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Rice. 178. Keys for tightening K01 nuts with external locking

Rice. 179. Relative weight of ring nuts with screwed elements various shapes

The groove profiles shown in Fig. 179, K-/X, can be obtained by a high-performance rolling method using a hob profile cutter.

Nuts, the design of which is shown in Fig. 179, K/ -/X, tighten only with tubular keys.

When tightening the attachment parts with ring nuts, it is necessary that the end of the nut rests on the part at least 4 times its height (dimension S in Fig. 180,/). If the height of the step on the shaft does not allow this condition to be met.

Rice. 180. Installation of a ring nut without a washer (U) and with a washer ()

A massive washer is installed between the nut and the part (Fig. 180).

It is important that the washer is centered. In Fig. 181,/ incorrect installation is shown: the washer may move into the recess behind the thread. In Fig. 181, -/V shows methods for centering a washer, of which the simplest is the method of centering along the outer diameter of the thread (Fig. 181,).

In cases where uniform pressure on the part being tightened is required, spherical washers are used (Fig. 182). Other ways to solve this problem are to maintain strict perpendicularity between the end of the nut and the average diameter of the thread, or to use threads with axial and radial clearances in the turns, allowing the nut to somewhat self-align on the nut.

In Fig. 183 -188 show the designs of round nuts with external threads, various shapes and with various elements for screwing.

Rice. 181. Centering under- [t;

insert washers: /-without centering; lino to the outer diameter of the thread; III-along the shoulder of the gantry; IV - according to details

Rns. 182. Spherical washers

Rice. 183. Ring nuts with external thread and internal grooves

Rice. 184. Ring nuts with external threads and external grooves

Rice. 185. Ring nut with external thread and end grooves

Rice. 186. Ring nuts with external threads, triangular splines and projections

Rice. 187. Ring nuts with external thread and RNS. 188. Ring nuts with external threads and axial holes, iodine wrench with internal hexagon

Rice. 189. “Non-locking” nuts. Fixation methods

SOME TYPES OF FASTENING PARTS

Non-locking nuts and captive bolts

In some cases, after unscrewing a nut with several threads, it is desirable to fix it in order to prevent the nut from completely unwinding from the threaded end of the bolt. Such “non-losing” nuts are used, for example, for hinged (“autoclave”) bolts, as well as in structures where it is required to loosen the nut one or two turns in order, for example, to adjust the position of one part relative to another, etc.

In Fig. 189,/ and shows methods of fixing by riveting or coreing the ends of the bolts, and in Fig. 189, /- by riveting the limit washer. If the design allows the nut to be screwed on from the opposite end of the threaded rod, then a smooth cylindrical belt is left with the screwed side (Fig. 189, IV).

From the fixation methods shown in Fig. 189, K-VIII, the simplest and most reliable method of fixation is the zeger - a locking ring (Fig. 189, V/). In the design in Fig. 189, V / at the end of the bolt is made

a recess with a height equal to the height of the threaded section of the nut. When screwing, the nut falls into the recess; the threaded collar at the end of the bolt to a certain extent protects against complete screwing of the nut.

In Fig. 190 gives an example of the use of “non-losing” nuts for fastening the lid

Rice. 190. “Non-locking” nuts. The case of attaching the cover to the body

• ordinary
• high
• low
• self-aligning
• anchor fixed
• floating
• special.

Rice. A.

Rice. B.

Table 1.

Research was carried out on M6 threaded pairs made of Z0KhGSA steel with 4h6h-4H6H and 6e-5H6H threads used in domestic industry. It was shown that 35 operational bulkheads (tightening the connection to a given torque, holding at 250 °C for 1 hour) withstood all 100% of the self-locking nuts of the 4h6h-4H5H threaded pair and only 50% of the self-locking nuts of the 6e-5H6H threaded pair. The average values ​​of the unscrewing torques of self-locking nuts for the 4h6h-4H5H threaded pair are 32-80% greater than for the 6e-5H6H threaded pair. This ensures higher locking stability of the threaded connection over fifteen operational bulkheads. For self-locking nuts made of heat-resistant materials, operated at high temperatures As a rule, reliable locking of threaded connections is limited to five operational bulkheads.

In order to reduce the labor intensity of installation and assembly work, increase performance characteristics products use self-locking ear nuts, fixed and floating in the cage (Fig. D). Fixed ear self-locking nuts are made in two-ear, one-ear and corner versions (Fig. D, a) and are used for fastening hatches, panels, etc.

Rice. D.

