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Fan Shaft Material

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  • Fan Shaft Material

    Hey fellows a question about material. A company recently replaced a fan shaft (a local machine shop made it for them) at our facility, it lasted about 3 days and started vibrating. They checked and found the shaft was bent .012". The fan is a 24" dia. BI (backward inclined)fan, the shaft 1 15/16" and operates at 1900 RPM. My question is will a shaft made of mild steel 1018 or 1045 be able to handle the rpm. Does the rpm matter? Does the duct static pressure matter?

  • #2
    We used to use Turned, Ground, and Polished
    1045 in 1 15/16 dia for fan shafting for air conditioner units for Donn Corperation before they sold out to an outfit near Buffalo, New York.
    We made a boat load of those shafts.
    Don't know how that relates to your instellation.

    Cold rolled material is frequently bent from the supplier. Cutting keyways can also warp crs.



    • #3
      If it ran two days w/o vibration it must have been OK when installed. I have to wonder if your problem isn't the fan instead of the shaft. Is it balanced? At those speeds just a little bit off balance and ...

      Paul A.
      Paul A.
      SE Texas

      Make it fit.
      You can't win and there IS a penalty for trying!


      • #4
        I always use Stressproof. C1144
        Keep it in various sizes in the shop.Great for everything, less welding.
        Ps check the bearings!!

        [This message has been edited by motorworks (edited 03-04-2004).]
        please visit my webpage:


        • #5
          Does the Stressproof machine real nicely?
          Lynn (Huntsville, AL)


          • #6
            The material won't make a difference relative to the vibration, both materials have the same stiffness. However, since 1045 is stronger then 1018, it will be better able to withstand vibration problems before it deforms.

            The problem could be the bearings used, if the clearance is too large or small, then problems occur. Too large makes for a soft system that lowers the natural frequency and the fan can then run too close to the natural frequency causing high vibration, which may cause the bent shaft if allowed to run too long.

            Too tight a clearance on the bearing causes excessive heat that can warp the shaft and cause the problem you are seeing. I have also seen improper grease used that caused overheating of the bearings and a bent shaft. Make sure you are using something recommended by the bearing manufacturer for the size bearing and running speed. Using the cheapest one you can find often leads to problems.


            • #7
              "Does the Stressproof machine real nicely?"
              It machines VERY nice!!
              please visit my webpage:


              • #8
                YES, it DOES!!


                • #9
                  Any feedback on what went wrong. Bearing, shaft, unbalanced load ?

                  Much appreciative


                  • #10
                    The bearings are new pillow blocks. It's a standard arrangement, bearings on either side of the fan, belt driven pulley on one end. The company is having another shaft made from 1045 and when they install it we'll throw a dial indicator on it and see. The senior tech said that they might have overtightened the belts trying to stop what was refered to as belt slap. More when we have it.

                    [This message has been edited by wrench (edited 03-05-2004).]


                    • #11
                      Belt slap? Didn't they match the belts?


                      • #12
                        Are the replacement bearings HVAC spec. HVAC bearings have different clearance requirements because of wide temperature range during operation.
                        North Central Arkansas