Views: 100 Author: L Publish Time: 2024-01-12 Origin: Panda fastener
Bolts are a common fixture tool. However, their long-term usage can cause many problems. These include connection relaxation, inadequate clamping force and bolt rust. The bolt connection slack will have an impact on the efficiency and quality of parts processing. How can the bolt be made to tighten?
Three anti-loosening techniques are commonly used: friction, mechanical and permanent.
The principle of the countertop jam nut is: When double nuts are jammed together, two friction surfaces are created. One is between nut, fastener and nut. During installation, preload is applied to the first frictional surface at 80% the amount of preload that is applied to the second frictional surface. During shocks and vibrations, friction on first friction surface disappears. However, at the same moment, the first nut compresses, causing friction to increase on second friction surface. To loosen the nut you must overcome both the first and second friction forces. The first friction force is decreasing while the second friction increases. The anti-loosening will be improved.
Tang Thread Anti Loosening: Tang Thread fasteners also have double nuts that are anti-loosening, but the nuts rotate in opposing directions. The friction on the first surface of the fastener decreases when shocks and vibrations are applied.
The first nut in the diagram (on the right) has a tendency of loosening and retreating, i.e. The nut rotates left. The second nut rotates in an opposite direction from the first one (left rotation in the image), so that the force used to loosen the first nut directly converts into the force needed to tighten the second. The nut won't loosen again.
2. 30deg wedge shaped thread anti-loosening technique
The bottom of the negative thread has a wedge-shaped bevel of 30deg. When the bolt and the nut are tightened together, the tip is pressed tightly against the wedge-shaped notch of the negative thread. This creates a strong locking force.
The normal force applied to the contact between threads due to the different angle of the teeth is 60deg, not 30deg, as it would be for ordinary threads. The normal wedge thread pressure of 30 degrees is obviously much higher than the fastening force, so the friction resulting from this must be increased.
DTFLOCK Thread Schematic
The figure below shows that the force indicated by two arrows in the form of Pa is the same for both threads. The traditional 60deg thread has an average pressure of 1.15Pa, while the 30deg thread has the wedge at the bottom bevelled at a 30deg angle. Both the angle and the size of the thread's normal pressure have been changed.
This way, between the 60 deg traditional thread and 30 deg, the normal pressure ratio is 12:7. The friction against loosening increases accordingly. The 30 deg thread can eliminate thread forces that are not uniform.
We mentioned that the 30 degree wedge threads we discussed above should be included in this category.
The self-locking nut products are divided into high-strength nuts for road construction machines, mining equipment, vibratory machinery and equipment and nylon nuts for aerospace, aviation and tanks.
To prevent the screw from loosening, wedges are inserted in between the nut.
4.Thread-locking adhesive
The thread locking adhesive is a mixture of (meth-)acrylate (initiator), co-promoter (polymerization inhibitor), dye, filler and stabilizer. in a certain proportion.
To tighten the nut to the torque specified, pass the bolt through a screwhole, then apply thread-locking adhesive to the threads on the engaging part.
If the screw hole depth is greater than bolt length, it is necessary that the locking adhesive be applied to the bolt threads. The bolt should then be assembled and tightened to the torque specified.
For blind hole condition: drop the locking adhesive to the bottom of the blind hole, then apply the locking adhesive to the threads of the bolt, assemble and tighten it to the specified torque; if the opening of the blind hole is downward, just apply the locking adhesive to the threads of the bolt, and there is no need to apply the adhesive inside the blind hole.
After assembling all other parts, locking glue is applied to the part of stud that engages with the nut. The nut will then be assembled and tightened to the specified force.
Adjustable screws): After assembly and tightening to the specified torque, drop the locking adhesive into threaded engagement so that it penetrates by itself. Adjustable screws: Drop the locking adhesive in the threaded engagement after assembly and tightening the torque specified.
5. Double stacked wedge type anti-loosening locking washers
The wedge locking washers have radial serrations that are covered by the surface they are in direct contact with. The displacement of the washer can only be caused by dynamic loads when the locking system is exposed to them.
The wedge locking washer can be extended further in the thickness direction than the bolt's longitudinal displacement in the thread direction.
The wedge locking method tightens bolts using clamping force instead of friction.
HEICO-LOCK has a history of 120 years. Products include wedge locking washers (including RING-LOCK), wedge locking nuts (including 316 stainless steel and carbon steel coated with Dacromet), and 254SMO (carbon steel).
6. Slotted nut, Cotter pin
Insert the cotter-pin into the hole of the bolt and the slot in the nut after the nut has been tightened. Then, twist the cotter-pin end to prevent relative rotation between the bolt and nut.
The cotterpin is mounted as shown in the image below.
Slotted nuts are used with the screw-perforated bolts and cotter pins to stop the bolt rotating in relation to the nut.
7. Tandem wire anti-loosening
Tandem steel wire anti-loosening is to put steel wire into the bolt head hole, the bolts in series, play the role of mutual restraint. This relaxation is very reliable, but disassembly is more troublesome.
This method of anti-loosening is often used in airplanes and rockets.
Single-stranded wires are generally commonly used for distributing small clusters of screws at close intervals or in very inaccessible places, as shown in the figure.
8.Stop Washer
Once the nut is tightened, either a single or double lug stop washer should be bent to rest against both it and its connector respectively, to secure and lock the nut. If two bolts require double locking, double brake washers may also be used so that both nuts brake against one another.
Spring washers employ the anti-loosening principle by producing continuous elastic force after flattening; this enables threaded connections between nuts and bolts to maintain frictional forces that create resistance, thus preventing loosening.
At the same time, the sharp corners of spring washer openings are embedded into both surfaces of bolt and connected part respectively, thus preventing rotation between bolt and connected part.
10. Hot-melt fastening technology
Hot melt fastening technology, without pre-opening holes, allows closed profiles to be connected directly with hot melt adhesive, with great success in the automotive industry.
This hot melt fastening technology is a kind of cold molding process through the center of the equipment to tighten the shaft of the motor's high-speed rotation to be connected to the frictional heat generated by the plastic deformation of the sheet material, self-tapping and screwing.
Hot melt fastening connection process steps and processes include six stages: rotation (heating) → penetration → through-hole → tapping threads → screwing threads → fastening.
As soon as a strength reaches ninety percent, its color changes from yellow to green; then once it hits one hundred percent it turns black.
12. Pre-Tensioning
High-strength bolted connections usually do not require additional anti-loosening measures, because high-strength bolts generally require the application of a large preload, creating strong pressure between nut and connection, with friction torque to stop rotation of nut, so as to keep nut from coming loose.
The above is Pandafastener proposed 12 specific measures to prevent the bolt from loosening, in addition, we also provide a variety of services and high-quality fastener products, if you need to contact us!
