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									Introduction to Synchronous Belts
  Introduction to Synchronous Belts
Timing belts were invented
in the late 1940’s by Richard
Y. Case, an engineer with
the former L.H. Gilmer
company, which was
eventually absorbed into
Uniroyal Inc. The sewing
machine provided the
impetus for the development
of a belt capable of
synchronizing two or more
 Introduction to Synchronous Belts

Applications required a very high modulus (no
stretch) tensile member to prevent distortion of
the pitch (the distance between the teeth) as it
rotated around the sprockets. Steel wire was
first used as a tensile member until later being
replaced by fiberglass and aramid fiber cords.
   Introduction to Synchronous Belts

Synchronous drives represent
a modern and efficient system
of power transmission. They
essentially combine the
advantages of mechanical
components (gears & chain)
and flexible components
(flat & V-belts) while
eliminating the inherent
disadvantages of these
         Basic Design Principles
Synchronous belts operate on a basic principle:
molded teeth of the belt and mating grooves of the
pulley make positive engagement. The teeth enter
and leave the pulley in a smooth rolling manner with
low friction. This positive engagement results in:
• Exact shaft synchronization
• Elimination of slippage and speed loss common to
• Synchronous operation at speeds higher than most
  chain drives.
         Basic Design Principles

All synchronous belts operate on the positive
engagement principle. Chains operate on the
same principle but synchronous belts have many
superior characteristics. Synchronous belts wrap
around the pulley by means of flexion and not by
rotation of articulated parts (as chains do). This
eliminates one of the causes of wear and noise.
             Basic Design Principles
To maintain the correct tooth
pitch as the belt flexes around
the pulley, the belt pitch line
(tensile cord) must coincide
with the pitch diameter of the
pulley. The difference between
pulley O.D. and pulley pitch
diameter is referred to as Pitch
Line Differential (PLD). For
proper tooth meshing the PLD
of the belt must match the PLD
of the pulley.
When to Use a Synchronous Belt Drive
•   Synchronous transmission between shafts is a must
•   High mechanical drive efficiency and energy savings required
•   Precise relative positioning of shafts (non-slip and minimal
•   Compact drive layout is necessary
•   Low maintenance is required
•   Combines power transmission and conveying needs
•   Low noise requirements (compared to chain)
•   Environmental or contamination concerns (no lubrication
•   High torque, low RPM requirements
         Synchronous Belt Advantages
                vs. chain
• Increased service life for belts and sprockets
• No need for lubrication
 - Improper lubrication of chain drives severely reduces life
 - Lubrication attracts dirt and leads to wear
• Reduction in noise over chain (& polyurethane drives)
• Environmentally cleaner – no grease or oil
• Increased productivity — less down time
  (vs. chain and v-belts)
• Increased efficiency and registration accuracy
          Synchronous Belt Advantages
                 vs. chain
• Chain is heavier than belt systems
• Limited take-up or inaccessible drives - with synchronous
  belts, the required take-up allowances for tensioning are
  significantly less (v-belts and chain).
• No Hidden Costs — chain cost of lubrication, disposal cost of
  lubrication, reservoirs
• Chain available only in full box lengths
  - (Typically 10 ft. in box)
     Synchronous Belt Disadvantages
             vs. chain
•Less initial cost (although synchronous payback is rapid
 due to reduced maintenance)
•Design Flexibility — larger availability of ratios and
•Less sensitivity to improper installation —
 alignment and tensioning
                  Belt Construction
           The main components of a synchronous belt are the
           tensile cords, the teeth, rubber backing and tooth
tensile cords
                                     rubber backing

tooth facing
                 Belt Construction
Steel was originally used as a tensile cord material. Most belts
today use high modulus (low-stretch) fiberglass or aramid fiber as
the tensile member. (Kevlar is the Dupont trademark for an aramid
fiber). Tensile cord is the load bearing element of the synchronous
The belt teeth are molded of a hard rubber compound jacketed with
a tough, abrasion resistant nylon tooth facing. The compressive
and shear strength of the teeth exceeds that of the tensile cords
when there are at least six teeth in mesh with the driver pulley.
Teeth in mesh is a critical design factor.
A durable rubber backing encases the load bearing tensile cord. It
protects the cords from dirt, oil and other contaminants, as well as
frictional wear when a backside idler is used.
                   Belt Construction
                         ―S‖ & ―Z‖ Twist
           " S " twist                       " Z " twist

To reduce lateral movement, synchronous belts are constructed by
alternately spiraling ―S‖ and ―Z‖ type cords. The synchronous belt cord
is made up of a number of small fiber strands twisted together. These
strands can be twisted either clockwise or counterclockwise. The two
twist directions are referred to as ―S‖ twist and ―Z‖ twist.
                     Belt Construction
                            ―S‖ & ―Z‖ Twist
Most synchronous belts are made with both ―S‖ and ―Z‖ twist
cord to minimize belt tracking forces on the pulley flanges.

