Repair and deal with fault problems of universal testing machine

Universal testing machineIt is widely used in laboratory laboratories of all walks of life. Some failures often occur during use. If not eliminated in time, it will affect the quality of the project and the accuracy and reliability of the inspection data. Hengsi Shanda Instruments summarizes the common fault machines and treatment methods in the verification of universal testing machines over the years as follows, so that we can be targeted in our future work, prescribe the right medicine, and achieve twice the result with half the effort.
1. Exceeding value exceeding the difference and processing
1. When the 1 display value exceeds 1%, find the reason from below:
(1) The heavy hammer number of the pendulum is inconsistent with the test machine.
(2) The body is inclined and the installation verticality does not meet the requirements.
(3) Deformation of push rods, press plates, pendulums, etc.
(4) The blade is loose or damaged.
(5) The fixture is twisted or different.
(6) Changes in the weight of the small hammer on the pointer shaft and other things.
In addition, if the display error exceeds 1%, the following situations should be considered:
(1) The resistance of the needle attached to the dial is too large.
(2) The resistance generated by the drawing mechanism is too large.
(3) The tooth rod and the gear are too dirty or the teeth are too tightly connected, and the reed may be controlled to press the tooth rod.
(4) The bearings and toothed rods at pendulum, pointer shafts, links, etc. are too dirty or rusty.
(5) The force measuring piston has greater friction.
(6) There is friction between the link rod or bearing and the body.
1. 2 The display error exceeds 11%, but the difference values ​​are basically the same?
(1) The ratio of lever arm changes. If the blade of the pendulum short arm is loose and it is severely displaced after being subjected to stress, it should be adjusted and tightened.
(2) The distance between the contact point between the push rod and the press rod and the pendulum axis changes. If the error is negative, try to increase this distance slightly, otherwise it should be reduced.
1. What is the reason for the inconsistency between the front and back of the 3-degree dial?
The starting point of the dial is >-1%, but it increases with the increase of load, which is caused by the following situation.
The force measuring mechanism is inclined toward the direction of the pendulum lifting, and its non-verticality should be adjusted as described above.
(2) The toothed rod is not perpendicular (or bent), and one end in contact with the pressure plate is low. Check the straight toothed rod or adjust and raise its contact end.
(3) The angle between the pressure plate and the perpendicular line of the tooth rod is reduced (the pressure plate is deformed inward), and the pressure plate should be checked and straightened.
1. 4 Reasons for errors of small dials (even including the starting point of the intermediate dials) exceeding -1%:
(1) The resistance of the secondary needle is too large. Clean it and add a little lubricating oil or adjust the rotation of the secondary needle to be flexible.
(2) The bearings or gears of the swing shaft and pointer shaft are too dirty and rusty. Lubricating oil with a very small concentration should be added after scrubbing.
(3) The force-measuring piston is not perpendicular, the force-measuring piston is too dirty, the surface is rusted or the device that reduces friction loses its function, the lower end of the piston does not fall correctly on the bracket, causing bending and twisting, etc., so that the friction of the force-measuring piston increases. Strictly check whether all parts of the force-measuring piston are correct and eliminate incorrect phenomena.
1. What is the reason for the prominent display error at a certain point in the middle of the 5-degree dial?
The display error of a point in the middle of the dial is prominent and the negative value may be due to:
(1) When the secondary needle turns to this direction, the friction resistance is particularly large, so the reed of the secondary needle should be cleaned and adjusted.
(2) The pointer shaft is bent or the teeth (including gears) are damaged, or there are obstacles, which increases resistance and should be inspected and repaired.
(3) The force measuring piston cylinder housing has a burr in some places in the two grooves that fix the force measuring piston position, so that the force measuring piston stops falling at this point, and should be checked and repaired.
(4) It is rare to see if the value error of a certain point in the middle of the dial is protruding and the positive value is biased. Even if it is present, it is possible to check whether the rack is raised at this point.
