How Do I Galvanize Leaf Spring?

You didn't say if you noticed any breakage prior to galvanizing.

You didn't say if the galvanize was hot dip or electro galvanizing.

Are you sure that there are no tool marks or sharp features at the points where these fractures occurred?

You didn't say how the pickling process ahead of the galvanize step is timed or controlled, or what acid is used or its strength, and what inhibitor or not is used.

but with high UTS and very fine grain size and poor pickling practice this could be the root cause.

You didn't say the ulltimate tensile strength achieved, My references are at work, I'd have to look up the grade and hardenability in AM tomorrow, but if UTSis >150 ksi(~1100mpa) you could have :

C) could be hydrogen embrittlement.

more facts and photos will make it easier to confirm.

milo

Dear milo,

I actually did for both hot dip & electro galvanizing. Most leave spring break on #1, for both process. Yup, there is no crack or sharp edge around the hole. Please refer attched photos.

SUP9 is a Manganese Chromium Steel. Grain size after tempering before galvanizing is A.G.S No. 5-9.

It is assembly set. Prior to assembly, all leaves in between actually has some gap, that produce some nip stress. #1 & #2 has 15mm gap, #2 & #3 has 5mm gap, & continue with reducing gap for following leaf springs. This is standard for spring manufacturing. After assemble with centre bolt, there will be no gap between leaves.

For pickling process, myself not very sure since it is done by third party. It is my first time to galvanize leaf spring.

Sim

Couple questions

1) is it just me, an illusion, or is width of punch hole B Between bottom two red lines wider than above at A?

2) Their are vertical striations visible clearly (blue arrow pointing to) which would have been around circumference of hole. thus possible nucleation sites for intitiation of fractiure.

3) dimples in material emanate out from hole (green arrows at bottom) these directional or tattletale dimples marks are typical of transgranular brittle failures if the material has already "lost its ductility by the punch out" at the bottom (b side) of the spring, then that explains the dimples pointing to the corners at the hole as the initiation site.

Inferences: Punched hole practice may cause initiation for cracking (Striations ); Taper in hole may aggravate the loading (see dimples ); embrittlement from pickling may also contribute (Brittle failure appearance).

I am not a designer, but if the hole has to be there, the texture a rotating drill would leave is 90 degrees to the current direction of crack propagation.

A sharper photo of the edge around at the top surface by the hole may shed more insight, the light to dark that i am seeing is tantalizing. the bright layer at the top A side of the hole tells me thats where the punch entered and material then sheared down?

Why again are these being galvanized?

What is lube used on punch?

milo

I gave you a GA for an excellent post and observation, thanks.

Dear Milo,

Sorry for replying late. It is too busy with my work.

1) Yes. You are right. Since this is a cold punch, so it's actually a cone shape hole.

The hole is needed for assembly.

Currently, i'm stil reproduce some sample & test it again.

Hi Sparkstation,

Yes. Springs break easily after hot-dip galvanizing.

I agree that it form into complex alloy where the Gamma layer (75%Zn 25%Fe) create highest hardness that may make spring brittle & break when during assembly. Most of the springs break on #1.

This spring use on small trailer.

The pictures as below:

I have not check the zinc quality since i'm not familiar with galvanizing process. This is my first time to galvanize spring.

Springs without galvanizing show no problem. Only those galvanized springs broken easily after assembly. I'll make few more samples with smaller nip stress / gap prior to assembly for testing purpose.

Thanks,

Sim

Dear sim, Bake the springs at abut 300 degrees for about an hour before testing. When they do not break, we will kinow it is hydrogen from pickling.

It can't be the galvanizing (Zinc,) you used both hot and electro, so it is independent of that.

also, is the plating free of transverse scratches? The photos in your last post (top view) have me puzzled.

Milo

I agree with SparkStation that cold punching weakens the area around the punched hole. This has been known for some time, and safety codes eventually disallowed punched rivet holes for structural joints and pressure vessels.

The holes should be drilled, not punched, and should be made while the steel is in an annealed condition, before any heat treatment.

My memory of leaf springs goes a long way back and if I remember correctly, they were never galvanized at all, in fact they rusted and needed to be sprayed with oil from time to time......

I still feel though that the hole punching is the heart of the problem as it would appear that the hole is the weakest point in your examples.....if a hole that appears to take up almost 1/3 of the width is drilled or punched, then this point on the leaf will always break first unless that area is held tightly in some manner and not allowed to flex.

I also feel that the leaves will break if used without galvanizing in exactly the same manner.....you will need a Metallurgist to examine the breaks to see what the real cause is. Galvanizing may contribute a little to the break, but not really much I feel, the basic design is the problem......

Leaf springs should be held tightly in the middle (usually where they meet the Axle) and not allowed to flex much by a sort of box arrangement with 4 nuts on 2 U-bolts, outside of the spring leaves......so perhaps the builder is also not doing a good construction job either.....

