They would have a case depth specified of I think 0.025”. Examples were guide plates for the large draw dies used to form a car door or trunk lid from a flat sheet. Most, if not all parts were tempered afterwards. Those jobs were nearly always left overnight, often soaking for several hours if a deep case was required. Low carbon steel parts to be carburised would be packed in carburising compound in metal boxes & placed in an oven for specific times depending on the depth of case required. All used in the manufacture of automotive body press tooling. From low carbon up to & including exotic tool steels. The tool and die company where I served my apprenticeship had an extensive heat treatment department that dealt with hardening & tempering steels of all grades. Carburised hardened surfaces can also be tempered after hardening to reduce the tendency of the glass hard surface to chip or otherwise break up under load. The costing of copper sulphate prevents the absorption of the carburising compound & thus retains the properties of the original steel. You can even apply it to a small area of a surface if you will need to drill a hole in a particular place after hardening. When it comes to selective carburising hardening of surfaces another method is to coat the surfaces to be left soft with copper sulphate solution. Where I done my time we had a big cyanide hardening shop, lovely place to be on a freezing cold winters day, the fumes also cured blocked up noses very effectively! Jason I seem to remember something about tempering to refine the core due to grain growth when quenching the case but cannot remember if that was just for cyanide hardening. If that is correct, I'm not sure why one would want to do that? Much simpler, and better, to leave the rods as they are and case harden the pins.Īndrew, I would have thought a lot less work to remake a worn pin some time down the line than a worn rod I would have a scratch rod to make sure the powder gets into the small hole. You only heat that end and dip it in the powder. The case hardening is only to provide a long-wearing surface on the 1/8" (?) dia hole on the one end.
If those are the parts you are working on, you only case harden the small end - not the entire part. Out of interest I put a brown paper tube in the canister to use up the oxygen which results in the nice clean finishĭalboy, - by the dimensions you stated it sounds like you are talking about Eccentric Rods. Not only do they come out a beautiful shade of grey but as some parts have thin star shaped teeth there is no chance of overheating as they are protected by the canister. Yes Martin you are quite right about box hardening, I use a it fir small-gears and other instrument parts. Heating and quenching will harden the target surface and leave the rest soft to ensure non brittle threads or in the case of the cam follower the ability to turn the outside cylindrical after hardening has distorted it. The surfaces to be left soft can be skimmed, thread cut or fully machined to remove the carburised surface.
For example on a part with a fine screw thread or something that will distort when heat treated like a cam follower bucket if the area to be hardened is finished machined but the rest is left oversize the part can be carburised but not quenched. On a somewhat more practical and up to date point it is possible to selectively harden parts of components by choosing when in the machining sequence the casing or carburisation is carried out. This is surmise on my part so I would be interested in comments. So maybe the term case hardening referred to the box. Later reading revealed that the process used to be done by enclosing the part in an iron box or “case” ? with carbon bearing materials like bone or leather.
#Case hardening has zebra pattern skin
It just gives a wear surfaceĪt first glance, like when I started model engineering, it’s easy to assume that case referred to the creation of a hard skin ‘encasing’ a component. You don't need to temper anything that is case hardened as the core's carbon content is not altered.
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