Testing of Various Types of Hard Lock Nut
Vibration Impact Test (Horizontal impact) (Vertical impact)
- We conducted our own original severe vibration impact tests based on the US NAS3350/3354 standard screw looseness test, and verified that all types of Hard Lock nuts exceed this evaluation standard by a clear margin. As self-locking nuts used in civil engineering applications such as railways, highways, bridges, pylons, etc., Hard Lock nuts are exposed to a wide range of vibrations and impacts on a continuing basis. However, the data from these tests proves that Hard Lock nuts maintain a stable tightened condition regardless of the type of impact to which they are exposed. A performance comparison with other general-purpose nuts demonstrates the clear superiority of Hard Lock nuts for tasks where vibration resistance is paramount. See video
Horizontal Impact Test
Vertical Impact Test
Junker horizontal screw looseness test
After Director Ohashi of the Japan Research Institute for Screw Threads and Fasteners (and originally from the Shonan Institute of Technology) along with others carried out tests at a variety of angles, we put in the manufacturing request with Iwata Tekkosho. This testing allows confirmation of the degree to which the initial axial force (tightening strength) drops under a variety of parameters, giving the results in both numerical and graph form. While not as extravagant as the NAS3350, this test provides reliable numerical data and has become established in Europe as a method for evaluating screw looseness.- Test conditions
Tested sizes: M10 to M16
Amplitude of vibration: ±0.25 mm to ±1.5 mm
Vibration frequency: 1 to 30 Hz
Axial force: 1 to 80 kN
Tensile Strength Test
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No. Test product Breaking load 1 General-purpose nut 9,050kg 2 General-purpose nut 8,950kg 3 Hard Lock nut 9,800kg 4 Hard Lock nut 9,800kg Size: Hard Lock nut M16 X P2.0 Material: SS400
- Amsler Tensile Test
Torque / Axial Force Test
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(Relation between tightening torque and bolt axial force)
Unlike conventional double nuts,with Hard Lock nuts there is no increase in the axial force applied to the bolt even when the upper (concave) nut is tightened, which means that in the case of Hard Lock nuts it is possible to control the amount of torque and axial strength. *However, from the point when the gap between the upper and lower nuts completely disappears, the axial force rises slightly. So care should be taken not to over-tighten the upper (concave) nut.
| Test sample | Test product | Size | Material | Tightening torque | Lower nut | Upper nut | Change in axial force % |
|---|---|---|---|---|---|---|---|
| No.1 | Hard Lock nut | M10×P1.5 | SS400 | 25N/M | 1.6 | 1.6 | 0 |
| No.2 | Hard Lock nut | M10×P1.5 | SS400 | 25N/M | 1.45 | 1.45 | 0 |
| No.3 | Double nut | M10×P1.5 | SS400 | 25N/M | 1.65 | 1.8 | 9 |
| No.4 | Double nut | M10×P1.5 | SS400 | 25N/M | 1.8 | 2 | 11 |
| *The tightening torque given here is common to both the upper and lower nuts. In the case of Hard Lock nuts, the lower nut is a convex nut. | |||||||
Applied Results Test
This test was carried out by gradually loosening the upper nut from the specified torque condition.
In this test, Hard Lock nuts maintained their completely connected condition regardless of the environment. This test was conducted based on the assumption that the nuts were not fully tightened during installation. For example, even when loosened by 45 degrees, in the case of an M12 Hard Lock nut more than half of the tightening torque remained. Moreover, when a vibration test was performed in this condition, no loosening occurred. This result is further evidence that in the case of Hard Lock nuts, a self-locking effect is exhibited even if the nut is not fully tightened.