                S - TWIST              Z - TWIST
               (TOP VIEW)              (TOP VIEW)

                       direction of
                       belt rotation                direction of
                                                    belt rotation

                                                    direction of
direction of                                        lateral belt
lateral belt                                        movement
                      Belt Construction
                                 ―Z‖ Twist
When necessary, the lateral movement of a belt can be pre-determined, if
the direction of rotation is constant (non-reversing drives).
A good example of this is Fin-Fan Drives. Because the fin-fan drive has a
vertical shaft, the belt is built with Z twist construction only. This gives the
belt an upward direction of lateral movement. This helps keep the belt off
of the bottom flanges and reduces excessive side belt wear. Carlisle offers
a special construction ―Z‖ twist construction for Fin-Fan air-cooled heat
exchanger drives.
                           direction of lateral belt movement

                                    direction of belt rotation

                                       Side View
                            Z-Twist construction Fin-Fan Drive
          Synchronous Drive Terms
Unlike the V-belt drive, the synchronous belt drive is not a friction
device. It is a positive engagement drive that is dependent upon
the meshing of the belt teeth with the pulley grooves.
The tooth profile indicates the type or shape of the belt teeth.
The spacing between two adjacent teeth on the belt (and pulley) is
referred to as the tooth pitch. The distance is measured from the
center of one tooth to the center of the next.
In synchronous belts, the belt length is determined by multiplying the
belt pitch by the number of teeth in the belt. This is known as pitch
In synchronous drive systems, backlash is the necessary clearance
between belt teeth and pulley grooves for proper meshing.
            Synchronous Drive Terms
The pitch diameter of the pulley or
(sprocket) refers to the diameter
determined by the tensile cord location
in the belt. Therefore, the pitch
diameter of the pulley will be
somewhat greater than the outside
diameter of the pulley across the teeth.
To maintain the correct tooth pitch as
the belt flexes around the pulley, the
belt pitch line (center of the tensile
cord) must coincide with the pitch
diameter of the pulley. The difference
between pulley O.D. and pulley pitch
diameter is referred to as pitch line
differential (PLD).
          Synchronous Drive Terms
Tooth pitch is one indication of overall belt size. The larger the
pitch, the larger the teeth and tensile cord. The larger and stronger
the belt, the more horsepower it can transmit.
In conventional trapezoidal tooth profile belts, letters indicate
pitch, (MXL, XL, L, H, etc.) which are measured in inches.
In curvilinear tooth profile belts, pitch is measured in millimeters
(3M, 5M, 8M, etc).
The terms synchronous belt and timing belt are used
Sprocket and pulley are also used interchangeably.
    Synchronous Belt Tooth Profiles

There are two types of synchronous belt tooth profiles that make up
the majority of synchronous drives in use today.

• Trapezoidal tooth profile — (original technology) refers to the
tooth configuration of MXL, XL, L, H, XH AND XXH type belts.

• Curvilinear tooth profiles — have rounded tooth profiles that
eliminate stress concentrations at the base of the tooth and allow
more uniform stress distribution. Curvilinear profiles transmit high
torque and represent the latest evolution of synchronous belt
technology. Available in 3M, 5M, 8M, 14M, and 20M pitch.
         Carlisle Tooth Profile Evolution
                               Trapezoidal Profile
A trapezoidal belt
tooth has a constant                                    Original synchronous
angle of pressure.                                       belt tooth profile

The profile of              Curvilinear (RPP Profile)
curvilinear teeth has
an angle that increases
from the base, to the                                   Modern tooth profile
top of the tooth and
allows for more
uniform stress
distribution resulting in
higher torque
transmission with
reduced occurrence of
tooth jump.
         Trapezoidal Profiles

