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About Vibration

In this article is as published in "Australian Bulk Handling Review" written by Ken Gower of Vibco Australia Pty Ltd, discusses its uses in bulk materials handling, Ken has over 20 years experience in the application of vibrators and vibratory equipment for a range of industries,

Good vibrations

Vibration has been around since the beginning of time - the earth certainly vibrates during earthquakes, sound is based on vibration, and many animals use it during mating calls - it is one of the very basic elements making up our world. 

When did you first use vibration?

Maybe it was when you learned how to get the cereal out of the packet, without spilling it over the table (too much shaking at a steep angle causes flushing of a flaky product). Or was it when you used the salt and pepper shaker for the first time, or sprinkling sugar into your tea or coffee.

We all use vibration within our daily life, often not realising how often we hit, shake, bump, or tap an object to get it to move.

 Industry is much the same with a vast range of opportunities to use vibration to achieve a desired result. The simple nature of vibrating, with minimum moving parts, easy cleaning, and having a wide range of applications, vibratory equipment can often solve your materials handling problems or create an environment to help the processing of a product.

However, engineers are generally taught that if they build a machine that vibrates they have done something very bad - most if not all education in this area is about how to remove the unwanted vibration from a machine. Even civil engineers are not fully instructed on the application of vibration of wet concrete to achieve the correct settling.

What does Iron Ore have in common with Potato Crisps?

When correctly applied vibrators can assist in the handling and processing of nearly all bulk products, As the flow characteristics of each product is different each needs to be considered in detail to establish the correct unit for the duty. Iron ore and potato crisps can both be handled using vibratory equipment, but due to the vast differences in these products, completely different vibratory units have to be used. Due to the natural absorption of soft materials, as in meat, some cheeses and some liquids its best to consult an experienced supplier to ensure that vibration is a practical solution. Even fine flour, milk powder, vegetables, scrap, and sugar are products that need special attention due to their different flow characteristics when vibrated.

Where can vibrators be used?

bulletSettling products into containers, bags, bins, and bottles. Also compacting of concrete in forms or moulds
bulletFreeing up materials to remove the contents of containers, bags, bins or hoppers, tip trucks, and bottles. Also helping concrete to run down a chute. (All very similar to the above!)
bulletFeeding of bulk material from bins or hoppers, at a controller rate and being able to stop and start it feeding as required
bulletConveying of product in a clean tray, and be able to distribute it via gates or chutes onto different conveyors as may be required by a process system
bulletElevating, by the clever application of vibration around an axis, product can be conveyed up and around a vertical spiral
bulletApplying the same axial vibration to a bowl with an internal spiral the orientating of components into a particular attitude for further processing. Caps for fitting onto bottles, small parts into assembly, or corncobs to cutters are some examples
bulletAligning flat sheets Products such as paper can be aligned using vibration (cheques or vouchers for processing, paper prior to printing)
bulletScreen to sort a bulk material into different size range, also separation of different products can be achieved.
bulletPolishing, burnishing, de-flashing of components by rumbling in a trough or tub, also grinding is possible.
bulletStress relieving of castings or fabrications by applying a range of different frequencies over time to the product
bulletTesting of packed products or electrical components for suitability in the field

There are a few practical limits in the applying vibration to a mechanical system, but as with most things it can be an expensive if incorrectly applied. The application need not be expensive, and can provide a unique solution to a flow problem with the application of a simple vibrator. Even complex bulk materials handing systems can be engineered to use vibration as the driving force in processing and handling of a large range of products.

As there are many yet undiscovered applications to solve difficult problems, engineers need to be innovative to examine all the possibilities.

A company wanted to separate the round pieces of glass from the angular pieces, all having a similar size. By setting up a feeder to with the pan slightly uphill and then slowly feed the mixture onto the pan, it was found that the angular pieces feed up the pan, and the round pieces rolled down.

In Europe a vibrator was attached to the plate under a counting system for day old chicks, the vibrating plate caused the chicks to hesitate, giving better separation for a more accurate count. 

We understand that a new alarm clock will utilize vibration to shake the sleeper awake.

And some cleaver guys in a Canberra University are looking at generating sufficient electricity, from the ambient vibration of a machine, to power remote sensors. Thus eliminating the often complex wiring required to power sensors.

What are the different types of vibratory action?

Rotary Vibration

A circular motion, which is generated by electric vibratory motors, air turbines, ball vibrators, and eccentric or out of balance shafts.

This is simply shaking an object, devise or machine to obtain product movement, whilst force and frequency can be controlled the actual vibrating action is subject to variation caused by the structure of the object. It is used for:

bulletScreening
bulletGrinding, Polishing & Mixing
bulletShaking of hoppers & Chutes
bulletPacking & Settling Tables
bulletConsolidation of products
bulletTesting

Linear Vibration

Achieved by using two contra rotating rotary vibrators, crank arm, piston vibrators, or Electro magnetic drives. By applying an even straight-line vibration at a selected angle a product can be thrown up and travel forward as the pan moves back. Uses:

bulletFeeding
bulletScreening
bulletConveying
bulletGrading, Inspection & Sorting
bulletShaking of hoppers & Chutes
bulletPacking & Settling
bulletTesting

Combination / Special

By vibrating a specially designed system an action can be achieved such as a linear stroke around an axis or modifying a Rotary or Linear vibration to become elliptical. Various changes can be applied to achieve a special action to make a product move in a particular way to achieve a desired result such as to get the product to travel up a spiral track, or increase the time the product stays on a screen. Applications:

bulletScreening - (Gyratory Screens)
bulletElevating - (Spiral Elevators)
bulletFeeding and Orientating - (Parts Feeders)
bulletHopper Discharges - (Bin Discharger)
bulletSpecial applications - (turn tables and special consolidation units)

How vibration can be generated?

