China has indigenized the main bearings of large tunnel boring machines (TBM). China had not been able to produce the bearing steels until the Chinese scientists created the
low oxygen rare earth steels after more than 10 years of research.
超大型盾构机有了“中国心”
记者从中国科学院获悉，我国成功研制超大型盾构机用直径8米主轴承。该主轴承重达41吨，是目前我国制造的首台套直径最大、单重最大的盾构机用主轴承。
更重要的是，该主轴承顺利通过国家轴承质量检验检测中心检测和专家组评审。专家组评审意见认为，该主轴承各项技术性能指标与进口同类主轴承相当，满足超大型盾构机装机应用需求。
主轴承是“最后一公里”
盾构机，全名叫盾构隧道掘进机，是一种隧道掘进的专用工程机械。一般情况下，我们不会经常看到这个“大国重器”，毕竟它常年在地下工作。
它是基础设施建设的重大装备，承载着穿山越岭、过江跨海的重任。“虽然我国已实现了盾构机的国产化，但其核心部件——主轴承却依赖进口，亟须打通自主可控制造的‘最后一公里’。”中国科学院金属研究所研究员李殿中坦言。
主轴承有盾构机“心脏”之称，是盾构机刀盘驱动系统的关键核心部件。盾构机掘进过程中，主轴承“手持”刀盘旋转切削掌子面并为刀盘提供旋转支撑。
“直径8米的主轴承在运转过程中承载的最大轴向力可达10^5千牛，相当于2500头成年亚洲象的重力。”李殿中说，为保证主轴承的高承载能力和高可靠性，制造主轴承的轴承钢必须要高纯净、高均质、高强韧、高耐磨。这对主轴承成套设计、加工精度、润滑油脂等提出了很高的要求。
李殿中表示，此前，我国盾构机用超大直径主轴承一直未能攻克的主要原因在于：制造轴承的材料和大型滚子的加工精度不过关，全流程技术链条不贯通。
氧含量是关键
攻关团队认为，要制造高纯净、高均质、高强韧、高耐磨的轴承钢材料，一定要从源头解决材料制造的问题，他们将目光瞄准了稀土轴承钢。
已有大量研究表明，钢中添加微量稀土能够显著提高钢的韧塑性、耐磨性、耐热性、耐蚀性等性能。
然而，“稀土钢在工业化生产时遭遇两大难题：一是工艺不顺行，浇铸时经常出现浇口堵塞的问题；二是稀土在钢中添加后，钢的性能剧烈波动，存在稳定性不好的问题。”李殿中指出。
通过长达十余年的机理研究和工业实验，中科院金属所研究团队发现，稀土钢性能波动、铸造时浇口堵塞问题的根源在于氧含量。
“我们发现，不仅钢液中的氧含量影响稀土钢的性能，更为重要的是，长期被学界和产业界忽视的稀土金属中的氧含量，对稀土钢的性能也具有十分重要的影响。”李殿中解释道。
“通过控制氧含量，我们制备出性能优越、稳定性好的低氧稀土钢。”李殿中说，与不加稀土的轴承钢相比，该稀土轴承钢拉压疲劳寿命提高40多倍，滚动接触疲劳寿命提升40%，有效解决了稀土钢工业应用中的瓶颈问题。
滚子也是一道坎
除了轴承钢，要想制造超大直径主轴承，大型滚子加工技术也是一道迈不过去的坎。
滚子是轴承运转时承受负荷的元件，是滚子轴承中最薄弱的零件，它的制造质量对轴承工作性能有很大的影响，是影响轴承使用寿命的主要因素。
“在主轴承研制过程中，我们发现，由于受到国外的技术限制，我国大型滚子加工精度只能达到二级，还不能实现一级精度加工。”中科院金属所研究员胡小强直言。
为此，胡小强带领研究团队深入生产一线，联合企业集智攻关，最终研制出直径100毫米以上的一级滚子，使我国轴承行业突破了一级大型滚子精密加工技术。
“通过与洛阳新强联股份有限公司等企业密切合作，我们实现了盾构机主轴承加工制造、装配调试、检测评价等全流程自主可控，同时带动了相关国产装备的研制。”胡小强说。
未来，新研制的主轴承将安装在直径16米级的超大型盾构机上，用于隧道工程挖掘。“该主轴承的研制成功，标志着我国已掌握盾构机主轴承的自主设计、材料制备、精密加工、安装调试和检测评价等集成技术。”李殿中说。
The main bearing, with a diameter of 8 meters and a weight of 41 tonnes..
