TPT May 2021

AR T I C L E

Shandong Province Sifang Technical Development Group

Sifang Group has focused on the research and development of sizing rolls for nearly two decades. In the late 1990s it developed high chromium alloy sizing rolls and supplied small amount of the rolls to TPCO, which were used on Ф250 seamless pipelines, with service life two times longer in contrast with imported nodular cast iron rolls and three times that of nodular cast iron rolls made in China when our rolls were used in rolling Ф139.7mm oil casing based on every turning. Details are shown in table 5.

wear resistance and need large turning forces and good cooling condition. Therefore PCD turning tools are selected in the experiment. The hard alloy is processed via grinding in common practice and it is impractical to grind hard alloy sizing rolls, so PCD cutter blades are selected in the experiment. If using machine tools available now to process sizing rolls made from materials such as high chromium alloy, high speed steel or hard alloy we will see low working efficiency, doubled working hours and also it cannot meet the requirements of changing sizing rolls frequently, this factor has become the main obstruction in popularising the mentioned rolls. The R&D team at Sifang Group restarted the development of sizing roll over the past few years, summarising what accounts for the difficulty in sizing roll popularisation and doing surveys for service condition, processing and operating requirements of sizing rolls, and reenacted development schemes to optimise material selection, foundry technique and heat treatment processes. As for the new material, on one hand it should have excellent wear resistance and outstanding strength and toughness, on the other hand it should be easily processed to meet the requirements of roll processing. To achieve this goal it designed new high chromium semi-steel material, which is completely different from any previous material used for making sizing rolls. Sifang Group also systematically discussed and analysed the corresponding foundry and heat treatment techniques. In this way, according to the designed plan, it made test samples, which were similar to rolls in use then did chemical content analysis, metallurgical structure observation and mechanical property tests with wear resistance test included. Meanwhile we cut the sample and tested hardness at different area. According to the test results, we finally determined the manufacturing process of sizing rolls after many adjustments. Based on this Sifang Group manufactured multiple sizing rolls and performed batch trials on Ø168, Ø250 and Ø258 pipe production lines of TPCO; Ø140 pipe production line of BAOSTEEL; Ø325 pipe production line of Yantai Lubao Steel Pipe Co Ltd; and Ø180 and Ø340 pipe production line of Hengyang Valin Steel Tube Co Ltd. At the same time it followed up the service results of the rolls. After two years of tryout the performance of Sifang Group’s new type sizing rolls has fully met the requirements of design and gained customers’ praise. When talking about new type sizing rolls Sifang Group mainly focuses on its brand new design idea, which cast away the

Amount of pipes rolled after sizing rolls being processed one time (pcs)

Name of rolls

Sifang high chromium alloy sizing roll Imported alloy nodular cast iron roll Alloy nodular cast iron roll made in China

12792

4500 – 6000

3000 – 5000 Table 5: Service result comparison between Sifang high chromium alloy sizing rolls and nodular cast iron rolls But at that time there was a problem with high chromium rolls, which has high hardness and can cause difficulties to the machining of roll grooves and result in low turning efficiency, thus the requirements of a pipe plant’s tool room regarding the desired turning efficiency were not fulfilled. So the high chromium alloy rolls were only produced in small numbers and not popularised at that stage. During this period other roll manufacturers also undertook research and development of other high wear resistance materials such as high-speed steel, hard alloy and so on to manufacture sizing rolls, but all failed due to difficulty in machining and unreasonable price ratios. When the international advanced seamless pipe production lines were introduced into China the special CNC machines for machining sizing rolls were imported at the same time. Normally three pieces of rolls are machined together after being fixed on the same stand. Since the alloy nodular cast iron was used as roll material in the original designs the machine tool and the turning tool were designed and manufactured based on machining nodular cast iron rolls. The ceramic tip turning tool was selected to process alloy nodular cast iron and worked well, but when it was used to process rolls made from high chromium alloy, high speed steel, or hard alloy, the result was not acceptable. The machine tools available at present are not workable for turning materials such as high chromium alloy and high- speed steel, which have high hardness and outstanding

traditional production ideas when selecting roll material and it resulted in excellent service performance. It is possible to summarise the distinguishing features of new type sizing rolls as follows. First, compared with tradi- tional sizing rolls it has better wear resistance. The new type sizing rolls’ service life

Metallurgical structure test of new type sizing roll

Finished new type sizing rolls

70

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MAY 2021