-YRT turntable bearing turntable bearings - Analysis of machine tool rotary table bearing selection
Into the 21st century, especially with the start of the special national "high-end CNC machine tools and basic manufacturing equipment," has greatly promoted the development of machinery and equipment industry, "high-speed, precision, complex, intelligent" machine tool development process gets further accelerated. NC rotary table as functional accessories CNC machine tools, also received attention, high-speed direct-drive NC rotary table, high-precision CNC rotary table, large heavy-duty NC rotary table, CNC rotary table and other oil-soaked several NC table directly included in the national major projects of the within the development plan.
NC table of the CNC machine tool as an important accessory, more precisely, one of the key features of the above four-axis CNC machine, can be directly used as a table of the machine tool, the fourth shaft can be mounted on the machine table of a machine tool using , two-axis rotary table mounted on a table may even make an ordinary three-axis machining center can be promoted to achieve spatial processing arbitrary shape five-sided machining center.
Whether as CNC machine tool accessories, NC NC rotary table or as a machine table, and whether used in conventional machining centers, or as a part constituting a flexible manufacturing cell, NC table or even a direct impact on the overall performance and determine the accuracy of the machine.
The turntable is determined that it is the fundamental properties of the support structure bearing the type and precision.
1. briefly describes the types of CNC turret at the:
NC rotary table is divided into different mounting method: Vertical and Horizontal and vertical turret NC / NC table horizontal; up from rectangular mesa shape can be divided into circular turret and turret; the turret from a uniaxial degree of freedom can be divided into several biaxial and multiaxial turret turret; the turret there is a rectilinear coordinate pallet and the like.
2. CNC turret support of evolution:
Regardless of the form of the turn table, the rotary table which are required axial and radial support. NC rotary table rotary support, originally derived from the rotation of the turntable mechanically supported. Before NC rotary table, the rotary table support base listing mechanical sliding bearings. As shown in FIG. 7, the radial rotary turret support B, the turret is axially supported by the A and C.
Taking into account the friction, wear and maintain the accuracy of the early eighties of last century, when the machine tool accessories designed to Yantai Institute of Electrical and Mechanical Services Department directly under the State developed the first domestic NC rotary table. Supporting turntable into a radial sliding bearing support, axial support to maintain the original cast iron mechanical turret slide rail. Until the late eighties, PTFE sheet application and verified on the machine tool, the NC table is axially supported by the slide was cast into a plastic coated guide rail, sliding coefficient of friction is reduced to 1/3 of the original, increased payload NC turntable. 8 configuration, the two radial support by a pair of angular contact ball bearings (B) provided after pretensioning, is responsible for the turntable radial loads; bearing support rail is plastic coated (A) sliding bearings and tapered roller bearings (C) composition, axial loads and overturning moments responsible for the turntable.
To around 2001, with the application of new technologies and new processes, machining capacity increase as technology methods more sophisticated, large-size roller bearings are increasingly used in the end face of CNC turret support structure began to change to full rolling basis. As shown in FIG. 9, the end faces of the roller bearings A, one pair of angular contact ball bearings
B, tapered roller bearings C, completed the support spindle CNC turret countertops.
Around 2003, now YRT complex for NC rotary table bearings, domestic Yantai Universal Machine Tool Accessory Group first began to be used NC rotary table, the support structure shown in Figure 10. Composite bearing rolling bodies divided into three parts: Part A, Part B, C section, A, C the two parts together to complete the axial support of the turntable, Part B provide radial support of the turntable.
In the turret smaller size, also the use of a double row tapered roller shown in Figure 11 of the bearing support structure, the load from the A, C provided two tapered roller bearings.
In recent years, there have been more than 5m in diameter, carrying more than 100 tons of large-sized CNC turret needs more support this type of situation no longer applies, load-bearing structure is reasonable and hydrostatic bearing precision cylindrical roller bearings portfolio.
