Formulas and definitions for thread cutting. Thread. Basic thread parameters. Classification What is a nut
Threaded connections are the most common type of detachable connections. They are carried out using fastening threaded parts (bolts, screws, studs, nuts, etc.)
Advantages: reliability, ease of assembly/disassembly, simplicity of design, low cost (due to standardization), manufacturability, ability to adjust the compression force.
Flaws: stress concentration in the thread gullies, low vibration cost.
On a development of a cylindrical surface, the helix is located at a certain angle ψ , this angle is called the thread lead angle.
The thread stroke, which is the distance between the points of the same name on one helix. The main characteristic of a thread profile is the angle between adjacent flanks in the plane of the axial section, called the thread profile angle. For triangular profile metric, inch, trapezoidal threads.
There are two main methods for making threads: cutting and rolling. Thread cutting is carried out with cutters, combs, dies, taps, threaded heads, and milling cutters.
Thread rolling is carried out using combs or rollers on thread rolling machines by plastic deformation of the workpiece. This method is highly productive and is used in mass production for the manufacture of standard fasteners.
The main geometric parameters of cylindrical threads are:
d– outer diameter (nominal thread diameter);
d1- internal diameter of the nut thread;
d2- average thread diameter, i.e. the diameter of an imaginary cylinder on which the thickness of the coil is equal to the width of the cavity;
p- thread pitch, i.e. the distance between the same sides of two adjacent turns in the axial direction;
ph- thread stroke, i.e. the distance between like sides of the same turn in the axial direction;
α
- thread profile angle;
42. Friction moment in the thread and at the end of the nut (screw). Calculation of threads for bearing and shear stress. Nut height and screwing depth.
The vast majority of threaded connections are pre-tightened. The tightening is created during assembly in order to prevent the joint from opening or moving the parts being connected after the application of the working load.
When screwing a nut (or a screw with a head), it is necessary to apply a screwing torque T to overcome the resistance moment T P in the thread and the resistance moment T T at the end of the nut:
T head = T R + T T, (2.1)
where T P = F t d 2 / 2 = 0.5 F zat d 2 tg(Ψ + φ 1) ; (2.2)
T T = 0.5 F zat f T d avg, (2.3)
F tightening – axial tightening force;
d2 – average thread diameter;
Ψ – thread lead angle;
φ 1 – reduced (taking into account the influence of the profile angle α) friction angle in the thread: φ 1 = φ / cos(α/2),
φ – friction angle of materials of the screw-nut pair;
f T – coefficient of friction of materials of the nut – part pair;
d av – average diameter of the ring (Fig. 2.2):
d av = 0.5(D + d h).
The operation of threaded connections shows that failure of bolts, screws, studs, etc. parts occurs due to the rupture (or stretching) of their rod along the thread or transition section at the head. Destruction or damage to thread elements occurs less frequently and is typical for parts that are often subjected to disassembly and assembly. If necessary, perform verification calculations of the thread for strength based on shear and crushing stresses.
The thread shear strength condition has the form
τ cp = Q/A cp) ≤[τ cp ],
Where Q– axial force; Aср – cutting area of the thread turns; for screw (see Fig. 1.9) A av = π d 1 kH g, for nut A av = π DkH Here N g – nut height; k– coefficient taking into account the width of the base of the threads: for metric threads for a screw k≈ 0.75, for nut k≈ 0.88; for trapezoidal and thrust threads (see Fig. 1.11, 1.12) k≈ 0.65; for rectangular thread (see Fig. 1.13) k= 0.5. If the screw and nut are made of the same material, then only the screw is checked for shearing, since d l < D.
Thread strength condition to crumple looks like
σ cm = Q/A cm ≤[σ cm ],
Where A cm – conventional crushing area (projection of the contact area of the screw thread and nut onto a plane perpendicular to the axis): A cm = π d 2 hz, where (see Fig. 1.9) nd 2 – length of one turn along the average diameter; h– working height of thread profile; z= N G / R - number of threads in nut height N G; R– thread pitch (according to the standard, the working height of the thread profile is indicated N 1).
