Drugs, Sex, Rock and Roll and Industrial Vibrators!  Well maybe not, how about pharmaceuticals, we still don’t make “those” kinds of vibrators, Rock and Roll and Industrial Vibrators.  The common factor in this list is the application of vibration to accomplish a specific goal.  As some folks that read these blogs might have noticed I’ve stated my interest  in building acoustic guitars, in comes the rock and roll part, and as I state in my bio, “It’s still all about vibration, just strings and wood and not bulk material”.

Guitar building is an interesting adventure, the more I read and build the more the road twists and turns.  I happened to innocently stumble down this path when my son off handedly asked me if I thought we could repaint his Strat.  Well, since then it’s gone from building electrics to building acoustics.  In both groups vibration of the strings and the support structure is critical. For many builders the goal seems to be to duplicate the sound and tone of what many consider the Holy Grail of acoustic guitars, “Pre-war Martins.”   Part of the “magic” of these instruments is the materials used, building process at the time and the natural “aging” of the instrument.   Aging as I understand, it is a combination of changes in the wood and the changes in the structure due to the vibration introduced by the strings.  One day a while back my son and I were talking guitars and vibration and I started to wonder out loud if you could attach a small turbine vibrator such as the CVT-P-1 to the bridge of the acoustic guitar, run it, vibrate the instrument and thereby reduce the break in time of the instrument, “open it up” more quickly and move the sound towards the Holy Grail sound.  Well, we never did attempt that but recently while reading some entries on an acoustic guitar forum; I came across the mention of a device that is designed to reduce the break in time for a guitar or other stringed instrument.  This unit is some type electrical device with an “intensity” controller that introduces vibration into the strings of the instrument.  Presumably this tries to duplicate the vibration of the strings that would occur when actually played.  One can only assume some sort of electromagnetic vibrator similar but smaller than our CM-5 or CM-10 vibrators produces the vibratory force.

There are a number of common means of producing industrial vibration, either pneumatic vibrators or electric vibrators.  On the pneumatic side of the house you’ll find air piston vibrators, ball vibrators and turbine vibrators.  Vibration produced by a piston vibrator, be it the VMS/VMSAC family of piston units or the smaller SA-EP line, is linear, back and forth.  As the piston moves back and forth in the confines of the body, vibration is produced as this mass shuttles and in some cases actually strikes the end of the unit as in the SA-EP line or VMS impact series.  This linear force is great for a wide range of applications, from flow aids, foundry compaction aids to drives for vibrator equipment such as feeders, screeners or vibratory packer tables (VP).  As the size of the piston increases, so does the force generated by the vibrator.  With the larger piston comes a drop in the operating frequency and increase in the air required to operate the unit.

Ball and turbine vibrators are the other common pneumatically powered industrial vibrators.  Both of these families of vibrators produce vibration as a result of a rotating “off center mass”.  As the mass rotates, vibration is produced and force radiates outward from the center of rotation.   In the ball vibrator, this force is produced by a hardened steel ball as is rotates around the inside of the unit’s body.  Air introduced into the body “pushes” the ball around the interior; the ball is the “off center mass”.   Turbine vibrators are more complex in their design but generate force in the same manner as the ball vibrator.  With the turbine vibrator, the design is based on a rotating impeller that contains an off center weight.  A stream of air enters the body of the unit and strikes the impeller causing it to rotate about its center.  Due to the design of the rotating impeller, the turbine vibrator is a more efficient means of producing vibration.  When comparing similar sized ball and turbine vibrators you’ll typically see higher force outputs and less air consumption on turbine vibrators.   In addition to the savings in compressed air, turbine vibrators generate less noise than their ball vibrator counterparts.  Since there is no ball rotating about the interior of the unit, no metal on metal contact, you notice a significant reduction in noise with the turbines when compared to ball vibrators.  I think it’s the combination of more force, less air consumed and reduction in noise that drives the use of turbines for many applications.  While they are more expensive it would appear that for many users the benefits outweigh the additional cost. You can further compare the two models by reading Cleveland Vibrator’s Turbine v. Ball Vibrator Application Report featured on our website.

