1. ~ 370-1320
31.039.2
TECHNICAL INFORMATION
Special print: WIREWORLD 4/92
J.-M. Rufer, Metallurgist
New hardening concept
for small profiles
and thin metal strips

3. •
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

4. Heat Treatment
Small parts therapy
New hardening concept
for small profiles and thin metal strips
Pay-offfollowedby a washingunit and feedsystem leadinginto the austenitizingfumace
M
Small parts that are mass-pro- ass
parts are being pro- course, to minimize production costs
duced 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 quality
are having to me et rising re- creasing rate of output. requirements but also in respect of
quirements 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 of
display exactly the right me- presses used on these production lines heat treatment plants have to offer
chanical 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-
material's 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

5. 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 the
tempering
• Discolouration is often observed on
profiles made of certain steel grades
which require a high hardening tempe-
rature or which have a surface that
oxidizes readily
• Starting the strands and replacing ~900'C
broken strands often poses difficulties
1
• The risk of Cire on fumace lines con- Il
taining oil quenching tanks must always "1 1
be taken seriously. ,
Most of the above problems can be
,,
,,
,,
solved or eliminated for small section
".... ....,~,
.... ~280'C
profiles or wires by hardening under
protective 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 cooling
ring, diverse small profiles and wires of gas' gas
unalloyed steel (e. g. CK75) of the types
which require high-speed cooling and
are generally quenched in oil can nowa- Figure 1: Exampleof a coolingsystem for graduai hardening (martempering) o(small
days be hardened under protective gas. profilesunder protective gas
With this method of cooling it is also
possible to adapt the hardening profile
to the particular requirements. For ex-
ample, the use of martempering and a
stabilization zone inserted between two X 1000
cooling steps can make the use of salt
or 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 protective
the level of martensitic transformation atmosphere, c) Temperingfumace for a maximumtemperature of 650°C,
(MS) long enough to permit the entire d) Qilspraying system
profile to stabilize, after which it is 10-
wered again to a point below the MS
line in order to obtain a martensitic
structure.
Used on small profiles, martempering metallic bright surface after hardening, there is none of the usual pollution
can 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 for
duce distortions du ring subsequent ma- words, it is possible for the product to steel profiles can be used to treat both
chining 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 is
Iing curve applied in a hardening fuma- A further great advantage of a harde- quickly adapted to a new product or
ce 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 of
through fumace line for hardening With no oil vapours in the fumace, the finished product it is also important to
small 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-

6. Heat Treatment
tective 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 the
use gas with a carbon potential requi- tempering fumace which features
ring 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 stand
and 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 treatment
bon steel (CK75) or stainless steel un- linefor the hardeningand temperingofsteel Closing remarks
der protective atmosphere has the fol- profiles Experience with the cooling systems
lowing operating features: described above prove that it is not
Ten strands can be treated simul- only desirable but also possible to
taneously. 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 day's requirements on quality, user
section 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 for
through the fumace the product passes with a cooling element under protective further improvements in the future. To
through the following treatment phases: gas (in this case N2 + 5 % H2) which achieve the set goals it is necessary to
After 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 protective
ting 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
•

7. 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-products
like wires, profiles and strips»
J.-M. Rufer, Technical Information SOLO 370-1280/01.038.8

8. 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 fumaces
carbonitriding, hardening, degreasing and tempering Double cham ber fumaces
Vertical retort fumaces with gas circulation for the High-temperature cham ber fumaces
heat-treatment of long parts Fumaces for solution annealing and precipitation
Bell fumaces with forced gas circulation hardening of aluminium alloys
ShaH fumaces Salt bath fumaces
Fumaces with forced air circulation Preheating fumaces for hot-pressing
Conveyor belt fumaces Sintering fumaces
Automatic conveyor belt tempering fumaces Smelting fumaces with metal or graphite crucible
Hardening fumaces for bright hardening of air-hardening Cupellation and incineration fumaces
chrome and high-speed steels under protective atmosphere Temperature control panels
Hardening fumaces with built-in quench tanks Washing and degreasing units
Generator for endothermic and exothermic atmospheres Laboratory muffle fumaces
Ammonia dissociators Laboratory heating cabinets
Car-bottom fumaces Electronic tacking machines