Please click on the links below to view details regarding Fenner Precision's timing belt comparisons and advantages:
Belt Profiles
Curvilinear vs. Trapezoidal
Fenner Precision’s High Torque (FHT) curvilinear timing belts are characterized by their deeper more rounded tooth profiles when compared to the older style MXL and XL trapezoidal belts. FHT belts and pulleys provide smooth drive, low noise and vibration, longer life, and increased torque with low backlash.
View Chart
FHT-1
belts are among the most precise in the industry. They are constructed with 1 mm pitch; uniformly formed injection molded polyurethane teeth and a choice of yarn reinforcements.
View PDF
FHT-2 Profile
belts are constructed with 2 mm pitch; uniformly formed injection molded polyurethane teeth and a choice of yarn reinforcements
View PDF
FHT-3 Profile
belts are constructed with 3 mm pitch; uniformly formed injection molded polyurethane teeth and a choice of yarn reinforcements
View PDF
FHT-5 Profile
belts are constructed with 5 mm pitch; uniformly formed injection molded polyurethane teeth and a choice of yarn reinforcements
View PDF
HTD-3 Profile
belts are an older style of 3 mm pitch curvilinear belt. They must be run in HTD-3 pulleys and are not compatible with FHT-3 belts and pulleys.
View PDF
HTD-5 Profile
belts are an older style of 5 mm pitch curvilinear belt. They must be run in HTD-5 pulleys and are not compatible with FHT-5 belts and pulleys.
View PDF
MXL Profile
belts have .080” (2.032 mm) pitch trapezoidal tooth profile. They are one of the earlier styles of mini-pitch timing belt. Fenner Precision FHT 2.032 belts and pulleys can replace MXL belts and pulleys for increased torque transmission and reduced backlash and can be used without changing center distance or drive ratios, only new pulleys are needed with the FHT-2.032 profile.
View PDF
XL Profile
belts have .20” (5.08 mm) pitch trapezoidal tooth profile. They are also an earlier style of mini-pitch timing belt. Once again Fenner Precision FHT 5.08 belts and pulleys can replace XL belts and pulleys for increased torque transmission and reduced backlash.
View PDF
T2.5 Profile
belts have 2.5 mm pitch trapezoidal tooth profile. They are also an older style of mini-pitch timing belt.
View PDF
T5.0 Profile
belts have 5.0 mm pitch trapezoidal tooth profile. They are also an older style of mini-pitch timing belt. Fenner Precision FHT-5.0 belts and pulleys can replace T5.0 belts and pulleys for increased torque transmission and reduced backlash.
View PDF
[Back to Top]
FHT vs. MXL
- Advantages Table
This graphic compares a curvilinear belt profile with a trapezoidal belt profile. The curvilinear profile belt/pulley system distributes the stresses uniformly through the tooth. The belt tooth to pulley forces are transferred up through the tooth as shown, dispersing critical stresses. The backlash is improved due to the curvilinear profile providing improved meshing with less backlash.
- Tooth Engagement Drawings
These drawings compare the torque transmission loadings of trapezoidal and curvilinear profile belts:
- Trapezoidal - The grid lines curve as the tooth is subjected to stress. In the figure, the tooth of a trapezoidal synchronous drive belt is shown together with its stress curve lines which are prominent, indicating extremely high stress at the base of the leading edge of the tooth and potential tooth shearing.
- Curvilinear - In the figure,it can be seen that the tooth of the curvilinear belt and the pulley arc interact, distributing the stresses so that deflections of the grid lines are barely perceptible. This shows the reduction of stress on the tooth at the critical leading edge point, the spread of force uniformly throughout the tooth, and the reduction of inward radial movement of the tooth. All contribute to the curvilinear profiles ability to perform better than previous synchronous drive belt designs.
- Noise Comparison Graph
The graph shown depicts the noise level in decibels vs. motor speed using the MXL (trapezoidal) compared to FHT-1mm (curvilinear) profile belts. Steel pulleys were used for the test. At 1500 rpm the improvement using the FHT-1 mm curvilinear is 3.5 decibels and 4 decibels at 2500 rpm. Significant improvements above 750 rpm can also be observed. The other factor to consider is the reduction in variation of belt/pulley noise when compared to the motor noise.
- Vibration Comparison Graph
This graph is an example of the measured vibration improvement on a scanner head drive. The data compares a MXL (2.032 mm) trapezoidal urethane belt and a 2.032 mm pitch curvilinear belt of the same construction. The induced vibration from belt/pulley meshing is drastically reduced. This type of improvement is very critical in applications such as scanners, printers, placement drives, etc. Additionally, smaller pitch belts like Fenner Precision’s FHT-1 show added improvements in vibration reduction.
[Back to Top]
FHT vs. Competitor Curvilinear Belt Revision 3
- Torque Curves
The torque curves show that a Fenner Precision FHT-3 belt running in Fenner FHT-3 pulleys delivers more torque than the Fenner FHT-3 belt running in the competitor’s 3mm pulleys. Also, in both instances the Fenner FHT-3 belt delivers more torque than the leading competitor's 3mm curvilinear belt/pulley combination.