The required height of the nut is determined from the condition of the bolt shaft being equal in tensile strength under the influence of axial load and the nut thread in bending, shearing and crushing. It has been established that the first thread turn from the point of application of force absorbs 34% of the total load, the second - 23%, the third - 15%, and the tenth - only 0.9%. Thus, all turns of the nut thread after the tenth do not take up practically any load.
Just like the threads of a nut, the threads of the socket into which the screw or stud is screwed work. Depending on what material the parts into which the studs are screwed are made of, the depth of screwing of the studs also changes. Here the magnitude of the axial load is already taken into account, because the greater it is, the larger the diameter of the stud, and the, therefore, the greater the depth of screwing.
The concept of a helix. If (Fig. 166, a) a right triangle ABC, cut from paper or thin tin, the side AB of which is equal to the circumference πD of the base of the cylinder E, is screwed onto the cylinder so that the side AB coincides with the base of the cylinder, then the side AC forms on the side the surface of its line, called a helical line.
Screw thread formation. Let us assume that a flat figure, for example triangle abc (Fig. 166, b), with side ab touching the generatrix of the cylinder E and is located in a plane passing through its axis. Let us further assume that this triangle moves while remaining in a plane passing through the axis of the cylinder E, and its vertex slides along a helical line marked on the cylinder. When the triangle is moved on the side surface of the cylinder E, a screw protrusion N and a screw groove M are obtained, forming an external screw thread.
If triangle abc were to move along a helical line marked on the inner cylindrical surface (on the walls of the hole), an internal screw thread would be formed on this surface.
The helical protrusion of the thread, resulting after one full revolution of the figure forming it, is called a turn.
Thread profile. Screw threads, adopted in practice, are formed by moving along the side surface of the cylinder not only a triangle, but also other flat figures (trapezoids, squares, etc.), selected depending on the conditions in which the thread operates. In accordance with this, the main feature characterizing the thread is its profile.
The thread profile is the cross-section of its turn by a plane passing through the axis of the cylinder (i.e., the diametrical plane) on which the thread is formed.
Rice. 166. Formation of screw threads
Thread profile elements. The elements of a thread profile are its sides, angle, crest and valley.
The profile angle is the angle between the sides of the coil, measured in the center plane. This angle (Fig. 167, a) is designated by the letter α.
Rice. 167. Profile elements (a, b) and thread pitch (c)
The top of the profile is the line connecting its sides along the top of the turn (P, Fig. 167, a, b).
The depression of the profile is the line forming the bottom of the helical groove (R, Fig. 167, a, b).
The outlines of the top and valley can be flat-cut (Fig. 167, a) or rounded (Fig. 167, b).
Thread pitch. The next element characterizing the thread is its pitch.
Thread pitch is the distance between two identical (i.e., right or left) points of two adjacent turns, measured parallel to the thread axis.
In Fig. 167, at such points are points A and A 1, points B and B 1, points C and C 1, etc. The distance between these points, measured parallel to line 00 (i.e., the axis of the thread), is the thread pitch, denoted by the letter S.
Almost all threads used in mechanical engineering have pitches measured in millimeters. There are, however, also threads in which the pitch is expressed by the number of thread turns per 1 inch of its length.
In addition to screws, worms with a modular or pitch pitch are cut on a lathe.
Thread diameters. There are three thread diameters: external, internal and middle.
The outer diameter of the thread (d) is the diameter of the cylinder described near the side surface of the thread.
For a bolt, the outer diameter corresponds to the diameter at the tops of the profile (Fig. 168, a), measured perpendicular to the thread axis, and for a nut - along the valleys of the profile (Fig. 168, b).
Rice. 168. Thread diameters: external and internal (a, b) and middle (c)
The internal diameter of the thread (d 1) is the diameter of the cylinder inscribed in the threaded surface.
