U.S. patent application number 13/130687 was filed with the patent office on 2011-10-13 for method for producing cemented carbide or cermet products.
This patent application is currently assigned to SECO TOOLS AB. Invention is credited to Per Jonsson, Regina Lundell, Mattias Puide.
Application Number | 20110248422 13/130687 |
Document ID | / |
Family ID | 42198362 |
Filed Date | 2011-10-13 |
United States Patent
Application |
20110248422 |
Kind Code |
A1 |
Lundell; Regina ; et
al. |
October 13, 2011 |
METHOD FOR PRODUCING CEMENTED CARBIDE OR CERMET PRODUCTS
Abstract
The present invention relates to a method for the production of
tungsten carbide based cemented carbide or cermet tools or
components using the powder injection moulding or extrusion method
comprising mixing of granulated cemented carbide or cermet powder
with an organic binder system whereby the mixing is made by adding
all the constituents into a mixer heated to a temperature above the
melting temperature of the organic binders. According to the
invention the organic binders are added into the mixer, waiting for
a melt to form and then slowly adding the cemented carbide or
cermet powder into the melt, making sure the temperature does not
fall below the melting temperatures of the organic binders.
Inventors: |
Lundell; Regina; (Norberg,
SE) ; Jonsson; Per; (Fors, SE) ; Puide;
Mattias; (Vasteras, SE) |
Assignee: |
SECO TOOLS AB
Fagersta
SE
|
Family ID: |
42198362 |
Appl. No.: |
13/130687 |
Filed: |
November 18, 2009 |
PCT Filed: |
November 18, 2009 |
PCT NO: |
PCT/SE09/51307 |
371 Date: |
June 23, 2011 |
Current U.S.
Class: |
264/128 |
Current CPC
Class: |
B22F 2998/00 20130101;
C22C 1/051 20130101; B22F 2998/00 20130101; B22F 3/225 20130101;
C22C 29/08 20130101; B22F 2998/00 20130101; B22F 3/20 20130101 |
Class at
Publication: |
264/128 |
International
Class: |
D04H 1/60 20060101
D04H001/60; B22F 3/00 20060101 B22F003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 21, 2008 |
SE |
0802439-0 |
Claims
1. Method for the production of tungsten carbide based cemented
carbide or cermet tools or components using the powder injection
moulding or extrusion method comprising mixing of granulated
cemented carbide or cermet powder with an organic binder system
acting as a carrier for the powder whereby the mixing is made by
adding all the constituents into a mixer heated to a temperature
above the melting temperature of the organic binders characterised
in that the organic binders are added into the mixer, waiting for a
melt to form and then slowly adding the cemented carbide or cermet
powder into the melt, making sure the temperature does not fall
below the melting temperatures of the organic binders.
2. Method according to claim 1 characterised in that the mixing is
performed in a batch mixer.
3. Method according to claim 1 characterised in that the mixing is
performed in an extruder.
4. Method according to claim 3 characterised in that the extruder
is a twin screw extruder.
Description
[0001] The present invention relates to a method for the production
of tungsten carbide based or cermet hard metal tools or components
using the powder injection moulding or extrusion method and a
method for producing a binder system therefore.
[0002] Hard metals based on tungsten carbide are composites
consisting of small (.mu.m-scale) grains of at least one hard phase
in a binder phase. These materials always contain the hard phase
tungsten carbide (WC). In addition, other metal carbides with the
general composition (Ti, Nb, Ta, W) C may also be included, as well
as metal carbonitrides, e.g., Ti (C, N). The binder phase usually
consists of cobalt (Co). Other binder phase compositions may also
be used, e.g., combinations of Co, Ni, and Fe, or Ni and Fe.
[0003] Industrial production of tungsten carbide based hard metals
often includes blending of given proportions of powders of raw
materials and additives in the wet state using a milling liquid.
This liquid is often an alcohol, e.g. ethanol or water, or a
mixture thereof. The mixture is then milled into a homogeneous
slurry. The wet milling operation is made with the purpose of
deagglomerating and mixing the raw materials intimately. Individual
raw material grains are also disintegrated to some extent. The
obtained slurry is then dried and granulated, e.g. by means of a
spray dryer. The granulate thus obtained may then be used in
uniaxial pressing of green bodies or for extrusion or injection
moulding.
[0004] Injection moulding is common in the plastics industry, where
material containing thermoplastics or thermosetting polymers are
heated and forced into a mould with the desired shape. The method
is often referred to as Powder Injection Moulding (PIM) when used
in powder technology. The method is preferably used for parts with
complex geometry.
[0005] In powder injection moulding of tungsten carbide based hard
metal parts, four consecutive steps are applied:
[0006] 1. Mixing of the granulated cemented carbide powder with a
binder system. The binder system acts as a carrier for the powder
and constitutes 25-60 volume % of the resulting material, often
referred to as the feedstock. The exact concentration is dependent
on the desired process properties during moulding. The mixing is
made by adding all the constituents into a mixer heated to a
temperature above the melting temperature of the organic binders.
