CS207095B1 - Means for phosphating the heat zinced steels - Google Patents

Description

CZECHOSLOVAK SOCIALIST REPUBLIC (1 ©) DESCRIPTION FIXED TO COPYRIGHT CERTIFICATE 207095 (11) (Bl) (22) Registered 05 12 79 (21) (PV 8444-79) i. (51) Int. Cl.3 C 23 F 7/10 OFFICE AND DISCOVERY OFFICE (40) Published 15 09 80 (45) Published Q1 07 84 (75)

The inventor KŘÍŽKOVÁ ZDEŇKA dr., ŘÍČANY,

MARČANOVÁ ZDEŇKA ing. And DOSTÁL JAROSLAV ing., PRAGUE (54) Means for phosphating galvanized steel

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition for phosphating zinc-galvanized steels based on phosphoric acid compounds with zinc, nickel, nitrates and alkali metal chlorates.

Zinc and its alloys are characterized by good corrosion resistance, especially against corrosive atmospheres. Therefore, this metal is used to form protective coatings on iron and steel. The good corrosion resistance of zinc is explained by the fact that a natural protective layer of oxides, which prevents further attack of the metal, is formed on its surface by the external environment. ie water and salts dissolved therein under certain conditions of zinc surface whitish crystalline airborne zinc alkaline compounds, i. white rust that reduces zinc corrosion resistance. In addition, it has been found that paints applied directly to the zinc surface have very poor adhesion and peel off. However, these unfavorable phenomena can be avoided by treating the zinc surface with conversion coatings, especially phosphate coatings, which both improve the adhesion of the applied coating and increase the corrosion resistance of the zinc surface.

For phosphating zinc and its alloys as well as for phosphating galvanized zinc steels, it is in some cases possible to use conventional phosphating baths 207095 based on zinc acid phosphate containing nitrates, nitrites and chlorates, which also apply to iron and steel treatment. In this way, however, it is not possible to treat hot-dip galvanized steel; aluminum is excluded at the surface, which is used as one of the alloying elements in hot-dip galvanizing. In fact, aluminum is dissolved in the phosphatizing bath during the phosphatizing process, it binds its layer-forming components, especially phosphoric acid, thereby reducing its effectiveness. The amount of 0.2 g of aluminum in a liter of bath is already considerably deteriorating in the phosphatization process, and at 0.3 g of aluminum in a liter of bath, the formation of the phosphate layer completely ceases. Therefore, this harmful effect of aluminum can be ruled out. This can be achieved either by pickling hot-dip galvanized steel in a 10-40% sodium hydroxide solution, but this is also not suitable in terms of the hygienic processing environment, as harmful vapors are formed, or in view of the possibility of corrosion of the surface, or special phosphatizing baths may be used which contain complexing agents capable of binding the release aluminum of the reinforcing complexes.

Rostschutz-Bonder 37 or Bonderite 37 phosphatizing agents for hot-dip galvanized steel are known to contain hydrofluoric acid and fluorosilicate in the base liquid concentrates for the preparation of baths.

Claims (2)

207095 in an amount of about 40 g / l, which binds aluminum to the complex. However, in the manufacture of this type of products, there are difficulties in terms of safety and hygiene, as the dissolution of the individual raw materials causes the release of hydrogen fluoride to dryness. The above-mentioned disadvantages are limited by the composition according to the invention for the phosphating of hot-dip galvanized steel, or the base of phosphoric acid compounds with zinc, nickel, nitrates and alkali metal chlorates, characterized in that it contains 8 to 12 g / l of phosphoric acid, 1.5 to 4 g / l. 1 zinc, 0.2 to 5 g / l of nickel, 0.5 to 3 g / l of nitrate ions, 2 to 6 g / l of alkali metal chlorates, 1 to 2 g / l of alkaline fluorides, 0.4 to 1 g / l boric acid and 960-987 g / l water, all based on the final bath concentration. ITento reliably removes harmful, the effect of aluminum on the course of the phosphatizing process and ensures virtually unlimited service life, bath. The phosphatizing agent according to the invention is applied by immersion or spraying at a temperature of 50 to 60% C for up to 3 minutes. During the process, 1 surface treated hot-dip galvanized steel forms a gray, uniform phosphate layer with a thickness of 1 to 3 μηι. The composition according to the invention is preferably prepared by making it in two concentrated portions, the first part being produced by mixing phosphoric acid with zinc, nickel, nitrates and chlorates of alkali metals, the second part by mixing alkali metal fluorides and acidborates. The advantage of the method of manufacturing the composition according to the invention is that the preparation is thus a suitable industrial production with the possibility of complete control. A composition for phosphating with hot-dip galvanized steel based on phosphoric acid compounds with seasoning, nickel, nitrates and alkali metal chlorates, characterized by that contains 8 to 12g. Γ1 phosphoric acid, 1.5 to 4 g. Inku1 zinc, quality and its transport to the consumer is not costly. Consumers can prepare the bath itself from the ready-made packaging. Another big one. The advantage of the method of manufacturing the composition according to the invention is the fact that the second part, i.e. the fluoride ion source, is produced separately by mixing two powders, alkali metal fluorides and acid borate, with no harmful waste products or vapors. Mixing of the two substances takes place in closed homogenizers for 20 to 20 minutes; 30 minutes. The invention is further illustrated by the following non-limiting examples. Example 1 The composition consists of 9.7 g / l phosphoric acid, 2.3 g / l zinc, 1.4 g / l nickel nitrate, 3.2 g / l sodium chlorate, 1.4 g / l sodium fluoride. of boric acid and 982 g / l of water, based on the final concentration of the bath. The working temperature of the bath is 50 to 60 ° C, exposure [time 1 to 3 minutes, method of application immersion or spray. Example 2 The composition is made in two concentrated parts, the first part containing 31% by weight. phosphoric acid, 7.4 wt. % zinc, 4.5 wt. nickel nitrate, 10.2 wt. % sodium hypochlorite and 46.9 wt. water, the other containing 70 wt. % sodium fluoride and 30 wt. boric acid. To prepare 100 liters of bath, use 3120 g of the first part, make 200 g of the second part with water to 100 liters. OF THE INVENTION 0.2 to 5 g. Γ1 nitrate ions, 2 to 6 g. Alkali metal chlorates, 1 to 2 g. Alkali metal I-1 fluorides, 0.4 to 1 g. Boric acid 11a and 960 to 987 g. Water, all based on the resulting bath concentration.