GOST 9484 – 81
Trapezoidal thread has a profile with an angle of 30°. Thread pitch measured in millimeters.
Trapezoidal thread used in mechanism units for conversion rotational movement into translational, for example: lead screws of machine tools, power screws of presses, lifting screws, etc. Threads of this type can withstand significant loads.
Trapezoidal thread indicated by letters Tr- English trapezoidal:
d – outside diameter external thread (screw)
D- outside diameter internal thread(nuts)
d 2– average diameter of external thread
D 2– average diameter of internal thread
d 1– internal diameter of external thread
D 1– internal diameter of internal thread
P– thread pitch
H– height of the original triangle
H 1– working height of the profile
| Trapezoidal thread | |||
| Thread diameters d | Step | ||
|---|---|---|---|
| Row 1 | Row 2 | ||
| 10 | 1.5; 2 | ||
| 11 | 2 ; 3 | ||
| 12 | 2; 3 | ||
| 14 | 2; 3 | ||
| 16 | 2; 4 | ||
| 18 | 2; 4 | ||
| 20 | 2; 4 | ||
| 22 | 3; 5 ; 8 | ||
| 24 | 3; 5 ; 8 | ||
| 26 | 3; 5 ; 8 | ||
| 28 | 3; 5 ; 8 | ||
| 30 | 3; 6 ; 10 | ||
| 32 | 3; 6 ; 10 | ||
| 34 | 3; 6 ; 10 | ||
| 36 | 3; 6 ; 10 | ||
| 38 | 3; 7 ; 10 | ||
| 40 | 3; 7 ; 10 | ||
| 42 | 3; 7 ; 10 | ||
| 44 | 3; 7 ; 12 | ||
| 46 | 3; 8 ; 12 | ||
| 48 | 3; 8 ; 12 | ||
| 50 | 3; 8 ; 12 | ||
| 52 | 3; 8 ; 12 | ||
| 55 | 3; 9 ; 14 | ||
| 60 | 3; 9 ; 14 | ||
| 65 | 4; 10 ; 16 | ||
| 70 | 4; 10 ; 16 | ||
| 75 | 4; 10 ; 16 | ||
| 80 | 4; 10 ; 16 | ||
| 85 | 4; 12 ; 18 | ||
| 90 | 4; 12 ; 18 | ||
| 95 | 4; 12 ; 18 | ||
| 100 | 4; 12 ; 20 | ||
| 110 | 4; 12 ; 20 | ||
| 1. When choosing a thread, priority is given to the first row. 2. Thread pitch highlighted in color is preferred. |
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The functioning of the drives of many machines, equipment and mechanisms is based on a process such as the transformation of rotational motion into translational motion. This principle applies, for example, to drives of measuring machines and equipment, control systems for gates and valves, scanning tables, robots and machine tools.
In order to effectively convert the rotation of one part into the translational movement of another part, a pair of screws and nuts is most often used. Such gears are products that have general machine-building applications, and it should be noted that the performance, functionality and reliability of the equipment largely depends on how well they are designed and manufactured. components which they are.
Due to the fact that the screw-nut transmissions have increased smoothness of engagement, they are almost completely silent during operation. Their design is relatively simple, and one of the undoubted advantages is that their use allows for significant gains in strength. By and large, the screw-nut transmission from a technical point of view is no different from a conventional threaded connection, however, since they are used to transmit movement, they are made in such a way that the friction force in the thread is minimal.
In principle, this can be achieved by using a rectangular thread, but it also has its disadvantages. For example, it cannot be cut on standard threading machines, and compared to trapezoidal threads, it has much lower strength. These factors lead to the fact that in screw-nut transmissions, rectangular threads are used quite rarely. The most common among them trapezoidal thread, having large, medium and fine pitch, as well as persistent thread.
Most often in screw-nut gears you can find trapezoidal thread, having an average step. It is used, but with small steps, when it is necessary to ensure small movement, and with large steps – when the device is operated in difficult conditions. In addition, thanks to the profile features, trapezoidal thread can be successfully used in mechanisms that require reverse movement. Such threads can be single- or multiple-start, right-handed or left-handed.
