Vibration Testing Equipment Suppliers From China

Vibration Test Machine FAQ Guide

1. What is a vibration test machine?

The vibration test machine is a machine condition monitoring instrument based on the latest microprocessor design and is equipped with vibration detection, bearing condition analysis, and infrared temperature measurement functions. It features simple operation, an automatic indicator state alarm, very suitable for field equipment operation, and maintenance personnel to monitor the state of equipment. This helps the personnel timely find out potential or existing problems in the tested equipment so as to ensure the normal and reliable operation of equipment.

To be specific, a vibration test machine simulates the vibration environment of certain equipment under laboratory condition, and test the impact strength as well as reliability of various vibration test applications. In the laboratory, with the help of a vibration testing system, simulations of extreme shock, the random push of outer force, resonant search and dwell, classical shock and road models, etc. can be achieved. It is necessary for product quality assurance, new product research, and development.

This test system generates vibration according to the parameters such as arbitrary force, acceleration, and frequency. It can evaluate various industrial products by applying vibration load.

This system can be divided into a vibration generator, a power amplifier, and a vibration control system. It can provide a vibration test to cope with various loads such as sine vibration, random vibration, mechanical shock pulse, and replication of real-time trace to provide technical support for establishing product quality inspection.

2. What’s the main structure of the Vibration Test Machine?

Here are the common structures of a vibration test machine:

1) Vibration Generator

Shaker drive coil current can be produced directly or inductively. The driving coil, the major component of the shaker, is added current directly from the amplifier output in the direct kind. The induction type involves applying an alternating current to a stationary coil in order to induce a current in the drive coil. The induction shaker has a straightforward structure and doesn’t need a drive coil with a lead-in connection, but its effectiveness isn’t very high. This structure is used by some of UD’s shakers in the United States. Because the driving coil lead-out cable issue has been satisfactorily resolved, our vibration system’s direct-type items are more useful.

Permanent magnet type and excitation type are two different ways that shakers generate magnetic fields. Because it is challenging to produce big magnets, the permanent magnetic field is produced by a long-lasting magnet, which is now only useful for tiny shakers. For big shakers, the excitation coil receives a DC current to provide a steady magnetic field.

Single excitation and double excitation are two categories for the excitation type shaker. A magnetic field loop is created by a single set of excitation coils in a single excitation. To ensure a low magnetic field on the working table despite this structure’s low excitation efficiency, high power consumption, and significant leakage, a demagnetizing coil is needed.

The magnetic field on the table is very small because double excitation is produced by two sets of excitation windings that are positioned on the upper and lower sides of the working magnetic gap. The magnetic fields in the working magnetic gap superimpose on one another while canceling out on the table  Additionally, the magnetic resistance is decreased and the excitation efficiency is greatly increased as compared to single-excitation due to the dual-excitation magnetic circuit’s reduction in length.

2) Cooling System

Shakers are cooled in several ways, including natural cooling, forced air cooling, water cooling, and oil cooling. Natural cooling is only applicable to small shakers with very low power. Oil cooling is not common in newly developed shakers due to the complex structure, and the oil-cooled shakers that are still in use should be careful to maintain the quality and quantity of oil.

Forced air cooling is a common cooling method used for small and medium-sized shakers, which uses a high-pressure fan to continuously pump hot air out of the table to achieve cooling. When cooling in this way, the structure of the drive coil and excitation coil is relatively simple, the equipment is easy to install, the cost is low, and there will be no water leakage, water circuit blockage, and other failures common to water-cooled tables.

However, the high-pressure fan is very noisy when working, which has a great impact on the operator. Air-cooled cooling efficiency is relatively low, and not suitable for large shaking table cooling. Water cooling is a common cooling method for large and medium-sized shaking tables.

Usually, the winding of a water-cooled table is wound with hollow enameled wire, and the cooling water is directly passed into the hollow enameled wire for cooling, which has high cooling efficiency and not much noise. But the shaking table structure is more complex, the cooling water quality requirements are higher, and commonly used distilled water or deionized water is.

In the water-cooled table, the equipment of several companies in the United States and Britain has serious defects, the structure of the drive coil lead-in cable and the water pipe is unreasonable and the water circuit of the excitation coil is unreasonable, this structure often leaks and the water quality requirements are extremely high, and the water should be changed frequently.

