DE2360466C3 - Process for producing a protective layer on a metal wire gauze by treatment with a chromic acid solution - Google Patents

Description

2. The method according to claim 1, characterized in that that the treatment is repeated at least one more time.

3. The method according to claim 1 or 2, characterized in that the gauze is heated to a temperature between 340 and 650 ° C. »

4. The method according to one or more of the preceding claims, characterized in, that the gauze is treated with a chromic acid solution that also contains zinc oxide, aluminum oxide and contains silicon oxide. * 5

5. The method according to one or more of the preceding claims, characterized in that that the gauze is treated with a chromic acid solution obtained by dissolving chromium trioxide in water, slowly boiling the solution, adding activated charcoal to the solution and continuing to cook until every noticeable reaction has ended.

6. The method according to claim 5, characterized in that the gauze with a chromic acid solution is treated, which contains 1 to 20 kg of activated carbon per 266 kg of chromium trioxide.

7. The method according to claim 3, characterized in that the gauze to a temperature is heated, during which the wire material is tempered at the same time.

8. The method according to one or more of the preceding claims, characterized in that the gauze is treated ^{with a chromic acid solution with a specific gravity of 1.66 to «1.75 g / cm 3.}

50

The invention relates to a method for treating metal wire gauze. Such gauze will used for many purposes and operating conditions often subject the gauze to abrasive wear, shock loads and corrosion will. For example, metal wire gauze is used for classifying systems for separating materials according to particle size, and the abrasive Wear and tear can be a serious problem. The sieves are usually vibrated or in some Moved way so that there is a relative movement between the sieve and the particles. That on The material in motion rubs against the sieve and the greatest wear and tear occurs on the sieve Crossing points of the wires. At these crossing points namely fine particles settle between the two wires, and the rubbing effect ^ he particles leads to a rapid destruction of the

During the manufacture of wire mesh gauze,

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the rubbing effect better, however
faster fatigue ruptures on the basis of this, it would be desirable to loosen or temper the wire in order to increase its elasticity limit.

Task of the ^^^^ VJiJSef'r ^ Method of treating metal wire mesh gauze to create through which the gauze for the above peeled Applications more suitable, st, d. H. that on the one hand an increase in the elastic limit and on the other hand the wear and tear caused by friction is counteracted assumed that the gauze is a thin, porous Having oxide layer; this oxide layer may be present naturally or it will be there for the method according to the invention is of importance, specially applied.

To solve the specified problem, according to the invention proposed that the gauze with a Chromic acid solution is treated and heated, wherein the chromic acid applied by heating in chromium oxide with the formation of a protective layer on the gauze and an adhesive coating at the wire crossing points.

It is already variously known to metal parts, in particular steel parts, by applying a Treat chromic acid solution. In this context, the US-PS 22 10 850 should be mentioned. In this Reference, the chromic acid solution is preferably proposed as a rust converter such that a porous oxide layer on the part to be treated is impregnated with the solution, after which the Allow the solution to dry in order to carry out a further surface treatment, for example by enamelling.

From US Pat. No. 3,421,494 it is known to apply an electrically insulating layer which _{contains CrO 3} to a metal body, the layer containing numerous other constituents being hardened by heating. Numerous other publications are available in which the surface treatment of steel parts with chromium compounds is described.

The use of such treatment methods on metal mesh gauze now brings about the surprising The advantage is that the screen gauze at the wire crossing points through the applied chromic acid coating a firm adhesive bond is obtained, so that there are no more particles at these critical points can get stuck between the crossing wires, leading to rapid wear during operation could lead. In addition, the method according to the invention has the advantage that in the heat treatment, by which the conversion into chromium oxide takes place, the metal wires of the sieve gauze are tempered v / earth, with which their creep strength can be increased considerably. The ones on the wire yourself The oxide layer that forms is very dense, smooth and wear-resistant. It has been shown, for example, that

a metal wire mesh gauze treated according to the invention and on top of an electrical one Drive vibrating classic machine was installed, had a 25% longer service life than the same material without the treatment according to the invention. This test was carried out with a fixed Load on the sieve so that only the fatigue strength could be compared.

