Wet Evaporative Type Air Cooled Heat Exchangers

V-belt drives in wet evaporative type air cooled heat exchangers are sometimes converted to synchronous belt drives for more constant fan speed, reduced maintenance and to reduce energy consumption.  While these benefits are often realized from belt drive conversions in many industrial systems, this particular application can be especially challenging.

Wet evaporative air cooled heat exchangers are sometimes structurally compliant allowing drive center distances to flex while in operation.  This allows belts to loosen dynamically resulting in accelerated belt tooth and sprocket groove wear.  Moisture seems to accelerate the rate of wear further with Poly Chain GT Carbon belts.   The first Poly Chain GT Carbon belt may last up to 6 months or so, then 2 to 3 months for the second and then maybe a couple of weeks for the third.  Belt teeth typically wear to a sharp point resembling “shark fins”.  By this time the sprocket grooves are often worn severely as well.

Poly Chain GT Carbon drive system life can be extended up to 12 to 15 months in these adverse applications with nickel plating on the sprocket groove surfaces.  Nickel plating is best applied to fresh cleanly machined sprockets as opposed to sprockets that have been painted or coated previously and then stripped.  In addition, sprocket finish diameters for freshly machined sprockets are corrected to account for the added thickness of nickel plating.  This improves the belt meshing quality reducing component wear.  Our Made-To-Order Metals Group can assist with properly plated sprockets that will perform well.  Contact them at makemymetal@gates.com or at 800-709-6001.

A quick and easy test for structural compliance is to stop the drive system, safely lock it out and then pull or push the belt spans together.  If any shaft or structural movement can be detected, the structure is not adequately sound for synchronous belt drive systems. In these cases V-belt drive systems are probably the better choice.

For further information feel free to contact us at ptpasupport@gates.com or at 303-744-5800. 

Synchronous Belt Drives in Wet Environments

Light and occasional contact with water (occasional wash downs) should not seriously affect synchronous belts. Prolonged contact (constant spray or submersion) results 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 more detrimental effect on the belts than pure water. Urethane timing belts also suffer from water contamination. Polyester tensile cord shrinks significantly and experiences loss of tensile strength in the presence of water. Aramid tensile cord maintains its strength fairly well, but experiences
length variation. Urethane swells more than neoprene in the presence of water. This swelling can increase belt tension significantly causing belt and related hardware problems.

Fiberglass vs. Aramid Tensile Members In Belts

Inquiries about belts manufactured with aramid tensile members are fairly common. Aramid fibers are known for their high strength and low stretch properties. DuPont’s registered trade name for their aramid fiber is Kevlar®. Both V-belts and synchronous belts can be manufactured with aramid tensile members and have definite benefits as well as drawbacks.

V-belts with Aramid Tensile Cord
Aramid tensile members provide greater tensile capacity and robustness to V-belts. V-belts utilizing aramid tensile members generally utilize premium materials throughout and can carry greater loads than standard belts with polyester tensile members. High tensile strength translates into higher working tensions. High tensile modulus (low stretch) is also beneficial in keeping belt elongation over time low. The Gates Predator® V-belt line is an example of ultra-high performance V-belts with aramid tensile members.

Material costs for aramid V-belts are greater than for standard V-belt constructions. Reduced belt elongation helps keep drive center distance adjustment ranges low, but belt tension levels drop more rapidly with the reduced elongation than with standard belts. In the end, belt re-tensioning intervals for aramid type V-belts and standard V-belts are the same.

Synchronous Belts with Aramid Tensile Cord
Aramid tensile members provide rubber synchronous belts with exceptional shock and impulse load resistance. Fiberglass tensile members used in standard rubber synchronous belts tend to break down when shock loaded as individual glass filaments buckle and fracture. Even though somewhat stronger, however, synchronous belts manufactured with aramid tensile members are not rated for higher working tensions because the load capacities of other belt components remain the same. Even though aramid tensile members may be capable of higher working tension levels, belt teeth limit overall belt load capacity as they become the weaker link.