                          tooth pitch

Trapezoidal profile belts are available in the following pitches:

             Pitch              Pitch
             Designation        Distance
             MXL =              0.080‖
             XL    =            0.20‖
             L     =            0.375‖ (3/8‖)
             H     =            0.50‖ (1/2‖)
             XH    =            0.785 (7/8‖)
             XXH =              1.25‖ (1-1/4‖)
                    Trapezoidal Pitch Sizes

MXL   =   Mini Extra Light
XL    =   Extra Light
L     =   Light Duty
H     =   Heavy duty
XH    =   Extra Heavy Duty
XXH   =   Double Extra Heavy Duty
Trapezoidal Construction

           • Fiberglass tensile
           • Synthetic rubber
             compound body
           • Nylon tooth facing
             Trapezoidal Features
• Fiberglass tensile member
   – High breaking load, length stability (low stretch)
   – Good resistance to repeated flexing
• Belt body synthetic rubber
   – Good resistance to fatigue
   – Resists heat, oil & ozone
   – Ground back for smooth operation – low vibration
• Nylon tooth facing
   – High resistance to abrasion
   – Low coefficient of friction for smooth engagement
   – Extended sprocket & belt wear
• Low backlash
   – Good for applications where high positional accuracy is
             Explanation of Part Numbers

                                                     100 = 1.0‖
                                       L = 3/8‖
   300 ÷ 10 = 30 inch pitch length                   Belt Width
                                      Tooth Pitch
  Pitch Length designated in tenths                 in hundredths
             of an inch                               of an inch

   (hundredths of an inch for MXL)
       example: 440 MXL 025
  440 ÷ 100 = 4.4 inch pitch length

D300L100 = dual sided
        Sycnhro-Cog® Dual Timing Belt

                      Standard Lengths and Widths
belt       belt          belt      pitch length
type   pitch (inch)   pitch (mm)   range (inch)   standard widths (inch)
DXL     0.20 (1/5)       5.080      15.0 – 33.0           .025 - .037
DL      0.375 (3/8)      9.525      15.0 – 66          .050 - .075 – 1.0
DH      0.50 (1/2)       12.7      24.0 – 140.0   .075 – 1.0 – 1.5 – 2.0 – 3.0
Curvilinear Tooth Profile
      Advantages of Curvilinear Profile
          vs. Trapezoidal Profile
• Higher power ratings allow narrower widths to be
  used than trapezoidal timing belts
• More compact drives
• Lower overhung bearing loads (narrower widths)
• Quieter than comparable trapezoidal belts
• Covers wider range of power
• Reduced sprocket wear
Evolution of Curvilinear Tooth Profiles

  • HTD - Curvilinear - Introduced by Gates in 1971

  • STPD - Modified Curvilinear - Introduced by Goodyear
    in the early 1970’s

  • GT - Modified Curvilinear - Developed by Gates in the
    late 1970’s

  • RPP - Parabolic – Dayco (Carlisle) introduced in the
    USA in 1985
              Curvilinear Profiles
Curvilinear profile belts are available in the following pitches:

           Pitch                   Pitch
        Designation           Distance (mm)
            3M               =        3
            5M               =       5
            8M               =       8
           14M               =      14
           20M               =      20
       Advantages of RPP Profile
• Interchangeable with existing deep groove
 profiles (HTD, HPPD, UPD)
• Sprocket availability - most major sprocket
 manufacturers provide RPP profile
• Sprockets use readily available QD bushing
• Quieter than competitive curvilinear belts
• RPP profile reduces sprocket wear
      RPP Plus Synchronous Belt

• Highly energy efficient
• High Torque capability
• Provides up to 50%
  more horsepower
  capacity than first
  generation high-torque
  belts (HTD)
                                  RPP Plus
                                                           Precision Ground
               Extra Strong                                Neoprene Backing
               Fiberglass Cords

Patented nylon self-                                     Tooth Indentation
lubricating graphite        Neoprene Rubber Belt Teeth   • Shock Absorbing
loaded tooth facing                                      • Reduces Noise
                                           RPP Plus
                    available in pitches of *3M, 5M, 8M, 14M, 20M

FEATURE                                                BENEFIT
Reinforced Parabolic Profile                           Positive slip-proof engagement
                                                       No speed variations
Wide range load capacities & speeds                    Speed range more than double of chain
                                                       High torque capacity
                                                       Wide range of applications

