最近网上流传一篇文章，介绍日本hardlock防松螺栓技术在高铁中应用。笔者作为该技术领域的亲历者与“防松螺母”等国家专利的持有者，读此文后百感交集。螺纹紧固件作为机械结构中运用最广的零部件，虽然结构简单，价格便宜，但是在动荷载强烈作用下的松动问题给人们带来的困扰至今依然是科技攻关的选题。

其实，如何防止螺母和螺栓之间的松动，从它诞生之日起人们就做出努力了。长期以来，人们研究各种各样的螺母防松措施，如采用双螺母、销钉和使用胶水等，可以说是花样繁多。然而这些方法和技术应用都局限在一定的使用条件下，它们在方便性、经济性通用性、高效和可重复性等方面总是存在这样那样的不足，其中一个核心问题就是在可重复使用条件下如何长期保持防松性能。

我国铁路系统很早就开始探索推广应用具有防松性能的螺母/螺栓了。早在20世纪80年代初，上海铁路局就针对轨道结构弹条I型扣件研制了-种防松螺母，其原理就是针对扣件弹条的结构特征,在螺母底面设计了与弹条相吻合的槽，能实现螺母止退，起到了很好的防松效果，在当时得到了-定的推广运用。但是，由于该技术是针对特定弹条扣件结构的防松螺母，并不适合在其他结构上应用。进一步的研究发现，弹条扣件在使用中产生松弛并不完全是由于紧固件的松动所致，它还受到了弹条自身弹性松弛导致的扣件扣压力损失影响。而且该防松螺母在安装时要比原有螺母复杂，因此该轨道扣件的防松螺母后来渐渐淡出了人们的视野。

铁路部门大规模推广运用防松螺母是在20世纪90年代，这起源于一种变牙型防松螺母在铁路编组站驼峰缓行器上的运用。缓行器是车辆在编组时的减速装置。缓行器中的制动轨在工作时夹住行进中的车轮，因此在工作时承受了巨大的振动冲击，导致缓行器制动轨上螺栓几乎每天都要复紧，工作量极大；另一方面，制动轨螺母为了满足检修需要,必须经常拆卸，所以螺母必须能够重复使用。此外，为工作方便，安装方法还必须简单。

针对以上特点,有关人员经过反复试验，研究出了-种变牙型结构的防松螺母。这种防松螺母的基本原理是改变了螺母内螺纹底部的螺纹牙角度，使得螺纹连接副在工作时外螺纹的大径与内螺纹的底部相接触受力,并对外螺纹大径形成一- 个契形作用,改变了传统螺纹紧固件螺纹斜面受力的特点,尤其是该防松螺母的安装操作与普通螺母基本相同。该技术经过现场使用,取得了良好效果。当时铁道部有关部门为此专门发文，要求在全国铁路驼峰缓行器上推广运用这种变牙型防松螺母。

变牙型防松螺母在技术上的特点是能够重复使用、安装简单、不需要其它附加装置，因此它的通用性强。后来变牙型防松螺母逐步在铁路的工务和车辆部门得到了全面推广运用，并在2000年制订了相应的铁路行业标准，成为我国当时铁路行业中应用最为广泛的防松螺母。随着变牙型防松螺母使用的不断深人,通过大量实践人们逐渐发现该技术还存在某些不足，如不同材料对它的防松性能有较大影响，尤其是不锈钢材料;又如，在重复多次使用以后，防松性能呈下降趋势。

进入21世纪以来，随着我国对外开放和技术交流的日益广泛，新技术不断进人我国并得到了应用发展，其中hard lock防松螺栓是比较有代表性的技术之一。由于它的重复使用性好、防松性能好,得到了一定认同，但是要作为一种广谱性的防松紧固件，该技术还存在着一定不足，尤其是它的制造和使用复杂以及成本过高，在我国铁路行业并没有得到广泛应用。

近几年来，随着制造技术和材料技术的不断进步，各行业运用防松紧固件技术的交流更加广泛，更多类型的防松紧固件不断地运用到了铁路行业。尤其是我国广大科技人员的创新意识不断增强，一此自主研发的防松紧固件新技术的如雨后春笋般涌现出来，并在铁路行业中得到了推广。但是我们对这些技术成果似乎还并不满足,我们理想中的方便、经济、通用、高效和可重复的、永不松动的防松螺母这一技术目标还没有完全达到，我们还需继续努力。

创新永远在路上。

Recently, an article about the application of Japanese hard lock self-locking bolt technology in high-speed railway is widely spread on the intemet. As the witmess of this specific field of technology and the holder of national patents including ' self-locking bolt', the author was overwhelmed with mixed feelings after reading it. Threaded fasteners are the most used parts in mechanical structures. Even though their composition is simple, and price is low, the problem of looseness under strong dynamic load is still a confusing subject needs scientific breakthrough.

