KALINIC STEFAN (SK)
| FR2395304A1 | 1979-01-19 | |||
| FR1480356A | 1967-05-12 | |||
| US3692583A | 1972-09-19 | |||
| US2137988A | 1938-11-22 |
DATABASE WPI Section Ch Week 7542, Derwent World Patents Index; Class M12, AN 75-69627W, XP002018287
| 1. | Sur ace treatment of products made of aluminium and aluminium alloys c h a r a c t e r i z e d b y a treatment with a solution of sodium hydroxide, concentration from 8% to 10% and temperature from 40°C to 55°C for 10 to 15 minutes, subsequently, products are treated with nitric acid and finally passivated with sulfuric acid. |
| 2. | Surface treatment of products made of aluminium and aluminium alloys according to claim 1 c h a r a c t e ¬ r i z e d b y a treatment with a 10% solution of sodium hydroxide at a temperature of 45°C for 10 minutes, subsequently, products are treated with nitric acid and finally passivated with sulfuric acid. |
Technical field
The invention concerns a method of surface treatment of products made of aluminium and aluminium alloys, in particular with respect to assuring good adhesion of coating systems - lacquers.
Background of the invention
To attain good adhesion of coating systems - lacquers, the -surface of aluminium and aluminium alloys must be chemically treated. Several different treatment methods are normally used, such as electrolytic oxidation or chromate surface treatment.
Electrolytic oxidation of aluminium, so-called elox treatment, is performed in a water solution of acid on the plate where the metal is partially dissolved and covered with an insoluble layer of non-metal character, consisting of hydrated aluminium oxides. This layer does not conduct electricity, it is hard and adhere well to the base material. This layer also resists normal corrosion and abrasive wear. There are a number of various methods based on this procedure. They differ mainly in the composition of the oxidation bath. Main groups are based on methods using sulfuric, oxalic and monochromic acid. Electrolytic oxidation is an effective treatment, however, it is very demanding for energy and time, especially when surface of larger products needs to be treated.
The chromate surface treatment is essentially passivating in monochromic acid or solutions of chromate, usually potassium chromate, which improves protection against atmospheric corrosion. The disadvantage of the chromate surface treatment is the necessity to use expensive chrome compounds which contaminate the environment. Using such compounds means increased demands both for the production technology and its operation.
Sumarv of the invention
The shortcomings described above are substantially improved by a surface treatment of products made of aluminium and aluminium alloys according to this invention. The invention is based on the following procedure. Products are treated with a solution of sodium hydroxide, concentration from 8% to 10% and temperature from 40°C to 55°C for 10 to 15 minutes. Subsequently, products are treated with nitric acid and finally passivated with sulfuric acid.
In optimal conditions, products are treated with a 10% solution of sodium hydroxide at a temperature of 40°C for 10 minutes. Subsequently, products are treated with nitric acid and finally passivated with sulfuric acid.
Treated products need to be rinsed between individual reactions. Treatment with sodium hydroxide dissolves the material surface which results in widening its physical-chemical grid. This also mean that the ability of the surface to bind to other materials improves.
In comparison to electrolytic oxidation, the procedure according to this invention is more advantageous with respect to energy consumption and demand for time, especially in treating larger products. Contrary to the chromate surface treatment, the procedure according to this invention uses less demanding chemical compounds which are less harmful to the environment. The invention decreases demands both for the production technology and its operation. The created protective layer does not contain fragile elements, such as chromate or eloxal coating, and therefore it is not sensitive to under-coat corrosion. This is especially advantageous with respect to durability of the coating - lacquer.
Detailed description of the preffered embodiments
The invention and its advantages will be explained in detail on a specific example of treatment of a product made of aluminium and aluminium alloys. The product was treated with 10% sodium hydroxide at a temperature of 45°C for 10 minutes. After a surface structure similar to the structure of chromate surface was created, the product was thoroughly rinsed and treated with nitric acid to oxidize the remaining alloyed elements. Subsequently, the product was again thoroughly rinsed and passivated in order to stabilize the surface layer with sulfuric acid. The treatment with sodium hydroxide caused dissolving of the product surface which resulted in widening its physical-chemical grid. This also increased the ability of the surface to bind to other components.
Industrial applicability
The surface treatment of products made of aluminium and aluminium alloys may be used especially in the construction industry as well as in the light industry and jewelry production.
Ve claim: