What is trapezoidal thread? Trapezoidal thread drawing.

In mechanisms where it is necessary to convert rotation into translational movement, they are used. In addition to its transformation function, this thread can withstand increased loads. This is a demanded type of thread in important units of mechanisms, machine tools. You can observe the principle of operation of this thread when tightening the screws, when the rotation of the screw makes it move in a linear direction. The force applied to transform the motion depends on the profile angle, thread pitch and part material.

The name of the thread is from the resemblance to the trapezoid.

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Main characteristics of trapezoidal thread

The trapezoid shape is formed by the angle of the thread profile. In this type, the profile angle can be in the range of 15 - 40 degrees.

In the work process, threads can cause excessive friction. This factor is influenced by the profile angle, the type of lubricant and the material used. Radial gaps in trapezoidal threads can be identified by positioning the thread in the middle of the diameter.

Trapezoidal thread 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.

Trapezoidal thread cutting methods

Production of this type Threads can be divided into two categories - one cutter and three cutters.

As an example, consider this designation: Tr 26 × 4 LH - trapezoidal thread, single-start, with a diameter of 26 and a pitch of 4, left.

GOST 9484-81 is used as the main standard.

Parts in machines, mechanisms, devices, as well as apparatuses and structures are connected to each other in some way. These connections perform different functions, and are divided, first of all, into two types: movable and fixed.

Fixed connection - connection of parts, ensuring the invariability of their relative position during operation. For example, welded joints, connections using fasteners, etc. A movable connection is a connection in which the parts have the possibility of relative movement in working condition. For example, a serrated connection.

Fixed and movable joints, in turn, are subdivided into detachable and one-piece, depending on the possibility of dismantling the connection.

One-piece connection is a connection that cannot be disconnected without disrupting the shape of the parts or their connecting element. For example, the connection is welded, brazed, riveted, etc.

Detachable connection - a connection that can be repeatedly disconnected and connected without deforming either the connected or fasteners. For example, threaded connection with a bolt, screw, wedge, keyway, gear, etc.

This article is devoted to an overview of threaded connections, a variety of which you often encounter in everyday life.

Threaded connection - connecting parts using a thread. Everyone knows what carving is, everyone has seen it. Many also know that the threads differ from each other, since they have different sizes, pitch, and so on. However, not many people imagine how this is regulated, and also that there is not only the metric cylindrical thread that is familiar to us, but also many of its other types.

1. Concept of thread

A thread is a surface formed by a 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

By 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 joint, ensuring its tightness, such threads are called fastening and sealing. There are also special threads that have a special purpose.

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 thread is subdivided into metric, pipe, tapered inch, trapezoidal thread - into trapezoidal, thrust, thrust reinforced.

By the size of the step, threads are distinguished large, small and special.

By the number of starts, threads are divided into single-start and multi-start.

In the direction of the helix, a right-hand thread is distinguished (the thread is cut clockwise) and the left-hand thread (the 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 parameters of the thread are determined by GOST 11708-82. These are the so-called standard threads. general purpose... Apart from them, there is the concept of special thread. Special threads are threads with standard profile but different from standard sizes diameter or 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. (For more details, see section 5. Operational purpose of the thread and its application).

3. Profiles and thread parameters

Thread profiles are characterized by the following features:

. metric thread has a profile in the form of an equilateral triangle with an apex angle of 60 °. The protrusions and valleys of the thread are blunt (GOST 9150-2002).

Metric threads are cylindrical and tapered.

. pipe thread has a profile in the form of an isosceles triangle with an apex angle of 55 °. Pipe threads can also be cylindrical and tapered.

. tapered inch thread has a profile in the form of an equilateral triangle.

Inch conical thread

. round thread has a semicircular profile.

. 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-isosceles trapezoid with an angle of inclination of the working side of 3 ° and of the non-working side - 30 °.

. rectangular thread has a rectangular profile. The thread is not standardized.

Non-standard rectangular thread

Thread parameters

The main thread parameters are:
Thread diameter(d) is the diameter of the surface on which the thread will be formed.

Figure 3 - Outside diameter

Thread pitch(P) is the distance along a line parallel to the thread axis between the midpoints of the closest side sides of the same name of the thread profile lying in the same axial plane on one side of the axis of rotation (GOST 11708-82).

