Author Topic: Zhejiang ST head?  (Read 6067 times)

Procrustes

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Zhejiang ST head?
« on: September 21, 2006, 06:45:22 PM »
Can anyone give me a review of Zhejiang Machinery & Equipment (http://www.zmec.com/) ST heads?  I'm thinking about buying one over the the internet.

Hampster

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Re: Zhejiang ST head?
« Reply #1 on: November 16, 2006, 03:30:46 PM »
Bump ;D

Procrustes

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Re: Zhejiang ST head?
« Reply #2 on: November 16, 2006, 05:18:44 PM »
I picked mine up yesterday actually.  It's 30kW, 2 3/8" keyed shaft.  The fit and finish is lacking, but for the price that is what I would expect.  No plastic.  560 pounds.  It will be awhile yet before I determine whether it works well or not.  I haven't looked at the bearings yet.  Also I've never seen another ST head, so I'm unqualified to pass judgment.

aqmxv

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Re: Zhejiang ST head?
« Reply #3 on: November 16, 2006, 09:01:26 PM »
I have yet to have any reason to believe that any ST head comes with really good bearings.  Given the low cost of replacement versus the high PITA factor of unexpected failures, I'd replace the originals prophylactically.

And, suiting my actions to my words, I ordered a set of bearings for my very used generac belt-drive genhead last night, with spares.  Total cost: $25 for two sets.
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Procrustes

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Re: Zhejiang ST head?
« Reply #4 on: November 16, 2006, 09:26:52 PM »
I ordered a set of bearings for my very used generac belt-drive genhead last night, with spares.  Total cost: $25 for two sets.

That sounds like good advice.  Where did you get the bearings?

Doug

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Re: Zhejiang ST head?
« Reply #5 on: November 16, 2006, 11:14:47 PM »
The failure rate of a ball bearing is directly proportional to the size of the hammer used to assemble the machine and suprizingly has less to do with the actualy quality of the bearing....

Grease, anyone who sells you a machine with open bearings in 2006 is on dope. 2Z minimum 2RS prefered...

What do I know about bearings?
Enough that the scrap dealer had a special pile of bearings he sold at a premium to the mill that I removed....

Doug

aqmxv

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Re: Zhejiang ST head?
« Reply #6 on: November 16, 2006, 11:21:03 PM »
My generac uses two very common bearings:

6205 on the drive end (RS seals preferred because it's out in the breeze).

99502H on the tail. (RS seals not as important, but still a good idea).

6205s are used in all kinds of things - snowmobile chaincases, riding mower decks, ATV wheel bearings, etc.  Very common and quite cheap.   99502H (funny number is because it's an inch measurement bearing) is used in a number of things as well - weed wackers, snowmobile bogies, lawnmowers, edgers, etc.  Also common, also cheap.

Accordingly, I got them from these people:

http://www.mfgsupply.com/m/c/index.html

Who also happened to have a really good price on the funky special throttle cable I needed for my 1988 Honda mower.

There are bearing suppliers all over everywhere.  If you need a big industrial bearing, like you probably have in your ST head, I'd start off by looking for a nearby bearing supply house.  There are several national ones as well.  SKF, FAG, NSK, NTN, and Timken are good names.  The Peers I took out were in pretty good shape (although I beat the front one up pretty badly getting it off the shaft, which had rusted oversize).

The speeds and loads on any gen head are very modest compared to some other uses of bearings this size.  If you buy good ones, you should get decades of wear out of them with a once/decade regreasing, because the load is constant and shaft speed is low.

George's major complaint with the bearings supplied with ST heads is not the bearings as much as the grease they're packed with.  Repack with a good synthetic grease and bob's your uncle, although the finish quality of them is not as good as a name-brand cartridge bearing.

