Advances in Binder-Treatment Technology
Sydney H. Luk
Hoeganaes Corporation, Cinnaminson, New Jersey USA
Abstract – The use of binder-treated premixes has grown dramatically since the introduction of the technology in the late
1980’s. Decreased levels of respirable dust coupled with reduced amounts of alloy addition segregation and significantly
improved powder flow have helped to stimulate this growth. More recently, binder-treated premixes have been developed
that significantly enhance the green strength of P/M parts. The higher green strength results in more robust green parts for
handling prior to the sintering operation and reduced levels of green scrap. In addition, the significantly higher green
strength provides the opportunity for “green” machining of the P/M parts prior to sintering. This paper will discuss recent
advances in binder-treatment technology and will review production experience with binder-treated premixes.
KEYWORDS: BINDER, PREMIX, BONDING, GREEN STRENGTH, SEGREGATION, DIMENSIONAL
TOLERANCE, POWDER FLOW, BONDING MECHANISM, WEIGHT CONTROL, DUST RESISTANCE
I. INTRODUCTION
The benefits of binder-treated mixes are well
recognized in the P/M industry in terms of substantial
improvements in flowability, segregation resistance,
green strength and compressibility1, 2.3. More recently,
developments in the technology have led to an even
stronger capacity to bond elemental powders such as
copper and high contents of alloying additives such as
graphite and nickel in excess of 4 w/o. Using a systems
approach to optimize the binder chemistry and premixing
process, the green strength of bonded mixes has been
improved over 50%4,5.
II. BACKGROUND
The original binder-treated premix, ANCORBOND®,
was developed in the late 1980’s and the binder acted
solely as a binder. The binder did improve die fill or
flowability and reduced segregation of the fines. It did not
exhibit lubricity enhancements measured in terms of the
pressure required to strip and slide parts out from a die.
Being an elemental “glue”, the binder actually reduced
the internal lubricity required for particle packing and
particle deformation during the compaction process. The
second generation of binder-treated premixes utilized a
binder that also acted as an internal lubricant. This binder
lubricant treatment reaped the benefits of the original
treatment while adding to it increased compressibility,
and equivalent or better lubricity. The third generation of
binder-treated premixes incorporated a systems approach
to develop ANCORDENSE® or warm compaction
technology5 based on a high temperature lubricant. The
main impact on parts manufacturing is higher
compressibility and higher green strength. With a green
strength approaching 4000 psi (27.6 MPa), parts can be
machined in the green state.
The latest generation, ANCORBOND® Plus
engineered materials, is designed for conventional
compaction to provide higher green strength and the
possibility for green machining. This advanced bonding
mechanism also provides better dimensional control in
the green state through better distribution of the alloying
additives. Binder treated premix can improve the ability
to maintain very narrow dimensional tolerance on
complex shape parts such as gears, cams, and multilevel
parts.
III. Bonding Mechanisms
The segregation of fine powder and efforts to simulate
the segregation pattern are well known7. Bonding of
fines to coarse particles will reduce segregation. The
bonding of powders having different chemistry, particle
size and shape is a very delicate and sensitive science.
The resultant properties of binder treated mixes are
heavily dependent on the processing and bonding agents
used. Not all binders are created equal. Some have
extremely good bonding capability but no lubricating
quality. This results in loss of compressibility and
increased ejection force. Some have good lubricating
quality but poor bonding capability. The ideal binder will
have good bonding capability during powder processing
and good lubrication quality during compaction and
ejection of the green compact. As the alloy additions are
mixed with the iron powder, many different bonding
mechanisms can be achieved with the ANCORBOND
process. As shown in Figure 1, there are different
bonding mechanisms and outcomes during the various
stages of bonding; some are desirable and others not.
Starting with a large iron particle, the ANCORBOND
process uses a binder system to bond the fines to the
particle surface. The fines can be fine irons, fine
lubricant particles, or alloying additives such as nickel,
copper, graphite and other ferroalloys.
The different mechanisms are:
a) The binder wets the fines preferentially and forms
sizable agglomerates. This could be copper
agglomerates or graphite balls. During sintering,
these will form large pores resulting in lower sintered
densities. The agglomerates can also induce
localized growth, surface pitting, and dimensional
tolerance problems.
b) The binder wets the iron powder and bonds the fines
evenly around the iron particle. This is the preferred
state, which evenly distributes the alloying additives
and improves dimensional tolerances.
c) The binder bonds the fines in such a way that
spherical shape iron agglomerate is formed. The
rounded agglomerates results in better packing
within the die cavity. They also improve
compressibility and dimensional tolerancing.
