Drum brake especially for a two-wheeled vehicle

A roller brake or drum brake for a two-wheeler includes a guide case rotating with a wheel, a ring of a sintered copper alloy that is fixedly fitted into the guide case, and a brake shoe of an iron material that is pressed against the inner peripheral surface of the ring thereby exhibiting a braking effect. The sintered copper alloy forming the ring contains hard particles dispersed in the interior of respective grains of copper alloy powder forming the matrix.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a braking device employed for a 
two-wheeler such as a bicycle or a motorcycle, and more particularly, it 
relates to a roller brake or drum brake for braking a two-wheeler under 
dry frictional sliding conditions without a solid or semisolid lubricating 
component such as grease or oil. 
2. Description of the Background Art 
FIGS. 1A and 1B show a conventional drum brake for a two-wheeled vehicle, 
which is generally called a roller brake for a two-wheeler herein. This 
roller brake comprises a guide case 1 which is fixed to a wheel and 
rotates with this wheel, and a brake shoe 2 which is pressed against the 
inner peripheral surface of the guide case 1 to exhibit a braking effect. 
The brake shoe 2 has an outer peripheral surface which is substantially 
identical in radius of curvature to the inner peripheral surface of the 
guide case 1. 
In the conventional roller brake, both the guide case 1 and the brake shoe 
2 are made of steel or an iron alloy. In order to prevent a discomfort 
phenomenon such as squeaking or chattering during braking, seizing of the 
guide case 1 and the brake shoe 2, or locking causing adhesion between the 
guide case 1 and the brake shoe 2, the inner peripheral surface of the 
guide case 1 is grooved in the conventional roller brake for allowing 
intervention of a solid or semisolid lubricant such as grease or oil. 
When the lubricant such as grease intervenes between the guide case 1 and 
the brake shoe 2, however, the braking force is disadvantageously reduced 
although the lubricity is improved. In this case, the roller brake can 
exhibit only a small braking force of about 0.1 in terms of the friction 
coefficient, for example. If maintenance such as supplementation of the 
lubricant such as grease is neglected, the grease or the like intervening 
between the guide case 1 and the brake shoe 2 is used up, which will 
result in locking of the brake shoe and the guide case. 
Recent high-performance two-wheelers aim to avoid the use of the lubricant 
such as grease, in order to improve the braking force for attaining a 
friction coefficient of at least about 0.1. However, it has been 
recognized that locking is caused by adhesion when a two-wheeler is braked 
under dry sliding conditions without intervention of grease in case of 
employing a conventional brake material such as a friction material for a 
brake disclosed in Japanese Patent Laying-Open No. 56-133441 (1981), 
56-120787 (1981), 2-11936 (1990) or 5-331451 (1993), for example. Thus, 
further improvement is necessary for a brake material to be used in such 
an application. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a roller brake for a 
two-wheeler which causes neither seizing nor locking when braking the 
two-wheeler under dry sliding conditions without intervention of a 
lubricant such as grease. 
Another object of the present invention is to provide a roller brake that 
is applicable to a wide-range of two-wheelers including a high-performance 
two-wheeler which is exposed to a high load of pressing force of 50 to 100 
kgf/cm.sup.2 for braking transmitted from a brake lever, and general 
two-wheelers such as a household two-wheeler and a children's two-wheeler 
which are exposed to a relatively small load of pressing force of 10 to 50 
kgf/cm.sup.2 for braking. 
Still another object of the present invention is to provide a roller brake 
for a two-wheeler which can exhibit a friction coefficient in the range of 
0.15 to 0.5. 
A further object of the present invention is to provide a roller brake at a 
low cost. 
The inventors have made various experiments and studies, to develop a 
roller brake for a two-wheeler which can stably exhibit a friction 
coefficient in the range of 0.15 to 0.5, preferably in the range of 0.2 to 
0.4, with neither seizing, nor locking, nor squeaking nor vibration when 
exposed to braking pressing force of about 10 to 100 kgf/cm.sup.2 under 
dry sliding conditions without intervention of a lubricant such as grease 
or oil. 
In more concrete terms, the inventive roller brake for a two-wheeler 
comprises a guide case, a ring, and a brake shoe. The guide case is fixed 
to a wheel of a two-wheeler, and rotates with this wheel. The ring is 
prepared from a sintered copper alloy, and fixedly fitted into the guide 
case. The brake shoe is prepared from an iron material, and pressed 
against the inner peripheral surface of the ring, thereby exhibiting a 
braking effect. 
Preferably, the sintered copper alloy contains hard particles dispersed in 
its matrix. 
In a preferred embodiment of the present invention, the hard particles are 
dispersed and present in the interior of respective grains of copper alloy 
powder forming the matrix. In another embodiment, the matrix of the 
sintered copper alloy comprises copper alloy powder grains containing 
dispersed hard particles, and copper alloy powder grains containing no 
hard particles. 
Preferably, the iron material forming the brake shoe has a tensile strength 
of at least 400 MPa. The sintered copper alloy forming the ring has a 
transverse rupture strength of at least 200 MPa. 
Preferably, the friction coefficient between the ring and the brake shoe is 
at least 0.15 and not more than 0.5 when braking the two-wheeler under a 
dry sliding environment without an additional solid and/or semisolid 
lubricant. 
The sintered copper alloy forming the ring preferably contains 10 to 50 
percent by weight of hard particles. The sintered copper alloy contains 5 
to 15 percent by weight of a solid lubricating component. In one 
embodiment, a copper alloy forming the matrix contains 3 to 20 percent by 
weight of Sn assuming that the composition of the overall matrix is 100 
percent by weight, with the rest consisting of copper and unavoidable 
impurities. The hard particles are typically those of at least one or two 
iron intermetallic compounds selected from a group consisting of FeMo, 
FeCr, FeTi, FeAl, FeSi and FeB. The solid lubricating component is 
preferably natural graphite powder. Preferably, the hard particles are not 
more than 30 .mu.m in maximum particle diameter, and not more than 15 
.mu.m in mean particle diameter. 
In another embodiment, the copper alloy forming the matrix contains 3 to 20 
percent by weight of Sn and not more than 3 percent by weight of Al 
assuming that the composition of the overall matrix is 100 percent by 
weight, with the rest consisting of copper and unavoidable impurities. In 
still another embodiment, the copper alloy forming the matrix contains 5 
to 40 percent by weight of Zn and/or Ni and 3 to 20 percent by weight of 
Sn assuming that the composition of the overall matrix is 100 percent by 
weight, with the rest consisting of copper and unavoidable impurities. In 
a further embodiment, the copper alloy forming the matrix contains 5 to 40 
percent by weight of Zn and/or Ni, 3 to 20 percent by weight of Sn and not 
more than 3 percent by weight of Al assuming that the composition of the 
overall matrix is 100 percent, with the rest consisting of copper and 
unavoidable impurities. 
In a preferred embodiment, the guide case is made of a material selected 
from a group consisting of an iron-based alloy, an aluminum alloy, a 
magnesium alloy, a copper alloy and a titanium alloy. In one embodiment, 
the ring has a convex part on its outer peripheral surface, and the guide 
case has a concave part for engaging with the convex part in its inner 
peripheral surface. The ring is press-fitted into the guide case and fixed 
thereto. 