Thread stroke(Рh) - relative axial movement of the threaded part in one revolution (360 °), equal to the product nР, where n is the number of thread starts. With a single-start thread, the stroke is equal to the pitch. A thread formed by the movement of one profile is called single-start, formed by the movement of two, three or more identical profiles, it is called multi-start (two-, three-start, etc.). In other words, not one spiral is cut at the same time on the bolt and nut, but two or three. Multiple threads are often used in high-precision equipment, for example, in photographic equipment, in order to uniquely position the position of parts during mutual rotation. Such a thread can be distinguished from the usual one by two or three beginnings of turns at the end.

Figure 4 - Thread pitch and thread path

The thread is characterized by three diameters: outer d (D), inner d1 (D1) and middle d2 (D2). Diameters external thread stand for d, d1 and d2, and the internal threads in the hole are D, D1 and D2.

Figure 5 - Thread diameters

outer (nominal) diameter d (D) - the diameter of an imaginary cylinder described around the tops of the external (d) or troughs of the internal thread (D). This diameter is defining for most threads and is included in the thread designation;
average diameter d2 (D2) - the diameter of the cylinder, the generatrix of which intersects the thread profile in such a way that its segments formed at the intersection with the groove are equal to half of the nominal thread pitch;
inner diameter d1 (D1,), the diameter of the cylinder inscribed in the troughs of the outer (d1,) or top of the inner thread (D1).

The construction of a helical surface in the drawing is a long and complex process, therefore, in the drawings of the products, 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 inner diameter.

Figure 6 - An example of an image of a thread on a rod and in a hole

4. Thread designation

Thread designation usually includes a letter designation of the thread type and nominal diameter. Additionally, the designation can contain the thread pitch (or TPI - threads per inch - the number of threads per inch), the number of starts for a multi-start thread, the diameter of the hole for the thread, the direction (left, right).

Metric thread- with pitch and basic thread parameters in millimeters. It is widely used with a nominal diameter from 1 to 600 mm and a pitch of 0.25 to 6 mm. The metric thread is the main fastening thread. This thread is single-start, mainly right-hand, with a large or small pitch. The designation of a metric thread includes the letter M and the nominal diameter of the thread, and the coarse pitch is not indicated: M5; M56. For threads with a small pitch, the thread pitch M5 × 0.5 is additionally indicated; M56 × 2. At the end symbol left-hand thread put the letters LH, for example: М5LH; M56 × 2 LH. The thread designation also indicates the accuracy class: M5-6g.

Example of designation:

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, with a fine pitch of 1.5 mm.

Although metric threads were never found wide application in sealed joints, but this possibility is laid down in the standards. These threads are metric conical and cylindrical.

Metric tapered thread performed with a taper of 1:16 and a nominal diameter of 6 to 60 mm in accordance with GOST 25229-82 (ST SEV 304-76). It is intended for self-sealing tapered threaded connections, as well as for connections of an external tapered thread with an internal cylindrical thread having a nominal profile in accordance with GOST 9150-2002. The designation of a metric tapered thread includes the type of thread (letters MK), nominal thread diameter, thread pitch. The letters LH are placed at the end of the left-hand thread symbol.

Example of designation:

MK 30 × 2 LН - left-hand metric tapered thread with an outer diameter of 30 mm, thread pitch 2 mm.

Metric straight thread (with profile)based on a metric thread (M) with a nominal diameter of 1.6 to 200 mm and a profile angle of 60 °. Its main difference is in the screw, which has an increased radius of the root on the thread (from 0.15011P to 0.180424P), which gives a threaded connection based on a cylindrical metric thread 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 field of the average diameter and the tolerance field of the diameter of the protrusions.

MJ female thread compatible with external thread M if the nominal diameter and pitch coincide, that is, a conventional metric screw can be screwed into a nut with such a thread.

Example of designation:

MJ6 × 1-4h6h - external thread on the shaft surface with a nominal diameter of 6 mm, a pitch of 1 mm, an average diameter tolerance field of 4h and a 6h projection diameter tolerance field.

