gap in closed end spring

[kkg123]

Dear friends

we receive closed & ground end spring.In ground coil & before the ground coil there is a gap of 0.005"in the coils, hence our products makes noise.We have confirmed this with no gap spring & gap spring & various trials. I want to know whether there should be gap OR no gap.I was unable to find answer on internet.Is there any standard available. Our supplier is talking about MICO standard, but I have not seen it.Please help me.

 

[israelkk]

What are the spring dimensions, OD, wire diameter, number of coils, material. What is the housing diameter hole for the spring or shaft diameter inside the inner diameter of the spring. How the spring is supported? A drawing can help.

The 0.005" is a very small gap. In 30 years of designing and using springs I have never faced the need to have an absolutely no gap. I also have no knowledge of a standard referencing this issue. I have looked at "MIL-STD-29A Springs, Mechanical drawing requirements for" and could not find a reference to the minimum gap allowed.

http://www.webspawner.com/users/israelkk/

 

[gaufridus]

I presume that your spring is a coiled tension spring with end loops? If this assumption is correct it would appear that your spring has been manufactured without any pre-tension. Talk to your supplier and specify that the springs should be pre-tensioned.

 

[israelkk]

gaufridus

Closed and Ground spring is a compression spring not an extension spring!.

On the other hand, the same technique used to create pretension in an extension spring may be used on the last 2 coils at each end of a compression spring to assure a zero gap. However, kkg123 didn't supply any specific information about the spring such as material, dimensions, heat treatment etc. A heat treatment can influence the pretension. The grinding operation too can heat the coil and loosen the pretension.

 

[diamondjim]

Keep the spring in compression.
It make sense rather than have
alternating forces being applied
to the spring. I would expect
greater life from the springs also.
Contact your spring manufacturer
technical department. Belleville
washer as an example are to be
always in compression and not
relaxed.

 

[MintJulep]

How about filling in the transion area to the closed off ends with silver solder, epoxy or something similar?

If that won't work, how about a sleeve?

It doesn't sound reasonable to expect absolutely zero gap to be consistently manufacturable.

 

[tbuelna]

kkg123,

Asked your spring manufacturer about supplying the springs "pre-set". This is common practice with automotive valve springs. It involves compressing the spring to coil bind, once.

 

[israelkk]

tbuelna

Preset is a process where the spring is made intentionally longer than needed such that when compressed to solid the stresses in the spring will be deep on the plastic zone.

The result is a permanent set where the spring length will shorten to the desired final spring length. The process creates a permanent residual negative stresses in the wire section outside diameter. This process has nothing to so with closing the two non-active coils in a squared and ground compression spring ends.

 

[kkg123]

Dear all

Thank you for overwhelming respone.I am answering various question raised.
1.it is a variable compression spring.
2.material: SAE 7178,music wire
3.wire dia 0.146"-.150"
4.no of coils 3.88-4.12
5.active coils 1.75-2.25
5.top coil OD 1.13"-1.15"
6.bottom coil OD 1.855"-1.885"
7.OD of component in which spring fits is 1.115"-1.124"
8.the spring is under load & is not free
9.flling the material adds cost, which now a days should be avoided
10. Most important The same spring was coming with no gap before 6 months& now the supplier says it is unavoidable giving freference of MICO standard.

 

[israelkk]

"1.it is a variable compression spring." this is not a clear statement.

What is variable, the diameter, the force vs deflection?

Is it a linear conical spring or a variable rate conical spring?

What are the force vs deflection requirements?

How is it working?

What is the frequency of loading?

What do you refer by "our products makes noise"? Is it the spring or the system? May be the system develops resonance?

If the system develop resonance when there is a gap and doesn't when there is no gap then your design is too sensitive. The spring rate when there is a gap is lower than the spring rate where there is no gap until the gap is closed.

 

[kkg123]

M<y primery requirement is whether there should be gap OR no gap OR there is really any standard.Closed ends means what?

 

[Philrock]

Regardless or what any standard may say, it is your prerogative to specify that there must be no gap. On the other hand, this may be difficult for your vendor to achieve. Has the vendor explained why he could provide springs with no gap earlier but can no longer do so?

 

[TVP]

There should be NO gap. Closed ends mean no gap between the inactive coils. I am not familiar with any standards that reference how much gap is allowed for closed ends, because it is understood that gaps lead to problems like contamination, premature failure, etc.

 

[kkg123]

Thanks to all & specially TVP/Philrock,as they have given me direct answer in right direction. request a help can anybody atleast give reference of design data handbook like machinary handbook etc. or some paper if standard is not known or non available.