Bushings and Keys

An often asked question is "will there be key stock provided with that bushing?" The answer is actually pretty simple; only if the bushing uses a shallow key. This means that for any drive that uses standard key stock, you will need to purchase the key stock separately. If your bushing uses a shallow key, the key stock will be provided with the bushing. The charts below can be found on page 80 of our Poly Chain GT Carbon Drive Design Manual. These charts will show you which shafts will use standard keys, and which will use shallow keys.

Sonic Tension Meter Accessories

The Sonic Tension Meter model 507C (7420-0507) is supplied with:

• a cord sensor (7420-0206)
• a storage case
• batteries
• a manual
• a mass constant quick reference card

Two additional sensors are also available for purchase separately. The flat flexible sensor (7420-0205) can be bent, making it easier to measure tension in tight spaces. The flexible sensor also allows for measurements with one hand. The inductive sensor (7420-0212) measures a magnetic field instead of sound. The inductive sensor is useful for very noisy or windy environments. Find out more at Gates.com.

Considerations for Synchronous Belt Drives on HVAC Applications

Some HVAC drives will experience high starting loads if the motor has an across the line start.  The fan will be forced to ramp up to speed nearly instantaneously, and the start up loads can be as much as 150% to 200% of the normal operating loads.

Designers that are considering using synchronous belts on HVAC drives need to be aware of this potentially high start up load.

If a soft start or variable frequency drive (VFD) is used on the drive, there is no need to take any special design precautions as the load is ramped up gradually.

If an across the line start up happens infrequently, simply applying a bit more installation tension will help prevent any ratcheting or start up issues.  

If start ups occur regularly and/or frequently, it is good practice to add .2 to the service factor when designing the synchronous belt drive.  This will provide a slightly more conservative drive design that will avoid any issues at start up. Learn more about HVAC drives and synchronous belts at Gates.com.

Taper Lock Bushings

I’ve been talking to people about Taper Lock bushings for quite a while now. However, the other day, I learned something new that I thought was pretty useful. Taper Lock callouts have always seemed a bit out of left field to me, but I figured there had to be a reason behind it. Turns out there is! A Taper Lock part number is called out by four numbers followed by the shaft bore that it will attach to. The first two numbers represent the maximum bore size, and the last two represent the total length. For example, a 2012 has a maximum bore of 2.0 inches, and a length through bore of 1.25. To properly call out a 2012 bushing to fit a shaft (let’s use 1.5” for example), you call out the whole inch followed by the fraction. This means our 1.5” 2012 bushing would be called out like this: 2012 1.1/2. Metric is pretty simple, you call out the bushing followed by the shaft diameter and include MM behind it; let’s use 20mm as an example size. The Metric convention would look like this: 2012 20MM I know this will certainly speed up my answers, hopefully it will help you too!

Synchronous Belts & Exposure To Water

Light and occasional contact with water (occasional wash downs) should not seriously affect synchronous belts in general. Prolonged contact (consistent spray or submersion) can result in significantly reduced tensile strength in fiberglass belts, and potential length variation in aramid belts.

Prolonged contact with water also causes rubber compounds to swell, although less than with oil contact. Internal belt adhesion systems are also gradually broken down with the presence of water. Additives to water such as lubricants, chlorine, anti-corrosives, etc. can have a greater detrimental effect on belts than pure water.

Poly Chain GT Carbon belts use polyurethane compound and carbon fiber tensile materials that are both very resistant to water. Poly Chain GT Carbon belts can withstand prolonged contact with water without detrimental effect.

Sprockets operating in the presence of water may be vulnerable to rust and corrosion unless resistant materials or coatings are used. Sprocket corrosion can result in accelerated belt wear and tension loss. These can both shorten belt life significantly. For assistance in the design and acquisition of rust and corrosion resistant sprockets and bushings, contact Gates Made-To-Order Metal team.

Gates Drive Design Manuals

Customers often ask where they can find technical information about Gates belt drives. The Gates Drive Design Manuals are a great resource for this type of information.

There are several manuals available at www.gates.com/drivedesign/:

• Poly Chain® GT® Carbon
• PowerGrip® GT2®
• Heavy Duty V-Belt
• HVAC
• Light Power and Precision
• Air-Cooled Heat Exchanger

Below is a sampling of the topics included in the manuals:

• Drive selection procedures (including power rating tables)
• Gates hardware specifications (for standard sheaves, sprockets, bushings, etc).
• Discussion of design considerations such as installation tension, conductivity, alignment, noise, flywheel effect, NEMA motors, tolerances, idlers, etc.
• Standard calculations
• General troubleshooting guidelines

Splicing and Clamping Synchronous Belts

The question is often raised if it's possible to cut a synchronous (timing) belt into a custom length and splice the belt back together when a standard length does not fit the application. To answer this question: yes it can be done, but not very easily. Splicing two ends of a synchronous belt can be done when the belt is made with a particular type of polyurethane construction and additional polyurethane is used as "glue" to attach the ends of the belt. After this splicing process you can expect about 40% of the initial strength of the belt. This is because once you cut the tensile cord you've eliminated the strongest part of the belt. The spliced section is now the weak link of the belt, and like your co-ed softball team, you're only as strong as the weakest link. There are currently no processes to splice together a rubber synchronous belt.

Clamps are often used to attach two ends of a synchronous belt together. If this is done, the clamp must be contained on the belt span between the two pulleys. If a clamp ever attempts to ride over a pulley, catastrophic results will surely follow. If a clamp is used to attach two ends of a synchronous belt, a minimum of 6 teeth in mesh on each side of the belt is recommended. Anything below 6 teeth will lower the belts available working strength (6 teeth = tensile strength of belt), and premature belt failure from tooth shear is more likely to occur.