As a matter of fact, great effort has been spared on how to prevent looseness between nut and bolt since the day they were invented. For a long time, the research was focusing on various nut self-locking measures, including double nut, pin or glue, with ideas out of-the-box. However, all the methods and technology applications are limited within scenarios , always having some sort of shortcomings in convenience , economy, adaptability, efficiency, repetitive usage and more. One core question is how to maintain self-locking performance under repetitive use over long- tem.

Railway system in China has been exploring and popularizing application of nut/ bolt with self-locking performance since early stage. Back to the beginning of 1980s，Shanghai Railway Admini stration developed a self-locking nut matching track structure springI-type buckle, the principle of which is that according to the structural characteristics of the buckle spring, a slot that matches thespring is designed on the back of the nut, so that the nut can be prevented from withdrawing , demonstrating noticeable self-locking performance. Application was promoted to certain extent. However, because this technology is self-locking nut targeting specific spring buckle structure, it is inapplicable to other structures. Further studies found that the looseness of spring buckle during service is not only caused by looseness of the fastener, but also influenced by the buckle pressure loss caused by loss of elasticity in the spring itself. The installation of the self-locking nut is more complicated than that of the original nut, thus the self-locking nut of that track fastener faded out of our sight gradually.

The wide promotion of self-locking nut by railway departments is around 1990s， which originated from the application of a tooth- varying self-locking nut in railway marshalling station hump shaped retarder. Retarder is a deceleration device of vehicle during marshalling. The braking rail of retarder claps the running wheels during operation, therefore huge vibration impact is received at the time, which requires the bolts on retarder braking rail to be fastened everyday, meaning huge amount of workload. On the otherhand, braking rail nut are often removed for maintenance purpose , therefore the nuts must be good for repetitive use, and the installation must be simple for work convenience.

Targeting the above features , researchers conducted tests repetitively, and developed a type of self-locking nut with tooth- varying structure. The basic principle of this type of self-locking nut is about changing the hread tooh angle of thread bottom inside a nut, so that the major diameter of external thread contacts with the bottom of inner thread when the thread connection pair is in operation. A wedge force is enacted on the major diameter of the external thread, changing the characteristics of force on the inclined thread plane of conventional thread fastener. Moreover, the installation of this self-locking nut is almost the same as a conventional one. Practical application of the technology demonstrates good performance. The concemed department of Ministry of Railway specially issued notice on this topic, demanding promotion of applying this tooth-varying self-locking nut in hump-shaped retarder nationwide.

The tooth-varying self-locking nut has technical characteristics of repetitive use, simple installation, and no auxiliary device, therefore it is generally applicable. From then on, tooth-varying self-locking nut went on full-scale promotion and application in railway maintenance and vehicle departments , and relevant railway industry standards are devised in 2000，becoming the most popular self-locking ut in railway industry. Over the years , huge amount of practice has led people to realize its shortcomings as well. For example，different materials have large impact on the self-locking performance, especially stainless steel. Also, after repetitive use , self-locking performance shows tendency of worsening.

Upon entry of 21st century, with the opening of China and increasing communication of technology, new technologies are entering China and developing, among which hard lock self-locking bolt is one of the representative technologies. Because it can be repetitively used and has good self-locking performance, it has received certain recognition. However, there are shortcomings of this technology when considered as normalized self-locking fastener , especially the complicated manufacture and applicaion, and overly high cost, so it is not widely applied in domestic railway industry. In recent years, with the advancement of manufacture and material technologies，the communication between industries about self- locking fastener technology has become more popular, and various types of self-locking fasteners are aplied in railway industry. Our scientific researchers are having stronger consciousness of innovation, thus independently developed self-locking fastener technologies are springing out and promoted in railway industry. However , it seems that we are still not satisfied with these achievements. To reach the technological goal of ideal self-locking nut as convenient, economical，applicable, efficient, repetitively usable, and always fastened, more efforts must be spared. Innovation is always on the road.

Translated by ZHANG Liman