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Anonymous Poster

Bushing Material and Heat Treatment

01/29/2010 6:54 AM

Dear Sir, by reverse engineering i m trying to develop a bushing used with pin inside in machines.

Function and stresses - As it is in continouly on impact loading and fatigue environment. It is used to transfer torque when machinhe is running from sprocket to other side via bushing.

Material- See as it need high wear resistence and fatigue load so i think 8620 is goig to work.

Heat treatment- carburising upto 1.5 to 2 mm with hrc 60-62.

I have folloowing queries and confusions, need ur geniune view if u know anything about this.thanz in advance.

1.Is that material ok. As i know carburising has to to be done later.

2. See i will ask the temper or induction guys and they will give me the heat treatment, how do i know what is case depth.and what is core hardness.

3.8620 has range eg. ni-0.4 to 0.7,Mn-0.7 to 0.9 etc so there is a range

by which material property very alot so what exactly be the 8620 constituents.

4.I heard from few experianced guys that even after this procedure life of bushing

is not that good,so what else i can do on 8620 to increase its life.Some suggested

toughening of bush(not able to understand their meaning as not tecnical term).

5. I m leaving .2 mm for gringing is that ok or shouls i reduce it more.

6 waht else i can do on 8620 to increase its life cycle.

7. Which physical prop. test need to determine the life of bushing.

Answer all these ques asap

reegards

Dp aggawal
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bhrescobar
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#1

Re: Bushing Material and Heat Treatment

01/29/2010 8:07 AM

Sorry if I am not able to answer correctly what you ask, but its a little confusing the way you have written...

1. Yes, the material is ok. Was developed to do basically what you want and surface hardened.

2. The hardness profile is determined mostly empirically. You can find ome good resources like metals handbook and so to give you some guidelines. But I'm afraid you'll have to cut some samples and measure.

3. Exactly. Standards and specs do give you a range of composition. Do not expect to find anything usually available with EXACT compositions. Most of time, it just does not mind.

4. They are suggesting making the bushing from a more resistant material. Before giving any advice, you should be aware of what the bushings are failling of. You mentioned fatigue. I bet on wear or low cycle fatigue. They are distinct different failure mechanisms. Before knowing it, changing material, treatment or process is wasting money.

5. You are talking about surface hardening and then grinding. Besides you do not reach the core metal, you may be still removing a good portion of material that remains with compressive tensions - one of the benefits of the indutcion hardening as you mentioned. Do you really need to grind it? Isn't there a way to manufacture the bushing and install it as is after heat treatment?

6. Please specify which is the failure mode to answer this one. Increase hardening depth, induction hardening and using a cold drawn material as base (with smaller grain size) always help, but you should investigate.

7. Again, search for the cause of the bushings failure. Depending on the failure mode, you should look for fatigue, strengh, wear, ..., tests.

Last recommendations:

This forum is made from professionals that like to use their time and knowledge to help other people. It's not made from kids that are used to spend several hours a day in MSN, Orkut, RPG gaming and other social web based things. So, take a look on the forum rules, use correct english to post your questions, and be kind. The quality of the answer you will get is a direct result of the quality of the information and the question you post.

Regards.

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dpaggarwal
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Posts: 6
#2
In reply to #1

Re: Bushing Material and Heat Treatment

01/29/2010 8:57 AM

thanks dear, thanx alot for so quick reply

See, the bushings are hllow cylinerical past with soild pins inside them.

now as there is everytime contact between the bushing od and the sprocket,

bushind id and pin.

Wear Patteren- bushin r not breaking from in beteen but its od gets distorted,

id become e centric.

Bacially new bushing has life double of which i m getting through all this.

orignal like -4000hrs and mine is 2200hrs

Id u can tell a bit more to how to increase life then plz tell.Or in general tell

the steps of increasin a hollow shaft or solid shaft like which in in continous fatigue

condition and has to bear high wear at surface.

2. U use the term cold drawn, may i know what is that. what properties it enhances?

advantage of small size grain . waht properties it changes?

whats advatage of that as per ur experiance.

Desperate for ur valuable views...

thanz again
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Anonymous Poster
#5
In reply to #2

Re: Bushing Material and Heat Treatment

01/30/2010 9:17 AM

Where is the fatigue?

What you describe, If i understand, is not a fatigue but wear.

Again the picture I make out is that there is a center pin (is it the axle?). You have a bush bearing and then the sprocket guided on it.

The OD is getting distorted? or is it wearing out on one side?

Assuming the picture is OK, this clearly shows that the bush bearing is not designed to take the eccentric loading.

Putting a harder bush will only result in wear on the sprocket/hub bore and the axle.

However it is only assumption, since the actual configuration may be something else too.

