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Bolt GOST 7798-70

High-strength bolt with hexagonal head GOST 7798-70

No matter how technology and technology develop, the main means of creating a detachable connection have been and remain bolts. Since the Industrial Revolution to this day, they have been widely used in all areas of the economy: mechanical engineering, instrument making, energy, transport, agriculture, mining, etc.

Bolts absorb shear, tensile and bending forces, and therefore are effective for connecting various parts - flanges, plates, beams. This fastener is indispensable in cases where:

• it is necessary to create a detachable connection;
• it is impossible to create a welded joint;
• the material of the parts does not allow threading;
• the material of the parts is not capable of providing sufficient strength and durability of the thread.

GOST 7798-70 defines the dimensions and main performance characteristics of hex bolts.

The GOST 7798-70 bolt is a rod with a metric thread and a hexagonal head, the material of which is steel grades 10, 20, 10 kp, 20 kp, 35, 30ХР, 40Х. The diameter of the threaded part ranges from 6 mm (M6) to 48 mm (M48).

The hex bolt GOST 7798-70 must comply with normal accuracy (class B) and strength classes 4.8; 5.8; 6.8; 8.8; 10.9. The first digit of the strength class is 1/100 of the tensile strength (in MPa). The second figure is the ratio of the tensile strength to the yield strength, multiplied by 10. Thus, the strength class allows us to judge the most significant performance characteristics of this type of fastener.

Bolts having a tensile strength of 800 MPa and above are called high-strength. They perceive high static and dynamic stresses. The high-strength bolt is capable of operating equally reliably in aggressive environments, under high-temperature loads and under low-temperature conditions. The material for this fastener is steel grades 30ХР, 40Х. It is used in metallurgy, in the chemical, pharmaceutical industries, for work in the Far North and in all cases where it is necessary to ensure high joint strength.

The GOST 7798-70 bolt can have a thread with a fine or large pitch. Threads with coarse pitches are most common, since their accuracy is less affected by manufacturing errors.

At the same time, fine pitch threads provide higher strength to the threaded part of the rod without reducing the strength of the thread. And, in addition, fine-pitch threads have higher self-braking reliability compared to coarse-pitch threads. Everything works together to increase the reliability of the connection.

Bolts are the primary fasteners for prefabricated structures. They are used to assemble cars, machines, airplanes, bridges and buildings. They are used in household appliances and a variety of electrical appliances. Whether screwed into blind holes or used in conjunction with nuts, they create strong, reliable connections. The special hex head configuration makes it easy to tighten the bolts either by hand or using wrenches and hex heads. To speed up the assembly and disassembly process, many different devices have been created, such as wrenches, ratchets, electric and pneumatic impact wrenches.

The most common in industry and mechanical engineering are those that consist of a pin and a hex head. The reference length, which is also indicated on the website, is the length of the hairpin without taking into account the height of the head.

They are produced with metric threads from M6 to M48 and lengths from 8 mm to 300 mm. The standard provides for the production of bolts with fine and coarse (main) threads. Depending on the length, the thread is not completely cut, which reduces its cost and increases the strength of the stud as a whole.

Bolt materials GOST 7798 70

They are manufactured with average accuracy class B, which has a slight deviation in thread dimensions and tolerances, and is also less expensive to manufacture.

Bolts are made from various materials:

• carbon steel;
• stainless steel;
• non-ferrous alloys;
• polyamide.

For use in aggressive environments, bolts are made of stainless and acid-resistant steels. The difference is that an aggressive environment, unlike moisture, quickly destroys the protective coating, and the metal of the bolt even faster. Hardware made of non-ferrous metals is used in specific operating conditions or devices. They have antimagnetic properties and are not subject to corrosion.

Bolts are available in different strengths from 5.6 to 10.9, which is indicated on the head. High strength is not always the best option for a threaded connection. Specifications require that the strength of the bolt be slightly lower than the strength of the threaded hole or nut with which it is used. For example, if a nut has a strength class of 9, then the bolt must correspond to a strength class of 8.8.

Protective coatings for bolts GOST 7798 70

Coatings are applied for the sole purpose of maintaining the geometry of the bolt for as long as possible and maximizing its service life. The durability and functionality of the bolt will depend on how high-quality the protective coating is.

Factors influencing the formation of rust, which destroys the metal, disrupting the profile of the thread and head, rendering the bolt unusable:

• atmospheric influence;
• high humidity;
• temperature changes.

Hardware, which is made of ordinary carbon steel, is produced with an anti-corrosion coating. The most common coatings are:

• zinc;
• cadmium;
• oxide;
• phosphate;
• tin;
• copper;
• zinc;
• silver;
• Nickel

If a bolt is corroded while in a threaded connection, it will be very difficult to unscrew it during repair or replacement. The threads of the bolt stick to the threads of the nut or hole, and the head loses its hexagonal shape, which makes it difficult to grip with a wrench.

