In a recent blog I talked about the importance of “Counter rotation and synchronization” in the successful operation and maintenance of a piece of Cleveland Vibrator Company’s vibratory equipment. In that blog I briefly touched on the procedure to be followed when adjusting the eccentric weights on a rotary electric vibrator. The procedure to set the weights correctly is rather straight forward but given how critical the proper set up is to the operation and the longevity of the unit to which the vibrator is attached, I decided to devote some additional time to this topic. This will give me an opportunity to go more in depth with a step by step procedure.
First a bit of math to help get a better understanding of the importance of the weight setting and its impact on the operation of the vibrator itself and more importantly on the piece of equipment. Any type of rotating vibrator, that includes rotary electric (RE), ball vibrators or turbine vibrators generate their “vibratory force” by rotating a mass about the center of the unit or shaft in the case of a rotary electric vibrator. The force produced is dependent on three parameters:
- Weight of the rotating mass
- The distance of the center of gravity of that mass from the center of rotation and
- The rotational speed
For a rotating mass vibrator, my old college vibration text book presents the formula Fo = moeω2 , where mo is the mass of the rotating unbalanced weight and e is the distance from the center of gravity of the rotating unbalanced weight to the center of rotation and ω is the circular frequency of the vibrator. I’ve used this equation for a number of years, converting and reorganizing it into a slightly more user friend configuration, F = 2.85E-5 x unbalanced x rpm2 where the unbalanced is the weight of the rotating mass times the distance from the center of gravity of that mass to the center of rotation, units being inch-pounds. When working on and designing our turbine vibrators, I’ve had to calculate the “unbalanced” of each particular unit. Fortunately, the center gravity of the unbalanced mass is easily determined with our 3d modelling software as well as its weight. For rotary electric vibrators and ball vibrators, the unbalanced value is listed in our old catalogs, but not currently available on the website. If this value is of interest, please contact one of our Sales Team members, they’ll be happy to get you that information.
The rotary electric vibrator is designed with two sets of weights mounted on the each end of the motor’s shaft. See the cut away photo below for the basic design. It is these weights that become the “unbalanced” mass that is used to generate vibratory force as the vibrator rotates. The key word here is Unbalanced, to produce the vibration we want, the rotating mass must not be balanced. Going back to the two sets of weights on the vibrator’s shaft, these weights can be rotated relative to each other to produce a maximum unbalanced value resulting in the highest force output at a given rpm. In the same way the weights can be adjusted so that they are oppose of each other and become balanced, the balanced rotating mass produces no vibratory force. In adjusting the weight configuration it’s critical to understand that what is done to one end of the vibrator must be done to the other end. Additionally, if the vibrators are mounted to a piece of equipment i.e. Screener (EMS), Feeder (EMF) or any one of the many Cleveland Vibrator vibratory tables (FA, FA-O or GT, etc.), any adjustment made to one of the two vibrators used on that equipment must also be done to the second vibrator.
Individually, the vibrator is not designed to operate with unequal weight settings end to end. This configuration will reduce the productive life of the vibrator and may produce destructive forces within a piece of equipment. Likewise, on a piece of equipment, both vibrators need to be set in the same manner; all weights on both vibrators must be in the same orientation relative to each other.
Steps to adjust the eccentric weights.
- Disconnect the power supply to the vibrator to prevent unintended or unexpected starting of the vibrator while adjusting the weights.
- Using the appropriated sized wrench, remove the four bolts that hold the vibrator’s weight cover in place. Repeat on the opposite end of the vibrator.
- Once the cover is removed the weights can be adjusted. As shown above, each end of the vibrator has two weights, an inner weight and an outer weight. To adjust the force output of the vibrator, only adjust the position of the outer weight. Do not adjust or move the inner weight. Loosen the bolt that clamps the weight to the shaft. Once the bolt is loosened the weight can be rotated about the shaft to a new position.Caution: If you’re making an adjust to a vibrator mounted on a piece of equipment or on a hopper where the shaft of the motor is perpendicular to the ground, once the weight clamp bolt is loosened the weight can drop off the vibrator.Be sure to maintain control of the weight as you rotate it on the shaft.The photo below shows the end view of the weights and the scale plate. As shown, the outer weight has an indented “punch mark” on its face that is used as a reference point when adjusting the weight. The scale plate is incremented from 100%, maximum force output, to 0%, a balanced weight arrangement, resulting in no vibration. Increments are in 10% interval for easy adjustment and alignment of the outer weight.
- Rotate the outer weight to the desired new setting. Use the punch mark as a guide; center the punch mark with the line on the scale plate that corresponds with the new setting. In the photo the vibrator is shown at its factory setting, 40%.
- After rotating the outer weight to its new location, retighten the weight bolt, clamping the weight securely to the vibrator shaft. After tightening the weight clamp bolt, double check to make sure that the weight didn’t move while being tightened onto the shaft, if the punch mark is off the desired scale plate mark, loosen the bolt and reposition the outer weight. Retighten the bolt and make sure the weight is fixed to its new location.
- Repeat the weight adjustment procedure on the opposite end of the vibrator. As stated before, it is very important that the outer weight on each end of the vibrator is set to the same position as indicated on the scale plate. For example, if one outer weight is set to 80% the other weight must set to the same position.
- Replace the weight covers on the vibrator. Ensure that all weight cover bolts are used and tightene
d in place.
- If the vibrator that was adjusted is mounted to a piece of vibratory equipment that uses two rotary electric vibrators, repeat this procedure on the second vibrator. Both vibrators must have identical weights settings on both ends of both vibrators.
- Record the new weight settings for future reference.
- Return the vibrator to service.
This completes the procedure to adjust the weights on a rotary electric vibrator. As mentioned several times, on vibrators mounted on equipment, it’s very important to make sure that the weight settings on both ends of both vibrators are the same. If the settings are not the same the eccentricity of one vibrator will be different from its partner’s. As shown in the equation in the second paragraph, if the eccentricity is different and the vibrators are operating at the same speed, the vibratory force generated by one vibrator will not match the amount produced by the second vibrator. This unequal force condition can be very destructive to the piece of equipment and must be avoided.
If you have any questions about adjusting a vibrator’s eccentric weights, please call Cleveland Vibrator and ask for assistance, we’re happy to help. For reference you can click the media imbedded in this blog post.
Check out the tutorial video on Cleveland Vibrator’s Youtube channel
Looking for a shorter version of this how to? Click the image below for a simplified infographic!