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Introduction of Easy-locking ^TM Thread Form Technology

 Or called as Locking Threads with 30° Wedge Ramp

What is Easy-locking ^TM ？

Easy-locking ^TM （中文商标：易锁牢）is a well-known brand of anti-loosening & self-locking nuts which have transformed the standard internal thread profile into a self-locking female thread form with the addition of a unique 30° wedge ramp at the root of the thread. It is compatible with standard 60° male thread fasteners.

The wedge ramp allows male fasteners to spin freely relative to the female threads until clamp load is applied. At that point, the crest of the standard male threads is drawn tightly against the wedge ramp, creating a continuous spiral line of contact along the entire length of the thread engagement. As clamp load increases, the wedge ramp pushes against the male thread from all sides, eliminating the radial clearance that allows fasteners to begin self-loosening under vibration.

Why choose Easy-locking ^TM thread form ?

l It has reliable, stable and safe seismic resistant performance, and overcomes limitations of the current many other locking methods;

l It can be reused while does not affect its anti-loosening locking properties;

l Free from the influence of high temperature and corrosion, a wide range of applications;

l Free rotation type, torque is applied until it has been tightened, convenient loading and unloading;

l It matches with the standard external thread and doesn’t need to replace the currently used bolt.

l Without any auxiliary lock components such as spring washer, locking gasket, etc.

l It has a significant effect to overcome sliding tooth problems on soft materials (such as aluminum alloy, stainless steel, etc.).

l Not only nut, the locking threaded hole with the same locking performance can be also made with Easy-locking tap and can be used for components widely.

Principle of Easy-locking ^TM thread technology

All types of machines and sub-assemblies will use fasteners during connecting or assembling operation. Fastener brings convenience to machinery industry, but it has an unavoidable weakness, i.e. it becomes loose on its own during excessive vibration and thus lead to damage or disassembly of a component or a complete set of equipment, or even a severe accident.

In order to solve the fastener loosening problem, many scientists and engineers in different countries have conducted extensive tests and researches. They took different kinds of measures such as locking pieces, pins, nylon inserts, deformed threads, chemical adhesives, etc. These approaches can prolong to some extent, the service life before the fastener gets loose. But the fastener loosening problem has not been fundamentally eliminated.

The key to the loose problem of the threaded fasteners lies in the thread structure shape. After studying the shape and the load conditions of fattener thread, US engineers redesigned geometrical shapes of the thread and in the late 1970s invented 30° wedge ramp thread technology -American Military Standard # MIL-N-85353. Since then, the fastener loosening problem has been completely resolved.

Why it can effectively solve the problem of loose bolts and nuts? This is because of its unique structure. There is a 30° wedge-shaped ramp under the bottom of the female thread tooth, when the bolt and nut are mutually tightened, the bolt cusp will be tightly supported on the inclined plane of the variable thread form anti-loosening threaded wedge, resulting in a significant tightening force. Since the tooth-shaped angle varies, the FN generated between the thread contact and the bolt axis are 60°, rather than an 30° as the standard thread. Normal pressure of the locking threads with Easy-locking is obviously much greater than the fastening pressure, therefore, anti-loose friction produced also greatly increases. (See Figure 1)

It can be seen from Figure 2 that the forces indicated by the two arrows are Pɑ, the normal pressure of the standard 60° thread angle is P=1.15Pɑ; since there is a 30° wedge-shaped ramp in the bottom teeth, the angle and magnitude of its normal pressure have varied, the normal pressure P=2Pɑ. Thus, the normal pressure ratio of the Easy-locking thread and the standard 60° thread is approximately equal to 12:7 and the friction of the Easy-locking thread increases accordingly. Wedge surface of the Easy-locking thread can also eliminate problems ，such as uneven stress, tripping seizure and so on. The standard 60° V-shaped thread bears more than 80% of the load in the first and second thread mating surface while the followed mating surfaces carry a small load. So under the condition of vibration load, standard fasteners can easily overcome the locking force on the thread contact surfaces, produce rotation, then loosening. This is the reason for loosening of the standard threaded fasteners. 

Because the main force of the standard thread fastener is just on nut contacts of the first and second thread and the other teeth basically don't endure the force, therefore, when the tightening torque is bigger, the first thread is prone to bend and shear deformation, and only then makes the second thread surface withstand the stress and generate a locking force. And so on, the load bearing surface sequentially transmits the force one by one and accordingly causes the shear and wear of the threads and the shear and abrasion damage of each tooth are very serious, resulting in a significant decline in the nut thread strength and ultimately produce sliding teeth. However, because of the unique structure of the Easy-locking thread, all cusps of the bolts are tightly supported on the wedge-shaped ramp, and load carried on each helix tooth is relatively uniform and can be dispersed to each surface and each point to make the thread locking friction caused similar everywhere and effectively fight the transverse vibration. The study made by University of Michigan shows that the first carrying surface of the variable thread form anti-loosening thread bears 24% of the load while and the last one also carries 17% of the load. So, in normal operation of the fasteners，each tooth of the Easy-locking thread can uniformly withstand the load and there is no stress concentration. Therefore, it will not produce problems like looseness or screw looseness , and fatigue strength has also been improved exponentially.

Load Distribution

Research studies performed by Lawrence Livermore National Laboratory, Massachusetts Institute of Technology, and others have confirmed that joints using Easy-locking threads carry load much more uniformly than ones with standard 60° threads. Additionally, they show that the percentage of load on the first engaged thread produced with a Easy-locking tap is significantly lower, 24% versus 64%, with five threads of engagement. (See Figure 2)

Torque/Tension Relationship

The unique 30° wedge ramp in the Easy-locking thread form contacts the male threads at a different angle than standard threads do. A greater portion of the assembly forces are redirected from an axial direction to a radial direction to create the locking capability, so Easy-locking threaded joints generally require 10% to 20% more torque to generate equivalent joint tension as a standard 60° thread.

Although higher torque is required in all Easy-locking threaded joints, the increase in required torque will vary depending on the types of materials and coatings being used (nut, bolt, mating surfaces, etc.). This torque/tension relationship should be evaluated in the actual joint to determine the proper torque required to develop the specified tension.

Testing performed by the Goddard Space Flight Center has shown that Easy-locking offers a consistent pattern of friction, especially when the threads are lubricated. Easy-locking’ s more consistent friction factor directly relates to a more consistent joint tension or preload.

Vibration Loosening Resistance

Extensive testing on Junker’s transverse vibration equipment has proven that the Easy-locking internal locking thread form outperforms other thread locking devices. In fact-unlike other locking devices, which lose preload within the 100 seconds of testing---Easy-locking joints remain tight until the bolts fail due to fatigue. (See Figure 3)

Photoelastic Test

In order to better observe the load distribution of variable thread form anti-loosening thread under load, we have conducted the photoelastic test experiment research both on standard nut and Easy-locking nut. The method is to use the same bolt with the two different nuts for the test. In comparison with the load distribution of bearing shown in Figure 4, it is obvious that the fastening force of Easy-locking nut distributed over the entire length of thread engagement and the force distribution is uniform. (See Figure 4)

Fatigue Life

Testing performed on ¼”-28 Easy-locking fasteners in conjunction with NAS624-32 bolts has shown that Easy-locking nut can enhance fatigue life 300% over standard fasteners. The even load distribution with Easy-locking consistently reduces the stress concentration that leads to fatigue failures. (See Figure 5)