Vibrating machines

Build your own machine (1)

It is quite easy. Follow next instruction:

• weld together few pieces of iron
• rest it on few springs or hang it on them
• apply one or more oscillation excitors – we advise you to buy our surface vibrators

Build your own machine (2)

If you followed exactly our previous instruction, then perhaps:

• your conveyor works, but it move the substance only a little or to another direction than you want
• your sieving machine transports material instead of its sieving
• in classified material remains the fractions which would be separated
• the springs are breaking
• together with machine vibrations occur also vibrations of the support construction. In limit case all around machine is oscillating but the machine stays put
• within few days the iron parts crack and after their reinforcement the vibrators will not be able to move the machine

The machines we supply perhaps seem to be simple and, really, often simple are. Nevertheless, they hide a large portion of know-how. If you do not really want to become a manufacturer of vibrating technology (we are not happy for it), then do not make waste experiments and buy a machine from our company. Believe us, you will save a lot of effort, time and money…

The principle of vibratory machine

It should be a task for independent thesis to present an overview of all types of vibratory machines and principles of their operation. Recently used vibratory machines work with such frequency and in such way, that the material moves in the machine by so called micro thrust.

Micro thrust

When we apply a cross section vertically through the working plane and parallel to the plane of oscillation, we will observe that each point of the working plane is moving on specific curve line (equal to shape of oscillation) and position of the point is changing periodically. The grains lying on the working plane (surface) are moving together with it until the plane begins to slow down. The grain separates from the plane and goes on flying copying ballistics trajectory. Of course, the flight is finished by touch down on the working plane – but a little farther from previous position. All happens in such a scale and frequency that this simple phenomenon is not visible by human’s eye. An observer gets a feeling that the substance is floating on the machine.

It is possible to describe this process mathematically and find such combination of machine parameters which conforms the fastest transport or the most effective selection.

Vibratory machine parameters

Operation of the vibratory machine may be described by combination of following parameters:

• the way of oscillation (= shape of oscillation)
• working frequency (= rotation speed, angular frequency)
• maximum value of shift (= amplitude of oscillation)
• angle of working plane

All the above mentioned terms and next few ones are explained on the page "BASIC TERMS"

The proper choice of the machine parameters

The machine parameters differs mainly according to technological application. The checkpoint value, if the machine is designed properly is the ratio between the vertical component of machine acceleration and gravity acceleration (= coefficient of thrust).

Does VIBROS company provide some catalogue types of machines ?

It is not possible to apply one type of machine for all applications. We are ready to design the machine according to specific demand and request of our customer. We are happy when it match to already designed and running machine (recently there are hundreds of them). But if you request a feeder 810x2105mm (width x length) and we will have feeder 800x2500, we will not force you to take it and we will present an offer concerning the machine of requested parameters. The most of our machines have been designed on tailor made executions according to specific situations and demands of our customers.

Are the machine modular assembly?

To some extent – yes; the design is composed of various unit elements. But it is the matter of the machine designer. For example the case of fully hermetic classifier BETA is in principle one type and usually only the shape of in- and outlet is adapted and only related parts (feeding and discharging hoppers), which are coupled to the machine by screws, are being changed.

The basic parts of the machine

Our vibratory machines are assembled of following parts:

• the machine body (frame and case)
• the vibration drive (the excitor of vibrations)
• the console of the drive unit - the part which transfers the force from vibrators to the machine frame body. The console may be either coupled or integrated to the frame of machine.
• the elements of flexible seating
• the lining securing conveyor exposed surface

The material of the machine body

The body is usually welded construction, alternatively made of:

• standard steel
• anticorrosive steel on customer’s demand

Drives for Vibratory machines

As the oscillation excitor it is possible to use:

• Surface vibrators are the simplest and the cheapest solution, we as manufacturer prefer their use
• electromagnetic drive unit is preferred when demand on exact feeding and batching is requested; we use the products of another manufacturer, but compared to surface vibrators, this solution is unfortunately more expensive
• the shaft with unbalanced counterweights we use this way of machine drive for screening machine ALFA line with circular oscillation motion; it is of our own design and manufacturing and compared to other competitors it enables easy replacement of bearings without complicated dismantling the whole shaft
• mechanical excitor a case with pairs of counter-running unbalanced elements coupled by gears; it is usually applied on the biggest machines, where the power of surface vibrators is not sufficient

In the last two examples the ordinary electromotor is placed outwards of the vibratory machines and with such oscillation excitors is coupled by V-belt or cardan joint.

