Axle Centers
Slide 1
Wet Brakes:
Materials and
Concepts
Slide 2
Wet Brakes – Materials
and Concepts
Rich Dowell
Chief Engineering Director – Asia Pacific
Carlisle Brake & Friction
INSTRUCTOR BIO Rich Dowell Carlisle Brake & Friction Rich Dowell has 39 years experience in designing, developing and testing wet friction products and systems for the Off‐Highway industry. Rich is called “Mr. Wet Friction” in the braking industry. Rich started his career in 1969 with Lear Sieglar as a design engineer and spent his first 5 years designing and testing power systems for airplanes. Rich joined Carlisle (SK Wellman) in 1974 and has been THE authority in wet friction ever sense. Rich has developed / directed the development of 2 semi‐metallic, 5 metallic and 7 paper friction materials. Rich holds U.S. Patent # 6,277,768 High Energy Friction Product. He has published three technical papers for the Society of Automotive Engineers and has published numerous journal articles. Rich has also presented technical seminars worldwide. Rich holds a Bachelor of Science in Aerospace Engineering and is a 6 Sigma Green Belt. Carlisle Brake & Friction (CBF) is a leading solutions provider of high performance and
severe duty brake, clutch and transmission applications to OEM and aftermarket
customers in the mining, construction, military, agricultural, motorsports, industrial and
aerospace markets. The strength of CBF’s brands, including Wellman Products Group,
Carlisle Industrial Brake & Friction, Hawk Performance, Cragar, Black Rock, Japan
Power Brake, VelveTouch, and Field Pro, gives our customers access to a diverse range of
the most highly engineered braking, friction, clutch, and transmission products available
to the market today. With eleven manufacturing facilities globally located in the U.S.,
U.K., Italy, China, Japan, and India and with over 2,200 employees, CBF serves over 100
leading original equipment manufacturers in 50 countries, making CBF the right choice
for your new brake or friction design, no matter where you are in the world or what you
want to be.
For more information visit www.carlisleCBF.com
United States +1 440 528 4000 United Kingdom +44 1495 767 300
Italy +39 030 9942 China +86 21 6100 5222
Wet Brakes - Materials and Concepts
October 30-31, 2012
Pune, India
Slide 4
Coefficient of Friction
4
Slide 5
Coefficient of Friction
Classic Definition
f

F
µ = coefficient of friction
ƒ = friction force
F = normal force
5
Slide 6
Clutches and Brakes
• CBF makes friction materials for Clutches and Brakes
• Clutches are a mechanism to force an output shaft to spin
at the same speed as the input shaft. It is a dynamic
coupling.
• A brake does the same as a clutch except that one shaft or
side of the brake is always at zero speed. It stops things.
6
Slide 7
Function of a Brake
• The primary function of a brake is to stop a vehicle in
motion.
• Friction material requirements:
– Minimal Stopping distance
– Smooth stopping
– No noise
– Good durability
7
Slide 8
Energy
• Energy is either Dynamic, Potential (Position), or heat.
• In the ordinary Newtonian world energy can neither be
created nor destroyed. The amount is constant.
• When we stop a vehicle or shaft with friction we turn the
energy from that of motion to heat.
• How we handle heat is the heart of designing brakes
and clutches.
8
Slide 9
Coefficient of Friction and Torque
• Equation for Torque is:
T  FRN
• Where:
–
–
–
–
T = Torque
lb-ft
F = apply force
lbs
R = Mean radius
ft
N = number of friction surfaces
or
or
or
N-m
N
m
• There are no units for coefficient of friction.
9
Slide 10
Torque
10
Slide 11
Types of µ
• Coefficient of friction can be measured at various times
during a stop. Typically we think of four important friction
levels:
– Initial µ
– Dynamic µ
– Lockup µ
– Static or Breakaway µ
11
Slide 12
Typical Torque Trace
Time →
12
Slide 13
Types of µ (cont’d)
•
Initial µ
– Measured when pressure is first applied. This is sometimes called touchup. Can be
important especially under inching conditions. A high initial coefficient may result in
difficulty inching a vehicle smoothly.
•
Dynamic µ
– Measured at half the initial speed. Typically it is desired to have a high dynamic
coefficient.