Our shaker adopts the new structure of parallel connection of water circuit, a series connection of circuit, and the threaded connection of water and electricity joints, which solves these problems very well, and it does not require high water quality, low water pressure, and rarely leaks.

3) Power Amplifier

The power amplifier is an important part of an electrodynamic shaker system, its own performance and matching condition with the shaker is directly related to the performance of the system. The development of power amplifiers has gone through three generations, from electronic tube amplifiers to transistor linear amplifiers to digital switching amplifiers.

Electronic tube amplifier in the new production equipment has been basically not used, switching amplifier have been developed abroad in recent years, it uses the switching characteristics of the transistor, tube consumption is very small, the efficiency can be as high as 90%, while the efficiency of an ordinary linear amplifier is only about 50%.

It is because the switching amplifier itself generates less heat, its cooling is very simple, and the output power of several tens of kVA amplifiers can be cooled down with only a very small axial fan, making the structure of the equipment simple and reliable. Whereas the same linear amplifier must be cooled down with water and has a complex structure.

The technical specifications of the electrodynamic shaker are: rated sinusoidal force, random force RMS, operating frequency range, *maximum acceleration, *maximum velocity, *maximum displacement, the effective mass of the moving part, allowable direct loading mass of the working table, allowable bias moment of the working table, stray magnetic field, distortion of the acceleration waveform, uniformity of acceleration of the working table and transverse vibration ratio, etc.

The excitation force of the shaker is the mass of its moving part multiplied by the acceleration that can be achieved at that mass, not just the weight of the test piece. The rated sinusoidal force is the effective mass of the moving part multiplied by the *maximum acceleration peak value, and the random force effective value is the effective mass of the moving part multiplied by the *maximum acceleration effective value that can be achieved when the shaker is experimented with the power spectral density curve according to the standard (such as ISO5344).

4) Horizontal slip table

The horizontal slip table is an auxiliary device for the vibration test machine to conduct horizontal tests to facilitate the testing of large samples. The horizontal slip table can be divided into hydrostatic bearing support type, ball-bearing support type, and oil film support type, and the large slip table adopts the oil film and hydrostatic bearing support method. Hydrostatic bearing supported slip table can work between very low frequency to very high frequency, with low distortion of acceleration waveform, high anti-tilting moment and anti-torsional moment, and low lateral vibration.

However, this kind of slip table is very costly and expensive. Ball-bearing slip tables can be used from medium frequency to high frequency, and when working at low frequency, the acceleration waveform should produce bearing noise. The oil film slip table has a simple structure, low cost, a good waveform in the low-frequency domain, and is easy to achieve large travel.

However, it has low resistance to overturning and torsional moment and high lateral vibration. Because of the difference in manufacturing cost, we recommend the right horizontal slip table according to the customer’s test so that it can meet all the test conditions of the customer, and the test table size can be customized according to the customer’s needs.

5) Fixture

The fixture is designed to hold the sample firmly on the vibration table and transmit the vibration energy from the shaker to the sample, and its quality is directly related to the quality of the test. The principle of fixture design is that under the premise of meeting the sample installation, the fixture should have as low weight and high stiffness as possible, and there should be as little resonance as possible in the test band. The material of the fixture is mostly magnesium and aluminum because these two metals are lighter than steel, the damping characteristics are better than steel, and the processing cost is low.

Small clamps are usually machined from a single piece of material, while large clamps are made using welding and casting methods. The design should first clarify the test conditions, such as sinusoidal and random vibration energy levels and tolerances, the frequency range of the sinusoidal sweep, the power spectral density curve of the random vibration, the installation conditions, the permissible acceleration unevenness, and the lateral vibration. Then calculate the resonance frequency and mass of the fixture to meet the test requirements.

For small specimens, the resonance frequency of the fixture is not allowed to be less than 1000Hz, and it should reach 3 to 4 times the low frequency of the specimen * at the same time. After the fixture processing is completed, the necessary inspection should be carried out, and for important and commonly used fixtures, such as adapter plates, expansion tables, etc., performance tests should be carried out to ensure the correctness of the test.

6) Vibration Test Machine with Agree chamber

There are three comprehensive test chambers and four comprehensive test chambers for comprehensive environmental tests, and the three comprehensive tests refer to the comprehensive tests of temperature, humidity, and vibration.

The shaker for the three comprehensive tests generally has a large working table, in order to install as many test pieces as possible and it is important to seal and insulate between the shaker and the environmental test chamber, and the silicone rubber plate is a commonly used sealing insulation material. We are developing four comprehensive experimental systems, four comprehensive refers to the temperature, humidity, vacuum, and vibration of the comprehensive environmental test.

