EB2015-BAS-005-

REDUCTION OF THE UNSPRUNG AND OF THE ROTATING MASSES

ON RAILWAY AXLES - Ceramic foam/aluminum alloy composite brake disc

for Fuel , Pollution and LCC reduction .

1Barberis, Dario

*,

2Fang,Shu ,

3Fang,Ming

1Technical Consultant, Italy,

2Engineer, Zhejiang Tianle New Material Technology Co., Ltd , PRC,

3General Manager, Zhejiang Tianle New Material Technology Co., Ltd , PRC

KEYWORDS – brake disc , ceramic MM composite , axle and wheel brakes , unsprung masses ,

High Speed Trains

ABSTRACT - The Aluminum Metal Matrix Composite Brake Discs seems to be a very promising

technological solution to give a strong and credible answer to the double request for Low Weight

solutions and low Life Cycle Cost during the full service life of the Friction Pair constituted by a

Brake Disc and the Pads acting on it , for different Railway applications .

Starting from 2005 the ZheJiang Tianle Group has been developing this new process to produce

a real breakthrough solution for the Rail Brake Discs and has been actively testing the new product.

The innovative Concept is based on the use of a high Temperature and low Wear Material (like the

SiC Foam ) filled with a metal alloy , able either to fully penetrate and fill the MM Foam and to

transmit , with a very high flow rate , the heat produced on the friction surface .

The air flow, cooling the internal part of the disc, is contributing to reduce the initial thermal shock

and also to stabilize, at lower level, the stationary temperature, during prolonged brake applications,

thanks to a better heat flow , “discharging” the energy from the friction surface .

The SiC Foam is placed on the external faces of the disc to be casted , then all the volume of the

disc is filled with a special low pressure die casting process , through the injection of the Al alloy .

The result is a noticeable reduction of the total weight ( up to -60% , compared to a conventional

steel disc of similar performances !); the average density of the Al MMC brake Disc is around 2.8

Kg/dm3 . Performances : this new technological solution is suitable for services requiring either

frequent brake applications , like on the urban, metro and commuter lines, or HS Trains as it has

been also tested up to 350 Km/h, with top speed tests up to 380 Km/h and max temperature below

500°C with a resulting friction coefficient (mu) of between 0.4 and 0.3. Other tests at 160 Km/h,

starting from a Temperature of 50°C, in about 43 sec , has shown a max Temperature of < 200°C .

Weight : the heavy reduction of the weight of this new technology can have a deep impact on all the

economical performances of a train . For example an HST with three Discs per axle, thanks to the

reduction of at least 50 Kg per Disc, can get a total reduction of 300 Kg per bogie. This corresponds

to more than 3 paying passengers per trip or at least 6 more tickets sold per day ! Even considering

a very low fare of 30/35 € , it means an higher income of 200 € per day per bogie !

OBJECTIVES

A strong technological breakthrough obtained with the selection of suitable foam and of particular

Aluminum alloys to obtain , at the same time, high resistance to heat and wear + high transmission

and evacuation of heat , without melting the light alloy . The optimization of each function and

the optimal marriage between the individual results is illustrated in the following 3 points :

1 ) Selection of SiC foam : during the R&D of brake disc for aircraft in China in 2003, Tianle has

investigated the ceramic foam/metal composites as friction materials . Aluminum oxide ceramic

foam and SiC foam filter are currently used worldwide. Al oxide ceramic foam was not choose due

to its low resistance to thermal shock. SiC foam filter was not suitable due to low SiC percentage

(60%-80%) , particles too large , low sintering temperature and binding phase problem, resulting in

low strength and low resistance to thermal shock . Besides, it can easily loose particles during

the braking at high speed, causing bad wear to the friction pair. Thus, Tianle has spent years on

R&D until a successful solution based on SiC powder with the average diameter of 0.5μm, after

2000°C heathing plus sintering , forming SiC foam containing over 98% of SiC . Its compression

resistance, fracture resistance and tensile strength are much higher than SiC ceramic foam filter.

Aluminum oxide ceramic foam SiC foam filter

Besides it’s highly resistant to thermal shock. Above all, it avoids the falling off of ceramic foam

filter particles, due to friction at high speed and high temperature that could result in higher wear of

the pads . So , after a large number of material comparison, subscale dyno tests and many computer

simulation, ceramic foam/aluminum alloy composite brake discs were successfully developed for

HST , metro trains and other automotive applications since April, 2013.

