Black Oxide coating

Advert

Black Oxide coating

Home Forums The Tea Room Black Oxide coating

Viewing 22 posts - 1 through 22 (of 22 total)
  • Author
    Posts
  • #419806
    Vic
    Participant
      @vic

      I had a tour of the Axminster Tools facility yesterday which was very interesting. In the manufacturing dept the guide explained that they have changed to using stainless steel for some of their products due to the fact that the Black Oxide coating applied to ordinary steels is no longer environmentally viable. At least I think that’s the term he used. Interestingly though I noticed they’re still using black Unbrako socket screws. I wonder how they’re blacked and if the process used will change soon? Well worth a trip there if you get the chance, they have some amazing Japanese CNC machines there and they’re installing an even bigger one soon requiring an extension to the building.

      Advert
      #35558
      Vic
      Participant
        @vic
        #419960
        David George 1
        Participant
          @davidgeorge1

          If you plate or other coat bolts and cap screws etc you can cause embritalnent or lower the tensile strength of items but there is no change to steel strength or structure with blackodising which is done by diping in to a caustic solution at 135 deg which causes a black coating Fe 3O4 which us rust preventative no change to steel structure. That is why Unbrako blackodise their cap screws.

          David

          Edited By David George 1 on 20/07/2019 10:03:50

          #419969
          Geoff Causon
          Participant
            @geoffcauson89285

            If you want to add a black finish to your homemade steel masterpiece, heat it to dull red & dunk it in old sump oil.

            Do this outside with the part on a longish wire, as it will flare & smoke.

            Obviously won't work with heat sensitive parts, but you will be amazed how professional it looks.

            #423604
            Vic
            Participant
              @vic
              Posted by Geoff Causon on 20/07/2019 10:36:05:

              If you want to add a black finish to your homemade steel masterpiece, heat it to dull red & dunk it in old sump oil.

              Do this outside with the part on a longish wire, as it will flare & smoke.

              Obviously won't work with heat sensitive parts, but you will be amazed how professional it looks.

              Yes I’ve done that in the past. I used to keep a small quantity of old oil for the purpose.

              #423696
              Grotto
              Participant
                @grotto

                I've been told used diesel oil is the best for this, haven't got around to trying it

                cheers

                #423701
                speelwerk
                Participant
                  @speelwerk

                  A little of topic but today I blued several small parts but two M1.7 mm screws which came from package which I bought did not colour. I replaced them with new ones I made from silversteel and that of course coloured without problems. Any idea what steel the others are made from, perhaps stainless? Niko.

                  #423705
                  Anthony Knights
                  Participant
                    @anthonyknights16741

                    For blackening steel my choice is used cooking oil as there are fewer nasty chemicals in it compared to old engine oil.

                    Speelwork, it's possible your screws were either stainless steel or bright zinc plated.

                    #423710
                    vintage engineer
                    Participant
                      @vintageengineer

                      Do you know what is in the caustic solution?

                      Posted by David George 1 on 20/07/2019 10:02:49:

                      If you plate or other coat bolts and cap screws etc you can cause embritalnent or lower the tensile strength of items but there is no change to steel strength or structure with blackodising which is done by diping in to a caustic solution at 135 deg which causes a black coating Fe 3O4 which us rust preventative no change to steel structure. That is why Unbrako blackodise their cap screws.

                      David

                      Edited By David George 1 on 20/07/2019 10:03:50

                      #423712
                      duncan webster 1
                      Participant
                        @duncanwebster1

                        I was given a 'home brew' recipe for blackening steel many years ago, it involves three different chemicals dissolved in water and boiling at some elevated temperature, sounds iffy, but if you want to try it I'll dig it out.

                        #423719
                        Stuart Bridger
                        Participant
                          @stuartbridger82290

                          The classic industrial blacking process is phosphating, which uses phosphoric acid to create the black surface, which is then sealed with oil. This maybe what the OP is referring to.

                          #423723
                          Douglas Johnston
                          Participant
                            @douglasjohnston98463

                            It does not need to be used engine oil (which I understand is rather toxic ) but unused oil works fine. I had some unused 5W-30 engine oil which I no longer needed and tried it with good results. Rapeseed oil from the supermarket also works a treat. Best done outside if possible, where the fumes don't stink the house and set off the smoke alarm, as I found to my cost.

                            Doug

                            #423724
                            SillyOldDuffer
                            Moderator
                              @sillyoldduffer

                              Lots of different processes for blacking/blueing or browning steel. Some – for example steam heating, or boiling in strong caustic soda solution – are mostly harmless. Others use chemicals covered by the Poisons Act or are licensed explosive precursors. Take your pick: A molten mix of Sodium Nitrite and Sodium Nitrate which fumes toxic Nitrogen Oxides, or wet mixes containing various combinations of Mercuric Chloride, Antimony Chloride, Bismuth Chloride, Selenium compounds, with Phosphoric, Oxalic, Hydrochloric and/or Nitric Acids. Now spoilsports have banned simply tipping toxic waste into the nearest river at zero cost, disposal of effluent is expensive.