Materials used in screw-nut transmissionThe main requirements for those materials that are used in screw-nut transmissions are wear resistance, strength and good machinability. As for those screws that are not subject to hardening, they are made of steel A50, St50 And St45, and those that are subjected to hardening are made of steels 40ХГ, 40X, U65, U10. Nuts are usually made of bronze BrOTsS-6-6-3 or Brofyu-1.
Parts in machines, mechanisms, devices, as well as apparatus and structures are somehow connected to each other. These connections perform various functions, and are divided primarily into two types: mobile and stationary.
A fixed connection is a connection of parts that ensures that their relative position remains unchanged during operation. For example, welded, connections using fasteners, etc. A movable connection is a connection in which parts have the ability to move relatively in working condition. For example, a gear connection.
Fixed and movable connections, in turn, are divided into detachable and permanent, depending on the possibility of dismantling the connection.
Permanent connection - a connection that cannot be separated without disturbing the shape of the parts or their connecting element. For example, a welded, soldered, riveted connection, etc.
A detachable connection is a connection that can be repeatedly disconnected and connected without deforming either the connected parts or the fastening parts. For example, a threaded connection with a bolt, screw, wedge, key, gear, etc.
This article is devoted to a review of threaded connections, the variety of which one often encounters in everyday life.
Threaded connection - connecting parts using threads. Everyone knows what carving is, everyone has seen it. Many people also know that threads differ from each other, since they have different sizes, step and so on. However, not many people realize how this is regulated, and also that there is not only the usual for us metric thread cylindrical in shape, but also many other types.
A thread is a surface formed by the helical movement of a flat contour along a cylindrical or conical surface, in other words, a spiral with a constant pitch formed on this surface.
Figure 1 - Thread
According to their purpose, threads are divided into fastening (in a fixed connection) and running or kinematic (in a movable connection). Often fastening threads have a second function - sealing the threaded connection, ensuring its tightness; such threads are called fastening and sealing threads. There are also special threads that have special appointment.
Depending on the shape of the surface on which the thread is cut, it can be cylindrical or conical.
Depending on the location of the surface, the thread can be external (cut on the rod) or internal (cut in the hole).
Depending on the shape of the profile, there are triangular, trapezoidal, rectangular, round, and special threads.
Triangular threads are divided into metric, pipe, conical inch, trapezoidal threads - into trapezoidal, thrust, and reinforced thrust.
Based on the pitch size, threads are distinguished between large, small and special.
Based on the number of starts, threads are divided into single-start and multi-start.
Based on the direction of the helix, a distinction is made between right-hand thread (thread thread is cut clockwise) and left-hand thread (thread thread is cut counterclockwise).
In Figure 2, the entire classification of threads is presented in the form of a diagram:
Figure 2 - Classification of threads
In addition to the above classification, all threads are divided into two groups: standard and non-standard; For standard threads, all their parameters are determined by GOSTs. The main thread parameters are determined by GOST 11708-82. These are the so-called standard threads general purpose. In addition to them, there is the concept of special thread. Special threads are threads with a standard profile, but different from standard sizes diameter or thread pitch, and threads with a non-standard profile. Non-standard threads - square and rectangular - are manufactured according to individual drawings, on which all thread parameters are specified. (More details in section 5. The operational purpose of the thread and its application).
Thread profiles are characterized the following features:
. metric thread has a profile in the form of an equilateral triangle with an apex angle of 60°. The projections and valleys of the thread are blunted (GOST 9150-2002).
Metric threads can be cylindrical or conical.
. pipe thread has a profile in the form of an isosceles triangle with an apex angle of 55°. Pipe threads can also be cylindrical or conical.
. tapered inch thread has a profile in the form of an equilateral triangle.
Inch conical thread
. round thread has a profile in the form of a semicircle.
. trapezoidal thread has a profile in the form of an isosceles trapezoid with an angle of 30° between the sides.