SiC ceramic foam Ceramic foam/aluminum composite

2 ) Selection of aluminum alloy : to ensure the safety and reliability during braking , an Al alloy

under ASTM and DIN standard was selected. Based on the requirement of energy absorbed, the

coefficient of friction, the braking distance and wear/life, Tianle applied computer to simulate the

highest surface temperature during braking and then tested relevant property of aluminum alloy

(matrix) and composite under different temperature situations .

Composite thermal property test

Tensile strength MPa

25℃ 75℃ 150℃ 225℃ 250℃ 300℃ 350℃

Aluminum alloy 338.99 326.23 319.28 287.92 250.3

7

Ceramic foam/al alloy comp. 188.17 178.75 184.3

6

165.9

3

3 ) Production of SiC ceramic foam/aluminum alloy composite brake disc

Ceramic foam Casting mold finished product sample after cut

First step , a high T° cooked SiC ceramic foam is cut into the desired shape and put into the mold.

Then cast ceramic foam and aluminum alloy are poured together to form the composite.

The composite friction layer is about 7mm thick (see finished product and sample after cut photos).

25℃ 200℃ 250℃ 300℃ 350℃

Thermal conductivity λ/Wm-1K-1

λ/Wm-1K-1

155 167 150 148 163

Specific heat capacity J kg-1K 906 970 1100 1186 1260

Density kg/cm3 2790 2788 2786 2786 2783

This process has the following advantages: one-step composite formation, simple process, good

formability and repeatability, few post-production processes with tight 3D net shape formation,

good strength and stiffness and good heat transfer from friction surface absorbed by the entire brake

disc body which enhanced the energy dissipation.

CONFIGURATION / DISC ARCHITECTURE

The SiC ceramic foam inserts can be cut in many different profiles and dimensions. Depending on

the desired final result , the dimension of the foam inserts are very variable , to cover the disc ring

with a suitable number of pieces ( from 6 , that is a typical configuration , to 24 , for very flexible

discs ) . The aluminum interval between two consecutive inserts is normally cut , in order to give

more flexibility to the whole disc. The discs can be poured in a single mould or can be produced in

parts and then bolt together.

Two examples of solid Discs poured with Ceramic Foam inserts

Examples of Discs with Ceramic Foam Inserts , manufactured in two rings , bolt together

SIMULATIONS

A wide and long simulation activity has been carried on to explore the different behaviors of a

variety of configurations and situations . The computer has been applied to simulate the highest

surface temperature during braking, at different speeds and force, and then to simulate the relevant

property of the aluminum alloy (matrix) and composite under different temperature situations .

The temperature distribution and flows have been extensively simulated to check the pattern of the

hot areas and the consequent thermal stresses. Additional simulations have been done to check the

stresses in the connections between the two rings and the central hub .

Examples of stress and thermal simulations on different configurations and speeds .

DYNAMOMETRE TEST

A long dyno test campaign has been carried on at different speed and braking forces. On Nov 2013,

350km/h dyno test were run , according to TJ/CL 310-2013 B.3 test programme issued by China

Railway Corp. on a RENK test system at CSR Qishuyuan Institute. Also a test at 380km/h was done

but it was suspended due to a small crack appeared at a ventilating groove. It was the result of poor

design of the chamfer angle , being too small ( see photo ) . This issue has been promptly solved .

SiC的SiC/Fe盘与SiC/Cu闸片摩擦副

空气流对制动盘温度影响

参考面，风速50km/h 参考面，风速80km/h 参考面，风速100km/h

考虑空气流，摩擦副的摩擦表面温度随制动次数变化，最高温度390℃。

380km/h，0.5MPa

Crack at ventilating groove Discs after Dyno test

On March 2014, dyno tests according to UIC 541-3 C.1 2A 1 (140km/h) were carried on , and then

repeated with mass per disc increased to 9T and force applied increased by 10%.

On July 2014 , 350 km/h dyno tests were run , once again , according to the same TJ/CL 310-2013

B.3 test programme , on the same RENK test system at CSR Qishuyuan Institute, with positive end.

With reference to the test data from 2013 and coefficient of friction, Tianle run the tests with lower

force applied (Fb) which can still meet the braking distance requirement set by the Railways .

Brief summary of performances and dyno tests results :

1. SiC ceramic foam and aluminum alloy within the composite friction layer are interconnecting

and interlocking in a 3D matrix . Thus the stiffness, compression resistance and shear resistance of

aluminum alloy are enhanced as well the thermal deformation resistance of the composite material .

