Screen Structure Failure
Greetings Sandeep from the soon to be frozen Eastern Wilderness @1140 feet above mean sea level.
What is it you are screening?
Can you post a picture?
If the screen is not allowed to move properly i.e. orbit inside the frame work the force delivered by the motor drive, weights and inertia has to go some where.
We need to know more about the screen type, how the screens are mounted, whether it is done by cable suspension from above, coil springs, airbags below frame arms etc. If the eye beam is suspect you would see the beam warping if it is a thin beam or beams. If you mount anything solid you will have vibrations transmitted to the mounting.
If the frame arms have rubber schock absorbers in the frame they need to be kept clean to allow for proper movement to absorb shock loads from screening material.
A worst case scenario is that the metal was fatiged before the screen was assembled or the steel was of poor quality, or the screens were assembled improperly. It is hard to give an idea when I am not there to see the screens.
George or gary will probably know what happened exactly.
Myself I like the Pennsylvania Crusher Bradford Breaker because of its simplicty and ease of maintenance ■
Re: Side Plates Ripped Apart
Sir ......... the screen is an inclined screen running at 100rpm. The screeen is used to screen the over size from the crusher. i.e. (+) 50mm. COAL .
The beams we used were lighter. i.e. we used a 250 beam to mount the screen instead of a 600 beam. The screen is mounted on coill springs and the plates are HUCK bolted.
The manufacturer feels that the Stiffening of the side plates was not sufficient( the reply i would least expect from a reputed manufacturer whose technical partner is carl schenck germany )
I will attach the pics soon. ■
Re: Side Plates Ripped Apart
Originally posted by sandeep
Sir ......... the screen is an inclined screen running at 100rpm. The screeen is used to screen the over size from the crusher. i.e. (+) 50mm. COAL .
The beams we used were lighter. i.e. we used a 250 beam to mount the screen instead of a 600 beam. The screen is mounted on coill springs and the plates are HUCK bolted.
The manufacturer feels that the Stiffening of the side plates was not sufficient( the reply i would least expect from a reputed manufacturer whose technical partner is carl schenck germany )
I will attach the pics soon.
Ok assuming you mean .250 thinkness and .600 thickness of beams - the next question is:
Eye (I) beam or (H) beam ■
Re: Side Plates Ripped Apart
H beams Sir,
The manufacturer had come to site today. Says it is due to some designing problem. But not specified anything.
Is scared to admit. But i want to know the reasons why it must have cracked. The VSMA handbook says that the screen can be fatigued due to critical frequency, welding etc on the side plates or build up under the screen which affects the motion. I still see only the critical frequency as the culprit.
Sir does lighter structural support causes the vibrations to transfer back to the screen body causing this breakage.
Sandeep ■
Re: Side Plates Ripped Apart
The truth of the matter is that any thing that vibrates or rotates in an elliptical motion, transmits energy in all directions and if there is
no isolation such as hanger cables, support arms, air bags or coil springs, you will have a mess on your hands because it transmits force to a stationary object and it will wear out from vibration and fatigue- try hanging the outer frame of the screen from supporting cables- but in this mechanics opinion support air bags are best-contact goodyear or firestone in India for help- you will continue to have this problem until you change the supports for the screens-it was irresponsible for your supplier to do this in my opinion with out frame support of some kind. ■
Cracked Sideplates Troubleshooting
Very interesting reading on this particular problem: Some generic comments for review:
- Why only 100 RPM? could be too slow and overload deal
- Does screen strike on hoppers upon shutdown at all, if overloaded it seems could be possible - must maintain miniumum 2" and sometimes 3" for bigger screens all around free floating vibrating body. A good hit against a stationary object over time will CRACK mr. sideplate easily
- Huck bolting is good - common tension on all bolts, means total unit running at same torque value as ONE vs a bunch of parts moving each at their own frequency.
- BEARING Housings: Are they huck bolted? if not, these bolts can loosen and you will not see movement but, thee sideplate will crack at the HOUSING position.
- STIFFENER PLATES: some screens have them, some don't. The burning question of course is.......WHY? The answer I was taught was as follows: Where do we have the biggest BORE in the sideplate (the hole where the shaft goes thru the sideplate) this is the weakess LINK......the place most likely to CRACK is no stiffener is utilized. A lot of mfrs use a 5/16" thick or 3/8" plate running from bottom to top of sideplate to increase the design integrity here. AND............it WORKS!
- Welding: If the sideplates were FILET welded.....they will crack again and again UNLESS, the welding it SELF RELIEVED or stitch welded. People generally FILET weld right on up the full length of the CRACK.......creating a nice, noticeable HEAT CHECK or weak spot. When the machine starts up......it goes....hmmmm a heat check........and cracks the sideplate out. WELD 2" skip 2" on one side then do same to fill in on the back side where you skipped and it will stay together. NOTE, Welding is never recommended on vibrating screens........it is undesirable at best. The use of FISHPLATE across crack after stitch welding can also be considered, BUT once again skip weld around full plate vs full weld. CONTROL HEAT IF must weld.
