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1.
What types of wear materials can be hardfaced?
2. What type of hardfacing
material do i choose?
3. Is it necessary to preheat?
4. Can segmented wearplates
be hardfaced?
5. How much hardfacing material
can be put on an hour?
6. How long time will it take
to hardface my mill?
7. How long will the hardfacing
last?
8. Should I start with built
up wear parts?
9. How thick a layer can be
built up per pass?
10. What is the maximum layer
thickness?
11. What are the wear properties?
12. How do I distinguish
between hardfacing materials?
13. How many times can
I weld table liners?
14. Welding of rollers
15. How do I inch the mill?
16. What is the price in
S / Kg. welding?
17. What is initial investment?
18. Is there a reliable
wear test taking into account the specific pressures?
19. What can possibly
go wrong?
20. Why has it not been
offered before?
21. How do I program the
PLC for the regulating equipment?
22. Can a corrugated wear
pattern be straightened out?
23. Can rollers be driven
by grinding table?
24. Should welding surfaces
be cleaned before welding?
25. How do I mount the
manipulators?
26. How do I control the
welding?
27. What mill sizes can
be welded?
28. What is the hardness
of the hardfacing?
29. Can a cracked / broken
edge be repaired / gouged?
1.
Most white cast irons, specially the softer type of white
cast irons, like Nihard 1
to 4. Also Cr 27 and Cr 20 for OK mills and Mat 364
for ATOX can be hardfaced.
2. HC-O and CN-o from WA are FLS
"Standard"
CN-O is approximately 30%
more wear resistant than HC-O
3. No. The temperature should be kept
lower than 70-80o C to produce as hard
a surface as possible. Smallest possible Carbides. When
welding at these temperatures
the hardfacing cracks continuously relieving stresses.
4. Both segmented grinding tables and
rollers can be hardfaced. In fact it is safer
to hardface segments than full rings. Rings have a tendency
to crack after a number of
reweldings. The segmented design is "pre-cracked"
but safely bolted on.
5. With one burner and 02,4 mm automatic
welding, typical figures are up
to 5-6 kg/hr.(T)
With one burner and 02,8 mm automatic
welding, typical figures are up
to 8-10 kg/hr.(T)
Manual welding gives around
1,8 kg/hr.(T)
3,8 kg/hr for inert shield
welding.(T)
6. At Leimen 4,2 tom took around
3 weeks all included. The time can be cut when
the equipment is designed for the specific mill. So that
no dismantling of the mill
is necessary.
Depending on the maintenance strategy
chosen. Number of guns etc.
7. Normally the wearlife is more
than double that of the initial cast wear parts.
8. If the wear pattern is known and
continued operation is essential, prewelded segments
could be an option. Normally it is better to find maximum
wear depth / profile and then
start hardfacing.
Storing hardfaced items can be a
problem due to corrosion problems.
9. Normally a bead around 3 x 8 mm using
02,8 wire and a welding speed
of 1-1,5m/min.
10. In principle there is no limit, up
to 80mm has been done. Typical layers
are in the range of
20-45 mm.
11. Compared to typical white cast
iron wear materials, the lifetime is approximately
2 times longer.
12. The higher the amount of carbides,
the more durable it is.
13. More than 25 times has been reported
for OK mill table.
14. 10 times or more times, for segmented
mills, has been reported.
One concern is
distortion, causing loosening segments. No problems reported
so far on OK mills.
For bandages max.
3 times (T).
15. A frequency regulated motor of
around 5 kw drives the gearbox through
a chain/belt drive
mounted to the gearbox coupling. Gear pump station must
be operated during welding.
16. The price differs from country
to country. In Western Europe the price is around
10 S/Kg. of welding material. Some offers from vendors indicate
a price of 20
S/Kg for the finished welding.
(Portugal, Germany
and Denmark).
17. The initial investment for two
manipulators with welding head, power pack, current
connection and a barring device is around 70,000 $. FLS
estimate.
WA has a full range
of welding equipment.
18. Wear is very much dependent on
specific pressures, iron content, carbide grain
sizes and hardness of ground material. Normal reference
is the ASTM
Rubber wheel test.
19. The segments can distortand come
loose. Grinding rings can crack. The welding
currents goes all the wrong directions, making burns on
bearings. During
barring a Michell bearing shoe can "run" dry.
In a coal mill a fire can
be started. The hardfacing cracks and leave parent material.
The Safest solution
is standard cast materials. The need to extend service life
of wear parts
to follow that of the kiln can justify the extra cost and
time involved
in hardfacing. So from the machine supplier's point of view,
we are not especially
interested, but can offer the welding apparatus if the customer
insists.
20. Only during the last 5 - 10 years
hardfacing on roller mills, has been tested and
accepted. Problems with accepting cracks in the welded surfacing
due to bad
experiences on roller presses being a major reason.
21. During commissioning of the equipment
the maintenance personal will
be trained.
22. The amps are regulated when encountering
a hole and the end product
will be adjusted
to a smooth surface, with the original pattern. The hardfacing
seems to prohibit regernation of the corrugated surface.
A different
grinding geometry is also possible to generate, if so wished.
23. Yes, but it is not recommended.
The table can be welded first, so as to obtain
an even surface to drive the rollers. All rollers can then
be welded simultaneously.
If possible
rollers should be turned individually during welding.
24. It is not necessary to grind the
surface before welding, only cleaning of
the grinding
bed is needed. On the rollers the slag falls of by itself.
25. The manipulators are mounted to
the rollers themselves, or the housing, whatever
is the most stable and convenient.
26. The welding is done in an automatic
mode, to avoid injuries to the eyes
of the
operators.
27. All the Ok 25-3 to 36-4 mills
can be welded in situ.
The
ATOX mill range can also be welded in situ, but with
the smaller
coal mills,
it is necessary to take the rollers out first.
28. The welding is done "cold"
and hardness obtained is 60-64 HRC.
29. In principle this is not possible.
But experience shows that it can be
done, the alternative
being to scrap the segments anyway. So gouging can
be utilised to take away high points on the grinding track.
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