. thrust thread has a profile of a non-equilateral trapezoid with an inclination angle of the working side of 3° and the non-working side of 30°.
. rectangular thread has a profile in the form of a rectangle. The thread is not standardized.
Rectangular non-standard thread
Thread parameters
The main parameters of the thread are:
Thread diameter(d) is the diameter of the surface on which the thread will be formed.
Figure 3 - Outer diameter
Thread pitch(P) - the distance along a line parallel to the thread axis between the midpoints of the nearest identical sides of the thread profile, lying in the same axial plane on one side of the axis of rotation (GOST 11708-82).
Thread stroke(Ph) - relative axial movement of a threaded part per revolution (360°), equal to the product nР, where n is the number of thread starts. For a single-start thread, the lead is equal to the pitch. A thread formed by the movement of one profile is called single-start; a thread formed by the movement of two, three or more identical profiles is called multi-start (two-, three-start, etc.). In other words, not one spiral is cut simultaneously onto a bolt and nut, but two or three. Multi-start threads are often used in high-precision equipment, for example, in photographic equipment, in order to unambiguously position the position of parts during mutual rotation. Such a thread can be distinguished from a conventional thread by two or three starts of turns at the end.
Figure 4 - Thread pitch and thread progress
The thread is characterized by three diameters: external d (D), internal d1 (D1) and middle d2 (D2). The diameters of the external threads are designated d, d1 and d2, and the diameters of the internal threads in the hole are D, D1 and D2.
Figure 5 - Thread diameters
Construction helical surface in the drawing it is a long and complex process, therefore, in product drawings, the thread is depicted conditionally, in accordance with GOST 2.311-68. On the rod, the thread is depicted with solid main lines along the outer diameter and solid thin lines along the internal diameter.
Figure 6 - Example of an image of a thread on a rod and in a hole
4. Thread designation
The thread designation usually includes a letter designation of the thread type and a nominal diameter. Additionally, the designation may include the thread pitch (or TPI - threads per inch), the number of starts for multi-start threads, the diameter of the thread hole, the direction (left, right).
Metric thread- with pitch and basic thread parameters in millimeters. Widely used with nominal diameters from 1 to 600 mm and pitches of 0.25 to 6 mm. Metric thread is the main fastening thread. This is a single-start thread, mostly right-handed, with large or small pitch. The designation of a metric thread includes the letter M and the nominal diameter of the thread, and the large pitch is not indicated: M5; M56. For fine-pitch threads, additionally indicate the thread pitch M5×0.5; M56×2. At the end of the left-hand thread symbol the letters LH are placed, for example: М5LH; M56×2 LH. The thread designation also indicates the accuracy class: M5-6g.
Example notation:
M 30 - metric thread with an outer diameter of 30 mm and a large thread pitch;
M 30×1.5 - metric thread with an outer diameter of 30 mm, fine pitch 1.5 mm.
Although metric threads were not found wide application in sealed joints, however, this possibility is included in the standards. These are metric conical and cylindrical threads.
Metric tapered thread performed with a taper of 1:16 and a nominal diameter from 6 to 60 mm according to GOST 25229-82 (ST SEV 304-76). It is intended for self-sealing conical threaded connections, as well as for connections of external conical threads with internal cylindrical threads having a nominal profile in accordance with GOST 9150-2002. The designation of a metric tapered thread includes the type of thread (letters MK), the nominal diameter of the thread, and the thread pitch. At the end of the left-hand thread symbol the letters LH are placed.
Example notation:
MK 30×2 LH - left-hand metric conical thread with an outer diameter of 30 mm, thread pitch of 2 mm.
Metric cylindrical thread (with profile)based on metric threads (M) with a nominal diameter from 1.6 to 200 mm and a profile angle at the tip of 60°. Its main difference is in the screw, which has an increased root radius on the thread (from 0.15011P to 0.180424P), which gives the threaded connection based on cylindrical metric threads higher heat-resistant and fatigue properties. The metric cylindrical thread is designated by the letters MJ, followed by the numerical value of the nominal thread diameter in millimeters, the numerical value of the pitch, the tolerance range of the average diameter and the tolerance range of the diameter of the protrusions.
