29th April 2005, 21:26
i have seen a lot of pictures of vibrating screens and in many of them i have noted that the electric motor is mounted on the fixed structure whereas the screen is vibrating.
as the vibration is provided by the action of the unbalanced shafts moved by the rotor, i asked my self: how it is the transmission of power between the engine (fixed) and the shafts of the screen (that vibrates with the whole screen)? is a belt based transmission?
another question that i have is:
are all the screens moved by a fixed mounted motor, or are some of them moved by a motor that it is coupled to the lateral structure of the vibrating screen?
if someone could publicate a photo of the mounting it will be really helpfull for me.
to keep in consideration, i am interested in big screens used in the open pit extraction process.
thanking all of you in advance,
cristián m v, from chile.
29th April 2005, 22:24
Greetings from the "Frozen Eastern Wilderness",
Christian, in regard to your question most screening equipment except for wobble feeders and stationary grizzlys utilize an electric motor connected by V belts driving an eccentric weight in an orbit around the drive shaft.
This is what forces the screen deck to go forward and back to pick up throw and lift material to screen it.
In the case of Tyler screens and many others they have the screening deck frame mounted inside a steel frame supported and suspended by rubber blocking to contain the movement of the screen in its entire length. The screen frame in its entirety is either supported by steel cables hung above it on a steel superstructure or supported by air bags or not at all in the case of simplicity screens being mounted on a screening floor base structure,
In my opinion you should always keep things simple and easy to take care of, this is why I have mentioned the Bradford Breaker manufactured by
Pennsylvania crusher www.penncrusher.com
It is simple to take care of and does two jobs it screens and breaks material at the same time by lifting the material with paddles and allows the material to drop to the bottom and be screened at the same time to a very small size if required.
Am I correct in assuming you are working in
please be sure to look at pennsylvania crushers web site.
29th April 2005, 22:33
i am not working with them directly, i am investigating in order to make some things related with the vibration analysis in them.
... and yes, in my country amost all open pits are copper ones
Motor Base Types & PICS
Big vibrating screens........ie 8x24 3 decks.....for example and others:
FIXED MOTOR BASE: usually if on a 4 bearing on a single shaft type design.....This typically has a shaft that incorporates a DOUBLE ECCENTRIC tooled into it.........which basically say.....for a 3/8" circle........would have a 3/16" and a 3/16" offset cut into it on top and bottom position.
This means unit has a double eccentric offset....which when it shuts down.........does so....QUIETLY....not a lot of JUMPING AND HOPPING on the RUBBER MOUNTS. Instead, these types of units shutdown smooth.....and DO NOT NEED A MOVING.......or pivoted type motor base. they use a fixed design motor base with a small hinged type point incorporated.
PIVOTED MOTOR BASE: Typically used on 2 bearing circle throw machines. ONE SHAFT with huge bellied offset....which gives us part of the circle.......and incorporates a flywheel with extra weights which are adjustable to add MORE OFFSET.....to attain a bigger circle throw. NOW.
WHEN this unit shuts down.....the big bellied offset shaft is trying to get SLOWED DOWN....to calm the exciting motion to a point where it will eventually SLOW DOWN, JUMP AND DOWN ERRACTICALLY...and eventually stop. THE PIVOT BASE job is to deal with and disperse the energy......so the big body weight of the machine DOES NOT RIP THE BASE OFF its moorings...
ROSTA PIVOTED BASE........same concept.....by much more user friendly design.....
GEORGE BAKER MODERATOR....
HERE IS A ROSTA PIVOTED MOTOR BASE.........
simple, effective, calming and mostly maintenance free design.
Technical Advisor Consultant
Dear Mr. cristián m v, from chile,
The earlier respondents have already given interesting information. Coming to your questions my seriatim reply is as below :
1) The screen arrangement can have motor mounted on fixed structure. The screen is mounted on springs and there is also one unbalanced mass attached to the vibrating deck. There is V belt drive between motor and the unbalanced mass shaft. The motor rotates the unbalanced mass which causes vibrations. Now, it seems you are concerned that what would be the repercussions on the V belt system with the vibration of the screen. Ideally, the V belt centerline should be right angle to the vibrating motion. In this case you will observed that there is insignificant variation in the centerline of drive pulley and driven pulley of V belt drive. Suppose there is 30” distance between centerline of drive pulley and driven pulley and if you have a amplitude of vibration 0.25” i.e. stroke 0.5” then if you calculate the maximum distance between centerline of these pulleys would be 30.00104 inch i.e. variation just by one thou (if you are familiar with inch system). This is insignificant for elastic item like V belt.
In this type of arrangement universal joint is also used to have connection between motor and rotating shaft attached to vibrating deck.
2) There are also vibrating screens where motor/s are mounted directly on vibrating deck. This motor shaft has unbalanced rotating mass. The motor will be also vibrating along with the deck and hence it is called vibration duty motor. Such arrangement is less common.
Ishwar G Mulani.
Author of Book : Engineering Science and Application Design for Belt Conveyors.
Advisor / Consultant for Bulk Material Handling System & Issues.
Email : firstname.lastname@example.org
Tel.: 0091 (0)20 25882916
I may be a bit late in replying to your post, I only found this great site today, but here goes:
Most screens nowadays are linearly vibrated using the principle of two sets of eccentric weights rotating in opposite directions. This can be achieved either by geared exciter boxes, unbalanced electric motors or unbalanced shafts. Without boring the living daylights out of you, suffice to say that there are pros and cons to each of these methods, pertaining to lifespan, ease of maintenance, capital costs and operational costs.
Geared exciters are bolted to a drive beam normally above the deck between the side plates, and driven by an electric motor which is mounted beside the screen on a static pedestal. The motor is connected to a jack shaft via pulleys, while the jack shaft is connected to the geared exciters via a cardan shaft which is equipped with a universal joint which allows the jack shaft end (which rotates concentrically) to be connected to the exciter (which rotates eccentrically).
Unbalanced electric motors are normally used on smaller screens (up to 8 foot wide single decks) and are bolted to a drive beam between the side plates such that a line connecting the centre points of the motors would be (normally - but can be varied) at a 45 degree angle to the horizontal. Rotating the two motors in opposite directions introduces a linear vibration through a line bisecting our first connection line through the centre of gravity of the screen body.
Unbalanced shafts run in bearing housings bolted to the side plates (again, normally above the deck), and are counter-rotated to introduce a vibration in a similar manner to the unbalanced motors. These shafts are driven via pulleys and v-belts from motors mounted beside the screen on something similar to the photo posted by Mr Baker.
Circular movement screens are always "inclined" or "downhill" screens where the screen is excited with a single set of eccentric weights which introduces a circular movement.
If you are interested in further information about the design constraints, possibilities and pros and cons of screen types, please contact me at my web address. Our company is a global one, and I can also furnish you with the details of my colleague Santiago. Otherwise, browse to our web site at www.schenck.co.za
Best Wishes and good luck
Thank you for all your answers, the photo that has been posted really helped me to undestand the fixed motor mounting.
do you know how is the mounting in the Nordberg Modular Vibrators (see photo attached)? these MV works with a fixed motor or with a motor fixed to the vibrating screen, or it depends...?
once again, thank you very much for your interest in this post
Cristián Molina Vicuña
I forgot the attachment... here it goes
I forgot the attachment...here it goes
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