|Guide for Sizing Air and Electric Vibrators
for Hoppers, Bins and Chutes
- A single vibrator will normally provide the necessary force to move materials from most hoppers and bins. The single vibrator installation requires that the force of vibration be transmitted to full 180° right and left of the vibrator mounting location. However, due to the special configurations or wall thickness or the characteristics of the material itself (sticky, lightweight, large particles, moisture, etc.) consideration should be given to a multiple of smaller vibrators evenly arranged around the hopper in place of one large vibrator. The maximum number of multiples is three mounted 120° apart, or two vibrators mounted 180° apart. Greater distribution of vibration will result and assure that all areas will be vibrated equally. This arrangement is of particular importance when attempting to move material from long rectangular shaped hoppers or from hoppers with a very shallow taper at the discharge.
- The mounting of a vibrator on a length of channel which is stitch welded vertically to the side of a hopper will provide a transmission line above and below the vibrator and will also reinforce the hopper wall as well. The width of the channel should be to suit the base dimensions of the vibrator. The length will also vary with the hopper size; however, a good rule to follow is to use the length of the scoping section of the hopper.
- Moisture content of the material to be moved is also important in the sizing of a vibrator. If the moisture content is 6% or more, it is advisable to use the next size vibrator or two vibrators.
- All vibrators provide a range of adjustability in their force output. Air vibrators can be adjusted with a simple air regulator; electric vibrators, with adjustable eccentrics; or others, with SCR controls. In selecting a vibrator, remember that it can be adjusted due to changes in material make-up, lower hopper contents, or vibrator over-sizing.
- There is a reduction in vibration intensity in the non-impacting type vibrators (air cushioned, rotary electric, ball) over the impacting piston vibration. Do not operate vibrators against closed hopper gates or valves.
- A short burst of vibration is normally more effective than continuous vibration. Do not operate vibrators against closed hopper gates or valves.
- Noise level of vibrators varies with the type. A general ranking from the loudest to the quietest is as follows: impact, ball, air-cushioned, rotary electric.
The information contained in these charts is the result of many years of experience. It is a reasonably accurate approach to giving you quick information to vibrator sizing on a hopper, bin or chute. Recommended vibrator sizes are predicted on a dry granular material weighing 100 lbs. per cubic ft. Considerations are as mentioned previously.
The sizing of rotary electric vibrators is based on the ratio of material weight on the sloped wall section to the force output of the vibrator. For the majority of applications, the ratio should be one pound of vibratory force for every ten pounds of material in sloped wall section on the hopper.
The 3600 rpm rotary electric vibrator units are used for the majority of applications and are well suited for materials which are in the "free flowing" to "difficult to flow" range. For particularly stubborn materials, the 1800 rpm units will provide greater amplitude than a 3600 rpm unit of the same force output. When selecting an 1800 rpm rotary electric vibrator, use the chart to determine the proper size 3600 rpm vibrator, then select the 1800 rpm unit which develops the same force output.
To determine the weight of material in the sloped wall section, multiply the bulk density of the product by the volume (in cubic feet) of the hopper section.
To calculate the volume of a conical hopper:
1.0472 x vertical height x [R² + (R x r) + r²] = Volume
where R is the radius of the cone at the transition point and r is the radius of the cone at the discharge.
To calculate the volume of a rectangular or square hopper:
Vertical height/3 x [B + ½(B x b) + b] = volume
where B is the area at the transition point and b is the area at the discharge.
Bins and Hoppers
Most bin or hopper applications will require only one RE rotary electric vibrator. CVC recommends mounting the single drive as indicated in figure 1, locating the unit at a point on the sloped wall section that is 1/3 the height of the wall.
Applications involved with particularly stubborn material or hoppers larger than 100-ton capacity may require two or more vibrators. The recommended mounting is shown in figures 2 and 3. Normally, not more than three rotary electric vibrators would ever be required on a hopper or bin.