The main remedy against self-unscrewing of nuts and studs is primarily right choice thread type. Usually all fastening threads are self-braking. They have an angle of helix always less than the angle of friction. In practice, despite correct selection threads, during the operation of the mechanism, spontaneous unscrewing of nuts and bolts is observed. Therefore, to ensure the reliability and failure-free operation of the connections, all nuts and bolts on the aircraft, engines, units and equipment are locked.
Nuts, bolts and shafts of detachable joints can be locked with cotter pins, wire, self-locking nuts, lock nuts, various washers, pins, etc. When replacing a unit, pipeline or part, the locking provided by the design must be used. Replacing one type of locking with another (for example, the use of single lock washers instead of double locks or spring locks instead of lamellar ones, etc.) is not allowed. Reuse of locking parts (cotter pins, wire, lamellar washers, etc.) is also prohibited.
The basic rules for locking nuts, bolts, coupling shafts and other parts of the main types of detachable joints are discussed below.
Locking plate washers. With this control, the following rules are observed:
Before the final tightening of the nut, a gap is selected between the stud and the inner diameter of the plate washer on the side opposite to the mustache, bent onto the flange or housing (Fig. 4.9);
The antennae bent onto the flange or body must have an emphasis in the direction of unscrewing the nut and bent to a snug fit (Fig. 4.10);
Both antennae of the washer, locking the nut, are bent after the final tightening of the nut on one or two faces (Fig. 4.11). .
Bending of the washer tabs to the angle of the nut is prohibited. A gap between the washer tongue and the face of the nut is not allowed. After bending the antennae, it is necessary through a magnifying glass
Rice. 4.9. Lamellar installation scheme
lock washer
check for cracks in the places where the tabs of the lock washer are bent.
Plate washers have several varieties.
Lock washers (Fig. 4.12, a and b). Lock washers connect two adjacent nuts in pairs with the help of antennae bent upwards, thereby preventing their self-unscrewing. This type of locking is widely used on jet engines.
Stop washers. A locking washer with an outer nose that enters a hole drilled in the fastened part is shown in fig. 4.13. After tightening the nut, the edge of the washer is bent to any face of the nut and thereby prevents its self-unscrewing.
nie. Lock washers with an internal toe are also used.
Cap lock washers (Fig. 4.14) are put on the nuts and screwed to the parts with screws.
Rice. 4.14. Nut locking with lock washers
The part hole is shaped to allow the nut to be rotated 30° around the axis and locked.
Cotter pins. When locking nuts with cotter pins, the following rules must be observed:
The cotter pin after normal tightening of the nut must pass through the slots of the castellated nut (Fig. 4.15). Unscrewing the nut to align the slots and the hole for the cotter pin is prohibited. If, when tightening the nut
The pin is placed with the head only up; in this case, when breaking off the antennae, the cotter pin does not fall out;
When bending the antennae of the cotter pin onto the crown of the nut or the stud, the smooth transition with a radius of curvature not less than the thickness of the cotter pin.
The separated ends of the cotter pin after bending should fit snugly against the nut, and the head should enter its slot (Fig. 4.16). When checking critical connections
Niy (aircraft, engine and aggregate control), the antennae of the cotter pins are bred in both directions and tucked into the nut crowns (Fig. 4.15). When locking ordinary connections (less responsible nodes), the antennae of the cotter pins are only spread in both directions and tightly pressed against the edges of the nut, bolt or stud. The rollers and fingers will be countered with cotter pins with the obligatory setting of the washer (Fig. 4.17).
When locking nuts and rollers, cotter pins are used, the dimensions of which are indicated in Table. 4.14 and 4.15.
_____________________________ #
Table 4.14
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Cotter Pin Sizes for Locking Standard Castle Nuts
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Locking with locknuts. The lock nut usually matches the dimensions of the main fastening nut. It is screwed onto the bolt (stud) after tightening the main nut (Fig. 4.18) and pressed against it, thereby creating an additional friction force in the thread. The locknut is tightened moderately with such an effort that it does not perceive the entire load of the tightened connection. Most tightening forces must be taken up by the main nut. The disadvantage of locknuts is that they increase the dimensions of the bolted connections and make the structure heavier, so they are rarely used.