The foregoing and other objects, features, aspects and advantages of the 
present invention will become more apparent from the following detailed 
description of the present invention when taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 2A and 2B, a roller brake for a two-wheeler according to 
the present invention comprises a guide case 1, a brake shoe 2, and a ring 
3. The guide case 1 having an opening 4 in its center is fixed to a wheel 
of a two-wheeler, and rotates with this wheel. The ring 3 is prepared from 
a sintered copper alloy, and fixedly fitted into the guide case 1. The 
brake shoe 2 is prepared from an iron material, and has an outer 
peripheral surface which is substantially identical in radius of curvature 
to the inner peripheral surface of the ring 3. The outer peripheral 
surface of the brake shoe 2 is pressed against the inner peripheral 
surface of the ring 3, thereby exhibiting a braking effect. 
The ring 3 is press-fitted into the guide case 1, and tightly fixed 
thereto. In order to sufficiently fix the ring 3, convex parts 20 and 
concave parts 21 may be provided on the outer peripheral surface of the 
ring 3 and the inner peripheral surface of the guide case 1 respectively 
for engaging with each other, as shown in FIG. 3. 
The characteristics of the roller brake for a two-wheeler according to the 
present invention are now described in detail in relation to the brake 
shoe, the ring and the guide case respectively. 
(Brake Shoe) 
When a general bicycle is braked with a brake lever, a load of about 10 to 
50 kgf/cm.sup.2 is applied to the brake shoe. This load is applied for 
about several seconds under dry conditions. The brake shoe must not be 
deformed or abrasively damaged under such pressurization or application of 
a braking load. 
The inventors have made various experiments, to discover that the material 
forming the brake shoe must have a tensile strength of at least 400 MPa in 
order to prevent the brake shoe from deformation or abrasive damage, and 
that the brake shoe for a racing two-wheeler may have tensile a strength 
of 1000 MPa. 
If the tensile strength of the material for the brake shoe is less than 400 
MPa, the brake shoe is easily abrasively damaged, or deformed by a 
pressing load during braking, which causes it to be locally in nonuniform 
contact with the counter ring. This may consequently lead to a problem of 
seizing. Therefore, a material having a tensile strength of at least 400 
MPa is suitable for the brake shoe. Further, it is desired that the 
material is at has a low cost. From this point of view, an iron material 
is desirable as the material for the brake shoe. 
While the iron material may be prepared from either an ingot steel material 
or a sintered alloy, the sintered alloy allowing near net shape or net 
shape compacting is economically advantageous, since the machining cost 
can be reduced. 
A ring of a sintered copper alloy described later and a brake shoe of an 
iron material slide with high pressing force relative to each other, 
thereby exhibiting a high friction coefficient. In order to attain uniform 
contact between the ring and the brake shoe, the inner peripheral surface 
of the ring and the outer peripheral surface of the brake shoe must be 
substantially identical in radius of curvature to each other. If the radii 
of curvature are different from each other, the outer peripheral surface 
of the brake shoe comes into nonuniform contact with the inner peripheral 
surface of the ring, and it is difficult to ensure a stable high friction 
coefficient. 
(Ring) 
According to the present invention, a copper alloy is selected as the base 
material for the ring, in consideration of seizing resistance (adhesion 
resistance) with respect to the brake shoe consisting of an iron material. 
In consideration of economy, further, selected a powder metallurgy method 
(sintering method) is selected, which can readily simplify or omit a 
machining step and easily provide a three-dimensional shape. 
In order to improve the abrasion resistance of the ring, hard particles are 
preferably dispersed in a matrix of the copper alloy. If the hard 
particles and copper alloy powder are merely mixed with each other and the 
mixed powder is thereafter solidified by compacting and sintering in this 
case, this results in a structural configuration shown in FIG. 4. 
Referring to FIG. 4, old powder grain boundaries 5 are present in a matrix 
6 of the copper alloy, and hard particles 7 are located along the old 
powder grain boundaries 5. The hard particles 7 may aggregate or 
segregate, depending on the method of or the conditions for the mixing. In 
the sintered alloy having such a structural configuration, the 
adhesiveness between the hard particles 7 and the copper alloy matrix 6 is 
so inferior that clearances 8 may be defined therebetween. In this case, 
the hard particles 7 drop from the surface of the ring during frictional 
sliding, and consequently serve as an abrasive powder attacking the ring 
itself or the brake shoe and inducing abrasive damage. If the hard 
particles 7 are present on the old powder grain boundaries 5 when stress 
is applied, the positions thereof may serve as starting points or 
propagation paths of cracks, to remarkably reduce the mechanical 
characteristics of the sintered body. 
From the aforementioned point of view, the inventors have discovered that a 
structural configuration shown in FIG. 5 is preferable. Referring to FIG. 
5, fine hard particles 70 are dispersed and present in the interior of 
respective grains, enclosed with old powder grain boundaries 5, of copper 
alloy powder forming a matrix 6. In more concrete terms, the fine hard 
particles 70 are previously dispersed in the interior of copper alloy 
powder grains that have not yet been compacted or sintered. In other 
words, a so-called hard particle dispersed composite copper alloy powder 
is employed as a raw material powder. Consequently, it is possible to 
prepare a ring of a sintered copper alloy which is excellent in seizing 
resistance and abrasion resistance, and can exhibit a stable friction 
coefficient over a long period of time. 
The hard particle dispersed composite copper alloy powder has a higher cost 
than copper alloy powder containing no hard particles. In order to 
suppress such increase of the cost, the raw material powder may be 
prepared from a mixed powder of hard particle dispersed composite copper 
alloy powder and copper alloy powder containing no hard particles. When 
the raw material powder is prepared from such a mixed powder, a structural 
configuration shown in FIG. 6 is obtained. Referring to FIG. 6, a matrix 6 
of a sintered copper alloy comprises copper alloy powder grains 6A 
containing dispersed hard particles 70, and copper alloy powder grains 6B 
containing no hard particles. 
(Hard Particle Dispersed Composite Copper Alloy Powder and Method of 
Preparing the Same) 
The hard particles contained in the sintered copper alloy forming the ring 
are finely and homogeneously dispersed in a sliding surface, for 
suppressing adhesion to the brake shoe and improving seizing resistance in 
frictional sliding under ordinary and high temperatures. Further, the hard 
particles are directly in contact with the surface of the brake shoe to 
cause frictional resistance, whereby the friction coefficient is improved. 
A necessary condition for attaining the aforementioned effects is that the 
hard particles do not drop out of the matrix of the sliding surface of the 
sintered material during frictional sliding. In order to implement this, 
the hard particle dispersed composite copper alloy powder is employed as a 
starting raw material. As a method of economically preparing the hard 
particle dispersed composite copper alloy powder, it is effective to use 
the following mechanical mixing/crushing method for powder. 
