U.S. patent number 3,802,847 [Application Number 05/187,953] was granted by the patent office on 1974-04-09 for rotary furnace for carburization.
This patent grant is currently assigned to Sumitomo Electric Industries, Ltd.. Invention is credited to Akio Hara, Masaya Miyake.
United States Patent |
3,802,847 |
Hara , et al. |
April 9, 1974 |
ROTARY FURNACE FOR CARBURIZATION
Abstract
An improved furnace of the rotating type comprises a rod-shaped
or tubular heating core of graphite or carbonaceous material
fixedly arranged in the central portion of the furnace. A rotary
cylinder having an inner wall of graphite or carbonaceous material
is secured to rotate around the heating core. A casing is provided
with means for rotatably holding the rotary cylinder, an opening
for feeding a raw material, means for supplying electric power, an
opening for discharging a product and a gas flow opening and is
secured to hold an atmosphere of carburization inside the
furnace.
Inventors: |
Hara; Akio (Itami,
JA), Miyake; Masaya (Itami, JA) |
Assignee: |
Sumitomo Electric Industries,
Ltd. (Higashi-ku, Osaka, JA)
|
Family
ID: |
26412346 |
Appl.
No.: |
05/187,953 |
Filed: |
October 12, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Oct 30, 1970 [JA] |
|
|
45-95243 |
Sep 16, 1971 [JA] |
|
|
46-71233 |
|
Current U.S.
Class: |
422/199; 219/389;
266/128; 266/252; 373/114; 422/209; 432/114; 266/173; 266/905;
373/116; 423/440 |
Current CPC
Class: |
F27B
7/06 (20130101); F27B 7/08 (20130101); C01B
32/90 (20170801); C01P 2006/42 (20130101); C01P
2006/80 (20130101); C01P 2004/62 (20130101); C01P
2006/90 (20130101); F27D 2099/0008 (20130101); C01P
2004/61 (20130101); Y10S 266/905 (20130101) |
Current International
Class: |
C01B
31/30 (20060101); C01B 31/00 (20060101); F27B
7/00 (20060101); F27B 7/06 (20060101); F27B
7/08 (20060101); F27D 23/00 (20060101); F27b
007/06 (); B01j 006/00 () |
Field of
Search: |
;23/279,227R,288J
;263/32 ;219/389 ;13/20,21,35 ;266/5E,18 ;423/440,441 ;432/114 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tayman, Jr.; James H.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Claims
1. A rotary furnace for carburization which comprises:
an enclosing casing constructed to maintain a carburization
atmosphere within said furnace, said casing having an opening at
the upper portion thereof for feeding a solid raw material therein,
an opening at the lower portion thereof for discharging a
carburized product therefrom, a gas feed inlet, a gas exhaust
outlet, and being inclineable to provide a downward slope
thereof;
a raw material feeding means communicating with said upper
opening;
a product collecting means communicating with said lower
opening;
a rotary hollow cylinder of graphite or carbonaceous material
having a large ratio of length to diameter, tubular supporting
member means of graphite or carbonaceous material arranged in said
enclosing casing, said rotary hollow cylinder being rotatably
mounted on said supporting member means and having means to receive
said raw material from said raw material feeding means and to
discharge said carburized product to said product collecting
means;
an elongated heating core of graphite or carbonaceous material
fixedly positioned substantially coaxially at the center of said
rotary cylinder;
means for supplying electric power to said heating core and
connected with the end of said heating core;
drive means for rotating said rotary hollow cylinder; and
a heat insulating material arranged round said rotary hollow
cylinder
2. The rotary furnace according to claim 1, wherein said supporting
member means is a fixed hollow cylinder of graphite or carbonaceous
material having a slightly larger diameter than said rotary hollow
cylinder, the inner periphery of said fixed hollow cylinder being
in contact with the outer periphery of said rotary hollow cylinder,
and said fixed hollow
3. The rotary furnace according to claim 2, wherein said rotary and
fixed hollow cylinders have holes therein, and said raw material is
fed to said
4. The rotary furnace according to claim 2, wherein said fixed
hollow
5. The rotary furnace according to claim 1, wherein said gas feed
inlet is provided at the product discharge end of said casing, and
said gas exhaust
6. The rotary furnace according to claim 1, wherein said raw
material
7. The rotary furnace according to claim 1, wherein said electric
power supplying means is a bus bar fixed by an insulator and
supported by a
8. The rotary furnace according to claim 1, wherein said drive
means
9. The rotary furnace according to claim 8, wherein said gear
mechanism comprises a plurality of gears and shafts supported by
carbon bearings, one of said shafts being air-tightly connected to
a power source outside said enclosing casing.