Locking with split spring washers. When locking with spring split washers, tighten the nut until the ends of the spring washer meet to the same level (Fig. 4.19). The split washer with its antennae cuts into the body of the nut and the part and thereby prevents the nut from self-unscrewing. A washer that has lost its elasticity and has a fracture is not allowed to be placed again.
Wire lock. Locking nuts with wire is widely used in threaded pipe connections.
iodine, mainly in the immobile. For locking with wire, special locking holes are drilled in the faces of the nuts. A wire is passed through these holes, then it is twisted and passed through
The locking of nuts and bolts of detachable connections with wire must be carried out in accordance with the requirements of the operating instructions for this type of aviation equipment. So, for example, general locking of bolts on a flange is prohibited if the instruction provides for locking bolts in pairs (Fig. 4.21).
Tander connections of cables are locked in such a way that the clutch cannot turn away from the tension of the cable (Fig. 4.22). Thunderbolts are countered with soft wire.
In some cases, nuts are counter-punched by punching, riveting the end of the bolt, or welding the nut to the bolt. Such connections become one-piece and are used in
Rice. 4.21. Wire bolt locking scheme
connections where bolt tightening is not required during operation.
Piercing is done after tightening the nut and filing the end of the bolt so that it protrudes from
nuts no more than 1 mm. Then, with the help of a core at the end of the bolt, three to four cores are made near the edge of the nut, due to which the end of the bolt is distributed and does not allow the nut to unscrew itself.
It should be noted that in all types of inspections of aviation equipment, the reliability of detachable connections and the locking of their parts are necessarily checked.
Author: elremont from 26-06-2015* lock nuts / bolts *
Fixing the nut in some cases is very important. So I'll list a few fixing methods for you and show you exactly how they are used. Is not complete guide, there may be more methods, but these are the majority of the methods that I know about.
*Lock-nut*
The basic way to secure a standard nut is to thread the nut onto the bolt and then tighten to the specified torque with a torque wrench, but for this demonstration we will just hand tighten it and you could use a counter nut.
That is, the locknut is designed to fix the nut and stop it from moving. After you tighten the first nut, the second nut or locknut will be placed behind the first and then we will tighten it. This will stop the nut from loosening. IN extreme cases, with high vibration, this type of nuts can actually come loose. This happens quite often when using two regular nuts, although you can buy a specially designed locknut like this one, made specifically for this purpose.
* thread locking compound *
You can use thread locking compound. It is a highly fluid anaerobic liquid. Since it displaces the air around it, it is actually used as an adhesive. You simply smear it onto the thread where you want it to be. Then you tighten the nut... Tighten and then wait for it to dry, this will compress the nut and stop it from moving. Thread locking compound is one of the most common ways to secure a nut or bolt. This is very effective method. There are quite a few different brands of compounds, so you have to make sure it's the right one for you. Some of them are so strong that you may need an impact wrench to loosen them. Loctite is a very common brand. I'm sure most people have seen it. So this is a quick and easy way to fix a nut.
* Spring washers *
There are also spring washers, they are made of spring steel, and they are designed so that when the nut is tightened, a load constantly acts on it, which can prevent it from unscrewing. Usually a spring washer is used along with a regular washer. First put the usual, and then the spring. They don’t always put a regular washer when using a spring washer, it depends on the specific location. After that, we bait the nut, and tighten it to the specified torque. This is a very common thread locking method, but in extreme cases, high vibration can cause the connection to become loose. I saw this, the spring washer broke into several parts, which meant that the nut could now be unscrewed. But in most cases, such a washer presses on the nut, which makes it difficult to unscrew it. Therefore, once everything is tightened, it is difficult to unscrew it. And it will work, but it won't perfect option with strong vibration, the vibration weakens this connection.
* Serrated washers *
Serrated washers can be used to prevent some nuts and bolts from coming loose, but they aren't perfect either. The problem is that if you tighten them too much, it can flatten the teeth and they end up just turning into regular washers. Once flat they are pretty much useless. But you can use them in certain circumstances, they are very popular in washing machines because they are very cheap. So you just put the washer on, screw on the nut, and turn it in to the specified torque with a torque wrench. It is important not to overtighten them so as not to flatten the washer, otherwise you will end up with something like this. As I said, they are very cheap, which is why they are used in many washing machines and the like. They can prevent nuts and bolts from loosening, but this is a local solution.