No lubrication                                         Clean, maintenance free
High mechanical efficiency                             Energy savings
Does not require friction to operate                   Reduced overhung bearing loads
                                                       Improved motor life. Less heat build-up.
                                                       Reduced maintenance

                  * 3M is non-stock. Contact Carlisle for availability.
                                                RPP Plus
                   available in pitches of *3M, 5M, 8M, 14M, 20M

FEATURE                                                       BENEFIT
High torque capability                                        Compact drive package
                                                               Lower cost
Precision ground rubber backing                               Consistent uniform thickness
                                                              Reduced vibration
                                                              Compatible with backside idler

Fiberglass cord                                               Length stability
                                                              High belt strength

Nylon fabric tooth cover                                      High resistance to wear and shear
                                                              Longer belt life
                         * 3M is non-stock. Contact Carlisle for availability.
                            RPP Plus
                  Explanation of Part Numbers


800 = 800 mm pitch length   8M = 8mm pitch   30 = 30 mm width
                                                        RPP Plus
                                 Standard Lengths and Widths
belt                          belt                      pitch length
type                   pitch (mm)                       range (mm)      standard widths (mm)
*3M                              3                       159 – 1263            6 – 9 - 15

5M                               5                       350 – 2525            9 – 15 – 25

8M                               8                       480 – 4400         20 – 30 – 50 – 85

14M                            14                        966 – 6860     40 – 55 – 85 – 115 – 170

20M                            20                       2000 – 6600    115 – 170 – 230 – 290 - 340
* 3M is non-stock. Contact Carlisle for availability.
                     Dual RPP Plus

- Used to drive shafts on (serpentine) multiple
 pulley drives in opposite directions
- Available in RPP 8M & 14M profiles
- RPP molded teeth both sides - full power rating on both sides
- Goodyear molded teeth one side – Ground teeth on opposite
   side - 33% rating reduction on ground tooth side due to lack
   of fabric reinforcement on teeth
                    Dual RPP Plus
            Standard Lengths and Widths
belt      belt        pitch length
type   pitch (mm)     range (mm)      standard widths (mm)

8M         8          720 – 4400        20 – 30 – 50 – 85

14M       14          1400 – 4956    40 – 55 – 85 – 115 – 170
                       Dual RPP Plus
                  Explanation of Part Numbers


D = Dual Sided   800 = 800 mm pitch length 8M = 8mm pitch   30 = 30 mm width
Introducing the New RPP Panther®

  The Panther Rules!
 The new RPP Panther
 with ULTRA-CORD and
 Able compound provides
 fierce, unequaled
 strength, efficiency and
New RPP Panther with ―Able‖ Compound
           The ―Able‖ Advantage
Reduces Tooth Shear
The new ―Able‖ compound is
reformulated for increased
performance. This advanced
polymer provides increased
resistance to tooth shear and
tooth jump.
New RPP Panther with ―Able‖ Compound
        The ―Able‖ Advantage

    Better Adhesion
    ―Able‖ adheres to the belt cords and
    nylon tooth facing better than the old
    Panther compound. This allows for
    reduced tooth deflection and improves
    belt life.
New RPP Panther with ―Able‖ Compound
          The ―Able‖ Advantage

  More Robust
   The ―Able‖ compound
   is a robust material
   that improves product
New RPP Panther with ULTRA-CORD!
     The ULTRA-CORD Advantage

Reduced Tension Decay
Holds drive tension better
than belts using aramid
fiber cords thus providing
dimensional stability for the
life of the drive.
New RPP Panther with ULTRA-CORD!
   The ULTRA-CORD Advantage

   Lower Installation Tensions
   With ULTRA-CORD, there is no need to
   ―over-compensate‖ for aramid tension
   decay. Lower tensions put less strain
   on drive components such as bearings
   and shafts.
New RPP Panther with ULTRA-CORD!
    The ULTRA-CORD Advantage

