Actually, VSMA does differentiate on materials of different weights per cubic foot. Wgt per cu ft is the plug in methodology for VSMA. In the formula, VSMA simply alters the facor for weight pcf to a bigger number if lighter density and smaller if heavier. Wider SCREEN = more tph longer SCREEN = more EFFICIENT or cleaner product.

VSMA bascially is a guidelines for vibrating screens generally, mostly aggregate or mining, mostly INCLINED circle throw machines and FLAT OR HORIZONTAL gear-driven 45 degree stroke angle machines.

BM&M woodchips screens....are different type of vibrating screen in that they OSCILLATE or move the product SIDE TO SIDE IN a sweeping action vs throwing the material up in the air like the aggregate machines. The RPM on a horizontal is 750 because it must co-incide with the stroke on the machine, which is typically plus minus nominal 1/2" stroke length. If we ran a horizontal at say 1000rpm the G factor would be too high and the sideplates would BLOW UP...or more correctly put.....CRACK.

Typical horizontal and even INCLINED screeners throw the coarse up in the air which allows the fines to sift down thru the BED DEPTH of sand and gravel and try to attempt to pass the opening in the wirecloth. When you put woodchips over a standard circle throw or horizontal screener, we throw the wood mass up...and find that the ELONGATES, carrot shaped, pieces of wood come down and stick into the hole and plug the hole as NEARSIZE. UNDESIRABLE of course. BM&M made a better mousetrap or mode of shaker screen WITH a reciprocating force which elimates that type of plugging problem.

the motion of THE BM&m is more gentile and not the same as the gear drive of a horizonal....and hence can be higher RPM without breaking the machine.

Originally Posted by kelleyb

Dear Sirs,

I am a mechanical design engineer and have been tasked with designing a small test screen for wood chips. I have been browsing on the forum and ordered and read the VSMA guide booklets. I was a little disappointed in the books as it didn’t seem to give guidelines for different densities of the material to be screened. For example, with 2” perfs, the VSMA guidelines has the rotational speed of a horizontal screen at 750 rpm, which more than twice what, say, BM&M run on their oscillating screens for wood chips. Am I missing something or misunderstanding these guidelines? I guess the easiest way to determine the counterweight design is to ask what acceleration (g’s) work best on mid-size wood chips on a low-angle horizontal screen. Does any one know this (or know where I can find that info?).

I was also hoping for some guidelines in estimating horsepower, but if I have the necessary g’s I can always solve for it. Just was curious if there was a formula where I could just plug the masses and rpm in and get a Hp out

The last question I have is, how does the location of the Center of Gravity affect the operation of a circle throw horizontal? If it isn’t close to the counterweight does the screen have additional motions or does vibration increase? This is something I can play with if we purchase a dynamic analysis program but I doubt I will be able to convince the powers that be to spend that money in this economy!

If you can recommend any literature that would assist in the design, especially as it relates to the math, I would certainly be interested. Thanks for your help and I hope I can help answer other questions in the future!

BK

■

BK

You can watch the video on BM&M screens on their website and these gyratory screens do not seem to be very complex.

Regards

Ziggy ■