•
Lockup µ
– Measured at zero speed. Can determine the shift quality in transmissions or the
noise level in brakes. If the lockup coefficient is higher than the dynamic coefficient,
this will result in rough shifts or noisy brakes. High lockup can be desirable in winch
or parking brake applications.
•
Breakaway µ
– Measured by applying torque with pack locked up until the pack breaks free.
Important to make sure that the friction pack does not slip after a stop has been
made or if a vehicle is parked on a hill.
13
Slide 14
Factors that impact µ
•
The coefficient of friction for a friction material is dependent on many factors,
including:
•
•
•
•
•
•
•
Oil type
Surface temperature
Friction material grade
Friction material density
Apply pressure
Rotational speed
Groove pattern
•
The same friction material could probably have a coefficient of friction from .07
to .17 depending on the above factors, so it becomes difficult to answer a
question like, “What is the coefficient of friction for N-401?”
14
Slide 15
Wet friction system
• Series of friction and reaction plates
• Usually 4-8 friction plates in a stack
15
Slide 16
Pros and Cons of Wet Brakes
Wet Con
Wet Pro
–
–
–
–
–
Longer Life
Smoother operation
Can run as retarder
Immunity to dirt
No sparks
–
–
–
–
–
Higher Weight
More expensive
Lower coefficient
Loss of oil is fatal
Performance
dependent upon oil type
– Parasitic Drag higher
16
Slide 17
Typical Wet Applications
–
–
–
–
–
–
–
–
Powershift/Automatic Transmissions
Axle Speed Brakes
Wheel Speed Brakes
Winches
Wet Master Clutches Tractors and Motorcycles
Steer Clutches and Brakes Tracked Vehicles
Synchronizers
Swing / Travel motors
17
Slide 18
Agricultural & Forestry Equipment
• Wet Transmission
Disks (powershift)
• Wet sump disk brakes
sandwiching the
differential
18
Slide 19
Construction & Earthmoving
Equipment
• Powershift
Transmission disks
• Wet steer clutches
• Wet steer brakes
19
Slide 20
Industrial & Material Handling
Equipment
• Powershift
Transmission Disks
• Axle / Wheel speed
brakes
20
Slide 21
Application Glossary
•
Wheel Speed Brakes
•
Axle Speed Brakes
•
Steering Brakes and Clutches
•
Swing/Travel Motor Brake
– Typically used in heavy duty off highway vehicles and can be forced cooled or
sump type oil systems. Friction material needs are a low static : dynamic ratio
and good durability and thermal stability.
– Run at higher speeds than wheel speed brakes. Often run in common sump
with differential. Similar properties to wheel speed brakes required, although
noise is usually less of an issue.
– Used in track type vehicles. When driving straight ahead, the clutch on each
side is engaged. When steering the vehicle the steer clutch is slipping and the
steer brake is applied to the side turning. Friction material needs are good
durability, smooth engaging, and thermal stability.
– Used in track type excavators to stop the boom rotation and to aid in hold
the vehicle stable while digging
21
Slide 22
Wet Friction Material Choices
22
Slide 23
Wet Friction Material Choices
•
Sintered Metallic
– Can withstand high pressure, but have low energy capability and low coefficient of
friction. Still used in military and severe duty applications.
•
Graphitic material (HDT-303)
– Can withstand pressures similar to bronze materials with a higher coefficient of
friction and higher energy capacity.
•
Carbon Cloth
– Very high energy material, but at a premium price
•
Paper materials are the material of choice for most of today’s designs, due to:
–
–
–
–
–
High coefficient of friction
High energy absorption
Low cost
Low weight
Can be tailored to specific performance requirements
23
Slide 24
Energy Capability Comparison
24
Slide 25
Summary of Friction Materials
85 J/cm2 - 21 bar - 2400 rpm - Cat TO-4 fluid
Paper
Dynamic
Lockup
Metallic
.060/.080
.150/.170
N-414-5
.090
.153
N-452-2
.135
.150
N-653-4
.113
.142
N-670-4
.121
.144
N-360-2
.135
.174
N-266-4
.130
.172
N-269-4
.140
.200
25
Slide 26
Spec 145 (bronze) in Cat TO-4 oil
Low dynamic
High lockup
26
Slide 27
N-414 in Cat TO-4 oil
Low coefficient paper
High ratio
27
Slide 28
N-266 in Cat TO-4 oil
28
Slide 29
N-670 in Cat TO-4 oil
Flatter Torque
Smooth engmt
29
Slide 30
Paper Friction Materials
•
Friction papers are papers only in the sense that they are produced on paper making
equipment. Typical friction material will contain one or more kinds of fibers, one or more
fillers and a binder.