And on preview - concur with Doug - installation technique is everything, and unless you had the option of being very, very nice to the bearings you removed, throw them in the trash.  That's where the old ones from my genhead are going once the new ones arrive.
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buickanddeere

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Re: Zhejiang ST head? Too good of bearings
« Reply #7 on: November 17, 2006, 04:04:58 AM »
  We had a ventilation system designed by our "quality at any cost" engineers. Bearing failures were the norm on the fan even though they where oversized and the highest load bearing weight money could purchase.
   After several failures the system engineers and depatment head allowed the use of some econo bearings one of the mechanics had suggested since the 1st set of ripped up rollers/races. 
  It seems there was not enough pressure from the machine to force the premium bearing rollers to roll. They just skidded along until the rollers developed flat spots. 

Andre Blanchard

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Re: Zhejiang ST head? Too good of bearings
« Reply #8 on: November 17, 2006, 01:39:12 PM »
  We had a ventilation system designed by our "quality at any cost" engineers. Bearing failures were the norm on the fan even though they where oversized and the highest load bearing weight money could purchase.
   After several failures the system engineers and depatment head allowed the use of some econo bearings one of the mechanics had suggested since the 1st set of ripped up rollers/races. 
  It seems there was not enough pressure from the machine to force the premium bearing rollers to roll. They just skidded along until the rollers developed flat spots. 

Yep, If the bearing clearance is not right for the RPMs then load rating does not mean a thing.  Really high speed bearings can be so sloppy you would swear they were worn out when you are installing them.
« Last Edit: November 17, 2006, 01:41:44 PM by Andre Blanchard »
______________
Andre' B

aqmxv

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Re: Zhejiang ST head?
« Reply #9 on: November 17, 2006, 04:46:07 PM »
Andre got me thinking - not everybody here has played with cartridge ball bearings as much as some of us seem to have.  Without regurgitating any of the several bearing manuals I've browsed over the years, I'll mention some useful things to know:

1) While friction (sleeve or shell) bearings have a theoretically infinite lifespan, ball and roller bearings have a finite lifespan.  At some point, the balls and races work harden and fatigue, slowly getting noisier and eventually failing.  They're a lot like light bulbs - if you run them clean at the low end of their design range at constant speed and constant load they will last a very long time.  If you shock load them, overload them, overspeed them, don't keep the lubricant available and clean, misalign them, etc, you won't get very good life from them.

2) better quality ball/roller bearings are made from better materials with better heat treatment and better finish.  This results in a bearing with a (considerably) longer life and quieter running during its life.

3) as Andre mentioned, internal bearing clearance (on a new bearing) is determined by expected running speed.  The internal components get hot and grow more the faster the bearing runs.  Use a low-speed bearing in a high-speed application and badness will happen in short order.

4) they're engineered components.  Bearing manufacturers publish detailed specification guides telling you just what you can expect a bearing of a particular size and rating to do.  Read the docs, folks.  They'll answer questions you didn't know you needed to ask.  Here, for example is NSK's online bearing handbook:

http://www.jp.nsk.com/app02/BearingGuide/html/bearing.html

5) Seal type and lubricant matter as much as any other design component.  If you're in a dirty environment, choose full-contact resin seals.  Match the lubricant to the environment and expected temperature.  But remember to check that speed rating column for the seal type and lubricant and make sure you're still in the sweet spot.

6) going way oversize on a bearing is a bad idea - they need a certain minimum amount of speed and load to work properly, or the rolling element slides instead of rolling.  That's what buickanddeere was talking about.  Trust the supplier handbook for sizing data.

7) Alignment is critical.  If you can't manage a good shaft-housing alignment, use a spherical race bearing.  They're more expensive, but they will fix your alignment problem.

8) preloads/lateral loads are sometimes good (tapered rollers) and sometimes bad (ball and roller).  Make sure you meet the spec or you'll be sorry.

Anything I forgot?
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Doug

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Re: Zhejiang ST head?
« Reply #10 on: November 17, 2006, 11:21:08 PM »
St heads should have a C3 bearing. This is a .003 clear and is an industry standard for rotating electrical machines 1200 - 3600 rpm. You can often feel the wigle in the shaft with a C3 if you grasp the shaft and lift, after a while you will get acustomed to the sounds of bearing and can hear a dry bearings asking for grease or the rumble that a bearing produces onloaded and of course the early sounds of failure.

