Spring setting 3

[Jh0an1]

Hello, Engineers.

Presetting is a process by the spring manufacturer in order to increasing the ability of the wire to withstand higher stresses.

The spring will be compressed to max deflection in the final device. So, is it allowable for the manufacturer omit this process? (Will lead the set on service to a worse ability?)

This question is related to costs reduction asked by an important client.

Thank you.

 

[MikeHalloran]

It's probably cheaper to design the device so that the spring is not being used to the extremes of its capability, so does not require extraordinary processing.

Looking at it another way, a perceived need to maximize the spring stress is a symptom that the assembly designer has painted himself into a corner by not allowing sufficient volume for a more robust spring.

... and usually, all the other parts are expensive, long lead, and there are several years' worth in inventory in anticipation of huge sales volume, etc.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

Pre-setting a helical compression spring does not really increase the ability of the wire to withstand higher stresses. The purpose of pre-setting is to ensure the installed length/force characteristics don't change over its service life due to compression set of the spring. Pre-setting a helical compression spring used in a high-performance application is definitely worth the small added cost.

 

[desertfox]

Hi

Pre-setting of a helical compression spring normally occurs when the spring you have designed has all the right characteristics but cannot be compressed to level required, without the spring taking a permanent set. So a spring manufacturer will make the spring longer than the required free length so that when the spring is compressed in service it returns to the required design compressed height.
Either the end user can compress the spring in service or the spring maker can perform the final setting and usually the spring doesn't take further permanent sets after this operation and so no detriment to the spring.

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

 

[Jh0an1]

Thank you for your replies.

We are the spring maker. I need to answer to my boss if we must to suggest to the client to reduce the spring mass (no feasible by stress), to omit the presetting or to lookfor other cost reduction in manufacture line. We can't to buy a new fastest coiler machine now.

MikeHalloran: It's true. The assembly designers restrict the spring space, so it's difficult to propose a robust design. So, the most spring designs are at the limit.

tbuelna: You are OK, the spring cost is very small Vs. assembly cost. But the client ask us to decrease the spring cost.

desertfox: Thank you for your answer. You confirmed me that the end user can compress the spring in service. I'll suggest to my boss to ask the entire assembled device to the client so we can to do make some tests with presetting by end user.

Best regards,

Jh0an1
Venezuela

 

[desertfox]

Hi JHOah1

you're welcome

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

 

[israelkk]

I would like to add that with proper designed spring you can gain between 30% to 60% more load from same spring (i.e. same No. Of active coils, same wire diameter, etc,). All the cased the previous post refer to were to spring set as a secondary operation to stabilize the spring against permanent set (due to relaxation or creep). However, by deliberately design the setting in the design process to induce permanent residual negative stress into the wire, you can gain much more load without increasing the wire diameter and still keep the spring rate.

If you could post your spring requirements or even drawing I can check if you can produce more load or same load in smaller space. Please include all requirements, including type of use, static, cyclic, life, environment, etc.

https://sites.google.com/site/israelkk/

 

[Jh0an1]

Hi, Israelkk.

The spring requirements are:

Material: ASTM A 227 class II
Wire diameter: 2,50 mm
Inner diameter: 9,20 mm
Bore diameter: 8,40 mm
Free length: 32,50 mm
Max. deflection: 6 mm
Total coils: 6
Rate: 60,4 N/mm
Ground
Use: in oil filters of cars
Static

Thanks by your help.

Best regards,

Jh0an1
Venezuela

 

[israelkk]

More questions? Why free length is important? It is best to give at least one point of load at compressed length of the spring. For example: At compressed length of 26.5 mm the load should be xx.x +/-10% or minimum xx.x maximum yy.y. I assume the spring is in static operation pressing a desired force, then, what is the force? Why say rate? how important is the rate? How long the spring will sit in the filter? what about relaxation of the force in the filter with time? Is it possible that the spring will need to seat 10 years in the filter (even at storage) or the filter has a shelf life?

 

[israelkk]

One more question, in your first post you mentioned that the spring will be compressed to max deflection. Do you mean to a length of 26.5 mm. The solid length of the spring is 15 mm (6 x 2.5). Why the extra 13.5 mm? You like to pay for useless wire?
What will happen if by mistake it will be pressed to 20 mm? It may yield. How you can avoid it?

 

[israelkk]

When you ground do you mean Sguared & Ground? Can you send a picture/drawing of the spring? When you say 6 coils total do you mean 4 active coils? If yes it is Squared & Ground. Otherwise, it will be less than 4 active coils.

 

[MikeHalloran]

I would dispute characterizing the service as 'static'.
The only possible use of a spring within a filter is as part of a differential pressure relief valve, which I would expect to open on every cold start.
Given the filter's finite life, that's not a lot of cycles in the fatigue world, but it's not none, either.



Mike Halloran
Pembroke Pines, FL, USA

 

[israelkk]

MikeHalloran

Even as static spring it it is not valid or sound design. This is why I try to ask questions to get the proper requirements before final check. I am sure Jh0an1 will do the most effort to answer my questions. I mentioned static because he defined only one deflection case of 6 mm and not two points of work. If there are two point of load the whole picture changes and life cycle comes to the game.

 

[Jh0an1]

Dear Israelkk, you are OK. Rate and free length are not requirements, but reference information. The mandatory requirement is force at height of 26.50 mm: 362,4 N ± 10 %.

The ends are closed and ground. Please, see attached sketch.

I see your suggestion about unused deflection, and why it could be a trouble. I think this design could to work:

Material: ASTM A 227 class II
Wire diameter: 2.50 mm
Inner diameter: 9.20 mm
Bore diameter: 8.40 mm
Free length: 14.00 mm
Max. deflection: 3 mm
Total coils: 4
Force @ height of 11 mm: 362 N ± 10 % (around 53 % of tensile strength)
Closed & ground ends

What do you think? I tried to avoid presetting but we need 2.75-3.00 mm wire and more mass: it's no a good choice.

About relaxation: The client have asked us to review this issue. They want to evaluate it for eight years. I don't know how to check this parameter for a long period. I am searching information about this issue.

About if static or dynamic service: the client have explained me the operation: similar as Mike explained it. It's not strictely static. But, for springs analysis, is it approximated as static?

Best regards, and thanks,

Jh0an1