The resulting feedstock is obtained as pellets of approximate size
4.times.4 mm.
[0007] 2. Injection moulding is performed using the mixed
feedstock. The material is heated to 100-240.degree. C. and then
forced into a cavity with the desired shape. The thus obtained part
is cooled and then removed from the cavity.
[0008] 3. Removing the binder from the obtained part. The removal
can be obtained by extraction of the parts in a suitable solvent
and/or by heating in a furnace with a suitable atmosphere. This
step is often referred to as the debinding step.
[0009] 4. Sintering of the parts. Common sintering procedures for
cemented carbides are applied.
[0010] Extrusion of the feedstock comprises steps 1, 3 and 4 above.
Instead of forcing the feedstock into a cavity of the desired
shape, the feedstock is continuously forced through a die with the
desired cross section.
[0011] The solids loading, .phi., of the feedstock is the
volumetric amount of hard constituents, compared to the organic
constituents. .phi. can be calculated using the following
equation:
.phi. = .rho. f - .rho. v .rho. s - .rho. v ##EQU00001##
where .rho..sub.S is the density of the cemented carbide as
sintered, .rho..sub..nu. is the mean density of the organic
constituents and .rho..sub.f is the density of the feedstock,
measured with a helium pycnometer.
[0012] When mixing the hard constituents with the organic binders,
it is a common problem that a part of the organic binder does not
spread properly in the feedstock. Instead, a small part of the
organic binder forms particles, considerably larger than the grain
size of the hard constituents, i.e. in the range of 10-30 .cndot.m.
During the debinding of the green body, these particles will be
removed, leaving pores in the structure. A common way to remove
these pores is to use sintering with applied hydrostatic pressure
of Ar, i.e., Sinter-HIP:ing. When using sinter-HIP:ing, the pores
will be filled with the metallic binder phase if the pores have no
physical connection with the applied pressure. Pores close to the
surface of the green body will instead collapse to form surface
pores, as will pores located directly in the surface of the green
body. The pores in the surface will severely decrease the
macroscopic mechanical strength of the sintered material. The
metallic binder filled former pores in the bulk of the material
will decrease the mechanical strength of the sintered material as
well. Another common problem in case of the particles of organic
binders being large, i.e. in the range of 20-30 .cndot.m, these
particles will pyrolyse with a too fast development of gases during
the debinding step, forming blisters in the material structure.
[0013] It is an object of the present invention to solve these
problems.
[0014] FIG. 1 shows a LOM, light optical micrograph, with a
magnification about 1000x of the microstructure of a cemented
carbide according to prior art.
[0015] FIG. 2 shows a LOM, light optical micrograph, with a
magnification about 1000x of the microstructure of a cemented
carbide according to the invention.
[0016] It has now surprisingly been found that by adding the
organic binders into the mixer, waiting for a melt to form and then
slowly adding the hard constituents into the melt, making sure the
temperature does not fall below the melting temperatures of the
organic binders, no organic binder particles are formed and the
abovementioned problems can be solved.
[0017] The method according to the present invention comprises the
following steps:
[0018] 1) Wet milling of the raw materials in water or alcohol, or
a combination thereof, preferably 80 wt-% ethanol and 20 wt-%
water, together with 0.1-1.2 wt-%, preferably 0.25-0.55 wt-%
carboxylic acid, preferably stearic acid as a granulating agent for
the subsequent drying. More carboxylic acid is required the smaller
the grain size of the hard constituents.
[0019] 2) Drying of the slurry formed during the above mentioned
wet milling process step.
[0020] 3) Mixing the dried powder by kneading with a binder system,
consisting of 30-60 wt-% olefinic polymers, 40-70 wt-% waxes and to
a solids loading of .phi.=0.54-0.56. The mixing is performed in a
batch mixer or a twin screw extruder. When using a batch mixer, the
organic binders are added first to the heated mixer. The polymers
are added first and then the waxes. When a melt is formed, the
powdered hard constituents are slowly added, making sure the
temperature does not fall below the melting temperatures of the
organic binders. When a twin screw extruder is used for the mixing,
the organic binders are added in the beginning of the screw and the
powdered hard constituents are added by side feeders, making sure
the powders are mixed into a melt and also making sure the
temperature does not fall below the melting temperature of the
organic binders. The powdered hard constituents can be added
through several side feeders along the twin screw extruder or the
material can be run through the twin screw extruder several times
to make sure the temperature does not fall below the melting
temperature of the organic binders. Alternatively, the powdered
hard constituents are pre heated before being added to the molten
organic binder to make sure that the temperature does not fall
below the melting temperature of the organic binders. The material
is then formed into pellets with a size of approximately 4.times.4
mm.
[0021] 4) Injection moulding of the feedstock in a conventional
injection moulding machine. Alternatively, the feedstock is
extruded in a single screw, twin screw or plunge type extruder. The
material is heated to 100-240.degree. C., preferably
140-160.degree. C., and then, in the case of injection moulding,
forced into a cavity with the desired shape. In extrusion, the
material is forced through a die with the desired cross section.
