Understanding In-Situ Balancing

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Portable balancer & Vibration analyzer Balanset-1A

£1,793.60 Izvorna cijena bila je: £1,793.60.£1,543.86Trenutna cijena je: £1,543.86.

Parts

Vibration sensor

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Optical Sensor (Laser Tachometer)

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Devices

Balanset-4

£6,178.15

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Magnetic Stand Insize-60-kgf

£41.77

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Reflective tape

£9.08

Devices

Dynamic balancer “Balanset-1A” OEM

£1,575.64 Izvorna cijena bila je: £1,575.64.£1,362.23Trenutna cijena je: £1,362.23.

Definition: What is In-Situ Balancing?

In-situ balancing (from Latin “in situ,” meaning “in place”) is the practice of balancing a rotor while it remains installed in its machine, in its normal operating location, and under actual operating conditions. This is also commonly referred to as field balancing, on-site balancing, or in-place balancing.

Rather than removing the rotor and transporting it to a specialized balancing machine in a shop, technicians bring portable vibration measurement and analysis equipment to the machine’s location and perform the balancing procedure without disassembly.

Advantages of In-Situ Balancing

In-situ balancing has become the preferred method for the vast majority of industrial machinery balancing due to its numerous practical and technical advantages:

1. No Disassembly Required

The most obvious advantage is that the rotor does not need to be removed from the machine. This eliminates:

• The labor cost of disassembling and reassembling the equipment
• The risk of damage during removal, transport, and reinstallation
• The time delay associated with shipping the rotor to a balancing shop
• The potential for introducing new problems during reassembly (misalignment, improper torque, etc.)

2. Balancing Under Actual Operating Conditions

This is perhaps the most significant technical advantage. In-situ balancing accounts for:

• Actual Bearing Stiffness: The real bearings and their installed stiffness characteristics affect how the rotor responds to unbalance, which can differ significantly from idealized shop conditions.
• Foundation and Support Structure Effects: The flexibility of the machine’s base, frame, and mounting structure influences vibration. These effects are automatically included in in-situ balancing.
• Operating Temperature: Thermal expansion and the effect of temperature on bearing clearances are present during in-situ balancing but absent in a cold shop environment.
• Process Loads: For equipment like pumps and fans, the aerodynamic or hydraulic forces present during actual operation affect the rotor’s balance state.
• Assembled Fit and Clearances: The exact way components fit together in their final assembly affects balance, and this is captured by in-situ methods.

3. Reduced Downtime

In-situ balancing can often be completed in a matter of hours, whereas removing a rotor, balancing it in a shop, and reinstalling it can take days or weeks. For critical production equipment, this reduction in downtime translates directly to increased productivity and reduced lost revenue.

4. Lower Cost

Eliminating transportation, shop labor, and disassembly costs makes in-situ balancing significantly more economical for most applications.

5. Immediate Verification

After installing correction weights, the machine can be immediately started and the results verified under actual operating conditions. If additional adjustment is needed, it can be made immediately without another round of disassembly.

When In-Situ Balancing is Most Appropriate

While in-situ balancing is widely applicable, it is particularly advantageous in these situations:

• Large Machinery: Equipment that is difficult or costly to disassemble and transport, such as large fans, blowers, and crushers.
• Permanently Mounted Rotors: Rotors that are assembled in place and not designed for easy removal.
• Field Equipment: Machinery at remote sites where transporting to a shop would be impractical.
• Emergency Repairs: Situations where rapid turnaround is critical to resume production.
• Routine Maintenance: Periodic rebalancing to correct unbalance caused by wear, buildup, or erosion.
• Custom or Non-Standard Equipment: Machines that would not fit standard balancing shop equipment.

The In-Situ Balancing Process

The procedure follows the standard influence coefficient method, adapted to the field environment:

Step 1: Initial Assessment

Before beginning, verify that unbalance is actually the problem. Check for other mechanical issues such as misalignment, looseness, or bearing defects that might be misdiagnosed as unbalance.

Step 2: Install Sensors

Attach vibration sensors (typically accelerometers) to the machine’s bearing housings using magnets, studs, or adhesive. Install a tachometer or keyphasor to provide the once-per-revolution phase reference signal.

Step 3: Initial Measurement Run

Run the machine at its normal operating speed and record the initial vibration vectors.

Step 4: Trial Weight Runs

Perform one or more trial weight runs as required by the balancing method (single-plane, two-plane, etc.).

Step 5: Calculate and Install Corrections

The portable balancing instrument calculates the required correction weights. These are then permanently installed by adding weights (such as weld-on patches, bolt-on masses, or set-screw weights) or by removing material (drilling or grinding).

Step 6: Verification

Run a final verification run to confirm vibration has been reduced to acceptable levels.

Equipment for In-Situ Balancing

Modern portable instruments have made in-situ balancing practical and accessible:

• Portable Balancing Instruments: Lightweight, battery-powered devices that combine vibration measurement, phase detection, and balancing calculations in a handheld or laptop-based package.
• Accelerometers: Piezoelectric or MEMS accelerometers with magnetic bases for easy attachment and removal.
• Tachometers: Optical or magnetic sensors that provide the phase reference signal.
• Weight Kits: Assortments of clamp-on, bolt-on, or adhesive weights for temporary trial weight and permanent correction installations.

Challenges and Considerations

While in-situ balancing is highly advantageous, it does present some challenges:

1. Access to Correction Planes

The rotor’s correction planes must be accessible while the machine is assembled. On some equipment, guards or covers must be removed to reach balancing surfaces.

2. Environmental Factors

Field conditions (temperature extremes, dirt, noise, vibration from nearby equipment) can complicate measurements compared to a controlled shop environment.

3. Safety Concerns

Working on operating machinery requires strict safety protocols. Technicians must ensure that trial weights are securely attached and that all personnel maintain safe distances from rotating components.

4. Mechanical Issues

If the machine has underlying mechanical problems (soft foot, misalignment, loose mounts), these must be corrected before balancing. In-situ conditions make some of these issues harder to detect and correct.

5. Limitations for Extreme Precision

For applications requiring extremely tight balance tolerances (such as precision grinders or high-speed spindles), shop balancing on dedicated machines may still be preferable or may be used in combination with in-situ balancing.

Comparison: In-Situ vs. Shop Balancing

Aspect	In-Situ Balancing	Shop Balancing
Disassembly Required	No	Yes
Operating Conditions	Actual conditions	Idealized conditions
Turnaround Time	Hours	Days to weeks
Cost	Lower	Higher
Precision	Good	Excellent
Applicability	Most machinery	Small to medium rotors

Industry Standards and Best Practices

In-situ balancing is recognized and covered by international standards such as ISO 21940-13, which provides criteria and safeguards for the in-situ balancing of medium and large rotors. Following these standards ensures safety, effectiveness, and consistent results.

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