When a mechanical mixing/crushing/alloying method for powder such as 
mechanical alloying, mechanical grinding or granulation is applied, an 
intermetallic compound or metal particles forming the hard particles can 
be finely crushed and the obtained fine hard particles can be 
homogeneously dispersed in the matrix of the grains of the copper alloy 
powder. The mechanical powder mixing/crushing/alloying treatment is 
carried out not in a wet type condition but in a dry type condition, 
dissimilarly to conventional ball mill crushing or mixing. A small amount 
of stearic acid or alcohol may be added as a PCA (process control agent) 
as needed, for preventing excessive aggregation. An attriter or a ball 
mill is suitable as the treatment apparatus. The attriter having excellent 
crushing efficiency is suitable for high-speed treatment. Although 
long-term treatment is necessary, the ball mill is economically excellent 
since the atmosphere can be readily controlled and a target structural 
configuration of the powder can be implemented in a relatively short time 
when the applied energy is properly set. 
As another method of preparing hard particle dispersed composite copper 
alloy powder, copper alloy powder containing hard particles dispersed in 
its interior may be prepared by introducing hard particles into a molten 
metal of a copper alloy having a prescribed composition, stirring and 
dispersing the same, and spraying the molten metal by atomizing. In this 
method, however, the hard particles cannot be finely crushed, and hence 
fine hard particles must be previously prepared, to be introduced into the 
molten metal. In this case, a sufficient stirring step is required for 
preventing the hard particles from segregation and aggregation in the 
molten metal, and hence this method is slightly disadvantageous in view of 
economy. In order to prepare a sintered copper alloy containing hard 
particles dispersed in its grains at a lower cost, therefore, the 
mechanical mixing/crushing/alloying treatment is preferable. 
The sizes of the hard particles and the content thereof are now described. 
The inventors have carried out mechanical mixing/crushing/alloying 
treatment on copper alloy powder having a prescribed composition under 
various conditions. Consequently, they have found that the sizes and the 
content of the hard particles dispersed in the matrix of the copper alloy 
powder are desirably within the following proper ranges, in order to 
obtain a sintered copper alloy for the ring which can stably ensure the 
target friction coefficient of 0.15 to 0.5: 
In order to ensure a stable friction coefficient without reducing the 
mechanical characteristics of the ring of the sintered copper alloy, it is 
desirable to set the sizes of the hard particles in the range of not more 
than 30 .mu.m in maximum particle diameter and not more than 15 .mu.m in 
mean particle diameter while setting the content of the hard particles in 
the range of 10 to 50 percent by weight with respect to the overall 
sintered copper alloy, and to disperse the hard particles in the interior 
of powder grains forming the matrix. 
If the content of the hard particles is less than 10 percent by weight, a 
friction coefficient exceeding 0.1 cannot be attained, and an effect of 
improving abrasion resistance cannot be attained either. If the hard 
particles are in excess of 30 .mu.m in maximum particle diameter, in 
excess of 15 .mu.m in mean particle diameter, or in excess of 50 percent 
by weight in content, the hard particles readily define starting points of 
cracks, to remarkably reduce the strength and toughness of the sintered 
copper alloy as the result. If the hard particles are added in an excess 
amount or have excessively large particle diameters, such hard particles 
remarkably abrade the counter material. Therefore, it is effective to 
homogeneously disperse hard particles of not more than 30 .mu.m in maximum 
particle diameter and not more than 15 .mu.m in mean particle diameter in 
the interior of powder grains forming the matrix with a content of 10 to 
50 percent by weight of these hard particles. 
The hard particles are preferably particles of at least one or two iron 
intermetallic compounds selected from a group consisting of FeMo, FeCr, 
FeTi, FeAl, FeSi and FeB. These iron intermetallic compounds having high 
hardness are suitable for the hard particles. In addition, these 
intermetallic compounds which are fragile are excellent in crushability, 
and are crushed during the mechanical mixing/crushing/alloying treatment 
into fine hard particles. While the friction coefficient of the sintered 
alloy can be improved if a metal oxide such as Al.sub.2 O.sub.3, SiO.sub.2 
or ZrO.sub.2 or ceramics such as SiC, TiC, AlN or Si.sub.3 N.sub.4 is 
contained in the alloy, particles of such a material are inferior in 
cuttability to the iron intermetallic compounds, and hence a small problem 
may result in view economy. 
The alloy composition of the matrix of the sintered copper alloy forming 
the ring is now described. The content of each element is expressed in 
weight percentage, assuming that the composition of the overall alloy 
matrix is 100 percent by weight. 
Sn 
Sn forms the matrix of the alloy with Cu, and improves high-temperature 
strength and toughness of the alloy. Sn also improves seizing resistance 
of the alloy with respect to the counter material under a high 
temperature. If the frictional sliding conditions are heavier, therefore, 
addition of Sn is effective. The aforementioned effects cannot be attained 
if the content of Sn is less than 3 percent by weight, while the strength 
and toughness of the alloy are reduced due to deposition of a hard and 
fragile layer if the Sn content exceeds 20 percent by weight. A proper Sn 
content which can attain the aforementioned effects is 3 to 20 percent by 
weight. 
Zn and/or Ni 
Both Zn and Ni form the matrix with Cu, and improve heat resistance as well 
as corrosion resistance of the alloy. In a braking device for a 
two-wheeler, the surface of a brake material is instantaneously heated to 
a high temperature by frictional heat, and hence the brake material is 
readily softened to be abraded or deformed. In a part which is directly in 
contact with rainwater or seawater, a problem such as abrasive damage or 
reduction of endurance results from corrosion. Such problems can be 
avoided by addition of Zn and/or Ni. A proper content of at least one of 
or both Zn and Ni is 5 to 40 percent by weight. If the content is less 
than 5 percent by weight, the effect of improving heat resistance and 
corrosion resistance cannot be sufficiently attained. If the content 
exceeds 40 percent by weight, on the other hand, the matrix of the copper 
alloy is hardened to disadvantageously attack the counter material during 
frictional sliding. 
Al 
Al reacts with Cu of the matrix to form a fine intermetallic compound such 
as Cu.sub.6 Al.sub.4 thereby improving hardness of the alloy, and serves 
as resistive particles during frictional sliding thereby improving the 
friction coefficient. If added in excess of 3 percent by weight, however, 
Al induces embrittlement of the alloy and reduces machinability and cold 
workability. Therefore, a proper content of Al added to the sintered 
copper alloy according to the present invention as needed is not more than 
3 percent by weight. 
The characteristics and the content of graphite powder serving as a solid 
lubricant are now described. 
The solid lubricant improves the attacking property and seizing resistance 
of the ring against the brake shoe, i.e. the respective counter material, 
under heavy frictional sliding conditions. Also when the frictional 
sliding conditions such as a sliding rate and pressing force fluctuate, 
the solid lubricant effectively stabilizes the friction coefficient of 0.1 
to 0.5 under dry sliding conditions. Further, the solid lubricant improves 
lubricity between the sliding surfaces, thereby effectively suppressing 
vibration or chattering in sliding. In more concrete terms, graphite 
powder, MoS.sub.2, CaF.sub.2, WS.sub.2 or BN powder is industrially 
employed as the solid lubricant. Particularly in case of adding the solid 
lubricant in a large amount, graphite powder is generally selected in 
consideration of economy. 
The inventors have tried to apply natural scaly graphite powder 
(hereinafter simply referred to as natural graphite powder) having 
superior characteristics to spherical graphite powder which has been 
employed for conventional powder metallurgy, or expanded graphite powder 
prepared by expanding the natural graphite powder in the direction of 
thickness, among graphite powder materials. The natural graphite powder is 
(i) superior in compactability and compressibility, and (ii) superior in 
lubricity to the conventional spherical graphite powder. Namely, the 
natural graphite powder, which is superior in compactability to the 
conventional spherical graphite powder, can be added in a larger amount, 
thereby further stabilizing the friction coefficient. In addition, the 
natural graphite powder can suppress reduction of the mechanical 
characteristics (strength) of the sintered body. 