2. SiC ceramic foam cells of diameter around 2mm confine the aluminum alloy matrix within a tiny

space, which suppresses the plastic deformation and thermo-softening of aluminum alloy. It avoids

the splicing , tearing off and severe third-body abrasive wear during braking when using particles

enhanced aluminum alloy composites . Friction and wear properties of the composite are greatly

improved .

3. The expanding and combining of thermal stress resulting holes and minor cracks are hindered by

ceramic foam, thus it’s very difficult the development and propagation of continuous cracks .

4. When used for 140km/h trains, the coefficient of friction between brake disc and brake pad

should be lowered properly to avoid overheat from too high-energy braking.

5. When used for 350km/h trains, the coefficient of friction between brake disc and brake pad

should be lowered properly, mainly decreasing the force applied with the precondition of complying

with the braking distance requirements and avoiding the overheat due to braking.

6. The thermal conductivity of aluminum is several times better than steel and iron materials, so it's

preferred to continue the cooling interval after the temperature of brake disc is dropped to specific

level because the brake pad has not yet been cooled to the same level as using steel and iron brakes.

7. Thermal Shock Tests : these tests are based on the heating of a section of disc material , up to

350°C , inside a muffle furnace, for 10 minutes, then plunging the sample in water @ 15°C ,then

again for 2 min. @ 350°C ; repeating this cycle for 2500 times . Final polishing of the sample for

evidencing any sign of cracking or micro-crack .

PADS

The innovative Discs have been tested with traditional composite and

sintered pads with the very promising results that have been evidenced ;

new pads solutions are also under development and test, based on some

innovative materials and solutions , more compatible with structure of

the disc itself . The new pad solutions are aimed at lengthening the life

of the consumables and also to reduce the cumulated damages on the

disc . The target is to overcome by far , the actual life of the Pads , as

currently used in normal service . The achievement of further positive

results , in term of longer life , without penalizing the braking stopping

performances , is further supporting a noticeable reduction of the LCC

of the complete Braking Station .

The initial results has shown a higher friction coefficient ( around 0.4 vs 0.35 of the sintered pads )

this means a shorter braking distance , but a higher energy flow in the unit time , so modified pads

will be developed , able to give the same performances of the actual UIC pads .

Life of the pads has shown to be comparable from the initial tests , that means a very promising

potential for the next steps of this development . Only the cooling capacity of these new pads is

lower than the previous solutions ( longer cooling capacity )

CONCLUSIONS

1. The Tianle Research Team has been working on ceramic foam/metal composites since 2003 ,

starting with aeronautical applications .

2. Demonstration scale production of ceramic foam/aluminum alloy composite brake disc for

railway use was done in the last few years inside a dedicated branch Company. Dyno test for

automotive cars were also carried on in August 2014 , and two test cars are running .

3. After the successful dyno tests Tianle has finalized the size and shape of ceramic foam’s pores.

4. During the dyno test according to UIC 541-3 C.1 2A 1 (140 km/h), the temperature of aluminum

brake disc reached less than 200° C and then dropped to 50～60℃ in 2-5 minutes only, whereas

steel brake disc would take 10-15 minutes. During the dyno test according to TJ/CL 310-2013 B.3

(350 km/h), the temperature of aluminum brake disc reached only 480° C and dropped to 50～60℃

in 10-60 minutes only whereas steel brake disc would take 30-120 minutes. On the other hand , the

Temperature of brake pad is much higher when using aluminum brake disc compared to steel disc.

5. Weight Reduction : a reduction of about 50 Kg per disc can be achieved for a HST running at

350 Km/h ; similar targets for EMU’s running at 140 Km/h . It means 300 Kg per bogie of HST

and 100/200 Kg per bogie for a frequently stopping Metro or EMU trainset .

6. This winning DISC TECHNOLOGY can become shortly the base for new competitive brake

solutions . On the base of the results of long lasting dyno test campaigns it appears that this new

Technology could be very promising and become the base for future winning braking solutions,

either for HST’s and for frequently stopping trainsets .

7. LCC and Economical aspects : on the base of at least 330 running days per year , for a HST , the

reduction of weight of about 300 Kg per bogie means an additional capacity of 3 passengers that ,

considering two travels /day , a coefficient of occupation of 66% and a fare of below 50 €/ ticket ,

gives an extra income of > 65.000 € / year per bogie , in comparison with “classic” dics .

This is the most evident economical advantage, without taking into account other advantages of

second order, like the reduced impact on the rail ( unsprung masses) and the reduction of fuel

consumption ( acceleration of the trainset ).

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