For a bolt, the internal diameter corresponds to the diameter along the valleys of the profile (Fig. 168, a), measured perpendicular to the thread axis, and for a nut - along the tops of the profile (Fig. 168, b).
The average diameter of the thread (d 2) is the diameter of the cylinder, coaxial with the thread, the generatrices of which are divided by the sides of the profile into equal segments.
In Fig. 168, this cylinder, having a common axis with the thread, is shown in dash-dotted lines. In the figure, AB = BC = CD, etc., and therefore d 2 is the average diameter.
Thread angle. When cutting threads on a lathe, it is necessary to take into account the angle of its rise.
The helix angle is the angle formed by the direction of the threaded protrusion of the thread with a plane perpendicular to its axis.
Right and left hand threads. According to the direction of the turn, right (Fig. 169, b) and left (Fig. 169, a) threads are distinguished.
Rice. 169. Left (a) and right (b) threads
If the rise of the thread of a screw placed on the palm of the right hand coincides with the direction of the bent thumb, this thread is right-handed.
The coincidence of the rise of the thread with the direction of the bent thumb of the left hand indicates that this thread is left-handed.
On a screw with a right-hand thread, the nut is screwed when rotating to the right (clockwise), on a screw with a left-hand thread - when rotating to the left (counterclockwise).
Thread (cylindrical) is characterized by the following parameters:
1) diameters - outer, middle and inner;
2) shape and dimensions of the profile;
3) parameters related to thread lifting - pitch, number of starts and leading angle.
Outer thread diameter d- the diameter of the cylinder described around the vertices of the external thread (screw); this diameter is the nominal thread diameter.
Internal thread diameter d 1- the diameter of the cylinder described around the tips of the internal thread.
Average thread diameter d 2- the diameter of an imaginary cylinder, on the surface of which the width of the threads and the width of the thread cavities are equal.
Thread profile- contour of the coil section in a plane passing through the thread axis.
Profile angle α- the angle between the sides of the profile, measured in the axial plane.
The designation of the main thread parameters is presented in Figure 2.1.
Figure 2.1 – Thread, designation of main parameters
The thread profile is also characterized by:
1. the height of the theoretical profile H, i.e. the height of the complete triangular thread profile obtained by extending the sides of the profile until they intersect.
2. the working height of the profile h, at which the contact between the turns of the screw and the nut occurs, equal to half the difference between the outer and inner diameters.
The profile height is measured in the radial direction.
The most important characteristic of a thread is the pitch. Thread pitch P - the distance between the parallel sides of the profile of two adjacent turns, measured along the axis.
For multi-start threads, an additional term is introduced - screw stroke, equal to the product of the pitch and the number of starts P t. Thus, the stroke is equal to the pitch of the screw thread surface - the distance by which the screw moves along its axis when turning one turn in a stationary nut. For a single-start thread, the concepts of pitch and stroke are the same.
Thread angle β - the angle formed by a helix along the average diameter of the thread and a plane perpendicular to the thread axis:
The listed parameters can be considered in general terms, since all profiles have common elements and can be obtained by varying the profile angle, profile height and curvature radii. For example, by reducing the profile angle, you can move from a triangular thread to a trapezoidal one, and then to a rectangular one.
Threads according to purpose are divided into the following groups:
1. Mounting threads , are intended for fastening parts. They are made, as a rule, of a triangular profile with blunted tops.
The use of a triangular profile is caused by the following:
a) increased friction, providing less risk of loosening a tightened thread;
b) increased thread strength;
c) ease of manufacture.
2. Fastening and sealing threads , serve both for fastening parts and for preventing liquid leakage (in pipeline connections and fittings). For these reasons, these threads are also made with a triangular profile, but without radial clearances to prevent liquid leakage. To prevent sharp edges from collapsing, the profile is made with smooth curves.
3. Threads for transmitting motion (running) , can be used in lead and cargo screws. To reduce friction, these threads are made trapezoidal with a symmetrical profile and an asymmetrical profile (thrust), and sometimes with a rectangular profile.