A preferable content of the solid lubricating component is 5 to 15 percent 
by weight with respect to the overall sintered copper alloy. If natural 
graphite powder or expanded graphite powder is added in excess of 15 
percent by weight with respect to the overall sintered copper alloy, the 
transverse rupture strength of the sintered body falls below 200 MPa, to 
induce abrasive damage. The natural graphite powder having superior 
lubricity can suppress problems such as chattering, vibration or squeaking 
during sliding, and can further stabilize the friction coefficient by 
improving fitness with respect to the counter material in an initial stage 
of sliding. If the content of the graphite powder is less than 5 percent 
by weight with respect to the overall sintered alloy, however, it is 
difficult to attain the aforementioned excellent sliding characteristics. 
Thus, the desirable content of the natural graphite powder or the expanded 
graphite powder added to the sintered copper alloy is at least 5 percent 
by weight and not more than 15 percent. 
When the aforementioned graphite powder is dispersed in a sintered body, 
compressibility of the sintered body itself is improved during 
pressurization or application of a pressing force due to the excellent 
compressibility of the graphite powder, whereby merely local nonuniform 
contact with the sliding surface of the counter material can be 
suppressed, total contact is enabled and frictional slidability can be 
stabilized. Thus, a sintered body obtained by mixing hard particle 
dispersed composite copper alloy powder and natural graphite powder 
(natural scaly graphite powder and/or expanded graphite powder) with each 
other and solidifying the mixture has excellent mechanical characteristics 
and frictional slidability, and can exhibit a stable friction coefficient 
from an initial stage of sliding in particular. 
(Method of Preparing Ring) 
As already described with reference to FIGS. 2A and 2B, the inventive 
roller brake for a two-wheeler comprises the guide case 1, the ring 3 
consisting of a sintered copper alloy which is press-fitted into this 
guide case 1, and the brake shoe 2 consisting of an iron material which is 
pressed against the ring 3. 
The ring 3 must have excellent mechanical characteristics (strength), not 
to be deformed or abraded when the brake shoe 2 is pressed against the 
same for braking the two-wheeler. In more concrete terms, a transverse 
rupture strength of at least 200 MPa is necessary as the material strength 
required for the ring 3, if the pressing force from the brake shoe 2 is 10 
to 50 kgf/cm.sup.2. Needless to say, a higher transverse rupture strength 
is required for the ring 3 if the pressing force exceeds 50 kgf/cm.sup.2. 
FIG. 7 successively illustrates steps of preparing the ring of a sintered 
copper alloy. The respective steps are now described. 
Step (a) 
Mixed powder is prepared by adding a solid lubricating component to hard 
particle dispersed composite copper alloy powder having the aforementioned 
prescribed alloy composition, and adding Al thereto if necessary. 
Step (b) 
The mixed powder is pressed/compacted, thereby forming a ring-shaped green 
compact. 
Step (c) 
The green compact is held at a temperature of at least 700.degree. C. and 
not more than the solidus curve temperature of the alloy matrix, and 
heated/held in an atmosphere of any of a reducing gas, inert gas an and a 
vacuum, thereby preparing a sintered body. In order to prepare a sintered 
copper alloy having a transverse rupture strength of at least 200 MPa, 
either of the following two steps is preferably applied: 
Step (d) 
The sintered body is heated to and held at a temperature of at least 
100.degree. C. and re-compressed under a closed mold temperature of not 
more than 400.degree. C. 
Step (e) 
The sintered body is heated to and held at a temperature of less than 
100.degree. C. and re-compressed under a closed mold temperature of not 
more than 400.degree. C., and re-sintered at a temperature of at least 
700.degree. C. and not more than the solidus curve temperature of the 
copper alloy in an atmosphere of any of a reducing gas, an inert gas and a 
vacuum. 
According to the aforementioned step (d), the sintered body is heated to 
and held at a temperature of at least 100.degree. C. and pressurized in a 
closed mold, whereby old powder materials strongly bond to each other and 
transverse rupture strength of at least 200 MPa can be a attained. In this 
case, the mold, which may be under the ordinary temperature, is preferably 
held at a high temperature of not more than 400.degree. C., and more 
preferably held at a temperature of not more than 200.degree. C. If the 
mold is at a high temperature, temperature reduction of the heated 
sintered body is suppressed and the old powder materials further strongly 
bond to each other. With regard to selection of a lubricant for preventing 
seizing of the mold and the sintered body in pressurization, however, a 
black lubricant such as that of graphite or molybdenum is required if the 
mold temperature exceeds 200.degree. C., leading to a possibility of 
damaging the appearance of the pressed sintered body. If the mold 
temperature is less than 200.degree. C., on the other hand, a white or 
transparent and colorless lubricant prepared by dissolving metallic soap 
powder such as zinc stearate or lithium stearate, for example, in an 
organic solvent such as myristic acid or ethanol can be applied, so as not 
to damage the appearance of the sintered body dissimilarly to the above 
described case in which a black lubricant must be used. The 
characteristics of the re-compressed sintered body are not remarkably 
further improved even if the sintered body is heated/held under a higher 
mold temperature exceeding 400.degree. C., and hence the mold temperature 
does not need to be more than 400.degree. C., in consideration of economy. 
If the sintered body is heated to and held at a temperature less than 
100.degree. C. and pressed in the closed mold in the step (e), on the 
other hand, the aforementioned re-sintering step is necessary in 
succession, and a sintered copper alloy having a transverse rupture 
strength of at least 200 MPa can be obtained as a result. However, it is 
recognized that the characteristics of the sintered body are further 
improved if the sintered body heated in the step (d) is pressurized in the 
closed mold and thereafter subjected to the aforementioned re-sintering 
step in succession. 
If the sintering atmosphere is an oxidizing atmosphere or the holding 
temperature is less than 700.degree. C. in the aforementioned method, the 
sintered body cannot attain sufficient strength due to insufficient 
progress of the sintering phenomenon, leading to poor handleability such 
that the sintered body may easily be broken during transport thereof. If 
the sintered body is heated to a temperature exceeding the solidus curve 
temperature of the alloy matrix, on the other hand, the amount of 
dimensional shrinkage of the green compact is so increased as to reduce 
dimensional accuracy in sintering. 
If the heated sintered body is pressurized in the closed mold or in a state 
heated in excess of 100.degree. C. in the subsequent step for further 
improving the strength of the obtained sintered body, bonding between the 
old powder materials of the sintered body is facilitated and a sintered 
body having a transverse rupture strength of at least 200 MPa can be 
prepared. When the sintered body is heated to a temperature less than 
100.degree. C. and pressurized as described in the step (e), however, it 
is difficult to attain a transverse rupture strength of at least 200 MPa, 
and hence the aforementioned re-sintering step is necessary for improving 
the bondability between the old powder materials. If the sintering 
temperature exceeds that in the first time, the sintering phenomenon 
further progresses to increase the amount of dimensional shrinkage of the 
sintered body, leading to reduction in dimensional accuracy of the ring 
sintered body. 
