1) The grinding head spindle is overheated and locked

The main reason for this is that the hydraulic oil is mixed with impurities. For example, dust, iron dust, etc. Impurities in the hydraulic oil will block the small oil hole in the bearing bush, resulting in no hydraulic oil in some hydraulic cavities, making the spindle unable to form a symmetrical pressure oil cavity. The spindle is not in a pure liquid state when rotating, and generates heat due to friction with the bearing bush. After disassembling the surface grinder spindle and checking all components, it is found that the spindle roundness is not out of tolerance, but the surface finish is poor. The roundness of the inner hole of the bearing bush does not exceed the tolerance, the inner hole surface has scratches, and the bearing bush section has scratches. The capillary oil hole in the bearing bush is blocked. After polishing the surface of the main shaft and the end face of the inner hole of the bearing bush with metallographic sandpaper, they can meet the use standard.

The difficulty of repair is how to remove impurities from the 0.5mm capillary oil hole in the bearing bush. Capillary pressure balance can be established in the bearing bush only when each oil hole is opened. The bearing bush is assembled in the cast iron bearing sleeve, and a special striker is required to separate the bearing bush from the bearing sleeve. After the bearing bush is separated, the bearing bush can be cleaned and all oil holes can be opened. Finally, clean the oil tank and replace it with new hydraulic oil. After all repair work is completed, it can be reinstalled for commissioning.

2) Poor finish of grinding moving parts

The radial runout of the spindle is out of tolerance, resulting in a large vibration of the grinding wheel during grinding, which leads to poor surface finish of the grinding workpiece.

The main reasons for the surface grinder spindle radial runout out of tolerance are:

(1) The spindle collides or deforms under force.

(2) The roundness of the inner hole of the supporting bearing bush of the main shaft is out of tolerance.

The grinding head of the surface grinder adopts the support mode of the front and rear bearing pads. The static pressure technology is applied to it. There are two oil return grooves with a depth of 0.8mm and a width of 4mm at the front end of the bearing pads. The machining and assembly accuracy of bearing bush will have a serious impact on the service quality of M7140 type hydrostatic grinding head. The clearance between the bearing bush and the main shaft in the diameter direction is 0.07mm, which can be used for fault finding and precision repair. After the main shaft was disassembled, it was found that the main reason for shaft vibration was that the roundness of the inner hole of the bearing bush was out of tolerance, which led to the destruction of the static pressure balance, and caused a large vibration of the main shaft during rotation. The method of grinding can also be used to repair the inner hole of bearing bush and restore the roundness of the inner hole of bearing bush.

First, three grinding rods with different sizes are made of cast iron. Three grinding rods with different sizes are used to repair and grind the inner holes of bearing pads for rough grinding and fine grinding respectively. The length of the grinding rods is 600 mm according to the size of bearing pads, and the grinding rods need to be made into a waist drum shape. Assemble the bearing bush of the main shaft and the steel sleeve in a unified way, and protect the oil path on the surface of the bearing bush during assembly. Use the chuck of the lathe to clamp and position the bearing bush and the steel sleeve, and pay attention to the leveling of the bearing bush surface to ensure the perpendicularity of the clamp. When the grinding rod is used for grinding, the crown block crane shall be used to lift the grinding rod up and down, and the grinding rod shall be manually rotated around the axis of the bearing pad. The grinding shall be carried out in accordance with the procedure of roughing first and then finishing. During finishing, dry grinding shall be carried out with a grinding rod whose outer diameter is 0.015-0.025mm smaller than the inner diameter of the bearing bush. During dry grinding, the number of grinding shall be controlled. After grinding, the surface finish of the inner hole of the bearing bush shall reach more than 0.8 of Dongguan Tuowa Machinery Manufacturing Co., Ltd., and then the bearing bush shall be reassembled for commissioning.

The extensive application of hydrostatic spindle components in machine tools has raised the level of machine tool design and manufacturing to a new level, and also brought new challenges to machine tool maintenance. The repair process of hydrostatic spindle is complex and delicate, and the repair period is long, which is easy to affect production. Therefore, the usual maintenance work is crucial.