Sand blasting Process on Titanium Alloy Surface

1, to adapt to the scope

This standard specifies the cleaning and descaling methods for titanium and titanium surfaces and is suitable for the production, use and manufacture of titanium and titanium alloys to remove general contamination, oxides and fouling during the heat treatment, as well as in the form of surface contamination Of foreign matter.

When titanium and titanium alloys are machined, cast or fabricated, these methods are not forcibly used to remove the presence of dirt, but rather to give a guide.

This standard is applicable to the removal of foreign matter that is resistant to corrosion, stability and final product quality in the presence of chemical etching, connection, plating, assembly prior to cleaning and in any condition.

When the surface of the oxidation of contaminated layer or α layer, after cleaning must be pickled.

2, QICHU procedures

For oils, oils and lubricants used in titanium, titanium alloy addition, forging and production operations, alkali or emulsion immersion cleaners and alkaline electrolysis systems are recommended. In electrolysis, the workpiece can be an anode or a cathode. The QICHU of these fouling is quite good before the heat treatment or 4.2 is prescribed by the acid treatment. When using electrolysis, should control the voltage, to prevent the spark discharge, resulting in the surface of the product pits.

3, the impact of cleaning

3.1 mechanical descaling methods, such as: sandblasting, shot peening, steam spray. State and cleaning methods described in Chapter 4 can be used for thermal processing of skin and lubricants on QICHU titanium surfaces.

3.2 sands for sandblasting should be high quality, after cleaning, iron-free silica sand. If carbon steel or low alloy steel products has been sandblasted by these equipment, the sand used in these products cannot be used for the cleaning of titanium surfaces, but should provide separate cleaning sand.

3.3 If all surfaces are sandblasted, the exposed surface will become rough due to coarse sand or fill sand. In order to protect the surface accuracy, should be a priority to local cleaning and with appropriate pickling procedures.

3.4 The use of grit or sand containing sand for sandblasting to clean up the titanium surface, sandblasting should be utilized after pickling to remove the titanium surface of steel particles.

3.5 Any grinding or shot blasting may cause residual compressive stress on the surface of the material or titanium structure and produce local deformation and should be handled by chemical milling or contour machining.

3.6 In most cases, sandblasting does not mean to say that the pickling is completely eliminated. Grinding cannot remove contaminants caused by gap elements such as carbon, oxygen and nitrogen. When these elements are present in excess, it is more apt to use the pickling control removal shown in 4.3.

4, pickling and descaling

4.1 In addition to the recommended titanium surface rapid sandblasting or grinding treatment, in order to ensure the complete removal of metallic iron, oxides, scales, and other surface contamination, but also according to 4.3.2 pickling. If the product uses chemical milling to remove the surface oxidation pollution layer, and the product shape is not conducive to the overall sandblasting, salt bath treatment can be used to avoid narrow surface corrosion.

4.2 For slim and lubricant residues formed during rolling, casting, forging, or assembly of titanium products, it is usually processed prior to final pickling in accordance with 4.3.2 using any of these industrial methods to obtain complete Contaminated surface.

4.2.1 All corrosive solutions are mixed with tap water at the manufacturer's recommended requirements.

4.2.2 Melt basic salt baths are carried out at 399 to 454 C (750 to 850 F) according to the prescribed procedure.

4.2.3 Melt basic salt baths are carried out at 204 C (400 F) according to the specified procedure.

4.2.4 Oxide and the color produced by heating at less than 593 ° C (1100 ° F), usually washed with pickling, acid ratio (10 to 20%) (150 to 300 g / L) nitric acid (70 %) + 1 to 2% (12 to 24 g / L) Hydrofluoric acid (60%) + water, 120 ° F (49 ° C)

4.2.5 Forged and thermally processed titanium alloys are usually mixed with graphite or glass lubricants to form hot skin, which can be completely dissolved in a molten salt base at a temperature of 454 C (850 F). Subsequent treatment, part of the provisions should be used to 4.3.2 pickling.

4.2.6 Mixed-hot skin with graphite and molybdenum disulfide residue produced by solution-treated and heat-treatable α + β and β alloys and treated at temperatures above 593 C (1100 F) C (400 F) in a molten base salt bath. After the part of the provisions should be used to 4.3.2 pickling treatment.

4.2.7 If the surface structure is easy to remove the skin, can be applied to the grinding method, such as wheel or belt grinding, cutting the sheet round, and grinding or shot peening.