Summarizing the above, copper alloy powder consisting of a prescribed 
composition and hard particles are mechanically mixed/crushed/alloyed so 
that the hard particles are finely crushed to not more than 30 .mu.m in 
maximum particle diameter and not more than 15 .mu.m in mean particle 
diameter and can be finely dispersed in copper alloy powder grains (in the 
matrix of the powder). Thus, hard particle dispersed composite copper 
alloy powder is obtained. Natural scaly graphite powder or expanded 
graphite powder is added to such copper alloy powder to form a mixed 
powder, the mixed powder is compacted/sintered, and further subjected to 
plastic working by pressurization/solidification in the closed mold, 
followed by a sintering step as needed. Thus, it is possible to prepare a 
sintered copper alloy ring exhibiting sufficient mechanical 
characteristics for serving as a brake ring member as well as excellent 
abrasion resistance and seizing resistance under dry sliding conditions, 
with the target friction coefficient of 0.15 to 0.5. 
(Guide Case) 
The sintered copper alloy ring prepared in the aforementioned manner is 
press-fitted into the inner periphery of the guide case as shown in FIG. 
2A, thereby preparing a roller brake body of a two-layer structure. The 
guide case is generally prepared from an industrial metal material such as 
an iron-based alloy, an aluminum alloy, a magnesium alloy or a copper 
alloy, in consideration of mechanical characteristics (particularly the 
strength of spline teeth parts at the central portion of the guide case 
engaging with the wheel) and economy. Particularly when a high pressing 
load is applied between the ring and the brake shoe, high frictional heat 
generated between the same must be dissipated. Therefore, an aluminum 
alloy having high heat conductivity and excellent heat dissipation with a 
remarkable effect of weight reduction is suitable as the material for the 
guide case. 
EXAMPLE 1 
Table 1 shows alloy compositions of inventive sintered copper alloy samples 
Nos. 1 to 21 and comparative samples (Nos. 22 to 36). 
TABLE 1 
__________________________________________________________________________ 
Solid 
Lubricating 
Hard Particles 
Composition of Matrix 
Component 
(Iron Intermetallic Compound) 
No. 
Sn 
Zn 
Ni 
(Zn + Ni) 
Al 
Cu A B Total 
C D E F G Total 
Remarks 
__________________________________________________________________________ 
1 9 0 0 0 1 Rest 
5 0 5 20 0 0 0 0 20 
2 9 
0 Rest 
6 
20 
0 
0 
0 
20 
3 9 
0 Rest 
10 
10 
20 
0 
0 
0 
20 
4 9 
0 
0 
Rest 
15 
15 
20 
0 
0 
0 
20 
5 9 
0 Rest 
0 
20 
0 
0 
0 
20 
6 9 
0 
0 
Rest 
0 
12 
20 
0 
0 
0 
20 
7 9 
0 
0 
Rest 
7 
0 
0 
20 
20 
8 10 
0 
0 
0 
Rest 
7 
0 
00 
0 
20 
9 9 
0 
0 
Rest 
7 
0 
20 
0 
0 
20 
10 11 
0 
0 
0 
Rest 
7 
0 
0 
00 
20 
11 9 0 
0 
Rest 
7 
0 
0 
20 
20 
12 9 0 
0 
Rest 
7 
10 
0 
0 
0 
20 
13 10 
0 
0 
0 
Rest 
7 
10 
10 
0 
00 
20 
14 10 
0 
0 
0 
Rest 
7 
12 
0 
0 
0 
12 
15 9 0 
0 
Rest 
7 
35 
0 
0 
0 
35 
16 10 
0 
0 
0 
Rest 
7 
0 
0 
0 
40 
17 9 0 
0 
Rest 
6 
20 
40 
0 
0 
20 
18 9 00 
(10) 
Rest 
6 
20 
0 
0 
0 
20 
19 9 15 
(15) 
Rest 
6 
20 
0 
0 
0 
20 
20 11 
10 
5 
(15) 
Rest 
6 
20 
0 
0 
0 
20 
21 15 
0 
0 
0 
Rest 
7 
20 
0 
0 
0 
20 
22 0 0 
0 
Rest 
7 
20 
0 
0 
0 
20 
23 2 0 
0 
Rest 
7 
20 
0 
0 
0 
20 
24 25 
0 
0 
0 
Rest 
7 
20 
0 
0 
0 
20 
25 9 0 
0 
Rest 
0 
20 
0 
0 
0 
20 
26 9 0 
0 
Rest 
3 
20 
0 
0 
0 
20 
27 9 0 
0 
Rest 
0 
20 
0 
0 
0 
20 
28 9 0 
0 
Rest 
18 
18 
20 
0 
0 
0 
20 
29 9 0 
0 
Rest 
6 
5 
0 
0 
5 
30 9 0 
0 
Rest 
6 
55 
0 
0 
0 
55 
31 9 05 
(45) 
Rest 
6 
20 
0 
0 
0 
20 
32 9 45 
(45) 
Rest 
6 
20 
0 
0 
0 
20 
33 9 0 
0 
Rest 
6 
20 
0 
0 
0 
20 
34 9 0 
0 
Rest 
7 
20 
0 
0 
0 
20 
*1 
35 10 
0 
0 
0 
Rest 
6 
6 
20 
0 
0 
0 
20 
*2 
36 10 
0 
0 
0 
Rest 
7 
20 
0 
0 
0 
20 
*3 
__________________________________________________________________________ 
Referring to Table 1, the contents of the hard particles (iron 
intermetallic compound(s)) and the solid lubricating component forming 
each sample are expressed in weight percentage with respect to the overall 
sintered copper alloy of 100 percent by weight. The contents of the 
respective elements forming the matrix of each sample are expressed in 
weight percentage with respect to the overall matrix of 100 percent by 
weight, with the rest consisting of copper (Cu). With reference to the 
solid lubricating components, symbol A denotes natural scaly graphite 
powder (40 .mu.m in mean particle diameter), and symbol B denotes natural 
expanded graphite powder (150 .mu.m in mean particle diameter). With 
reference to the iron intermetallic compounds forming the hard particles, 
symbols C to G denote the following compounds respectively: 
C: FeMo 
D: FeCr 
E: FeAl 
F: FeTi 
G: FeSi 
Except the comparative sample No. 36, each of the sintered copper alloys 
was obtained by mixing hard particle dispersed composite copper alloy 
powder with a prescribed amount of solid lubricating powder and then 
compacting and sintering the mixed powder, and exhibited a transverse 
rupture strength of at least 200 MPa. The hard particle dispersed 
composite copper alloy powder was obtained by mechanically alloying mixed 
a powder of copper alloy powder having a component composition for forming 
a matrix and hard particles. 
Referring to Table 1, the comparative samples Nos. 34, 35 and 36 provided 
with numerals *1, *2 and *3 were obtained as follows: 
Comparative Sample No. 34: Starting raw material powder was mechanically 
mixed and crushed while the treatment conditions therefor were changed so 
that the maximum particle diameter of the hard particles was 60 .mu.m, and 
the mixed powder was compacted and sintered. 
Comparative Sample No. 35: Starting raw material powder was mechanically 
mixed and crushed while the treatment conditions therefor were changed so 
that the maximum particle diameter of the hard particles was 60 .mu.m, and 
the mixed powder was compacted and sintered. 
