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 shafts.


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.


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 components.

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 v-belts.• Synchronous operation at speeds higher than most chain drives.


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.


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 backlash)

• 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 required)

• High torque, low RPM requirements

Synchronous Belt Advantagesvs. 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 Advantagesvs. 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 lengths

•Less sensitivity to improper installation — alignment and tensioning

tooth facing teeth

tensile cords rubber backing

The main components of a synchronous belt are the tensile cords, the teeth, rubber backing and 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 belt.

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

Belt Construction“S” & “Z” Twist

" Z " twist" S " 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.

direction of

belt rotation

direction of

belt rotation

S - TWIST (TOP VIEW)

direction of lateral belt movement

Z - TWIST(TOP VIEW)


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 belt rotation

Side ViewZ-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 length. In synchronous drive systems, backlash is the necessary clearance between belt teeth and pulley grooves for proper meshing.


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).


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 interchangeably.

Sprocket and pulley are also used interchangeably.

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.

Synchronous Belt Tooth Profiles

Trapezoidal Profile

Carlisle Tooth Profile Evolution

Curvilinear (RPP Profile)

Original synchronous belt

tooth profile

Modern tooth profile

A trapezoidal belt tooth has a constant angle of pressure.

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

Trapezoidal Profiles

Pitch PitchDesignation DistanceMXL = 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 profile belts are available in the following pitches:

tooth pitch

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 member

• 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

required

Explanation of Part Numbers

300L100

300 ÷ 10 = 30 inch pitch length

Pitch Length designated in tenths of an inch

(hundredths of an inch for MXL)

example: 440 MXL 025

440 ÷ 100 = 4.4 inch pitch length

L = 3/8”

Tooth Pitch

100 = 1.0”

Belt Width

in hundredths of an inch

D300L100 = dual sided

Sycnhro-Cog® Dual Timing Belt

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

Standard Lengths and Widths

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

Pitch PitchDesignation Distance (mm)

3M = 3 5M = 58M = 8

14M = 1420M = 20

Curvilinear profile belts are available in the following pitches:

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

Tooth Indentation• Shock Absorbing• Reduces Noise

Extra Strong Fiberglass Cords

Precision Ground Neoprene Backing

Patented nylon self-lubricating graphite loaded tooth facing

Neoprene Rubber Belt Teeth

RPP Plus available in pitches of *3M, 5M, 8M, 14M, 20M

Reinforced Parabolic Profile

Wide range load capacities & speeds

No lubrication

High mechanical efficiency

Does not require friction to operate

Positive slip-proof engagement

No speed variations

Speed range more than double of chain

High torque capacity

Wide range of applications

Clean, maintenance free

Energy savings

Reduced overhung bearing loads

Improved motor life. Less heat build-up.

Reduced maintenance

FEATURE BENEFIT

* 3M is non-stock. Contact Carlisle for availability.

RPP Plus available in pitches of *3M, 5M, 8M, 14M, 20M

High torque capability

Precision ground rubber backing

Fiberglass cord

Nylon fabric tooth cover

Compact drive package

Lower cost

Consistent uniform thickness

Reduced vibration

Compatible with backside idler

Length stability

High belt strength

High resistance to wear and shear

Longer belt life

FEATURE BENEFIT



800-8M-30

800 = 800 mm pitch length

8M = 8mm pitch

30 = 30 mm width

RPP Plus

RPP Plus

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



- 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

Dual RPP Plus

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



D800-8M-30


8M = 8mm pitch

30 = 30 mm width

Dual RPP Plus

D = Dual Sided

Introducing the New RPP Panther®

The Panther Rules! The new RPP Panther with ULTRA-CORD and Able compound provides fierce, unequaled strength, efficiency and durability.

New RPP Panther with “Able” CompoundThe “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.


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.


More Robust

The “Able” compound is a robust material that improves product consistency.

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.



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.

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.





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!


Some things didn’t need to be improved...

SAME High Quality Fabric FacingThe 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.


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.


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.

Nylon Tooth Facing• Graphite-loaded• Self-lubricating• Wear resistant

Tooth Indentation• Shock absorbing• Reduced noise

Proven RPP Profile• Greater transfer of power • Jump & shear resistant• Reduced sprocket wear

ULTRA-CORD• Improves belt life• Higher strength• Reduced tension decay• Dimensional stability

Precision Ground Backing• Smooth operation with backside idlers

The New RPP Panther® Synchronous Belt

Able Compound• Engineered polymer• Increased performance• Increased belt life

• Panther improves energy efficiency - 98% operating efficiency• Reduces energy consumption - As much as 5% over other PT systems

The Energy Efficient RPP Panther®


3600-PTH8M-35


PTH8M = 8mm pitch 35 = 35 mm width

RPP Panther®

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


RPP Panther®

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 belts.

Panther vs Competitive System

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

NOISE COMPARISON

rpm

db

A

600 1200 1800 2200 2800 3500

6576

82 849088

5767

73 768380

0

10

20

30

40

50

60

70

80

90

RPP PTH POLYURETHANE

RPP Panther®

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 time• 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 effective.

• 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

www.CarlisleBelts.com [email protected]

introduction to synchronous belts

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