Fastener products include bolts, screws, studs or nuts, washers, etc., some of which are blackened, which can meet the requirements of fasteners and rust prevention, low cost and high production efficiency; It is good to reduce the quenching stress, so that the fastener is not easy to break under the stress condition. Let's share with you the principle, purpose, processing flow and operation points of the fastener blackening process.
1. The principle, purpose and process of the blackening process of fasteners
1.1 Principle of blackening
The fastener to be blacked is placed in a solution tank (145±5 ° C) of sodium hydroxide (NaOH) and sodium nitrite (NaNO 2 ) oxidant to heat and oxidize to form a layer on the surface of the metal fastener. A magnetic ferroferric oxide (Fe 3 O 4 ) film having a thickness of generally 0.6 to 0.8 μm is black or blue-black.
1.2 The purpose of blackening
1 anti-rust effect on the surface of the fastener;
2 increase the appearance and gloss of the surface of the fastener;
3 reduce the stress effect of the quenching process.
1.3 blackening process
Loading→Boiling alkali aqueous solution to oil→water cleaning→hydrochloric acid solution rust→water cleaning→boiling water heating→oxidation→water cleaning→saponification→water cleaning→self-drying→immersion oil→oil control→inspection→into the warehouse.
2, blackening process operation points
(1) Mounting to ensure the surface quality of the black fasteners to be sent is uniform, and the fasteners should be in point or line contact.
(2) The boiling alkali solution is degreased, first add water to the alkali solution tank, then add 15g/L water-soluble sodium hydroxide (NaOH) to the boiling point, put the fastener into the tank, wash for 5-10min, non-smooth The surface increases the time as appropriate.
(3) The water cleaning is washed with boiling water, and the cold water is used to rinse the residual alkali liquid on the surface of the fastener.
(4) Add hydrochloric acid solution to the rust acid tank, then slowly pour hydrochloric acid into clean water at a concentration of 14%-18% (tested with Baume concentration meter), temperature ≤30 °C, put the fastener to be pickled In the tank, the pickling time is 3-5min, and the non-processed surface increases the cleaning time as appropriate.
(5) Wash the water with cold water and rinse off the residual acid on the surface of the fastener.
(6) Boiling water heating The washed fasteners are placed in boiling water, heated to above 90 ° C, and placed in an oxidation tank.
(7) Distribution ratio in the oxidation oxidation tank: 600 g of sodium hydroxide (NaOH), 60 g of sodium nitrite (NaNO 2 ), and 20-40 g of trisodium phosphate (Na 3 PO 4 ) containing crystal water are added per liter of water. 2 Preparation method: first put 2/8 volume of water in the oxidation tank, then add slowly sodium hydroxide (NaOH) slowly. When the solution reaches about 100 °C, add trisodium phosphate (Na 3 PO 4 ). , made of oxidizing solution. 3 oxidation temperature time: the boiling water heated fasteners are placed in the oxidation temperature (145 ± 5 ° C) oxidizing solution (tested with 0-200 ° C glass thermometer, with boiling water calibration), oxidation time 30-50min.
(8) Water washing Rinse the residual oxidizing solution on the surface of the fastener with water to be saponified.
(9) Saponification 1 The rinsing fastener is placed in a saponification tank and saponified to form a film of iron stearate on the surface of the fastener. Use 10 pieces of household soap, melt into 100L of water, adjust the concentration and capacity according to the ratio, and make the saponification liquid. 2 Heating temperature and saponification time: saponification liquid temperature 80-90 ° C (measured with a glass thermometer), saponification time 2-3 min. A bar of soap is added to the saponification solution daily according to the size of the saponified fastener, and an appropriate amount of water is added to maintain the solution concentration.
(10) Water washing The surface soap of the fastener is rinsed with water and heated with boiling water.
(11) Self-drying and self-drying by using its own heat.
(12) Immersion oil Immerse the fasteners from the dry water-free ones in the L-AN15 total loss system oil at 80 ° C (measured with a glass thermometer) for 1-3 min.
(13) After the oil-immersed oil-impregnated fastener leaves the oil tank, the surface of the fastener and the surrounding oil drop are controlled.
(14) Inspection 1 Appearance inspection: Place the fastener under the fluorescent light source, 300mm away from the naked eye, observe the surface. If the color is uniform and uniform, no obvious spots and rust are present, the color is black or blue-black. 2 oxide film looseness measurement: on the fastener after degreasing, drop a few drops of 3% copper sulfate solution, and the copper color is not qualified within 30s.
(15) After entering the warehouse, it will be put into storage after passing the inspection according to the quality inspection requirements, otherwise it will be reworked according to the original process procedure.
Attachment: Handling of common quality problems
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