4. Thrust threads designed to withstand large axial forces acting in one direction.
5. Special(round and others).
It must be borne in mind that the given division of threads by purpose is not strict. For example, triangular threads are sometimes used for particularly precise lead screws with small pitches, and thrust threads are used as fastening threads.
Due to guaranteed clearances, threads generally cannot be used as centering elements.
Triangular profile are performed with blunting of the tops of the turns and the bottom of the depressions in a straight line or along a circular arc, which is necessary in fastening threads to reduce stress concentrations, to increase tool life and to reduce damage (nicks), and in sealing threads - also to ensure tightness due to closure at the tops .
Metric thread(Figure 2.2) is the main triangular thread. It is characterized by a profile angle α = 60°, blunting of the vertices of the screw thread profile in a straight line at a distance H/8 and the tops of the nut thread profile at a distance H/4 from the tops of the theoretical profile. The profile of the screw cavities may be blunt or rounded with a radius r=H/6 ≈ 0.866P. The height of the original triangle of the theoretical profile. Working height of profile .
Metric threads are divided into threads with large and small pitches. With decreasing thread pitch R for a given outer diameter d, the inner diameter d 1 increases and, consequently, the cross-sectional area and strength of the cut rod increase. Triangular thread profiles with coarse and fine pitch are geometrically similar.
Figure 2.2 – Triangular metric thread
A thread with a large pitch is taken as the main one. For products such as bolts, screws and studs, triangular threads with a large pitch are mainly used as the most technologically advanced. The static load-bearing capacity of this thread is higher and the strength is less affected by manufacturing errors and wear than threads with fine pitches. The endurance limit of screws made of high-strength steels decreases with decreasing pitch, and the endurance limit of screws made of low-carbon steels increases.
Application areas for fine pitch threads:
a) dynamically loaded parts and parts whose diameters are mainly determined by bending and torsion stresses (shafts);
b) hollow thin-walled parts;
c) parts in which threads are used for adjustment.
The pitches of all metric threads form a stepped arithmetic series.
Metric threads with large pitches are designated by the letter M and a number expressing the diameter of the thread in mm, for example M20, and for metric threads with small pitches the pitch is additionally indicated, for example M20x1.5.
Pipe thread(Figure 2.3), which is a fastening and sealing type, is used for connecting pipes and pipeline fittings in the range of nominal sizes from 1/8 to 6.
Pipe thread is a fine inch thread, which is made with profile roundings and without gaps along the protrusions and recesses for better sealing. The main (nominal) size characterizing the threads and indicated in the thread designation is the nominal internal diameter of the pipe (clear passage). 
| r |
Figure 2.3 – Pipe thread
Trapezoidal thread(Figure 2.4) is the main thread for screw-nut transmissions. It has lower friction losses than triangular threads, is easier to manufacture and is more durable than rectangular threads. If necessary, it allows the selection of gaps by radially bringing the nut halves together (if the nut is split along the diametrical plane). Trapezoidal thread has a profile angle of 30°, working profile height, average diameter 
, the gap depending on the thread diameter is from 0.25 to 1 mm. Trapezoidal threads are standardized in the diameter range from 8 to 640 mm; It is possible to use threads with small, medium and large pitches.
Figure 2.4– Trapezoidal thread
Thrust thread(Figure 2.5) is used for screws with a large one-sided axial load in presses, pressing devices of rolling mills, in load hooks, etc. The profile of the turns is asymmetrical trapezoidal. Angle of inclination of the working side of the profile to increase efficiency. a sufficiently small 3° was chosen (threads with a profile inclination angle of 0° are inconvenient to manufacture), the inclination angle of the non-working side of the profile is 30°, and a significant radius of curvature of the cavity is provided to reduce stress concentration. Working height of the profile h = 0.75S. Reinforced thrust threads have an angle of the non-working side of the profile of 45°.