Comparative Sample No. 36: Starting raw material powder was compacted and 
sintered without a mechanical mixing/crushing/alloying treatment. 
Table 2 shows results of evaluation of maximum particle diameters, mean 
particle diameters, mechanical characteristics (transverse rupture 
strength) and frictional sliding characteristics (friction coefficients 
.mu. and abrasion loss of frictional and counter materials). 
TABLE 2 
__________________________________________________________________________ 
Hard Particles .mu.m 
Transverse 
Friction Sliding Characteristics 
Maximum Mean Rupture Abrasion Loss mg.sup.1) 
Sample 
Particle 
Particle 
Strength of 
Sintered 
Counter 
No. Diameter 
Diameter 
Sintered Body 
.mu. value 
Material 
Material 
State of Damage 
__________________________________________________________________________ 
1 17 9 325 0.38 
20 7 no damage 
2 22 
no damage 
3 25 
no damage 
4 25 
no damage 
5 20 
no damage 
6 21 
no damage 
7 18 
no damage 
8 21 
no damage 
9 19 
no damage 
10 19 
no damage 
11 20 
no damage 
12 22 
no damage 
13 25 
no damage 
14 25 
no damage 
15 22 
no damage 
16 24 
no damage 
17 21 
no damage 
18 19 
no damage 
19 17 
no damage 
20 19 
no damage 
21 20 
no damage 
22 3 .times. 10.sup.3 
-3 .times. 10.sup.2 
seizing 
23 1 .times. 10.sup.3 
-2 .times. 10.sup.2 
seizing 
24 3 .times. 10.sup.3 
-3 .times. 10.sup.2 
seizing 
25 3 .times. 10.sup.3 
-2 .times. 10.sup.2 
seizing 
26 6 .times. 10.sup.3 
-3 .times. 10.sup.2 
seizing 
27 7 .times. 10.sup.3 
-3 .times. 10.sup.2 
seizing 
28 7 .times. 10.sup.3 
15 
abrasive damage 
29 2 .times. 10.sup.3 
-2 .times. 10.sup.2 
seizing 
30 2 .times. 10.sup.3 
-2 .times. 10.sup.2 
seizing 
31 2 .times. 10.sup.3 
-2 .times. 10.sup.2 
seizing 
32 2 .times. 10.sup.3 
-2 .times. 10.sup.2 
seizing 
33 2 .times. 10.sup.3 
-2 .times. 10.sup.2 
seizing 
34 97 
no damage 
35 76 
no damage 
36 3 .times. 10.sup.3 
-3 .times. 10.sup.2 
seizing 
__________________________________________________________________________ 
Referring to Table 2, the negative symbol "-" in the column of abrasion 
loss of the counter materials indicates an increase in weight resulting 
from adhesion. In a friction test, friction coefficients were measured 
with a ring-on-disc friction tester shown in FIG. 8 after continuous 
driving for 30 minutes in a dry atmosphere. The counter materials were 
prepared from iron sintered materials having tensile strength of 650 MPa. 
When the friction coefficients exceeded 0.7, seizing took place. Referring 
to FIG. 8, reference numeral 10 denotes a fixed sintered copper alloy 
ring, and reference numeral 11 denotes a rotating iron counter material. 
The test conditions were as follows: 
Pressing Force: 30 kg/cm.sup.2 
Speed: 2 m/sec. 
Friction Time: 30 min. 
Testpiece Shape: fixed sintered copper alloy (ring of N60.times.N50.times.5 
mm) 
Counter Material: rotating iron material (discoidal sintered material of 
N80.times.5 mm with tensile strength of 650 MPa) 
In correspondence to Table 1, Table 2 shows the results of the inventive 
samples Nos. 1 to 21 and the comparative samples Nos. 22 to 36. 
The inventive samples Nos. 1 to 21, which were prepared from sintered 
copper alloys having desirable component compositions, exhibited 
transverse rupture strength values exceeding the target value of 200 MPa. 
Further, the inventive samples Nos. 1 to 21 exhibited friction 
coefficients (.mu.) within the target range of 0.15 to 0.5 with no seizing 
to the counter materials or abrasive damage, and were recognized as 
sufficiently applicable to ring materials. 
On the other hand, the comparative samples Nos. 22 to 36 caused the 
following problems: 
Comparative Sample No. 22: The alloy containing no Sn was reduced in 
abrasion resistance, to finally cause seizing with the counter material. 
Comparative Sample No. 23: The alloy was reduced in abrasion resistance and 
seizing resistance due to the small Sn content of 2%, to finally cause 
seizing with the counter material. 
Comparative Sample No. 24: The matrix was extremely hardened and attacked 
the counter material due to the large Sn content of 25%, to finally cause 
seizing with the counter material. 
Comparative Sample No. 25: The alloy containing no solid lubricating 
component caused seizing with the counter material. 
Comparative Sample No. 26: The alloy caused seizing with the counter 
material due to the small content of 3% of the solid lubricating 
component. 
Comparative Sample No. 27: The alloy caused seizing with the counter 
material due to the small content of 2% of the solid lubricating 
component. 
Comparative Sample No. 28: The sintered body was reduced in strength due to 
the large content of 18% of the solid lubricating component. 
Comparative Sample No. 29: A sufficient abrasion resistance was not 
attained due to the small content of 5% of the hard particles, and the 
alloy finally caused seizing with the counter material. 
Comparative Sample No. 30: The sintered body was reduced in strength and 
attacked the counter material, due to the large content of 55% of the hard 
particles. 
Comparative Sample No. 31: The matrix was extremely hardened and attacked 
the counter material due to the large Zn content of 45%, to finally cause 
seizing with the counter material. 
Comparative Sample No. 32: The matrix was extremely hardened and attacked 
the counter material due to the large Ni content of 45%, to finally cause 
seizing with the counter material. 
Comparative Sample No. 33: The sintered body was extremely hardened, 
reduced in strength, and attacked the counter material due to the large Al 
content of 5%, to cause seizing. 
Comparative Sample No. 34: The sintered body was reduced in strength due to 
the large maximum grain diameter of 50 .mu.m of the hard particles. 
Comparative Sample No. 35: The sintered body was reduced in strength due to 
the large maximum and mean particle diameters of 40 .mu.m and 32 .mu.m of 
the hard particles. 
Comparative Sample No. 36: Respective powder materials having prescribed 
components were merely mixed with each other and thereafter sintered with 
no mechanical crushing/mixing, and hence no reaction layer was formed 
between the hard particles and the matrix. Due to presence of coarse hard 
particles, further, the hard particles dropped out of the matrix during 
sliding to cause seizing with the counter material, while the sintered 
material was reduced in strength. 
