Core hints: the handling of the plunger of Hyuadai HE-280 excavator hydraulic pump: a South Korean Hyuadai HE-280 excavator after the overhaul and replacement of the cylinder and plunger of the hydraulic pump, when it is started after starting (the temperature of the night is -30 C), the hydraulic pump does not work and is accompanied by abnormal sound, the dismantling found, the plunger and the cylinder. Stick together, "bite the dead" state.
A South Korean Hyuadai HE-280 excavator, after the overhaul and replacement of the cylinder and plunger of the hydraulic pump, should be opened after the start of the pump (the temperature of the night is -30 C), the hydraulic pump does not work and is accompanied by abnormal sound. The dismantling found that the plunger and the cylinder are stuck together and "bitten" state.
At the beginning, it was thought that the hydraulic oil was not clean, but the plunger "bitten" occurred after the replacement of the clean oil. For this reason, the cylinder and plunger of "bitten" were analyzed by metallographic analysis. Through analysis, the room temperature of the plunger (20 degrees C) was organized as martensite + retained austenite. But when the plunger material reaches room temperature, the Ms point (the starting point of the austenite transformation martensite) is above room temperature, and the Mf point (martensite transition end) is at room temperature, so a considerable amount of unconverted retained austenite will be retained. Because the retained austenite is an unstable phase, it will change in the following two cases: at the Ms point, the plastic deformation of austenite will cause the normal martensite transformation, the larger the deformation, the more martensite variable; when the temperature of the material is lower to the room temperature, the residual austenite will continue to change into martensite, temperature and temperature. The lower the degree, the greater the amount of change.
Since austenite is a surface centered cubic structure, martensite is a body centered cubic structure, and in the cubic lattice of the center of the center, 74% of the volume is occupied by the atom, and the other 26% is the clearance volume. In the body centered cubic lattice, 68% of the volume is occupied by the atom and the other 32% is the clearance volume. So when austenite is transformed into martensite, the volume will expand.
For the first transformation, the vibration between the cylinder and the plunger is smaller because of the smooth operation of the excavator, so even if the austenite turns to martensite, its turn variable is very small, but for the second transformation, the minimum temperature in winter in the northeast can reach below -30 C, in such a cold day. Under the air, the residual transformation will be completed in a short period of time, causing the plunger to "bite" because of its instantaneous volume. The cause of the failure of the machine is also the same.
In order to solve the above problems, the unused cylinders and plungers can be processed according to the following procedures:
(1) use special measuring tools to measure the fit clearance between the cylinder block and plunger of the hydraulic pump at room temperature.
(2) cold treatment of cylinder block and plunger shall be carried out at -50 ~ -60 C, and removed after 30min.
(3) match dimensions of the plunger during grinding to room temperature with a grinder.
(4) laser quenching on the surface of the plunger
(5) polishing the surface of the plunger with metal polishing paste.
After being treated by the above method, there is no phenomenon that the plunger is killed.