To carry out the procedure, the gauze is first cleaned to remove grease or oil residues remove from the surface. If the wire is excessively oxidized, the oxide is also removed, such as by treatment with acid, and then re-oxidized somewhat by rapid heating and cooling. This reoxidation step forms a porous oxidizing layer. The wire is then turned into a Chromic acid solution, which penetrates the oxide layer on the wire surface. The gauze cloth is then taken out of the solution and heated to convert the chromic acid to chromium oxide, according to the following equation:

4 CrO ₃ - * 2Cr ₂ O ₃ + 3 O ₄ ,

This heat treatment creates a strong oxide bond between the porous oxide and the Base metal of the wire. The cycle, consisting of a dipping process and a heating process, is repeated as many times as is necessary to achieve the desired layer thickness, and to densify the porous oxide surface. Because chromium oxide is a very hard material with a Mohs hardness of 9.3, this compacted coating on the metal makes it resistant to abrasion.

For example, for three different types of chromic acid solutions for coating wire mesh gauze are the following:

Solution a

Chromium trioxide - technical purity
Water to create a solution with a
specific weight of 1.7 g / cm ³

Solution b

Chromium trioxide
Technical purity
Water to produce a
Solution with a specific gravity of 1.7 g / cm ^s
Activated carbon

Preferred area
266 kg -

10 kg 1 to 20 kg

This solution B is prepared by dissolving the chromium trioxide in water and heating the solution to a low boil, after which the activated charcoal is added very slowly while stirring. True is the exact reaction that occurred is not known, but it is believed that the heating of the solution involved the activated carbon removes some of the oxygen that remains in the solution. The slow cooking continues until no more noticeable chemical reaction occurs. The resulting solution hai an increased viscosity.

Solution C

Preferred Beieich
Chromium trioxide, technical
Purity 100 kg -

Zinc oxide, technical

Purity J 6.3 kg 10 to 20 kg

Water to produce a
I solution with a specific gravity of 1.7 g / cm ^{: i}

Then a mixture of:

Preferred area
Aluminum oxide (0.044 mm

max.grain size) 61 kg 40 to 80 kg

Silicon oxide (0, J mm

max.grain size) 39 kg 20 to 60 kg

The effect of the added zinc oxide is to increase the viscosity of the solution so that

ao thicker layers applied with each treatment step will. Alumina and silica are also added to a suitable consistency for coating the wires. The amount of substances is chosen so that

S ₅ results in a coating in which the thermal expansion and elasticity of the coating is very similar to that of the base material.

It has been found that the wires were originally loaded with either solution A or solution B.

can be traded. However, it is preferred to first coat with solution A and then the Increase the thickness of the coating using Solution B until the desired thickness is achieved is. For screens that are coarser than 3.3 mm

Mesh size, the layer thickness can be increased more quickly are made using Solution C, preferably after three initial coating passes with solutions A and / or B. The solution C would normally not be for fine mesh

Sieves should be suitable because they build up quickly to form a thick layer and would greatly reduce the mesh size with smaller sieves. Although a specific weight of 1.7 ς / cm ^{3 has been} specified above, this specific weight can be in the

Range from 1.66 to 1.75 g / cm ³ ; after all, 1.70 g / cm ^{3 is} the most favorable value found for the impregnation.

The wire mesh gauze with the coating of chromic acid is then heated to around 340 to 650 ° C, for example by induction heating or by radiant heat, which converts chromic acid into chromium oxide is converted. The exact determination of the temperature depends on the base metal of the screen and the effect of this temperature on the

Properties of this metal. The wire mesh gauze is then cooled to about 175 ° C or lower and re-immersed in the desired chromic acid solution. The gauze is then reheated, to add another layer of chromium oxide

form. As the chromic acid solution completely wets the wire gauze and moves into the porous oxide layer penetrates the wire, there is a firm bond between the chromium oxide of the oxide layer on the Wire and the base metal.

Claims (1)

Patent claims: • I " ^ ^eiiahl _A ^{en ZUI} B ^ andlung von Metalldrahts.eb gauze which has a thin, porous oxide layer, characterized in that the gauze is treated and heated using a chromic acid solution in a manner known per se, the chromic acid applied by the Heating converted into chromium oxide with the formation of a protective layer on the gauze and an adhesive layer at the wire crossing points