Figure 2.5– Thrust thread
Round threads(Figure 2.6) are mainly used for screws subject to high dynamic stresses, as well as those often screwed in and out in a polluted environment (fire fittings, car ties). Round threads can be used in hydraulic fittings due to their good sealing properties. Finally, round threads with a low profile height are rolled onto thin-walled products, such as bases and lamp sockets.
The profile of a round power thread consists of arcs connected by short sections of a straight line; profile angle 30°. Large radii of curvature eliminate significant stress concentrations. Contaminant particles entering the thread are squeezed out into the gaps.
Figure 2.6 – Round thread
Round threads used on thin-walled products are characterized by a low profile height and the absence of a straight section, which is important for reducing metal deformations during the rolling process.
Tapered thread(Figure 2.7) is used in cases where it is necessary to ensure the tightness of the connection, that is, it provides tightness without special seals; it is also used for connecting pipes, installing plugs, oilers, etc. Impermeability is achieved by tightly fitting the profiles at the tops. By tightening the tapered thread, you can compensate for wear and create the required tension. In addition, these threads allow for fast screwing and unscrewing.
Figure 2.7 – Tapered thread with profile angle
It is advisable that conical threads be able to screw together with cylindrical ones. Therefore, tapered threads have profiles similar to those of the corresponding cylindrical threads, and they are cut with a bisector of the profile angle perpendicular to the axis of the screw.
GENERAL INFORMATION ABOUT THREADED CONNECTIONS
Threaded connections are the most common detachable connections. They are created by bolts, screws, studs, nuts and other threaded parts. The main element of a threaded connection is a thread, which is obtained by cutting grooves on the surface of parts along a helical line. The helix is formed by the hypotenuse of a right triangle when screwed onto a straight circular cylinder (Fig. 3.1).
If a flat figure (triangle, trapezoid, etc.) is moved along a helical line so that its plane during movement always passes through the axis of the screw, then this figure forms a thread of the corresponding profile (Fig. 3.2)
Classification of threads
Depending on the shape of the surface on which the thread is formed, cylindrical and conical threads are distinguished (Fig. 3.3).
Depending on the shape of the thread profile, they are divided into five main types: triangular (Fig. 3.4, a), thrust (Fig. 3.4, b), trapezoidal (Fig. 3.4, c), rectangular (Fig. 3.4, d) and round ( Fig. 3.4, d).
Depending on the direction of the helical thread, there are right and left (Fig. 3.5). For a right-hand thread, the helix rises from left to top to right. Left-handed threads have limited use.
Depending on the number of starts, threads are divided into single-start (Fig. 3.5, b) and multi-start (Fig. 3.5, a).
Multi-start threads are obtained by moving several adjacent profiles along helical lines. The thread lead rate can be easily determined from the end of the screw by the number of running turns. As a rule, all threaded fasteners have single-start threads.
Depending on their purpose, threads are divided into fastening threads and for transmitting motion. Fastening threads are used in threaded connections; they have a triangular profile, which is characterized by:
a) high friction, protecting the thread from self-unscrewing; b) high strength; c) manufacturability.
Threads for transmitting motion are used in screw mechanisms and have a trapezoidal (less often rectangular) profile, which is characterized by less friction.
Geometric thread parameters
The main geometric parameters of a cylindrical thread are (Fig. 3.6):
d - outer diameter, nominal thread diameter;
d 1 - internal thread diameter;
d 2 - average thread diameter, that is, the diameter of an imaginary cylinder on which the width of the thread is equal to the width of the cavity;
S-thread pitch, i.e. the distance between the same sides of two adjacent turns in the axial direction;
S 1 - thread stroke, i.e. the distance between like sides of the same turn in the axial direction (see Fig. 3.5);
for single-start thread S 1 =S,
for multi-start threads S1=zS, where z is the number of starts;
α - thread profile angle (see Fig. 3.4);
λ - thread elevation angle (see Fig. 3.1), i.e., the angle formed by a helical line along the average thread diameter and a plane perpendicular to the screw axis;
Main types of threads
Metric thread (see Fig. 3.6). This is the most common of the fastening threads. It has a profile in the form of an equilateral triangle, therefore α = 60°. The tops of the turns and cavities are blunted in a straight line or arc, which reduces stress concentration, protects the thread from damage, and also satisfies safety standards. The radial gap in the thread makes it not airtight.