* Self-locking nut *
The self-locking nut has a nylon ring at the top that catches the bolt when you tighten it. That is, you can start turning quite easily, just like a normal nut, but once you get to the nylon, then it becomes difficult to turn, you will need a tool to screw the nut onto the bolt. This can take quite a bit of time because the wrench will need to be turned all the way, with a regular nut you can just turn it down quite easily by hand. So self-locking nuts are very useful, they are used in many places, but it takes a lot of time to turn them. Self-locking nuts are useful, you will find them in all machines, but they are not very suitable for critical machinery, as they can be loosened by vibration.
* Deformed knot *
Sometimes you can't see a nut with a deformed thread on the inside, it's actually only slightly deformed, so it's pretty easy to screw it on initially until you get to the deformed spot, and then it sticks really tight. Then it will take wrench or head to be able to tighten the nut. Once you've tightened everything holds up very well, but in extreme conditions, again with high vibration, they can come loose.
* Nord washers *
They are unique in that they have cams on front side washers. They should be placed in pairs, like this. That is, you put two pieces together with the cams out and tighten the bolt on them. You can put a nut. Tighten to the specified torque. Once the nut is tightened, these two washers will grab each other and the joint will be very difficult to unscrew. They are very good at vibrating. It is highly unlikely that any of these washers, if properly seated, will come loose with vibration.
* Castellated nut *
They are often used in critical machinery such as aircraft. On board the aircraft, after tightening it, a piece of wire will be threaded through it, and this will prevent the nut from ever being unscrewed. So, to use one of them, you bait it on a bolt, tighten it to the specified torque, or as long as it drags. Now I will drill through the bolt with a small drill bit. But such a drill better fit for larger nuts and bolts than this one. This stainless steel so I'll work carefully and slowly. I'll put some more lube on the bit. Once you've done that, you can put the pin in and wrap it around and it won't loosen the nut until you pull the pin out.
Hope this demo was helpful to you. I have covered some of the methods you can use to stop nuts and bolts from loosening. There are also washers that I don't have, but it's just a washer and a tab that flexes and prevents the nut or bolt from coming loose.
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The simplest and one of the earliest methods is known as locking a bolted joint with an additional nut called a locknut. The installation of the lock nut precedes the installation of the main one, as shown in the figure. Locking with locknuts is rarely used due to insufficient reliability. When tightening, the lock nut (see Fig.), pulling the bolt, takes on the entire load, while the main nut is unloaded. This sometimes forces the use of reverse circuit: the lock nut is placed under the main nut, which provides a more favorable distribution of forces.
Locknuts are indispensable in cases where stepless fixation of the position of the nut on the bolt is required, especially when the nut moves significantly along the bolt
The use of conical lock nuts increases the adhesion between the lock nut and the main nut. To increase thread engagement, conical locknuts are provided with slots that increase cone compliance in the radial direction. Excessive cone compliance can make it difficult to fully tighten due to jamming of the nut on the threads in the last stages of tightening. The disadvantage of conical locknuts is the complication of processing the seating surfaces of the cone and the occurrence of increased collapse stresses on the supporting surfaces.
Common types of castellated nuts:
- DIN 935, 937, 979
- ISO 7035-7038
- GOST 5918-73, 5919-73, 5932-73
GZO Group
INDUSTRY STANDARD
Checked in 1986. To be checked in 1996 (Revised edition, Rev. No. 1, 2). This standard establishes the following types of locking of bolts, screws, studs, and nuts in threaded connections and pins: - 1 - locking with lock washers; - 2 - locking with cotter pins; - 3 - locking by metal deformation; - 4 - locking with wire. Other types of locking can also be used in threaded connections, for example, locking with self-locking nuts, spring and gear washers, lock nuts. (Changed edition, Rev. No. 1 , 2).1. LOCK WASHER
1.1. Stopping by type 1 must correspond to that indicated in Fig. 1, 2 and 3.
Execution 1.1.
