Gates Polyflex belts have some unique characteristics. Therefore, special considerations may be needed in designing drive systems and in assessing operating environments:
Liquids act as lubricants – Because of the broad 60° groove angle, belt wedging forces are reduced making the coefficient of friction between belts and sheave grooves critical in transmitting load. Liquid contaminants such as water, chemicals or oils can decrease the coefficient of friction, allowing belt slip. Belt slip can result in belts turning over in the sheave grooves. Heat from belt slippage may also cause belt softening or melting, resulting in catastrophic failure. Adequate shielding should be used when liquid contaminants (either airborne or splashed) are present near Polyflex drive systems.
Damage from debris – The 60° belt sidewall angle and thin cross section both make these belts susceptible to debris. Debris can cause belt instability resulting in belt turn-over, which will result in catastrophic failure. Adequate shielding should be used when debris is present near Polyflex drive systems.
Backside idlers – Polyflex belts running on flat backside idlers can create objectionable noise due to the molded ribs on the back of the belts. Perceived sound level is inversely proportional to the sheave diameter, so using larger idlers can reduce generated noise.
Static conductivity - Polyflex V-belts do not meet the RMA requirements for belt conductivity. Polyflex V-belts should not be used in potentially explosive or flammable environments without the use of adequate static dissipating devices such as grounding brushes.
GATES BELTS, HOSES, AND APPLICATIONS
Tuesday, April 26, 2011
Friday, April 15, 2011
Measuring A Synchronous Belt
We get a lot of questions from people trying to find a suitable replacement belt. There seems to be a lot of confusion as to what information they need to provide for us to try to ID the particular belt. It’s not as difficult as it seems. The first question that we are going to ask you is to get us any print on the back of the belt. Industry callouts are pretty similar, and if you can find a part number, a lot of times we can ID it from that alone. Now if it comes down to measurements, there are only a couple that we need: length, width, and pitch. We also need to know the shape of the teeth. This is pretty simple, as there are only about 3 different types that we can interchange for power transmission belts; square/trapezoidal, half circle, and curvilinear with a flat spot on the top of the tooth. These shapes help us ID the type of belt, from here, all we need are the other three measurements to really get going.
Length: measure the outer circumference of the belt. If the belt is broken in half, just measure the total length.
Width: measure the width across the back of the belt. This could be in metric or imperial units; it doesn’t matter which one you give us, we just need the best measurement you can get.
Pitch: measure from the center of one tooth to the center of the next tooth. Simple, but sometimes the teeth are small. Getting as close as possible on this really helps – see above about the metric/imperial units issue.
We will also ask you to count the teeth, it’s not that we don’t trust your measurements, but this is verification of the correct length and pitch measurements. I know, I know… There may seem to be a lot of them, but even a belt with 200 teeth will only take a minute or two to count.
That’s it, from here, all it takes is knowledge of our product line to ID the type of belt, and a catalog to see if it’s a stock size. Sometimes we can’t cross a belt because it was made special for someone. In these cases you will have to go back to the manufacturer of the machine that your belt came on – even if we made the belt in the first place.
Length: measure the outer circumference of the belt. If the belt is broken in half, just measure the total length.
Width: measure the width across the back of the belt. This could be in metric or imperial units; it doesn’t matter which one you give us, we just need the best measurement you can get.
Pitch: measure from the center of one tooth to the center of the next tooth. Simple, but sometimes the teeth are small. Getting as close as possible on this really helps – see above about the metric/imperial units issue.
We will also ask you to count the teeth, it’s not that we don’t trust your measurements, but this is verification of the correct length and pitch measurements. I know, I know… There may seem to be a lot of them, but even a belt with 200 teeth will only take a minute or two to count.
That’s it, from here, all it takes is knowledge of our product line to ID the type of belt, and a catalog to see if it’s a stock size. Sometimes we can’t cross a belt because it was made special for someone. In these cases you will have to go back to the manufacturer of the machine that your belt came on – even if we made the belt in the first place.
Tuesday, April 5, 2011
Fan Drives: High Start Up Loads and Synchronous Belt Drives
Start up loads can be a significant concern when evaluating potential drives for conversion to PowerGrip® GT®2 or Poly Chain® GT® Carbon belt drives. PowerGrip® GT®2 and Poly Chain® GT®Carbon belt drives will transmit all of the start up torque, where V-belts may slip if the load is excessive. Due to the inertia of the fan, start up loads can potentially be 150% to 200% of the normal operating load. This is obviously much more of a concern when the drive will be operating on a system that frequently cycles on and off. Drives that run continuously will only see the start up load intermittently, so are not as sensitive to the combination of high start up loads and weak structures. It is important that the start up load be considered when evaluating a drive. If the structure is weak, a high start up load will further adversely effect the PowerGrip® GT®2 or Poly Chain® GT® Carbon belt drive's performance by allowing center distance collapse. This reduction in center distance results in an under tensioned belt which may wear prematurely from being undertensioned, or even worse, premature failure from ratcheting. If an electrician or properly trained technician is available, an ammeter can be used to compare the start up amperage to the steady operation amperage. If the amperage is 1 1/2 to 2 times the steady state amperage, the structure should be carefully inspected to insure that it is robust enough to prevent center distance collapse upon start up. With the drive shut off and safely locked out, the structural rigidity can be checked by pushing the two belt spans inward toward each other and looking for any relative movement in the structure.
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