Description
BRIEF SUMMARY OF THE INVENTION
This invention relates to a furnace for carburization, and more
particularly it is concerned with a rotary furnace for
carburization, which is suitable for the production of carbides of
elements of Groups IV-A, V-A and VI-A of Periodic Table, actinide
elements, boron and silicon.
Various attempts to produce carbides of the kind by gaseous
cementation have hiterto been made, but have proven unsatisfactory
on an industrial scale. Only the method has been put to practical
use wherein a powdered metal or metal oxide is mixed with a
carbonaceous powder such as carbon black by means of a ball mill
and, optionally after formed into a certain size by a press, the
mixture is then charged in a graphite boat and heated in hydrogen
or in vacuum. However, there is no choice but to do employ batch
production by use of this method. Furthermore, this method has a
disadvantage that, since the reaction of forming these carbides is
accompanied by the generation of heat, an abnormal generation of
heat takes place in the lower portion of the boat, resulting in a
localized grain growth, and the degree of cementation differs
between the upper portion and lower portion of the boat in the
carburization in hydrogen, being accompanied by cementation,
resulting in unevenness of the quantity of carbon combined. In
order to solve this disadvantage, it is necessary to advance the
reaction in a continuous manner with agitation of the
reactants.
To this end, the use of rotary furnaces is recommended, but those
used in the cement manufacturing industry or for the hydrogen
reduction of tungsten oxide cannot resist high temperatures such as
required for the production of the foregoing carbides. There is
nothing but carbon as a material for the rotating tube used in a
protective atmosphere such as hydrogen gas at a high temperature of
up to 2,000.degree.C. Carbon materials, however, are porous so that
leakage of hydrogen gas occurs as a troublesome problem. The
heating system of carbon materials, in addition, requires a large
electric current and large slidable contacts. Therefore, rotation
of the furnace itself is very difficult. Since carbon has such a
high thermal conductivity that, when the temperature of the central
portion of a carbon tube is raised to 800.degree.-2,200.degree. C,
the end portion thereof will also be of a high temperature, and
even bearings in the furnace system have to be resistant to high
temperatures.
It is an object of the present invention to provide a rotary
furnace for carburization, whereby the above mentioned
disadvantages of the prior art are overcome.
It is another object of the invention to provide a rotary furnace
for carburization, whereby carbides with a uniform composition and
very narrow grain size distribution are produced continuously.
It is a further object of the invention to provide a process for
the production of carbides by the use of this furnace for
carburization.
Still more objects will be apparent from the following detailed
description .
BRIEF DESCRIPTION OF THE DRAWING
The accompanying drawings are to illustrate the principle and
merits of the invention in more detail.
FIG. 1 shows schematically one form of the rotary furnace for
carburization according to the invention.
FIG. 2 shows a cross sectional view of the furnace of FIG. 1 at the
central portion thereof.
Located at the center of furnace body 18 is heating core 1, around
which rotating cylinder 10 and fixed cylinder 11 are arranged.
FIG. 3 shows a dispersion of the quantity of carbon in tungsten
carbide powder carburized by the prior art furnace.
DETAILED DESCRIPTION OF THE INVENTION
It has been found as a result of various studies that the foregoing
objects can be accomplished by providing a fixed, rod-shaped or
tubular heating core of graphite or carbonaceous material in the
center of a furnace for carburization and arranging a rotating
cylinder having a graphite or carbonaceous material inner surface
coaxially around such heating core.