Inch thread differences from metric in that the angle at the top of the thread they have is 55 degrees for the British standards BSW (Ww) and BSF or 60 degrees (as in the 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 denoted by a double prime 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 mean the size of the thread, but the conditional clearance in the pipe, while the outer diameter is actually much larger. A 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 working pressure for which the pipes are designed. Therefore, the inch standard for pipe threads is understood and accepted around 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 consider: thread depth, thread pitch, outer and inner diameter, angle of the thread profile. It is worth noting that the thread pitch in this case is calculated not in inches or even in millimeters, but in threads. A thread is a cut groove. Therefore, the calculation is based on how many grooves are cut on one inch measured pipe segment. 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 - 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.

If possible, do not use threads marked *.

Naturally, such peculiar standards for calculating the diameter and pitch only add confusion to the determination of the required values. Therefore, tables have been developed to determine the number of threads and the diameter of pipes in the presence of inch threads. In addition, any packaging always indicates its value and standard. But all the same, the data are 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 °, tops and troughs are rounded (GOST 6357-81).

A thread callout consists of the letter G, the nominal diameter of the thread in inches, and the accuracy class of the average diameter. For left-hand threads, the designation is supplemented with the letters LH.

Example of designation:

G 1 1/2-A - cylindrical pipe thread with size 1 1/2 ", accuracy class A;

1 / 4-20 BSP - Whitworth parallel pipe thread according to standard B. S.93 (England).
has a profile similar to that of a cylindrical pipe thread. It is possible to connect pipes with a tapered thread (taper 1:16) with products with a cylindrical pipe thread GOST 6211-81.

The thread callout consists of the letters R, the size of the nominal diameter in inches. The Rc designation is used for tapered female pipe threads. The left-hand thread symbol is complemented by the letters LH.

Example of designation:
R 1 1/2 - external conical pipe thread with size 1 1/2 ";
R 1 1/2 LH - left conical pipe thread;

Rс 1/2 - female tapered pipe thread;

BSPT 1 1/2 - female conical pipe thread according to standard B. S.93 (England).

With a profile angle of 60 °, GOST 6111-52 is cut on a tapered surface with a taper of 1:16.

The designation consists of the letter K and the size of the thread in inches with an indication of the dimension, it is applied on the shelf of the leader line, as in the case of pipe threads. Example of designation:
K 3/4 ″ in accordance with GOST 6111-52. 3 / 8-18 NPT designation per ANSI / ASME B 1.20.1 (USA).

Serves to transmit movement and effort. The profile of the trapezoidal thread is an isosceles trapezoid with an angle between the sides of 30 °. For each diameter, the thread can be single-start and multi-start, right and left GOST 9484-81.

The main dimensions, diameters, pitches, single-start thread tolerances are standardized according to GOST 24737-81, 24738-81, 9562-81. For multi-start threads, these parameters are in GOST 24739-81.

The symbol of a single-start thread consists of the letters Tr, the value of the nominal diameter of the thread, the pitch, the tolerance field.

Example of designation:

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 - the same make-up length 85 mm;

Tr 40 × 6LH-7H - the same for the inner left.

The numerical value of the lead is added to the multi-start thread callout:

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.

Has a profile of an uneven trapezoid. The profile valleys are rounded and there are three different pitches for each diameter. Serves to transmit motion with large axial loads GOST 10177-82.

Thrust threads are designated by the letters S, then indicate the nominal thread diameter in millimeters, the thread pitch (stroke and pitch, if this thread is multi-start), thread direction (for right-hand threads do not indicate, for left-hand threads LH), and thread accuracy class.

Example of designation:

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: Cn M40 × 1.5 - 6g.

Rectangular thread (square)... Thread with a rectangular (or square) non-standard profile, therefore, all its dimensions are indicated on the drawing. It is used to transmit the movement of heavily loaded movable threaded connections. Usually performed on cargo and lead screws.

Has a profile obtained by joining 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 a pitch P = 2.54 mm.

Example of designation:

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 of 8 ... 200 mm) according to ST SEV 3293-81, which was put into effect directly as State standard... The thread is used for crane hooks, as well as in aggressive environments.

Example of designation:

Rd 16 - round thread with an outer diameter of 16 mm; Rd 16LH - round thread with a diameter of 16 mm, left-hand.

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, threads are distinguished general use and special, designed to connect one type of parts of a certain mechanism. The first group includes threads:

1.) Fasteners- metric, inch, used for detachable connection of machine parts. Their main purpose is to ensure a complete and reliable connection of parts under various loads and under various temperature conditions during long-term operation.