- SQUARENESS: Most reputable vib mfg companies use a JIG System that absolutely ensures SQUARENESS or trueness all around the box. If not completely square the unit will rip apart fairly quickly.........when folks build their own or have non-OEM fabricators build this is usually the biggest problem.
- Some of the component parts........IE say.....welded support frames can be unsquare.......most companies will use a TIGER TORCH to relax the welds and let the unit relieve any torquing that happened in the welding stage. THIS WORKS and is pretty critical. Some companies put in ovens to relax after welding the full component and some others utilized SONIC VIBRATION to relax welds.
Hopes this helps.
George Baker ■
Did You Find The Origin Of The Problem?
SANDEEP: did you find the reason the sideplates cracked yet? ■
Re: Side Plates Ripped Apart
Dear mr.baker,
The manufacturer had actually used flats welded along the corners of the screen side plates instead of angles for stiffening. He welded those flates perpendicular to the side plates so that it looks like angles.
Second thing is that the beams that are generally square in shape were actually round. The plates cracked from the bottom of the screen and stopped at one of the huck bolts which fastened the round beams.
But visibly we can see that while the screen is in operation the side plates flutters a lil.
The manufacturer has replaced the side plates yesterday with angle used as stiffeners and say that it'll be ok now. Though he has not disclosed much details.
What do you think. ■
Flutters?
I love that word........FLUTTERS..........I have used it only once and it was on a massive BACKCHARGE. Our company many years ago manufactured 10 new 6x20 HORIZONTAL SCREEN BOXES.
We had installed ..........4 WASH TROUGHS down the length of 20 feet. The machines blew apart........sideplates all cracked out of them. Our job was to be the factory and go out and analysis why.
THE WASH TROUGHS........were bolted across the 6' of width of the machine, at the end of 40" long wirecloth sections. The troughs were 8" long x 6' wide...........in a V type trough design.
LONG STORY SHORT, these troughs,,,,,,3/8" thick actually FLUTTERED.....as we described them in our report to headoffice....like a ruler....when you spin it on its edge. THEY FLUTTERED at their own frequency.........and tore the sideplates apart at the bolts that held them to the sides.
THE DETERMINATION: they needed to be attached to the 6" dia cross tubes to make them part of the whole vibrating mass.
We fabricated and installed standoffs which picked up the round cross support tubes and problem was rectified in this instance.
PS: we also put a 3" x 3" bent plate along full 20' of sideplate edges to give structural integrity to the sideplates. INTERESTINGLY enough....we did originally try using 3" x 3/8" x 20' long FLAT BAR at first......and did zip all to help.
Sounds like they may...........have it under control. Keep me posted.
PS: the backcharge on those 10 machines to pull out, rebuild at Christmas time break........and reinstall......was $400,000.....and that is a hard education.
If I can find the pic of the cracked sideplate I will post same.
THANKS........George Baker MODERATOR ■
Side Bump
FLUTTERING Of sideplates...............or SIDE BUMP..........is not a desired movement..........kinda means the box is NOT FREE FLOATING in a true circle throw motion...........nice and parallel in between the coil springs.
We look at the end of sideplate as it vibrates and see if we get sideways movement which AINT GOOD.
George ■
Re: Side Plates Ripped Apart
Dear Mr. Baker.
Sir i would like to know If your company assist other companies to design & engineer vibrating screens. We have a business proposal in case your company is interested in doing business in india.
The mining and the mineral processing industry is boooming and there is only 1 reputed manyfacturer of vibrating screen. METSO.
Then the International combustion and the TATA robins& fraser screens are not doing very well in the market. The delivery period demanded by these manufacturers are very high.
What i mean to say with all this is that there is a huge potential to manufacture and sell high quality screens in india. The price though has to be kept very reasonably.
Please consider this a seroius business proposal and your response to this is awaited.
Regards
SANDEEP ■
Side Plates Ripped Apart
We recently purchased 3 inclined screens from a reputed manufacturer in india.
The side plates of the screens tore apart like a piece of paper on both sides together and in the same spot.
What could be the reason.
Is it resonance?
Some people are of the view that there was not enough stiffening oon the side plates. Thus there was resonance.
Some of my ppl feel that We had installed the screen on undersize beams and thus the beams transfered the vibrations back to the screen and thus resonance and due to which the screen cracked.
What are the different reasons the experts on the forum feel could be the reason for this cracking.
Please help Me with this.
Regards
Sandeep ■