3. Why is the vibration test machine needed?

By tracking a machine, a building, or a structure over time, we can determine what is normal behavior for a system, and therefore identify when a system isn’t operating as we expected. Using analytical methods such as Fast Fourier Transforms or Power Spectral Density – allows us to get a deeper insight into the vibration trace. So we can focus our attention and spend our efforts on a specific area.

We can check out mechanical unbalance, looseness of a machine or a system, or unexpected vibration levels, as well as obtain early indications of wear and fatigue of a system. Furthermore, allowing us to avoid certain frequencies, such as resonant frequencies, which could have catastrophic damage to our systems.

The vibration test machine is needed for its functions. To be more specific, it meets different needs in different user scenarios. Here we would like to make a detailed explanation of the necessity of a vibration test machine in different conditions.

• Vibration testing made by a vibration test machine is done by replicating conditions (under a test environment) that a product, machine, or structure might go through or see in its lifetime, including conditions during transit as well as operations. Hence, the vibration test machine helps preempt performance issues and potential failures even before they start or occur.
• Also, industries with 24-hour production cycles need critical vibration testing and monitoring processes and systems. In production-intensive industries like Oil & Gas, Power Generation, Metals & Mining, etc., failing to check the current statement of any machinery or device may lead to loss of efficiency and even lead to higher production costs and an unsafe working environment. Hence, these industries need continuous and regular vibration monitoring and testing.
• Vibration testing and monitoring help in detecting early warning signs for imminent machine failures.
• It is necessary to increase maintenance intervals. If machine health or the building current condition is tracked regularly, maintenance can be scheduled in accordance with the experience of the managers rather than depending on hours of operation.
• It helps in saving costs and making machinery reliable, as there are fewer unexpected failures.
• Vibration test machine also promotes safety as when operators have insight into machine health, they are able to take faulty equipment offline before any accident or catastrophe occurs.
• By providing data that promotes a better understanding of machine health, efficiency and better productivity can be achieved.
• It helps manufacturers ensure the reliability, durability, and end quality of their products and components by testing the shock and stress that the product can handle within the service life.
• A vibration test machine is an instrument for measuring the amount of vibration of objects. It is widely used in bridges, buildings, earthquakes, and other fields. A vibration test machine can also be composed of a vibration measurement system and an acceleration sensor for object acceleration, velocity, and displacement measurement.

4. What are the main features of a vibration test machine?

The vibration test machine is a multi-functional testing machine with a wide range of applications. Its main features include:

• The rugged suspension system and linear motion guiding
• Strong carrying capacity, high stability
• Good guiding functions
• Its load center airbag has high static stiffness and low dynamic stiffness
• Strong carrying capacity
• Perfect performance on amplitude variation
• High efficiency
• Its 3-sigma peak current provides the finest power consumption and minimizes harmonic distortion
• Quick self-diagnosis with safety interlock, high safety reliability
• Airbag shock isolation device for vibration platform reduces the need for additional foundation and can make perfect reproduction of vibrational wave and reduce vibration transmittance
• Provide horizontal and vertical expansion platforms for different application
• Simple controller operation
• Its operating temperature ranges from 5℃to35℃
• Ambient humidity: not greater than 85%RH
• The electronic control, vibration frequency, and amplitude can be adjusted
• Its driving force is large and its noise is small
• It features high efficiency and low fault
• The controller of a vibration test machine is easy to operate, fully closed, and safe
• It has an efficient vibration pattern
• It has a mobile work base that is easy to place, beautiful and generous
• It is suitable for a full inspection of the production lines and assembly lines.

5. What are the applications of vibration test machines?

A vibration test machine is generally applied to the measurement of equipment noise and the maintenance of each element. The vibration test machine is widely used in trade areas and must be verified. It is also applied in the railway survey, the smooth operation of the railway. Its application is related to the safety of people’s lives and property, so it must be strictly verified. A vibration test machine is also used in the medical sector, the building survey aspect, and the detection of earthquake aspect. In the above-mentioned areas, the vibration test machine plays an important role. Besides, there are also other fields that the vibration test machine that is broadly used. These include:

• Automotive parts and systems—qualification testing
• Electronic assembly, computer equipment testing
• Avionics and military hardware testing
• Satellite component testing
• Product and package testing
• General stress screening