Look at these diagrams (click on the links), I feel that the basic design that you have with a hole is likely to break galvanized or not if the area around the hole is not clamped correctly and fully and kept from flexing....

Checkout the following links for some good diagrams:-

http://www.tpub.com/content/construction/14273/css/14273_303.htm

http://www.circletrack.com/techarticles/ctrp_0602_leaf_spring_tech_terminology/index.html

Hello Andy Germany,

FYI, these springs' broken prior installation onto vehicle. Some break during assembly, some after few days.

sim

Please can you show a picture of an installed one, prior to breaking! we need to see how well it is mounted and how flexing in the hole area is kept to a minimum - or not!!

I suspect the answer is not. If so, another method of mounting needs to be devised without having a hole OR, the width of the blade needs to be doubled in the hole area and for several inches before and after, to reduce flexing and increase strength.

No hole would probably be better......

This is all supposition at this time, but all that you have written up to now supports a hole problem......at least to me personally.....

Andy, I don't think they can do completely without a hole there. Something has to resist longitudinal shifting, or the spring package will come all away from together. Maybe a relatively smaller hole and pin/bolt would do the job...

You could well be right, but all the springs I have examined hold that area stiff and stop it from flexing.....which is why i want to see a picture of how it gets mounted....

But some breaking before mounting, now that is a worry!!

Have two questions:

1. Did you allow time after punching for stress relieving? Why not trying to MagnaFlux™ the punch area?

From what you are saying now I have little doubt in my mind that the punching process is at fault.

2. why are you galvanizing a spring.? Are you aware of the fact that hot galvanizing causes modifications in the molecular structure?

Unless you (and even if you do...) install your springs onto a boat trailer, I wouldn't galvanize it. A bare spring of reasonable quality will give you long life even under highly corrosive conditions, if regularly protected by some sort good corrosion protection paint or alike or even some heavy oil is applied.

Wangito.

Good post.

Years ago we just sprayed them with oil several times a year.....

Why not try to move the hole few inches up or down on a test leaf, run a flex test, and if no problem, galvanize it with all the previous parameters remain the same. maybe the present hole location is a hi-stress point. Run second flex test, if it still breaks, than try another sample this time drilling the holes, (before any other heat treatment is done.) If it still breaks after both tests, you have the culprit identified, and take it from there.

Hope it helps.

Wangito.

I agree with Bubapepi, Aandy, and Wangito, but if baking makes it go away, that is your easiest to pursue test... If not, then the design issue of having the hole, and the workmanship issue of the hole finish, and striations nucleating the cracking are the areas to pursue.

But pickling of springs with out post bake gives me pause.

milo

Concur, Wangito, the empirical method is likely to give as good a result as a metallurgical analysis. But I also agree with Larry G. that the presence of the hole is most likely the main culprit. It may simply be too much hole for the spring size; since something has to keep the leaves from shifting longitudinally, there needs to be a center hole of SOME size. But if the galvanizing is the culprit, a little testing during the process (as mentioned elsewhere, check before and after each step) should find the flaw(s). I wonder if a cold-galvanizing process might not be sufficient? This uses a zinc-rich aerosol coating.

I am willing to play the Village Idiot here and ask some really dumb questions.

1) Why do you want to galvanize a leaf spring?

2) Why do you want to put a hole in a leaf spring?

Thank you for your indulgence and your reply.

Orpheuse

I gave you a GA (good answer) it should have been for "good questions"!

Is it me ? Why would you want to galvanise leaf springs, these things are tempered to exacting tolerances and galvanising will do all sorts of damage to the steel, if these are multi-leaf springs the friction caused will stop the spring working as it should, to riterate why would you want to galvanise leaf springs?

Bazzer

I want to add my two cents to this thread.

First, it is wrong to cold punch hard tempered spring steel. It will create a lot of stresses, why not drill it? Second, why do you want galvanizing"? If you need corrosion protection, use heavy grease bvetween the leaves, I remember a long time I had a car that had leaf springs and each leaf had longitudenly running shallow groove in it on both sides whhere we were supposed to put heavy grease and then the whole spring was encapsulated in sheet metal witchh had a grease nipple not only to protect against corrosion but help the individual leaves in the spring assembly to smoothly rub against each other during flexing as the vehicle moves on a rough road. Then the next suggestion: It is well known that hot dip galvanizing does contribute to brittleness in the steel, so use the metal spray process which will give you a two fold advazntage, there will be some shot peening, adding to the strength to the matereal during the blast cleaning process and then sprayin with a Combustion Wire spray gun with zinc wire will protect it from corrosion without ever exposing the material to any heat. Think about it, it is a win, win solution

Hello vishmayor.