•
Fibers:
–
•
Fillers
–
•
The fibers used are cellulose, aramid, glass, mineral and carbon based. The fibers serve to
establish the desired porous structure of friction papers and to also act as a carrier for the fillers
during the paper making process.
The fillers are many and varied, with materials such as diatomaceous earth, graphite, coke and
metal oxides being very common. The various fillers act as friction modifiers and may also
improve the material’s heat resistance.
Binders
–
The binders are almost always thermosetting resins introduced into the papers by a saturation
process. The resin binder is the major contributor to the final strength of the material. The resin
also affects friction and durability characteristics.
30
Slide 31
Oil Types / Function
31
Slide 32
Function of the Oil
•
The oil used in a wet friction application has many purposes:
– Cool the friction material pack by removing heat energy from the
system
– Lubricate the gears
– Prevent corrosion
– Disperse and neutralize contaminants etc.
•
A variety of oils are available. The type of oil used can have a big
impact on friction material performance.
•
There are three main constituents that affect oil quality:
– Viscosity
– Base oil
– Additives
32
Slide 33
Oil Additives
•
Additives are put into the Base oil to improve properties of the oil. Our
testing has shown that the additives have a greater impact on
performance than the type of Base fluid.
Dispersants
Sludge & varnish control
Antioxidants
Prohibit oxidation
Antiwear
Planetary gear, bushing, thrust washer protection
Friction modifier
Modify friction performance
Corrosion inhibitor
Prevent corrosion and rust
Seal swell agent
Prevent loss of fluid via seals
Viscosity Improver
Reduce rate of change of viscosity
Pour Point Depressant
Improve low temperature fluidity
Foam inhibitor
Foam control
Red dye
Identification
33
Slide 34
Friction Modifier and Antiwear
Additives
•
Friction modifier additives are put in some oils to reduce the lockup coefficient
of friction. This allows for smooth shifts in a transmission or noise reduction in
brakes.
•
There are a variety of types of additives on the market. In addition, oils can
contain different amounts of the additives.
•
Some oils also contain additive packages that are designed to protect the gears
at elevated temperatures. At elevated temperatures, the additives precipitate a
protective coating on the gears for protection against wear.
•
Unfortunately, the additives also precipitate out on the friction surface at
elevated temperatures. This can reduce the porosity of the material and result
in glazing and friction fade.
34
Slide 35
N360 Paper Friction in Various Oils
Wear and Friction Level
0.160
0.140
0.120
Friction Level
0.100
0.080
Dynamic
Lockup
0.060
Wear
0.040
0.020
0.000
0
1
2
3
4
Citgo 80W90
Shell Donax TD
J20‐C
5
6
TO‐4
TO‐4 Emerest
Mobil DTE 150
7
Slide 36
Oil Categories
• The main categories of oils are:
–
–
–
–
–
–
–
Engine oils
Automatic Transmission fluids (Dexron III)
Caterpillar TO-4 Transmission fluids
Tractor Hydraulic fluids
Gear lubes
Synthetic fluids
Biodegradable oils
• Oils within each category usually have similar
performance.
• Each category of fluids is designed to give specific
properties.
36
Slide 37
Oil Summary
• There are a lot of different oil types in use with
friction materials and gears. Each is designed to
give properties to meet specific applications.
• Differences in the oil include:
– Viscosity
– Base fluid
– Additive type and amount
37
Slide 38
Brake Testing
38
Slide 39
Brake Testing in different oils
• Brake noise is a common problem in wet brakes. It can be
caused by a number of things:
– Friction material type
– Type of oil used
– Brake design itself
• We can evaluate noise using a full scale wheel end brake.
Noise is sometimes audible and can be seen in the torque
trace.
