Hardlock

Hard Lock Nut FAQs

What is the HL (Hard Lock Nut)?
How is the Wedge Principle Employed in the HL (Hard Lock Nut)?
Why is the HL (Hard Lock Nut) Resistant to Loosening?
HL (Hard Lock Nut) Self-Locking Function FAQs
Have Measures Been Taken to Prevent Galling and Seizing?
What Are the Best Environments for Using the Hard Lock?
Is the Hard Lock Reusable? Is Its Self-Tightening Performance Affected by Reuse?
HL (Hard Lock Nut) Specification Selection FAQs
Is the Hard Lock Nut Limited to Metric Screw Thread Specifications?
Should a special bolt be used the Hard Lock Nut?
What details should be taken into account when selecting the Hard Lock Nut?
How about environmental specifications such as hot and or cold temperature use, anti-corrosion or chemical resistance?
Is the self-locking effect sustainable even when the nut is subjected to extreme temperature swings?
Does the Hard Lock Nut require the use of a plain washer or a spring washer?
Do you supply the Hard Lock Nut in configurations other than three standard types (H-1, H-2 and H-3) described in the catalogue?
HL (Hard Lock Nut) Installation FAQs
Is it necessary to lubricate the bolt?
How about in the case of installing hot dip galvanized nuts?
Are any special tools required?
Can an impact wrench be used?
In the case that a gap remains between the convex and concave nuts after tightening, will this cause any problems?

Is the fastening torque different for the concave nut and the convex nut?
HL (Hard Lock Nut) Post-Installation Maintenance FAQs
What subsequent maintenance is required after Hard Lock Nuts are fastened (such as further tightening)?
What special care should be taken when removing Hard Lock Nuts?
Are there any cautions to be observed when reusing Hard Lock Nuts?
What factors can contribute to looseness when Hard Lock Nuts are used?

 

What is the HL (Hard Lock Nut)?

FAQ1

The Hard Lock Nut is a self-locking nut developed by Hard Lock Industry through a process of trial and error as an elegant solution to the technical question: “Can the wedge principle be employed for the purpose of loosening prevention?”

How is the Wedge Principle Employed in the HL (Hard Lock Nut)?

FAQ2A

In general, forcing a wedge into the gap between a cylinder and its surrounding tube makes it possible to create a powerfully locked assembly (as shown in the figure).

FAQ2B

Likewise, creating matching key grooves in both a nut and a bolt, and then using a hammer to drive a wedge into those grooves can be used to produce a powerful self-locking effect. However, this method is unsatisfactory from the standpoint of operability.

FAQ2C

The solution employed in the Hard Lock Nut is to use two nuts to play the roles of the hammer and wedge respectively. A small eccentricity in the sliding part of the convex top surface of the lower nut acts as the wedge. When the upper nut with its concave bottom surface is tightened, the effect produced is exactly the same as that produced by a hammer driving in a wedge. Moreover, it is much more effective to use a screw as this makes it very easy to drive the wedge into place

Why is the HL (Hard Lock Nut) Resistant to Loosening?

FAQ3A   FAQ3B

This is because when fastened, the Hard Lock Nut produces stress both in the direction of the axis and in a direction perpendicular to the axis. Firstly, the convex fastening nut generates axial torque in the same way as a normal nut. 

Then, as the concave lock nut is tightened, the wedge effect generates stress perpendicular to the axis, which pushes the convex nut against to the screw thread. When the concave nut is completely tightened, the HLN produces a stable self-locking force by means of the combined stresses of P1 + P2 + P3 (in the figure above), with the result that it remains unaffected by the external vibration or impact.

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HL (Hard Lock Nut) Self-Locking Function FAQs

Have Measures Been Taken to Prevent Galling and Seizing?

Yes. The Hard Lock Nut is well lubricated against galling and seizing.

What Are the Best Environments for Using the Hard Lock?

The Hard Lock Nut can be used in a wide range of locations including:
• Locations subject to harsh impacts and/or vibration
• Locations where joints are welded or bonded but it is necessary to remove them for maintenance or servicing
• Important locations where post-installation maintenance not feasible
• Dangerous locations involving a hazard to human life
• Locations subject to extreme temperature variations
• Locations where very strong fastening is not possible
• Locations in extremely tough environments

Is the Hard Lock Reusable? Is Its Self-Tightening Performance Affected by Reuse?

In principle, the Hard Lock Nut can be reused many times. The actual suitability for reuse will depend on the environmental conditions of previous use, but as long as the nut's material has not deteriorated or been excessively deformed, its self-tightening performance will not decline.

When considering reusing a nut, remove the concave portion, and then manually screw it in until it touches the convex portion. As long as there is a gap of about one pitch between the two, they can be used again. If there is not an adequate gap, the concave portion may undergo a plastic deformation, rending it unfit for further use.

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HL (Hard Lock Nut) Specification Selection FAQs

Is the Hard Lock Nut Limited to Metric Screw Thread Specifications?

No. Other threads such as Whitworth, unified screw thread and high-tension specifications are also available.

Should a special bolt be used the Hard Lock Nut?

