Spring Engineering Tips

What are the important considerations when designing a spring?
Smart spring designs are dependent on many factors including dimensional and load requirements.

Consideration should be given to the following:

1. Environment: Will the spring be operating in a cold or hot environment? Will it be in contact with corrosive media? If so what kind?
2. Life expectancy: How long must the spring survive or work under the specified conditions without breaking or setting?
3. Load: Is a load required and if so over what range of deflection must it be maintained? What is the frequency and velocity of the load application?
4. Space: Where will the spring be functioning? During what application and in how much space? Is there sufficient room for the spring to operate fully without causing high stress that can increase the risk of failure?

What kind of tolerances can be imposed on a design?
In most basic terms, tolerances should allow spring makers to fabricate quality parts by ordinary production means in the most economical way. Therefore the critical dimensions should be determined early to allow the spring maker to make adjustments or to compensate for the allowable variations in both the size and mechanical properties of the spring materials.

Product designers often impose the "standard tolerance box for machined dimensions" to spring designs which prove impractical based on history and the nature of spring materials. Such boxes must be reviewed and more realistic tolerances applied.

Our design review team would be glad to help product designers determine what is critical and what specific tolerances should apply.

The print says, "Remove all burrs and break all sharp edges." Does this affect performance and/or cost?
Burrs can be minimized during the wire forming process. However, sharp edges are a natural result of the cut-off operation. Sharp edges are generally harmless and removal of such can add more costs without adding any value to the spring performance. Give a second thought to adding the requirement to your drawing.

What does stress relieving do to the spring dimensionally?
Stress relieving does change spring dimensions. Temperature and length of time in the oven, as well as material type, vary the spring dimension changes. We anticipate these changes so final product meets specifications. In general the following is true:

Stress relieving or heat treating affects the type of springs as follows:

1. Extension: reduction in initial tension; change in hook position; change in spring diameter
2. Compression: reduction in initial tension; change in spring diameter
3. Torsion: reduction in initial tension; low temperature stabilizes position of ends

If I change the material size, what does that do to a spring?
If you change a wire diameter by 1%, your spring rate will change 4%. So an increase in wire size by 1% will result in a 4% stronger spring. The converse is also true. A decrease in wire size of 1% will result in a 4% weaker spring.

If I change the material size by 1%, how much change in torsional stress will I get?
You will get a 3% change in torsion stress.

What is the effect of changing the mean diameter by 1%?
If you increase the mean diameter by 1%, the change in spring rate will decrease by 3%.

If I add a coil, what does that do to the rate?
Adding a coil weakens the rate. Removing a coil strengthens the rate.

e.g. If you have a compression spring that has ten active coils and a spring rate of 90 lbs./inch, and you want to get a rate of 100 lbs., how many active coils do you need?

Active Coils	=	(Single Coil Rate) / (Spring Rate Required)
Single Coil Rate	=	(# of Active Coils) X (Spring Rate)
Single Coil Rate	=	(10 Active Coils) X (90 lbs./inch)
	=	900 lbs./inch rate
Active Coils	=	(900 lbs./inch rate per single coil) / (100 lbs. rate required)
Answer:		9 Active Coils

What type of finishes are available, and what are the benefits?
Master Spring & Wire Form Co. offers several coating options to improve the look or durability of your products. These finishes do require additional lead times and may increase cost. However, finishes may prove cost effective down the road by improving life and performance of a spring.

Zinc plating

• Description:
  Electroplating; available in clear, yellow, black, and other colors
• Benefits:
  Enhances appearance and performance.
  Improves resistance to chips and abrasion.

Passivation

• Description:
  Acid treatment of stainless steel to remove contaminants.
  Recommended for medical and food industries.
• Benefits:
  Cleans product.
  Improves corrosion resistance.

Other

• Anodizing:        available in clear or various colors
• Black oxide:      results in a black appearance
• Chrome:            decreases surface friction; provides resistance to erosion
• Copper:            often used in electronic applications
• Dykem:             process where parts are dipped; good for identification purposes
• Nickel/Tin:         bright and shiny in appearance
• Paint or Powder Coat:    numerous colors available

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