Flexible mounting – spring types

• coiled (helical) steel support springs (push)
• coiled (helical) steel suspension springs (pull)
• rubber support elements (push)
• pneumatic actuators (bellows)

Flexible mounting - execution of machine

• supported
• suspended - hanging
• combination of suspended and supported

Lining

The working surface on which an abrasive material is being delivered through feeders, conveyors and classifiers must be covered by the replaceable lining made of resistant materials:

• abrasion resistant sheet (HARDOX 450)
• anticorrosive sheet (AISI 304,316) - where the conveyor deck must behave chemically neutral or to prevent it against adhesion of sticky material
• plastics (HDPE,SOLIDUR) - against adhesion of sticky material

Hermetization

When manipulating dusty materials it is advisable to construct the machine hermetically closed. The sealing then consists of following elements:

• cover of the transport and technological decks – screwed decks, decks with clasps, tarpaulin covers
• hermetic sealing of the entry and exit points – system TRELLEX flexible hoses, ruber sleeves
• revision apertures with clamping decks standard diameter 100mm and 180 mm

Control switchboard box

A control switchboard case may be supplied as optional choice with following functions:

• connecting the vibrators of the machine to power supply
• security and thermal protection of the vibrators
• choice between local and remote control
• switching on in local control mode
• contacts for supervisory control system
• implementation of direct current brake block for run-down
• optional implementation of frequency converter

Control of oscillation

We can supply a system for control of machine oscillations, which comprise one or more accelerometers with evaluating unit. Its main functions are:

• messaging of set on machine if such independent information is requested
• watchdog of maximum value of amplitude - provides security of especially big machines when one of vibrator pair is damaged. The machine is switched off within few seconds and the risk of total machine damage is eliminated
• indication of adhesion of sticky materials or another overload

The power or output?

The output power is a physical quantity, its unit is Watt. In relation to vibratory machine we rather speak about output capacity or throughput.

The output of the machine may be indicated for example in m³/hour or ton/hour as well as number of shaked-out moulds per hour.

Determination of the output by calculation

We can calculate the output for these machines:

• Conveyors According to theory assigning the speed in dependence on parameters of vibrating machine.
• Separators/Classifiers We use standard calculation for classifiers.

Determination of the output by empiric way

We are able to define exactly the output of many machines comparing with another machines which have been already in operation.

Experimental determination of the output

When we are not sure due to any reason with expected output, we insist then on supplying us a sample of material and we will make an experiment (transportability, selectability). A customer’s presence at the experiment is often suitable. Usually a sample volume around 10 litres is needed. We will evaluate the results ourselves, or in cooperation with the customer. He may take the selected sample back to his home laboratory for test of quality.

Quality of selection

When designing the classifier, it may happen the demands on the output and the quality of selection are standing against each other. The selective quality is considered according to residue of the undersized product (what should get through, but it did not and remained above the sieve), or the oversized underflow (which should not get through but it did). We are able to evaluate the quality of the selection on our laboratory classifier.

Transportability

This is the ability of the substance to be delivered by vibrating conveyor. It is effected by

• moisture
• adhesivity - for strong sticky materials vibrating transport is not suitable
• granulometry grading - substances like powder, flour, cement are hardly transportable and if so, then only in thin layer and small quantity.

Ideal substance from the transportability aspect is dry silica sand.

Shape of oscillation

Different vibrating machines oscillate different way. Draw a point on the side wall of the machine and when the machine is running, observe a pattern the point creates. It may display

• line (abscisse) - we speak about linear (unidirectional) oscillation
• circle - circular oscillation
• ellipse - elliptical oscillation
• something undefined - common oscillation

The above mentioned is valid in case the motion of the machine is planar, i.e. occurs in the planes parallel to the side wall of the machine. Anyway there are machines which really oscillate spatially (vertical conveyor, circular sieve, vibratory silo).

