1、 Comparison between Roller Screw Pair and Ball Screw Pair

The load-bearing capacity of a rolling screw mainly depends on the curvature radius of the contact surface between the rolling elements, the number of contact points, and the hardness and smoothness of the contact surface.

Under the same conditions of contact surface hardness, smoothness, and accuracy, roller screws have more contact points than ball screws, and the curvature radius of the envelope circle of the roller contact surface is also much larger than that of the ball screw steel ball. This determines that roller screws have higher load-bearing capacity than ordinary ball screws.

Comparison diagram of the number of rolling elements, curvature radius, and contact surface circle of roller screw rolling elements

　2、 Classification and Application of Roller Screw Pair

Roller screw pairs can be divided into two types based on their structure: planetary roller screw pairs and cyclic roller screw pairs. The two have essential differences in the operation of the rollers: the rollers of the planetary roller screw pair do not move axially relative to the nut during revolution and rotation, while the cyclic roller screw pair has axial cyclic movement relative to the nut except for revolution and rotation.

The differences in structure determine that the two have different application fields. Planetary roller screw pairs are mainly used in heavy-duty fields, while cyclic roller screws tend to be used in precision equipment.

Planetary roller screw has high load-bearing capacity and high reliability, mainly used in:

● Injection molding ● Pressure machine tools ● Steel industry ● Military equipment ● Nuclear industry

The circulating roller screw has a high lead resolution due to its small helical lead (1-2mm), coupled with its high load-bearing capacity and reliability, and is mainly used for:

● Precision Instruments ● Precision Grinding Machines ● Medical Devices ● Aerospace

3、 Contact analysis of planetary roller screw pair under given load

Taking the 3020 planetary roller screw as an example, analyze its contact stress under a given axial load. The mesh elements in contact with each element are hexahedral elements to improve the computational accuracy of CAE contact analysis. The analysis process is shown in the following figure:

Based on the above analysis, it can be determined that the maximum contact stress of each contact element surface is located on the surface of the roller spiral raceway. After verifying relevant literature, when the surface hardness of GCr15 material used for ordinary screw reaches HRC63 after heat treatment, its allowable contact stress can reach 4000MPa. Therefore, it can be inferred that the rated static load of 3020 type roller screw can meet the requirements.

4、 Numbering rules and meanings

5、 Planetary roller screw by-product series

Product series of planetary roller screw pairs (GZR) with nut flange located at the center and no axial preload:

　6、 Circular roller screw by-product series

Nut flange centered, non axially preloaded circulating roller screw pair (GZV) product series: