screw mechanism analysis 1

[hpon]

Hi,

The product I'm am analyzing contains a screw mechanism. And I need to verify the structural integrity of this mechanism.

How do I analyze the thread? Both static strength and fatigue properties need to be assessed. I'm sure there are hand calculation methods available, but I have not been able to find any (where should I look?).

Best Regards,
hpon

Regards,
hpon

 

[flash3780]

Check Bickford's book: An Introduction to the Design and Behavior of Bolted Joints.

 

[PetieSmo]

hpon,

Just about any machine design book should have a discussion on loading of threads. It sounds as though you are running some type of linear actuator or auger.

I suggest either:
1) Machinery's Handbook
2) Shigley & Mischke

PetieSmo

 

[hpon]

Thank you flash3780 and PetieSmo!

I shall look into the literature you have suggested.

The machine is a fixture for a solid block of steel. The gripping mechanism is very forceful, and its motion is driven by the mentioned screw. My primary goals regarding the thread of the screw-mechanism, are to ensure that it is:

1) stronger than the cross-section of the bolt
2) suitable for repeated use

Any advice on how to achieve these goals would be greatly appreciated.

/hpon

Regards,
hpon

 

[PriamEngineering]

VDI 2230 is a good place to start for the 'bolt' strength against 'nut' strength calculation. Several factors are involved. You should do the calcualtion youself for your own satisfaction.

if you keep the stress range below 6% of the UTS (taken as a max of 785MPa) fatigue of the 'bolt' won't be a problem (BS7608)

http://www.priamengineering.co.uk

 

[flash3780]

I just reread your post; Shigley's book has calculations specifically for power screws that are likely going to be more useful for your situation than Bickford's book. However, they're both books worth having. I'd wager your mechanism will have some bolted joints somewhere, so you may consider getting yourself a copy both texts.

 

[hpon]

Thank you flash3780. That sounds promising. I'm not sure which one of Shingly's you mean though. Is it "Standard handbook of machine design"?

hpon

Regards,
hpon

 

[flash3780]

I have Shigley & Mischke, "Mechanical Engineering Design", however the "Standard Handbook of Machine Design" is supposed to be more thorough. Either one should have the information that you're looking for.