Balancing a coupling is putting the center of mass on the center of rotation. There are two main ways a manufacturer can accomplish this.
- Option #1 – Manufacture using tight tolerances and tight fits.
- Option #2 – Correct the imbalance after manufacturing by drilling holes in the coupling face.
Most manufacturers use a combination of both or purely option #2 because it is the least costly. Balance classes and specifications are defined for couplings; however they are often misunderstood or misapplied by customers. This often results in customers specifying a tighter balance specification “just to be sure” that the imbalance in the coupling will not cause problems in the system. Sometimes customer’s specification intended for an improved balance is actually not as precise as the standard balance tolerance. In terms of balancing designation, there are two main types.
- Potential Imbalance
- Potential imbalance is generally governed by ANSI-AGMA 9000. This balancing protocol is more of a manufacturing standard. It is the maximum potential misalignment of the axis of rotation to the center mass of rotation measured in micro-inches.
- No matter what size coupling or speed of operation, the potential imbalance in micro inches would be the same for each Class balance.
- The potential imbalance is almost universally misunderstood throughout the coupling industry. For example, a customer may request a coupling “balanced” to ANSI-AGMA 9000 Class 10.
- AGMA 9000 is a manufacturing standard, and balance corrections are not allowed.
- This standard refers to a maximum potential imbalance, so if a customer requests a coupling balanced to AGMA Class 10, most manufacturers may say that isn’t a good balance. The reality is they don’t understand the standard: the manufacturer is thinking residual imbalance. So if you get a coupling that is AGMA Class 10 or 11 with holes drilled in it for balancing you know the manufacturer didn’t know what they were doing.
- Residual Imbalance
- Residual imbalance is generally governed by ISO 1940. This balancing protocol is the actual balance of the coupling that is being shipped.
- This standard is a velocity measurement based on the distance between the axis of rotation and the center mass of rotation.
- This standard is predicated on the speed of the coupling in operation. If two identical couplings were rotating at different speeds in operation but were balanced to the same ISO 1940 G2.5, the faster coupling would have to have a tighter balance in order to meet the ISO standard.
Key Differences between Residual Balancing (ISO) and Potential Balancing (AGMA)
- Many manufacturers complete a residual balance to allow the use of loose tolerance parts. Once the residual imbalance is removed, the coupling is now a unit, and parts cannot be switched and swapped with other spare parts. This can make proper coupling maintenance costly and difficult to manage.
- An AGMA Class 10 coupling has completely interchangeable components. This means all parts are manufactured with tight geometric tolerances to insure the center of mass close to the center of rotation. Prior to ordering an AGMA Class 10 coupling, it is appropriate for the customer to ask for the balancing calculations. This analysis determines whether or not their coupling is actually AGMA Class compliant.
PSC – AGMA 9 rated couplings for speeds up to 3600 RPM for most coupling sizes
- At PSC, all standard couplings are true AGMA 9 rated as a result of our robust design and high quality manufacturing processes. PSC’s couplings incorporate a Disc Cartridge design which includes a friction lock coating. This design results in a very well balanced, high-torque coupling as standard and allows drive bolts to be easily installed into position (which can be challenging with the AGMA rated designs of other manufacturers).
- Many manufactures may claim to be AGMA 9, but many may not be true AGMA 9. This is very easy to check by verifying the critical positioning features geometrically run out to the bore within 0.002 inch. Achieving this level of runout can be very difficult, for example, if a manufacture sources rough hubs from one location and imports them into a different location where the finished bores are machined.
- PSC machines all critical positioning features in one process, so our customers can be ensured a high level of quality. In addition, all hardware is precision weight balanced and all components are 100% made in America.
PSC – AGMA 10 rated couplings for speeds in excess of 3600 RPM
- PSC takes quality and performance to another level of precision with high speed applications more than 3600 RPM. Our AGMA 10 rated coupling has a finer level of precision in the disc pack pilot features when compared to an AGMA 9. AGMA 10 couplings require some mild tapping to seat into place due the tight tolerance fit. All hardware also is precision weight balanced and all components are 100% made in America.
PSC – AGMA 11 rated couplings for ultra-high speeds
- PSC is in a class all on its own for ultra-high speed applications. Ultra high speed is defined based on coupling size where the maximum speed is calculated based on rotor dynamics. An AGMA 11 rated coupling has the highest level of precision in the disc pack pilot features. AGMA 11 couplings also require some mild tapping to seat into place due the tight tolerance fit. These couplings also have all ultra-precision weigh balanced hardware, and all major components (Hubs, Center member, Disc Pack Cartridge) are precision balanced individually. Also, none of our couplings are match marked and all components are interchangeable with in AGMA ratings. This is a precision balance yet still maintaining full part interchangeability.