1. Hair is blue (nigrescent) principle
To raise steel antirust ability, with strong oxidant steel exterior oxidation becomes compact, smooth 4 oxidation 3 iron. This kind of 4 oxidation 3 iron layer protects steel effectively interior does not suffer oxidation.
Fall in high temperature (about 550 ℃ ) the 4 oxidation that oxidize 3 iron are shown sky-blue, friend says to send blue processing.
Fall in microtherm (about 350 ℃ ) formation 4 oxidation 3 iron present dark black, friend says nigrescent processing.
Make in enginery in, commonly used is hair blue processing; In industrial production, commonly used is nigrescent processing.
Whether the 4 oxidation with steely surface compact, smooth oxidation 3 iron, the key is the oxidant that chooses eager to do well in everything. Strong oxidant is change sodium by oxyhydrogen, inferior 3 natrium form sodium nitrate, phosphoric acid. The steel of manage of melt fluid place to go that they use when hair is blue; Nigrescent when the steel of manage of aqueous solution place to go that uses them. Commonly used nigrescent solution composition sees next tables.
The density of this solution is 1.4g/cm3, boiling point is 130 ℃ . Here the action of solution falls, the combustion process of iron is such:
Fe3O4 of Na2Fe2O4 → of → of Fe → Na2FeO2
Specific chemical response is:
3Fe+NaNO2+5NaOH=3Na2FeO2+NH3+H2O
6Na2FeO2+NaNO2+5H2O=3Na2Fe2O4+NH3+7NaOH
Na2FeO2+Na2Fe2O4+2H2O=Fe3O4 ↓ + 4NaOH
Production carries out experience to prove, should obtain shining, compact 4 oxidation layer of 3 iron film, in oxidation solution inferior the scale of sodium nitrate and hydrogenous oxidation natrium, should maintain in 1: 3 ～ 3.5 between.
2. Hair is blue (nigrescent) operation
Hair is blue (nigrescent) operate circuit:
→ of workpiece outfit clip goes oily → cleans → pickling → to clean → oxidation → to clean hot water of → saponification → to boil the examination that wash → .
(1) workpiece outfit clip wants the appearance according to workpiece, size, design special clamping apparatus or spreader. The purpose is to make stay between workpiece have enough space, cannot contact each other between workpiece, should make every workpiece can be over immersion is oxidized into oxidation fluid.
(2) go oily purpose is eliminate workpiece surface is smeary. After course machine is machined (hair is blue, nigrescent it is last working procedure) , workpiece surface hard to avoid does not stay smeary, make with antirust oil antirust is more between working procedure such. Any smeary, can affect 4 oxidation badly of 3 iron generate, must be so before hair is blue, nigrescent eliminate. Divide oily solution recipe commonly usedly.
Heat the solution that remove oil to 80 ～ 90 ℃ , next workpiece immerge, immerge time is 30min to control, if smeary more, return so that extend the time that remove oil, allow with dividing oil to be thoroughly.
(3) the rust that the purpose of pickling pickling is eliminate workpiece surface is slash. Because rubiginous mark, rusty spot is met,block up generates compact 4 oxidation 3 iron layer. Although workpiece does not have rubiginous mark, also should undertake pickling, because it makes smeary farther purify clean, and the activation energy that pickling can increase workpiece surface member, be helpful for issueing the oxidation of one working procedure, can generate thicker 4 oxidation 3 iron layer.
Pickling solution is 10 ～ commonly 15 ％ pH indicator is vitriolic solution, temperature is 70 ～ 80 ℃ , workpiece immerge in vitriolic solution, immerge time is 30min to control, rustily lighter steel but dip 20min, rustily and serious person, need dip 40min above.
(4) oxidation oxidation is the main working procedure with blue, nigrescent hair. 4 oxidation layer of 3 iron film is whether compact, smooth, whether to have enough ply, depend on oxidation phase.
