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consistency of wire diameter, saving raw metal material
up to 1~2%. Additionally, nano-dies are welcomed in
high-speed wire drawing and they are highly applicable
to environmentally friendly ‘non-pickling’ wire drawing
processes.
4.2 Water lubricating application perspective in
Al wire and coaxial cable/Al-plastics compound
pipe drawing process with nano-dies
There is another dominant advantage of nano-dies studied
in this paper. That is the change of lubricating method with
a most attractive green element in addition to direct cost
savings. Most production lines with TC dies use oil-based
lubricants to cool the dies and decrease the friction in the
reduction and bearing zones of the die.
Another consideration is the finish of aluminium products.
TC dies need an oil-based lubricant in order to achieve a
satisfactory surface finish. However, oil-based lubricating
systems also bring lots of concerns. For example, the
cost of lubricants is high, expensive accessory equipment
is required, and there is consumption of oil resources
(in oil-based lubricant manufacturing processes).
Additionally, oil-based lubricants carry pollutants into the
workshop (smog, chemical particles and microbes) and
there are great difficulties in recycling aluminium scraps.
For drawing customers, the latter two factors are big
problems, especially aluminium scrap recycling.
A kind of water-based lubricating system can be
successfully introduced to replace the conventional
oil-based lubricating system when using nano-dies for
producing coaxial cable and Al-plastics compound pipe.
This is becoming very popular in Chinese production in
recent years[5][6].
Success is the direct result of the unique structure
of sp 2-bonded carbon in the layer of nano-crystalline
diamond coating of nano-dies. It brings not only very low
friction in the interface with aluminium (and with good
self-lubricating, similar to some graphite-like structures),
but also better wetting with lubricating film in water-based
lubricants (vs conventional multi-crystalline coating).
Conventional TC dies will also meet difficulties of strong
oxide etching and adhesive wear (to form abrasive dust
etc) when using water-based systems. By contrast, the
process is completely worry-free when using nano-dies
because of the high degree of chemical inertness and very
low wear rate of diamond coatings.
Figure 5 shows the water lubricating application in
the Al-plastics compound pipe drawing process with
nano-dies at a customer’s plant in Zhejiang Province of
China and the final appearance of the aluminium product.
Used in this manner, the customer saves a large amount
of cost of lubricating oil, accessory thermostat cleaning
equipment and other processes, and significantly reduces
environmental pollution. The Al-plastics compound pipes
they produce are more consistent, have a more accurate
diameter and a better finish than anything previously
achieved using TC dies and an oil-based lubricating
system.
The same story has been repeated in multiple aluminium
wire drawing applications in China. Nano-dies are
welcomed by big manufacturers in China for the green
element of water lubricating.
5 Conclusions
Nanocrystalline diamond composite coatings are
deposited on the interior surfaces of tungsten carbide
(YG6) drawing dies using HFCVD processes. According
to the analysis results of SEM and Raman spectroscopy,
nanocrystalline diamond coatings also contain a useful
large percentage of multi-crystalline diamond structures
with very small grain sizes of about 50nm and a large
number of grain boundaries. These coatings provide very
good wear resistance, high finish and low friction with
aluminium.
The application of nano-dies in the aluminium wire or
tube (coaxial cable or aluminium-plastics compound pipe)
drawing process can not only increase the working life
of drawing dies dramatically (10~25 times of TC dies),
largely reduce change-over time and increase productivity,
but also ensure fundamental consistency of wire diameter
and improve the quality and finish of drawing products,
saving significant amounts of raw material. Additionally,
nano-dies are highly adaptable to high-speed wire
drawing.
In particular, a water lubricating system can be adopted
to replace the conventional oil-based lubricating system
when using nano-dies for producing aluminium coaxial
cable, aluminium-plastic compound pipe and aluminium
wire, providing immediate economic benefits, reducing
environmental pollution and implementing a green
manufacturing process.
6 References
[1] Dieler M Gruen, ‘Nanocrystalline diamond films’, Annu Rev Mater Sci
1999, 29: 211~259
[2] Sun Fanghong, Zhang Zhiming, Guo Songshou, Shen Hesheng et al,
‘Industrialisation of CVD Diamond Films: Diamond coated drawing
dies and cutting tools,’ Bilateral Chinese-Russian scientific seminar
(Hangzhou), 27th-29th December 2010
[3] Zhang Zhiming, He Xianchang, Shen Hesheng, Sun Fanghong, et al,
‘Pre-treatment for diamond coatings on free-shape WC-Co tools,’
Diamond and Related Materials, 2000, 9:1749~1752
[4] Zhang Zhiming, He Xianchang, Shen Hesheng, Sun Fanghong,
et al, ‘Fabrication and application of chemical vapour deposition
diamond-coated drawing dies,’ Diamond and Related Materials,
2001,10:33~38
[5] Li Zhenquan, Zhou Yan, Liu Yang, et al, ‘Application of nanocrystalline
diamond composite coating compacting dies,’ Electric Wire & Cable
(Chinese), 2005, 2:46~48
[6] Guo Songshou, Zhang Zhiming, Shen Hesheng, Sun Fanghong, et al,
‘Characterisation and Application of Nanocrystalline Diamond-coated
Welding and Drawing Dies,’ Optical Fiber & Electric Cable (Chinese),
2007, 1: 9~12
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