That is to say, there is the provision of a rotary furnace for
carburization, which comprises a rod-shaped or tubular heating core
of graphite or carbonaceous material fixedly positioned in the
central portion of the furnace, a rotary cylinder having an inner
wall of graphite or carbonaceous material and positioned to rotate
coaxially around the heating core, and a casing provided with means
for rotatably supporting the rotary cylinder, an opening for
feeding a raw material, means for supplying electric power, an
opening for discharging a product and a gas flow opening and being
constructed to maintain an atmosphere of carburization within the
furnace. The most important aspect of this furnace lies in that
rotation of the rotary cylinder is independent of the fixed heating
core and, consequently, sliding electrical contacts are
unnecessary. Since the furnace is of an internal heating type, an
outer wall for shielding hydrogen gas can be kept at normal
temperature by inserting a heat insulating material between the
inner and outer walls, and the problems of insulating materials can
thus be solved.
In accordance with the second feature of the invention, the
rotating cylinder is modified into a double structure of a rotating
cylinder and fixed cylinder. In this case, the furnace comprises a
rod-shaped or tubular heating core of graphite or carbonaceous
material fixedly positioned in the central portion of the furnace,
a rotary cylinder having an inner wall of graphite or carbonaceous
material and positioned to rotate coaxially around the heating
core, a fixed cylinder fixedly positioned to surround the rotary
cylinder, and a casing provided with means for rotatably supporting
the rotary cylinder, means for fixedly supporting the fixed
cylinder, an opening for feeding a raw material, means for
supplying electric power, an opening for discharging a product, a
gas flow opening, and being constructed to maintain an atmosphere
of carburization with the furnace.
By these carburizing furnaces, carbides of high melting point
metals such as tungsten, titanium, tantalum, columbium, hafnium,
zirconium, vanadium, chromium and molybdenum having a substantially
stoichiometric amount of combined carbon and a very narrow grain
size distribution are economically produced from the high melting
point metals or oxides thereof. The features and merits of these
furnaces are summarized below:
1. Since rotation of the rotary section is independent of the fixed
heating core, slidable contacts for supplying electric power are
not necessary.
2. Since the furnace is of the internal heating type with a heating
core provided therein, it is relatively easy to maintain high
temperatures, the raw material is directly exposed to the heat
radiation from the heating core, and the furnace can be adapted for
the continuous production of hard carbides without the use of
expensive heat insulating materials.
3. Since the heating core is fixedly arranged in the central
portion of the furnace, the thermal efficiency is raised and a
large electric current can be supplied independently of the
rotating mechanism of the cylinder.
4. Since the cylinder is of a double structure of a rotary cylinder
and fixed cylinder, rotation of the cylinder can smoothly be
effected, and accordingly, feeding of powdered raw materials can be
carried out corresponding to movement of the powder in the
cylinder. Moreover, leakage of hydrogen gas can be prevented.
5. Since the cylinder is of a double structure, the furnace
structure is so simple that the driving mechanism is composed of
shafts only.
Reactants fed into the rotary furnace of the invention flow down
between the inner wall and the heating core little by little in the
form of powder or granules. The diameter of the heating core and
the inner diameter of the rotary cylinder may be varied with the
quantity of reactants and reaction temperature. When it is further
desired to increase the surface area of the heating core, it may be
tubular shaped. Moreover, the inclination of the furnace body may
be varied depending on the desired reaction speed.
The invention is further illustrated in the accompanying drawings.