1. What is the reason why the error of a 6-degree dial is particularly negative?
(1) The safety switch position should be adjusted improperly.
(2) If there is an obstacle under the pendulum or linkage, it should be checked and eliminated.
(3) The thread sinker on the pointer axis should be eliminated.
(4) The starting point of the drawing mechanism or push rod is adjusted improperly and there is an obstacle before reaching the limit position. The adjustment contact head should be checked.
1.7 What is the reason for the display error of a certain degree dial (the errors of each point are basically the same)?
The main weight of the code removal does not meet the design requirements. The code removal number and weight should be checked, and the weight should be calculated. The loading test should be performed by using the loading test. After knowing that the value is qualified, the code removal code should be replaced according to the new weight. However, if the weight of the original code exceeds the weight, it is generally not advisable to use the method of reducing the weight of the code removal before sufficient accounting basis. The code removal code should be replaced, and the original code should be temporarily saved. It is not advisable to drill holes in the code removal code to reduce the weight.
1. 8 What is the reason for the difference in the display value change?
(1) Caused by unstable friction, such as the bearings inflexible at pointers, push rods, pendulums, etc., the working pistons and force measuring pistons cause abnormal friction, and should be cleaned.
(2) The blade is loose or defective, and it should be checked to be fixed tightly. If the blade is defective, it should be replaced.
1. 9 Vibration
When the test machine is started, especially during loading, when the pointer shakes or the extensometer measure the deformation of the sample, the reason for the scale shake in the measurement mirror is:
(1) Mechanical resonance: It comes from the vibration of other machines near the test machine, such as forging, stamping, heavy machinery, metal cutting machine tools, high-power motors, etc., which causes the resonance of the test machine. Therefore, try to avoid this factor when the test machine is installed.
(2) If the installation foundation is not firm or the anchor screws are loose, the anchor screws should be fixed and the foundation should be strengthened if necessary.
(3) There is still gas in the oil pump and oil circuit system. Since there is air in the oil pump, the oil output is intermittent, which causes vibration. At this time, relax the screws in the nut and let the oil pump rotate by itself until the air in the pump is discharged, and then tighten the screws. Air will also exist after the main cylinder is taken over, which will also affect the jitter of the pointer, so the air must also be eliminated. The method is: start the oil pump, close the oil return valve, open the oil supply valve, and after the main working piston rises for a certain distance, open the oil return valve, so that the oil in the main oil cylinder returns to the oil tank quickly. This way, repeats several times, and the air in the oil circuit system can be exhausted.
1. 10 Reasons for the loading pointer to swing very much or the load cannot be maintained:
(1) The viscosity of oil is too small;
(2) A large amount of air exists in the oil pressure system;
(3) The oil leakage or the oil return valve of the oil pressure system is not tightly closed;
(4) The spring force of the pressure regulator valve is too small;
(5) There are impurities in the oil supply valve.
In this case, first eliminate the gas from the hydraulic system or check for oil leakage (including the oil return valve not closed tightly). If a large amount of oil overflows around the piston, it is necessary to check whether the overflow pipe is blocked, the piston is worn or the viscosity is too low, and it is treated separately according to different situations. If there is no oil leakage after exhaust, but the load cannot be eliminated, the oil supply valve should be cleaned and the spring of the pressure stabilizer valve should be strengthened.
1. 11 Reasons for not adding loads or not adding loads:
(1) The oil tank does not store enough oil;
(2) The viscosity of the oil is too small;
(3) The oil pressure system has severe oil leakage;
(4) The belt that drives the oil pump to loosen;
(5) The spring pressure of the pressure regulator valve is insufficient;
(6) The throttling pin hole in the oil supply valve is blocked;
(7) The oil pump is not working properly.
In this case, first check whether the high-pressure oil circuit system is leaking, whether the oil storage in the oil tank is enough, whether the pulley is loose, and whether the oil flow at the return oil pipe is increased when the load cannot be increased. Under normal circumstances, the larger the load, the oil flow of the return oil pipe will not change or become smaller (for different test machines). Check the working conditions of the oil supply valve, oil pump, etc.