Listen and touch and your machine will tell you how its feeling.

Doug

aqmxv

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Re: Zhejiang ST head?
« Reply #11 on: November 18, 2006, 05:29:01 AM »
St heads should have a C3 bearing. This is a .003 clear and is an industry standard for rotating electrical machines 1200 - 3600 rpm. You can often feel the wigle in the shaft with a C3 if you grasp the shaft and lift, after a while you will get acustomed to the sounds of bearing and can hear a dry bearings asking for grease or the rumble that a bearing produces onloaded and of course the early sounds of failure.

A very good point there from Doug.  Healthy ball bearings have a quiet "swish" to them when running normally.  On things like ST heads, the sound of the brushes against the slip rings is usually considerably louder.  If you can hear a bearing, or, worse yet, feel a bearing when it's spun up there's a problem and you'd best look into it right now.

Incidentally, Noisy ball bearings can be run for quite a while if whatever made them noisy is corrected (usually meaning removing the seals and thoroughly flushing the insiides out with brake cleaner and then repacking with fresh grease) and they're carefully monitored.  They run noisier and a little hotter, but if the lubricant is up to the job and the damage is pitting or light brinelling you can get quite a bit of wear out of them before clearances get excessive or balls start to slide.  I don't recommend doing this, and strongly encourage everybody to keep spares of critical ball and roller bearings, but knowing how to get the seals off of an alternator bearing, flush the grease and debris out, and then repack and reseal has saved my bacon on more than one occaision.  For this reason, I tend to prefer open bearings and separate seals, but hardly anybody designs for them and it's hard to retrofit individual seals where they weren't considered in design.  And, to be fair, a lot of apes tend to contaminate anything like that in field service anyway...

Listen and touch and your machine will tell you how its feeling.

Doug

That last is probably the one great truth of mechanics.  If you really understand a machine, and you really know the machine, then simply being in the room with it running will probalby tell you as much as anybody could learn from a room full of specialized diagnostic gear.  Get to know your equipment and you'll know when something's going wrong.  And chances are that you can put a stop to the wrongness before something really bad happens.

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Doug

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Re: Zhejiang ST head?
« Reply #12 on: November 18, 2006, 10:13:30 PM »
but knowing how to get the seals off of an alternator bearing, flush the grease and debris out, and then repack and reseal has saved my bacon on more than one occaision.  For this reason, I tend to prefer open bearings and separate seals, but hardly anybody designs for them and it's hard to retrofit individual seals where they weren't considered in design.  And, to be fair, a lot of apes tend to contaminate anything like that in field service anyway...

As far as open and ore sheilded bearings are concerned I wouldn't bother with an old open type anymore if a sheild is available. This type pf bearing will pump grease into itself if there is a reserve on one side and void on the other to discharge from. The main thing to rememebr is not to over grease this type ( or any other for that matter ). No bearing should need more than a pump or twoa 6 months to a year if under 2000 hours service. There's a lot of wigle room in that statement because like I said beofre you have to know how much grease is passing threw the bearing and the amount used will varry with the type and class of grease used.

I prefer NLG1 greases with a moly or full synthetics if its realy cold. The thinner greases move a lot faster so you have to be aware that in the heat of summer you may need that shot of grease where in winter you probably won't.

Grease itself is complicated and a little long winded a subject for me to get into right now but a brief explanantion of what greas is will probably help. Grease is OIL suspended in a binder that is designed to bleed lubricant into something. The binder can be anything from soap to clay. The oil generaly has a viscossity measured in an SUS number so understand the oil itself can be tricky. Additives just like engine oil stuff is added to grease to improve it.
Grease has a shelf life find an old tube and look at it, sometimes the oil bleeds out and you can see the cracks form in the binder. All oils oxydise and if you look at cheap Lithium complex greases that have sat around exposed to air you actualy see the yellowing of the lubricant and bleeding out of the oil.
So in conclusion grease is good, greasing is good, grease with good grease, and don't buy a lot of tubes and let them sit for years.

Doug