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  1. ebarba

    Mysteriously increased natural frequency in structure

    The inspection revealed no changes to the machine, other the removal of that 4% worth of mass The floor mounts are helical springs (steel) working on their lower range of load and they are not clamped in any way to the floor, they just rest on it
  2. ebarba

    Mysteriously increased natural frequency in structure

    Hello all, a customer complained one of our vibrating-table machines was not working. These are reactive machines - i.e. two-degree-of-freedom systems - where the vibrating table is the second DOF and sits on springs (circular steel bars). The bars are attached to a structure (first DOF) where...
  3. ebarba

    Fracture location in large cast iron part

    The cast in itself is not very valuable, but a lot of other stuff is attached to it. If it's really cracked it will mean stopping a 24/7 line for at least one week to replace it. There is no effective pressure on the wet nor dry side. The outer part is constantly sprayed with process water and...
  4. ebarba

    Fracture location in large cast iron part

    It’s impossible to pressurize, the top part is large and practically impossible to make airtight
  5. ebarba

    Fracture location in large cast iron part

    The thickness of the wall is 10, 15 and 20 mm, depending on the specific part of this cylinder-like structure. Internally it's very clean and the surface is raw casting (no machining). Externally we expect it to have some deposits after thoroughly cleaning it and unmachined in most of...
  6. ebarba

    Fracture location in large cast iron part

    Hi, We’re going to attempt to locate a suspected fracture in a large cast iron machine part. The part is a shallow, hollow cylinder with vertical axis, about 400 mm tall and 1500 mm in diameter. To access the inner part of the cylinder there are a number of inspection doors about 120 mm día in...
  7. ebarba

    6 Permanent Magnet AC motors driven by one VFD

    we already considered that option, but we can't go at double frequency (the speed would be too high) and in any case, the increase in power would not be enough, unfortunately.
  8. ebarba

    6 Permanent Magnet AC motors driven by one VFD

    Thanks to all you guys! So, the conclusion is that the strategy is possible, albeit complicated. An effective and FAST way of monitoring the speed of each of the motors has to be implemented and the control system has to disengage power and load quickly if any of the six motors loses sync. We...
  9. ebarba

    6 Permanent Magnet AC motors driven by one VFD

    Well, PMAC was chosen for its higher energy density, we needed more power in less space. There is no particular need for speed and or position control. The issue about the separate cables was something we mechanic guys totally overlook: we have a similar machine with 20 squirrel-cage motors...
  10. ebarba

    6 Permanent Magnet AC motors driven by one VFD

    but in that case we still need to bring separate cables for each motor, which is what we need to avoid. From school days, I remember that the issue with synchronous motors was the starting, once you got them up to speed, they behaved "normally". The other issue was not to overload them as...
  11. ebarba

    6 Permanent Magnet AC motors driven by one VFD

    Hi all, because space constraints we are considering to drive six 4 kW, 400 V identical 10-pole, PM AC, sensorless motors with only one VFD. The applied torque on each of the six motors is NOT the same and varies with time. I understand the logic that the VFD will fail to determine the...
  12. ebarba

    Enclosure noise attenuation assessment

    This issue was addressed by making both layers of the walls/roof as structurally independent as possible. Originally we offered an enclosure within an enclosure, with the inner one being mounted on air springs, but the manufacturer of the noise source showed that a floating inner booth wasn't...
  13. ebarba

    Enclosure noise attenuation assessment

    There is no practical/cheap way to test walls or roof this large, before they are actually built on site. We rely on past experience and good engineering practice to design our noise enclosures. To be certain that the performance will be as expected, we use certified materials, so it all boils...
  14. ebarba

    Enclosure noise attenuation assessment

    Greg, Max noise outside the enclosure must be 85 dB
  15. ebarba

    Enclosure noise attenuation assessment

    Can you please elaborate a little further? Why you suspect the booth is not related to the noise source it will contain? The customer is (very) late with the plant that goes inside the booth, so it was agreed that if we provide reasonable evidence the booth works, then they will fulfill the...
  16. ebarba

    Enclosure noise attenuation assessment

    Greetings, We must assess the noise attenuation of a sound enclosure designed to contain a 135 dBA noise source with a reduction of 50 dB. The noise source is not yet active and won't be until late September, but an assessment of the noise enclosure is necessary for payment purposes. A...
  17. ebarba

    starting 100 kW AC motor using inductance

    Just wanted to let you all know what the conclusion was: we decided to go with the lower inductance instead of the "delayed" D/Y starter, for simple economic reasons. After discussing with the inductor manufacturer, he realized that the original one was oversized for the short period of time it...
  18. ebarba

    starting 100 kW AC motor using inductance

    In this particular case, we can de-energize and keep it that way even a couple of minutes, it's something we do right now to allow for even heating of the engin, so it isn't a problem. Can you elaborate a little more, for the electrically challenged (i.e. Me)? Do you mean a 1:1 auto-transformer?
  19. ebarba

    starting 100 kW AC motor using inductance

    Costs issues: a new inductor doesn't add more gear, wiring, labour, other than -of course- paying the new one and switching the existing. On the other hand, the Y starter needs contactors, wiring for control and power, a new box because we don't have the extra space and the like. We have to...
  20. ebarba

    starting 100 kW AC motor using inductance

    taking on Lionel's suggestion, but with a twist... what if we do a "delayed" Y/D start? [ol 1] We start the generator using a Y connection, this will make the engine start. Once the engine is running, we open the Y connection to the generator After the engine has reached a stable operating...

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