Application and Maintenance Guidelines for the Universal Testing Machine
Universal Testing Machines (UTMs) are widely used for tensile testing of metals, rubber, plastics, and other engineering materials. With appropriate fixtures, the same machine can also be used for compression, flattening, and bending tests.
Field statistics show that approximately two thirds of UTM failures are not caused by the machine itself, but by improper operation and insufficient maintenance.
Based on practical experience, this document outlines the correct operation, routine maintenance, and key precautions for the Universal Testing Machine, with tensile testing taken as a representative example.
Field statistics show that approximately two thirds of UTM failures are not caused by the machine itself, but by improper operation and insufficient maintenance.
Based on practical experience, this document outlines the correct operation, routine maintenance, and key precautions for the Universal Testing Machine, with tensile testing taken as a representative example.
Operation of the Universal Testing Machine and Key Precautions
Before any test is conducted, the machine itself must be confirmed to be in proper working condition. The testing machine shall be periodically calibrated in accordance with JJG 475-2008 “Verification Regulation of Electronic Universal Testing Machines” by an authorized metrology body. Only machines that have passed verification may be put into service. In addition, intermediate checks should be performed regularly by inspection personnel to ensure measurement accuracy and long-term stability.
All operators must receive proper training before using the universal testing machine. They should understand the basic structure, operating principles, and performance characteristics of the machine, and be familiar with relevant testing standards or technical specifications as well as correct operation and maintenance procedures. Where necessary, detailed operating instructions should be documented. Operation should be restricted to designated personnel, and unauthorized use must be prohibited.
Before the test, the operator should estimate the maximum load expected during testing or the anticipated failure load of the specimen. The load range (dial range) should be selected according to the following principles:
the estimated maximum test load should be approximately 75 percent of the maximum dial capacity, or the expected failure load of the specimen should be no less than 20 percent of the dial’s full scale.
Based on the selected dial range and the three available measurement ranges of the testing machine, the appropriate pendulum weights should be installed in ascending order, namely weight A, weights A plus B, or weights A plus B plus C.
After installing the selected dial and pendulum weights, the indicator needle must be accurately set to zero to ensure correct load measurement.
During testing, no tools or miscellaneous items are allowed on the boat-shaped working table. Machine vibration during operation may cause objects to fall, posing a risk to personnel or causing damage to the equipment.
For specimen gripping, suitable grips must be selected according to the specimen’s shape and dimensions. The specimen should be clamped along the full effective length of the grips to avoid insufficient contact area, which may lead to specimen deformation, crushing, or damage to the grips themselves. The upper and lower grips must be symmetrically aligned, with the specimen centered along the loading axis.
All operators must receive proper training before using the universal testing machine. They should understand the basic structure, operating principles, and performance characteristics of the machine, and be familiar with relevant testing standards or technical specifications as well as correct operation and maintenance procedures. Where necessary, detailed operating instructions should be documented. Operation should be restricted to designated personnel, and unauthorized use must be prohibited.
Before the test, the operator should estimate the maximum load expected during testing or the anticipated failure load of the specimen. The load range (dial range) should be selected according to the following principles:
the estimated maximum test load should be approximately 75 percent of the maximum dial capacity, or the expected failure load of the specimen should be no less than 20 percent of the dial’s full scale.
Based on the selected dial range and the three available measurement ranges of the testing machine, the appropriate pendulum weights should be installed in ascending order, namely weight A, weights A plus B, or weights A plus B plus C.
After installing the selected dial and pendulum weights, the indicator needle must be accurately set to zero to ensure correct load measurement.
During testing, no tools or miscellaneous items are allowed on the boat-shaped working table. Machine vibration during operation may cause objects to fall, posing a risk to personnel or causing damage to the equipment.
For specimen gripping, suitable grips must be selected according to the specimen’s shape and dimensions. The specimen should be clamped along the full effective length of the grips to avoid insufficient contact area, which may lead to specimen deformation, crushing, or damage to the grips themselves. The upper and lower grips must be symmetrically aligned, with the specimen centered along the loading axis.
After starting the oil pump and opening the oil supply valve slightly to raise the working piston, the oil valve should be closed. One end of the specimen is then clamped in the upper grip. After zeroing the indicator, the lower grip is adjusted to securely clamp the lower end of the specimen.
At the beginning of the tensile test, the oil supply valve may be opened more widely to raise the working table efficiently and reduce auxiliary time, allowing the pump output to fully enter the cylinder. Once the specimen begins to bear load, the loading rate must be adjusted strictly according to the relevant test standard or technical specification. The oil supply valve must not be closed abruptly, as a sudden drop in load may affect the accuracy of test results.
After specimen fracture, the oil supply valve should be closed, and the return oil valve should be opened slowly to allow oil to flow back into the tank, unloading the system and returning the working piston to its original position. Care should be taken not to overtighten the oil supply valve handwheel, as this may damage the needle valve tip. The return oil valve must be firmly engaged to prevent load instability caused by leakage.
Test data should then be recorded, the passive indicator needle returned to zero, and the fractured specimen removed.
After completing the tensile test, the working piston should be left approximately 20 mm above the bottom of the oil cylinder. This facilitates subsequent operation and helps prevent air from entering the hydraulic system. Any debris or fragments in the grips should be cleaned promptly. If grip teeth become clogged, they may be cleaned using a steel brush dipped in gasoline. Sharp or hard tools must not be used to avoid damaging the grip surfaces.
At the beginning of the tensile test, the oil supply valve may be opened more widely to raise the working table efficiently and reduce auxiliary time, allowing the pump output to fully enter the cylinder. Once the specimen begins to bear load, the loading rate must be adjusted strictly according to the relevant test standard or technical specification. The oil supply valve must not be closed abruptly, as a sudden drop in load may affect the accuracy of test results.
After specimen fracture, the oil supply valve should be closed, and the return oil valve should be opened slowly to allow oil to flow back into the tank, unloading the system and returning the working piston to its original position. Care should be taken not to overtighten the oil supply valve handwheel, as this may damage the needle valve tip. The return oil valve must be firmly engaged to prevent load instability caused by leakage.
Test data should then be recorded, the passive indicator needle returned to zero, and the fractured specimen removed.
After completing the tensile test, the working piston should be left approximately 20 mm above the bottom of the oil cylinder. This facilitates subsequent operation and helps prevent air from entering the hydraulic system. Any debris or fragments in the grips should be cleaned promptly. If grip teeth become clogged, they may be cleaned using a steel brush dipped in gasoline. Sharp or hard tools must not be used to avoid damaging the grip surfaces.
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