Ok, so we joke about how enclosures are sometimes a "rat's nest" inside, and we have actually found dead mice in enclosures and drives, but is it safe? Remember, when older enclosures were designed (if they were actually designed), they met different thermal needs, and more importantly different electrical standards. Standards change over time to incorporate safety and be sure when people work on equipment, that they can stay employed for years to come! Needless to say, when you modify the panels in the field, you no longer meet UL requirements, and how much liability falls on the company if you skip steps in safety?
Want to get the best price? Just ask someone for a specific HP drive and forget to define the application as Heavy Duty, which is what extruders are rated unless lightly loaded. The Heavy Duty designation gives the drive 150% overload for one full minute, rather than 110-120%. Unfortunately, asking someone to give you a drive in the box seems like a great deal initially, until you find that you are now having nuisance tripping of the drive shutting down your production!
If someone tells you that a 300HP/1150RPM motor can be replaced with a 300HP/1750RPM motor...RUN! Torque is what turns the screw on the extruder, and the torque characteristics of an 1150 motor is SIGNIFICANTLY MORE!!! For example, on a 4.5" extruder, a 300HP/1150RPM motor produces approximately 1,313 ft-lbs of torque, on the otherhand, the 300HP/1750 RPM motor produces about 875 ft-lbs of torque, a difference of aboutHALF the Torque!! The inverse is also a big deal, imagine what would happen to your gearbox if it were rated for a 300HP/1750RPM motor and you replaced it with a 300HP/1150RPM motor on it! Yikes!
If you want a quick delivery, you need to understand what is a standard, and what is typically in limited supply! At ICT we have one of the biggest stocks for large HP systems available, but even we have limitations on what we can do quickly. Motors that are NOT 1750 RPM are not usually stocked by anyone, and almost all motors stocked are F1 conduit box location. Add changes to the bearings and the lead-time jumps as well. Plan ahead! If you can't we're here!
Just because the AC drive fits in the same space as the old DC drive, does not mean it is a good idea to use the same enclosure. DC drives and AC drives have different thermal characteristics and putting an AC drive in the old enclosure means you also have to upgrade the cooling. Of course, once you do this, you have spent enough to do it right and change out to a new enclosure; moreover, the rule of air conditioners is simple... they eventually fail, and when they do, your drive is basically cooking in a small oven, quickly derating the life, and likely soon to fail! Should we have to say that opening the door and pointing a fan at the drive is not actually going to work?!
AC Drives have significant advantages over DC motors, but the drive can have serious impact on the motor bearings. In seeking a path to ground, the bearings are in the way, so they end up becoming a conductor, this results in pitting, and eventually bearing failure. For this reason, creating a better path to ground around the bearings are not only preferred, but highly recommended. Aegis bearing rings are a great solution for this issue and we can help. For more information on bearing currents, download the whitepaper to the right.
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