25th March 2015
-Experience over the years leads to changes, improvements, progress and better quality, says Flame Hardeners' managing director Roger Haw.
-Since we published our 1952 brochure over 60 years to reflect the changes it's interesting to see what we said then and what we say now. Here are some examples relating to the advantages of the Shorter Process or Flame Hardening, together with the reasons why the message is different: 1952 There is no scaling a grey matt finish results. Today There is no scaling the finish is usually dark blue or black. If desired we can lightly shot-blast the item to give a grey finish. Modern quench mediums are a great improvement in obtaining the correct quenching rate to give the desired levels of hardness, which have increased over the years. These mediums tend to leave a different surface colour. 1952 The dimensional change is usually negligible with the minimum of distortion but the material ordered should be suitable for flame hardening and steel supplier should be informed that it is intended to flame harden the material. The steel should have the correct metallurgical history (e.g. long slender rollers should not be made from steel that has been cold worked), there should be no cold straightening at any stage. Today The dimensional change is usually minimal, subject to our advice on processing routes and material recommendations. We can advise upon the manufacturing routes, the necessity (or otherwise) to introduce stress relieving at an intermediate machining stage, possible changes in the dimensional shape of any component which may improve stability. 1952 The core strength is unimpaired by the process. Today The core strength is unimpaired by the process. The selling point of surface hardening is that only the area of the component requiring hardening requires heating and that the depth of such heating is less than 1mm deeper than the required hardened depth. 1952 Hardening can be the last operation. Today Hardening can be the last operation, but sometimes we advise against this. Why? (As explained with regard to dimensional change) 1952 Hardening is easily restricted to localised areas. Today Hardening is easily restricted to localised areas. Because we have years of experience in designing heating tools (for both flame and induction hardening) in order to achieve this. 1952 The full potential surface hardness is obtained with a high impact value in the core. Today The correct design requirement of balance application between the surface hardness and depth and the core hardness for any particular application can be achieved. It is not always desirable to harden to the maximum surface hardness attainable. 1952 It's quick and economical. Today The process is cost advantageous when compared with other hardening techniques, particularly when considering the total energy input. However, the process of heating and quenching is controlled by the volume rate of change and different surface hardening processes have different rates of heat input and subsequent quenching, e.g. spin hardening puts heat more gradually than progressive hardening. With progressive hardening there is an optimum traverse speed that can be employed and, as all flame and induction hardening is a machine operation rather than a furnace operation, such speeds affect the processing time and hence the cost. Therefore, the speed of production for a one-off component is very likely to be quicker than a similar furnace treatment, but the time taken to produce a thousand of the same component may be longer than the time taken to harde3n similar items by other treatment methods. 1952 There is a good depth of hardening that can be varied usually 0.090 at high hardness. Today Hardened depths of up to 20mm can be achieved, providing the component geometry and the material are suitable. 1952 There is a wide range of steels from which to choose. Today The process of flame and induction hardening can be applied to components manufactured in plain carbon steels, low alloy steels, cast irons and SG irons. The trend by steel manufacturers to produce a smaller range of steels restricts the total range of steel specifications available. The materials suitable for use, therefore, fall into the four categories mentioned above. Roger Haw explains why the message has changed: -We have the benefit of almost 62 years' development of techniques and improvement of materials and quenching mediums, the combination of which makes flame and induction hardening a valuable and economic treatment. One statement made in the Foreword of Flame Hardeners' 1952 brochure requires an apology (even 61 years later) believes Mr. Haw, and it is this: 'We think Shorter Process Flame Hardening is an art'. -This is absolute rubbish, he stresses. -The processes of flame and induction hardening are a science; they always have been and always will be. That unfortunate statement made so long ago totally detracts from the skill and knowledge of all companies engaged in the technique.