2.) Running gear or kinematic - trapezoidal and rectangular, used for lead screws, machine tool and table support screws measuring instruments etc. Their main purpose is to ensure accurate movement with the least friction, and for rectangular threads also to exclude self-unscrewing under the action of an applied force; Persistent (in presses and jacks) and round, designed to convert rotary motion into linear motion. They perceive great efforts at relatively low speeds. Their main purpose is to ensure smooth rotation and high load capacity (metric threads of increased accuracy are used for precision micrometric instruments). Round thread is 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-technical water-folding fittings).

3.) Fastening and sealing (pipe and reinforcement) - tubular cylindrical and conical, metric inch and conical, used for pipelines and fittings, their main purpose is to ensure the tightness of the joints (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, valves, etc.).

Tapered pipe threads in accordance with GOST 6211-81 are used in pipe joints at high pressures and temperatures (in valves and gas cylinders) when increased tightness of the connection is required.

Referred to the second group, special threadhas a special purpose and is used in certain specialized industries. These include the following:

1.) metric tight thread- thread made on the rod (on the hairpin) and in the hole (in the socket) for the largest limit sizes; designed to form tightly threaded connections.

2.) metric clearance threads- the thread required to ensure easy make-up and loosening of threaded connections of parts operating under high temperatures when conditions are created for the setting (splicing) of oxide films, which cover the surface of the thread.

3.) watch 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 devices; thread profile - isosceles trapezoid with an angle of 60 °.

The performance requirements for threads depend on the purpose of the threaded connection. Common to all threads are the requirements for durability and make-up without fitting independently manufactured threaded parts while maintaining the performance of the connections. Briefly summarizing the main threads used for the operational purpose, you can deduce in the form of the following table:

6.Determination of thread size

Typically, the threads on different fittings look similar, making it difficult to visually identify the thread type. The thread on the fittings is determined by measuring the main parameters with a thread gauge and vernier calipers and comparing the results obtained with the thread table.

Figure 7 - Measurement of thread parameters

There are two types of thread gauges: with the M 60о stamp - for metric threads with a profile angle of 60о and with the D 55о stamp - for inch and pipe threads with a 55о profile angle. On each manifold of a thread gauge for metric threads, a number is stamped indicating the thread pitch in mm for inch and pipe threads - the number of steps on a length of 25.4 mm (1 "= 25.4 mm).

7.Methods of threading

The main methods for making threads are:

cutting them with cutters and combs on lathes;
tapping with dies with thread-cutting heads;
cold and hot rolling with flat or round knurled dies;
milling with special thread mills;
grinding with abrasive wheels.

The choice of threading method depends on the type of thread production, its accuracy of the workpiece material, etc.

Figure 8 - Threading tool

1. Cutting of a thread with incisors. Using threaded cutters and dies on screw-cutting lathe on machines, both external and internal threads are cut (internal thread starting from a diameter of 12 mm and above). The method of threading with cutters is characterized by a relatively low productivity, therefore, at present it is used mainly in small-scale and individual production, as well as in the creation of precise screws of lead screw calibers, etc. The advantage of this method is its simplicity cutting tool and the relatively high precision of the resulting thread.

2. Cutting of a thread with dies and taps. Dice by their own design features are divided into round and sliding. Round dies used for assembly blanks and other works are designed for cutting external threads up to 52 mm in diameter in one pass. For larger threads, special design dies are used, which actually serve only to clean the thread after preliminary cutting with other tools. Sliding dies consist of two halves gradually converging during the cutting process. The tap is a threaded steel rod divided by longitudinal straight or helical grooves forming cutting edges. The same grooves serve for the exit of chips. According to the method of application, taps are divided into manual and machine.

3. Thread rolling. The main industrial method of manufacturing threads at the present time is rolling on special thread rolling machines. The part is clamped in a vice. In this case, with high productivity, a high quality product (shape, size and surface roughness) is obtained. The thread rolling process consists in 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 with a threaded profile and a thread of the same profile is extruded on the rod. The largest diameter of the rolled thread is 25 mm; the smallest is 1 mm; the length of the rolled thread is 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, with a radial feed, cuts into the body of the part and mills the thread on its surface. Periodically, there is an axial movement of the part or cutter from a special copier by an amount equal to the thread pitch during one revolution of the part.

