Leaf Spring Design: Choosing the Right Material & Stress Limit

[alexlyf]

Hi guys,

We need help on deciding which type of leaf springs to use for our vibratory feeder. I did some research on the topic which leads me to some questions.

1. We need to know the Flexural Modulus of different materials, like stainless steel 304, 316, and plastics. Is there any free source on the net that provides this kind of information? We have searched on Internet but so far only come up with very limited information. Or is there any simple way to determine the modulus ourselves?
2. We also need to know the maximum stress the spring can withstand, so that we don’t break the spring by putting the feeder under long operation. Again, if there isn’t an information table, can we work that out by experiment?

Thank you for any help.
Alex

 

[Gokul43201]

Flexural Moduli for plastics are much easier to find that for metals

If you have access to a UTM, you can do flexural tests yourself, perhaps with the help of the UTM operator.

Also, if it's only rough numbers you want, and the flexural modulus is hard to come by, you might be able to make do with the linear elastic (Young's) modulus instead. This is usually pretty close to the and often about 5-10% lower.

http://www.matweb.com/search/GetProperty.asp

Matweb also lists flexural yield stresses for many plastics and some metals. But if you are doing a test to determine the modulus, going a little further to find the yield/breaking stress will not take a whole bunch more of effort.

 

[Gokul43201]

I hope this (and thousands more) is what you see when you click the link :

Material Name Flexural Modulus, GPa Modulus of Elasticity, GPa
1 Overview - Acrylonitrile Butadiene Styrene (ABS), Molded 1.606 - 5.903 1.79 - 3.2
2 Overview - Acrylonitrile Butadiene Styrene (ABS), Heat Resistant, Molded 2.07 - 2.69 1.79 - 2.7
3 Overview - Acrylonitrile Butadiene Styrene (ABS), Impact Grade, Molded 0.21 - 2.6 1.7 - 2.4
4 Overview - Acrylonitrile Butadiene Styrene (ABS), Transparent, Molded 1.8 - 2.65 2 - 2.1
5 Overview - Acrylonitrile Butadiene Styrene (ABS), Extruded 1.2 - 2.8 1 - 2.6
6 Overview - Acrylonitrile Butadiene Styrene (ABS), Unreinforced, Flame Retardant 1.93 - 2.7 1.93 - 2.6
7 Overview - Acrylonitrile Butadiene Styrene (ABS), Glass Fiber Filled, Flame Retardant 3.3 - 6.9 3.3 - 9.7
8 Overview - Acrylonitrile Butadiene Styrene (ABS), 10% Glass Fiber Filled 3.4 - 4.897 3.4 - 4.8
Overview - Acrylonitrile Butadiene Styrene (ABS), 40% Glass Fiber Filled 7.8 - 9 7.8 - 10.3
Overview - Acrylonitrile Butadiene Styrene (ABS), 40% Carbon Fiber Filled 15 - 19.3 21 - 24.8

Source : www.matweb.com

If not, go to matweb.com, and use the property search feature. Among properties, select flexural modulus from the first property list and say, elastic modulus from the second and yield stress from the third (or whatever else you like). Select your min/max range according to your design requirements, or if you have none, make the range 0.01 to 200 GPa (or something safe like that).

 

[Chronos]

I'm uncomfortable with that question. You are asking for 'book' answers to a simple question you should have been able to solve without any help. What is the real nature of your problem? Is it an application problem? If so, please elaborate. I've had many of those, as have many other engineers. It's OK, I won't compromise any trade secrets... so long as you help me solve my bearing problem...

welcome to pf, alex!

 

[Q_Goest]

Hi Alex, welcome to the board.

1. We need to know the Flexural Modulus of different materials, like stainless steel 304, 316, and plastics.

To calculate spring rates for a steel such as stainless or spring steel, you will use textbook beam equations, and those equations use modulus of elasticity, not flexural modulus. Plastics typically use the term flexural modulus because the material is often not isotropic. The ASTM standards that are used as the basis for testing plastics use flexural modulus, but those used for metals use modulus of elasticity. Note also that 304 and 316 is rarely used for spring material. If you want an austenitic stainless for spring material, you can use 301 or 302, just specify "AISI 301 or 302, spring temper" to your manufacturer. Here's a quicky list of "modulus of elasticity" for various metals. These are all in psi.
- Aluminum = 10,400,000 psi
- Berylium Copper = 18,500,000
- Brass or Bronze = 16,000,000
- Copper = 17,500,000
- Nickel Alloy = 30,000,000
- Steel, carbon or alloys = 30,000,000
- Stainless Steel = 27,500,000

2. We also need to know the maximum stress the spring can withstand, so that we don’t break the spring by putting the feeder under long operation.

