DE1803022C - Protective coating against scaling during the heat treatment of metals - Google Patents

Description

In the production of e.g. steel strips, steel plates or steel sheets, the slabs or Steel plates and billets are subjected to a series of heat treatment operations, the Heat good usually to a temperature in the range of 900 to 1250 "C during a suitable Period of time to be heated for tempering or tempering. This heating takes place while the metal surface is in contact with air. It finds thus an atmospheric oxidation takes place. The to The resulting oxide, which is usually formed as adhering scale, must subsequently be removed either mechanically or by pickling. This Treatments are time consuming.

It is known to apply protective coatings to prevent the formation of scale on metal surfaces before the heat treatment, which prevents the ingress of oxygen to prevent the metal surface. These known paints generally comprise an organic cation modified clay and refractory ao Sintered or fritted material that is contained in an organic Solvents, e.g. B. toluene, is dispersed to give a spreadable or sprayable mixture. These compositions form an adherent continuous coating. By discontinuing the as Thermal expansion coefficient of the coating formed in such a way that this of that of the metal subject to the treatment is different, it can be achieved that on cooling the The coating will peel off the metal surface by itself and the ingots, plates or slabs in clean Condition, essentially not oxidized and ready for the subsequent machining process will.

The production of suitable protective coatings previously required the modification of clays by means of an ion or base exchange reaction in order to convert it into an organophilic state. At this Base exchange reaction is the clay generally with an "onium" compound, for example with an alkylammonium salt, converted to the catalysts on the surface of the clay particles, usually alkali or alkaline earth cations, by a long-chain organic onium cation. z. B. by a Dodecylammonium cation. These modified clays are for use in painting and coating compositions, particularly as suspending agents, generally known, and some types, e.g. B. Alkyl ammonium montmorillonite, are widely used. The modified tones are each like that however, they are comparatively expensive and the paints produced with them can sometimes have storage stability problems.

The purpose of the fringing is to provide protective coatings against scale formation during the heat treatment of M ro pops, which is not only a cute, whereby the frit material makes up 20 to 80 percent by weight of the coating, is characterized in that a nonionic cellulose derivative is used as the suspending agent.

According to an expedient embodiment, the cellulose derivative can consist of hydroxypropyl cellulose.

It has been found that protective paints against scale formation using such Cellulose derivatives have extremely good storage properties and a very low tendency to settle of solid components, even when standing for a long time. Besides, the separation or detachment is a separation of the coating of the coated metal on cooling compared to paints soft clays can be used as suspending agents. will.

Preferred cellulose derivatives for use according to the invention are methyl, ethyl and propyl cellulose and hydroxypropyl cellulose.

The liquid medium of the paints according to the invention preferably consists of a lower alcohol or toluene, isopropanol is particularly preferred.

Suitable ceramic frit materials that are used in the Protective paints can be used according to the invention have the following composition in Weight percent:

PbO. Al ₁ O ₈ SiO,. Na ₁ OK ₁ O. CaO. MgO. B ₁ O ₁ . ZnO. Fe ₁ O,

Frit A Frit B Frit C Frit D

61.0

7.0

32.0

9.37

62.0

3.6

2.73

7.31

0.15

14.84

6.7 65.8 5.44

3.68

2.2

15.35

0.9

6.95 83.5 5.9 1.8 1.58 0.08 0.1

0.03

SS

ten hi

the AMAMiHt after edging has

t »it has now been found that at MaHa from dar · *» nlmbrtdende MHtalfttr Schutwimrtebe pay scale

HtftraCtpJ vWHfpQM ^ VffVete VvTwvwQQf WmQf) H BvftfMtt

The paints according to the invention are applied to the metal surface before the heat treatment. During the treatment, the coating melts to form a ceramic, oxygen-impermeable coating on the metal surface which, when cooled, flakes or flakes off the metal surface, leaving a clean and shiny metal surface.

It is believed that the specific effect of such a coating is as follows. , During de · heating "a Obetflächenoxydation of

doeb at higher temperatures, t. B. starts at about 800 * C is Übertut ta tcnmetsen and forms a glaze MeBflhige, but the "fen dia metal surface autbreitet and daa oxide waajaet it. CT finds no further "Oxidation Matt. At the Kimen the Gtour sJattt due to the different warmth)

irmeatNdahunpkoefAxienten de · MaUtt »and the glaze off and MBt a deaf onvd-free metal

Vp ^ bH ^ V a ^ ejH ^ fnf eXW / vvPvM *

The requirements for the invention are from OberiMkhcnwhuU for nickel, cobeh and

Claims (1)

