Abstract: The cylindrical roller bearing with locating pin is a new type of bearing structure. It is difficult to meet the requirements of finished products for its end face with locating pin and raceway rib according to the conventional processing method. After repeated tests and analysis, the fine grinding rib of the conventional grinding process is changed to two grinding plus one polishing, and the polishing rib process is added after the final grinding rib, so that the product's accuracy meets the user's requirements.
Keywords: roller bearing; Grinding; workmanship End face with pin; Welt
1 Product structure characteristics and accuracy requirements
The cylindrical roller bearing with locating pins on the end face is a new type of structural bearing (Fig. 1). The structural feature of the bearing is that the reference end face of the outer ring is equipped with locating pegs. Its diameter series is an ultra light 8 series bearing, and the accuracy requirement is P4. The single variety of products is small in batch, and the material is Gr4Mo4V steel, so it is very difficult to process. The requirements are:
(1) The reference end face of the outer ring is provided with arc positioning pins, and the non reference end face is normal. The parallelism difference between two end faces is 3 μ m.
(2) The double rib has an angle of 35 ', and the parallel difference between the rib and the datum plane is 3 μ m.
(3) The clearance between the end face of finished bearing roller and the ring rib is required to be 0.03-0.06 mm.
Fig. 1 Cylindrical roller bearing with locating pin
2 Preliminary proposed grinding process
The grinding process preliminarily proposed with reference to similar products is as follows: rough grinding non datum end face → rough grinding datum plane → rough grinding outer diameter → rough grinding outer diameter → rough grinding rib → rough grinding outer raceway → stable → final grinding non datum end face → final grinding datum plane → fine grinding outer diameter → final grinding outer raceway → fine and final grinding outer raceway → final grinding rib → polishing rib → rough grinding outer raceway → fine grinding outer raceway → grinding outer diameter.
At present, there are M7475, MG7340 and M7120 surface grinding equipment in our factory. In view of the strict requirements for end face parallelism, we try to use MG7340 for machining.
MG7340 high-precision horizontal axis surface grinder uses the grinding wheel to grind in the circumferential direction. Its processing method is to suck the workpiece onto an electromagnetic circular table, which drives the workpiece to rotate, and the worktable makes a vertical linear reciprocating motion to grind the end face of the workpiece. In order to process the base surface with pins on this machine tool, the pins must not rotate. The length of the peg is 6 mm, and the thickness of the peg is less than 3 mm. If the peg is approximately regarded as a rectangle, then the diameter of the outer circle of the rectangle is less than 7 mm. Therefore, when the work-piece pin is rotated as the center, it is equivalent to taking the center of the rectangular circumscribed circle as the center of the circle. Outside the circle with a diameter of 7 mm, the grinding wheel cannot grind the pin. The width of the overtravel groove on one side of the pin is 2 mm and the total length is 10 mm.
The processing method is to make the center of the locating peg on the bearing end face concentric with the center of the disk. When the disk rotates, the pegs on the bearing end face rotate in place, and the planes outside the pegs rotate around the center, and there are 2 mm empty knife grooves on both sides of the pegs. At this time, the left end surface of the grinding wheel should be aligned as close to the side of the pegs as possible, and the side that cannot grind the pegs should prevail. The end face can be grinded by moving the workbench from left to right, as shown in Figure 2.
3 Problems and solutions in processing
3.1 The parallelism of the base plane with pins is out of tolerance
3.1.1 Cause analysis
The machining of the datum plane with pins is a difficult point. Repeated tests on the MG7340 high-precision horizontal spindle grinder found that the parallelism always fails to meet the requirements when finishing the datum plane. The reason may be that when the workpiece rotates, the grinding wheel cannot grind the end face of the workpiece uniformly, and always starts grinding from one side of the pin, and then leaves the grinding end face from the other side of the pin, which causes the contact arc length between the workpiece and the grinding wheel to change from time to time, resulting in the end face parallelism exceeding the tolerance.
