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A DSC study of the dewaxing of cemented carbide powder
323
Acta, 65 (1985)323-326 Elsevier SciencePublishers B.V., Amsterdam-Printed
Thermochimica
A DSC STUDY
B.O.
OF THE DEWAXING
in The Netherlands
OF CEMENTED
CARBIDE
POWDER
Haglund
AB Sandvik S-126
Hard Materials,
12 STOCKHOLM,
P. 0. Box
42056
Sweden
ABSTRACT To press cemented carbide powders to compacts different lubricants are used to lower the friction coefficient (1). These lubricants must be almost completely removed in a "dewaxing" process before sintering. Normally dewaxing is performed by heating the compacts in a suitable furnace atmosphere. Several reactions occur during the dewaxing. The furnace atmosphere is also an important parameter. By a careful control of the temperature cycle the lubricant can be removed at a suitable rate without damaging the compacts. A DSC study has been made to determine the specific heat capacity during the different stages of the dewaxing process. An example is given of the extraction of polyethylene glycol in hydrogen-containing atmospheres.
INTRODUCTION In the production powder
metallurgical
pressing
of milled
and binder tion
of cemented
metal
methods powder
in the pressing
dies
mixture
before
the sintering
carbon
or carbon-containing
the carbon The
blanks.
lubricants
process
methods
In order
which
at a low rate to a moderate
depends
on what
of lubricant
suitable compact
atmosphere
or in vacuum
from oxidation.
gen, participate
to protect
0040-6031/85/$03.30 0 ElsevierSciencePub1ishersB.V.
to
influence
by generally
temperature occurs
the remaining
in the decomposition
to the
removed
piece.
Dewaxing
Some of the protective
actively
added
process
the compacts
was used.
the fric-
severely
heating
kind
i.a.
may decompose
may
etc.
carbides
to lower
carbide
the dewax
parts
imply
metal
be carefully
otherwise
sintered
during
tips, wear
are generally
residues,
is removed
These
must
as they
of the final
tool
of different
(1). These'lubricants
balance
lubricant
are used.
consisting
to compacted
powder
carbide
gases,
which in a
powder
e.g. hydro-
of the lubricant.
324
Reactions heat.
occur
which
The heating
reactions tional
may absorb
necessary
to what
temperature
to make
the different
appreciable
rate may thus be retarded
in comparison
transient
or evolve
or accelerated
can be calculated
analysis
of the dewax
of
by such
from the conven-
equat.ions. It has thus been
a quantitative
periods
amounts
of the heat
found
exchange
in
process.
MATERIALS The cemented tained
3 % by weight
of the powder mately were
carbide
400°C
tested,
Table
was dewaxed
were
spray
glycol
dried
and con-
(Peg). A part
in flowing
Two different
for 1 hour. see Table
hydrogen
grades
of each
at approxi-
of cemented
carbide
1.
materials
were
tested
of polyethylene
batches
As standard sten carbide
powders
pure
crystalline
alpha
alumina
used
in dewaxing
studies
and tung-
used.
1
Specification
of powders
Powder Ni
Composition (w/o) co WC Cr
1-o
1-P 2-o 2-P
11.0 11.0 13.2 13.2
15.3 15.3
89.0 89.0 70.0 70.0
Lubricant Molecular weight
1.5 1.5
Dewaxed Peg 4000 Dewaxed Peg 1500+4000
METHOD Instrument
and conditions
The experiments analyzer between
performed
in a Mettler
150 mg for the alumina
carbide.
All crucibles
were
The experiments gas mixture.
As reference of platinum were
The gas was
evacuated
ment
filled with
and 400-800
with
was
a perforated
to less than the gas mixture
ranged
samples
were
mg for the crucible
tias used.
lid.
in a 5 % hydrogen 50-60 ml/min
Thermo-
weight
of standard
for DSC an empty
performed
flow-rate
thermobalance and then
TA 2000C
TG and DSC. The sample
200 and 500 mg and the weight
approximately tungsten
were
for simultaneous
and 95 % argon
(NTP). The entire
1 mbar before to atmospheric
each experipressure.
325
Experiments The experiments
were made
fur determination
according
of specific
heat
capacity
c . The sample crucible and an empty P placed on the DSC holder and a trace recorded.
A blank
to obtain
the base
test with
dt
mc - dTp ' dt
where
m
sample
of heat
is the mass
heat
were
time was
crucible
was then made
The difference
in the two experiments
of sample
is the specific
against
(2)
pressure,
crucible
of dH/dt
an empty
programme
at constant
reference
line for the system.
due to the absorption
dH =
to a Mettler
in signal may be written
in g capacity
in J/g,K
cP is the programmed
dTp
increase
dt
The procedure
in K/min
was
mina
or tungsten
heat
of the standard
capacity
known
carbide)
signals
values
intervals
with
and another
substance
of lO.OOC
value
was then calculated
capacities
substance
The specific
of
heat
from the ratio
substances
were
(alu-
for the absorption
run and the standard
for the standard
P heat
a standard
was obtained.
from the sample
of c
The specific
RESULTS
then repeated
of the sample
the dH/dt
rate of temperature
between
run and
from
(3,4).
determined
as averages
over
from 95OC to 305OC.
