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Shaft modification or manufactured new one

Shaft modification or manufactured new one

Shaft modification or manufactured new one

(OP)
Hello all,

I am dealing with a problem with a shaft, the story is, I have a shaft to replace a damaged shaft in a system but this is shorter by 300 mm that I am requiring, my question is Can I add a piece of 300 mm to the shaft(welded or mech. coupling), to complete the total required length or This could be a little dangerous and it is necessary to manufacture a new shaft.

The shaft specs are:
Material= carbon steel
OD= 600
thickness= 30mm
actual Length= 6400mm
final length including the 300mm=6700mm
RPM=1-5

Another info, this shaft is part of a RBC system in a sewage treatment plant.

Thanks in advance.

RE: Shaft modification or manufactured new one

stub shaft repairs are a viable solution for some elements/failures.

A drawing of the element and marking where the current failure occured would help with the determination if it is possible in your case

RE: Shaft modification or manufactured new one

The additional info. that you should provide are the function of the shaft for which the starting torque could be a problem area and the horsepower that the shaft is to be exposed?

RE: Shaft modification or manufactured new one

You should draw a FBD and determine the stresses and forces at the junction. You should also look at deflections and make sure they won't be a problem with the longer shaft.

RE: Shaft modification or manufactured new one

At that low an rpm, you have the advantage of fewer vibration problems when the repaired/re-machined shaft is extended. As above, torque and starting load and shock/start-stop stresses are going to determine method.

CS weld - assuming a good weld prep of sufficient size with a competent welder, the joint is straightforward.

RE: Shaft modification or manufactured new one

jor1492,

Is your shaft heat treated? This make welding more complicated.

--
JHG

RE: Shaft modification or manufactured new one

(OP)
Attached you can see a draft of the shaft.
I am thinking in use a shaft coupling or welding to join the 300 mm missing length and of course do the recalculation of the stresses and deflection.

But my question here is: Base in your experience you think that is good idea do this or is better a new shaft.

RE: Shaft modification or manufactured new one

  • How does the 600 mm diameter relate to the 150mm diameter?
  • Is this a turned down solid shaft, or a 600 mm round shell mounted on a 150 mm shaft?
  • Is it a weldment or are shaft and shell mechanically coupled?
  • 150 mm shaft diameter for a 6.4 m span does not seem good.
  • Per ANSI/CEMA B105.1 Welded Steel Pulley Design, pulley shell strength should not be included in the shaft strength calculations.
  • It is not clear the usage, design, loading or fabrication of this component, but it may not have been designed per industry standards.

RE: Shaft modification or manufactured new one

I am with dvd on this. How was the shaft made?
I presume that the center section is hollow?
Does the smaller shaft run full length? Or is it welded to the ends?
I would rather see you replace the entire stub end instead of splicing it.
If the smaller shaft runs full length them putting the splice inside of the shell would lessen the bending load on it.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Shaft modification or manufactured new one

(OP)
The problem with this piece is That I dont know how it is built. The smaller shaft go inside of the bigger but it is sealed, so I dont have a 100% information of how this is built and doesnt exist drawings of this.

Another problem is, if I do some modification in the shaft, this could affect the position of another equipment in the system.

I recommended to design and fabricated a new shaft and the new shaft will be with a hollow section and two smaller shaft at the ends to fit with the bearings. The shaft that we have in stock can be used like spare part for other system where this shaft can fit perfectly.

Thanks by your help and recommendations.

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