The internal MJ thread is compatible with the external M thread if the nominal diameter and pitch match, i.e. a regular metric screw can be screwed into a nut with such a thread.
Example notation:
MJ6×1-4h6h - external thread on the shaft surface with a nominal diameter of 6 mm, a pitch of 1 mm, a tolerance range of 4h for the average diameter and a tolerance range of 6h for the diameter of the protrusions.
Differences between inch threads from metric in that the angle at the top of the thread is 55 degrees for the British standards BSW (Ww) and BSF or 60 degrees (as in metric) in the American system (UNC and UNF), and the thread pitch is calculated as the ratio of the number of turns threads per inch of thread length. It is not possible to combine metric and inch threads, therefore, in countries with the metric system, only inch pipe threads are used.
For inch threads, all thread parameters are expressed in inches (most often indicated by a double stroke placed immediately after the numerical value, for example, 3 "= 3 inches), thread pitch in fractions of an inch (inch = 2.54 cm). For inch pipe threads, the size in inches does not indicate the size of the thread, but the conditional clearance in the pipe, while the outer diameter is actually significantly larger. A special feature of pipe threads is precisely the fact that it takes into account the thickness of the pipe walls, which can be thicker or thinner depending on the material of manufacture and the operating pressure for which the pipes are designed. Therefore, the inch standard for pipe threads is understood and accepted throughout the world as an exception to the metric rules.
Inch thread diameters are not the only parameter that is important when choosing pipes. It is necessary to take into account: thread depth, thread pitch, outer and inner diameters, thread profile angle. It is worth noting that the thread pitch in this case is calculated not in inches or even in millimeters, but in threads. Thread refers to a cut groove. Therefore, the calculation is based on how many grooves are cut on one inch measured piece of pipe. For example, ordinary water pipes have only two types of thread pitch: 14 threads, which corresponds to a metric pitch of 1.8 mm, and 11 threads, which corresponds to a metric pitch of 2.31 mm.
Table 2 shows the main differences between “inch” and “pipe” cylindrical threads in relation to “metric” threads for the most common sizes of the above threads.
Threads marked *, if possible, should not be used.
Naturally, such unique standards for calculating diameter and pitch only cause confusion in determining the required values. Therefore, tables have been developed to determine the number of threads and the diameter of pipes with inch threads. In addition, any packaging always indicates its meaning and standard. But still, the data is approximate, and you should never exclude a possible error.
*When determining the size, preference should be given to the values of row 1.
It has a profile in the form of an isosceles triangle with an apex angle of 55°, the peaks and valleys are rounded (GOST 6357-81).
The thread symbol consists of the letter G, the designation of the nominal thread diameter in inches, and the accuracy class of the average diameter. For left-hand threads, the designation is supplemented with the letters LH.
Example notation:
G 1 1/2-A - cylindrical pipe thread with size 1 1/2", accuracy class A;
1/4-20 BSP - Whitworth pipe cylindrical thread according to B. S.93 standard (England).
has a profile similar to the profile of a cylindrical pipe thread. It is possible to connect pipes having a conical thread (taper 1:16) with products having a cylindrical pipe thread GOST 6211-81.
The thread designation consists of the letters R, the size of the nominal diameter in inches. The designation Rc is used for pipe conical internal threads. The symbol for left-hand thread is supplemented with the letters LH.
Example notation:
R 1 1/2 - external conical pipe thread with size 1 1/2";
R 1 1/2 LH - conical pipe thread, external left;
Rс 1/2 - internal conical pipe thread;
BSPT 1 1/2 - internal conical pipe thread according to B. S.93 standard (England).
With a profile angle of 60°, GOST 6111-52 is cut on a conical surface with a taper of 1:16.