3. summary, the combination of several types of support compared as follows:
CNC turret widely used in a variety of CNC milling machine, CNC boring machine, CNC vertical lathes, machining centers, CNC boring and milling machine. In addition to requiring rotary table can well withstand the weight of the workpiece, but also need to ensure that the rotating accuracy under load. Turntable bearing, as a core component of the turntable, the turntable during operation, not only has a high load carrying capacity, need to have high precision turning, overturning capability and high resistance to high speed capability. In the design of rotary table, the use of more types of bearings can be divided into the possible combinations of the above. Comparison specifically described as follows:
3.1. 向心推力球轴承+圆锥滚子轴承+滑动导轨
推力球轴承虽然能承受一定的轴向力，但在这种组合的情况下，向心推力球轴承不受轴向力的作用，仅承受径向力的作用（鉴于安装于此位置的轴承，仅受径向力的作用，在径向载荷较大的场合也有直接用径向滚子轴承的情况，原理相同，不在赘述）。起定位作用。滑动导轨和圆锥滚子轴承的组合用来承受工件重量和外加轴向载荷；外加倾覆力矩由滑动导轨和圆锥滚子轴承承受。
此类支撑向心推力球轴承需要预紧，圆锥滚子轴承和滑动导轨也需要预加载荷。由于存在滑动摩擦，轴向预加载荷容易产生较大的空转摩擦力矩，造成空转动力消耗偏大。
3.2. 向心推力球轴承+圆锥滚子轴承+端面滚子轴承
此类组合，从承受载荷来讲，与第一类组合类似，但由于端面滚子轴承的采用，减小了由滑动导轨导致的空转摩擦力矩，降低了空转动力损耗。
3.3. 双圆锥滚子轴承
双圆锥滚子轴承的结构，对圆锥滚子轴承的要求较高，并且轴向负载对转动力矩影响较端面滚子轴承类支撑大。
3.4. 复合轴承（交叉圆柱或圆锥滚子轴承和YRT转台轴承）
复合轴承类支撑不仅包括图10所示的YRT转台轴承（图14）类支撑，还包括交叉圆柱、圆锥滚子轴承（如图12、13，应用见图15），这三种轴承都有结构比较紧凑和负载能力高的特点，是当前数控转台类产品首选的支撑轴承。 图12 交叉圆柱滚子轴承
图13 交叉圆锥滚子轴承
图14 YRT转台轴承
图15 交叉圆柱、圆锥滚子轴承支撑
图16 YRT转台轴承的应用结构图
Bearing the above structure is an internationally renowned company DMG (DMG), CYTEC (SeaTac), IDAM (direct drive Schaeffler companies), Taiwan Tan Xing, Tan Jia, Fang Jia and other machine tools, direct drive NC rotary table and domestic manufacturers Shenyang machine tool company, Global Yantai, Dalian machine tool, Qinchuan machine, Yantai Constant machine tool accessories, CNC control turntable, turntable torque motor, double pendulum milling head, indexing plate and other products bearing preferred, I can production of alternative Schaeffler brands INA rotary table bearings YRT50-1200 series, SX011814-SX0118 / 500 series and TIMKEN the XR496051-XR897051 (inner diameter 203.2-1549.4mm) series;
3.5. + Hydrostatic bearing precision cylindrical roller bearings
Is a hydrostatic bearing by the oil pressure supplied externally, to establish the hydrostatic bearing sliding bearing oil film in order to achieve a liquid lubricated bearing. Hydrostatic bearings from start to stop are always operating at liquid lubrication, wear, long life, in addition, this support also has a high rotation accuracy, load capacity, etc; it requires a dedicated fuel supply system, a complex structure, high maintenance costs. Precision cylindrical roller bearing has good radial load capacity, and the rotation precision can be obtained well guaranteed.
In short, it is easy to see from the NC rotary table in the history of decades of development of domestic, NC rotary table bearing as a core component of the performance CNC turret has played a pivotal role in the current number of high precision and large size bearings on imports dependence are still relatively large. Improve the grade from the NC rotary table is concerned, is to choose the right type of support, you need to consider a variety of working conditions, such as speed, lubrication, load, precision requirements, the type of support on the basis of selection can play a bearing the best performance.
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