The length instability of aramid tensile members creates challenges in belt manufacturing processes and in actual belt drive applications. Aramid materials change length as they absorb and release moisture. Changing humidity influences belt manufacturing length targets as well as how belt teeth mesh with sprockets in actual belt drive applications. In addition, aramid tensile members have a negative thermal coefficient causing them to expand and contract opposite that of metal. As machinery warms up in usage and structures expand, aramid belts shrink and become tighter. Aramid belts also loose tension rapidly with structural contraction during cooling as they lengthen. In addition to belt length and tension challenges, material costs for aramid synchronous belts are greater than for standard belt constructions and aramid synchronous belts are all manufactured on a made-to-order basis in minimum order quantities.

Summary
Aramid tensile members are beneficial in increasing the load capacity and performance of V-belts and in improving the resistance of synchronous belts to shock and impulse loading. These benefits come along with belt length instability issues that must be considered when making belt selections. The potential drawbacks of aramid tensile members may not be realized in some applications while they may create serious performance challenges in others.

Online Catalog and Drive Design Manuals

Have you looked at your current copy of the Gates Power Transmission Products Catalog recently?  If you have and noticed that your Catalog doesn’t look like the image below then you are potentially missing changes and updates that may affect your ability to select the best, most up to date product for the specific application in question. 



Gates 2012 Power Transmission Products Catalog



If keeping the latest version of the Catalog on the shelf becomes daunting, then it is important to note that the most current Catalog is also available for download from our Gates Catalog Page online (click link to be taken to Catalog Page).  In addition to downloading the entire Catalog, individual Catalog sections can be downloaded in the event only a specific product type or category is needed.  If you have the most current version of the Catalog on hand but need information from one of our Drive Design Manuals, these too can be downloaded in PDF form from the Gates Catalog Page. 

Finally, this Catalog page also contains PDF documents regarding belt interchange, belt identification, the Sonic Tension Meter manual and Preventative Maintenance manual.   Overall, having the ability to navigate to the Gates Catalog Page is a great reference tool to build on your knowledge of Gates products and design support.

Design Flex® Mobile

Gates is proud to introduce another resource for designing belt drives and/or calculating installation tension. You may be familiar with Design Flex Pro or Design Flex Web, but now Design Flex Mobile is available. Design Flex Mobile bridges the gap between our web based software and phone app, PT Toolkit. Unlike Design Flex Web, this mobile version can be accessed on ANY device connected to the internet. This puts the power of Design Flex in the palm of your hand, without having to download the PT Toolkit app.

507C Sonic Tension Meter Warranty and Repairs

The Gates 507C Sonic Tension Meter is an excellent tool for measuring belt installation tension accurately by reading the frequency of vibrating belt spans.  It is widely used in industry and is considered to be one of the finest belt tension measuring tools available. Gates provides full support for 507C meters including troubleshooting, accuracy certifications and repairs when needed.

Gates 507C Sonic Tension Meters are warranted for 2 years (sensors not included). No-charge repairs are available for meters within the warranty period. Repairs are also available for meters outside of the warranty period. Meters are evaluated in house and repair estimates are provided before work is completed.

New meters are not factory certified for accuracy, but traceable accuracy certifications are available as needed for ISO quality requirements. Certified meters are returned with a sticker and certificate verifying accuracy and the date of inspection. Note that certifications are not included in the meter warranty.

Meter repairs and certifications must be initiated through authorized Gates industrial distributors. Meters cannot be returned to Gates directly. Your local distributor is familiar with the returning process and will be happy to provide assistance. They will provide quotations for repairs or certifications and handle the paperwork and shipping. Go to http://www.gates.com/industrial/distributors  to use our distributor locator tool.

For assistance with 507C Sonic Tension Meters or any additional questions feel free to contact us at ptpasupport@gates.com or 303-744-5800.

Calculating Synchronous Belt Speed

For linear belt applications, it is often desirable to determine belt speed. The speed depends on both the sprocket pitch diameter and rpm.  It is calculated as follows:

S = (pd x rpm)/3.82

     Where:
      S  is the belt speed in feet/minute
      pd is the sprocket pitch diameter in inches
      rpm is the sprocket speed