The designation consists of the letter K and the thread size in inches with an indication of the dimension, applied on the shelf of a leader line, as with pipe threads. Example notation:
K 3/4″ according to GOST 6111-52. 3/8-18 NPT designation according to ANSI/ASME B 1.20.1 (USA).
Serves to transmit movement and effort. The profile of a trapezoidal thread is an isosceles trapezoid with an angle between the sides of 30°. For each diameter, the thread can be single-start or multi-start, right-handed or left-handed, according to GOST 9484-81.
The main dimensions, diameters, pitches, tolerances of single-start threads are standardized according to GOST 24737-81, 24738-81, 9562-81. For multi-start threads, these parameters are found in GOST 24739-81.
The symbol for a single-start thread consists of the letters Tr, the value of the nominal thread diameter, pitch, and tolerance range.
Example notation:
Tr 40×6-8e - trapezoidal single-start external thread with a diameter of 40 mm with a pitch of 6 mm; Tr 40×6-8e-85 - same make-up length 85 mm;
Tr 40×6LH-7Н - the same for the inner left.
The numerical value of the stroke is added to the symbol of a multi-start thread:
Tr 20×8(P4)-8e - trapezoidal multi-start external thread with a diameter of 20 mm with a stroke of 8 mm and a pitch of 4 mm.
It has a profile of an unequal trapezoid. The profile depressions are rounded and there are three different pitches for each diameter. Serves to transmit motion with large axial loads according to GOST 10177-82.
Thrust threads are designated by the letters S, then they indicate the nominal diameter of the thread in millimeters, the thread pitch (lead and pitch if this thread is multi-start), the direction of the thread (for the right-hand thread they are not indicated, for the left-hand thread they are indicated with the letters LH), and the thread accuracy class.
Example notation:
S 80×10 - single-start thrust thread with an outer diameter of 80 mm and a pitch of 10 mm;
S 80×20(P10) - double-start thrust thread with an outer diameter of 80 mm, a stroke of 20 mm and a pitch of 10 mm.
Special thread with a standard profile, but a non-standard pitch or diameter, denote: Sp M40×1.5 - 6g.
Rectangular thread (square). A thread with a rectangular (or square) non-standard profile, so all its dimensions are indicated in the drawing. It is used to transmit the movement of heavily loaded moving threaded connections. Typically performed on weight and lead screws.
It has a profile obtained by conjugating two arcs of the same radius. GOST 13536- 68 defines the profile, basic dimensions and tolerances of round threads. This thread is used for valve spindles of mixers and toilet taps GOST 19681-94 and water taps. There is only one diameter d = 7 mm and pitch P = 2.54 mm.
Example notation:
Kr 7×2.54 GOST 13536-68, where 2.54 is the thread pitch in mm, 12 is the nominal thread diameter in mm.
A similar profile has a round thread (but for diameters 8...200 mm) according to ST SEV 3293-81, put into effect directly as State standard. The thread is used for crane hooks, as well as in environments exposed to aggressive environments.
Example notation:
Rd 16 - round thread with an outer diameter of 16 mm; Rd 16LH - round thread with a diameter of 16 mm, left.
5. Operational purpose of the thread and its application
Threaded connections widespread in mechanical engineering (in most modern machines, over 60% of all parts have threads). By operational purpose distinguish between threads general use and special ones, designed to connect one type of parts of a certain mechanism. The first group includes threads:
1.) Fastening- metric, inch, used for detachable connection of machine parts. Their main purpose is to ensure complete and reliable connection parts under different loads and at different temperature conditions during long-term operation.
2.) Running gear or kinematic - trapezoidal and rectangular, used for lead screws, machine support screws and tables measuring instruments etc. Their main purpose is to ensure accurate movement with the least friction, and for rectangular threads to also prevent self-unscrewing under the influence of applied force; Thrust (in presses and jacks) and round, designed to convert rotational motion into linear movement. They perceive great forces at relatively low speeds. Their main purpose is to ensure smooth rotation and high load capacity (for precision micrometric instruments, high-precision metric threads are used). Round threads are widely used for water taps in accordance with GOST 20275-74 and in such elements as mixers, taps, valves, spindles in accordance with GOST 19681-94 (Sanitary water fittings).