• A negative sloping torque trace (as speed approaches
zero) is desirable to eliminate noise.
39
Slide 40
Dynamometer 17
HDT-303 in Mobil 424 fluid
Quiet
Flat Torque trace
40
Slide 41
Dynamometer 17
HDT-303 in Elf C4 fluid
Very noisy
Positive slope
41
Slide 42
Dynamometer 17
N-653in Elf C4 fluid
Quiet
Negative slope
42
Slide 43
Dynamometer 17
N-653 in Mobil 424 fluid
Quiet
Negative slope
43
Slide 44
Dynamometer 17
N-670in Elf C4 fluid
Slight noise
Negative slope
44
Slide 45
Dynamometer 17
Carbon Cloth in Elf C4 fluid
Very quiet
Negative slope
Smooth torque
45
Slide 46
Dynamometer 17
HDT-303 in Elf C4 fluid
Very noisy
No Sturaco
46
Slide 47
Dynamometer 17
HDT-303 in Elf C4 fluid with 2% Sturaco additive
2% Sturaco
No noise
47
Slide 48
Dynamometer 17
N-670in Elf C4 fluid
Slight noise
No Sturaco
48
Slide 49
Dynamometer 17
N-670in Elf C4 fluid with 2% Sturaco additive
2% Sturaco
Quiet, smooth
49
Slide 50
Brake Testing Summary
• The shape of the torque curve is indicative to the amount of
noise. Sloping down is quieter.
• It remains very important to establish the proper friction
material – oil combination for the application.
• Individual brake designs may contribute more or less noise
than what we test on the dynamometer. In general, noise
is less of an issue in axle speed brakes than wheel speed
brakes due to lower torque loads of axle speed brakes.
• Top adds may be used as a temporary fix for noise
problems.
50
Slide 51
• Vehicle Simulation Test
testing
• CASE STUDY
: Case Study – Friction drag
Slide 52
• Vehicle Simulation Test
testing
: Case Study –Friction drag
•
A customer had a condition in a forklift transmission with overall
performance
– One material had good frictional output but had high wear
– One material had low wear but friction fade
•
After discussions with the customer, the following test plan was
developed to simulate the inching conditions of the application
Slide 53
• Vehicle Simulation Test : Inching Tests
•
•
•
•
•
•
•
•
•
•
•
•
10 second drags to simulate inching conditions.
Test Conditions
133 mm OD ( 2 plates)
2400 rpm
620 J/cm²
52 W/cm²
Pressure = 3.6 bar (u = 0.1)
Slip time = 10 sec
Oil flow variable to achieve temp.
Critical opposing plate temp determined to be 245C
5,000 cycles
Frequency = every 30 sec.
Slide 54
•
Inching Comparison (Cat TO-4 fluid)
245 C Center Plate temperature
Problem at critical temp
Slide 55
•
Inching Comparison (Cat TO-4 fluid) Solution using N-670
245 C Center Plate temperature
Slide 56
•
Inching Comparison (Cat TO-4 fluid)
245 C Center Plate temperature
Solution using N-670
Slide 57
Inching Test for Dana - Dynamometer 41
N-670-3 - Caterpillar TO-4 fluid
245 C (475 F) Rxn plate temp
290 C (550 F) Rxn plate temp
A v g. Wear
Midpoint
A vg. Wear
0.20
0.20
0.20
0.15
0.15
0.15
0.15
0.10
0.10
0.10
0.10
0.05
0.05
0.05
0.05
0.00
0
1000
2000
3000
4000
0.00
5000
Coefficient of Friction
0.20
Cumulative Wear - mm
Coefficient of Friction
Midpoint
System temp limit
0.00
0
1000
Engage m e nt No.
Excessive high temperature will lead to poor
performance
2000
3000
Engage m e nt No.
4000
0.00
5000
Cumulative Wear - mm
•
Slide 58
Inching Summary
• Tests were run to simulate inching a vehicle. Friction fade
and wear were analyzed.
• Opposing plate temperature was determined to be key to
eliminate fade and reduce wear. N-670-3 did not fade if
plate temperature was kept at 245 C (475 F).