There are various methods to cause a structure to vibrate. The ideal vibration is dependent on the application and result required - high frequency at low stroke or high stroke at low frequency. Also you need to know of how much force and its direction to achieve the required result

For instances if you are testing products, it may be better to have a low frequency and high stroke when testing cartons for transport, however if testing electric circuit boards a high frequency at low stroke may be more appropriate.

To vibrate a structure, an engineer can use a simple cam, a reciprocating air cylinder or electric actuator, sound waves, or even a piezoelectric element, however the following are the more common methods currently used to obtain a controlled vibration of a machine or structure.

Crank mechanism

A simple crank and arm mounted onto the devise to be shaken. Commonly used to vibrate long conveyors, as the mass is usually high and 'G' forces relatively low this is suitable for high strokes and low frequency.

Eccentric shaft

By making a shaft "out of balance" the result is that the devise onto which is mounted will vibrate. The shaft usually mounted to the machine with a belt drive from a static mounted motor.

Rotary vibrators

There are many manufactures who make different types of rotary vibrators. Air or hydraulic driven turbines fitted with eccentric weights, vane type turbines as eccentric will induce vibration. Air driven balls, or rollers, running around a track also give an eccentric force. Motors, usually electric can be fitted with eccentric weights on one or both ends. When these are mounted onto a devise, it will vibrate. There are many manufactures of these rotary vibrators making the selection relatively easy.

Electromagnetic

By continually pulsing a coil or solenoid, which is mounted onto a devise, will induced vibration. To achieve the desired result with this system designers need to understand electrical service both voltage and frequency, coil characteristics and electromagnetic fluxing, mechanical limitation of the system, and application restraints. Manufactures of electro magnetic units normally have a great deal of experience in how to design a suitable unit for duty requirements.

Pistons

A simple reciprocating piston will shake a devise. Piston vibrators are especially made for the high forces and frequencies that are required by the 'jack hammer' action often needed.

Each of the above have various advantages and problems all of which need to be examined in regard to the duty requirements before finalising the selection.

What needs to be considered in the application, selection, and design process?

The first consideration is to examine the product characteristics, how it will move under vibration, and clearly identify what is actually required to be achieved.

To build a vibratory machine the engineer needs to know what type of vibration is best for application, how much is required, and the direction to achieve the desired result. Then to be able to make the unit as light as possible, for the smallest drive, and still provide a rigid structure to be able to withstand the "G" forces required to perform the duty without the unit bending causing the structure to crack and break under load.

What is the connection between Diva's, Jericho, and mud flaps?

If you apply a vibrator directly to a structure or a machine you are vibrating with brute force, you are in effect forcing the structure to shake in relationship to the force applied.

An area often ignored, and sometimes misunderstood, is that all things, and their parts, have a natural frequency. This is the frequency at which they want to vibrate at, and will do so with very little force. Consider the opera singer who generates a sound at a frequency that matches a glasses natural frequency which can be at the other side of the room - keep it up long enough and the glass breaks. This idea was used in, biblical times, to bring the walls down at Jericho and is why that mud flap on the truck next to you at the lights shakes violently when idling but stops when the truck takes off.

When applying vibration to any structure consider the effect it may have on the surrounding equipment and how to control the vibration by isolating or altering the drive frequency to suit the environment. The mud flap needs a brace, a different mounting, or a change in weight to alter its natural frequency from the trucks idle frequency.

Many vibratory units utilise this feature to magnify the vibration of a unit allowing a smaller vibrator to be used. These are natural frequency units and tuned systems need to be treated as such, just like a musical instrument, any changes to their structure will change the natural frequency making it different to the drive frequency, hence the unit will no longer operate as it is out of tune.

Other things to consider.

A simple vibrator mounted to a hopper to assist with product flow, will over a week, (at only 20% on time) vibrate the hopper in excess of 50,000 times. With this many "blows" to the hopper it's best to get the installation correct or risk damage to the hopper or personnel.

Timing is also important, a contractor had a client with a hopper that stopped flowing. The client showed the contractor that all he had to do was knock the hopper to get it working again. The contactor duly fitted a vibrator only to complain that this did not solve the problem. The client had the advantage of knowing when to shake the hopper, and its possible that the vibration was in fact compacting the product, actually making the situation worse. Care needs to be taken to set the vibrator up for correct thrust and not to run it too long or ideally only turn it on if there is a flow problem.

Another common problem is apply vibration in a violent way to a structure in the hope it will solve the problem - beware as this is akin to shaking the baby to stop it crying - a very bad application of vibration.

Summary

Whilst vibration is a relatively simple action, and is indeed a part of our everyday life. The correct application and design of a suitable system can be very involved and is best left to the experts.

VIBCO are available to assist with your special application, regardless of size or complexity, and will confirm if vibration can be beneficial, and would be pleased to recommend the best course of action. As for vibrators for matting in the animal world, this is a completely separate field in which we do not have any expertise's, we can only suggest ways for shaking the building or structure for an outcome but not the individuals within it.

 

 

 

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