Hardening for small profiles


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Hardening for small profiles

  1. 1. ~ 370-1320 31.039.2 TECHNICAL INFORMATION Special print: WIREWORLD 4/92J.-M. Rufer, MetallurgistNew hardening conceptfor small profilesand thin metal strips
  2. 2. •International Technical Magazine for the Wire and Cable Industries Small parts therapy New hardening concept for small profiles and thin metal strips J-M. Rufer
  3. 3. Heat TreatmentSmall parts therapyNew hardening conceptfor small profiles and thin metal stripsPay-offfollowedby a washingunit and feedsystem leadinginto the austenitizingfumace MSmall parts that are mass-pro- ass parts are being pro- course, to minimize production costsduced from profiles or strips duced from small profiles and to optimize manufacturing condi- and thin strips at an in- tions not only with regard to the qualityare having to me et rising re- creasing rate of output. requirements but also in respect ofquirements on quality. More The high-performance safety and environmental regulations.than anything else they must machine tools and modern blanking This in turn means that the builders ofdisplay exactly the right me- presses used on these production lines heat treatment plants have to offerchanical and metallurgical place accordingly high demands on the high-performance equipment that quality of the semi-finished feed stock. scores high marks for on-the-job con-properties. Here the key quality criteria are the venience and safety as weil as for tech- materials mechan:jcal characteristics, nology and economic efficiency.J.-M. Rufer* metallurgical properties, geometry, sur- face finish and surface regularity. For manufacturers of such semi- Hardening of small profiles in finished products it is also important, of a puII·through furnace Conventional pull-through furnaces * J.-M. Rufer is head of the research and develop- for the hardening of carbon steel are ment department at a manufacturer of heat treat- generally equipped with oil quenching ment plants in Biel, SwitzerJand. facilities. Such facilities can certainly
  4. 4. Heat Treatment produce good results, but they do have a number of drawbacks, for example: Austenitising fumace Adaptable cooling system • A large quantity of quenching oil Austenitisierofen AnpaBbares Kühlsystem must be kept in stock • Maintenance of pumps, filters, coo- lers, etc. is often expensive • Oil vapours and possible oil blee- ding inside the hardening fumace chan- nel can shorten the life of heat-resistant fumace elements considerably • Washing is always necessary before tempering as otherwise the tempering fumace will be polluted and the semi- finished product oxidized during thetempering • Discolouration is often observed onprofiles made of certain steel gradeswhich require a high hardening tempe-rature or which have a surface thatoxidizes readily • Starting the strands and replacing ~900Cbroken strands often poses difficulties 1 • The risk of Cire on fumace lines con- Iltaining oil quenching tanks must always "1 1 be taken seriously. , Most of the above problems can be ,, ,, ,,solved or eliminated for small section ".... ....,~, .... ~280Cprofiles or wires by hardening underprotective gas. For large-section pro-files and for steels of low hardenability,oil quenching is still essential. Thanks to modem fumace enginee- Quenching Quenching under protective Stabilization under protective Air coolingring, diverse small profiles and wires of gas gasunalloyed steel (e. g. CK75) of the typeswhich require high-speed cooling andare generally quenched in oil can nowa- Figure 1: Exampleof a coolingsystem for graduai hardening (martempering) o(smalldays be hardened under protective gas. profilesunder protective gasWith this method of cooling it is alsopossible to adapt the hardening profileto the particular requirements. For ex-ample, the use of martempering and astabilization zone inserted between two X 1000cooling steps can make the use of saltor melted alloyed lead baths super-fluous. Figure2: Heat treatment fumace line for the hardening and tempering of steel ln the martempering process the profiles:a) Austenitizingfumace for a maximumtemperature of 1150°C,temperature is raised and held above b) Washingunit preceding heat treatment, M) Coolingelement under protectivethe level of martensitic transformation atmosphere, c) Temperingfumace for a maximumtemperature of 650°C,(MS) long enough to permit the entire d) Qilspraying systemprofile to stabilize, after which it is 10-wered again to a point below the MSline in order to obtain a martensiticstructure. Used on small profiles, martempering metallic bright surface after hardening, there is none of the usual pollutioncan decrease hardening distortions and without the need for any subsequent nuisance.reduce the thermal stresses which pro- cleaning, washing or pickling. ln other This particular heat treatment line forduce distortions du ring subsequent ma- words, it is possible for the product to steel profiles can be used to treat bothchining or forming. pass directly into the tempering fumace unalloyed and stainless steels. The Figure 1 shows an example of a coo- aiter leaving the hardening fumace. geometry of the cooling elements isIing curve applied in a hardening fuma- A further great advantage of a harde- quickly adapted to a new product orce for small profiles. One of the most ning fumace that works under protecti- profile.important arguments in favour of a pull- ve gas is the absence of quenching oil. To guarantee a high quality ofthrough fumace line for hardening With no oil vapours in the fumace, the finished product it is also important tosmall profiles under protective gas is usefullife of the heat-resistant steel ele- select the right protective gas. For sim-that it tums out a perfect, clean and ments is prolonged considerably and ple hardening a sufficiently pure pro-