Slide 59
• Vehicle Simulation Test : Case Study –Brakes
• CASE STUDY
Slide 60
Case Study – Brake Noise
•
•
•
•
•
A customer using a sump brake on a loader had field
complaints of brake noise
A visit to the work site revieled the use of a different oil
being used in the brake system
Carlisle agreed to evaluate this oil on our SAE#2 dyno
under the J2490 µPVT test
This procedure is recognized worldwide as a method to evaluate friction couples for noise
We looked at our N611 friction paper in two oils
• Mobil HD80W90 ‐ the recommended oil
• China Gear oil ‐ being used at the site
Slide 61
SAE J2490 Dyno
results
Slide 62
N-611 in Mobil HD 80W90 oil
Slide 63
N-611 in China gear oil
Slide 64
Case Study – Brake Noise Summary
• The J2490 µPVT testing indicated the following;
-The N611 operation in the Mobil HD80W-90 oil
developed µm/µe ratios of less than 1 indicating no
propensity for noise
-The N611 operation in China Gear oil developed µm/µe
ratios greater than 1 indication that noise can be
generated
• It was recommended the site switch back to the proper oil
Slide 65
Wet Brake Guidelines
• To properly size the brake some initial work must
be done to determine energy going into the brake
• Remember storing and/or removing the heat is key to success
• Calculate the energy to dissipate during the duty
cycle
• Include level, uphill, downhill and any retarding
• Result will be Energy/min/cycle
• Determine the number of brakes on the vehicle
• A material selection can be determined by filling
out an application data sheet
Slide 66
System Design Criteria
66
Slide 67
System Designs
•
Coefficient of friction (or Torque) is one requirement for a friction material system.
Different systems will have different requirements as to which coefficient of friction is
most important.
–
–
–
–
Minimum Break Away static is most important in truck clutches
Minimum dynamic friction is most important in aircraft brakes
Ratio between lockup and dynamic is most important in nvh sensitive applications
Stability of breakaway static is most important in overload clutches.
•
Other important parameters to consider are:
– Unit energy
– Unit power
– Apply pressure
– Oil flow and resulting system temperature
•
Friction materials have limits in which they can run so material recommendations are
made considering the above parameters as well as performance requirements for each
application.
67
Slide 68
Unit Energy
•
E = ½ m V2 , where:
m = mass
V = velocity
•
E = ½ I ω2 , where:
I = inertia
ω = rotational speed
The number and size of the friction discs is designed to keep the unit
energy reasonable. In general
–
–
–
•
or
Low energy is considered to be less than 80 J/cm2 (400 ft-lbs / in2)
Moderate energy is between 80 -160 J/cm2 (400 – 800 ft-lbs / in2)
High energy is above 160 J/cm2 (800 ft-lbs / in2)
The higher the unit energy of a system, the more important sufficient
oil flow, oil flow distribution, and low apply pressure becomes.
Otherwise the system temperature and unit power become too
severe for paper materials to survive.
68
Slide 69
Energy Capability
450
410
400
Unit Energy J / cm^2
350
280
300
230
250
200
150
115
100
85
50
0
Bronze
N-266 Paper
N-401 Paper
N-653 Carbon Paper TC-120 Carbon Cloth
69
Slide 70
Apply Pressure
• In brakes, apply pressure is calculated based on stopping
distance requirements.
• High apply pressure may result in high friction wear or
fatigue. In general:
– Low pressure is considered to be less than 2,000 kPa (300 psi)
– Moderate pressure is between 2,000 – 4,000 kPa (300 – 600 psi)
– High pressure is above 4,000 kPa (600 psi)
• Apply pressure may dictate which materials can be used
based on the materials chemistry and density.
70
Slide 71
Oil flow
•
Oil is introduced to the friction pack either by a force fed system or a
sump. A sump is not as effective for cooling the friction pack as a force
fed system during long stops. But for short duration stops it is more
effective but at the expense of parasitic drag.
•
Oil flow can be critical for friction material life. The amount of oil
required is largely dependent on the amount of energy for each stop.
In general:
– For low energy applications, .003 l/min/cm2 may be sufficient
– For moderate energy applications, at least .009 l/min/cm2 is recommended
– For high energy applications, .018 l/min/cm2 may be used
•
The surface temperature at the friction interface must be kept cool
enough to not precipitate out additives causing friction fade.