Zinc protective coating is simple and inexpensive to manufacture, and therefore has become the most common for a variety of hardware. Zinc coatings differ slightly in the method and method of application. The most common ones are:

• galvanic galvanization;
• thermal diffusion galvanizing;
• hot galvanizing.

Zinc coating can be of two colors: white and yellow. The color of the coating does not affect the quality and durability in any way and depends on the method of applying zinc.

In the manufacturing industry, bolts with protective coatings are widely used:

• oxide impregnated with oil;
• phosphate impregnated with oil.

Mainly used for assembling machines, components, assemblies and they are easily distinguished by appearance, as they are characteristically black. Due to this, no additional metal is applied to the bolt; they are cheaper than galvanized ones, but less resistant to moisture.

The standard allows the manufacture of bolts without any coatings (as is). They are significantly cheaper, but can only be installed in areas where there is no exposure to moisture or the parts will eventually be painted.

Buy bolt GOST 7798 70

There is a large selection on the online store website bolts GOST 7798 70. Here you can choose bolts of any strength, both coated and uncoated. If required, you can purchase bolts of the same size, but in different designs. The company's warehouses have a sufficient number of finished products to instantly satisfy even large wholesale orders.

Fill out an application online yourself, or contact the managers who will give more detailed information, take the order or arrange delivery.

• 1. This standard applies to hex head bolts of accuracy class B with a thread diameter from 6 to 48 mm.
  The standard fully complies with ST SEV 4728-84.
  (Changed edition, Amendment No. 4).
• 2. The design and dimensions of the bolts must correspond to those indicated in the drawing and in the table. 12. (Changed edition, Amendment No. 2-6).
• 3. Thread - according to GOST 24705. Thread run-out and undercut - according to GOST 27148. Bolt ends - according to GOST 12414. (Changed edition, Amendment No. 5).
• 3a. The radius under the head is according to GOST 24670.
• 3b. Tolerances of dimensions, deviations in shape and location of surfaces and control methods not established by this standard are in accordance with GOST 1759.1.
• 3c. Permissible defects in the surface of bolts and control methods - according to GOST 1759.2. 3a - 3c. (Introduced additionally, Amendment No. 4).
• 4. (Deleted, Amendment No. 4).
• 5. The head design options are determined by the manufacturer.
• 5a. It is allowed to produce bolts with a diameter of the smooth part of the rod d 1
  approximately equal to the average thread diameter.
  (Introduced additionally, Amendment No. 3).
• 5 B. To apply markings, it is allowed to manufacture bolts of versions 1 and 2 with a hole on the end surface of the head with dimensions that do not reduce the strength of the head, while the depth of the hole should be no more than 0.4k. (Introduced additionally, Amendment No. 5).
• 6. Technical requirements- according to GOST 1759.0.
• 7. (Deleted, Amendment No. 2).
• 8. The weight of the bolts is indicated in Appendix 1.

Notes:

• 1. Bolt sizes enclosed in brackets are not recommended.
• 2. It is allowed to manufacture bolts with the dimensions specified in Appendix 2.

Notes:

• 1. Bolts with length dimensions enclosed in brackets are not recommended.
• 2. Bolts for which the b values ​​are located above the broken line are allowed to be manufactured with a thread length up to the head.

Example symbol bolt version 1 with thread diameter d=12 mm, turnkey size S=18 mm, length l=60 mm, with large thread pitch with tolerance range 6g, strength class 5.8, uncoated:
Bolt M12 - 6gx60.58 (S18) GOST 7798-70
The same, version 2, with turnkey size S=19 mm, with a fine thread pitch with a tolerance range of 6g, strength class 10.9, made of steel grade 40X, with coating 01 6 microns thick:
Bolt 2M12x1.25 - 6gx60.109.40X.016 GOST 7798-70

INFORMATION DATA

• 1. DEVELOPED AND INTRODUCED by the Ministry of Ferrous Metallurgy of the USSR DEVELOPERS I. N. Nedoviziy, Ph.D. tech. sciences; B. M. Rigmant; V. I. Mokrinsky, Ph.D. technical sciences
• 2. APPROVED AND ENTERED INTO EFFECT by Resolution of the Committee of Standards, Measures and Measuring Instruments under the Council of Ministers of the USSR dated 04.03.70 No. 270
• 3. The standard fully complies with ST SEV 4728-84 4. INSTEAD GOST 7798-62
• 6. The validity period was lifted according to Protocol No. 5-94 of the Interstate Council for Standardization, Metrology and Certification (IUS 11-12-94)
• 7. REISSUE with Amendments No. 2, 3, 4, 5, 6, approved in February 1974, March 1981, March 1985, March 1989, July 1995 (IUS 3-74, 6-81 , 6-85, 6-89, 9-95)

Weight of steel bolts (version 1) with coarse thread pitch

Additional requirements reflecting the needs of the national economy

This type of bolt is the most sold and widely used. Please note that galvanized fasteners are recommended for use only in dry rooms. For outdoor work and structures in aggressive environments, it is better to use bolts with hot-dip galvanized coating or stainless steel A2-70, A4-70 or A4-80. For highly loaded connections, fastenings of strength classes 10.9 and 12.9 are used. In projects of particularly important structures, such as bridges, sports structures, bolts with a controlled tightening torque are installed.

The closest analogue of DIN 933 bolts is DIN 931, which also correspond to GOST 7798-70. The size range of these bolts, as a rule, differs from DIN 933 in being longer.

Along with bolted connections, screw connections are used. There are two main differences between one and the other:

• bolts are used in pairs with a nut, and screws are screwed directly into a part in which a threaded installation hole is pre-provided;
• to install the bolt, use a wrench that requires side access to the nut or hex head of the bolt, and the screws are installed various types screwdrivers that require access to the end of the screw head.

Bolt markings

Hex head bolts are marked according to ISO 3506-1 or ISO 898-1. A general view of the marking is shown in the figure. In the conditionally lower part of the end of the bolt head a mark with the strength class is affixed, in the conditionally upper part - the manufacturer's mark. Another marking option is a strength class mark on one of the sides of the bolt head. The ISO 898-1 standard does not provide a manufacturer's mark, only a strength class.

Bolted connections

Bolted connections used in mechanical engineering are usually removable connections because this allows them to be easily installed and removed, they are quite reliable and can be used in a variety of conditions. In addition, standard fasteners are cheap connecting parts.

Among the disadvantages of bolted connections, we can mention, for example, their reliability, which largely depends on the difficult-to-control torque (alternative: bolts with controlled tightening torque). In addition, there are break points in the bolts where the stress value reaches a maximum. The load in many bolted connections is a force directed along the axis of the bolt, as well as a transverse shear force in the perpendicular direction.

In thin-plate and lapping bolts, the lateral shear force can act directly on the bolt, causing shear stress to occur. The corresponding connections are designed in such a way that the frictional force caused by the axial force of the bolt transfers the lateral shear force from one part to the other. In this case, the torsional stress associated with the torque of the nut is only the shear stress that occurs in the bolt shank.

It follows that the most important characteristic of a bolt, from the point of view of joint strength, is its tensile strength. When a bolt is statically loaded, it can fail as follows:

• the bolt fails when the tensile stress exceeds the tensile strength;
• the bolt thread is cut off;
• the thread of the nut is cut off.

If the threads of both the bolt and the nut are strong enough, then when the axial load is transferred from the bolt to the nut, the bolt should fail. It is cut off either at the thread or at the rod, provided that the head has not separated.

The method of thread cutting has a great influence on the fatigue strength of the bolt metal. There are two ways to make threads: tapping (cutting on a lathe) or forming (rolling). Standard bolts are made almost exclusively by forming, and for particularly large or strong bolts, by cold forming (cold rolled bolts). When producing bolts of very large or, conversely, very small diameters, it is possible to use hot rolling. The fatigue strength of bolts with hot-rolled threads is higher than that of hardened bolts. The increase in fatigue strength is due, for example, to finishing of the thread surface, molding at the base of the thread, and also to the compressive stress caused by plastic molding at the thread surface.

To achieve a reliable bolted connection, the correct amount of pre-tightening is critical. It should be sufficient, but not too large. The more precise the pre-tightening is, the easier and cheaper it will be to design the joint, but on the other hand, as the precision of the pre-tightening increases, the cost of the bolting installation procedure increases.

Insufficient pre-tightening can result in:

• displacement of the connection surface under the influence of axial load;
• increase in bolt stress amplitude;
• bolt aging;
• unscrewing the nut during vibration;
• sliding of the connection under the influence of shearing moments.

Too much pre-tightening can result in:

• static overload of the bolt during external load;
• unscrewing a bolt under an external tensile load as a result of plastic elongation;
• tearing of the bolt when it is pre-tightened.

Sufficient tension in the bolted connection must be maintained throughout operation. The following reasons may cause damage to the connection thread:

• bolt rupture;
• thread cutting;
• unscrewing the nut;
• subsidence of connection parts.

Examples of using bolts GOST 7798-70 / DIN 933