Trapezoidal thread. Application of trapezoidal thread. Methods for cutting trapezoidal threads

GOST 9484 – 81

Trapezoidal thread has a profile with an angle of 30°. Thread pitch measured in millimeters.

Trapezoidal thread used in machine units to convert rotational motion into translational motion, for example: machine lead screws, press power screws, lifting screws, etc. Threads of this type can withstand significant loads.

Trapezoidal thread indicated by letters Tr- English trapezoidal:

Tr 28 × 5- diameter 28mm pitch 5mm
Tr 28 × 5 LH- diameter 28mm pitch 5mm left thread
Tr 20 × 8 (P4)- diameter 20 mm, pitch 4 mm and stroke 8 mm multi-start thread
Tr 20 × 8 (P4) LH- diameter 20 mm, pitch 4 mm and stroke 8 mm multi-start thread left

d- outside diameter external thread(screw)

D– outer diameter of the internal thread (nut)

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

Thread diameters d		Step
Trapezoidal thread
Row 1	Row 2	Step
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.

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 a certain part into forward movement other parts, a screw-nut pair 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 the usual 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 transmission

The 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 hardened, 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.

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.

Single pass diameters and steps 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 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 pipe connections 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 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. Symbols for cylindrical and tapered pipe threads: a) cylindrical pipe thread G 1 1/2;

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

Table 5. Main dimensions of cylindrical pipe threads

Profiles and thread sizes

(GOST 9484-81)

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

MAIN PROFILE

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

Tg 20 x 4 -7e

NOMINAL PROFILES
external and internal threads

h 3 - height of the external thread profile; H 4 - internal thread profile height; d 3 - internal diameter of the external thread; D 4 - outer diameter of the internal thread; R 1 - rounding radius at the top of the external thread; R 2 - radius of torsion in the root of the external and internal threads; a c is the gap 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 of tolerances of diameters and pitches - according to GOST 9562-81

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

Notes:
1. Steps outlined in a box are preferred steps.
2. The steps indicated in parentheses are not recommended for use when developing new designs.
3. Threads with a stroke value marked * have a lead angle of more than 10 o. For these threads, the deviation of the profile shape must be taken into account during manufacturing.
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, you should prefer the first row to the second.

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

Tg 20-8 (P4) - 8e

The same, left:

Tg 20-8 (P4) LH - 8е

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

Tg 20-8 (P4) LH - 8е - 180

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

The fit 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 for diameters d 2, d 3 and D 2 - according to GOST 24739-81.

Application of trapezoidal thread

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

Trapezoidal threads are used to convert rotary motion into linear motion and are used primarily for linear motion. It also finds its use 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 movements on machine tools (e.g. adjusting and lead screws);
- movement on the manipulator;
- regulation of movement on lifting mechanisms and forklifts;
- movement of the shutter when locking injection molding machines;
- moving movement on assembly containers;
- vertical movement when working with the press.

Types of thread

Today there are the following types:

Metric. It serves to secure several elements. The cutting conditions are established in the regulatory documentation. The profile is a triangle with equilateral angles. This indicator is 60°. Screws with metric thread performed in small and large steps. The first type is used to secure thin-sheet elements to create increased tightness. This type of connection can be found in precision optical instruments.
Conical. It is manufactured in the same way as the previous type, but twisting is done to a depth of 0.8 mm.
Inch. To date, there is no regulatory document that would indicate thread sizes. Inch threads are used in the repair of various equipment. As a rule, these are old instruments and devices. Its main indicators are the outer diameter and pitch.
Pipe cylindrical. This type is an isosceles triangle, top corner which is equal to 55°. This internal thread is used to connect pipelines, as well as parts made of thin sheet material. It is recommended when presented special requirements to the tightness of the connection.
Pipe conical. Internal thread must comply with all regulatory requirements. The sizes are completely standardized. It is used to connect various types of pipelines.
Persistent. This type is an unequal trapezoid, where one side is inclined by 3° and the other by 30°. The first side is the working side. The shape of the profile, as well as the diameter of the steps, are determined regulatory documents. In accordance with them, threads are made with a diameter from 10 to 600 mm, with a maximum pitch value of 24 mm. They are used where increased holding forces are required.
Round. The thread profile consists of 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 environments.
Rectangular. It is not supported by any regulatory documents. Its main advantage is high efficiency. Compared to the trapezoidal type, it is less durable, and also causes many incomprehensible moments during 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, is used to connect various elements production equipment.

Manufacturing conditions

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

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

Making a screw with one cutter

Single-start trapezoidal threads are manufactured as follows:

the workpiece is prepared and channels for sharpening are created;
The cutter is sharpened according to a special prepared template;
The sharpened element is installed and secured. It should be positioned so that the centers coincide and are parallel to the cutting axis;
the equipment is turned on and the workpiece is fed for thread cutting;
the finished part is checked in accordance with the finished template.

Three-cut slicing

This method is as follows:

the workpiece is prepared;
three incisors are sharpened - straight, narrow and profile;
The prepared elements are installed and secured. They can be located either perpendicular or parallel to the thread axis. It all depends on the angle of inclination.

Common production method

It is in production that cutting trapezoidal threads 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 trapezoidal threads is carried out;
the finished part is checked in accordance with ready-made templates.

Trapezoidal thread: dimensions

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

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

Where is it used?

For the functioning of any element, such as a machine or mechanism, it is necessary to perform mandatory condition: Rotational movements must be converted into translational ones.

This principle is used for the manufacture of various machines, devices, and control systems used in the industrial sector.

Advantages of thread

Efficiency of conversion work rotational movements translational is carried out using a nut and screw. Even though these parts look simple, they require care when making them. 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 provide the screw with strength characteristics and increase its stroke, multi-start trapezoidal threads are used. In this case, all parameters, such as the height of the thread, its diameter, are absolutely the same, with a single-start appearance. The only difference is the number of moves per step. For example, three-start threads have a stroke three times their pitch. All this can be seen in the pictures.

Let us give an example so that this type becomes clear to every person. Everyone uses regular lids for canning vegetables and fruits. To open them you need to make a minimum of effort. When using large diameter cylinders, it is much more difficult to get into the grooves of a single-thread thread. That is why multi-pass ones are used.

This type of carving can be determined visually, just look at the drawing.

You can see exactly how many turns go from the beginning of the screw. Multi-way threads are manufactured according to complex technologies, and accordingly they cost more.

Other advantages

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

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

Disadvantages of connections

There are not many negative aspects to this type of connection. One of them is the occurrence of high stress in the depressions. In addition, they cannot be used in devices and mechanisms that have high vibration, since the screws can unscrew on their own, which is not a good sign.

Therefore, it is necessary to monitor this, and if such a situation arises, correct the position of the screws.

Quality such as cost can be attributed to both positive and negative aspects.

Single-stroke threads cost significantly less than multi-stroke threads. Here everyone chooses according to personal preferences. Many design organizations use multi-pass threads, as 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.

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