5. Grinding of precise threads. Grinding as a method of creating a thread is mainly used to obtain accurate threads on relatively short threaded parts, for example, threaded plugs - thread roller gauges, etc. The essence of the process is that grinding wheel located to the part at an angle of rise of the thread during fast rotation and with simultaneous slow rotation of the part with feed along the axis by the amount of the thread pitch per revolution, cuts (grinds) a part of the part surface. 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 of such countries as Great Britain (BS), Germany (DIN), France (NF), Japan (JIS), USA (UNC) are applied in the world. The main reasons for their difference are traditionally different systems of measures and methods for specifying the sizes of threads in different countries as well as special applications for threads. However, over the past century, the ISO metric standard, the International Organization for Standardization, has strongly established its position in the world, which in turn has contributed to the mutual understanding of technicians.

The most common types of foreign threads are:

Metric ISO
Whitword Thread
Trapezoidal thread
Round thread
Thrust thread

The given summary table describes the correspondence of more than twenty types of threads (general machine-building 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 abundance different kind threads and the documents regulating them and the large amount of data does not allow to fully compare and compare the threads of domestic and foreign standards, consider, for example, compliance different types triangular thread which is most often found in general mechanical engineering.

and couplings to them. Technical conditions "

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 thread can be single-start and multi-start, right-hand and left-hand.

The diameters and steps of a single-start trapezoidal thread in the range of diameters 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 designation:

trapezoidal single-thread 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 NS 9 (RZ)

Examples of thread designations in the drawing are shown in Fig. 5. at

Table 2. Diameters and steps of a trapezoidal single-start thread 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 marked with *.

Table 3. The main dimensions of the trapezoidal multi-start thread according to GOST 24739 81, mm

d	Thread pitch	Thread lead 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 with travel in parentheses have a lead angle greater than 10 °.

The thread is persistent.

The main purpose of the thread is to transfer axial load by means of a screw in one direction, for example, in jacks, presses, etc. The thread profile is an unequal trapezoid (Fig. 3, d).

:> v Diameters and steps of the thrust thread in the range of diameters from 16 to 42 mm are given in table. 4.

Examples of thread designation: "

thrust one-start right-hand with a diameter of 32 mm with a step 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 steps of the thrust thread 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 over the second.

Steps to be preferred when developing new designs.

Cylindrical pipe thread.

This thread is used in cylindrical pipe connections and connections of an internal cylindrical thread with an external tapered thread.

The profile (Fig. 3, b) and the main dimensions are established by GOST 6357 81. The values of the main dimensions of the cylindrical pipe thread are given in table. 5.

The pipe thread designation (Fig. 7, a, b) consists of the letter G and the thread size in inches, for example:

This designation is conditional, since indicates the diameter not of the thread, but of the hole in the pipe (nominal bore DN at a certain wall thickness). The outer diameter of the pipe thread will be larger than that indicated in the drawing. For example, the notation G1 corresponds to pipe thread having an outer diameter d = 33.25m m designed for pipes with an inner diameter of 1 "(25.4 mm).

Straight pipe thread of the same diameter (nominal size DN) can be made on pipes with different wall thicknesses and even on a solid rod.

Rice. 7. Legend for cylindrical and tapered pipe threads: a) cylindrical pipe thread G 1 1/2;

b) left-hand internal thread of the same size; c) external pipe tapered thread; d) inner pipe conical

Table 5. The main dimensions of the cylindrical pipe thread

Trapezoidal thread is widely used to make various screws, which are used for various production equipment. For example, for machine tools, lifting devices, presses. Such a thread has the form of an isosceles trapezoid, while the profile angle can have different values: 15, 24, 30, 40 °. During the operation of the screw, on which the trapezoidal thread is cut, frictional forces occur due to the natural way. That is, due to the presence of lubricant, surface roughness, as well as the profile angle.