6. What are the main parameters you need to know for using a vibration test machine?

• Exciting force
• Maximum displacement
• Maximum acceleration
• maximum frequency
• Maximum velocity
• Max. payload
• Test table size and the mounting hole size
• The number of channels of the controller
• The function of the vibration testing machine
• Number of accelerometers and length of accelerometer cable

7. How to choose a proper vibration test machine?

Understanding your needs is essential to selecting the proper shaker system. Shaker type, size, and exciter power level are dependent on test requirements. If you’re not familiar with options for your tests, you may want to consult our engineer for guidance. It’s best to seek advice early in the selection process because other factors may influence what shake table or vibration system is recommended.

These include:

1) Determining Shaker Sizing

Proper Shaker selection requires the application of Newton’s Second Law of Motion:

• Force = Mass x Acceleration (F=MA)

Vibration systems have output forces ratings defined in terms of:

• Sine force: kg. f (kN) peak
• Random force: kg. g (kN) rms
• Shock force: kg. f (kN) peak

Applying Newton’s Law In Shaker Selection

The suitability of a Specific Test System can be evaluated in terms of the following:

F=Moving MASS x G  x 1.30= Desired Force Shaker System

• Maximum Displacement
• Maximum Velocity
• Maximum test frequency

2) Specimen Specifics

In addition to your test specification, the following test article data is required to determine the appropriate system for your test requirements:

• Specimen Description
• Specimen Test Mass
• Specimen Dimensions
• Specimen Center of Gravity (CG)
• Specimen Mounting Considerations

3) Fixture Specifics

Test fixtures affect mass and resonance and must be considered carefully.  The following concerns should be addressed in selecting a shaker system:

• Do your fixtures exist or will they require design and fabrication?
• What are or will be the approximate dimensions (estimate if necessary) of the fixturing?
• What is or will be the approximate mass (estimate if necessary) of the fixturing?
• Are there any mounting issues (bolt pattern, size)?
• Will a head expander be required?

4) Test Specifications (F=ma)

The maximum Acceleration for the F = MA estimate is derived from the test specification:

• for Sine vibration (G-peak)
• for Random vibration (G-RMS)
• for Classical Shock pulses (G-peak)

The operator must be cognizant of the maximum displacement and velocity of any given test parameter to ensure they don’t exceed the system’s capabilities

5) Evaluating the Test Specifications

Waveform:

• Sine
• Random
• Classical Shock
• SRS Shock
• Mixed Mode (Sine on Random and Random on Random)

6) Understanding Random Vibration

Random vibration-stated force ratings are determined with the guidance of ISO 5344.  ISO 5344 specifies the use of a flat 20 Hz to 2000 Hz spectrum with a test load of three to four times the armature mass. This is done to achieve continuity of ratings between different manufacturers. By use of the non-resonant three to four-time armature mass load the resonant frequency of the shaker armature under test typically will fall below 2000 Hz.  This enables the system to gain free energy at higher frequencies.

7) Effects of Resonance

Every mechanical structure has a resonant frequency, which may result in a significant dynamic force absorber at certain frequencies. This phenomenon must be taken into account during the estimating process. The force rating defined by the manufacturer is rated at the armature surface.

If the test system has associated fixtures, head expanders, slip tables, etc. that act as force absorbers and have been defined as a control accelerometer location, then the shaker may be overdriven. It is always advisable to have a monitor accelerometer attached to the armature surface to determine the “truth force” that is being achieved.

8. What safety precautions should you take before using a vibration test machine? 

•  The specimen must be tightly fixed on the test table in order to avoid resonance and waveform distortion, which will impair the test results of the specimen. The specimen should also not be dismantled while it is vibrating; if you must, stop the vibration system first.
• In order to prevent equipment damage and personal injury, the test fixture should be operated carefully and secured.
• Immediately terminate the test if any anomalies are encountered to prevent harm to the equipment.
• During the vibration system’s operation, the operator cannot touch the sensor.
• Avoid putting magnetic or improperly magnetized things, such as watches or other jewelry, near the vibration testing machine.
• The power amplifier leakage circuit breaker must be disconnected after cooling for 7 to 10 minutes after the signal is turned off in order to give the power amplifier module and the vibration generator enough time to cool.
• Avoid turning off the power amplifier before turning off the control box and power supply to avoid harm from falling objects and the vibration table.