TPT March 2011

There is also press quenching for cooling thin or complex parts such as gears, bearing races and cams, which would distort excessively if directly quenched in oil. Thermochemical methods where a chemical element is combined with thermal energy, like carburising, car- bonitriding and case hardening generally, produce a hard, wear-resistant surface on quenching, with a softer, tougher core that retains the material’s inherent properties. Keighley Labs’ pit furnace facilities accommodate components up to 1.72m long x 0.965m diameter, in single pieces or batches up to 2 tonnes. Depending on size, parts are usually quenched in oil, or molten salt to mini- mise distortion, with case depths between 0.15 and 4mm+. Sealed quench furnace processing is also avail- able for the heat treatment of smaller components in a protective environment, in sizes to 485mm x 355mm and maximum weights of 250kg. Induction hardening involves the more rapid heating and quenching of components using high frequency electric fields, and can be used for local surface hardening, without heating the whole product. This method is typically used for hardening shafts and pins up to 1.5m long, treating internal bores and the spin and contour hardening of individual gear teeth or complete gear wheels up to 4m in diameter. Tufftride treatment, or salt-based ferritic nitrocarburising, is a comparatively low temperature, low distortion salt bath process that can be applied to most ferrous materials and improves component quality by increas- ing fatigue strength, inhibiting wear, resisting corrosion, maximising hardness and generally enhancing ap- pearance. Anti-corrosive properties can be further enhanced by subsequent oxidation treatment, promoting a black finish, while a quench, polish, quench (QPQ) process gives a lustrous black finish with high corrosion resistance. Process times are fairly rapid, typically in the region of 90 minutes. Austempering is a comparatively unusual hardening process for ferrous alloys, steel and iron castings, in- cluding ADI (austempered ductile iron), in which the material is quenched from hardening temperature in a molten salt bath, producing greater durability, increased wear resistance and higher impact and fatigue strength. Available for maximum charges of 400kg in component sizes to 715mm diameter x 1,320mm deep, this process offers low distortion and predictable stability, allowing parts to be cast close to finished shapes and minimising subsequent machining. Martempering is another isothermal process, involving a molten salt bath, and effectively carries out harden- ing and tempering operations concurrently, keeping distortion to a minimum. Conventional hardening and tempering, to produce the optimum combination of hardness, strength and toughness in most commercially- available steels, is carried out in Keighley Labs’ pit and sealed quench furnaces, for components up to 1.72m long, with a choice of quench media according to customer specifications. Other heat treatment processes include annealing for reducing the hardness of materials for subsequent machining, normalising to refine existing grain size and create a more homogenous structure for further pro- cessing, and stress relieving to remove residual stresses generated by previous manufacturing processes. Keighley Laboratories provides certification of all heat treatment processes, with the option of metallurgical inspection by its UKAS accredited, in-house testing facility; metallographic test pieces and records are ar- chived for a minimum of six years, ensuring full traceability for customers. Its heat treatment team, supported by technical director Keith Blower, can carry out failure mode and effects analysis (FMEA) studies for identifying and eliminating potential component reliability problems, and is able to assist with the formulation of specifications for materials, heat treatment processing and testing. Планируется рост спроса на услуги по специальным видам термообработки Деби Мелор, специалист по проведению металлургических и лабораторных исследований компании Keighley Laboratories, предполагает 25% рост развития бизнеса компании в области термообработки. Возросший спрос продиктован возможностями шахтных печей с газовым обогревом, небольшое количество которых расположено в Великобритании, в которых загрузка металлических деталей производится вертикально и, которые позволяют осуществлять такие процессы, как цементация, нитроцементация и закалка с последующимотпускомсминимальными отклонениями и в соответствии с жесткими техусловиями заказчика. Компания ввела в эксплуатацию новое устройство для возможности обработки более широкого ассортимента деталей, включая крупные прямоугольные блоки. Как только будет завершена новая запланированная программа, подразделение термообработки компании предложит обширный ассортимент услуг специалистам Великобритании по модифицированию поверхностных слоев, которые включают индукционную закалку, закалку и отпуск, снятие поверхностных напряжений, ферритное азотонауглероживание или процесс нитрирования поверхности деталей в расплаве цианат-цианидных солей с использованием продувки расплава