So now let’s have some fun with the math and see what else we can learn about industrial vibrators and in particular, vibrators that produce a rotational force.  From my old college vibrations course textbook, “Vibration of Mechanical and Structural Systems” by M. L. James et al, we find that an off balanced rotating mass will produce a vibratory force where  F = m_Oeω^² .  With some work we can change that into a form that’s more user friendly for industrial vibrators.  Eventually we can get to the force output being equal to the rpm squared times the “eccentricity” or unbalanced value of the particular vibrator and a conversion factor.  The two parameters that we are always interested in on rotational vibrators regardless of the type, ball vibrators, rotary electric vibrators or turbine vibrators, is that “eccentricity” value and the operating speed.

The “eccentricity” of a vibrator is sometimes referred to as its “un-balance” , this parameter is a product of the weight of the unbalanced rotating “mass” and the distance from the center of gravity of that “mass” to the center of its rotation.  Some manufacturers will list this in their literature; some refer to it simply as “in-lbs” in their data.  Here at The Cleveland Vibrator Company we show it as an “un-balance” value with units given as inch-lbs.  If you look at our web site for our literature on our turbine vibrators, ball vibrators or rotary electric vibrators, you’ll note this value.  Using the previously mentioned equation and knowing the unbalanced value for a given vibrator it’s easy to calculate the force output of the vibrator at any desired rpm, very helpful if you’re interested in the performance of a particular vibrator at a speed not given in the literature.

Reviewing the equation provides insight into what is actually happening with the vibrator.  It’s easy to see the importance of rotational speed to the generated force. With the rpm squared even small increases in speed will yield significant increases in the force output.  For example, if we had a ball vibrator with a known unbalance of say 6 in-lbs and run it at 2000 rpm we get 684 lbf from the unit.  If we were able to double the speed to 4000 rpm we get a new force output of 2736 lbf, or four times the force, due to the rpm² factor.  Increasing the weight of the rotating mass will also increase the force output but not as significantly as the increase in speed.  Increasing the weight of the rotating mass will usually result in a drop in the operating speed so while you might pick up some potential for additional force with the heavier rotating weight, if you sacrifice speed for  weight, you’ve probably lost any increase in force you might hope to see.

The last item worth looking at is the amplitude of vibration produced by a rotating mass and making a couple of observations.  I have previously written a blog about the “amplitude” of a given vibrator, as I mentioned then, it doesn’t work that way.   A vibrator by itself does not have an inherent amplitude.   But if we attach a vibrator to a body we can calculate a reasonable estimation for the amplitude or movement of that complete body-vibrator assembly.  The equation we use at The Cleveland Vibrator Company is Amplitude = (conversion factor x vibratory force) / (weight vibrated x rpm²) we’ve found this equation to be fairly accurate over the years.  So what’s its importance to the application of say a CVT-A-50 vibrator or perhaps a 1200 VMSAC vibrator?  Well, if we hold the vibrating weight constant and we apply the same vibratory force, we can see the influence that the operating frequency will have on the amount of movement we’ll generate when we attach that vibrator to “something”.    As the frequency of vibration increases, we see the resulting amplitude of vibration drop.  This is helpful in understanding the dynamics of a piece of vibratory equipment such as a flat deck vibratory table or a vibrator functioning as a bin vibrator or bulk material flow aid.  Just because the force output is listed as being the same, if the operating frequency is significantly different the amplitude of vibration will also be significantly different.  For example if we take a turbine vibrator running at 33,000 rpm with a force output of 839 lbf, attach this to an isolated 600 pound “thing”, we’d predict an amplitude of displacement of 9.1E^-5 inches, quite small due to the high frequency.  If we were to attach a 1300 VMSAC piston vibrator to the same “thing”, the force output at 60 psi would be 769 lbf at an operating frequency of 1900 vibrations per minute (VPM).  The calculated amplitude of vibration for the 1300 VMSAC pneumatic piston vibrator would be 0.025”, significantly larger than the higher frequency turbine.  Is that relevant to a customer’s application?   Hard to know for sure, but it is helpful to understand the differences in results that two different vibrators even with similar force outputs will yield.  Just because you introduce a similar amount of force into a “thing” you can’t expect the same movement in that “thing” or similar results in the end process.

While all this math and calculations may seem a bit confusing, I’m still thinking that it’s probably easier to design and build a vibratory feeder (EMF) or flat deck compaction table (FA) than it is to crack the code on the Holy Grail guitar sound!  I’ll continue to try my hand at guitar building and spend my days designing electromechanical vibratory screeners (EMS) or expanding our line of pneumatically powered turbine vibrators.  As my Girl Scout sisters used to say “make new friends but keep the old, one is silver and the other gold”