With particular reference to FIG. 1, carbon heating core 1 is fixed
by copper electrode 2 and furnished with a large electric current
through bus bar 3, which is fixed by insulator 4 and supported by
metal fitting 5. Copper electrode 2 is cooled by water supplied by
conduit 8. Rotary cylinder or tube 10 is located coaxially around
heating core 1 and rotated within and in contact with fixed
cylinder or tube 11 and carbon ring 12. That is to say, rotary
cylinder or tube 10 is set by carbon ring 12 and moved in fixed
cylinder or tube 11. Fixed cylinder or tube 11 is positioned in the
center of the furnace by carbon disk 13. The driving mechanism of
rotary cylinder 10 consists of stainless steel gears 14 supported
by carbon bearings 15 and shafts 17 in gear box 16, the driving
being effected through shafts 17. The above mentioned mechanism is
enclosed in furnace body or casing 18. The space between fixed
cylinder 11 and furnace body 18 is filled with heat insulating
material 19 so that the temperature of the central portion may be
raised up to 2,200.degree.C. Hydrogen gas enters hydrogen inlet 20
and leaves from hydrogen outlet 21. Teflon 22 is used for the
purpose of insulation and preventing leakage of hydrogen from
around bus bar 3. Furnace body 18 is provided with cooling water
tube 23 on the outer surface thereof to prevent it from
overheating.
Referring to FIG. 2, carbon tube pyrometer 31 for measurement of
the outer surface temperature of rotary cylinder 10 is positioned
to extend through furnace body 18 and fixed cylinder 11. Furnace
body 18 is mounted on support frame 32 in such a manner that its
inclination may be varied in accordance with the desired reaction
speed.
In operation of this furnace for carburization, a raw material
powder is charged in hopper 24 from a feed opening (not shown) of
hopper cover 25 and moved downwardly by screw 26 upon rotation of
shaft 27. Then the raw material powder is fed to rotary cylinder 10
through a hole in fixed cylinder 11 when such hole aligns with a
hole formed in rotary cylinder 10. The powder is reacted while
flowing through cylinder 10, and the reacted powder is discharged
from discharge port 29 via receiver 28.
Using the rotary furnace for carburization according to the
invention, as illustrated above, various reactions for the
production of carbides are carried out and the following results
are obtained.
EXAMPLE 1
Using a rotary furnace of the invention (having no fixed cylinder),
tungsten carbide was produced by the following condition: Inner
diameter of rotary cylinder (graphite tube) 60 mm Outer diameter of
heating core (carbon) 30 mm Whole length of rotating part 2 m
Inclination of furnace body 4 .degree. Rotation Speed 6 rpm Flow
rate of hydrogen 10 l/min Electric power 20 KW
A mixed powder of tungsten and carbon was pressed in a mold and
crushed, and the resulting granule was continuously fed, while
keeping the furnace at 1,450.degree.C over about 60 cm, thus
obtaining continuously tungsten carbide with a uniform property at
a rate of 8 kg/hour.
EXAMPLE 2
Tungsten powder of 0.7.mu. was mixed with 6.25 % of carbon powder
in a ball mill and the granulated powder having a grain size
distribution of 1 mm to 0.02 mm was obtained. The resulting
granulated powder was subjected to carburization reaction by the
use of a rotary furnace for carburization according to the
invention as shown in FIGS. 1 and 2, to obtain WC powder. The
various conditions of the furnace are as follows:
Inner diameter of rotary cylinder 60 mm.phi. Outer diameter of
heating core 20 mm.phi. Whole length of rotating part 1500 mm
Inclination of furnace body 4 .degree. Rotation speed 2 rpm Flow
rate of hydrogen 15 l/min Electric power 10 KW Carburization
temperature 1400 .degree.C
The granulated powder was fed in the hopper and moved at a rate of
5 kg/hr continuously in the cylinder. The reaction proceeded
smoothly and the product was discharged as WC powder without
adhesion to the inner wall of the cylinder. No troubles occurred
when 1 ton of the product was produced.
In the case of carrying out the reaction using a carbon case in a
horizontal Tammann furnace according to the carburization method of
the prior art, there occurred a dispersion of the quantity of
carbon depending on the position in the boat, as shown in FIG. 3.
When the position in the carbon case was numbered to the flow of
hydrogen gas as follows:
Front upper 1 Center upper 4 Back upper 7 middle 2 middle 5 middle
8 lower 3 lower 6 lower 9
the quantity of carbon (% by weight) in the each position was as
tabulated below.
1 6.39 4 6.37 7 6.28 2 6.14 5 6.06 8 6.06 3 6.18 6 6.20 9 6.15
When carburization was continuously carried out using the furnace
of the invention, on the other hand, the fluctuation of carbon
quantity was much reduced as shown in Table 1.