The nut is secured to the part being connected using two rivets. They are made by extracting sheet material on multi-position presses or cold heading from wire. Locking properties are ensured by compressing the bonnet, and sealed blind eye self-locking nuts - by compressing the threaded part of the cap (Fig. D, b). For sealed compartments, ordinary ear nuts vulcanized with rubber are also used (see Fig. D, b). Self-locking nuts in a cage (Fig. D, c, d) make it possible to compensate for technological errors that are inevitable when assembling large-sized parts of complex configurations. The nut is fastened to the cage in grooves or slots that limit its movement and prevent it from falling out of the cage. Depending on the standard size, the minimum movement of the nut in the plane of the cage is 0.5-1.0 mm. Options for the design of the clip are determined, as a rule, by the design of the product. In addition to those discussed, self-locking nuts floating on a bracket, floating in clip-on clips (Fig. 4, e, f), etc. are widely used.

Where are nuts used?

Under different operating conditions, as well as with different magnitudes and types of loads absorbed by the connection, the following nuts are used:

• ordinary
• high
• low
• slotted for locking joints
• self-locking of various designs
• self-aligning
• anchor fixed
• floating
• special.

Rice. A. Nuts used in mechanical engineering

Tall nuts (height 0.8d) are used for connections that work in tension and can withstand large alternating loads. Often, for such connections, “reinforced” nuts with a height of 1.2d are used. This significantly increases the creep of the connection, eliminates the destruction of connections along the shear of the turns of the bolt-nut threaded pair, this gives full use bolt strength when working in tension.

In order to reduce the weight of structures, tall nuts with a diameter of 12 mm or more are made with a cylindrical hexagon groove having a size approximately equal to the wrench size.

Low nuts are used in connections that bear small tensile loads, as well as in shear connections.

Slotted hex nuts are used in critical connections operating under vibration loads. They are secured to the bolt using cotter pins or wire. For the same purposes, hex nuts with a bolt that is rolled onto the bolt are often used (Fig. A, a).

Blind hex nuts are used for decorative purposes. Blind nuts for pressing are used in detachable connections where mounting approaches to the nut are difficult. Round spherical nuts are used as decorative and to eliminate bending loads on the bolt in the connection. Wing nuts are used for quick-release connections, as well as in hinged bolts, etc. (Fig. A, b).

Round nuts with internal and external threads, with slots at the end and along the perimeter, are widely used in connections with a diameter of 14 mm or more. The smaller weight and dimensions of round nuts compared to hex nuts can significantly reduce the weight of structures as a whole. Round nuts with internal threads and splines at the end (usually 2 splines) are widely used in small diameters, starting from 1.4 mm, providing the same advantages of connections (Fig. A, c).

To prevent self-unscrewing of threaded connections during operation, in most cases it is necessary to lock them. However, the weight of structures, the low reliability of locking, the high labor intensity of manufacturing and installation and assembly work for locking threaded pairs led to the creation and widespread introduction of self-locking nuts in all branches of mechanical engineering. The basis of locking with self-locking nuts is to create a guaranteed tension and increase friction in a threaded pair due to deformation of the threaded part of the nut or the use of threadless elastic inserts.

A typical self-locking nut is a regular hex or other nut with a thin-walled threaded cylindrical section at the non-supporting end - a flange. The bolt has longitudinal slots (4-6), deformed along the perimeter by a conical mandrel to create tension in the threaded pair (i.e., the locking properties of the nut). Such nuts are called self-locking slotted nuts (Fig. A, d, f). Depending on the operating conditions, the following self-locking slotted nuts are used: hexagonal high and low, twelve-sided, round with knurling for press-fitting, if the design of the unit allows for an increase in the hole in the part being connected, and the approach to installing the nut is difficult.

Now, due to the high labor intensity of milling splines, slotted self-locking nuts, especially sizes M3-M10, have practically been replaced by more technologically advanced, but not inferior to them in terms of locking reliability, self-locking nuts with a continuous deformed bolt (Fig. A, e, f). Self-locking nuts with a continuous bolt are also used high and low, press-fit, dodecahedral, with a groove configuration, etc. The scope of application of high and low self-locking nuts, dodecahedron and with a groove configuration is determined by the same operating conditions as conventional nuts.

In connections that work primarily for shear, hexagonal self-locking nuts without a flange, with a support collar and a reduced size of a hexagon wrench (thin-walled hexagon) are widely used. Self-locking of such nuts is achieved by deforming the hexagon itself (see Fig. A, e). In automated assembly of threaded connections, self-locking nuts with a washer rolled onto the support collar are used.