Execution 1.2.
(Changed edition, Rev. No. 1).1.2. Bend the washer petals on the face of the hexagon of the nut (bolt) to produce in the position of the washer turned in the direction of unscrewing along its stop with the toe in the nest of the part (Fig. 4) or with the foot in the end of the part (Fig. 5).
1.5. Fitting the coincidence of the washer petals with the faces of the nut (bolt) is carried out by tightening the nut (bolt) at an angle of not more than 30 ° or replacing the nut (bolt). Fitting by unscrewing the nut is not allowed. allowed. (Changed edition, Amendment No. 2). 1.6. The petals of the washers must be pressed against the faces of the nuts. 1.7. The washer petals can be bent on one or two faces of the nut (bolt). Bend to the edge of the reinforced petals to produce that part of the bent petal, which provides the largest area of contact with the edge of the bolt (nut). 1.8. It is not allowed: - shearing or shifting of the material, cracks and tears at the place of bending of the washer petals; - nicks and flattening of the washer petals during bending; - bending the petals more than once; - protrusion of the petals above the nut (bolt) by more than 2 mm; - blows with a hammer at the place of bending of the washer petals; - leave the washer petals not bent. 1.9. The washer petals should be bent with special tongs according to the technology for assembling the product. In hard-to-reach places, it is allowed to bend the washer petals using special mandrels or punches made of copper and aluminum alloys. (Changed edition, Amendment No. 1).
2. STOP WITH COTTON PINS
2.1. Stopping by type 2 must correspond to that indicated in Fig. 7, 8 and 9.
Execution 2.1.
Execution 2.2.
l = 0.5d ¸ 0.75d
d - diameter of the bolt, screw, stud
Execution 2.3.*
2.2. Alignment of the hole for the cotter pin in the bolt, screw and stud with the slot in the nut should be done by tightening the nut at an angle of not more than 30 °, by replacing the nut or bolt, screw, stud or by selecting the thickness of the washers. Adjustment by loosening the nut is not permitted. When tightening the nut, the maximum allowable tightening torque must not be exceeded. ________ * Apply in hard-to-reach places (Changed edition, Rev. No. 2). 2.3. The cotter pin should enter the hole freely or under a slight unimpacted load. 2.4. The cotter pin should be buried in the slot of the nut. The protrusion of the cotter pin above the slot of the nut is allowed by no more than 0.4 of the nominal diameter of the cotter pin. 2.5. Allowed: - loose fit of the ends of the cotter pin to the surface of the nut within 0.1 ¸ 0.3 mm; - touching the bent ends of the cotter pin of the thread of the bolt, screw, stud; - biting off cotter pins with subsequent deburring. If necessary, the areas disturbed as a result of biting off are covered with a paint and varnish coating assigned by the product developer. (Changed edition, Amendment No. 1). 2.6. Not allowed: - crushing of the cotter pin head; - tears and cracks at the ends of the cotter pin; - flattening and twisting of the ends of the cotter pin; - rocking of cotter pin after installation; - use of the cotter pin more than once. 2.7. Bending of the ends of the cotter pin on the edge of the nut should be done with a punch made of copper or aluminum alloys, filling the ends of the cotter pin in the slot of the nuts with a blunt screwdriver.
3. STOPPING BY METAL DEFORMATION
3.1. Stopping type 3 must comply with the following: - in hell. 10, 11 and 12 - for bolts, screws and studs; - to hell. 13 and in table. 1 - for set screws; - to hell. 14 and in table. 2, damn. 15 and in table. 3 - for cylindrical pins; - to hell. 16 - for conical and cylindrical pins. (Changed edition, Rev. No. 1).
Execution 3.1.
End punching
(Revised edition, Rev. No. 1).
Execution 3.2.
Thread punching
(Revised edition, Rev. No. 1). ___________ * Dimensions provided. instr.
Execution 3.3.
Hole punching
Execution 3.4.
Punching set screws
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View A |
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For permanent connections |
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For screws |
For screws |
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with M6 thread or less |
with thread over M8 |
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Table 1
Execution 3.5.