3.) Fastening and sealing (Pipe and fittings) - pipe cylindrical and conical, metric inch and conical, used for pipelines and fittings, their main purpose is to ensure the tightness of connections (without taking into account shock loads) at low pressures.
Cylindrical pipe threads in accordance with GOST 6357-81 are used on water and gas pipes, parts for their connection (couplings, elbows, crosses, etc.), pipeline fittings (gate valves, etc.).
Tapered pipe threads in accordance with GOST 6211-81 are used in pipe connections for high pressures and temperature (in valves and gas cylinders) when increased tightness of the connection is required.
Relegated to the second group, special threadhas a special purpose and is used in certain specialized industries. These include the following:
1.) metric tight thread- threads made on the rod (on the pin) and in the hole (in the socket) according to the largest maximum dimensions; designed for forming threaded connections with interference fit.
2.) metric thread with clearances- thread necessary to ensure easy screwing and unscrewing of threaded connections of parts operating at high temperatures, when conditions are created for the setting (merging) of the oxide films that cover the surface of the thread.
3.) hour thread (metric)- thread used in the watch industry (diameters from 0.25 to 0.9 mm).
4.) thread for microscopes- thread designed to connect the tube to the lens; has two sizes:
4.1) inch - diameter 4/5"" (20.270 mm) and pitch 0.705 mm (36 threads per 1"");
4.2) metric - diameter 27 mm, pitch 0.75 mm;
5) ocular multi-start thread- recommended for optical instruments; thread profile - equilateral trapezoid with an angle of 60°.
The operational requirements for threads depend on the purpose of the threaded connection. Common to all threads are the requirements for durability and screwability without adjusting independently manufactured threaded parts while maintaining the performance of the connections. Briefly summarizing the main threads used according to their operational purpose, they can be displayed in the following table:
6.Determination of thread size
As a rule, the threads on different fittings look similar, which makes it difficult visual definition type of thread. The thread on the fittings is determined by measuring the main parameters with a thread gauge and caliper and comparing the results obtained with the thread table.
Figure 7 - Measuring thread parameters
There are two types of thread gauges: with the M 60o stamp - for metric threads with a profile angle of 60o and with the D 55o stamp - for inch and pipe threads with a profile angle of 55o. On each thread gauge comb for metric threads there is a number stamped indicating the thread pitch in mm for inch and pipe threads - the number of steps over a length of 25.4 mm (1" = 25.4 mm).
7.Methods of thread cutting
The main methods for making threads are:
The choice of thread production method depends on the type of production, the dimensions of the thread, the accuracy of the workpiece material, etc.
Figure 8 — Threading tool
1. Thread cutting with cutters. Using thread cutters and combs on turning-screw-cutting machines cut both external and internal threads (internal threads starting with a diameter of 12 mm and above). The method of cutting threads with cutters is characterized by relatively low productivity; therefore, currently it is used mainly in small-scale and individual production, as well as in the creation of precision screws, lead screw calibers, etc. The advantage of this method is its simplicity cutting tool and comparatively high accuracy the resulting thread.
2. Thread cutting with dies and taps. Dies according to their own design features divided into round and sliding. Round dies used in assembly procurement and other work are designed for cutting external threads with a diameter of up to 52 mm in one pass. For larger threads, dies of a special design are used, which actually serve only to clean the thread after preliminary cutting it with other tools. Sliding dies consist of two halves that gradually move closer together during the cutting process. The tap is a threaded steel rod divided by longitudinal straight or helical grooves forming cutting edges. These same grooves serve to release chips. According to the method of application, taps are divided into manual and machine.
3. Thread rolling. Basic industrial method At present, thread production involves rolling on special thread-rolling machines. The part is clamped in a vice. In this case, with high productivity, it is possible to obtain High Quality products (shape, size and surface roughness). The thread rolling process involves creating a thread on the surface of a part without removing chips due to plastic deformation of the surface of the workpiece. Schematically it looks like this. The part is rolled between two flat dies or cylindrical rollers having a threaded profile and a thread of the same profile is extruded onto the rod. Largest diameter rolled thread 25 mm, smallest 1 mm; length of rolled thread 60...80 mm.