Rice. B. Self-locking, sealed nuts with fluoroplastic (a) and with a nylon liner (b)

A sealed self-locking nut is shown in Fig. B, a. A sealing liner based on fluoroplastic is mounted in the bore of the nut with an interference fit and protrudes above the end by 0.5-0.8 mm. When assembling the connection, the conical transition from the thread to the smooth part of the bolt fits tightly into the insert, sealing the thread along the inner and outer diameters of the insert. When tightened, the part protruding from the nut seals the connection along the joint plane. Locking is ensured by compressing the nut against the hexagon.

A self-locking hex nut with an elastic nylon liner is shown in Fig. B, b. The nylon liner is rolled into the top of the nut. The inner diameter of the liner is approximately equal to the inner diameter of the bolt thread. The thread in the liner is formed by the bolt when it is screwed in, providing the necessary tension for locking the threaded pair. Nuts with a nylon liner can be round, twelve-sided, eye, etc.

Rice. WITH. Types of compression of the bonnet of self-locking nuts

In Russian industry, the locking element of self-locking nuts is obtained by compressing the bolt by a given amount at two points, at two points along an ellipse or at three points parallel to the axis or at an angle of 12-16°. It is possible to obtain a counter element by settling the bonnet (Fig. C). The thread accuracy of the nuts is 5N6N.

Self-locking nuts remain functional even after repeated overhauls of threaded connections. The maximum moment of the first screwing of the nut and the minimum moment of the fifteenth unscrewing (M1zav and M15otv) are normalized. In domestic industry, they correspond to the values ​​​​indicated in table. 1. ISO standards for the fifteenth unscrewing torque are higher due to the use of precise threads: for bolts 4h6h, for nuts 4H5H.

Table 1.

Standards for the locking properties of self-locking nuts

Research was carried out on M6 threaded pairs made of Z0KhGSA steel with 4h6h-4H6H and 6e-5H6H threads used in domestic industry. It was shown that 35 operational bulkheads (tightening the connection to a given torque, holding at 250 °C for 1 hour) withstood all 100% of the self-locking nuts of the 4h6h-4H5H threaded pair and only 50% of the self-locking nuts of the 6e-5H6H threaded pair. The average values ​​of the unscrewing torques of self-locking nuts for the 4h6h-4H5H threaded pair are 32-80% greater than for the 6e-5H6H threaded pair. This ensures higher locking stability of the threaded connection over fifteen operational bulkheads. For self-locking nuts made of heat-resistant materials operated at high temperatures, as a rule, reliable locking of threaded connections is limited to five operational bulkheads.
The final quality control of self-locking nuts consists of measuring the tightening and unscrewing torques. This allowed foreign companies, when standardizing self-locking nuts within the ISO framework, not to specify design documentation the outer diameter of the bonnet, the height, size and shape of the crimp, leaving these issues at the discretion of the manufacturer.
In order to reduce the labor intensity of installation and assembly work and increase the performance characteristics of the product, self-locking ear nuts are used, fixed and floating in the cage (Fig. D). Fixed ear self-locking nuts are made in two-ear, one-ear and corner versions (Fig. D, a) and are used for fastening hatches and panels.

Rice. D. Self-locking ear nuts, fixed and floating
The nut is secured to the part being connected using two rivets. They are made by drawing from sheet material on multi-position presses or by cold heading from wire. Locking properties are ensured by compressing the bonnet, and sealed blind eye self-locking nuts - by compressing the threaded part of the cap (Fig. D, b). For sealed compartments, ordinary ear nuts vulcanized with rubber are also used (see Fig. D, b). Self-locking nuts in a cage (Fig. D, c, d) make it possible to compensate for technological errors that are inevitable when assembling large-sized parts of complex configurations. The nut is fastened to the cage in grooves or slots that limit its movement and prevent it from falling out of the cage. Depending on the standard size, the minimum movement of the nut in the plane of the cage is 0.5-1.0 mm. Options for the design of the clip are determined, as a rule, by the design of the product. In addition to those discussed, self-locking nuts floating on a bracket, floating in clip-on clips (Fig. 4), etc. are widely used.
In some industries, profiles with self-locking floating nuts are widely used (Fig. E). Pressed profiles are made from aluminum alloys, bent profiles - from steel sheet. The position of the nuts on the profile is fixed using local stampings (see Fig. E, a) or paws bent along the cuts (see Fig. E, b).

Rice. E. Profiles with self-locking floating nuts

The length of the profile with self-locking floating nuts is determined by the design of the product, and it can reach 1.5 m. The profile is fastened to the part being connected using rivets with a pitch of 150-250 mm. The use of profiles with self-locking floating nuts makes it possible to reduce the weight of the structure and also increase the strength of the connection. Strength is increased by reducing the number of holes for rivets in the parts being joined.