this is one of the most important breakthrough and critical for heavy engineering. for long time, high end bearings/nuts/bolts concentrated in west and Japan. they kept monopoly for so long. but after years of hard work finally China broken this.
recently China also break the foreign monopoly in high end bearings of aviation , aero engines , high speed railway , heavy duty gas turbine and other critical industries.
On October 24, 2022, the anti-fatigue life test of key components of aero-engines carried out by the Beijing Institute of Aeronautical Materials exceeded 50,000 hours, marking a new breakthrough in China’s high-end equipment manufacturing technology.
The key component of this fatigue test is the aero-engine main shaft bearing independently developed by China. The fatigue life of the equivalent accelerated test on the tester did not fail for 50,000 hours, setting a new record in China.
According to reports, during the operation and service of high-end equipment such as aircraft and high-speed railways, key components will experience fatigue, cracks and fractures, resulting in product failure, which is a major problem in the world’s engineering field.
Through technical research, Chinese researchers have independently developed a number of key technologies for anti-fatigue manufacturing, established an anti-fatigue manufacturing technology system, solved the problem of fatigue failure of key components, and laid a more solid foundation for the comprehensive autonomy of China’s high-end equipment.
Zhao (researcher of Beijing Institute of Aeronautical Materials) Said: Our anti-fatigue manufacturing technology can do almost all key components. The life and reliability of equipment are reflected by key components. With key components, high-end equipment can be made. Therefore, the overall improvement of China’s manufacturing technology has reached three limits: limit life, limit reliability, and limit weight reduction, which means it is at the international leading level.
In 2009, the relevant national departments deployed the major project “Basic Research on Anti-fatigue Manufacturing of High-strength Anti-fatigue Aeronautical Components”, requiring the study of a verification piece to evaluate whether the anti-fatigue manufacturing theory and method are available. Because the main bearing of the aero-engine is the most important and difficult key component, the team of Academician Zhao selected a main point main shaft bearing, which can not only complete the verification, but also solve the problem.
In the next 13 years, Academician Zhao presided over the purification research of new bearing gear steel M50NiL. Through the process routes of “purifying raw materials, refining outside the furnace, VIM+VAR double vacuum smelting, and pulling the billet out of the pier”, the purity of M50NiL has exceeded the international leading level. He also designed a case-hardened stainless gear bearing steel composition system, bringing gear bearing steel to ultra-high strength, high toughness and ultra-high hardness levels for the first time.
On July 28, 2021, the aviation main bearing using the new bearing gear steel M50NiL and the most advanced products in the world were “competed on the same stage” in the anti-fatigue test. The ball life of China’s main bearing reached one million hours, 15 times higher than that of foreign products; Under the maximum load of 1.6 times the load spectrum, the accelerated test life (conversion) exceeds 30,000 hours without failure, breaking the international record of 20,000 hours without failure of similar products. The relevant national departments have successfully accepted and passed the basic research project of anti-fatigue manufacturing, including five mechanisms of anti-fatigue manufacturing, four methods of anti-fatigue manufacturing, and technical standards such as 100% increase in fatigue strength and 100 times increase in fatigue life have been completed. This is an epoch-making milestone, and another world record in the mechanical engineering manufacturing industry was born!
