G,day guys
I'm having problems remedying ever increasing vane pass on one of our impellor fans.
A little bit of history, last september this fan slipped through the bearings and the impellor hit the housing, the night shift fitter got back into service and we followed up replacing brg's, correcting pulley alignment and so on, ever since this event vane pass has continued to climb, this is a fixed speed, steady load application with no dampers.
I've checked impellor to housing clearance which is the same as other identical fans, crack tested the impellor, ok, and regularly checked impellor for buidup, negligable buildup and cleaning what was there has made no difference to the steady increase, in the attachment you will also see 3 X how does this happen, any body out there got some suggestions as to where to go next?

mat_trim_saw_fan_4-6-08.rtf (538 Kb, 99 downloads)

It is a 6 vane impellor, but the 3x has gone up, with running speed sidebands. The autocorrelated waveform is showing a peak at once per rev.

I'm not sure that you have got a vane pass problem per se

Did you check the radial and axial runout on the impellor after it kissed the housing? Open or closed impellor?

Ian

I agree with Ian. I don't see a "vane pass" problem. For high vane pass you whould have either a mechanical rub of all siz blades or aerodynamic pulsation caused by the fan operating away from its best efficiency point (BEP). The third possibility is that the structure has become resonant due to changing structural properties.

Given that the fan shaft was loose in the bearings before, and that 3xSS is dominant with 1xSS sidebands (from modulation), I would suspect looseness is developing again.

Walt

Have you checked the blade pitch? Are all angles the same? Any signs of cracks either in blades or structure?

thanks for your input, we're having a shutdown next thursday 12th, I'll be doing all the checks myself, and will post findings. in the meantime are there any other suggestions?

I would suggest checking bearing clearance to the housing.

A clue I gather, "last september this fan slipped through the bearings". Why did the bearings let go, did set screws come loose? Did you change belt size recently? In your comments it does not sound like you replaced the shaft. My experience tells me the shaft is undersized and the inner race is spinning on the shaft. If you have a strobe light, freeze the shaft and look at inner race to see if it is spinning at a different speed. The inner race and fan shaft should rotate together, another method would be to use a dial indicator with a long bar, indicator at top dead center, raise the shaft and record the readings, also rotate shaft 180 degrees to see if shaft is bent, check several locations....
Dave

i AGREE WITH DANNY AND DAVE;LOOKS LIKE A BEARING PROBLEM;

[QUOTE]Originally posted by SUDIN:
i AGREE WITH DANNY AND DAVE;LOOKS LIKE A BEARING PROBLEM;Do check runout on shaft.

Recently, I had a fan problem with 1x axial vibration on motor DE being highest with 6.5 mm/sec. The bearing outer race was found interference fit in the housing. Housing was machined to provide clearance fit as per SKF (Bearing manufacturer) recommendation. Also,bearing of NDE side was preloaded with Belleville washer to compensate for axial thrust. vibration dropped down to 2. Pl. check the bearing fits and tolerances.
Regards.

I would agree with Dave. Check the shaft to make sure it is not undersize or bent. Many times bearings get changed out with no regard to shaft condition.

attached are the findings from todays fan checks, If you can decipher my scrawls is there anything here that would ring alarm bells?

whoops had to get a file conversion done so you could see it

axial runout of impellor = 1.45mm
radial runout of impellor = .75mm
shaft bow = .07mm
lift check at D.end bearing = .1mm
brg internal clearance at D.end = .04mm
lift at NDE = .12mm
internal clearance at NDE = .07mm

Do any alarm bells ring for you guys?

Impeller
axial runout is ok
radial runout is ok
Shaft
.07mm=.0027" marginal, especially when the number is higher between the bearings (should be .02mm)
So do I add the .1 and .04mm and .12 and .07mm?
Evidence of brown/rusty colored grease indicates looseness, was the outer race of the bearing shiny/rusty?

G,day Dave.
subtract .04 from .1 and .07 from .12 this is shaft lift with brg clearances taken out of the equation, so .06 lift for D.end and .05 mm for NDE.
there was an indication of slight wear in the D.end brg cap.

Jonesy.

Some questions for Jonesy!
A check on the coupling condition (between the motor and fan)has this been done?
Has a lift check been carried out on the motor? Have you looked for soft-foot and is thermal growth a problem with these fans?

Hooch`

Hooch
sorry, I didnt specify this is a belt drive set up, so your Q's may not apply.
thanks anyway.

The blade pass you thought you were getting may then be related to your belts, how many and what is your belt speed?or pulley may be moving on the shaft? just some thoughts off the top of my hairless head

Hooch,
just wondering how you would associate vee belts with vane pass, I'm still pretty new at this game and willing to learn anything i can, belt speed? not sure what you mean but they are SPB 3550, .248 orders
and 1.196:1 step up from motor rpm.
by the way, is that newcastle nsw australia?