4.Thread milling. Milling of external and internal threads is carried out on special thread milling machines. In this case, a rotating comb cutter, when fed radially, cuts into the body of the part and mills threads on its surface. Periodically, an axial movement of the part or cutter from a special copier occurs by an amount equal to the thread pitch during one revolution of the part.
5. Grinding precision threads. Grinding as a method of creating threads is used mainly to obtain precise threads on relatively short threaded parts, such as threaded plugs, gauges, thread rollers, etc. The essence of the process is that grinding wheel located to the part at an angle of rise of the thread with fast rotation and with simultaneous slow rotation of the part with feed along the axis by the value of the thread pitch in one revolution, it cuts out (grinds) part of the surface of the part. Depending on the design of the machine and a number of other factors, the thread is ground in two to four or more passes.
8.Types of foreign threads
Several well-deserved, respected standards are used in the world from countries such as Great Britain (BS), Germany (DIN), France (NF), Japan (JIS), USA (UNC). The main reasons for their differences are traditionally different systems measures and methods for specifying thread sizes in different countries as well as special applications for threads. However, over the past century, the metric standard ISO - International Organization for Standardization ( International Organization on Standardization), which in turn contributed to the mutual understanding of technical specialists.
The most common types of foreign threads include:
The above summary table describes the compliance of more than twenty types of threads (general engineering oil and gas assortments), and refers to the regulatory and technical documents, domestic and foreign, regulating this area. 
Since the above Table 8 only gives general idea about abundance different types threads and documents regulating them, and the large volume of data does not allow us to fully compare and contrast threads of domestic and foreign standards; let us consider, as an example, compliance various types triangular thread, which is most often found in general mechanical engineering.
and couplings for them. Technical specifications"
OST NKTP 1260 “Inch thread with a profile angle of 55 degrees”
The thread profile is an isosceles trapezoid with an angle of 30° between the sides (Figure 3, c). Trapezoidal threads can be single-start or multi-start, right-handed or left-handed.
The diameters and pitches of single-start trapezoidal threads in the diameter range from 12 to 50 mm are given in table. 2. The same dimensions and number of starts for multi-start threads are given in table. 3.
Examples of thread designations:
trapezoidal front entry with a nominal diameter of 36 mm and a pitch of 6 mm:
TgZbhb; the same, left-hand thread:
Tg 36x6 LH;
trapezoidal, three-way with a nominal diameter of 40 mm, a pitch of 3 mm and a stroke of 9 mm:
Tg 40 X 9 (RZ)
Examples of thread designations in the drawing are shown in Fig. 5. at
Table 2. Diameters and pitches of trapezoidal single-start threads according to GOST 24738 81, mm
| Diameter d | row | - | - | -" | - | - | ||||||
| - | - | - | - | - ■ | 30, | |||||||
| step | p | |||||||||||
| R* | 3;8 | 3;8 | 3;8 | 3;8 | 3; 10 | |||||||
| Diameter d | row | - | - | - - | ||||||||
| - | - | - | - | - | ||||||||
| step | R | 8, | ||||||||||
| R* | 3; 10 | 3;10 | 3;10 | 3;10 | 3;10 | 3;10 | 3;12 | 3;12 | 3;12 | 3; 12 |
Note: 1. When choosing a thread, the first row should be preferred to the second;
2. Preferred steps are indicated by *.
Table 3. Main dimensions of trapezoidal multi-start thread according to GOST 24739 81, mm
| d | Thread pitch | Thread stroke at number of starts | ||||
| Row1 | Row 2 | R | R* | |||
| (8) | ||||||
| - | - | |||||
| - | - | |||||
| - | - | |||||
| ,-. - | - | (16) | (20) | |||
| - | - | |||||
| - | (20) | |||||
| _ | - | |||||
| - | (24) | |||||
| - | - | |||||
| - | (24) | |||||
| - | - | |||||
| - | (21) | (28) | ||||
| - | - | |||||
| _- | (28) | |||||
| ■ - | - | |||||
| - | (32) | |||||
| (24) | (36) | (48) | ||||
| - | - | |||||
| - | (32) | |||||
| - | (24) | (36) | (48) |
Note: Threads whose stroke value is enclosed in brackets have a lead angle greater than 10°.
