TPT May 2021

AR T I C L E

Shandong Province Sifang Technical Development Group

Researching new sizes of roll – and reducing roll – for seamless steel pipe By Houzhi Yuan and Ning Zhang from Shandong Province Sifang Technical Development Group, China

As for sizing rolls Sifang Group normally indicates rolls used on sizing mills or reducing mills, which are parts of seamless pipe mills. The rolls used on reducing mill are also called reducing rolls and the rolls are sometimes called roll rings or rolls, which are exclusively used on sizing mills and reducing mills for seamless pipe production. In production the physical dimension of pipes are specified via adjusting the profiles of sizing rolls and reducing rolls thus the production of high precision pipe is guaranteed. The sizing rolls work under the unceasing stretching stress of turning and radial compact stress, therefore the rolling friction and sliding friction occur between the profile of rolls and surface of pipes, which aggravates the abrasion of rolls. Since rolls and hot pipe blank repeatedly touch and separate and suffer from the chilling of cooling water, the roll profile must endure the alternating thermal stress. Therefore, the common reasons for sizing rolls losing effectiveness include excess wear, cracks, sticking steel and defects of the rolls. A sizing process is essential for steel tube and pipe production, and it results in a high consumption of sizing rolls, thus the quality and delivery period of sizing rolls directly influences the quality and production plans of tube and pipe companies. At present seamless pipe manufacturers worldwide commonly use rolls made from indefinite chill cast iron or alloy nodular cast iron. Indefinite chill cast iron is achieved with molten iron self super cooling and chilling of the mould surface. The white chill emerges on the surface of indefinite chill cast iron rolls, so the hardness is high and wear resistance is good. This material has been used to manufacture rolls for a long time. Back to the early 1920s indefinite chill cast iron rolls were widely used in hot rolled strip mill. But the thickness of chill zone of the indefinite chill cast iron is limited, especially as the sizing rolls are abnormal shape rolls with non-cylinder contour, therefore it is more difficult to form enough chill zone, so the chill zone wears off and its wear resistance will be decreased remarkably. Roll manufacturers and specialised institutions such as universities and colleges are continuously working on the optimisation of roll materials in recent years, and they have developed numerous alloy ductile iron materials with the structure and performance optimised and improved. At present most sizing rolls are still made from ductile iron material. During the 1980s and 1990s alloy ductile iron sizing rolls and reducing rolls were imported into China to be used in the seamless pipe production lines. Some of the imported rolls were dissected to do the analysis. The chemical composition, metallurgical structure and properties are as shown in table 1 to table 4.

Shandong Province Sifang Technical Development Group Co Ltd (Sifang Group) has been dedicated to the research, development and production of high efficiency tools and moulds used for pipe production for many years. The high-quality tools and moulds manufactured by Sifang Group have been extensively used and recognised by pipe manufacturing enterprises in China and abroad, among which the high chromium alloy straightening roll and rolls for welding steel pipe have become world famous and particularly popular brands. The straightening roll market share in China is over 80 per cent. High chromium alloy rolls for welding steel pipe have successfully replaced rolls made from materials such as D2, X155CrVMo121, SKD11 and Cr12Mo1V1 in the country. High chromium alloy has been the preferred material for top grade heavy section rolling mills. Sifang Group has supplied numerous rolls of multiple specifications to a number of famous international equipment manufacturers for their mills and also directly delivered products and services to many welding pipe manufacturers worldwide. Sifang Group presided over the drafting of Chinese national standard ‘Rolls for Welding Steel Pipe’ (GB/T 31936-2015), which was put into effect in 2016. The company recommends the new type of rolls for sizing mills and reducing mills, which were researched and developed by Sifang Group in recent years.

Function sketch of sizing roll & reducing roll

Assembly stand of sizing roll & reducing roll

68

www.read-tpt.com

MAY 2021