Anyone know what spring type this is? 4

[Dillinpolish]

Hello everyone,

I'm working on a mechanism that uses this "latch" type spring to clamp something down.

Does anyone know of any reference material or literature that would explain some basic calculations or a design methodology for this type of spring form?

I've looked around a lot and haven't been able to find anything. The goal would be to design a spring form that is displaced/deformed X amount and provides Y force when displaced/deformed.

 

[JohnRBaker]

I've always called them an 'Overcenter Latch':

https://www.google.com/search?sxsrf...oAhWVsp4KHUW3BfsQsAR6BAgKEAE&biw=1744&bih=960

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[BrianE22]

I'd call it an "over center" latch. The calculations would be pretty straight forward when you understand how it works (moment about pivot reverses polarity).

 

[JohnRBaker]

They're also sometimes called a 'Draw Latch' if that helps you find some specs.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[JohnRBaker]

Southco is one of the companies that sell these sorts of 'Overcenter' and 'Draw Latches' and they have a downloadable catalog which includes some limited specs, as shown below:

Their website is:

https://www.southco.com/en-us/product/hierarchy.html?hid=7320

Hope this helps.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[desertfox]

Hi

I would call it a toggle latch.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[drawoh]

Dillinpolish,

I cannot imagine that there would be literature explicitly for forms like this. You have a curved beam. It is symmetric, so you need only work out one side of it. Read up on your strain energy methods. This is an easy problem to set up in FEA.

--
JHG

 

[Dillinpolish]

@BrianE22 the part of the mechanism that I need to design is the spring form. When it's bent like the image that I attached, I don't know how to determine how much force the spring exerts when deformed a certain amount. Would you know of any references or literature that could help with this?

@John R. Baker thank you, I just found the same website as I was looking for reference material to design the spring form.

 

[dhengr]

Dillinpolish:
The primary difference btwn. the latch that you show and the one JohnRB shows is that yours has some spring action in the connecting link. John’s latch requires much more accurate locating on installation to assure a proper operating tension in the link. Yours is a more tolerant of slight misalignment, and still applies sufficient tension for proper operation. Of course, the latch end/side of the system must be slightly lower than the fixed side pivot so there is always a downward force component to keep the latch engaged.

Otherwise, draw a side view of your latch, particularly the bent spring/link. There is a tension force on the spring/link, trying to straighten it out. That line of forces tries to act on a line btwn. the hook on the fixed end, and the pivot on the latch end. The fact that these forces are slightly off-line is what imparts the holding/downward force on the latch. Draw some free body diagrams of the system parts and study them. Look at the link/spring as a bent beam and the tension forces are trying to straighten it out, thus applying the tension forces. Look at your Engineering Mechanics, Strength of Materials, and Machine Design textbooks for how to analyze and understand the workings of these components.

 

[TheTick]

I've done a few of these. Easiest way is to use FEA to determine spring forces. The rest is basic statics.

Using a leaf spring simplifies things. Once you have a spring value for a given profile, it is linear to width.

Using a wire, your choices are vary profile and/or wire diameter. Neither is linear.

 

[Jboggs]

Your original question was "what type spring is this?" I would call it a torsion spring because that's basically how it functions. One normally pictures a torsion spring as having a coil of one or more wraps, but still, that's how this one functions. It resists the torque induced by the pulling force on each end.