AND DISCUSSION
The results calculated
c
of the measurements values
are given
for WC according
to
in Fig.
1, where
(4) are shown.
also
It is
P obvious
that
the higher lubricant
the higher
the content
is also the specific also
an increase
increases
the curves
the specific
to coincide
understood
from the
decomposition
at higher
representing
cant tend
pronounced
heat
capacity. heat
phase
(Ni, Co or Cr)
The presence
capacity,
of a
as also does
in temperature.
It can also be seen that 250°C,
of binder
temperatures,
material
with
and without
for each of the two grades. fact that the lubricant
in this
for sample
temperature 2-P.
range.
above
This
disappears
This
tendency
240lubri-
can be due to is most
Fig.
1 Specific
without curves
heat capacities
lubricant are also
The curves
as function
of two powder of temperature.
grades
with
and
Thermogravimetric
shown.
can be interpreted
according
to the following
formula:
'Omp(T)
= xwC
. cpwc(T)
+
(1-xwC)
. cpbind(T)
+
cP ' YLubr
’ 'p
lubr(T)
is the specific composite temperature
heat
cemented
capacity
carbide
of the
powder
at
T
is the same of tungsten
is the same of binder
carbide
metal
forming
elements is the same of the lubricant
is the weight
fraction
tungsten
carbide
of the powder is the excess remaining carbide
weight
lubricant
weight
fraction
of the
if the total
is taken
cemented
as 1.00
REFERENCES studies of frictional 1 P. Samuelson and B. Bolin, Experimental behaviour of hard metal powders sliding on cemented carbide 12 (1983) 315-322. walls, Stand. J. Metallurgy, 2 Mettler Application Information TA 2000 No. 5. 3 JANAF Thermochemical Tables, US Dep. Commerce, Washington, 1971. properties of tungsten carbides, 4 B. Uhrenius, Thermodynamic Internal report, Royal Inst. of Technology, Stockholm 1980, p. 9.
Acta, 65 (1985)323-326 Elsevier SciencePublishers B.V., Amsterdam-Printed
Thermochimica
A DSC STUDY
B.O.
OF THE DEWAXING
in The Netherlands
OF CEMENTED
CARBIDE
POWDER
Haglund
AB Sandvik S-126
Hard Materials,
12 STOCKHOLM,
P. 0. Box
42056
Sweden
ABSTRACT To press cemented carbide powders to compacts different lubricants are used to lower the friction coefficient (1). These lubricants must be almost completely removed in a "dewaxing" process before sintering. Normally dewaxing is performed by heating the compacts in a suitable furnace atmosphere. Several reactions occur during the dewaxing. The furnace atmosphere is also an important parameter. By a careful control of the temperature cycle the lubricant can be removed at a suitable rate without damaging the compacts. A DSC study has been made to determine the specific heat capacity during the different stages of the dewaxing process. An example is given of the extraction of polyethylene glycol in hydrogen-containing atmospheres.
INTRODUCTION In the production powder
metallurgical
pressing
of milled
and binder tion
of cemented
metal
methods powder
in the pressing
dies
mixture
before
the sintering
carbon
or carbon-containing
the carbon The
blanks.
lubricants
process
methods
In order
which
at a low rate to a moderate
depends
on what
of lubricant
suitable compact
atmosphere
or in vacuum
from oxidation.
gen, participate
to protect
0040-6031/85/$03.30 0 ElsevierSciencePub1ishersB.V.
to
influence
by generally
temperature occurs
the remaining
in the decomposition
to the
removed
piece.
Dewaxing
Some of the protective
actively
added
process
the compacts
was used.
the fric-
severely
heating
kind
i.a.
may decompose
may
etc.
carbides
to lower
carbide
the dewax
parts
imply
metal
be carefully
otherwise
sintered
during
tips, wear
are generally
residues,
is removed
These
must
as they
of the final
tool
of different
(1). These'lubricants
balance
lubricant
are used.
consisting
to compacted
powder
carbide
gases,
which in a
powder
e.g. hydro-
of the lubricant.
324
Reactions heat.
occur
which
The heating
reactions tional
may absorb
necessary
to what
temperature
to make
the different
appreciable
rate may thus be retarded
in comparison
transient
or evolve
or accelerated
can be calculated
analysis
of the dewax
of
by such
from the conven-
equat.ions. It has thus been
a quantitative
periods
amounts
of the heat
found
exchange
in
process.
