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Surface Phosphating Treatment Method
During various heat treatment, machining, transportation, and storage processes, the metal surface is inevitably oxidized, forming a thick and uneven oxide layer. Additionally, it may be contaminated with oils and other impurities that adhere to the surface. For light oil stains and certain contaminants, a thin oxide layer can be treated using solvent cleaning, chemical treatment, or mechanical methods, or directly through chemical treatment. However, for heavily oxidized surfaces with a thick oxide layer, solvent cleaning and chemical treatment alone may not be sufficient. In such cases, mechanical treatment should be performed first to remove the bulk of the oxide layer. After treatment, the metal surface becomes highly reactive and is prone to recontamination from dust, moisture, and other environmental factors. Therefore, it is important to bond the metal as soon as possible after surface preparation.
The recommended storage period for metals after surface treatment is as follows:
(1) Aluminum alloy after wet blasting: 72 hours
(2) Steel after sandblasting: 4 hours
(3) Anodized aluminum alloy: 30 days
(4) Stainless steel treated with sulfuric acid: 20 days
(5) Aluminum alloy treated with chromic acid-sulfuric acid: 6 hours
(6) Brass after wet blasting: 8 hours
Method for Surface Phosphating Treatment
Surface Preparation Methods for Aluminum and Aluminum Alloys
[Method 1] After degreasing, immerse in the following solution at 60–65°C for 10–30 minutes:
Concentrated sulfuric acid 27.3 g/L, Potassium dichromate 7.5 g/L, Water 65.2 g/L.
Rinse with water, dry, or dry below 80°C. Alternatively, after washing in the following solution:
Phosphoric acid 10%, n-Butanol 3%, Water 20%. Then dry. This method is suitable for bonding with phenolic-nylon adhesives.
[Method 2] Degreasing: Wipe with a damp cloth soaked in a solvent such as trichloroethylene, ethyl acetate, methyl ethyl ketone, or gasoline. Then wipe with a clean cloth to remove any remaining oil.
[Method 3] After degreasing, treat in the following solution at 15–30°C for 10–15 minutes:
Phosphoric acid 7.5%, Chromium oxide 7.5%, Alcohol 5%, Formaldehyde (36–38%) 80%.
Rinse at 60–80°C and dry.
[Method 4] After degreasing, anodize in the following solution:
Concentrated sulfuric acid 22g/L. Apply direct current at 1–1.5 A/dm² for 10–15 minutes, then immerse in a saturated potassium dichromate solution at 95–100°C for 5–20 minutes. Rinse with water and dry.
[Method 5] After degreasing, treat in the following solution at 25–40°C for 4.5–6 minutes:
Ammonium hydrogen fluoride 3–3.5%, Chromium oxide 20–26%, Sodium phosphate 2–2.5%, Concentrated sulfuric acid 50–60%, Boric acid 0.4–0.6%, Water 1000 mL.
Rinse with water and dry. This method provides high bonding strength and should be used within 4 hours of treatment. It is suitable for epoxy and epoxy-butyronitrile adhesives.
[Method 6] After degreasing, treat in the following solution at 65°C for 5 minutes:
Sodium silicate 10g/L, Non-ionic detergent 0.1g/L. Rinse with water at 65°C or lower, then rinse with distilled water and dry. Suitable for bonding aluminum foil.
[Method 7] After sandblasting or sanding, anodize in the following solution:
Chromium oxide 100g/L, Sulfuric acid 0.2g/L, Sodium chloride 0.2g/L. Increase voltage from 0V to 10V at 40°C over 10 minutes, hold for 20 minutes, then increase from 10V to 50V over 5 minutes, hold for 5 minutes. Rinse with water and dry at 70°C. Note: Free chromium oxide concentration should not exceed 30–35g/L.
[Method 8] After degreasing, immerse in the following solution at room temperature for 1 minute:
Sodium fluoride 1%, Concentrated nitric acid 15%, Water 84%. Rinse with water, then immerse in the following solution at room temperature for 1 minute:
Concentrated sulfuric acid 30%, Sodium dichromate 7.5%, Water 62.5%. Rinse with water and dry.
Surface Phosphating Treatment Method
Surface Preparation Methods for Magnesium and Magnesium Alloys
[Method 1] After degreasing, immerse in the following solution at 70–75°C for 5 minutes:
Sodium hydroxide 12%, Water 100%.