The thread is persistent.
The main purpose of the thread is to transmit an axial load through a screw in one direction, for example, in jacks, presses, etc. The thread profile is an unequal trapezoid (Fig. 3, d).
: > v The diameters and pitches of the thrust threads in the diameter range from 16 to 42 mm are given in table. 4.
Examples of thread designations: "
thrust single-thread right with a diameter of 32 mm with a pitch of 6 mm:
the same, left-hand thread:
S32x6LH. In the drawing, the thread is indicated as shown in Fig. 6.
Rice. 6
Table 4. Diameters and pitches of thrust threads according to GOST 10177 82, mm.
| Diameter d | Step | ||
| Row1 | Row 2 | R* | R |
| - | |||
| - | |||
| - | 3;8 | ||
| - | 3;8 | ||
| - | 3;8 | ||
| - | 3;8 | ||
| - | 3;10 | ||
| - | 3;10 | ||
| - | 3;10 | ||
| - | 3;10 | ||
| - | 3;10 | ||
| - | 3;10 |
Note^. When choosing thread diameters, the first row should be preferred to the second.
Preferred steps when developing new designs.
Pipe cylindrical thread.
This thread is used in cylindrical connections pipes and connections of internal cylindrical threads with external conical threads.
The profile (Fig. 3, b) and main dimensions are established by GOST 6357 81. The values of the main dimensions of cylindrical pipe threads are given in table. 5.
The designation of pipe thread (Fig. 7, a, b) consists of the letter G and the thread size in inches, for example:
This designation is conditional, because indicates the diameter not of the thread, but of the hole in the pipe (nominal diameter DN at a certain wall thickness). The outer diameter of the pipe thread will be larger than that indicated on the drawing. For example, the designation G1 corresponds to a pipe thread having an outer diameter d=33.25m designed for pipes with an internal diameter of 1" (25.4 mm).
Pipe cylindrical thread of the same diameter (nominal diameter DN) can be performed on pipes with different wall thicknesses and even on a solid rod.
Rice. 7. Legend cylindrical and conical pipe threads: a) cylindrical pipe thread G 1 1/2;
b) thread of the same size, internal, left; c) external pipe conical thread; d) internal pipe conical
Table 5. Main dimensions of cylindrical pipe threads
In mechanisms where it is necessary to convert rotation into translational motion, they are used. In addition to its transformative function, this thread can withstand increased loads. This is a popular type of thread in important components of mechanisms and machine tools. You can observe the principle of operation of this thread when turning screws, when the rotation of the screw causes it to move in a linear direction. The force applied to transform the movement depends on the profile angle, thread pitch and part material.
The name carving comes from its resemblance to a trapezoid.
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Main characteristics of trapezoidal thread
The trapezoidal shape is formed by the angle of the thread profile. In this type, the profile angle can range from 15 to 40 degrees.
In the working process, threads may cause excessive friction. This factor is influenced by the profile angle, type of lubricant and material used. Radial clearances in trapezoidal threads can be identified by placing the thread in the middle of the diameter.
Trapezoidal threads are quite simple to manufacture. In most cases, the profile angle is set to 30 degrees. The quality of the thread depends largely on the accuracy of the workpiece used, as well as the material.
Methods for cutting trapezoidal threads
The production of this type of carving can be divided into two categories - one cutter and three cutters.
As an example, consider the following designation: Tr 26 × 4 LH – trapezoidal thread, single-start, with a diameter of 26 and a pitch of 4, left-handed.
GOST 9484-81 is used as the main standard.