Table 1 ______________________________________ Dispersion of carbon
quantity of WC power in rotary furnace for carburization TC (Total
Carbon) FC (Free Carbon) ______________________________________ 1
6.17 0.05 2 6.17 0.05 3 6.18 0.05 4 6.18 0.05 5 6.17 0.06 6 6.16
0.07 7 6.17 0.05 ______________________________________
Note: Sampling was carried out every 15 minutes.
EXAMPLE 3
Tungsten powder of 2.mu. was mixed with 6.25 % of carbon powder in
a ball mill, pressed in a mold under a pressure of 1 ton/cm.sup.2
and crushed to obtain a powder having a grain size distribution of
0.5 mm to 0.02 mm. The resulting powder was subjected to
carburization using the carburizing furnace of the invention under
the following conditions:
Inner diameter of rotary cylinder 80 mm.phi. Outer diameter of
heating core 20 mm.phi., rod-shaped Inclination of furnace body 6
.degree. Rotation speed of rotary cylinder 2 rpm Flow rate of
hydrogen gas 10 l/min Electric power 12 KW Carburization
temperature 1500 .degree.C
The reactants were fed to the furnace body from the hopper at a
rate of 10 kg/hr. The so obtained WC powder had a total quantity of
carbon of 6.19 % and free carbon of 0.06 %, and the grain size
distribution was much better than in the case of using a
carburizing furnace of the prior art.
To this WC powder was added 7 % of cobalt powder and mixed with
acetone for 100 hours in a ball mill having an inner diameter of
200 mm.phi. and cylinder length of 270 mm, followed by drying by
heating at 100 .degree.C. The resulting mixed powder was pressed in
a mold under a pressure of 1 ton/cm.sup.2 and sintered at 1,450
.degree.C for 1 hour in vacuum. The mechanical properties of the
resulting alloy are shown in Table 2:
Table 2
__________________________________________________________________________
SG H.sub.RA H.sub.V TRS 4.pi..sigma. H.sub.C WC powder of the
invention 14.90 91.2 1500 210 140 165 WC powder of the prior art
14.87 91.0 1475 170 140 160
__________________________________________________________________________
Note:
Sg = specific gravity
H.sub.ra = rockwell hardness, A scale
H.sub.v = vickers hardness
Trs = transverse rupture strength
4.pi..sigma. = saturated magnetisation quantity
H.sub.c = coercive force
From the WC powder produced by the prior art method and from the WC
powder produced by means of the carburizing furnace of the
invention alloys were respectively prepared and compared regarding
their properties. The latter is favourably compared with the former
in the fact that the grain size distribution of WC in the alloy is
better, abnormally grown WC crystals are less and the transverse
rupture strength is higher.
EXAMPLE 4
As in Example 3, tungsten powder of 5.mu. was mixed with 6.25
percent of carbon powder in a ball mill, pressed in a mold under a
pressure of 1 ton/cm.sup.2 and then crushed to obtain a powder
having a grain size distribution of 0.5 mm to 0.02 mm. The thus
size-controlled powder was subjected to carburization using the
carburizing furnace of the invention under the following
conditions:
Inner diameter of rotary cylinder 80 mm.phi. Outer diameter of
heating core 20 mm.phi. Inclination of furnace body 4 .degree.
Rotation speed of rotary cylinder 2 rpm Flow rate of hydrogen 10
l/min Electric power 18 KW Carburization temperature 2000
.degree.C
The reactants were fed to the furnace from the hopper at a rate of
10 kg/hr. The so obtained WC powder had a total carbon quantity of
6.23 % and free carbon quantity of 0.10 and the grain size
distribution was much better than in the case of using a
carburizing furnace of the prior art.
To this WC powder was added 10 % of cobalt powder and mixed with
acetone for 80 hours in a ball mill having an inner diameter of 200
mm.phi. and cylindrical length of 250 mm, followed by drying by
heating at 100 .degree.C. The resulting mixed powder was pressed in
a mold under a pressure of 1 ton/cm.sup.2 and sintered at 1,450
.degree.C for 1 hour in vacuum. The mechanical properties of the
resulting alloy are shown in Table 3.