Some mechanisms will result in deteriorated green and
sintered properties. These problems can stem from an
inadequate binder in terms of process capability, capacity
to bond, preferential attraction towards certain particles,
viscosity, or the binder’s ability to distribute and wet
surfaces. The second (b) and third (a) mechanisms
illustrated in the diagram would obviously be the most
effective in achieving properties such as segregation
resistance, flowability, and homogeneity. The coupling
of this processing knowledge with the engineered binder
systems used in this study contributes to the enhancement
in properties relative to conventionally processed
premixes.
B in d e r
(F e , C u , N i, C r, L u b e )
F e
(a )
(b )
(c)
F e
FF e e
F e
Figure 1 (a-c): Bonding Mechanisms involving
alloying additives, lubricants and iron powders in the
ANCORBOND process.
IV. Experimental Procedure
All the premixes were made from the same lot of
iron powder (Ancorsteel 1000B). The 123 nickel was
from INCO, 8081 copper was from ACuPowder
International, Acrawax C was from Lonza Inc., and the
3203HS graphite was from Asbury Graphite Mills. To
evaluate the green and sintered properties, transverse
rupture strength (TRS) bars were prepared according to
ASTM B 312. The reported values are the average of
three bars. The TRS bars in the Ancorsteel 45P studies
were pressed at a nominal 63°C (145°F) die temperature
to a pressure of 415, 550 and 690 MPa, (30, 40 and 50
tsi). The bars were sintered at 2050°F (1120°C) for 30
minutes in an atmosphere of 75v/o/25v/o N2. The
tabulated data in the Part Fabrication section was
produced and compiled using a 220-ton Cincinnati press
at the Technical Center of Cincinnati Incorporated.
Additional data were generated at the Hoeganaes R&D
Laboratory.
V. Ancorsteel 45P
The higher green strength and higher green density
achievable in green compacts is becoming more critical in
making robust green compacts. Ancorsteel 45P was the
premix compositions chosen for this study. The total
content of binder plus lubricant, in each mix was kept
constant at 0.75 w/o. In each case, an unbonded regular
premix with 0.75 w/o Kenolube was used as the
reference. The first generation ANCORBOND, improved
ANCORBOND, and ANCORBOND Plus products,
referenced in this paper as Mix A, Mix B and Mix Plus,
respectively. ANCORBOND Plus is a new-engineered
binder-treated material system with no zinc content. It is
aimed at increasing the green and sintered density for the
conventional compaction process with the additional
benefit of a 100% increase in green strength. The
advantage of such high green strength is the possibility of
green machining without resorting to warm compaction8.
Experience has shown that a green strength of 27.6 MPa
(4000 psi) is needed for green machining. High green
strength is also required to eliminate green cracks due to
handling and excessive ejection stresses. Ancorsteel 45P
(atomized iron powder + 0.45 w/o phosphorus) green
properties are shown in Table I. It exemplify the
capability of enhancing green strength and green density
with the improved ANCORBOND (Mix B) and
ANCORBOND PLUS (Mix Plus). The two reference
mixes are the original ANCORBOND (mix A) and
unbonded premix with 0.75% Kenolube. The higher
compressibility of the new system extends the capabilities
of existing compaction press. The green strength of
mixes B and Plus are 50-55% and 85-122% higher than
the reference premix and mix A. Mixes B and Plus
exhibit the better compressibility than the other mixes, up
to 0.09 g/cm³ at higher compaction pressures. At low
compaction pressures, the ejection characteristics of
mixes B and Plus are better than the reference premix
having the high performing Kenolube. At higher
compaction pressures, the data suggests a division in
ejection among the mixes. In regard to the higher
compaction pressure ejection characteristics, the
reference premix is similar to the Plus mix. The Plus mix
and reference premix displays better lubricity than mixes
A and B.
Table I: Green Properties of Ancorsteel 45P Mixes
Mix
Mix A
Mix B
Mix Plus
Ref.
Premix
Grn
Slide
Comp.
Grn Strip
Den
Pres
Press.