Check up the load on the bush and then decide on the type of the guide, may be you should go for antifriction(roller bearings) or graphite/ceramic bushes.
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Anonymous Poster
#3

Re: Bushing Material and Heat Treatment

01/29/2010 8:58 AM

Agree with BHRE

What is the exact mode of failure? is it surface fatigue? Assuming there is a relative motion between the pin and a bushing, just hardening the bushing will not help. As you may be aware that the coefficient of friction between the two materials matter, and you will see more of brass bushings than steel bushings.

Consider using coated steel if these are the case. there are manufacturers, better to contact them rather than designing yourself, with the specific application and load patterns- you may land up with ceramic, or graphited bronze bushings which will serve your purpose better.
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nick name
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#4

Re: Bushing Material and Heat Treatment

01/29/2010 1:14 PM

As you describe you have a chain and you are confronted with low life of the pin-bushing pair. There are several questions you should answer before getting the right answer:

where is the chain used in crawlers? excavators? industrial transmissions?

Is the chain working dry or do you have a lubrication?

Which is the environment where the chain works?

Which is the speed of the chain? Which is the ratio between chain length and pitch?

Nominal dimensions of the pin and bushing? clearance?

Is the space between pin and id of bushing sealed or free to ingression of abrasive components?

How big is the wear at bushing OD and after how many hours? How big is the pin wear and the ID bushing wear and again after how many hours?

What pressure is applied in function on contact area between pin OD and bushing ID?

All those data are needed in order to give a correct answer, as you will notice by the kind of questions I was involved in the design and manufacturing of heavy chains so that I can give you a hint but only if I have enough input.
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dpaggarwal
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Join Date: Jan 2010
Posts: 6
#6
In reply to #4

Re: Bushing Material and Heat Treatment

02/03/2010 12:00 PM

hi Mr nick name

Thanx u very much for ur reply. My name is dugra prasad and last yr i finished my btech
mechanical.I m in job now at JINDAL . My father has small workshop of making cycle chains.
Now side by side to utilise my engg. i m trying to increase his product base.

We have 2 old lathes. We have new local clients who asked us to make a bushing and pin in mild steel (they provided the sample, cylinderical parts) we make it in mild steel and then delivered.
They havenot told me where they use them.They just provided the hint that it is used in cranes.


Now by internet i found that cranes hs mostly to big chains- propeller chain and the track chain.

Now as propeller chain is very different i found that its must me the bushing and pin of the track chain of crane, similar to crawler chain.

By internet and meeting few guys and reading alot of techinical stuff i found that
it is made of 8620 mostly and then induction hardened(carburised).

Still i m in doubt of material and also the bushing and pin heat treatment to be given.
questions in mind-
1. Material to be choosen.
2. Heat treatment to be given.- we have local method in which we heat the
material in upto red heat by approxication and then put inside water/oil for hardening and then temper it. It is non technical way without any calculatiion, just of experiance. and it sometimes become too hard and sometimes remains soft.

so i need the proper temp or what should i say to heat treatment guys (professals)
which follows proper procedures.

Somedetais u needed-

1. Chain use- as far as i know in cranes(crawlers).
2. It is dry type not lubricaled.
3.As its crain so operate at sites/mines- harsh environments.
4.Speed of the maching(hence the track) is usually 3-8km/hr, chain pitch-230mm
chain lenght=9430mm.
5.bushing is hollow cylinder with of = 79 mm and id is= 49.6 mm, length is 189 mm.
Pin is solid cylinder with od is 49 mm and length is 295 mm.Clearence is about 0.6 mm between bsuhing id and pin od.
6.Space betwenn tese two is sealed by a seal to avoid abrasive particels entry.

7. Wearing patterrn is as follows-
In bushing - Outer surface due to rubbing with hard sprocket teeth.
Both ends which r inside the links.
Inner surface due to contact with pins(become e centric)
breaking from in betweenthe lenght due to bad heat treatment.

In Pin Corners in links
Od in contact with bushing id.
breaking from in betweenthe lenght due to bad heat treatment.

8. normally life is 2000 hrs want to make it 4000hrs or more.

Need-
Bushing is in continous contact with sprocket so has to wear as it is cheaper then
sprocke.As there is contact of bushing od with sprocket and id with pin so
these twp surfaces should be hard and as machine whole load continously is on track
so for that continous regular load(force) fatigue strenght is need in core.

Now this is all the info which i got by meeting few crane users, temperwala's,
and internet, ebooks. Now i didnot know how to calculate forcces pressure on this part.

Plz help me suggesting the material, heat treatment (temp to follow for ncie grain structure,hardness)and also any other precation/suggestions.

if u can help a bit i will be very thank ful to u.If possible reply at
dpaggarwal@gmail.com.

Desperately looking for ur reply/sugesstions.

Thanks again for ur kind help.

Regards
Durga Prasad
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