FINISHING AND STRENGTHENING ROTARY RUNNING-IN TECHNOLOGY FOR LONG THIN-WALLED PIPES

An analytical solution for the elastic plastic contact strain problem is proposed in relation to the processes of finishing and strengthening machining of long thin-walled pipes by rotary run-in using cylindrical and pseudospheric toroidal rollers. Technological and instrumental support of these processes is viewed. It contributes to the improvement of pipe surfaces quality and eliminates errors in the geometric shape of the cross-section. The conditions for self-feed of pipes being treated are determined. An algorithm has been developed for calculating rational modes of surface plastic deformation of long thin-walled pipes in the Mathcad software package, taking into account their special geometry and increased flexibility, as well as strict requirements for products in terms of accuracy of diametrical size and quality of treated surfaces. The proposed method for calculating some rational technological modes of finishing and strengthening treatment has been experimentally tested on thin-walled pipes (sometimes flattened to 1 mm in diameter) made of 30 steel with a hardness of HB160 with an initial surface roughness of Ra = 1,25...1,6 microns. The pipes were run-in using a 3-roller running-in device at a rotational speed of about 80 rpm with cylindrical rollers. The calculated rollers decline in the shell of the running-in device and the technological parameters of the processing mode made it possible, with a five...eightfold overlap of the initial trace of the tool tip, to ensure not only the conditions for self-feeding of the pipe and high process productivity, but also to obtain the required riveting depths and strain hardening degree for its surface. At the same time, the surface roughness decreased by almost an order of magnitude (to Ra ≤ 0,2 microns) without noticeable traces of undulation and peeling, and the initial out-of-roundness of the pipe section was almost completely prevented. The developed rotary running-in technology for long thin-walled pipes is recommended for wide practical use in machine-building enterprises.