Strn Press
(g/cm³
s
(tsi)
(psi) (psi)
(psi)
)
30
40
50
30
40
50
30
40
50
30
40
50
6.75
7.05
7.22
6.75
7.06
7.26
6.81
7.09
7.28
6.79
7.07
7.19
1800
2500
3200
2700
3800
4800
4000
5100
5900
2200
2900
3000
3600
4200
4500
2700
3600
4000
2300
3200
3900
3100
3400
3800
1800
1900
2100
1500
1900
2200
1200
1500
1700
1500
1600
1700
The sintered properties of Ancorsteel 45P tabulated
in Table II are an indication of what can be achieved with
better compressibility and sinterability of the lubricantbinder systems used in mixes B and Plus. At higher
compaction pressures, the density (up to 0.13 g/cm³
increase in sintered density) and correspondingly, the
strength of the B and Plus mixes are 7 to 27% higher than
the other mixes. The apparent hardness of the Mix B and
Plus are similar or slightly higher. By optimizing the
bonding mechanism on particle morphology and
distribution, it is possible to improve the distribution of
the bonded ferrophosphorus. This is shown by the
increased shrinkage during sintering. It can also lead to
consistent dimensional control.
Table II: Sintered Properties of Ancorsteel 45P Mixes
Mix
Mix A
Mix B
Mix Plus
Ref.
Premix
Comp.
Press.
(tsi)
Grn
Den.
(g/cm³)
Grn
Exp
(%)
Sin.
Den.
(g/cm³)
Dim.
Chg.
(%)
30
40
50
30
40
50
30
40
50
30
40
50
6.79
7.07
7.23
6.80
7.09
7.27
6.84
7.12
7.32
6.82
7.07
7.19
0.08
0.10
0.14
0.10
0.13
0.18
0.11
0.12
0.13
0.12
0.12
0.14
6.78
7.06
7.25
6.84
7.14
7.31
6.86
7.16
7.35
6.84
7.11
7.22
-0.11
-0.09
-0.07
-0.29
-0.25
-0.22
-0.20
-0.19
-0.14
-0.12
-0.11
-0.11
App.
TRS
Hard.
(10³psi)
(HRB)
97
119
142
112
140
154
109
147
165
102
120
130
39
53
61
48
59
68
45
57
66
44
56
64
VI. ANCORBOND Trial of a Large Sprocket
This trial involved the comparison of 10,000 lb lots of
binder treated FN0205 premix to regular premix at a
customer request. The part chosen for the test was a 24
teeth large sprocket. During the heat treat process of this
sprocket, there exits the common problems of density
variation and size stability. By converting to the binder
treated premix, the parts producer anticipated less
dusting, improved cleanliness, reduced segregation of
nickel and carbon in the base powder, and improved
dimensional stability. The improvements in cleanliness
and reduced dusting were documented in a previous
report2. The parameters used to compare the performance
between the mixes are weight control, dimensional
stability (-inside diameter between pins, taper), nickel and
carbon variability, and Q&T Hardness. The trial was
carried out in a hydraulic press set at a stroke rate of 6
pieces/min. A total of 500 parts were made for each mix
for data analysis. Table III shows the improvements in
weight control and dimensional control. The range of
weight variation for the run is reduced by 50% from 18.1
gm to 9.2 gm. More importantly, the number of press
adjustment during the production shift is reduced from
ten adjustments to two. The overall green scrap during
the shift is reduced by 80%.
Analysis for both nickel and carbon were determined
on the as-sintered sprocket samples and are shown in
Table IV. A total of 50 samples were collected by
selecting every tenth sprocket out of the total 500 pieces
run. Chemical analysis was done by drilling to a depth of
0.18 inch from the surface of each sprocket with a 0.25inch drill bit and analyzing the chips. This depth is
important since it represents both the percentage of
admixed graphite and effects of sintering atmosphere on
the parts surface carbon. The ANCORBOND mix shows
significant improved uniformity in both nickel and carbon
content.
Table III: Weight Control / Dimensional Responses
Weight Control
Mean
Std. Dev.
Range
Minimum
Maximum
Press Adjustment
Dim. Control (in.)
I.D. between Pins
Mean
Std. Dev.
I.D. Taper
Mean
Std. Dev.