P.S. The term “Shape of oscillation” is used by people from field of vibratory technology who wish to make impression as experts....

Amplitude of oscillation

It is the maximum shift from middle to limit point for linear oscillation and radius of circle for circular oscillation. The amplitude is half value of peak-to-peak complete wave. This term is usually used for description of (maximum) deflection.

Peak-to-peak shift

It is double value of amplitude of linear oscillation and diameter for circular oscillation. This peak-to-peak shift (die Schwingweite) is favoured in German technologies. If one does not realize the difference, a mistake conclusion may arise, that German machines have double output compared to the other ones...

Harmonický pohyb

It is regular periodic motion, when the instantaneous value of deflection (speed, acceleration) is changing according to goniometric sinus function ( x - deflection, v - speed, a – acceleration)

Most of the vibratory machines oscillate harmonic way.

Accelerometer

This term is understable according to circumstances as:

• an instrument for measurement of acceleration, it consists of probe and evaluating unit
• an independant probe for scanning an accelerationsamostatné čidlo pro měření zrychlení

Vertical acceleration

There is a relation among the deflection of the machine, instant speed and acceleration. The vertical component of acceleration is important for designing the machine.

The value of the vertical acceleration may be calculated or evaluated by accelerometer.

Coefficient of thrust Kv

It is a ratio between maximum vertical and gravity accelerations. For example the value Kv=2.5 shows that vertical component of the machine is double-and-half higher than gravity acceleration, i.e. 25 m/s₂ . The necessary value of Kv depends on the type of machine and its technological use.

Operation frequency

Frequency is the number of machine oscillations per second. The unit is Hertz (Hz). For machines driven by surface vibrators or excitor with asynchronous drive without any gearbox usual frequencies are used:

Take note, that the last number in our description shows the number of poles and thus their working frequency.

The working/operation frequency is selected according to machine technological application.

The supply frequency

The frequency of the electric current supplying the (surface) vibrators is usually 50Hz. It may be changed by frequency converter which results proportionally in change of working frequency. The output capacity may be adapted by frequency converter taking into account strictly conditions for operations the machine.

One-mass system

The simplest mechanical oscillating system with one mass attached to a linear spring responds also to the simplest vibratory machine.

In real-world such motion stops after a while, it is damped. Of course, it can be calculated too...

There exists also more complicated examples, when there is system of more springs and mass points, even bound together, then we speak about multi-mass systems or coupled oscillators.

Own natural frequency

To keep the mass from animated picture in motion, it is necessary to apply external force and excite the oscillation. In our case the magnitude of the force is harmonically changing. The displacement of the mass besides the force magnitude depends also on exciting frequency. Under some circumstances there exists a frequency under which the displacement extremely rises (even to infinity when no damping exists). This phenomenon is called resonance, the corresponding frequency of exciting force is calld own natural or resonance frequency.

Vibrating machine over resonance

Working frequency of such machine is higher than their resonance frequency. This is the case of so called freely oscillating machines when the applied shape of oscillation is reached solely by position of surface vibrators (excitors).

There are also machines operating in resonant frequency or bellow. The advantage of resonant machines is minimum consumption of supplied energy. But they have also another disadvantage.

Resonant run-down phenomenon

After switching off the running surface vibrators their rotor shafts with unbalanced counterweights are rotating long time until they stop. At the moment when their frequency match the own frequency of the machine occurs an example resonance and extremely rises a displacement. This is not desirable for heavy and big machines or when hermetic in- and outlets are applied

The described phenomenon may be reduced by preventing the vibrators to stop free run-down and application by special some brake system. The best way for surface vibrators is application of direct current brake. A direct current is supplied into coil of stator for a short period. Then the motor brakes within few seconds. We recommend such system for all the machines we supply and we offer a direct current brake block – DCBB - see Braking the vibratory rundown BSB.