EXAMPLE 2 
The sintered copper alloy sample No. 2 according to Example 1 of the 
present invention was worked into rings of N60 mm in outer diameter and 
N50 mm in inner diameter, which in turn were press-fitted into guide cases 
of an aluminum alloy for preparing roller brake bodies of two-layer 
structures. On the other hand, iron materials having various tensile 
strength values shown in Table 3 were prepared and worked into brake shoes 
having outer peripheral surfaces which were identical in radius of 
curvature to the inner diameters of the rings, thereby preparing roller 
brakes with no grease lubrication. These roller brakes were mounted on 
rear wheels of 24-inch bicycles, and an endurance test of 10000 cycles in 
total was made by pedaling the bicycles at a speed of 10 km/h., applying a 
lever input of 8 kgf (surface pressure by pressing force: about 30 
kgf/cm.sup.2) thereto, stopping the bicycles in five seconds and pedaling 
the same at a speed of 10 km/h. again every cycle. Friction coefficients 
.mu. in 100, 1000 and 10000 cycles were calculated from effectiveness 
factors (braking force), while states of damage of the brake shoes and the 
rings were investigated. Table 3 shows the results. 
TABLE 3 
__________________________________________________________________________ 
Tensile 
Friction Coefficient .mu. in Endurance Test 
Sample 
Type of Material for 
Strength 
Cycle No. 
No. Break Shoe 
of Shoe MPa 
100 
1000 10000 State of Damage 
__________________________________________________________________________ 
1 iron sintered material 
450 0.40 
0.41 0.40 no damage on shoe and ring 
2 iron sintered material 
650 
no damage on shoe and ring 
3 ingot steel material 
no damage on shoe and ring 
4 iron sintered material 
200 
seizing caused 
seizing caused 
shoe deformed to cause seizing 
5 iron sintered material 
300 
seizing caused 
shoe deformed to cause seizing 
6 ingot steel material 
seizing caused 
test stopped 
shoe deformed to cause seizing 
(locking) 
7 ingot steel material 
seizing caused 
shoe deformed to cause seizing 
8 iron sintered material 
450 
seizing caused 
test stopped 
shoe and ring caused seizing 
and locking 
9 iron sintered material 
450 
seizing caused 
ring attached shoe to cause 
seizing 
10 iron sintered material 
350 
no damage on shoe and 
__________________________________________________________________________ 
ring 
As understood from Table 3, neither nonuniform contact nor abrasive damage 
of the brake shoes and the rings was recognized in the 10000 cycle 
endurance test on the actual bicycles when the brake shoes were prepared 
from the iron material samples Nos. 1 to 3 according to Example 2 of the 
present invention having the radii of curvature to be uniformly in contact 
with the inner peripheral surfaces of the rings with a tensile strength of 
at least 400 MPa, and it was possible to confirm that the roller brakes 
stably exhibited a braking force corresponding to friction coefficients of 
about 0.4. 
On the other hand, the brake shoes prepared from the iron material 
comparative samples Nos. 4 to 7 having a tensile strength of less than 400 
MPa were deformed by the pressing force from the brake levers to be 
nonuniformly in contact with the rings, leading to seizing or locking (no 
rotation of wheels), with occurrence of remarkable abnormal sounds 
(squeaking). 
Referring to Table 3, the samples Nos. 8 and 9 were prepared by employing 
an S35C steel material and an Al--SiC composite material (SiC particle 
dispersed aluminum alloy) for the rings respectively. Both these samples 
Nos. 8 and 9 were incapable of attaining the target friction coefficients 
and caused seizing or locking, and it was recognized that these materials 
are not applicable to rings. 
On the other hand, the sample No. 10 was obtained by preparing both a ring 
serving also as a guide case and a brake shoe from an S35C steel material 
and filling up the clearance between the shoe and the ring with grease for 
lubrication, similarly to the prior art. In this case, the roller brake 
caused neither seizing, nor locking nor abnormal sound, while it was 
recognized that its friction coefficient was at a low level of 0.09. 
A shoe having an outer peripheral surface which was smaller in radius of 
curvature than the inner peripheral surface of the ring was prepared from 
the inventive sample No. 1 in Table 3 and subjected to an endurance test 
similarly to the above. In this case, the shoe was only locally in contact 
with the ring, to cause seizing. 
EXAMPLE 3 
The sintered copper alloy sample No. 2 according to Example 1 of the 
present invention was worked into the shape of rings of N60 mm in outer 
diameter and N50 mm in inner diameter and thereafter press-fitted into 
guide cases prepared from various types of materials shown in Table 4, for 
preparing roller brake bodies of two-layer structures. Further, brake 
shoes made of an iron sintered material having a tensile strength of 650 
MPa were assembled into the roller brake bodies, thereby forming dry 
roller brakes with no grease lubrication. Similarly to Example 2, these 
roller brakes were mounted on rear wheels of 24-inch bicycles, and an 
endurance test of 10000 cycles in total was made by pedaling the bicycles 
at a speed of 10 km/h., applying a lever input of 8 kgf (surface pressure 
by pressing force: about 30 kgf/cm.sup.2) thereto, stopping the bicycles 
in five seconds and pedaling the same at a speed of 10 km/h. again every 
cycle. Thereafter states of the damage of spline teeth parts of the guide 
cases engaging with the rear wheel shafts and receiving high stress were 
observed, and friction coefficients .mu. between the brake shoes and the 
rings were measured in 1000 cycles. Table 4 shows the results. 
TABLE 4 
__________________________________________________________________________ 
State of Damage of Spline Teeth Parts in Endurance 
Test 
Sample 
Type of Material 
Friction 
Number of Times of Endurance Test (Cycles) 
No. for Guide Case 
Coefficient .mu. 
100 1000 10000 
__________________________________________________________________________ 
1 aluminum alloy 
0.41 excellent 
excellent 
excellent 
(no damage) 
(no damage) 
2 cast iron 
excellent 
excellent 
excellent 
(no damage) 
(no damage) 
3 copper alloy 
excellent 
excellent 
excellent 
(no damage) 
(no damage) 
4 magnesium alloy 
excellent 
excellent 
excellent 
(no damage) 
(no damage) 
5 titanium alloy 
excellent 
excellent 
excellent 
(no damage) 
(no damage) 
6 silicon nitride 
excellent 
excellent 
teeth parts damaged 
(no damage) 
in 2500 times 
7 aluminum nitride 
unmeasurable 
excellent 
teeth part damaged 
test stopped 
in 630 times 
8 zirconia 
excellent 
excellent 
teeth parts damaged 
(no damage) 
in 3200 times 
__________________________________________________________________________ 
As clearly understood from Table 4, no problems such as abrasive damage or 
breaking were caused in the spline teeth parts of the guide cases engaging 
with the rear wheels when the guide cases were prepared from metal 
materials having excellent strength and toughness. On the other hand, it 
was confirmed that the teeth parts were broken when the guide cases were 
prepared from ceramic materials which are strong and lightweight but 
inferior in toughness. 
EXAMPLE 4 
Sintered bodies were obtained by pressing and compacting mixed powder 
materials of hard particle dispersed copper alloy powder having the 
blending composition of the sample No. 2 in Table 1 and solid lubricating 
components (natural scaly graphite powder) in a true density ratio of 72% 
and solidifying the mixed powder materials on the basis of conditions 
shown in Table 5 respectively, and were then subjected to evaluation of 
transverse rupture strength. Table 5 shows the results. In 
re-pressurization steps, lubricants for inner walls of molds were prepared 
by dissolving zinc stearate in organic solvents. 