Table 3
__________________________________________________________________________
SG H.sub.RA H.sub.V TRS 4.pi..sigma. H.sub.C WC powder of the
invention 14.60 87.0 1100 300 196 70 WC powder of the prior art
14.60 86.5 1080 270 190 65
__________________________________________________________________________
From the WC powder produced by the prior art method and from the WC
powder produced by means of the carburizing furnace of the
invention alloys were prepared respectively and compared regarding
their properties. The latter is favourably compared with the former
in the fact that the grain size distribution of WC in the alloy is
better, abnormally grown WC crystals are less and the transverse
rupture strength is higher.
EXAMPLE 5
Tungsten oxide (WO.sub.3) powder of 0.2.mu. was mixed with 16 % by
weight of carbon powder and 2 % by weight of stearic acid in a ball
mill, pressed in a mold under a pressure of 1 ton/cm.sup.2 and then
crushed to give a powder having a grain size distribution of 2 mm
to 0.2 mm. The resulting powder was subjected to carburization in
two steps by the use of the rotary carburizing furnace of the
invention. The first step was carried out at 1,400 .degree.C in
nitrogen and the second step, at 1,800 .degree.C in hydrogen.
Various conditions of the furnace are shown in Table 4.
Table 4
__________________________________________________________________________
First step Second step carburization carburization
__________________________________________________________________________
Inner diameter of 60 mm.phi. 80 mm.phi. rotary cylinder Heating
core rod-shaped tubular heating core heating core Dimension of
heating 20 mm.phi. .times. 1700 30mm.phi. .times. 20mm.phi. .times.
1700 core Inclination of furnace 6 .degree. 4 .degree. Rotation
speed 4 rpm 2 rpm Atmosphere N.sub.2 H.sub.2 Carburization
temperature 1400 .degree.C 1800 .degree.C
__________________________________________________________________________
The WC powder had a total carbon quantity of 6.32 % and free carbon
quantity of 0.20 % and a grain size of 1.mu. .
EXAMPLE 6
Hafnium oxide (Hf.sub.2 O.sub.5) powder of 0.2.mu. was mixed with
15 % by weight of carbon powder and 2 % by weight of stearic acid
in a ball mill, pressed under a pressure of 1 ton/cm.sup.2 and then
crushed to obtain a powder having a grain size of 1 mm to 0.1 mm.
The thus size-controlled powder was subjected to carburization in
two steps using the rotary furnace of the invention. The first step
was carried out at 1,600 .degree.C in argon and the second step, at
1,900 .degree.C in hydrogen. Various conditions of the furnace are
shown in Table 5.
Table 5
__________________________________________________________________________
First step Second step carburization carburization
__________________________________________________________________________
Inner diameter of 60 mm.phi. 80 mm.phi. rotary cylinder Heating
core rod-shaped tubular heating core heating core Inclination of
furnace 6 .degree. 4 .degree. Rotation speed 4 rpm 2 rpm Atmosphere
Ar H.sub.2 Carburization temperature 1600 .degree.C 1900 .degree.C
__________________________________________________________________________
The HfC powder had a total carbon quantity of 6.44 % and free
carbon quantity of 0.20 %, and a grain size of 1.mu. .
EXAMPLE 7
Titanium hydride (TiH.sub.2) powder was mixed with 21 % of carbon
and 5 % of stearic acid for 20 hours in a ball mill, pressed in a
mold and crushed to obtain a size-controlled powder having a grain
size distribution that 80 % consists of 10 meshes to 20 meshes. The
thus size-controlled powder was reacted at 1,200 .degree.C in
H.sub.2 atmosphere by means of the furnace as shown in Example 2.
Feeding of the powder was carried out in such a manner that the
thickness thereof did not exceed 5 mm in the cylinder. A TiC powder
with a combined carbon of 19.5 % was obtained without explosive
reaction in a yield of 98 %.
