1b) to 6b) each with a glaze slip coated and dried. Then both layers are baked in together.

In these examples 25 to 30, the frit II from the Examples 7 to 12 replaced by a crystallizing frit. This will be the mechanical properties of the coatings compared to those according to the examples 7 to 12 still improved. Gradual improvements are made through partial replacement achieved. Because of the ti2O content of the crystallizing frits, however, these are comparatively expensive, so that they can only be used for very extreme requirements is justified.

Evaluation of the coated metal objects according to Example 1 bis 30: The coated steel plates obtained in Examples were as follows Subjected to tests: a) Thermal cycle treatment: the steel sheets were heated 10 times to a temperature of 7000C and 2 hours each time at this Maintained temperature, the steel sheets between each two heat treatments Air cooled down to room temperature. Furthermore, the steel sheets were also heated ten times to a temperature of 550 0C and by immersion in cold Water quenched to 200C.

b). Spray mist treatment: The steel sheets became one for 7 days Spray mist treatment with a 5% sodium chloride solution (according to SS DIN 50 021, May 1975 edition, according to ASTM Designation B 111-73 "Standard Method of Salt Spray (fog) testing ").

c) Alternating condensation water climate: The samples were placed in a chamber with a volume of 300 1 initially 8 hours at a temperature of 400C and one rel. Humidity of 100% and then 16 hours of room temperature and a rel. Humidity of 75% exposed, with 2 1 S02 were introduced into the chamber (according to SFW 2.0 S DIN 50018, December 1963 edition). The treatment cycle was repeated 5 times.

d) Acid treatment: citric acid The samples were tested according to DIN 51 151 Boiled in 6% citric acid for 2.5 hours e) Acid Treatment: Sulfuric acid The samples were in an apparatus according to DIN 51 157, sheet 2, 2.5 Boiled in 0.5 liter sulfuric acid for hours.

f) Bending test The coated steel sheets were wrapped around a steel pipe from 50 mm in diameter bent by 900. The steel sheet was damaged after the Coating examined.

Result: There was no change in the layer in any of the samples or the metallic substrate determined due to the temperature treatment will. Damage or cracks due to the quenching treatment and bending no tests were observed.

After the spray mist treatment, there was no corrosion attack on any of the samples to be established. After the condensation water alternating climate test, the samples showed no change. A metallographic examination did not reveal any corrosive effects either Changes to the layer and no corrosive attack on the substrate. The loss in weight per unit area after each of the acid treatments was less than 10 g / m². On the metallic one No acid attack was found on the substrate.

Claims (10)

Claims 1. Coated metal object with closed Surface, characterized by a first layer made of a cermet and a second, chemically and corrosion-resistant silicate glaze. 2. Article according to claim 1, characterized in that the silicate Glaze has an average layer thickness of 15 to 25 µm. 3. Article according to claim 1 or 2, characterized in that the silicate glaze has a minimum layer thickness of 5 µm. 4. Object according to one of claims 1 to 3, characterized in that that the silicate glaze has the following composition: SiO2 40 - 65% by weight B2O3 0 - 20% by weight Al2O3 0 - 5% by weight alkali oxides 10 - 35% by weight alkaline earth oxides 0-20% by weight TiO2 and / or ZrO2 0-20% by weight P205 0-2% by weight V205 and / or MoO3 0-3% by weight F G - 5% by weight. 5. Object according to one of claims 1 to 3, characterized in that that the silicate glaze at least partially through a spodumene or B-eucryptite outgoing crystallizing frit is produced. 6. Process for making the coated metal article according to one of claims 1 to 5, characterized in that initially a cermet generating first system is applied to the metal object, and thereafter if necessary, after firing in the first system, a second system producing the glaze System is applied and baked in. 7. The method according to claim 6, characterized in that the first System is applied in the form of an aqueous slip by electrophoresis 8th. Method according to claim 7, characterized in that the aqueous slip 3 to 20 wt .-%, preferably 5 to 9 wt .-%, based on the total solids content of a organic, water-soluble, electrically insulating substance after deposition contains. 9. The method according to claim 7 or 8, characterized in that the second system in a second electrophoresis step in the form of an aqueous slip is applied before the first system is fired in, and then both systems together to be burned in. 10. The method according to any one of claims 6 to 8, characterized in that that the second system as a dry powder after a treatment for adjustment of the electrical powder resistance on the layer of the cermet generating, damp, dried or already burned-in system, applied electrostatically and then burned in.