Common Problems of Machining Grinding Machines
May 23,2020
1) The grinding head spindle overheats and seizes.
The main reason for this phenomenon is the presence of impurities in the hydraulic oil, such as dust and iron filings. Impurities in the hydraulic oil can clog the small oil holes in the bearing, causing some hydraulic chambers to lack hydraulic oil, preventing the spindle from forming a symmetrical pressure oil chamber. When the spindle rotates, it is not in a pure liquid state, leading to friction with the bearing and generating heat. After disassembling the spindle of the surface grinder and inspecting each component, it was found that the spindle roundness was within tolerance, but the surface finish was poor. The roundness of the bearing's inner hole was within tolerance, but there were scratches on the inner surface, and scratches were also found on the cross-section of the bearing. The capillary oil holes in the bearing were clogged. Polishing the spindle surface and the end face of the bearing's inner hole with metallographic sandpaper can meet the usage standards.
The difficulty in repair is how to remove impurities from the 0.5mm capillary oil holes in the bearing. Only by clearing all the oil passages can a static pressure balance be established within the bearing. The bearing is assembled in a cast iron sleeve, and a special puller needs to be made to separate the bearing from the sleeve. Once the bearing is separated, it can be cleaned, and all oil passages can be cleared. Finally, clean the oil tank and replace it with new hydraulic oil. After all repair work is completed, it can be reassembled for testing.
2) Poor surface finish of the ground workpiece.
The radial runout of the spindle exceeds the tolerance, causing significant vibration of the grinding wheel during the grinding process, resulting in a poor surface finish of the ground workpiece.
The main reasons for the radial runout of the surface grinder spindle exceeding the tolerance are:
(1) Spindle collision or deformation due to force.
(2) The roundness of the inner hole of the spindle's supporting bearing exceeds the tolerance.
The grinding head part of the surface grinder uses a support mode of two bearings at the front and back, applying static pressure technology. Two oil return grooves with a depth of 0.8mm and a width of 4mm are opened at the front end of the bearing. The processing and assembly accuracy of the bearing will have a serious impact on the usage quality of the M7140 type static pressure grinding head. The gap between the bearing and the spindle in the diameter direction is 0.07mm, which can be used for fault finding and precision repair. After disassembling the spindle, it was found that the main reason for the spindle vibration was the roundness of the bearing's inner hole exceeding the tolerance, which disrupted the static pressure balance and caused significant vibration during spindle rotation. Repairing the roundness of the bearing's inner hole can also be done using grinding methods.
First, make three grinding rods of different sizes from cast iron. The three grinding rods of different sizes are used for rough and fine grinding repairs of the bearing's inner hole. Depending on the size of the bearing, the length of the grinding rods needs to be unified to 600mm, and the grinding rods need to be made in a waist drum shape. The bearing of the spindle is assembled with the steel sleeve uniformly, and care should be taken to protect the oil passage on the bearing surface during assembly. Use the lathe's chuck to clamp and position the bearing and steel sleeve, ensuring the bearing surface is leveled to ensure verticality during clamping. When using the grinding rod for grinding, it is necessary to use a crane to lift the grinding rod for up and down reciprocating motion, and manually rotate the grinding rod around the axis of the bearing. Grinding should be done in the order of rough to fine, and for fine grinding, use a grinding rod with an outer diameter 0.015-0.025mm smaller than the inner diameter of the bearing for dry grinding. During dry grinding, the number of grinding cycles should be controlled, and after grinding, the surface finish of the bearing's inner hole can reach
above 0.8 before reassembling for testing.
The static pressure spindle components are widely used in machine tools, raising the design and manufacturing level of machine tools to a new stage, but also bringing new challenges to machine tool maintenance. The repair process of static pressure spindles is relatively complex and meticulous, with long repair periods that can easily affect production. Therefore, regular maintenance and care work is crucial.
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Tianjin Jinghai County Jia Xuyan Hydraulic Machinery Co., Ltd.
Address: Fengjia Village, Duliu Town, Jinghai District, Tianjin
Contact:18902087888,13802191288
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