Fig. 2 Base surface of grinding belt locating pin on MG7340
3.1.2 Improvement measures
The existing M7120A horizontal spindle surface grinder is used for processing. The grinding wheel is used for grinding in the circumferential direction. The workpiece can be directly fixed on the machine tool workbench or absorbed on the electromagnetic rectangular workbench with screws and pressing plates. The workbench makes a vertical linear reciprocating motion to achieve the grinding of the workpiece end face. The processing method is to divide the end face into two processes by taking the pin as the boundary line. During the first processing (Fig. 3), install a dial indicator in the height direction of the workpiece of the machine tool, and rotate the workpiece positioning pin relative to the longitudinal workbench for a certain angle to try grinding, so that the pin can not be grinded, and the position beyond the overtravel groove on one side can be grinded slightly over the symmetrical line. First, process the plane on one side of the pin and record the position indicated by the dial indicator; For the second time, re process the remaining plane, grind it to the same position, measure the height difference between its two sides, and then grind it. With this method, the parallelism difference between two end faces can reach 4~5 μ m。 But at this time, the parallelism difference between the two ends of the finished product is still not 3 μ Therefore, manual grinding is also required. Specifically, first measure the high points on the end face, and then grind the high points on the flat cast iron grinding table (a groove is made on the cast iron plane in advance), so that the parallelism between the two end faces can reach 2-3 μ m.
Fig. 3 Base surface of grinding belt locating pin on M7120A
3.2 The axial clearance of the rib is unqualified
3.2. 1 Cause analysis
Grind the rib with a bowl shaped grinding wheel on the 3MZ1410 grinder. Grind the base surface rib first, and then the non base surface rib. The tolerance range of the rib is+0.02 mm. Because the rib is narrow, the grinding allowance is small each time, and the grinding resistance is small, the size can be completely controlled within the tolerance range. During the whole grinding process, no problems were found, and all dimensions, shape and position accuracy met the process requirements. Roller length tolerance is - 8 μ Within m. Theoretically, the axial clearance of the ring can be guaranteed to be 0.03-0.06 mm, but the qualified rate of the clearance between the roller end face and the outer ring flange is only 50%~60% during bearing assembly. The cause was analyzed and it was found that the problem was in the edge polishing process.
For the edge polishing process, 180 # abrasive cloth is used for manual polishing, with a margin of 0.005mm. Because the manual polishing amount is not easy to control and the bevel of the flange is easy to be damaged, the size, shape and position accuracy of the polished flange are out of tolerance. Moreover, in order to avoid damaging the surface quality after the flange polishing, only the plug gauge is used to control the raceway width at a single point, and the bevel angle and form and position accuracy of the flange are not measured, thus causing the above problems.
3.2.2 Improvement measures
The improved grinding process route is as follows: rough grinding end face → rough grinding base surface → rough grinding outer diameter → rough grinding outer diameter → rough grinding rib → rough grinding outer raceway → stability → final grinding end face → final grinding base surface → fine grinding plane → final grinding outer circle → final grinding outer diameter → fine and final grinding outer raceway → final grinding rib → smooth grinding rib → polishing rib → rough grinding outer raceway → fine grinding outer raceway → grinding outer diameter.
After the final edge grinding, add the process of polishing the edge. Use 320 # chrome corundum vitrified bond grinding wheel or CBN500 # grinding wheel for fine grinding, and the roughness Ra reaches 0.16~0.18 μ m. The parallelism difference of the rib is within 0.003mm; Finally, use 600 # ointment cloth to polish. The size tolerance of polished rib is the same as that of polished rib, which basically does not consume size, but only improves the surface quality, making the rib surface more delicate without damaging the processing accuracy after final grinding, and the roughness Ra reaches 0.16 μ m.
After the flange is polished, take 6 points in the circumferential direction to evenly distribute and use a plug gauge to check the width of the inner race raceway, which should be all qualified. The bevel angle and roughness of the rib are measured accurately and easily by grinding the sample.
After the new grinding process is adopted, the parallelism between the two end faces meets the requirements, and the parallelism between the rib and the datum plane is ensured. The fine grinding of the rib is changed into two grinding and one polishing, which not only ensures the precision of the rib but also meets the requirements of the surface roughness. All the precision of the products meet the technical requirements.
More about KYOCM tapered roller bearing:
KYOCM tapered roller bearing adopts outer ring and inner ring components. The outer ring is composed of an outer ring, and the cone assembly is composed of an inner ring, a roller and a cage. This bearing structure can withstand combined loads and provide low friction during operation. Rigid bearing applications can be achieved by adjusting a single row tapered roller bearing to a second tapered roller bearing and applying preload. KYOCM tapered roller bearings include single row tapered roller bearing, double row tapered roller bearing and four row tapered roller bearing.