The thus obtained TiC powder was mixed with 10 % of nickel powder
and 10 % of molybdenum powder for 10 hours by means of a vibrating
mill using balls each having a diameter of 10 mm and being a cermet
ball and alcohol in an amount of two times the powder. The mixed
powder was pressed under a pressure of 2 tons/cm.sup.2 and sintered
at 1,375 .degree.C for 1 hour in a vacuum having a degree of vacuum
of 2 .times. 10.sup..sup.-4 to obtain an alloy having the following
characters:
Table 6 ______________________________________ SG H.sub.RA H.sub.V
TRS 4.pi..sigma. 5.55 91.9 1570 170 60
______________________________________
EXAMPLE 8
52 % of tungsten powder of 1.mu. and 30 % of titanium dioxide
(TiO.sub.2) powder of 0.2.mu. were mixed with 18 % of carbon powder
and 2 % of stearic acid for 1 hour by the use of a high speed
mixer. The mixture was pressed by a powder roller and passed
through a sieve to obtain a size-controlled powder having a grain
size distribution of 1.0 mm to 0.1 mm. The resulting
size-controlled powder was reacted at 2,000 .degree.C in hydrogen
using the rotary furnace of the invention under the following
conditions:
Table 7
__________________________________________________________________________
Inner diameter of rotary cylinder 150 mm.phi. Heating core tubular,
outer diameter 50 mm.phi. inner diameter 30 mm.phi. Whole length of
rotating part 3 m Inclination of furnace body 8 .degree. Rotation
Speed of cylinder 6 rpm Carburization temperature 1900 .degree.C
Electric power 30 KW
__________________________________________________________________________
Using the above mentioned furnace, a solid solution of (W.Ti)C was
produced at a rate of 20 kg/hr, having the following
composition.
Table 8
__________________________________________________________________________
TC FC CC O.sub.2 H.sub.2 N.sub.2 9.80 % 0.02 % 9.78 % 0.02 % 0.0003
% 0.0002 %
__________________________________________________________________________
From the resulting solid solution (W.Ti)C and WC powder of 2.mu.
obtained in Example 3 a cemented carbide was prepared by the
following recipe:
Table 9 ______________________________________ Blending composition
2 .mu. WC 50 % by weight (W.Ti)C solid solution 40 do. cobalt
powder 10 do. ______________________________________
The foregoing composition was ball-milled for 100 hours and
sintered by holding at 1,450 .degree.C for 1 hour in a high vacuum
furnace. At the same time, another cemented carbide was prepared
from WC and (W.Ti)C solid solution type carbide obtained by the
prior art method. Comparison of their cutting properties was
carried out by the following cutting test:
Workpiece Cr-Mo steel, hardness H.sub.B 250
Cutting speed 110 m/min, feed 0.54 mm/rev, depth of cut 2 mm
As a result of this test it was found that our cemented carbide had
a life of about 1.3 times as long as the comparative cemented
carbide, such life being that continued until the Flank wear
reached 0.3 mm.
EXAMPLE 9
30 % of tungsten powder, 22 % of tantalum oxide (Ta.sub.2 O.sub.5)
powder and 30 % of titanium dioxide (TiO.sub.2) powder were mixed
with 18 % of carbon powder for 1 hour by means of a high speed
mixer. The mixture was granulated by a pan type granulator while
spreading acetone thereon. The thus granulated powder was subjected
to carburization under the following conditions:
Inner diameter of rotary cylinder 150 mm.phi. Heating core 80
mm.phi. .times. 60 mm.phi. .times. 2500 Inclination of furnace body
10.degree. Rotation speed 2.5 rpm Flow rate of hydrogen 20 l/min
Carburization temperature 1900 .degree.C
The granulated powder was fed to the furnace in such a manner that
the thickness thereof equaled 10 mm and stirring was adequately
carried out to complete the reaction. The charge was processed at a
rate of 15 kg/kr thus to obtain a complete solid solution of
(W.Ti.Ta)C. The carbide of such solid solution type was well
available as a raw material of cemented carbides.
