1Universal material testing machineScope of Application
This regulation applies to the internal calibration of universal tensile and compressive testing machines (hereinafter referred to as "testing machines") with a maximum test force range of 2.5kN to 2000kN for new manufacturing, use, and repair, covering initial calibration, subsequent calibration, and in-service inspection.
2、 Verification basis
JJG 139-2014/2017 "Verification Regulations for Tensile, Compressive, and Universal Testing Machines"
Clarifying the technical requirements, calibration conditions, calibration items, and methods of the testing machine is the core basis.
GB/T 228-2010 "Tensile Test Method for Metallic Materials at Room Temperature"
Specify the requirements for setting experimental parameters and processing results.
GB/T 16491-1996 "Electronic Universal Testing Machine"
Special requirements for electronic testing machines.
3、 Verification conditions
Environmental Requirements
Temperature: (10-35) ℃, temperature change during calibration process ≤ 2 ℃.
Relative humidity: ≤ 80%.
Power supply: Dedicated stabilized power supply, using the "five wire connection method", with stable voltage.
Vibration and corrosion: Keep away from vibration sources and corrosive gases.
Verification equipment and supporting tools
Standard force gauge: covering the range of the tested machine (such as BZL-1kN to BZL-2000kN).
Coaxiality tester: used for coaxiality testing of high-precision testing machines.
Level, stopwatch, vernier caliper, steel ruler: auxiliary measuring equipment for levelness, time, displacement, etc.
Electronic extensometer: measures deformation with accuracy that meets test requirements.
Standard weights and hardness testers: used for force and functional testing.
4、 Verification items and methods
Appearance and preliminary inspection
Check whether the identification of the testing machine name, model, factory number, manufacturer name, etc. is clear.
Confirm that all components are securely connected and free from looseness or damage.
Check if auxiliary equipment such as power supply, air source/hydraulic source are functioning properly.
Zero position check and adjustment
The testing machine needs to be able to automatically zero after replacing different dials or stopping for a long time.
When manually adjusting the zero point, ensure that the dynamometer is close to the upper pressure plate and clear the gross weight.
Test force verification
Selection of verification points: Usually, five points are selected, namely 20%, 40%, 60%, 80%, and 100% of the maximum test force.
Operation steps:
Place the standard force gauge at the center of the lower clamp, connect the display and adjust it to the corresponding channel.
Pre press three times to the maximum test force and eliminate mechanical clearances.
Apply the test force steadily to each inspection point and record the readings.
Repeat the verification three times, take the average as the standard value, and calculate the error.
Error requirement: The indication error must comply with the allowable range corresponding to the testing machine level (such as 0.5 level testing machine error ≤± 0.5%).
Coaxiality inspection
Applicable objects: 0.5 level testing machines need to be calibrated every time, and 1 level testing machines will not be tested after the first calibration.
Detection method:
Connect the standard test bar to the testing machine fixture.
Install an electronic extensometer in each symmetrical direction of the test bar.
Apply initial force (1% of maximum test force) and adjust the zero point.
Gradually increase to 4% of the maximum test force, record the elastic deformation on both sides, and repeat three times.
Rotate the test rod 90 °, repeat the above steps, and calculate the coaxiality after completing six measurements.
Judgment criteria: The coaxiality error must meet the requirements of the regulations (such as ≤Φ 0.2mm).
Calibration of displacement measuring devices
Use a standard ruler or laser interferometer to measure displacement readings.
Compare the displayed values of the testing machine with the standard values and calculate the relative error.
Functional and stability testing
Functional testing: Verify whether parameters such as load capacity, displacement, and deformation meet the design requirements.
Stability test: Run continuously for a period of time to observe control stability and measurement repeatability.
5、 Processing of verification results
Error calculation and judgment
Based on indicators such as indication error, zero drift, coaxiality, etc., determine the accuracy level of the testing machine (0.5 level, 1 level, 2 level).
Example: If the indication error of a testing machine at the maximum test force 100% verification point is+0.4%, it meets the requirement of level 0.5.
Calibration report and identification
Attach the certificate of conformity to the qualified testing machine, fill out the calibration report, and indicate the calibration date, validity period, and inspector information.
Unqualified testing machines need to be repaired or scrapped, and re calibrated after repair.
Record keeping
Calibration records must be kept for at least 3 years for traceability and review.
6、 Verification cycle
Regular cycle: generally not exceeding 1 year.
exceptional case:
When used frequently or in harsh environments, shorten the cycle to 6 months.
After repair or replacement of critical components, re calibration is required.
7Universal material testing machinePrecautions
Preheating and stabilization: The test machine needs to be powered on for the first time by pressing the open/close button three times, preheating for 30 minutes before calibration.
Safety protection: When operating high-voltage or high load testing machines, wear protective equipment to avoid accidental injuries.
Standard substance management: Standard force measuring instruments, weights, etc. need to be traced regularly to ensure accurate measurement values.
Environmental monitoring: Continuously monitor temperature and humidity during the calibration process, and suspend calibration when exceeding the standard.