TABLE 5 
__________________________________________________________________________ 
Transverse 
Sintering Condition 
Re-Pressurization Condition 
Re-Sintering Condition 
Rupture 
Temp- Sintered Body 
Mold Surface 
Temp- Strength of 
erature 
Time Temperature 
Temperature 
Pressure 
erature 
Time Sintered Body 
No 
.degree. C. 
Min. 
Atmosphere 
.degree. C. 
.degree. C. 
t/cm.sup.2 
.degree. C. 
Min. 
Atmosphere 
MPa Remarks 
__________________________________________________________________________ 
1 850 30 nitrogen 
400 150 8 -- -- -- 325 excellent sintered 
alloy 
obtained 
2 900 30 hydrogen 
350 200 8 -- -- -- 317 excellent sintered 
alloy 
obtained 
3 780 30 nitrogen 
200 180 8 -- -- -- 312 excellent sintered 
alloy 
obtained 
4 900 20 vacuum 
150 150 8 -- -- -- 319 excellent sintered 
alloy 
obtained 
5 900 30 hydrogen 
350 200 8 850 30 vacuum 
388 excellent sintered 
alloy 
obtained 
6 900 30 hydrogen 
ordinary 
ordinary 
8 850 30 nitrogen 
322 excellent sintered 
alloy 
temperature 
temperature obtained 
7 750 30 nitrogen 
80 ordinary 
8 750 30 nitrogen 
318 excellent sintered 
alloy 
temperature obtained 
8 600 60 hydrogen 
-- -- -- -- -- -- 165 sintered body broken 
in 
the process of 
carriage 
9 900 5 hydrogen 
-- -- -- -- -- -- 140 sintered body broken 
in 
the process of 
carriage 
10 
850 30 in the 
-- -- -- -- -- -- 155 sintered body broken 
in 
atmosphere the process of 
carriage 
11 
1050 
30 vacuum 
-- -- -- -- -- -- 395 dimension remarkably 
changed by effusion 
of 
liquid phase 
12 
900 30 hydrogen 
ordinary 
ordinary 
8 -- -- -- 188 
temperature 
temperature 
13 
800 30 nitrogen 
ordinary 
ordinary 
8 900 60 nitrogen 
335 dimension remarkably 
temperature 
temperature changed by progress 
of 
sintering 
14 
900 30 hydrogen 
ordinary 
ordinary 
2 850 30 nitrogen 
175 
temperature 
temperature 
__________________________________________________________________________ 
In Table 5, "--" indicates no execution. 
As understood from Table 5, sintered bodies having sufficient strength 
(transverse rupture strength of at least 200 MPa) necessary for ring 
materials were obtained from the inventive sintered copper alloy samples 
Nos. 1 to 7 under proper sintering, re-pressurization and re-sintering 
conditions. 
On the other hand, the comparative samples Nos. 8 to 14 caused the 
following problems: 
Comparative Sample No. 8: Due to the low sintering temperature of 
600.degree. C., the sintering phenomenon insufficiently progressed to 
result in of the sintered body during breaking in the process of carrying 
the sintered body to the re-pressurization step. 
Comparative Sample No. 9: Due to the short sintering time of five minutes, 
the sintering phenomenon insufficiently progressed to result in breaking 
of the sintered body during the process of carrying the sintered body to 
the re-pressurization step. 
Comparative Sample No. 10: Due to the sintering in the atmosphere, the 
sintering phenomenon insufficiently progressed to result in breaking of 
the sintered body during in the process of carrying the sintered body to 
the re-pressurization step. 
Comparative Sample. No. 11: Due to the heating up to 1050.degree. C. beyond 
the solidus curve temperature of the copper alloy forming the matrix, a 
liquid phase resulted in the sintered body to increase dimensional change. 
Comparative Sample No. 12: Because a no re-sintering process was not 
carried out, it was not possible to attain a sufficient strength for 
serving as a ring material. 
Comparative Sample No. 13: Due to heating up to 900.degree. C. in the 
re-sintering step beyond the first sintering temperature (800.degree. C.), 
the sintering progressed again to increase dimensional change in the final 
product. 
Comparative Sample No. 14: Due to the small surface pressure of 2 
t/cm.sup.2 in the re-pressurization step, a sufficient strength for 
serving as a ring material was not attained. 
EXAMPLE 5 
A sintered copper alloy prepared by sintering and solidifying a mixed 
powder having the composition of the inventive sample No. 8 in Example 1 
was worked into the shape of rings of N75 mm in outer diameter and N65 m 
in inner diameter under the inventive conditions, which in turn were 
press-fitted into guide cases of cast iron for preparing roller brake 
bodies of two-layer structures. Table 6 shows transverse rupture strength 
values of the obtained sintered copper alloys. Brake shoes prepared of an 
iron sintered material having tensile strength of 650 MPa were assembled 
into the roller brake bodies, for preparing dry roller brakes with no 
grease lubrication. 
Similarly to Example 2, these roller brakes were mounted on rear wheels of 
24-inch bicycles, and an endurance test of 1000 cycles in total was made 
by pedaling the bicycles at a speed of 25 km/h., applying various lever 
inputs shown in Table 6 thereto, stopping the bicycles in five seconds and 
pedaling the same at a speed of 25 km/h. again every cycle. Friction 
coefficients .mu. between the brake shoes and the rings were measured. 
Table 6 shows the results. 
TABLE 6 
______________________________________ 
Transverse Friction Coefficient 
Rupture Strength 
Lever Number of cycles of 
Sample 
of Sintered Alloy 
Input Endurance Test (times) 
No. MPa kgf/cm.sup.2 
100 1000 Remarks 
______________________________________ 
1 280 10 0.42 0.41 no damage 
2 280 38 
0.41 
0.41 
no damage 
3 345 45 
0.41 
0.42 
no damage 
4 345 85 
0.42 
0.40 
no damage 
5 280 140 
0.39 
-- 
ring body 
abraded 
6 345 150 
0.41 
-- 
ring body 
abraded 
______________________________________ 
As seen from the inventive samples Nos. 1 to 4 in Table 6, it was possible 
to exhibit stable friction coefficients (braking force) with no abrasive 
damage of the sintered copper alloy ring materials when lever inputs 
(force for pressing the shoes against the rings) of about 10 to 100 
kgf/cm.sup.2 were applied thereto in racing cycles and general bicycles to 
which the present invention is directed. As seen from the comparative 
samples Nos. 5 and 6, on the other hand, it was confirmed that the ring 
materials were abrasively damaged when overloads of about 150 kgf/cm.sup.2 
were applied thereto as lever inputs. 
According to the inventive roller brake, as hereinabove described, a high 
braking force corresponding to a friction coefficient of 0.1 to 0.5 can be 
stably exhibited with neither seizing/locking, nor abrasive damage, nor 
abnormal sound such as squeaking between the ring and the brake shoe 
forming the roller brake when a pressing force of about 10 to 50 
kgf/cm.sup.2 is applied thereto under heavy frictional sliding conditions 
without intervention of a lubricating component such as grease or oil. 
Therefore, the roller brake according to the present invention can attain 
high effectiveness with a relatively small lever input without locking 
causing seizing of the roller brake during running, and has excellent 
braking efficiency. 
Although the present invention has been described and illustrated in 
detail, it is clearly understood that the same is by way of illustration 
and example only and is not to be taken by way of limitation, the spirit 
and scope of the present invention being limited only by the terms of the 
appended claims.