According to GOST 9150-59, metric threads are divided into threads with coarse and fine pitch (see Table 3.1). Threads with a coarse pitch are used as the main fastening thread, since it is less sensitive to wear and manufacturing inaccuracies. Threads with a fine pitch differ from each other by the grinding coefficient, i.e., the ratio of the large pitch to the corresponding small pitch (Fig. 3.7). Threads with a fine pitch weaken the part less and are characterized by increased self-braking, since with a small pitch the helix angle λ is small (see formula 3.1). Fine threads are used in threaded connections subject to variable and alternating loads, as well as in thin-walled parts (on plastic parts, metric threads are made according to GOST 11709-66).
Inch thread (1 inch equals 25.4 mm). (Fig. 3.8). It has a profile in the form of an isosceles triangle with an apex angle α=55°. It is used only when repairing parts of imported cars. Manufactured according to OST NKTP 1260.
Pipe thread . Pipe cylindrical thread (Fig. 3.9) is a small inch thread, but with rounded projections and depressions. The absence of radial clearances makes the threaded connection airtight. Used for connecting pipes. Manufactured according to GOST 6357-52.
High connection density is achieved by tapered pipe threads (GOST 6211-69).
Trapezoidal thread (Fig. 3.1.). This is the main thread in the screw-nut transmission (see below). Its profile is an isosceles trapezoid with an angle α = 30°. Characterized by low friction losses and technologically advanced. Efficiency higher than for threads with a triangular profile. Used to transmit reverse motion under load (lead screws of machine tools, etc.) Thread dimensions are given in table. 3.2.
Thrust thread (Fig. 3.11). It has a profile in the form of a non-equilateral trapezoid with an angle of 27°. To make threads possible by milling, the working side of the profile has an inclination angle of 3°. Efficiency higher than that of trapezoidal threads. Rounding the dimples increases the fatigue strength of the screw. It is used in screw-nut transmissions with large one-sided axial loads (load screws of presses, jacks, etc.). Manufactured according to GOST 10177-62.
Table 3.2
Trapezoidal thread according to GOST 9484-60 (extraction)
Dimensions in mm according to fig. 3.10
| Outside diameter d | Thread pitch S | Average diameter d 2 | Inner diameter d, |
| 30,5 | 28,5 | ||
| 2i | |||
| 38,5 | 36,5 | ||
| 48,5 | 46,5 | ||
| 58,5 | 56,5 | ||
Rectangular thread (Fig. 3.12). Thread profile is square. Of all the threads, it has the highest efficiency, since the thread profile angle, α=0. Has reduced strength. When worn, axial gaps form, which are difficult to eliminate. It has limited use in lightly loaded screw-nut transmissions.
Round thread (Fig. 3.13). The thread profile consists of arcs connected by short straight lines. Profile angle α=30 o. The thread is characterized by high dynamic strength. There is no standard. Has limited use under severe operating conditions in polluted environments. Technologically suitable for production by casting, rolling and fishing on thin-walled products.
Threaded connections
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Crane operators and slingers
Threaded connections
What connections are called threaded?
Connections that are made by machine fasteners through threads are called threaded.
What is carving?
A thread is a helical groove of a certain shape cut into the side surface of a cylindrical or conical rod.
What are the main parameters of thread?
A thread (cylindrical) is characterized by the following basic parameters: shape and profile, outer diameter, average diameter, inner diameter, helix angle, pitch and thread stroke, number of starts, i.e. the number of threads per thread stroke.
What is a thread profile?
The profile of a thread is the outline of its protrusions and recesses (in a longitudinal section).
What is the outer diameter of the thread d?
The outside diameter of a thread is the largest diameter measured at the top of the thread. What is the average thread diameter d.