71
Slide 72
Groove patterns
•
The grooves are put in the friction material to allow the oil to flow
across the friction surface. The friction disc is generally considered
worn out when the disc wears halfway through the groove depth.
•
A variety of groove patterns are used depending on the application.
–
–
–
–
Waffle patterns with wide grooves are common in sump applications.
Two pass multiple parallel patterns are common in force fed applications.
Large parts (> 380 mm) often incorporate three pass groove patterns.
Oil viscosity and oil flow determine groove width. Higher viscosity oils or
sump type lubrication dictate wider grooves.
– Sunburst and spiral radial patterns are more common in metallic and HDT
parts.
– Embossed grooves are better for parasitic drag and cleanliness vs cut
grooves. However, they sacrifice groove depth.
72
Slide 73
Typical Groove Patterns
73
Slide 74
Failure Modes
74
Slide 75
Failure Modes
• There are basically only 3 common causes of failure for
paper friction materials:
– Rough Opposing Surface – Papers require surface Ra <
0.5ųm
– Excessive Heat
– Excessive Pressure
75
Slide 76
Friction Wear vs. Separator Plate Finish
Procedure R‐79‐398
TO‐4 Oil
Incremental Wear (mm)
Surface Finish
N653‐4
N266‐4
Total
1k
25k
50k
75k
0‐75k
10‐11 uin (0.28 um)
0.053
0.074
0.106
0.129
0.362
39‐45 uin (1.14 um)
0.070
0.352
0.426
0.395
1.243
57‐60 uin (1.52 um)
0.088
0.225
0.537
0.302
1.152
11‐12 uin (0.30 um)
0.065
0.114
0.110
0.238
0.527
26‐32 uin (0.81 um)
0.077
0.441
0.317
0.291
1.126
Slide 77
Excessive Heat Failures
• Three causes of excessive heat:
– High Unit energy/power
• The energy absorbed by the friction material system will dictate
the amount of heat to be dissipated.
– Low Oil Flow
• The oil cools the friction pack, so insufficient oil flow across the
entire pack will lead to overheating.
– Not enough Heat sink
• The thickness of the opposing plates and the fixture can allow
for more heat absorption.
77
Slide 78
Excessive Heat Failures (cont’d)
• High heat can cause several types of failures.
– Hot spotting / Warping
• Hot spots can be generated on the steel opposing plates due to
excessive power stops. This can lead to distortion or erratic
torque behavior.
– Wear
• Excessive heat can break down the binder or fibers in the
friction material causing premature wear.
– Friction fade
• Heat can cause the additives in the oil to precipitate out onto the
surface of the paper. This glazing can lead to loss of coefficient
over time.
78
Slide 79
Reaction plate: Moderate discoloration
and material transfer
Discard
reaction plate
Slide 80
Reaction plate: Heavy discoloration
and material transfer
Discard
reaction plate
Slide 81
Excessive Pressure Failures
• Excessive apply pressure can lead to failure for a variety of
reasons:
– Fatigue
• Paper friction materials contain fibers which can fatigue and break with
continuous high loading.
– Compression / Wear
• High pressure can lead to early compression and / or wear of paper
friction materials due to their porous nature.
– Increased Power
• High apply pressure leads to shorter stop times, so the energy being
absorbed is dissipated in a shorter time, causing high power stops.
81
Slide 82
Approximate Pressure Limits for Paper Materials
(Can be affected by other system parameters)
•
Material
psi
MPa
•
•
•
•
•
•
•
•
•
N-360
N-401
N-420
N-414
N-452
N-611
N-266
N-670
N-653
350
400
400
400
550
600
800
1000 +
1000 +
2.5
2.8
2.8
2.8
3.8
4.2
5.6
6.9
6.9
82
Slide 83
Design Techniques to Maximize Clutch or
Brake Energy Dissipation
• High Thermal Conductivity of components
• More conformable friction material
• Reduce the difference between the outside and
inside diameters of the friction couple
• Higher pressures force conformable materials to
have a larger effective surface area resulting in
lower peak temperatures
• Groove configuration fitting the application
• Specify a high energy friction material
83
Slide 84
Careful – Accidents can happen
10/24/2012
84