Unloading a ship, depending on the bulk material to be moved, will process faster and more effectively when a vibrator is used. Vibrators assist truck loading (shown in photos) by keeping the flow of material consistent through the hoppers and into the trucks, eliminating downtime in clogged hoppers. Even as the buckets overhead are unloading large quantities into the hoppers, there will be no heavy discharge into the trucks, no material hung up, and no sticking to the side walls. Getting the right size, force, and frequency as well as placement are critical for your success. See the box ‘Selecting the right vibrator’ for details on how to calculate the size/type of vibrator needed.
There is another added variable toward even material flow here, and that is the dampness caused by the dust control sprayers. In selecting a vibrator today, you must take these factors into consideration. There are many variables such as climate, material, humidity, size of the hopper, flow rates, etc. In this application a high amplitude pneumatic vibrator was selected. With high amplitude you have your choice of electric versions on the market from 900rpm, 1,200rpm, 1,800rpm, and 3,600rpm. These all must be calculated into the type of material that is being loaded, and the variation of the material from day to day. Is the material coarse or fine and is the hopper designed with a high slope or a shallow slope?
A vibrator will keep material moving and will reduce costly shutdowns even when materials are damp and sticky.
Depending on the power available at the location, there are vibrator models which conveniently operate on electricity, pneumatics, or hydraulics. Shown in these photos is a pneumatic unit with a muffler which reduces noise and keeps the unit free from contamination.
Selecting the right vibrator
STEP 1: Determine the needed vibrator force for your application bins, hoppers
To move the material in a bin or hopper, the friction between the material and the bin skin has to be broken. Once this is done the material cannot cling to the bin sides and it will flow out through the discharge. The vibrator force needed to accomplish this, for 80% of all applications, is very simply calculated as follows:
Calculate the weight of the material in the transition or sloping part of the bin. Normally this is the only place where the friction between the material and the bin sides has to be broken. Do not calculate the total weight, only what is in the transition part.
* For CONICAL BINS, calculate as follows: .261 x dia.2 x height x material density in lbs/cu. ft.
* For RECTANGULAR BINS, length x width x height x 1/3 x material density.
When the weight has been calculated, divide by ten. The figure you get is the force or impact needed on your vibrator _____________ lbs. For example: the conical part of a 25-tonne bin contains 7,000 lbs. Divide 7,000 by ten, you need a vibrator with 700 lbs. of centrifugal force or impact.
NOTE: Additional considerations when sizing vibrator to bins.
* If bin side angle is below 30º, select next larger vibrator.
* If bin thickness is extra heavy, select next larger vibrator.
* On very sticky and hard-to-move materials, it is better to use two small vibrators instead of one large one (find the smaller one by figuring half the material weight.)
STEP 2: Find available vibrator models
Look for a manufacturer that has a vibrator product that meets your requirements. VIBCO’s catalogue can be viewed at the company website.
STEP 3: Select electric, pneumatic or hydraulic operation
In general, electric vibrators are initially higher in cost than pneumatic vibrators; however, the operational cost is considerably less and the difference in price and installation cost is recaptured in a few months of operation. The electric units have the lowest noise readings, 60–70dB, no more sound than from an electric motor. The life expectancy is two to three times that of an air-operated unit. The life of an air-operated unit is, to a great extent, determined by the cleanness of the compressed air and the operating pressure. Maximum operating pressure is 80PSI, above 80PSI, the life of the pneumatic vibrator diminishes rapidly. The dBa reading on piston vibrators is 80–110, on ball vibrators, 80–115.
The only pneumatic units with a dBa reading of 60–80 are the TURBINE VIBRATORS. The least air-consuming are the piston vibrators, then the turbine, ball and SVR high-frequency vibrators. As a general rule: for standard applications, limit your selection of vibrators to the SCR Electric Vibrator Line and the Turbine Pneumatic Vibrators. They will give you the latest in vibration technology and design with the lowest noise, the best life, the least maintenance, and the lowest energy consumption.
The hydraulic vibrators are fast gaining acceptance but still primarily used on OEM equipment for food and related products.