                              Bloody tree-huggers, there's no proof Mercury in drinking water ever harmed anybody…devil

                              As always in engineering, production is a series of balanced compromises with cost playing the major part. Methods using heat alone are cheap and safe but the protective film is thin and the metal can be damaged internally. Chemical methods produce thicker protection and lower temperatures but are expensive and likely to involve unpleasant chemicals requiring special handling. The good safe cold processes don't always fit the bill. When all the costs are added up a particular blackening process could be more trouble than it's worth, and dodging the bullet by switching to stainless steel could well be advantageous. But blackening is still available and appropriate in the right circumstances.

                              Dave

                              #423727
                              John McNamara
                              Participant
                                @johnmcnamara74883

                                Hi All

                                One of my treasured books.

                                Howe does an outstanding job describing formulas on metal and wood finishing.
                                Also high precision toolmaking in general from an old school manual perspective.

                                I bought mine many years ago. for the tech info, The gunsmithing part is secondary.

                                **LINK**

                                Regards
                                John

                                #423737
                                Phil H1
                                Participant
                                  @philh196021

                                  Slightly different question but on the same theme….. I have flame blued steel successfully (dunked in clean engine oil by the way) but I have never tried to 'blue' a mixed steel and brass assembly. Has anybody tried it? Does the brass just go dull?

                                  Phil H

                                  #423740
                                  thaiguzzi
                                  Participant
                                    @thaiguzzi
                                    Posted by Douglas Johnston on 12/08/2019 08:25:35:

                                    It does not need to be used engine oil (which I understand is rather toxic ) but unused oil works fine. I had some unused 5W-30 engine oil which I no longer needed and tried it with good results. Rapeseed oil from the supermarket also works a treat. Best done outside if possible, where the fumes don't stink the house and set off the smoke alarm, as I found to my cost.

                                    Doug

                                    Beg to differ.

                                    New motor oil leaves a browned finish. The best for a dark, deep black is used diesel oil. I've tried them all inc cooking oil, used diesel oil leaves the best consistent deep black.

                                     

                                    phone photos to sept 2017 545.jpg

                                    Edited By thaiguzzi on 12/08/2019 10:44:18

                                    #423749
                                    Vic
                                    Participant
                                      @vic

                                      I agree about used engine oil but it’s nasty stuff, especially from a diesel. I used to do it outside being careful not to breath in any fumes. It may be worth wearing gloves as well.

                                      #423750
                                      Martin Kyte
                                      Participant
                                        @martinkyte99762

                                        Does the colour make any odds to the corrosion resistance?

                                        Regards Martin

                                        #423752
                                        JA
                                        Participant
                                          @ja

                                          I am sure there is a correct oil to use.

                                          About a year ago I blacked a batch of small steel fixings using fresh clean Morris 32 hydraulic oil. I am more than happy with the results. The parts have been kept with a little bit of oil in a jar which is why there is a slight glint on some items in the photograph.

                                          Blacked small steel fixings

                                          Blacking produces an porous coating which holds oil. As long as the item is kept damp with oil it should not rust. I don't think the colour of the coating is of any importance as far as holding oil.

                                          JA

                                          #423753
                                          Bazyle
                                          Participant
                                            @bazyle

                                            Off topic story. Some time ago we were making a part for a military aircraft from white plastic (type of ptfe I think) and someone accidently set the drying oven too hot so they turned black throughout. We were allowed to deliver them on concession but then got a request to make them all black as they had never liked the white finish (too visible).

                                            #423767
                                            jimmy b
                                            Participant
                                              @jimmyb

                                              I usually just heat and dunk in some old engine oil.

                                              This weekend I tried a 3 stage chemical blacking kit I got off Ebay. I must say it is far easier and quicker (and probably a lot safer) than heating things up.

                                              Jim

                                              #423768
                                              Phil H1
                                              Participant
                                                @philh196021

                                                Ill try a few test components with a flame because last time I did this, I used new engine oil and the result is a lovely dark blue colour – but then I must admit to being a bit colour blind.

                                                Ill will also check to see what happens with brass and steel mixed because nobody has reported back. Lets see what happens.

                                                Phil H

                                              Viewing 22 posts - 1 through 22 (of 22 total)
                                              • Please log in to reply to this topic. Registering is free and easy using the links on the menu at the top of this page.

                                              Advert

                                              Latest Replies

                                              Home Forums The Tea Room Topics

                                              Viewing 25 topics - 1 through 25 (of 25 total)
                                              Viewing 25 topics - 1 through 25 (of 25 total)

                                              View full reply list.

                                              Advert

                                              Newsletter Sign-up