invar36 can be used instead of spring steel 1

[gettoritesh]

Dear friends,
Want to make a spring which has stable or very less thermal expansion coeff. Material Invar(FeNi36)(UnsK93600) or Thermelast were found to be very ideal with negligible thermal expansion (ie ~1ppm/K).But can it provide almost same performance as Spring steel;if endurance limit,fatigue etc are consider.Any alternative materials which can be used.Please help friends.....!!

 

[desertfox]

Hi gettoritesh

Without any spring details or loads how do you expect anyone to give you an answer,

desertfox

 

[gettoritesh]

hey hi desertfox...
will try to explain with example.
now i m using spring steel spring,
for force P1 my spring deforms X1
when i apply force P2 my spring deforms X2
again when i apply Force P1 my spring deforms to X3 and not X1 due to temperature (thermal expansion coeff)
So when i use Material Invar with negligible thermal expansion coeff this error is reduce drastically .But i m afraid in doing so Spring steel properties like fatigue,endurance limit etc will be compromised .
force is not a concern as they are not very high i m worried about the deformation.need a repeatable deformation on every force.with spring steel this repeatability is good at const temperature.to eliminate this temp. effect wanna use invar material

 

[desertfox]

hi gettoritesh

Without specific numbers for your spring no one can give you an answer

desertfox

 

[btrueblood]

What little I know of Invar suggests that using it as a clockspring is a poor idea - Invar has a low reported tempco only in the fully annealed state (and even then, has dimensional instabilities of 10's of ppm per year "due to impurities"). It creeps quite readily at very low stresses (i.e. a wound clockspring would relax over time) at room temperature. If work-hardened to improve its yield strength and presumably creep rates, its tempco can increase by a factor of 2 to 4 or more. Instruments using Invar for its low expansion properties must be calibrated to compensate for the real tempco of the given lot of material. Other low expansion alloys exist, e.g. Inovco, Nivarox.

There are alloys which have very small changes in Young's modulus vs. temperature (important if constant spring force is the requirement, e.g. a torsion spring), examples include Elinvar, Nivaflex.

To get REALLY low, really repeatable tempco, use fused silica or quartz.

 

[RPstress]

btrueblood: what sort of value might we expect for fused silica or quartz?

 

[TVP]

Elgiloy (UNS R30003) is a cobalt-based alloy that was developed for high stress spring applications where stable performance due to temperature variation and stress relaxation are desired. It has a nominal composition of 40 Co–20 Cr–15.5 Ni–15.3 Fe–7 Mo–2 Mn–0.15 C–0.04 Be. Use the following link for more information:

http://elgiloyspecialtymetalsdiv.thomasnet.com/viewitems/all-categories/cobalt-alloys-2?&forward=1

 

[btrueblood]

A quick lookup gives values of 0.5 ppm/C for 0-100 C, for fused silica. Ref. CRC Handbook of Chem. & Physics, 1958 ed. It also lists crystalline quartz at 7.97 ppm/C for 0-80C, um - so I guess the fused silica is what I was recalling (we always called it quartz, because it has optical properties in the UV nearly identical to quartz).

Invar "super" at best is 0.8, but "regular" grade is 1.5, and can be as high as 6. Point being it can vary depending on stress, time, composition variables, prior heat treatment history.

 

[Compositepro]

Fused silica filaments have been used as ultralight torsion springs in scientific instruments. The design concepts would be very different from metal spings. the strain capability would be much lower.

 

[israelkk]

Springs for temperature compensated accurate mechanisms that should be stable over a range of temperatures are usually made of Ni Span C or Iso Elastic spring alloys.

 

[jedward]

a- low expansion materials: think Zerodur, a glassy material
b- all glasses will be brittle and will endure only limited strain and are "difficult" to fabricate
c- are there other ways to compensate for ther thermal effects?
d- are your other materials parameters controlled enough to justify such as search beyond those listed?