In Fig. 143 showing the main ones types of hex nuts: with one-sided chamfer with diameter D 1 = S (Fig. 143, I); with a one-sided chamfer with a diameter D 1 = 0.95 S (Fig. 143, II); with a double-sided chamfer (Fig. 143, III); with ring sharpening at the supporting end (Fig. 143, IV); with a collar on the supporting end (Fig. 143, V).

In Fig. 144 and 145 nuts are given various types; slotted (Fig. 144, I); crowned (Fig. 144, II); slotted with a shortened hexagon (Fig. 144, III); with a conical crown (Fig. 144, IV); with shortened hexagons (Fig. 145, I); with an entry cone for a socket wrench (Fig. 145, II); with conical and spherical supporting surfaces (Fig. 145, III, IV).

Depending on the purpose, nuts can have different heights from 0.3d to 1.25d (d is the thread diameter). Low nuts are used as locknuts and for lightly loaded connections, high nuts are used for heavily loaded connections, as well as for frequently disassembled connections. For average working conditions, nuts with a height of (0.8-1)d are used. At these ratios, the condition of equal strength of the nut and the threaded rod is approximately met.

In Fig. 146—153 show nuts with in different forms wrapped elements; in Fig. 154 - nuts with internal screw elements (hexagon, splines), used in cases where force tightening is required with limited radial dimensions; in Fig. 155 - cap nuts, used in cases where it is necessary to ensure the tightness of a threaded connection; in Fig. 156, 157 nuts with external threads are presented.

Spline nuts. The design of a cylindrical nut with small triangular slots along the generatrices (Fig. 158) is progressive.

Such nuts may in the future replace hex nuts. Their main advantage is a more favorable distribution of forces when tightening the nut. From Fig. 159 it can be seen that the shoulder of the forces acting when tightening on a triangular profile spline with an apex angle of 60° is approximately 2 times greater than in the case of tightening a hex nut.

The number of splines on the circumference of the nut can be 6-7 times greater than the number of hexagon faces. Consequently, with the same tightening torque, the force exerted on each spline will be 12-15 times less than the force acting on the edge of the hex nut when tightened with a tubular wrench, and 36-45 times less than when tightened with a ring wrench. The danger of crushing the tightening surfaces, which is so real with hex nuts, is in this case excluded. Thanks to the shape of the screw elements, the danger of the key being torn off when tightening is eliminated.

Another advantage is that the nut can be turned to almost any angle when tightening, making it easier to tighten in tight spaces where the span of the wrench is limited.

Spline nuts with the same thread diameter have smaller radial dimensions and less weight than hex nuts. The disadvantage of slotted nuts is that they can only be tightened with a tubular wrench.

When designing fastening units with slotted nuts, free space should be provided above the nut for putting on a tubular wrench. The height of this space when tightening with an open tubular wrench can be reduced by reducing the thickness of the wrench. Reducing the height of the splines (Fig. 160, I-III) makes it easier to manipulate the key: when removing and putting it on again, the key is centered by the cylindrical part of the nut. It is also possible to use special keys with adjustable jaws allowing access to the nut from the side.

The margin of safety for crushing of spline nuts (Fig. 161, I) is so large that it is possible to reduce the number of splines without much damage to reliability (Fig. 161, II-IV). The mass of the nut decreases; the advantages when tightening the nut are fully preserved if the slots on the key are cut along the entire perimeter.

1) diameter of the nut along the recesses of the splines D1 = (1.35—1.50)d where d is the nominal diameter of the thread; the upper limit (1.5) applies to small nuts, the lower limit to medium and large ones;

2) outer diameter of the nut along the protrusions of the splines D = (1.10—1.15) D 1 ; here the upper limit also applies to small nuts, the lower limit to medium and large ones;

3) nut height H = (0.8—1.0)d.

Spline nuts (Fig. 160) are most often secured with cotter pins.

Ring nuts. Ring nuts are used for tightening mounted parts, rolling bearings and similar parts on shafts large diameter.

This type of nut includes nuts called round spline nuts according to GOST 11871-80.

The peculiarity of ring nuts is their relatively low height with a large diameter. Due to the large diameter of the thread, a nut of normal height is overly strong and very heavy.

It is not difficult to determine the height of the nut required by the condition of equal strength of the nut and the shaft (for the case of a hollow shaft).