PREMIX
ANCORBOND
995.15
2.251
18.1
986.1
1004.2
10
999.192
1.144
9.2
994.6
1003.8
2
0.96637
0.00037
0.96762
0.00017
0.00050
0.00028
0.00053
0.00028
Table IV: Nickel-Carbon Distribution
Sintered Carbon (%)
Mean
Std. Dev.
Range
Minimum
Maximum
Sintered Ni (%)
Mean
Std. Dev.
Range
Minimum
Maximum
PREMIX
ANCORBOND
0.523
0.043
0.11
0.47
0.58
0.529
0.010
0.02
0.52
0.54
1.76
0.233
0.62
1.50
2.12
1.84
0.020
0.05
1.81
1.86
The sprockets were heat treated in a batch type gas
carburizing furnace through a carbonitride cycle followed
by a direct quench in agitated 115 – 127°C (240 – 260°F)
hot oil for distortion control while maintaining quenching
capabilities. It then went through a 350°F tempering
procedure for one hour. The dimensional response and
apparent hardness were compared and shown in Table V.
Again, the binder treated premix showed a significant
improvement in dimensional control. The standard
deviation for the ID between pins is reduced by 30%
when a binder-treated premix is used.
Table V: Heat Treated Dimensional Responses
Dimensional Control
I.D. between Pins
Mean (inch)
Std. Dev.
I.D. Taper
Mean (inch)
Std. Dev.
Hardness (HRB)
Top
Bottom
PREMIX
ANCORBOND
0.9682
0.000167
0.9688
0.000117
0.00043
0.00034
0.00027
0.00019
118
119
119
119
VII. Crown Tonnage Variation of a FN0208 mix
Average: 39.61 tsi
Variation: 7.72%
Minimum: 38.0 tsi
43
St.Dev. 0.509
6 Sigma 3.05
Maximum: 40.9 tsi
42
Crown Tonnage (tsi)
The more consistent ANCORBOND powder fill and
flow leads to more consistent parts production of a
bushing with dimensions of 2.5 cm I.D. X 3.8 cm O.D X
3.3 cm H. The relationship between the fluidity and the
particle characteristics of metallic powder has been
investigated9. Both apparent density and powder flow
rate are strongly influenced by the product of two
parameters i.e. the particle size and particle shape.
Binder treated premix allowed the manipulation of both
the shape and size of agglomerates. The significance of
lower tonnage variation is that it implies a movement
towards more consistent apparent density and Hall Flow
rate within a lot of powder. Due to the increase in
compressibility of the improved ANCORBOND and
ANCORBOND Plus mixes, a lower compaction tonnage
would be needed to reach the desired density. Figure 2
and 3 displays graphically the improvements in lowering
tonnage variation. The lines above and below the plot
represent the plus and minus 3 sigma values.
44
3 Sigma UCL
41
40
39
38
3 Sigma LCL
37
1
31
61
91
121 151 181
Part Number
211
241
271
Figure 3. Crown Tonnage Variation of an
ANCORBOND Plus FN-0208 Composition
VII. Summary
45
3 Sigma UCL
1) Various generations of binder-treated products can be
engineered to satisfy specific market niches.
2) ANCORBOND Plus, provides higher green strength
for green machining possibilities and higher
compressibility to extend press capabilities.
3) Significant improvements in dimensional tolerancing
were achieved with a binder-treated premix in production
runs of a large sprocket.
44
Crown Tonnage (tsi)
43
42
41
40
3 Sigma LCL
39
Reference:
Average: 41.67 tsi
Variation: 10.87%
Minimum: 39.6 tsi
38
37
St. Dev:
0.755
6 Sigma: 4.53
Maximum: 43.3 tsi
1.
36
1
31
61
91
121
151
181
211
241
271
2.
Part Number
Figure 2. Crown Tonnage Variation of an
ANCORBOND®FN-0208 mix.
3.
The weight variation of ANCORBOND relative to
unbonded premix for FN-0208 is 1.02 % vs. 2.02 %. The
data is based on the measurement of every tenth part
during a 500 parts run. The dimensional variation of the
ANCORBOND Plus mixes are 24 to 48% lower than that
of first generation ANCORBOND mixes. Relative to
unbonded premixes4, ANCORBOND processed premixes
used in industry usually exhibit a reduction in
dimensional variability by 25-60%; weight and density
variability by 30-50%, press speed improvements of 1050%, reduced green scrap by 97% as well as reduction in
dusting and press adjustments.
4.
5.
6.
7.
8.
9.
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