The average thread diameter is the distance between two lines drawn along the middle of the thread profile between the bottom of the groove and the top of the thread, parallel to the axis of the stud or bolt. What is the internal thread diameter d.
The internal diameter is the smallest distance between opposing thread roots, measured in a direction perpendicular to the axis of the stud or bolt.
What is the thread lead angle p?
The helix angle of the thread is the angle between the helix along the average diameter of the thread and the plane perpendicular to its center line.
What is thread pitch S?
The thread pitch is the distance between the same sides of two adjacent turns, measured in the direction of the center line of the thread.
What is thread thread?
A thread (turn) of thread is a part of the thread formed during one full revolution of the profile.
How are threads divided depending on the number of threads?
Depending on the number of threads, threads are divided into single-start, double-start, three-start, etc. For single-start threads, only one end of the thread is visible at the end of a bolt, screw or nut, and for multi-start threads - two, three or more turns. Single-start threads have small helix angles and high friction.
In threaded connections, exclusively single-start threads are used as they are the most reliable in terms of self-locking of threaded parts, protecting them from self-unscrewing. Multi-start threads are used in screw-nut transmissions.
How are threads divided depending on the direction of rotation of the contour forming the thread?
Depending on the direction of rotation of the contour forming the thread, right-handed and left-handed threads are distinguished. If the thread is right-handed, then the nut is screwed onto the bolt from left to right (clockwise), and if it is left-handed, then the nut is screwed onto the bolt from right to left (counterclockwise). Moreover, in all cases where there is no need for a left-hand thread, only right-hand threads are used.
How are threads classified by purpose?
Depending on the purpose, threads are classified into fastening, fastening and sealing threads for motion transmissions. Fastening threads are used to fasten parts, fastening and sealing threads are used to fasten and create a tightness in a connection, and threads for motion transmissions are used in screw-nut transmissions and in worm gears.
How are threads divided depending on the profile shape?
Depending on the shape of the thread profile, they are divided into triangular, rectangular, trapezoidal, etc.
Rice. 1. Metric thread
In turn, triangular threads are divided into metric and inch.
Which triangular thread is called metric?
Metric is a triangular thread whose diameter and pitch are expressed in the metric system of measures - in millimeters, and whose profile angle is 60°. In addition, the metric thread profile is flat-cut” (Fig. 1). All triangular metric threads are divided into coarse pitch threads (for diameters 1-68 mm) and fine pitch threads (for diameters 1-600 mm).
The most widespread are metric threads with a large pitch, since compared to threads with a fine pitch, their influence on wear and errors in its manufacture is less.
What thread is called inch thread?
An inch thread is a thread whose outer diameter is measured in inches, and the thread pitch is the number of threads per 1 inch (an inch is equal to 25.4 mm). Thread profile angle 55°. Inch threads are used in old machines, as well as in imported machines brought to us from countries where the inch system is used.
In what cases is trapezoidal thread used?
Trapezoidal threads are used in screw-nut and worm gears (worm gears), as they have less friction than triangular threads and are more durable.
What parts are the main fasteners of threaded connections?
The main fasteners of threaded connections are bolts, studs, screws and nuts.
What is a bolt?
A bolt is a part, usually of a round cross-section, having a head at one end and a thread at the other. Bolt heads can be hexagonal, square, semicircular, countersunk, etc. The primary use is for bolts with hexagonal heads having the following standard sizes: 7, 9, 10, 11, 12, 14j 17, 19, 22 mm, etc.
In what cases are bolts used to fasten parts?
Bolts for fastening parts are used in cases where the parts have a relatively small thickness or when the material of the parts cannot provide the necessary reliability of the thread.
What is a hairpin?
A stud is a rod with threads on both ends; At one end it is screwed into the part being fastened, and at the other end of its rings a nut is screwed.
There are studs of increased and normal precision, manufactured with the same nominal diameters of the thread and the smooth part or with a nominal thread diameter greater than the diameter of the smooth part.
In what cases are pins used to fasten parts together?