It is usually good practice to read previous posts before adding 2 or less cents. This way you avoid repetitions, save yourself and other's some unnecessary reading.

Wangito.

i did read all the postings and found that nobody mentioned anything about an alternative to galvanizing, which I did with an added advantage of shot peening during the blast cleaning process. Of course I admited that cold punching does cause stresses and also because of my age which is 88, I do not think anyone knew about the grooves in the leaf springs for lubrication purposes and the encapulation of the assembled springs with a grease nipple for further greasing. I wonder also if you are old enough to have seen this.

vshwn7@aol.com

Hello vishmayor,

My post meant no offence, just trying to improve the system if I can...

Greasing the springs was never a good idea. It collected dust, mud and all kinds of dirt, which acted as sand paper, causing more damage to spring than good. And you be surprised I do know about it...even though you have finished your studies when I was recently born...(last year of WW ll)

All I can hope is that I will get to be 88, and capable of participating as you do.

wishing you all the best, keep us all posted.

Wangito.

I personally did know that leaf springs need lubricating and a little protection from rust, we used oil formulated for this purpose when I used to help out in a service garage while at school....

I did not know that a groove was made, and having only taken car leaf springs apart, cleaned and reassembled, I might guess that that was for heavier duty reasons only....

I personally felt that there was enough new material in your post to accept it as it was without jumping on you for repeating some things......

I must also compliment you on your mental agility to both use a computer and to make good posts at 88! Long may you rain I mean reign!!!

I am giving you a GA for your efforts!!

Shame on you Wangito......!!!

We used to take them apart after 3 or 4 years of usage and clean them before re-assembling them.....I never did see any real problems of leaving them dirty though as many did.......perhaps because I lived in the UK with a relatively mild climate with no desert sands (as yet!!)

Hey Andy,

You are right,

I did apology, didn't I?...

Wangito.

I was only Joshing!!! Do not take it too seriously!!! I guess "Funning" might be an even better word!!

I wasn't too serious either...

Wangito

Good!

Hello again, sim

Presumably you are using a single leaf spring, on those trailers.

If you have multiple leaf springs, these should not be galvanized, as others above have pointed out, because the extra friction between adjacent leaf springs will be increased, thus putting more strain on the spring-set.

Also the galvanizing on the springs would rapidly be polished off, and fall out onto the road, in the form of flakes/dust of metallic zinc.

The earlier Land-Rover Workshop Manuals, up to Series 3, stated that "Once each year, dismantle the leaf spring assemblies, buff off all rust down to smooth metal, and grease with a water-resistant grease between all leaves, then re-assemble."

I remember that same procedure was recommended by many heavy truck makers, including Bedford of the UK.

Of course, most owners did not bother with this yearly work on the leaf springs, because of costs and inconvenience.

I personally found it easier to spray kerosene (paraffin for the UK readers) at the sides of the leaf spring assembly, where it was drawn in by capillary action, and if that was done once each six months, the springs did not rust, and gave a nice "cruisy" ride, just like new springs, there was no rusting at all.

Kind Regards....

That fits in with my recollections quite well.....

It was worth a GA I feel too.....

Hi all,

New to the forum and would like to add a few comments regarding the metal spraying alternative to galvanising.

The metal spraying (or thermal spraying) process is metallurgically cold, e.g. does not impart enough temperature to the substrate to metallurgically change it or create heat distortion. You need to blast before metal spraying as the bond is generally mechanical. However, bond strengths can exceed those of galvanising.

The surface finish of metal spray is similar to 120 grit sandpaper. However, the zinc (or other materials that can be sprayed) are ductile and also built up in a layer formation, so are unlikely to affect the action of the spring. The coating would effectively 'move' to meet the requirements of the spring but maintain corrosion protection.

Alternative materials can also be sprayed. For example, boat trailers frequently in sea water and stored by the coast would be better protected with aluminium than zinc.

Having said all of this, I'm not aware of an organisation that commercially sprays (or galvanises) leaf springs. Most of our experience has been with employees doing a 'homer'!

Hope I've not reposted anything or offended anyone - I'll await the telling off if I have!

I had suggested metal spraying with zinc right at the beginning of this thread, only a couple of people seem to have heard or known about this process. I have been in this industry for over 40 years and have extensive experience in protective spray coatings having done hundreds of thousand sft of zinc spray on ships' interiors and know for sure that it works and there are a number of companies in the US that would do this for anyone interested in getting this service

vshwn7@aol.com

I still feel that the metal is too weakened (cracks as well from hole punching) by the hole.

If a hole is needed, the area around the hole has to be mad thicker to prevent flexing in the hole area, or a plate has to be added above or below or both to stop flexing in the hole area....

I do believe (from memory) that it only breaks in the area of the hole, but please correct me if I am wrong....