4.3 After mechanical grinding or chemical treatment, the material can be further treated as follows to completely clean the surface.

4.3.1 salt bath and water after cleaning, titanium and titanium alloy can be immersed in sulfuric acid solution to remove the deterioration of the skin, the use of acid is very good at 66 ℃ (150 ℉), the concentration: 10 to 40% ) Sulfuric acid (95% by weight). The final finished surface whitening treatment can be achieved by short-term soaking of the acid as specified in 4.3.2.

4.3.2 According to 3.1 mechanical grinding or by 4.2.1, 4.2.2, 4.2.3 for chemical treatment of the material, can be used to immerse the acid in the way to complete the clean finishing, acid ratio: 10 to 30% (60 to 450 g / L) nitric acid (70%) + 1 to 3% by volume (12 to 36 g / L) hydrochloric acid (60%) at 49 ° C (120 ° F) The ratio of acid is 10: 1.

5 Handling Precautions

5.1 In the high temperature oxidation of titanium in the cleaning, the workpiece contact with the iron-based material will produce current. Titanium forms a positive or anode with these iron-based materials to form an open circuit voltage of approximately 0.60V. The result of release from the rack to the workpiece can cause the surface to overheat and may catch fire. This effect can be reduced by maintaining a bath temperature of no more than 455 C (850 F) and using titanium fixtures or aluminum insulation between the workpiece and fixture.

5.2 thick skin thick forging or hot-rolled materials, in the salt bath before treatment, mechanical grinding can be used to remove excessive surface contamination.

5.3 In the titanium alloy thermoforming or annealing process, the silicon-based protective layer can reduce the formation of skin scales. All coatings should be done before acid treatment.

5.4 Hot-formed or heat-treated titanium in the production or assembly, the formation of a mixed surface contamination, including titanium oxide with graphite or molybdenum disulfide, should be utilized to clean the molten salt bath. The treatment temperature should be at 204 C (400 F) to avoid thermal deformation.

5.5 In the salt bath or lye treatment, the titanium oxide on the metal surface will produce a chemical reaction to produce sodium titanate. They can be removed in sulfur and nitrogen - hydrogen fluoride containing acid. Sulfuric acid on titanium or titanium alloy without any corrosion, while the increase of 0.25 ~ 1.0% copper sulfate or ferric sulfate and thus inhibit the corrosion.

5.6 Most of the pickling-treated pickling are carried out in an acid containing sulfur and nitrogen-hydrogen fluoride. The material is recycled by dissolving salt, water rinsing, and sulfuric acid until all the scales are completely removed. The final bright treatment is done in a short period of time in nitric acid and hydrochloric acid bath soak.

5.7 In nitric acid and hydrochloric acid baths, the ratio of nitric acid to hydrochloric acid is more important than the concentration of any of these acids. When the ratio is kept at 10: 1, the absorption of hydrogen during the pickling process is relatively small.

5.8 In the production of titanium rolled products, it is unavoidable that the oxygen-enriched layer appears on the exposed surface in a high temperature or oxidizing atmosphere. In the use of strong nitric acid and hydrochloric acid solution pickling to remove oxygen-enriched layer and α layer, it is very important that all the residual oxides and scales should be completely removed to prevent the finished product from giving priority to corrosion.

5.9 Exceeding the prescribed amount of hydrogen can be eliminated by vacuum annealing of the cleaning workpieces.

6 test

6.1 The materials to be cleaned according to this standard shall be visually inspected without any significant contamination of the coating, oil, grease, glass, graphite, lubricants, dirt, abrasives, iron, or other forms.

6.2 According to the procedure described, hydrogen absorbed during the cleaning process should be controlled to a relatively small extent and within the permissible limits. Periodic monitoring of the cleaning system should be carried out with a sample of known hydrogen content and the system can be refined by chemical analysis. Hydrogen content beyond the original product analysis results 20ppm, the acid should be replaced or adjust the acidic composition, in order to reduce the degree of hydrogen absorption.

6.3 Product cleanliness can also be accomplished by using a simple test piece. The test piece is quite safe to use about 0.001 to 0.002 in. (0.025 to 0.05mm) and corrodes from both sides. After chemical corrosion, the sample surface should be smooth and smooth, and bright, no residual scales caused by bulging and pollution.