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Torsion- Shafts

Why do we use solid shafts for transfer of power in case of pumps/ turbines & other machines why we use a hollow shaft (pipe) in universal joints of automobiles; although the rated load and twist is approx. the same.
Asked by: prasanth77 | Member Since Dec-2007 | Asked on: Dec 8th, 2007

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devangmehta

Answered On : Feb 8th, 2009

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In pumps & turbine applications shaft rotates at constant speed except during starting.While in case of automobile speed & torque changes continuously . Hollow shaft can withstand  this good as compare to solid shaft.

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Solid shafts bear stresses only on its periphery. Where as in hallow shafts stress occur on the periphery as well as the inner surface. So deformation can easily occur in hallow shafts as compared to solid shafts. Solid shafts has high density and can withstand the torsional stress. (If my answer is wrong kindly correct me)

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I think we use hollow shafts instead of solid shafts because it is lighter in weight and reduces the bending moment in automobiles....as all know both the shafts have equal rated load... so why not use hollow shafts and the cost and material can also be saved by using hollow shafts..

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This question can be answered analytically.We know the Torson Equation             T                           t            ---            =           ---                J                            r                                                                  JFrom this,  the Section Modulus     =         ---                                                                   tSection modulus of the hollow shaft may be more than that of solid shaft in the case of automobiles. And the Section Modulus of the solid shaft may be more than that of hollow shaft in the case of pumps, turbine, etc.

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akash.2929

Answered On : Aug 7th, 2009

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The rated load and twist cannot be same. Had it been same the hollow shaft would have failed. Provided that they have different loads, hollow shafts are used for lower loads and twist , and they are made hollow for cost control. Please check your question again.

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A hollow shaft has a greater strength and regidity than solid shaft of equal wieght.As per principal stress theory and torsional rigidity. Therefore hollow shaft is used for large power transmission.

  
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Hollow shaft is good for transmitting torque than a solid shaft how ever its shear stress is low because of the less material content...so if a power transmission in a machine is dominated by torque than the shear stress then hollow shaft is used where as for the ones in which the stresses are critical the solid shafts are used..

  
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Sonu kumar

Answered On : Nov 4th, 2011

I think that a hollow shaft can withstand high variable torqe due to high torsional strength and its bending moment is low due to its low weight.so it is used in auto for power transmission.

  
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In case of turbine and pump there is an axial component of force present so solid shaft can deal better than hollow shaft...and in automobile only pure torsion is present and also hollow shaft have less weight for same torque transmission in comparison to solid shaft ..which increases efficiency of vehicle.

  
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Arun Govind Neelan

Answered On : Feb 27th, 2012

In automobile application we have to consider weight in addition to torque and strength. Hollow shaft has high torque transmitting capacity per unit mass compared to solid shaft. If you consider bending stress diagram for hollow it is min at centre so material requirement is minimum at centre.

  
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