Thread types

Today there are such types:

Metric. It serves to secure several elements. The slicing conditions are set in regulatory documents... The profile is a triangle with equilateral corners. This indicator is 60 °. Metric screws are available in small and large pitches. The first type is used to fix thin-sheet elements to create increased tightness. This type of connection can be found in precision optical instruments.
Conical. It is made in the same way as the previous type, but twisting is performed to a depth of 0.8 mm.
Inch. To date, there is no normative document that would indicate the dimensions of the thread. Inch thread is used for repair various equipment... As a rule, these are old devices and devices. Its main indicators are the outer diameter and pitch.
Tubular cylindrical. This view is an isosceles triangle, top corner which is 55 °. Such an internal thread is used to connect pipelines, as well as parts made of thin sheet material. It is recommended when there are special requirements for the tightness of the connection.
Tubular conical. The internal thread must meet all the requirements of the regulatory documents. The sizes are completely standardized. It is used to connect various types of pipelines.
Persistent. This view is an unequal trapezoid, where one of the sides is inclined by 3 °, and the other - by 30 °. The first side is working. The shape of the profile, as well as the diameter of the steps, are determined by regulatory documents. In accordance with them, the thread is made with a diameter of 10 to 600 mm, while the maximum value of the pitch is 24 mm. They are used where higher holding forces are required.
Round. A thread profile is represented by various arcs connected by straight lines. The profile angle is 30 °. This type of thread is used for those connections that are exposed to aggressive media.
Rectangular. It is not enshrined in any normative documents. Its main advantage is its high efficiency. Compared to the trapezoidal view, it is less durable, and also causes a lot of confusing moments in its production. The main place of application is jacks and different kinds screws.
Trapezoidal. It has the shape of an isosceles trapezoid with a profile angle of 30 °. Trapezoidal thread, the dimensions of which are fixed in the documentation, are used to connect various elements of production equipment.

Manufacturing conditions

Compared to other types, trapezoidal threads are much easier to manufacture.

That is why it is often used in various fields. The most popular is the trapezoidal screw with a 30 ° profile angle. The production technology is very similar to that used for cutting rectangular threads. But there are still significant differences in terms of precision and cleanliness. Cutting trapezoidal threads is no different from the same procedure with a rectangular look. At the moment, there are several such methods.

Making a screw with one cutter

Single-start trapezoidal thread is made as follows:

the workpiece is prepared and the channels for sharpening are guided;
sharpening of the cutter is performed according to a special prepared template;
installation and fastening of the sharpened element are made. It should be located so that the centers coincide and are parallel to the cutting axis;
the equipment turns on and the workpiece is fed for threading;
the finished part is checked in accordance with the finished template.

Cutting with three incisors

This method is as follows:

a blank is being prepared;
sharpening of three cutters is performed - straight, narrow and profile;
the installation and fastening of the prepared elements is carried out. They can be located both perpendicular and parallel to the thread axis. It all depends on the angle of inclination.

Common manufacturing method

It is in production that trapezoidal threading takes place in this way:

working equipment is checked and adjusted;
thanks to the slotted cutter, small indentations are made on the screw;
using a narrow slotted element, the screw is cut to a certain diameter;
with the help of a profile slotted element, the final production of the trapezoidal thread is carried out;
the finished part is checked in accordance with the ready-made templates.

Trapezoidal thread: dimensions

As stated earlier, given view the thread has the shape of a trapezoid, in which the angle between the sides can have different values. All basic dimensions are set in accordance with GOST.

For a single-start type, the trapezoidal thread (dimensions - GOST 9481-81) has sizes and pitches of various diameters - from 10 to 640 mm. In addition, it can be multi-threaded, as well as twisted to the left or right side. These indicators are standardized by GOST 24738-81.

Where is used

For the functioning of any element, for example a machine or mechanism, it is necessary to fulfill a prerequisite: rotational movements must be transformed into translational ones.

This principle is used for the manufacture of various machine tools, devices, control systems used in the industrial field.

Thread advantages

The efficiency of work on converting rotary movements into translational ones is carried out with the help of a nut and a screw. While these parts look simple, they require care in their manufacture. It is on these parts that performance and reliability depend, not only constituent elements but also all working equipment.

Features of multi-start thread

To endow the screw with strength characteristics and increase its stroke, a multi-start trapezoidal thread is used. In this case, all parameters, such as the height of the thread, its diameter are absolutely the same, with a single-start view. The only difference is the number of moves per step. For example, three-start types of threads have a stroke three times their pitch. All this can be seen in the figures.

Let's give an example to make this view understandable to every person. Everyone uses regular lids for canning fruits and vegetables. To open them, you need to make a minimum of effort. When using cylinders large diameters it is much more difficult to get into the grooves of a one-way thread. That is why they use multi-way.