MATERIALS The cemented tained
3 % by weight
of the powder mately were
carbide
400°C
tested,
Table
was dewaxed
were
spray
glycol
dried
and con-
(Peg). A part
in flowing
Two different
for 1 hour. see Table
hydrogen
grades
of each
at approxi-
of cemented
carbide
1.
materials
were
tested
of polyethylene
batches
As standard sten carbide
powders
pure
crystalline
alpha
alumina
used
in dewaxing
studies
and tung-
used.
1
Specification
of powders
Powder Ni
Composition (w/o) co WC Cr
1-o
1-P 2-o 2-P
11.0 11.0 13.2 13.2
15.3 15.3
89.0 89.0 70.0 70.0
Lubricant Molecular weight
1.5 1.5
Dewaxed Peg 4000 Dewaxed Peg 1500+4000
METHOD Instrument
and conditions
The experiments analyzer between
performed
in a Mettler
150 mg for the alumina
carbide.
All crucibles
were
The experiments gas mixture.
As reference of platinum were
The gas was
evacuated
ment
filled with
and 400-800
with
was
a perforated
to less than the gas mixture
ranged
samples
were
mg for the crucible
tias used.
lid.
in a 5 % hydrogen 50-60 ml/min
Thermo-
weight
of standard
for DSC an empty
performed
flow-rate
thermobalance and then
TA 2000C
TG and DSC. The sample
200 and 500 mg and the weight
approximately tungsten
were
for simultaneous
and 95 % argon
(NTP). The entire
1 mbar before to atmospheric
each experipressure.
325
Experiments The experiments
were made
fur determination
according
of specific
heat
capacity
c . The sample crucible and an empty P placed on the DSC holder and a trace recorded.
A blank
to obtain
the base
test with
dt
mc - dTp ' dt
where
m
sample
of heat
is the mass
heat
were
time was
crucible
was then made
The difference
in the two experiments
of sample
is the specific
against
(2)
pressure,
crucible
of dH/dt
an empty
programme
at constant
reference
line for the system.
due to the absorption
dH =
to a Mettler
in signal may be written
in g capacity
in J/g,K
cP is the programmed
dTp
increase
dt
The procedure
in K/min
was
mina
or tungsten
heat
of the standard
capacity
known
carbide)
signals
values
intervals
with
and another
substance
of lO.OOC
value
was then calculated
capacities
substance
The specific
of
heat
from the ratio
substances
were
(alu-
for the absorption
run and the standard
for the standard
P heat
a standard
was obtained.
from the sample
of c
The specific
RESULTS
then repeated
of the sample
the dH/dt
rate of temperature
between
run and
from
(3,4).
determined
as averages
over
from 95OC to 305OC.
AND DISCUSSION
The results calculated
c
of the measurements values
are given
for WC according
to
in Fig.
1, where
(4) are shown.
also
It is
P obvious
that
the higher lubricant
the higher
the content
is also the specific also
an increase
increases
the curves
the specific
to coincide
understood
from the
decomposition
at higher
representing
cant tend
pronounced
heat
capacity. heat
phase
(Ni, Co or Cr)
The presence
capacity,
of a
as also does
in temperature.
It can also be seen that 250°C,
of binder
temperatures,
material
with
and without
for each of the two grades. fact that the lubricant
in this
for sample
temperature 2-P.
range.
above
This
disappears
This
tendency
240lubri-
can be due to is most
Fig.
1 Specific
without curves
heat capacities
lubricant are also
The curves
as function
of two powder of temperature.
grades
with
and
Thermogravimetric
shown.
can be interpreted
according
to the following
formula:
'Omp(T)
= xwC
. cpwc(T)
+
(1-xwC)
. cpbind(T)
+
cP ' YLubr
’ 'p
lubr(T)
is the specific composite temperature
heat
cemented
capacity
carbide
of the
powder
at
T
is the same of tungsten
is the same of binder
carbide
metal
forming
elements is the same of the lubricant
is the weight
fraction
tungsten
carbide
of the powder is the excess remaining carbide
weight
lubricant
weight
fraction
of the
if the total
is taken
cemented
as 1.00
REFERENCES studies of frictional 1 P. Samuelson and B. Bolin, Experimental behaviour of hard metal powders sliding on cemented carbide 12 (1983) 315-322. walls, Stand. J. Metallurgy, 2 Mettler Application Information TA 2000 No. 5. 3 JANAF Thermochemical Tables, US Dep. Commerce, Washington, 1971. properties of tungsten carbides, 4 B. Uhrenius, Thermodynamic Internal report, Royal Inst. of Technology, Stockholm 1980, p. 9.