1. The reason for the return oil pipe spraying and vibrating in the middle of the loading:
When some material testing machines load into their range, the oil flow rate of the oil return valve of the test machine suddenly increases to oil injection. At this time, the oil pressure system vibrates violently and the load cannot increase any further. The reason is:
(1) The spring pressure of the pressure regulator valve is insufficient;
(2) The throttle pinhole is blocked.
In this case, the throttle valve should be cleaned and the pressure spring of the pressure regulator valve should be observed to be invalid. You can add a gasket to the back of the spring to increase the spring pressure.
1. 13 Poor pendulum falls:
Under normal circumstances, the function of the buffer must be that when the load gradually increases, the high-pressure oil passes through the buffer into the force measuring cylinder smoothly. When the sample breaks, the swing rod and the pendulum can slowly return to the vertical position. The oil set in the force measuring cylinder can slowly flow back to the oil tank, and it must not affect the sensitivity when the pointer returns to zero.
1. 14 Reasons for the pendulum not to be adjusted to the vertical marking position:
(1) The force measuring mechanism should be tilted to one direction and should be adjusted to be vertical.
(2) The weight of the upper chuck part of the test machine does not meet the design requirements. The weight should be checked to make it equal to the original clamp weight.
(3) If the weight of the balance hammer changes, or its rod is seriously bent and deformed, it should be straightened and tried to check whether its weight meets the requirements, otherwise it should be corrected.
1. The reason why the pointer zero point is cleverly adjusted (especially when the small order) is poor, or the pointer zero point position often changes during use.
(1) Caused by unstable friction, such as the bearings inflexible at pointers, tooth rods, pendulums, etc., the working pistons and force measuring pistons should be cleaned if there is abnormal friction.
(2) The buffer oil return valve is in poor condition or has friction, so it should be cleaned and adjusted.
(3) The force-measuring piston does not rotate, causing friction. Check the motor and belt to rotate.
(4) Use oil with high viscosity, and replace oil with low viscosity.
1. Reasons for the 16th reason why the pendulum cannot be lifted to the limit position:
(1) The position of the baffle on the link is too low. If the pointer has not been turned for a while, the safety button should be touched.
(2) When the balance hammer touches the body, the balance hammer should be adjusted.
(3) The position of the pointer or push rod is adjusted improperly.
(4) The vertical position under the pendulum is incorrect, and the vertical position of the pendulum should be adjusted.
(5) The control screws on the square iron partition plate of the pendulum spindle are too high. The control screws should be adjusted to the pointer that can rotate slightly more than 2 to 3 small grids for one round. At this time, the baffle on the linkage first touches the safety button, and then the square hammer comes into contact with the control screws one after another. If you do not pay attention to this situation, the instrument will be damaged unexpectedly after driving.
(6) When the lower end of the force-testing piston link touches obstacles, it must be carefully inspected and eliminated.
1. 17 When the working piston rises at no load, the pointer swings or points out the reason for a certain load:
(1) The weight balance of the force measurement system has not been adjusted yet. If the vertical position of the pendulum is not adjusted, the pendulum should be adjusted first to align it vertically and point to zero.
(2) There is a large friction among the working piston or four pulleys on the main body. The pulley should be adjusted. If there is friction on the piston, the piston should be raised to the limit position, cleaned and observed carefully. If there is rust or mechanical damage, it should be carefully corrected.
1. When unloading, the pendulum has returned to the vertical position, while the dial pointer is still in the middle. What is the reason:
(1) The tooth rod and the gear teeth are too tightly connected or there are dirt attached therein.
(2) The tooth rod is bent or the tooth tip is deformed.
(3) Pointer wiper or bearing rust.
(4) Control the weight of the small hammer of the push rod to change.
Use the hand-pull push rod to see if it can be returned to position after gently release. If it cannot be returned to position, check whether the tooth rod is flexible and whether the teeth are damaged, clean or trim separately.

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