Belt run over the periphery the job give drive the job
Identifying and correcting the mass distribution and thus minimizing the force and resultant vibration is the technique known as dynamic balancing.
Causes
Fig 1
Manufacturing - Causes
Many causes are listed as contributing to an unbalance condition, including material problems such as density, porosity, voids and blowholes. Fabrication problems such as misshapen castings, eccentric machining and poor assembly. Distortion problems such as rotational stresses, aerodynamics and temperature changes. Even inherent rotor design criteria that cannot be avoided. Many of these occur during manufacture, others during the operational life of the machine. Whilst some corrections for eccentricity can be counteracted by balancing, it is a compromise. Dynamic balancing should not be a substitute for poor machining or other compromise manufacturing practices.
Fig.2
Installed Machines - Causes
When unbalance has been identified and quantified, the correction is straightforward. Weight has to be either added or removed from the rotating element. The ultimate aim being to reduce the uneven mass distribution so that the centrifugal forces and hence the vibrations induced in the supporting structures are at an acceptable level.
Field Balancing
· The effects of temperature, pressure, distortion and other environmental influences can be incorporated.
· The resultant vibration can be the tolerance applied to the rotor, rather than the published balance tolerances normally used in a balancing machine. This is particularly advantageous if the supporting structure is close to a resonance. The unbalance in the rotor may have to be adjusted to abnormally fine levels to minimize the resultant resonant structural vibration. Modern instruments such as vibration analyzers, data collectors and portable balancers provide accurate information to assist in the balancing process. The vibration level measured at the rotating speed frequency is used as an indicator of the amount of unbalance. The location is determined by measuring the phase. Phase, (the relative motion of one part of a machine to another) is measured by means of a stroboscopic light or by an indicator in the instrument, triggered by a photocell.
A device that holds and spins the rotor while you balance it.
Balancing machines can be divided into two different types:
be either dedicated or separate. The same instrument that is used for field balancing can also be used in the balancing machine. Maintenance type balancing machines are a necessity in repair depots such as motor rewind shops, pump overhaul facilities and turbine repair workshops. All industrial rotors that have been overhauled should include
a balance check as the last task before re-assembly.
• Minimize noise
Airborne noise is often directly attributable to mechanical vibration.
• Increase machine life
The time between outages can be extended if the machine is running smoothly.
• Increase personnel safety
Dangers associated with machine failure are minimized.
Conclusions
Everything that rotates needs to be in a state of balance to ensure smooth running when in operation. Precision balancing is essential to the manufacture of rotating equipment and to the repair and renovation of installed machines. As machine speeds increase, the effects of unbalance become more detrimental. Modern technology allows for accurate balancing to be performed both in the field and in the workshop.
ABRO also has a range of soft bearing dynamic balancing machines which are given when any such type of enquiry is received.
ABRO DYNAMIC BALANCING MACHINES COMES WITH PRECISION ELECTRONICS
Digital electronics type DS12C for dynamic balancing of 6-throw crankshaft.
Digital electronics type SSAP (D)/9C/EREC. Single plane electronic unit with component and polar indication and electronic remount error compensation to eliminate tje effect of adaptor unbalance and run out.
Recently, the above manufacturers have purchased ABRO designs and are shifting to ABRO designs for the machines they make in their plants in London, Rochester, Torino and Barcelona.
WORLD-FIRST DEVELOPMENTS
Large, high-speed balancing and over-speed testing machines which can also do accurate low speed balancing of rotors upto 90 tons. While these machines have high dynamic load capacities, they also have a good sensitivity at low speeds.
Precision vertical two-plane balancing machines of ‘hard bearing’ design for balancing small rotors in their own bearings (textile flyers and spindles).
‘ABRO’ also undertakes modification/ augmentation of machines maked by other manufacturers. ABRO has modified various dynamic balancing machines madeby Hoffman, Schenck Avery, Reutlinger, ,etc.
RANGE OF ‘ABRO’ DYNAMIC BALANCING MACHINES.
PRODUCTION MACHINES: - Modular design of ABRO machines makes it possible to produce machines for low, medium or high level of automation suitable for different production requirements.
SPECIAL MACHINES: - Special requirements require special machines. ‘ABRO’ manufactures special purpose machines. A very few examples are given below:
Dynamic Balancing Machine used for balancing vertical textile spindle in their own bearings.
1.1 WEIGHT CAPABILITIES
Maximum work piece weight for symmetrical rotor : 450 kg
Maximum diameter range : 400 mm
Minimum diameter under belt : 30
These balancing speeds correspond to a normal motor
speed of 1500 rpm
TYPE : AC SQ CAGE POWER : 3 HP
SPEED : 1500 RPM
3.1 SPEED/SENSITIVITY
Minimum dial setting : 047
Maximum dial setting : 1047
3.2.1 Surface belt drive:
In case of surface belt drive machine, a belt is run over the periphery of the job to give drive to the job, surface belt drive to the job. Surface belt drive system consists of:
The motor is positioned on the back side of the bed .This motor base can be clamped to the bracket or side of the bed or separately grouted. On the motor shaft, one or more than one pulley are mounted which have normally a quick change arrangement.
ii)IDLER BRACKET
D1 = Diameter of under belt
The speed may vary due to slip variation as the belt tension may vary .the belt tension is adjustable from the wheel provided on the front side .The belt should not be too tight or too loose and it should run in the centre of pulleys without touching the pulley collars.
i) A bracket with a slot on the end.
ii) A square /round rod
The A.C. drive control the speed of motor with a10 dial provided on the front panel of the converter .As it is moved in clockwise direction, the speed of motor increases.
The A.C drive is housed in a separate cabinet The push buttons ,speed control potentiometer and speed/voltage /current meters are either located on panel machine headstock.
The electronic system consists of electronic box, pick ups and phase generator .An electrical signal whose amplitude is proportional to the unbalance is generated by pick ups.
There are two pick ups, one for left plane in left pedestal and the other for right plane in right pedestal.