 Doesn’t Absorb Moisture
 The use of ULTRA-CORD eliminates the need
 for special handling such as plastic bags and
 desiccants used with aramid belts to prevent
 shrinkage from moisture absorption.
 New RPP Panther with ULTRA-CORD!
      The ULTRA-CORD Advantage
Improved Flex Life
Aramid tensile strength
degrades over time with
repeated flexing.
ULTRA-CORD resists tensile
degradation & dramatically
improves belt life and
shock load resistance.
New RPP Panther with ULTRA-CORD!
    The ULTRA-CORD Advantage
Improved HP Ratings
The new RPP Panther
construction permits
increased drive horsepower
ratings as much as 20%
over the previous Panther.
The New RPP Panther…
 Some things didn’t need to be improved…
  SAME Great RPP Tooth Profile
  The new RPP Panther still
  utilizes the same RPP tooth
  profile for reduced noise
  levels, resistance to tooth
  jumping, and improved
  meshing with either RPP or
  HTD sprockets!
The New RPP Panther…
 Some things didn’t need to be improved...
 SAME High Quality Fabric Facing
 The New RPP Panther still
 utilizes the same graphite-
 loaded, self-lubricating nylon
 fabric facing for exceptional
 wear resistance, low
 coefficient of friction, and
 superior drive efficiency.
The New RPP Panther…
 Some things didn’t need to be improved…

  SAME Industry Standard Sprockets
  The New RPP Panther still
  operates with the same
  readily available, industry
  standardized RPP Panther
  sprocket systems.
The New RPP Panther…
 Some things didn’t need to be improved…

 Still Works on Backside Idlers
 The new RPP Panther is still the
 best choice (and sometimes
 your only choice) for high
 torque drive systems that
 require backside idlers.
The New RPP Panther® Synchronous Belt
        • Improves belt life
        • Higher strength         Precision Ground Backing
        • Reduced tension decay   • Smooth operation with backside idlers
        • Dimensional stability                                              Able Compound
                                                                             • Engineered polymer
                                                                             • Increased performance
                                                                             • Increased belt life

  Nylon Tooth Facing               Tooth Indentation             Proven RPP Profile
  • Graphite-loaded                • Shock absorbing             • Greater transfer of power
  • Self-lubricating               • Reduced noise               • Jump & shear resistant
  • Wear resistant                                               • Reduced sprocket wear
The Energy Efficient RPP Panther®

   • Panther improves energy efficiency
     - 98% operating efficiency
   • Reduces energy consumption
     - As much as 5% over other PT systems
                        RPP Panther®
                       Explanation of Part Numbers


3600 = 3600 mm pitch length   PTH8M = 8mm pitch      35 = 35 mm width
                    RPP Panther®
               Standard Lengths and Widths

Belt   Belt           Pitch Length
Type   Pitch (mm)     Range (mm)      Standard Widths (mm)

8M         8          480 – 4400         12 – 22 – 35 – 60

14M       14          966 – 4956      20 – 42 – 65 – 90 – 120
          Panther Advantages
            over Poly-Chain
• Poly-Chain has a ribbed belt backing that does
not work well with backside idlers.

• Poly-Chain is made of polyurethane and has a
lower maximum operating temperature (185° F).

• Panther belts (rubber) have lower noise
characteristics than (polyurethane) Poly-Chain
                                   RPP Panther®
                                        NOISE COMPARISON
                                    Panther vs Competitive System

                                                                88          90
            90                           82         84
                             76                                              83
                                                    76          80
                   65                  73
                  600      1200        1800        2200        2800         3500     rpm

                                                          RPP PTH                POLYURETHANE

Test on belt pitch 8 mm / 20 mm wide, 2 pulleys Z=44, tension 46kg/strand
                Energy Efficiency

• One third of the electric motors in the industrial and
commercial sectors use belt drives
• Certain types of belts are more efficient than others,
offering energy cost savings
• V-belts can have a peak efficiency of 95% to 98% at the
time of installation but deteriorates by as much as 5% over
• Synchronous belts offer an efficiency of about 98% and
maintain that efficiency
• V-belts have a sharp reduction in efficiency at high
torque due to slippage
          Selling Energy Efficiency

• Conduct a survey of belt driven equipment in a plant or
facility. Gather application and operating hour data.
Then, determine the cost effectiveness of replacing existing
v-belts with a synchronous system.
• Replace wrapped v-belts with Gold Ribbon Cog Belts
where the retrofit of a synchronous belt drive is not cost
• Consider synchronous belts for all new installations
because the payback overcomes the price premium over
v-belt drives.
U.S. Customer Service: 866-773-2926
              Canada: 866-797-2358

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