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J

anuary

2011

29

I

ndustry

N

ews

www.boilertubes.de

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:

info@keighleylabs.co.uk

Website:

www.keighleylabs.co.uk

Pit carburising