I would guess that this feeder you're referring to will put the spring under cyclic stress. If you can't find the fatigue limit of the material you decide on, I'd suggest using 100,000 psi as a limit for most spring steels under cyclic stress, and personally I'd try to design a spring with slightly less stress than that. You can look into the fatigue strength of individual materials in various sources, but I generally prefer to limit stresses to a slightly lower value just to be on the safe side (around 80,000 psi). I'm assuming here you'll have this spring made by a reputable manufacturer who specializes in springs, something I'd highly recommend.

 

[Astronuc]

Welcome to PF Alex.

2. We also need to know the maximum stress the spring can withstand, so that we don’t break the spring by putting the feeder under long operation.

What's a long time? There are roughly 31556950 seconds in one year, so with a frequency of 100 Hz, then one year of operation is 3,155,695,000 cycles.

Just adding to what the other say, there will be limited information available on the internet, and perhaps it will be rather general.

Organizations like ASME, SAE, ASM International, and TMS (all engineering/technical societies) publish Handbooks which give material properties. Or you could go to a site of a vendor who supplies a particular material, e.g. SS316 and or acrylonitrile, and perhaps find properties.

 

[Chronos]

Again, I need more application details to give an informed opinion. What property is giving/not giving the desired result? And, moreso, what performance parameters are you looking to meet? Application details are everything in engineering. Applied science is the most difficult discipline in all the sciences. Everything pushes the envelope.

 

[heathcotes]

Hello Alex I have just seen this very old item and I wondered if you have ever looked into composite springs that have been specially made for vibratory machinery. This is not an AD but if interested I suggest that you check out www.heathcotes.com and others! Most vibrating conveyors and feeders worldwide use composite leafsprings due to their higher Fatigue performance.

 

[sasaue]

Good afternoon,

Can someone help me with leaf spring selection for vibtaroty conveyor? I would like to make a vibratory conveyor (feeder) and I would like to select proper leaf springs for it. First of all, can somebody tell me which material is the best solution for it? I think it should be glass fiber, but what kind of glass fiber should be used (in matweb site I found properties of glass fiber, but there are few tipies of it: A-glass fiber, C-glass fiber, G-glass fiber...and I would like to know which type of fiber glass is the best for it)? Also, can someone tell me who is supplier of springs and send me web-site of manufacturing?
Thank you advance

 

[heathcotes]

Good afternoon,

Can someone help me with leaf spring selection for vibtaroty conveyor? I would like to make a vibratory conveyor (feeder) and I would like to select proper leaf springs for it. First of all, can somebody tell me which material is the best solution for it? I think it should be glass fiber, but what kind of glass fiber should be used (in matweb site I found properties of glass fiber, but there are few tipies of it: A-glass fiber, C-glass fiber, G-glass fiber...and I would like to know which type of fiber glass is the best for it)? Also, can someone tell me who is supplier of springs and send me web-site of manufacturing?
Thank you advance

See http://www.heathcotes.com/ and go to products/springs also check out the spring manual in the downloads which explains how to design springs for vibrating machinery.

 

[sasaue]

Hello,

Can anybody give me a piece of information who is vibratory motor supplier (manufacture) in Europe? I found Renolds Ajax Company in USA, but I would like to have the contact of European supplier.

 

[heathcotes]

Electro magnetic drives (Magnet-Schultz). Larger drives are usually either direct hydraulic or pneumatic but there are also a number of manufacturers of out of balance motors such as Vibrotechniques.

 

[sasaue]

Hello again,

I would like to have a small advice from you.I would like to calculate elastificity of leaf springs for my vibratory conveyor and I will do it by elastificity of all system. My question is: is elastificity of all system including mass of all components of system (pan, frame, drive and supporting structure) or this components without mass of supporting structure? Also, how to determinate an elastificity of all system: either sum of elastificity vibratory components (leaf springs and tension springs), by the formula K syst=K leaf springs + K tor.springs or by the formula: 1/K sys = 1/K leaf springs + 1/K tor.springs?
Thank you very much advance

 

[heathcotes]

To calculate this you assume that all the structure is inelastic. Ie not elastic! This leaves only the leaf springs to bend as the elastic part of the system.

 

[sasaue]

To calculate this you assume that all the structure is inelastic. Ie not elastic! This leaves only the leaf springs to bend as the elastic part of the system.

Yes, but to calculate spring, I have to calculate the elastifivity of all vibratory system and this elastificity should be equal to elastificity of one leaf multiplied with number of leafs. From these equation, assuming the width, length and material property of one leaf spring, I can determine the thickness of leaf, which is very important data for proper vibration work. Am I right or not?