Properties of HSFG Bolts

Bolts are extensively used as a fastener. They serve various purposes and there may be various types of bolts. We at 

Indiana Steel

HSFG bolts what they are? How they are made?

High Strength Friction Grip Bolts are popularly known are HSFG bolts. They are made from bars of medium carbon steel. These bolts have great strength. Their high strength is built through the process of quenching and tempering. 

This process is also known as alloying steel. Steel washers of hard steel or carburized steel are provided to evenly distribute the clamping pressure on the bolted member and to prevent the threaded portion of the bolt from bearing on the connecting pieces.  

If the bolts are tightened by the turn of nut method, the nut is made snug and is tightened a half turn more by hand wrenches, then the washers are not required. The vibrations and impact resistance of the joint is also improved. The nut and head of the bolts are kept sufficiently large. This is done to provide an adequate bearing area.

The advantages of using HSFG bolts

There are many advantages of using the HSFG bolts. These are as follow:

1.  HSFG bolts are very strong. This is why they provide a rigid joint. When they are used there is no slip between the elements connected

2. When they are made the HSFG bolts, large tensile stresses are developed in bolts. This in turn provides large clamping force to the elements connected. High frictional resistances are developed. This therefore provides a high static strength the joint.

4. The frictional resistance is effective outside the hole. As a result of this lesser load is transmitted through the net section. The possibility of failure at the net section is therefore minimized to some extent by using HSFG bolts.

6. The tension in bolts is uniform. Also the bolts are tensioned up to proof load hence; the nuts are prevented from loosening

7. Cost gets reduced to some extent by making use of such bolts since  fewer  persons are require to make the connections.

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8. Noise nuisance is not there as these bolts are tightened with wrenches.

9. Since these bolts have great strength the hazard of fire can be avoided

10. Alterations can be done easily.

11. To acquire greater strength lesser number of bolts are required as compared to rivets. This brings in cost cutting.

1) Raw materials

HSFG bolts are made of high-strength materials. The screws, nuts, and washers of HSFG are made of high-strength steel, commonly used as 45# steel, 40# boron steel, and 20# manganese titanium boron steel. Ordinary bolts are usually made of Q235 steel.

2) Strength grade

HSFG bolts usually have two strength grades of 8.8s and 10.9s, most of which are 10.9. The strength grade of ordinary bolts shall be low, generally 4.4, 4.8, 5.6, and 8.8.

3) Stress characteristics

HSFG bolts exert pre-tension and transmit external force by friction. Ordinary bolt connection transmits shear force by means of bolt rod shear resistance and hole wall pressure bearing. The pre-tension generated when tightening the nut is very small, and its impact can be ignored. In addition to its high material strength, HSFG bolts also exert a large pre-tension on the bolt, so that there is a large friction force perpendicular to the screw direction, and the pre-tension, anti-slip coefficient, and steel type directly affect the bearing capacity of HSFG bolts. The minimum specification of HSFG bolts is M12, and M16 &#; M30 is commonly used. The performance of oversized bolts is unstable, so they should be used with caution in design.

4) Usage

The bolt connection of the main components of the building structure is generally connected with HSFG bolts. Ordinary bolts can be reused, while HSFG bolts cannot be reused. HSFG bolts are generally used for permanent connection. HSFG bolts are pre-stressed bolts. The torque wrench is used to apply the specified pre-stressed force for friction-type bolts, and the box head is screwed off for pressure-type bolts. Common bolts have poor shear resistance and can be used in secondary structures. Ordinary bolts only need to be tightened.

5) Durability

HSFG bolts can bear more load and have a longer service life, but at the same time, the use cost will be higher.

The core difference between high-strength friction grip bolts and ordinary bolts is not the strength of the materials used, but the form of stress. The essence is whether to apply preload and use static friction to resist shearing. Under the same grade, the design values of tensile strength and shear strength of ordinary bolts are higher than those of high strength friction grip bolts. The design strength of tensile and shear resistance of high-strength friction grip bolts is lower than that of ordinary bolts. The essence of its high strength is that no relative slip is allowed in the joints during normal operation, that is, small elastic-plastic deformation and large joint stiffness.

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