Flat woven endless belts combine many desired features, such as a good strength/ thickness ratio, adaptability to a wide range of speeds (from slow moving conveying to the driving of grinding spindles up to 100,000 RPM), quiet vibration-free operation; truly endless construction (no joints or seams to inhibit flex life), excellent dimensional stability and uniformity throughout their length, and maximize efficiency because the pitch line of the belt is close to the surface being driven.
Stable belts are used on drives having some means of belt tensioning, such as a movable pulley location or an external tensioning pulley, either spring loaded or locked in place after tensioning of the belt is completed.
These belts are typically used on individual belt drives or group drives where each belt is separately tensioned. Applications include high-speed power transmission, woodworking machinery, card readers, sorters, and printing machinery.
Semi-Stable belts allow the use of multiple belts with common take-up, or length adjustment. They can be used on wide belt conveying and on applications requiring good edge wear resistance for flanged or guided tracking. Specific applications include paper handling, food conveying (FDA approved) and check-weighing.
Semi-Stretch/Elastic belts were designed for fractional horsepower drives requiring a controlled stretch belt to provide the driving tension, at a specified circumference, when length adjustment or external tensioning is not available. Their major uses are as low-tension drive belts using fixed-center pulleys and as paper transport belts used in multiple sets on a common shaft, with either common take-up or no take- up at all (fixed-centered shafts). These belts are found in business and office machines, currency transports, vacuum transports,instrumentation, disk drives and film transports.
Stretch/Elastic (no woven carcass used) belts find similar applications to those of the semi-stretch types but provide greater range of elasticity, at a lower tension, per equivalent belt widths. Common applications include light-duty drives, paper, film and currency transports, vacuum transports and light-duty conveying.
Type of drives:
- Individual, single drive, two pulleys
- Open, crossed drive and quarter turn (90 degree twist)
- Multiple-Belt Groups or Sets
- Multiple pulleys (serpentine), four pulley quarter turn (mule drive), multiple belts on common shafts with backside idlers, multiple belts common tensioning or fixed-center shafts.
The next considerations are the allowable space to accommodate belt width and the type of pulley on which the belt will run. Is the pulley face open or are flanges used to retain the guide belts? Are any pulleys crowned for guidance and belt tracking? If so, what type of crowning is being used and how severe is the crown? What is the face width of the open pulleys or what is the dimension between the flanges? These answers are required for proper belt selection.
Not all belts are designed to withstand running against flanges. Most types of flat woven endless belts will track well over a minimum of pulley crowning. If flanges are required, always use straight sides at 90 degrees to pulley face surface and maintain sharp corners, minimizing any rounding which causes the belt to climb the flange.
Circular/radius crowns are preferred over bevels with flats.
For belts up to 3″ wide:
Min. Crowning=1.6% of belt width (1″ belt=.016 crown)
Max. Crowning=2.5% of belt width (1″ belt=.025 crown)
For belts over 3″ wide:
Min. Crowning=0.5% of belt width (5″ belt=.026 crown)
Max. Crowning=1.6% of belt width (5″ belt=.080 crown)
Unless unusual tracking problems exist, minimum recommended crowning should be chosen, since ideal properties are developed through uniform belt to pulley contact. If an extreme crown is chosen for use with a stable belt, the full belt width will not be able to stretch and conform to the pulley crown, leaving the percentage of the belt width, not the pulley width. Crown choice is primarily affected by belt styles, installation tension and the degree of precision found in the machine drive alignment.
Additional considerations include specific drive details such as required torque or horsepower to be delivered, pulley diameters and drive speeds which must be known for proper belt selection and adequate belt sizing for the application.
Any adverse conditions which the belt may encounter, such as extreme temperatures, hostile chemical environments or severe abrasion should be considered as should other specific properties required, such as specific belt thickness, anti-static requirements or FDA approval.
L = Belt Length
C = Centerline Distance (distance between centers of the two pulleys)
D = Outside Diameter of Larger Pulley
d = Outside Diameter of Smaller Pulley
π = 3.14159
L = π D + 2C
Two pulleys, equal diameters, open-drive configuration
L = 2C + π (D + d) + (D – d)2
Two pulleys, unequal diameters, open-drive configuration
L = 2C + π (D + d) + (D + d)2
Two pulleys, unequal diameters, cross-drive configuration
Flat endless belts have a maximum operating or working tension equivalent 10% of their breaking or tensile strength. Total tension (see discussion below) on a belt should never exceed the operating or working tension.
Belts in motion on pulleys develop tight side tension (T1) slack side tension (T2). Tight side tension is created on that section of belt approaching the driveR pulley. Slack side tension is created on the section of belt approaching the driveN pulley.
These tensions are illustrated as follows:
Tight side tension plus slack side tension is equal to to total tension (TT).
This can be stated as T1 + T2 = TT.
Tension available to do work is stated as effective tension (Te). Effective tension can be found by subtracting slack side tension from tight side tension (Te = T1 – T2) or can be computed using the following formula:
Te (in pounds) = 33,000 X Horsepower (hp)
Belt speed in feet per minute
Please contact the factory for complex drives and any questions.