Studs are used in cases where the material of the fastened parts with a cut hole when using screws does not provide the necessary durability of the thread during frequent assembly and disassembly of joints.
What is a screw?
A screw is a piece of circular cross-section, usually with a thread at one end and a head at the other, but in some cases screws without heads are used in threaded connections. Screws in threaded connections are not fastened with nuts, but are screwed with the threaded end into one of the parts being fastened: According to their purpose, screws are divided into fastening screws, which are used to fasten the parts being connected, and installation screws, which, unlike fastening screws, have threads along the entire length of the rod and prevent mutual displacement of the parts .
Mounting screws are made with a wrench head or a screwdriver head, and installation screws are either with a wrench head or without a head with slots or with a wrench recess. The mounting heads of the screws are hexagonal or square; semicircular, secret, etc.
In what cases are screws used to fasten parts?
Screws for fastening parts are used in cases where one of the parts being fastened is relatively thick, or when it is impossible to place nuts, or when there is a strict requirement to reduce the mass of a threaded connection, or to give the connections a more beautiful appearance.
What is a nut?
A nut is a fastener with a threaded hole that is screwed onto the end of a bolt or stud and serves to lock the connected machine parts using a bolt or stud. The shape of the nuts can be hexagonal with one or two chamfers, hexagonal castle nuts with standard sizes between opposite edges 7, 9, 10, 11, 12, 14, 17, 19, 22 mm, etc. In addition to hexagonal nuts, square nuts are also used in mechanical engineering , round and cylindrical nuts.
What are the washers used for?
Washers serve to avoid denting the surface of the parts being fastened and to increase the surface area: They are placed under the heads of bolts and screws, as well as under nuts.
What are nut locks used for?
Nut locks are used to keep threaded connections from unscrewing during movements, shocks and impacts to which machine parts are exposed during operation.
What kind of nut locks are used in mechanical engineering?
In mechanical engineering, various nut locks are used, for example a split (spring) washer, which, due to its elasticity, keeps the nut tightened. In addition to spring washers, lock washers with internal and external teeth, lock washers with one and two legs are used. In some cases, pins, screws and elastic locknuts are used to tighten the nuts.
What material are bolts, studs, screws, nuts, washers and nut locks made from?
Bolts, studs, screws and nuts are made from steel grades St. 3 KP, St. 5, 10, 10KP, 15, 15KP, 20, 30, 35, 45, 40G, 35Kh, 40Kh, 35KhA, 30KhSA, etc., and washers and nut locks (except spring locks) are usually made from steel grades St. 0, St. 1, Art. 2, Art. 3, OD 10, 15, 20 and 25. Spring locks are made from steel grades 65, 70, 75, 65G, etc.
What tool is used to screw and unscrew bolts and nuts?
Screw and unscrew bolts and nuts with wrenches - simple, universal and special.
Plain (open) keys are single-sided and double-sided; the dimensions of the jaw must correspond to the standard sizes of bolt heads and nuts. In our country, the following jaw sizes for double-sided keys (in millimeters) are accepted: 5X7, 7X9, 9X11, 10X12, 12×14, 14X.17, 17X19, 19XX22, etc. In addition to simple keys, socket wrenches, tubular or solid, which are also single-sided and double-sided, are widely used in mechanical engineering.
What material are wrenches made from?
Wrenches are made from tool steel, carbon steel, and sometimes alloy steel. The key heads are hardened and tempered. The size of the wrench mouth must exactly match the size of the nut or bolt size.
What tool is used to unscrew and tighten slotted screws?
Screws with a slot (slot) are unscrewed and tightened with screwdrivers, the working part (blade) of which must correspond to the dimensions of the slot. The working part of screwdrivers, as well as the heads of wrenches, are hardened.
In what cases in mechanical engineering are power tools used to tighten nuts and screws?
Mechanized tools in mechanical engineering are used when assembling machines and mechanisms in mass production, due to which labor productivity sharply increases. Power wrenches and screwdrivers are driven by electric and pneumatic motors.
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