The part obtained in injection moulding is cooled and then removed
from the cavity. The extrudates are cut in pieces of desired
length.
[0022] 5) Debinding the obtained part. The debinding is performed
in two steps.
[0023] 5a) By extraction of the wax and petroleum jelly in an
apolar solvent, at 31-70.degree. C., preferably at 31- 55.degree.
C. It is within the purview of the skilled artisan to determine by
experiments the conditions necessary to avoid the formation of
cracks and other defects according to this specification.
[0024] 5b) By heating in a furnace, preferably in a flowing gaseous
medium atmosphere at 2 mbar to atmospheric pressure up to
450.degree. C. It is within the purview of the skilled artisan to
determine by experiments the conditions necessary to avoid the
formation of cracks and other defects according to this
specification.
[0025] 6) Presintering of the part in the debinding furnace in
vacuum at 900-1250.degree. C., preferably at about 1200.degree.
C.
[0026] 7) Sintering of the parts using conventional sintering
technique.
[0027] The invention can be used for all compositions of cemented
carbide and all WC grain sizes commonly used as well as for
titanium carbonitride based materials.
[0028] In one embodiment the WC or Ti (C, N) grain size shall be
0.2-1.5 .mu.m with conventional grain growth inhibitors.
[0029] In another embodiment the WC or Ti (C, N) grain size shall
be 1.5-4 .mu.m.
Example 1
[0030] A WC-13 wt-% Co submicron cemented carbide powder was made
by wet milling 780 g Co-powder (OMG extra fine), 38.66 g
Cr.sub.3C.sub.2 (H C Starck), 5161 g WC (H C Starck DS80), 20.44 g
W metal powder, 16 g Fisher-Tropsch wax (Sasol H1) and 22 g stearic
acid in 1.6 1 milling liquid consisting of ethanol and water (80:20
by weight) for 40 h. The stearic acid is added in this stage of the
process to work as a granule forming agent, when spray drying the
slurry. The resulting slurry was spraydried to a granulated
powder.
Example 2 (Comparative)
[0031] The powder made in Example 1 was mixed by kneading 2500 g
powder from Example 1 with 50.97 g Polypropylene-polyethylene
copolymer (RD360 MO, Borealis) and 50.97 g Paraffin wax (Sasol Wax)
in a Z-blade kneader mixer (Werner & Pfleiderer LUK 1, 0). The
Z-blade kneader was heated to 170.degree. C and the raw material
was added. The mixer was run until a smooth viscous feedstock
developed. This resulted in a feedstock with a density of 8.23
g/ml, corresponding to a .phi. of 0.553.
Example 3 (Invention)
[0032] The powder made in Example 1 was mixed by kneading 2500 g
powder from Example 1 with 50.97 g Polypropylene-polyethylene
copolymer (RD360 MO, Borealis) and 45.87 g Paraffin wax (Sasol Wax)
and 5.06 g petroleum jelly (Merkur VARA AB) in a Z-blade kneader
mixer (Werner & Pfleiderer LUK 1, 0). The Z-blade kneader was
heated to 170.degree. C and the organic binders were added to the
mixer. The polymer was added first and then the waxes. When a melt
was formed, the powdered hard constituents were slowly added,
making sure the temperature did not fall below the melting
temperatures of the organic binders. The mixer was run until a
smooth viscous feedstock developed. This resulted in a feedstock
with a density of 8.23 g/ml, corresponding to a .phi. of 0.553.
Example 4 (Comparative)
[0033] The feedstock made in example 2 was fed into an injection
moulding machine (Battenfeld HM 60/130/22). The machine was used
for the injection moulding of a Seco Tools Minimaster 10 mm endmill
green body.
Example 5 (Invention)
[0034] The feedstock made in example 3 was fed into an injection
moulding machine (Battenfeld HM 60/130/22). The machine was used
for the injection moulding of a Seco Tools Minimaster 10 mm endmill
green body.
Example 6 (Comparative)
[0035] The parts from example 4 were debound by extraction and
sintered in a Sinter-HIP furnace (PVA COD733R) at 1420.degree. C.
with a total soaking time of 60 min. After 30 min at the peak hold
temperature, the furnace pressure was raised to 3 MPa Ar.
[0036] After sintering, the parts were cut for inspection. The
parts from example 4 were free from carbon pores, eta-phase and
pores, i.e. A00 B00 C00 according to ISO 4505. The parts showed
Co-lakes and open surface pores. See FIG. 1.
Example 7 (Invention)
[0037] The parts from example 5 were debound by extraction and
sintered in a Sinter-HIP furnace (PVA COD733R) at 1420.degree. C.
with a total soaking time of 60 min. After 30 min at the peak hold
temperature, the furnace pressure was raised to 3 MPa Ar.
[0038] After sintering, the parts were cut for inspection. The
parts from example 5 were free from carbon pores, cracks, eta-phase
and pores, i.e. A00 B00 C00 according to ISO 4505. There were no
surface pores and the microstructure showed an even cobalt
distribution. See FIG. 2.
* * * * *