No. You can use the same commercially available bolts (the old JIS2 class and the new JIS 6g) you use at present. When we make special bolts in-house, they are manufactured to match the nut, but a difference in tolerance may result between the two such as when the nut is made to the old JIS2 class or new JIS 6H specifications. In this case, the bolt may deviate a great deal from the JIS standard range. Be aware that this may result in the Hard Lock Nut not fitting in or the concave and convex parts not fitting together very well.

What details should be taken into account when selecting the Hard Lock Nut?

After confirming the material and length of the bolt intended for use, pay attention to the design and ensure that there are at least 2 threads extended beyond the top of the nut assembly.

How about environmental specifications such as hot and or cold temperature use, anti-corrosion or chemical resistance?

The Hard Lock Nut does not contain any specialized materials. It is designed to withstand any environment when the material is properly selected and coated.

Is the self-locking effect sustainable even when the nut is subjected to extreme temperature swings?

Yes. When heated, the material of the nut expands and the fastening force decreases. And when cooled, the material contracts and the fastening force increases. In the case of conventional nuts, this repeated expansion and contraction of the material causes the nut to loosen. However, the Hard Lock Nut maintains its fastened condition because of the wedge effect, s it does not loosen even under repeated exposure to extremes of temperature.

Does the Hard Lock Nut require the use of a plain washer or a spring washer?

A plain washer prevents the material of the nut from becoming embedded while a spring washer or a conical spring washer provides relief from stress. We recommend using the Hard Lock Nut together with a washer appropriate for the environmental conditions.

Do you supply the Hard Lock Nut in configurations other than three standard types (H-1, H-2 and H-3) described in the catalogue?

Yes. We can supply other types to a customized design as long as the wedge effect-generating mechanism can be incorporated into the part requiring the self-locking performance. Accordingly, the Hard Lock Nut can meet virtually any situation or condition.

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HL (Hard Lock Nut) Installation FAQs

Is it necessary to lubricate the bolt? 

Yes. Apply lubricant where the environment permits. And when so doing, there is no need for concern about any loss of self-locking performance. Lubricating the bolts will ease the work involved in any subsequent removal of the nuts.

How about in the case of installing hot dip galvanized nuts?

Due to the thickness and rough surface of the coating, it is advisable to lubricate both the bolt and nuts before tightening.

Are any special tools required?

No. You can use an ordinary commercially available spanner or wrench.

Can an impact wrench be used?

It is OK to use an impact wrench provided that you tighten the convex nut first, followed by the concave nut.

In the case that a gap remains between the convex and concave nuts after tightening, will this cause any problems?

No. There should be no problem. The concave nut controls the amount of torque regardless of the size of any gap. Even if all Hard Lock Nuts are tightened with same torque, the gap will vary from one set to another due to slightly different thread accuracy of each nut.

Is the fastening torque different for the concave nut and the convex nut?

Basically, as the convex nut is for fastening, tighten it to your own specified value and then tighten the concave nut (lock nut) with the recommended amount of torque. In the case that you want to employ the same torque value for both concave and convex nuts, please consult with t Hard Lock Industry directly.

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 HL (Hard Lock Nut) Post-Installation Maintenance FAQs

What subsequent maintenance is required after Hard Lock Nuts are fastened (such as further tightening)?

After completing the initial clamping, it is recommended that the nut assembly be given an additional turn to ensure a smooth engagement of the threads. In the case that additional tightening is not possible, please take into account the anticipated decrease in the bolt’s axial tension(10%-20%) by applying additional torque when performing the initial clamping.

What special care should be taken when removing Hard Lock Nuts?

First, apply lubricant to the bolt and the nuts. Then remove the concave nut first, followed by the convex nut. Do not attempt to remove both nuts together as this will cause the nuts seize up.

Are there any cautions to be observed when reusing Hard Lock Nuts?

Do not use a Hard Lock Nut if when tightening the concave nut until it is pressed against the convex nut (in general, a gap of one screw pitch is needed between the concave and convex portions), no gap whatsoever is found between two nuts, as this means that the wedge effect will not function. In such a case, please contact Hard Lock Industry directly. (The class of bolt used can also be a problem.)

What factors can contribute to looseness when Hard Lock Nuts are used?

There are two factors with respect to looseness, namely a relative rotation of the nuts against the counterpart bolt and a decrease in bolt-axial tension.
Loosening of the nuts due to rotation is limited to the following cases in which the wedge-effect does not function.
  1. Where the upper concave nut is not tightened with the specified torque
  2. Where after repeated use, the upper nut is deformed and does not function
  3. Where the nuts have been incorrectly installed
Next, potential factors contributing to a decrease in bolt- axial tension include the following.
  1. Where the lower convex nut is not sufficiently tightened
  2. Where axial tension between the nut and the corresponding bolt decreases after a considerable lapse of time following the initial clamping.
  3. Where the clamped part becomes deformed over time
  4. Where he clamped part becomes embedded causing the nuts loosen
  5. Where dissimilar products made of metals with different coefficients of linear expansion are fastened in conditions subject to significant temperature swings.
Apart from the above, there are many other conceivable factors that may contribute to looseness, but these have absolutely no relation to the construction of the Hard Lock Nut.

 


 

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