TPT January 2011

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January 2011 29 ›
Industry N ews
1/4-Seite (60 x 180 mm) Satzspiegel
(Tube & Pipe Technology + TubeProducts Int.)
Pipes . Tubes . Services
new components as they introduce new
products or enter new markets, suggesting
the most cost-effective heat treatments and
even developing non-standard processes
for complex products.”
The precise control of all heat treatment
processes is undertaken by dual-loop PLCs
and measured by thermocouples and
oxygen probes, which enable temperature
and atmosphere cycle times to be monitored
accurately. Endothermic gas for the heat
treatment of metals is generated on-site
and fed to the furnaces to reduce the
scaling and decarburisation of steel at high
temperatures, and this can be enriched
with natural gas to increase the carburising
potential. The exhaust gas from furnaces is
measured by an infra-red analyser, which
applies a corrective factor as necessary to
the PLC, for accurate carbon control.
Avariety of quenching media is employed
by Keighley Laboratories, including fast
and medium speed mineral oil and molten
salt for processes like martempering
and austempering, as well as air and fan
cooling. 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, carbonitriding
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 minimise distortion, with case depths
between 0.15 and 4mm+. Sealed quench
furnace processing is also available 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
increasing fatigue strength, inhibiting wear,
resisting corrosion, maximising hardness
and generally enhancing appearance.
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, including
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 hardening and
tempering operations concurrently, keeping
distortion to a minimum. Conventional
hardening and tempering, to produce the
optimum combination of hardness, strength
andtoughnessinmostcommercially-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 homogeneous structure for further
processing, 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
archived 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.
Keighley Laboratories Ltd – UK
Fax: +44 1535 680604
Email:
Website:
Pit carburising