Analysis of Repeatability Anomalies and Common Errors in Testing Machine Calibration

　　Universal Material Testing MachineandPressure Testing MachineThese are the main equipment for testing construction engineering materials. Due to the characteristics of the construction industry, testing machines are often moved along with the project, and their operating environment is relatively poor, making them prone to errors and anomalies. Therefore, testing machines must not only undergo measurement calibration after each move but also be calibrated periodically. When errors and anomalies in repeatability are found during the calibration process, it is essential to gradually investigate the causes, eliminate errors, and rule out anomalies.

1. Analysis and Handling of Anomalies in Repeatability of Indications 1.1 Repeatability Exceeding Tolerance Due to Loose Fixing Screws of the Active Needle This type of problem is generally not easy to detect, but it does occur from time to time. During the transportation and use of the testing machine, the fixing screws of the active needle may loosen due to vibration and insufficient tightening, causing the position of the active needle to change at any time during use, leading to the inability to adjust the zero position of the testing machine and significant fluctuations in indications.

This problem manifests as: when using the progressive zeroing method, it is always impossible to adjust accurately and cannot strictly align with the zero position. In practical work, this can be confirmed by the following method: fix the screw rod with the right hand, and with the left hand, move the pointer device in the center of the dial glass, allowing the follower needle to gently strike the active needle. If the active needle moves, it can be concluded that the fixing screw is loose. Retightening the screw will resolve the issue.

　　1.2Testing MachineRepeatability Exceeding Tolerance Due to Issues with the Main Swing Bearing Since the main swing bearing is in a relatively sealed environment, external dust and impurities are not easy to enter. The most likely problems are: 1) Rusting of the bearing, which increases friction when rotating. This is due to the humid environment in which the testing machine is used, without controlling the relative humidity of the operating environment; 2) Long usage time of the testing machine or inherent quality issues, leading to fatigue detachment or jamming. Such problems have a significant impact on small force values, not only causing relative errors to exceed tolerance but also increasing the variability of indications.

Since such problems cannot be directly observed, they often require experience to judge. If there is not much certainty, do not easily disassemble the main swing, as disassembling and installing the swing assembly is quite troublesome. After determining that there is a problem with the main swing bearing and disassembling it, rust stains can often be found on the bearing, accompanied by jamming phenomena. For handling such problems, we generally advocate directly replacing the bearing with a new one. Care must be taken during installation to avoid any damage. To reduce friction while preventing rust, a few drops of clock oil or transformer oil can be added to the bearing, and reassembly can resolve the issue. 2. Common Causes of Errors and Methods of Elimination 2.1 Errors Caused by Incorrect Installation of the Testing Machine If the testing machine is not installed level, it will increase the friction between various moving parts, affecting vertical installation, thus introducing errors into the testing machine.

1) The main unit is not installed level. Friction will occur between the working piston and the working cylinder, and friction will also occur between the testing machine's working platform and the guide wheel on one side, resulting in errors, generally manifesting as positive errors, which decrease as the load increases. 2) The force gauge part is not installed level. If the force gauge is not level front and back, it will create friction between the swing axis and the bearing, and its error generally manifests as negative errors.

The characteristics of errors caused by the above two factors are that they have a significant impact on small loads and a small impact on large loads.

2.2 Errors Caused by Friction Resistance 1) Friction resistance in the main unit. The friction resistance of the testing machine mainly occurs between the working cylinder and the working piston. In addition to being installed unlevel, dirt in the cylinder and excessive oil viscosity can also increase friction resistance. Additionally, improper positioning of the guide wheels on the working platform can also increase friction with one side of the column. 2) Friction resistance in the force gauge part. There are many reasons for friction resistance in the force gauge, such as dirt between the force cylinder and the force piston, excessive oil viscosity, high friction of the follower needle on the indicating device, dirt on the gear rack, or the limit piece on the rack being pressed too tightly, and wear or breakage of the belt on the force piston.

2.3 Methods of Elimination For the above errors, first check whether the testing machine is installed level. Use a frame level to level the main unit in two mutually perpendicular directions outside the working cylinder. For the force gauge, adjust the front and back level of the force gauge on the front of the swing rod, aligning the edge of the swing rod with the inner scale line and fixing it, then use a level against the side of the swing rod to adjust the left and right level of the machine body. For dirt in the cylinder, oil can be drained for cleaning, and suitable viscosity oil can be replaced. If the friction of the follower needle on the indicating device is too high, and the gear rack is too dirty, it can be cleaned with gasoline, and the tightening screws and limit pieces on the rack can be adjusted, and the belt on the force piston can be replaced. All these measures can achieve the goal of eliminating errors and ensuring the testing machine is in a qualified state for use.Tai'an Tiancheng Testing Equipment Co., Ltd. was established in

2009 and is a new technology enterprise integrating design and development, production and sales, after-sales maintenance, and import and export trade. The company is located in the western part of Tai'an, 5 kilometers west of Tai'an Station.Since its establishment, our company has continuously innovated and developed, steadily advancing, and has successively passed the EUCE certification, ISO9001 quality system certification, and

our products cover all over the country and are exported to countries such as South Korea, Japan, Malaysia, Vietnam, the Philippines, Myanmar, Thailand, Indonesia, Angola, Saudi Arabia, Congo, Spain, Germany, Austria, Peru, and the United States.The company adheres to the corporate spirit of "Quality Creates Brand, Service Seeks Development," continuously innovating, striving to build a skilled and high-quality after-sales service team to relieve customers of worries.CE certification, ISO9001 quality system certificationWe sincerely hope to work hand in hand with colleagues from all walks of life to develop together and create brilliance!