  5. 5. Heat Treatmenttective gas and perfect tightness of the distortions and to optimize the harde-fumace will provide good protection ning structure. Once the product is har-against oxidation. There is no need to dened, it can pass directly through theuse gas with a carbon potential requi- tempering fumace which featuresring regulators or other control devi- strong convection to guarantee a preci-ces, since the passage time through the se and homogeneous tempering tempe-fumace is very short and the protective rature.gas serves only to prevent oxidation Before arriving at the take-up standand decarburation of the product. with a sophisticated winding and tra- versing system, the product is spray- A hardening and lempering coated with anticorrosive oil. The key furnace in action technical data of the fumace are shown A pull-through fumace for hardening in the diagram and tables in Figure 2.and tempering various profiles in car- Figure3: Overallviewof the heat treatmentbon steel (CK75) or stainless steel un- linefor the hardeningand temperingofsteel Closing remarksder protective atmosphere has the fol- profiles Experience with the cooling systemslowing operating features: described above prove that it is not Ten strands can be treated simul- only desirable but also possible totaneously. With an output capacity of trasonics. The austenitizing and harde- adapt heat treatment pro cesses to to-approximately 130kg/h for a profile ning fumace is built for a maximum days requirements on quality, usersection of 1.8 mm2, the pull-through tempe rature of 1150°C so as to treat convenience and environmental pro-speed equals 17rn/min. During its way stainless steels as weIl. It is equipped tection. There are good prospects forthrough the fumace the product passes with a cooling element under protective further improvements in the future. Tothrough the following treatment phases: gas (in this case N2 + 5 % H2) which achieve the set goals it is necessary toAfter the laminated product is unwound also allows for a stabilization stage at a perfect the various construction tech-and straightened, the residual lamina- temperature above the level of marten- niques and the application of protectiveting oi! is removed by washing and ul- sitic transformation in order to reduce atmospheres. HEAT TREATMENT FURNACE-LINES for WIRES, PROFILES, TUBES, SCREWS and MASS PRODUCTS Automatic heat treatment line for SCREWS and MASS PRODUCTS up to 1300 kg/h Hardening Carburising Carbonitriding Tempering Washing www.soloswiss.com •
  6. 6. Supplementary «Technical Information» available«The new 321 Pratic System furnace with conveyor belt»Technical Information SOLO 321/01.037.9«Equipment for Hardening of Tools»E. Meinhard, Technical Information SOLO 1320/15.128.1«The Present Practice of Nitriding and Nitrocarburising»E. Meinhard, Technical Information SOLO 1220/10.058.2«Experience report concerning the heat-treatment installation type SOLO-202»Or. Tschierschke, Technical Information SOLO 202/7.068.5«Flexible computer controlled heat treatment»F Cramme, Technical Information SOLO 202/955-10.118.7«Influence of the mode of heat treatment on the quality and characteristics of semi-productslike wires, profiles and strips»J.-M. Rufer, Technical Information SOLO 370-1280/01.038.8
  7. 7. Continuous heat treatment furnace-lines under protective gas with integrated quenching,tempering furnaces, washing machines.Maximum capacity up to 1350 kg/h, electrically or gas heated.«From the small furnace to the large heat-treatment plant»Automatic treatment lines for soldering, brazing, carburizing, Large chamber fumacescarbonitriding, hardening, degreasing and tempering Double cham ber fumacesVertical retort fumaces with gas circulation for the High-temperature cham ber fumacesheat-treatment of long parts Fumaces for solution annealing and precipitationBell fumaces with forced gas circulation hardening of aluminium alloysShaH fumaces Salt bath fumacesFumaces with forced air circulation Preheating fumaces for hot-pressingConveyor belt fumaces Sintering fumacesAutomatic conveyor belt tempering fumaces Smelting fumaces with metal or graphite crucibleHardening fumaces for bright hardening of air-hardening Cupellation and incineration fumaceschrome and high-speed steels under protective atmosphere Temperature control panelsHardening fumaces with built-in quench tanks Washing and degreasing unitsGenerator for endothermic and exothermic atmospheres Laboratory muffle fumacesAmmonia dissociators Laboratory heating cabinetsCar-bottom fumaces Electronic tacking machines