This type of thread can be determined visually, just look at the picture.

You can see exactly how many turns go from the beginning of the screw. Multi-lead threads are manufactured using complex technologies, and, accordingly, are more expensive.

Other advantages

Trapezoidal joints have many positive qualities... That is why they are used in various manufacturing industries. The most common area is mechanical engineering. So, their advantages include the following:

the ability to assemble and disassemble various devices unlimited number of times;
convenient process of disassembly and assembly;
reliability of the threaded connection;
easy manufacturing process;
independent regulation of the compression force;
production of parts in various designs.

Disadvantages of connections

There are not so many negative aspects of this type of connection. One of them is the occurrence of great tension in the valleys. In addition, they cannot be used in devices and mechanisms that have high vibration, since the screws can unscrew themselves, which is not a good sign.

Therefore, it is necessary to monitor this, and in case of such a situation - to correct the position of the screws.

Such quality as cost can be attributed to both positive and negative sides.

Single-start threads cost significantly less than multi-start threads. Here everyone chooses according to personal preference. Many design organizations use multi-lead threads, since they are reliable and durable.

So, we found out what this type of connection is, such as a trapezoidal thread, its dimensions, advantages and disadvantages.

Thread profiles and sizes

(GOST 9484-81)

The standard applies to trapezoidal threads and sets the profiles and dimensions of its elements.

MAIN PROFILE

An example of a symbol for a trapezoidal single-start thread with a nominal diameter of 20 mm, a pitch of 4 mm and a tolerance field of an average diameter of 7e:

Tg 20 x 4 -7e

RATED PROFILES
external and internal thread

h 3 - the height of the profile of the external thread; H 4 - the height of the internal thread profile; d 3 - inner diameter of the outer thread; D 4 - outer diameter of the internal thread; R 1 - radius of rounding at the top of the external thread; R 2 - radius of twisting in the cavity of the external and internal threads; a c - clearance at the top of the thread.

DIAMETERS AND STEPS
trapezoidal single-start thread according to GOST 24737-81

Preferred diameters and pitches are specified in GOST 24738-81. Numerical values tolerances of diameters and pitches - according to GOST 9562-81

DIAMETERS AND STEPS
trapezoidal multi-start thread according to GOST 24739-81

Notes:
1. The steps outlined are preferred.
2. The steps in parentheses are not recommended when developing new designs.
3. Threads for which the stroke value is marked with * have a lead angle of more than 10 o. For these threads, it is necessary to take into account the deviation of the profile shape during manufacture.
4. In technically and economically justified cases, it is allowed to use other values of nominal thread diameters in accordance with GOST 24738-81.
5. When choosing thread diameters, the first row should be preferred over the second.

An example of a symbol for a trapezoidal multi-start thread with a nominal diameter of 20 mm, a stroke of 8 mm, a pitch of 4 mm and a tolerance field of 8e:

Tg 20-8 (P4) - 8e

The same, left:

Tg 20-8 (P4) LH - 8e

The make-up length, if it differs from the thread length, is indicated in millimeters at the end of the thread designation, for example:

Tg 20-8 (P4) LH - 8e - 180

The numerical values of the make-up lengths related to the N and L groups are in accordance with GOST 9562-81.

Landing in a threaded connection is indicated by a fraction

Tg 20-8 (P4) LH - 8Н / 8е - 180

Numerical values of tolerances of diameters d and D 1 - according to GOST 9562-81.
Numerical values of tolerances of diameters d 2, d 3 and D 2 - according to GOST 24739-81.

Application of trapezoidal thread

A trapezoidal screw thread is a lead thread that has a relatively great strength friction, it is self-braking. The advantage for lifting technology - in the resting position does not require additional fixation.

Trapezoidal threads are used to convert rotary motion into translational motion and are used primarily for rectilinear motion. It also finds its application as a lead screw in lathes or as a drive thread for screw presses on tables or vehicle bridges.

Application examples for trapezoidal spindle threads:

Feed movement on machine tools (eg adjusting screws and lead screws);
- movement on the manipulator;
- regulation of movement on lifting mechanisms and forklift trucks;
- the movement of the shutter when locking the injection molding machines;
- movement of movement on collection containers;
- vertical movement when working with a press.