Roll pin punching
table 2
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Pin diameter d |
Execution 3.6.
Roll pin embossing
Table 3
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Pin diameter d |
Housing material |
Aluminium alloy |
Execution 3.7.
Caulking of conical and cylindrical pins
d 1 \u003d d - 0.2 ¸ 0.8
d 2 \u003d d + 0.2 ¸ 0.8
___________ * Amount of collateral instr. (Changed edition, Rev. No. 1). 3.2. When punching into a thread, put the center punch at the exit point of the bolt, screw, stud from the nut. 3.3. The size and location of the core points are not controlled.4. WIRE STOP
4.1. Stopping by type 4 must correspond to that indicated in Fig. 17-22.
Execution 4.1.
(Revised edition, Rev. No. 1).
Execution 4.2.
Execution 4.3.
(Changed edition, Rev. No. 1, 2).
Execution 4.4.
Nuts are shown conditionally. This design can also be used on hexagonal bolt heads
(Revised edition, Rev. No. 1). When locking three or more parts (versions 4.1 and 4.4), the number of bolts or nuts locked with one wire is established by the design documentation or the product manufacturing technology. (Changed edition, Amendment No. 2). 4.2. The wire must be positioned in such a way that when an arbitrarily oriented load is applied to it, the threaded connection is tightened. 4.3. The wire must be twisted without gaps between the turns. A turn is understood as one complete revolution of one end of the wire relative to the other. The number of turns must be at least three for a length of 10 mm for wire with a diameter of up to 0.8 mm inclusive, and at least two for a length of 10 mm for a wire with a diameter of more than 0.8 mm. By agreement with the customer, it is allowed to reduce the number of turns in the grafting to 1.5. (Changed edition, Amendment No. 2). 4.4. In hard-to-reach places with small distances between the locking parts, it is allowed not to twist the wire. Note. Hard to reach places are installed according to reference samples of products agreed with the customer. (Changed edition, Amendment No. 1). 4.5. The ends of the wire must be twisted (3-4 turns) and tightened. 4.6. When performing locking, tears and twisting of the wire are not allowed. 4.7. The wire must be taut, deflections and slack are not allowed. An example of an entry in the design documentation for blocking execution 2.1:
Stopping 2.1 - OST 1 39502-77
Parent organization for standardization
Text matches source
Threaded connections are quite reliable and efficient. They are considered one of the most common and cost-effective. However, when exposed to vibration, there is a possibility of weakening them. This can often be seen in the example of nuts that randomly unwind during the operation of various devices. Therefore, methods have been developed that can reduce this effect or completely eliminate it.
Ways to avoid loosening the nut
1. Use of washers. This method is one of the most common. It is used in the manufacture household appliances and some types industrial equipment. It does not have a high degree of reliability and assumes protection against arbitrary unwinding. A soft metal washer is put on the thread, and then the nut is tightened, squeezing it out.
2. Washer and Grover. A more reliable way, practiced as well as the transport industry. Protects the threaded connection from arbitrary unwinding even in the presence of slight vibration. First, a regular washer is put on the thread, and then a grover. After that, tighten the nut. Grover here serves as a kind of spring, creating tension that prevents unwinding.
3. Special lock nut. The method using a special nut cannot be called the most effective. However, it takes place in world practice, and is used in some types of production.
4. Using a thread locker. The composition is applied to the place where the nut will be, after which it is put on the thread. This is a fairly effective way to prevent arbitrary unscrewing, but its effectiveness is affected by temperature changes, high humidity and exposure to active substances. Therefore, its scope is limited.
5. Application of two or more nuts. One of the most reliable methods. Two nuts are screwed onto the thread at once. After clamping the first, the second is tightened separately, holding the first in its original position and even trying to unscrew it a little.
6. Fixation with cotter pin. This is the most reliable method, able to withstand almost any external impact and strong vibration. It is used in critical areas. The nut is fully tightened. Then, using a drill and a thin drill, a hole is made through it, along with the bolt. A hairpin is inserted into the resulting hole, the antennae of which are unbent, preventing falling out. Such a nut can only be torn off by a very strong rotational force in the direction of the thread.