EXAMPLE 10
Chromium oxide (Cr.sub.2 O.sub.3) powder was mixed with 26 % of
carbon powder and 2 % of stearic acid in a ball mill, pressed under
a pressure of 1 ton/cm.sup.2 and crushed to obtain a powder having
a grain size distribution of 2 mm to 0.2 mm. The thus
size-controlled powder was subjected to carburization by the rotary
furnace of the invention at 1,500 .degree.C in hydrogen. The
conditions of the furnace are as follows:
Inner diameter of rotary cylinder 80 mm.phi. Outer diameter of
heating core 20 mm.phi. Inclination of furnace body 6 .degree.
Rotation speed 2 rpm Flow rate of hydrogen 10 l/min Electric power
12 KW Carburization temperature H.sub.2, 1500 .degree.C
Thus a Cr.sub.2 O.sub.3 powder with a quantity of carbon combined
of 12 % was given.
EXAMPLE 11
Columbium oxide (Cb.sub.2 O.sub.5) powder and 24 % of carbon powder
were ball-milled, pressed and crushed to obtain a controlled grain
size. The resulting powder was heated at 1,500 .degree.C in
hydrogen by the use of the rotary furnace of the invention to give
a CbC powder with a theoretical amount of carbon, TC 11.50 % and FC
0.05 %. The conditions of the furnace are as follows:
Inner diameter of rotary cylinder 80 mm.phi. Heating core rod
shaped, 20 mm.phi. Inclination of furnace body 4 .degree. Rotation
speed 1 rpm Flow rate of hydrogen 5 l/min Whole length of rotating
part 3 m The furnace, yielding the product at a rate of 5 kg/hr,
was fit for use as a rotary furnace on a commercial scale.
EXAMPLE 12
Tantalum oxide (Ta.sub.2 O.sub.5) powder and 16 % of powder were
ball-milled, pressed and crushed to obtain a controlled grain size.
The resulting powder was heated at 1,700 .degree.C in hydrogen by
the use of the rotary furnace of the invention to give a TaC powder
with a theoretical amount of combined carbon, TC 6.30 % and FC 0.11
%. The conditions of the furnace are as follows:
Inner diameter of rotary cylinder 80 mm.phi. Heating core
rod-shaped, 20 mm.phi. Inclination of furnace body 6 .degree.
Rotation speed 2 rpm Flow rate of hydrogen 5 l/min Whole length of
rotating part 3 m
The furnace, yielding the product at a rate of 5 kg/hr, was fit for
use as a rotary furnace on a commercial scale.
EXAMPLE 13
Vanadium oxide (V.sub.2 O.sub.5) powder and 29 % carbon powder were
ball-milled, pressed and crushed to obtain a controlled grain size.
The resulting powder was heated at 2,100 .degree.C in hydrogen by
the use of the rotary carburizing furnace to give a V.sub.4 C.sub.3
powder with a theoretical amount of carbon, TC 19.00 % and FC 4.02
%. The conditions of the furnace are as follows:
Inner diameter of rotary cylinder 80 mm.phi. Heating core tubular,
30 mm.phi. Inclination of furnace body 4 .degree. Rotation speed 2
rpm Flow rate of hydrogen 5 l/min Whole length of rotating part 3
m
The furnace, yielding the product at a rate of 3 kg/hr, was fit for
use as a rotary furnace on a commercial scale.
EXAMPLE 14
Zirconium oxide (ZrO.sub.2) and 23 % of carbon powder were
ball-milled, pressed and pulverized to obtain a controlled grain
size. The resulting powder was heated at 2,100 .degree.C in
nitrogen by the use of the rotary furnace of the invention to give
a ZrC powder with TC 11.30 % and FC 0.20 %. The conditions of the
furnace are as follows:
Inner diameter of rotary cylinder 100 mm.phi. Heating core tubular,
40 mm.phi. Inclination of furnace body 4 .degree. Rotation speed 3
rpm Flow rate of nitrogen 5 l/min Whole length of rotating part 3
m
The furnace, yielding the product at a rate of 7 kg/hr, was fit for
use as a rotary furnace on a commercial scale.
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