Rinse with cold water, then immerse in the following solution at 20°C for 5 minutes:
Chromium oxide 10%, Water 100%, Anhydrous sodium sulfate 2.8%.
Rinse with cold water, then with distilled water, and dry at 40°C.
[Method 2] Degreasing: Use solvents like trichloroethylene, ethyl acetate, or methyl ethyl ketone.
[Method 3] Immerse in the following solution at 20°C for 3 minutes:
Chromium oxide 16.6%, Sodium nitrate 20%, Glacial acetic acid 105%, Water 100%.
Rinse with cold water, then with distilled water, and dry at 40°C or below.
[Method 4] After degreasing, immerse in a 6.3% sodium hydroxide solution at 70°C for 10 minutes, rinse with water, then immerse in the following solution at 55°C for 5 minutes:
Chromium oxide 13.8%, Calcium sulfate 1.2%, Water 85%.
Rinse with distilled water, then immerse in the following solution at 55°C for 3 minutes:
Chromium oxide 10%, Sodium sulfate 0.5%, Water 89.5%.
Rinse with water and dry below 60°C.
[Method 5] Immerse in the following solution at 60–70°C for 3 minutes:
Sodium dichromate 10%, Magnesium sulfate 5%, Manganese sulfate 5%, Water 80%.
Rinse with cold water, then with distilled water, and dry at 70°C or below.
[Method 6] Anodize at a current density of less than 0.45 A/m² in a 10% ammonium hydrogen fluoride solution at 30°C or lower, with a voltage of 90–120 V. Rinse with water and dry.
[Method 7] After degreasing, wash in the following lye at 70°C for 5–15 minutes:
Sodium hydroxide 23–34%, Water 400%.
Rinse with cold water for 5 minutes, then immerse in the following solution for 5–15 minutes at 55°C:
Chromium oxide 57–68%, Calcium nitrate 5%, Water 450%.
Rinse with cold water for 2 minutes, then immerse in the following solution for 3–12 minutes at 55°C:
Chromium oxide 45%, Sodium phosphate 8%, Water 450%.
Rinse with cold water for 2 minutes, then dry at 40°C for 30 minutes.
Surface Phosphating Treatment Method
Surface Preparation Methods for Copper and Copper Alloys
[Method 1] Immerse in the following solution at 25–30°C for 1 minute:
Concentrated sulfuric acid 8%, Concentrated nitric acid 25%, Water 17%.
Rinse with water and dry at 50–60°C.
[Method 2] Immerse in the following solution at 60–70°C for 10 minutes:
Concentrated sulfuric acid 40%, Iron sulfate 4.5%, Water 38%.
Rinse with water and dry at 60–70°C.
[Method 3] Common solvents for degreasing: trichloroethylene, methyl ethyl ketone, ethyl acetate.
[Method 4] Roughen the surface by sandblasting or using a sanding cloth, then degrease.
[Method 5] Immerse for 1–2 minutes at 25–30°C in the following solution:
[Method 6] Immerse in the following solution at 25–30°C for 10–15 minutes:
Concentrated sulfuric acid 10%, Sodium dichromate 5%, Water 85%.
Rinse with water and dry at room temperature.
Ferric chloride 15%, Concentrated nitric acid 30%, Water 200%.
Rinse with water and dry at room temperature.
[Method 7] Oxidize in the following solution:
Potassium persulfate 1.5%, Sodium hydroxide 5%, Water 100%.
Immerse at 60–70°C for 15–20 minutes. The surface turns black, and it should be scrubbed with carbon tetrachloride before bonding. This method is used for copper foil treatment.
[Method 8] After degreasing, etch in the following solution at 66–71°C for 10 minutes:
Iron sulfate 4.5%, Concentrated sulfuric acid 3.4%, Water 450%.
Rinse with cold water at 20°C for 5 minutes, then immerse in the following solution:
Sodium dichromate 5%, Concentrated sulfuric acid 10%, Water 85%.
Rinse with cold water, immerse in ammonium hydroxide (d=0.85) for 10 minutes, rinse with cold water for 5 minutes, then with distilled water, and dry at 40°C. This method is used for brass and bronze treatment.
[Source: Hefei Xianghe Phosphate Coatings Co., Ltd. http:// Please cite the source! ]