[Back to Top]
Polyurethane vs. Neoprene
- Tooth profile photographs
The top photo shows how the pressure forming technique used to make the neoprene belt results in some cord deformation and tooth hairiness. The lower photo shows how the liquid injection molding technique used to make the Fenner Precision urethane belt results in a uniform cord lay and clean low dusting tooth profile.
- Advantages table
This chart compares polyurethane with various materials including neoprene. In the areas of abrasion resistance and high load bearing capability, urethane surpasses the other materials.
- Hardness Table
The hardness chart shows Fenner Precision's elastomer hardness range in comparison with other materials.
- Polyurethane Strength at 100% Modulus
This graph compares the strength at 100% modulus for 60, 70, 80 and 90 shore A durometer urethanes used in timing belts.
- Wear of Urethanes
This graph compares the wear characteristics of 60, 70, 80 and 90 shore A durometer urethanes. It is important to remember that the hardness measurement alone is not the best quality indicator. Urethane compounds of the same hardness can exhibit drastically different physical and engineering properties.
- Effect of Modulus on Vibration
The graph compares the noise characteristics of two different 1 mm pitch curvilinear profile belts of two different constructions. The urethanes are the same durometer but have different formulations. The reinforcements are in the same base family but have different properties. The testing was run at a belt speed of 40 ips (inches per second) to determine which combination of urethane and reinforcement would reduce the belt/pulley meshing amplitude at a 25.4 frequency. The TG-3 urethane with FR-7 reinforcement transmits less vibration which is shown as lower amplitude at the belt/pulley meshing frequency of 25.4 cycles/inch.
- Urethane Useful Temperature Range
This chart compares the useful temperature range of polyurethane -110° F to +250° F (-79° C to 121° C) with Neoprene -40° F to +250° F (-40° C to 121° C) showing that urethane has superior cold temperature capabilities.
- Standard Urethane
Fenner Precision has developed eight standard polyurethane compounds for timing belt use. The compounds range in hardness from 75 to 90 Shore A. Other properties are listed in the table.
- Elastomer Comparison Data Table
This chart lists the different urethane compounds manufactured by Fenner Precision. In comparing a Fenner Precision 75 Shore A urethane with a competitor 73 Shore A neoprene it can be seen that the Fenner Precision material has better tensile strength, modulus, tear resistance, rebound and tensile set.
- Urethane Tensile Stress Properties Chart & Table
This chart and table show that a softer 75 Shore A TG-3 urethane has a lower modulus than 80 to 90- Shore A compounds.
- Urethane Chemical Resistance Table (PDF)
[Back to Top]
Reinforcement Comparisons
- Types - Kevlar, Fiberglass & Polyester
Reinforcement fibers used in mini and micro pitch belts will vary to meet the application requirements. Fenner Precision engineers have a full understanding of reinforcement fibers and the characteristics they exhibit that will achieve the application requirements and process well.
Heat Stability, thermal rate of expansion, Young's Modulus, break strength, water absorption rate, flexibility, and deniers are all factors that can affect belt performance. Other factors that affect the end performance in a belt are the twist rate, cabled or single bundle, etc.
- Yarn Twist Direction
The sketch in the link above shows a yarn twisted in the "S" direction and the sketch on the right shows a yarn twisted in the “Z” direction.
- Benefits of Twisting
Most timing belt applications require an S & Z (left & right hand) twist reinforcement fibers side by side to balance the belt, preventing the belt from tracking to one side of the pulley. There are some designs that may require an “S” or “Z” twist only. Another factor that has to be taken into consideration is the number of threads (fiber bundles) per inch of width of belt, commonly referred to as TPI. The TPI, fiber material, and denier determine the modulus and break strength of a belt. The TPI is limited by the denier of the fiber. The reinforcement fibers must have enough space between them to allow the elastomer to surround the fibers during the injection process.
- Modulus Comparisons
The primary reinforcement fibers used in mini and micro pitch belts are aramid and polyester. Fiberglass is also used. The stress strain curves shown in the graph above give you a comparison of some of the common aramid and polyester fibers used by Fenner Precision. Each fiber has unique properties which affect the overall performance of the belt in varied applications. Some aramid fibers have a high modulus, negative thermal rate of expansion and have some shrinkage as they absorb water while another aramid fiber is length stable but increases in length as water is absorbed. Aramid fibers flex fatigue quicker than polyester fibers when to flexing around pulleys. Polyester has a lower modulus, is not affected by water absorption and has better flex fatigue characteristics, and is not affected by water absorption.
- Reinforcement Characteristics
- FR-2 Kevlar Load vs., % CD Change
As an example, a .375” wide FR-2 reinforced Kevlar belt loaded to 200 lbf (91 kgf) stretches 1.1%
- FR-17 Kevlar Load vs., % CD Change
As an example, a .375” wide FR-17 reinforced Kevlar belt loaded to 200 lbf (91kgf) stretches 1.1%
- FR-23 Fiberglass Load vs. % CD Change
As an example, a .375” wide FR-23 reinforced Fiberglass belt loaded to 200 lbf (91 kgf) stretches 1.4%.
[Back to Top]