Sending blue craft temperature is 550 ℃ . Nigrescent craft temperature is 130 ～ 145 ℃ . Immerge time is 50 ～ 80min. Contain carbon to measure tall high-carbon steel, oxidation rate is rapidder, immerge time but some shorter. Contain carbon to measure low mild steel, oxidation rate is slow, immerge time need is some longer. Alloy steel especially tall alloy steel, workpiece surface has certain leftover austenite, have to alkaline solution stronger fight instead to use, generate Fe3O4 not easily, consequently immerge time needs a few longer.
Next watches listed concerned steel is planted oxidation (nigrescent) the temperature of Shi Rong fluid and immerge time.
The normal color of groovy fluid is white. If groovy fluid is shown gules or brown, express inferior saltpetre natrium chroma is too big, answer to adjust the composition of groovy fluid in time. If solution shows green, state iron ion chroma is too big, answer to update solution in time.
(5) saponification is alleged saponification, it is to use suds solution to immerse below constant temperature workpiece. The purpose is to form film of acerbity iron of a tristearin, with improving work fight corrode ability. Commonly used saponification fluid chroma is 30 ～ 50g (soap) / L. Heat saponification fluid to 80 ～ 100 ℃ , put the work after oxidation saponification fluid to immerse 10min left and right sides.
(6) examination
After oxidation ends, want to undertake checking to workpiece, see Fe3O4 film layer eligible. The method of the examination is: Random is draw-out 3 workpiece, 20s immerses in the bluestone solution that park chroma is 2 ％ , the person that do not retreat black is qualification. There is an above in 3 workpiece unqualified, workpiece of whole chamfer regards as unqualified, need to oxidize again, in order to deepen 4 oxidation the ply of 3 iron.
3. The blemish that appears possibly and solve measure
Steel nigrescent craft, in unit process of cargo bandling, may appear as follows a few blemish.
(1) oxidation film is loose
Oxidation film should very compact, very as firm as main union. If generate oxidation film is loose, easy erase, this is abnormal phenomenon. Appear this kind of circumstance, as a result of,basically be new the oxidation solution that make up lacks iron ion to cause. Settle way, it is to add a few old oxidation solution, perhaps add a few clean steel bit, boil 30min, in order to increase the iron ion concentration of oxidation solution, this phenomenon can be eliminated.
(2) workpiece surface shows rufous rusty spot
Oxidation film should present deep black, shining and flowing. If workpiece surface appears rufous stain or become repeatedly, because the oxyhydrogen in oxidation solution changes sodium,this basically is too thick, generate ferric oxide overmuch be caused by. Settling way is to adjust solution composition, complement is joined a few inferior sodium nitrate and water, in order to reduce NaOH concentration.
(3) workpiece surface shows weak gray
Workpiece surface loses pitch-black luster, show weak gray, this is caused. Settle way, complement joins natrium of right amount hydrogenous hydrogen sulfide.
(4) do not make oxidation film
Via handling 40 ～ 50min hind, workpiece surface still not chromatically (make oxidation film) , because solution temperature is too low,this basically is, inferior inadequacy of sodium nitrate chroma causes. Settling way is to raise solution temperature, increase appropriately inferior sodium nitrate quantity.
(5) see things in a blur of oxidation film surface
Workpiece appears on black matrix fragmentary white spot, sometimes white spot is more concentrated, worker of this kind of phenomenon says for " see things in a blur " . Basically oxidation time causes cause of see things in a blur not quite. Settle way, it is to extend oxidation time (immerse namely time) , still can complement join a few oxyhydrogen to change sodium.
(6) workpiece surface shows green
If the oxidation film of workpiece surface is not black black, however green, this is the result that workpiece oxidizes too, because oxidation solution temperature is exorbitant,be, inferior sodium nitrate chroma is exorbitant cause. Settling way is to add right amount cold water (attention: Old protection must have appareled to provide when adding water, slowly join, lest groovy fluid splatters, cause burnable accident) and join a few oxyhydrogen to change sodium, reach in order to drop solution temperature inferior the chroma of sodium nitrate.
