Ball screw is a transmission mechanical component in which the steel ball moves between the nut and the screw, converts the sliding contact of the traditional screw into rolling contact, and then converts the rotational motion of the steel ball in the nut into linear motion. In order to achieve high-speed feed, relevant manufacturers at home and abroad have continuously taken measures to improve the high-speed performance of ball extruder screws.
The main measures are:
1. Appropriately increase the speed, guide and number of thread heads of the extruder screw
At present, the nominal diameter of the commonly used large guide ball screw is matched with the guide: 400mm*20mm, 50mm*25mm, 50mm*30mm, etc. Its feed speed can reach more than 60m/min. In order to improve the stiffness and bearing capacity of the ball screw, the screw of the large-guide ball extruder generally adopts double-headed threads to improve the effective number of ball bearing rings.
2. Improve the structure of the extruder screw and improve the fluency of ball movement
Improve the ball cycle reverse device, optimize the curve parameters of the ball ball groove, and use a three-dimensional bead guide tube and a ball returner to truly introduce the ball into the nut body along the direction of the guide angle of the internal thread, so that the direction of ball movement is tangent to the raceway rather than intersect. In this way, the impact loss and noise can be minimized.
3. The extruder screw adopts hollow strong cooling technology
The high-speed ball extruder screw produces high temperature during operation due to friction, resulting in the thermal deformation of the extruder screw, which directly affects the machining accuracy of the high-speed machine tool. Using hollow strong cooling technology is to pass the constant temperature cutting fluid into the hole of the hollow screw, force the ball screw to cool, and keep the ball pair temperature constant. This measure is an effective way to improve the high-speed performance and working accuracy of screws of medium and large ball extruders.
4. For high-speed feed systems with large strokes, the fixation of the extruder screw and the rotation of the nut can be adopted.
At this time, the nut rotates while moving axially along the fixed extruder screw. Because the screw does not move, it can avoid being limited by the critical speed and avoid various problems when the screw of the slender ball extruder runs at high speed. The nut has small inertia, flexible movement, and high rotation speed.
5. Further improve the manufacturing quality of the ball extruder screw
Through the above measures, some problems existing in the screw of the transmission ball extruder can be overcome to a certain extent. Its maximum fast movement speed can reach 60m/min, in some cases it can even reach 90m/min, and the acceleration can reach 15m/s2.
Due to the long history, mature process, wide application and low cost of ball extruder screw, it is still often used in general high-speed machining centers and other economical high-speed CNC machine tools with medium load bearing, low feeding speed requirements and not too large stroke range.