The condition for the equal strength of a hollow shaft, working in tension from the action of a tightening force, and a threaded belt, working in shear from the action of the same force, has the following form:

where [τ] is the permissible shear stress in the thread; [σ р ] - permissible tensile stress of the shaft; H is the length of the working thread belt (nut height); D c p and D 0 are the average diameter of the thread and the diameter of the hole in the shaft, respectively.

For average conditions, taking into account the stress concentration in the thread turns, it can be assumed that the permissible shear stress in the thread is 2 times less than the permissible tensile stress for the shaft. Then

From this expression it is clear that the height of the nut decreases with increasing diameter of the shaft hole (Fig. 163).

When standardizing ring nuts, it is difficult to take into account the factor D 0 /D cp; Usually the height of the nuts is set only depending on the diameter D of the thread. In this case, the height H of the nuts (Fig. 164) is approximately (0.15-0.25) D (smaller values ​​refer to nuts of large diameter, and larger values ​​​​of smaller diameter).

Due to the low height of ring nuts, they use only fine pitch threads. The use of large threads (Fig. 165, I) would lead to a decrease in the total number of threads on the nut with a decrease in strength (due to a relative decrease in the number of threads with a full profile), would worsen the axial direction of the nut along the shaft and, in addition, would weaken the shaft from for reductions internal diameter thread.

Thread pitch s for ring nuts is usually taken approximately equal to (0.015-0.050)D, where D is the thread diameter; the upper limit applies to threads of small diameter (20-50 mm), the lower limit to threads of large diameter (100-120 mm). When designing ring nuts, it is recommended to select the thread pitch (and nut height) so that the total number of threads on the nut is at least 5-6 (Fig. 165, II).

As in everyone threaded connections, thread reserves should be provided on both sides of the nominal position of the nut. Recommended reserve values ​​are shown in Fig. 166.

The size of the nut along the recesses of the splines, which determines the minimum thickness of the working ring of the nut, is made equal to S = (1.2-1.3)D. Outside diameter nuts D 2 fluctuates within ~(1.4-1.5)D (Fig. 164).

The areas of the nut on which the grooves are located should not extend onto the supporting surface of the nut end, since when the side edges of the grooves are crushed when tightening or unscrewing, the nut will not fit tightly to the part being tightened. To do this, recesses or chamfers are made, one-sided or (better) two-sided (Fig. 167). The outer diameter D 1 of the supporting surface must be smaller size S between the depressions of the grooves by at least 0.5-1 mm.

In Fig. 168 presents ring nuts with internal threads and with different locations of screw grooves; in Fig. 169—177 — nuts with screwed elements of other types.

Most often, nuts with external grooves are used, the number of which ranges from 4 to 12. Such nuts are tightened with open-end wrenches (Fig. 178, I) or wrenches with socket (Fig. 178, II) or internal radial (Fig. 178, III) teeth.

The number and shape of the grooves and protrusions of the nut significantly affect its mass. In machines where weight reduction is a priority and where a large number of ring nuts are used, significant attention is paid to the design of the grooves.

In Fig. 179 shows the relative masses of nuts with grooves various designs. The mass of a nut with four grooves is taken as one. As can be seen from Fig. 179, I-IV, a simple increase in the number of grooves can significantly reduce weight. The mass of a nut with twelve grooves (Fig. 179, IV) is 86% of the mass of a nut with four grooves (Fig. 179, I). Further reduction in mass is achieved by selecting non-working areas of the protrusions between the grooves (Fig. 179, V), reducing the height and width of the protrusions (Fig. 179, VI) and reducing their number (Fig. 179, VIII).

The most advantageous design is (Fig. 179, IX) with a small number of protrusions of a triangular profile; the mass of the nut is 53% of the mass of the original nut. The groove profiles shown in Fig. 179, V-IX, can be obtained by a high-performance rolling method using a hob profile cutter.

Nuts, the design of which is shown in Fig. 179, VI-IX, are wrapped only with tubular keys.

When tightening the attachment parts with ring nuts, it is necessary that the end of the nut rests on the part at least 3/4 of its height (dimension S in Fig. 180, I). If the height of the step on the shaft does not allow this condition to be met, a massive washer is installed between the nut and the part (Fig. 180, II).

It is important that the washer is centered. In Fig. 181, I shows incorrect installation: the washer may move into the recess behind the thread. In Fig. 181, II-IV shows methods for centering a washer, of which the simplest is the method of centering along the outer diameter of the thread (Fig. 181, II).

In cases where uniform pressure on the part being tightened is required, spherical washers are used (Fig. 182). Other ways to solve this problem are to maintain strict perpendicularity between the end of the nut and the average diameter of the thread, or to use threads with axial and radial clearances on the threads, allowing the nut to somewhat self-align on the shaft.