3 4 their alloys and numerous steel alloys, PbO 61 ° / _n In particular stainless steel alloys, suitable, Al _a O ;, 7 ^q / ₀ It is important to consider the properties of the SiO ₈ 32 ° / _{q used} frits or fries related to the treated, Metal to match. In general, the mean 5 H e ι s ρ ι e I I coefficient of linear expansion of the above Any metals and alloys in the range between the following are raised (percent by weight). 14 and 17 · 10- · each ° C. The frits used ßleisilicate frit A 64 · / " However, they generally have a substantially low hydroxypropyl cellilose 0.25 »/“ Rigeren expansion coefficients, for example in io [ _t " _nrftn , _nn i ₁₁₇ " of the order of 5 · 16- · each ^Q C. (The frit A isopropanoi n, n / " of the table above has a linear pattern. The paint was made to a thickness of about 101.6 expansion coefficients of 5.4 · 10 "· per ⁰ C.) to 203.2μ on a sheet of stainless steel for a Oxidizable materials can be tempered or tempered at 1050 ° C in the paints According to the invention, applied for 15 times up to 10 minutes. After To increase the paint's ability to remove oxide. Heat treatment peeled the paint under Aluminum and ferrosilicon can be used for this leaving behind a clean, untargeted top-end be included. Area from. requiring no further treatment, like /. B. a It is also important to ensure that the Vis pickling, required, viscosity of the composition at the maximum »o. Heat treatment temperature is not too low. Hey play otherwise there is a tendency to break away the over- A protective coating against the formation of scale was like Zugs produced leaving exposed metal succession (percent by weight), areas exists. The viscosity at high temperature lead silicate frit A 40 °; can be obtained by _{ingesting a 5} hydroxypropyl cellulose particulate. ".''.... '.'. '..'". ' 0.25 ··. solid material up to 35 percent by weight, e.g. els-magnesium oxide 20 »/ ₀ wise of silicon dioxide, magnesium oxide, feldspar, silicon dioxide 3 ° / Aluminum oxy <\ zinc oxide, andalusite, kyanite, silli-nepheline syenite 10 0 » manite, mullite, talc, olivine and nepheline or syenite, kaolinite (present as refractory 'mate-' ° increase. 30 rial and not as a suspending agent) ... 2 ° / ₀ It is also important that the _{natural resin of} southern pine (acid number Coating has a low surface tension, around ₉₄ saponification number 165) 1.2 /, the tendency to break the coating at high tem- hopropyl alcohol 23.55 ° " keep temperatures to a minimum. For this Purpose, chromium oxide can be incorporated. At 35 The paint indicated above was applied to an effective application of the coating composition to a stainless steel ingot which It is desirable to ensure a small amount of heat treatment at 1250 ° C for 4 hours incorporate a wetting agent, such as. B. was subjected to the needles. The painting was done in a trium salts of alkylarylsulfonates or secondary thickness of about 381 to 5Ο8μ applied. The an-alkyl sulfates or in particular sodium dioctyl sulfo-coated fell off the metal succinate after the heat treatment. surface and left a clean shiny surface. The above-mentioned components of the area back. The added resin served the paving compositions according to the invention can in tion of the film-forming properties of the paint,
a wide range of relative proportions or _D ...
Shares are available. In general, the 45 rate claims make:
first constituent preferably 20 to 80 ° ₀ , in particular 1. protective coating against scaling in which preferably 30 to 70 percent by weight, of the heat treatment of metals, consisting of coating. The nonionic cellulose derivative is a suspension of a ceramic frit material only in small proportions , e.g. B. from 0.1 to ¹⁰ / "in an organic solvent, with that of the paint required. Above 50 angege- frit material 20 to 80 weight percent of the ben, the particulate refractory material can, if paint constitutes, gekennvorhanden by up to 35 ° / ₀ Removing the composition is characterized in that not "make as suspending a. The other beionic cellulose derivative listed above is used,
constituents may be present in smaller proportions. 2. Protective coating according to claim 1, characterized in that in each case the remainder to 100 ° "of the S5 indicates that the cellulose derivative from Hy- vtrwnd" Hn oraMiKhm Lotunpimuel nlicfvrt wild. droxypropylcellulo & e. Mt EftadMf is nacthw on hand mn M- 3. Sehutanrtrteh ηββη Anprall I or 2. da · tAlMr «grease. Dm Hi «mn BeitpMtn vtr- durch gekeoneteimet, dsS« r Ms m JJOtwteMv PritMMMterial has the following «percentage« promt! «Me» icilchenfönnifBn («uerfoten Mate · Contains a · rials.