In modern industry, reciprocating compressors are widely used, covering industries such as petroleum refining and gas transportation.

The piston component of the compressor is a key component in the design and manufacturing of reciprocating compressors, as it always bears alternating loads and comes into contact with the compression medium. The piston nut, which plays a connecting and fixing role between the piston body and piston, is also an important part in the piston component. Its service life directly affects the maintenance cycle of the compressor and also affects the continuity of factory production. Once the connection between the piston nut and piston rod breaks, it may even cause damage to the main pressure bearing and moving parts of the compressor.

1. Common structure and characteristics of piston nuts

The piston nut of a reciprocating compressor is usually installed and tightened using a large wrench in conjunction with an electric heater (Figure 1).

The installation method of this type of nut is as follows: tighten the nut with a wrench until the front half piston body, rear half piston body, and piston rod shoulder come into contact, and there is no gap. Insert the electric heating rod into the electric heating hole at the end of the piston rod, and mark the nut at the same time. After the piston rod is heated, turn the nut 62.9 °, which is equivalent to 70.4mm on the upper chord of a 135 circle (the above data is the installation data of a certain piston). Mark the chord length on the front half piston body, take out the electric heating rod, cool it down, and tighten the thin edge of the nut into the groove on the end face of the piston rod, that is, the tightening is complete. This type of piston requires a slender hole to be drilled in the middle of the piston rod, which is prone to deviation during processing, resulting in uneven wall thickness at the head of the piston rod, greatly reducing its strength and service life. The installation of electric heating method is time-consuming and labor-intensive, and the rotational torque is extremely difficult to control. When the pre tightening force is insufficient, it is easy to cause nut loosening accidents. When the pre tightening force is excessive, it is easy to cause plastic deformation of the material and reduce its service life.

2. Structural Principles and Advantages of Super Nuts 2.1 Structural Principles of Super Nuts

In the piston component of the super nut structure (Figure 2), the piston is connected to the piston rod using a super nut structure. The compressor piston nut is composed of a super nut, a top screw, and a gasket (Figure 3). The top screw is installed into the super nut from the inside of the nut, and the super nut is then rotated and installed on the piston rod (Figure 4). The super nut structure adopts multi push pre tightening technology, consisting of circular nuts with multiple push bolts and superhard washers. When tightening, only one torque wrench is needed to tighten step by step, and ordinary torque wrenches can also achieve extremely high tightening force. It is suitable for connecting nuts such as pistons that withstand alternating loads.

2.2 Advantages of Super Nut Structure

(1) The tool is simple, the disassembly and assembly time is short, and the labor cost is low: only a regular torque wrench is needed to complete it, without the need for traditional bolt tightening methods such as hammering.

(2) Time and effort saving: Easy to install and disassemble, can be operated by multiple people at the same time, and can also be tightened with a pneumatic wrench. (3) Tight and secure: As long as installed correctly, it can resist compressor specific working conditions such as alternating loads and vibrations, greatly reducing downtime caused by installation issues.

(4) Accurate pre tightening force: It can achieve precise tightening control and maintain uniform and consistent bolt tension.

(5) Suitable for small spaces: quick disassembly and assembly of piston rods can be achieved without requiring a large amount of space.

(6) Strong flexibility: can increase the elasticity of bolted connections, which can more effectively withstand high temperatures and impacts.

(7) Avoid bolt breakage: After installation, the nut body undergoes slight deformation, which will release stress concentrated on the first few threads. The precise load control and stress release characteristics prevent screw fracture.

(8) Economical and practical: The push bolt is just a simple mechanical component, which is much more economical compared to other fastening methods and can be reused.

(9) The screws of the super nut adopt an internal installation structure, so even if one screw breaks, it will not fall in

Go into the cylinder to ensure long-term stable operation.

(10) The result of the super nut is that it does not require a large wrench, so the surface of the piston is designed as a flat structure, making it compatible with the

The structure of the cylinder head that matches it has become simpler, reducing the clearance volume, improving volumetric efficiency, designing more compact, and reducing costs.

Instructions for using 3 super nuts

Due to the structural characteristics of the super nut, installation and disassembly must also be strictly carried out in accordance with technical requirements. The steps are as follows:

3.1 Preparation work

(1) Confirm that molybdenum disulfide or other lubricating grease is used on the screws;

(2) Confirm that all screw compression ends do not protrude from the bottom of the super nut;

(3) Lubricating the main thread;

(4) Install the gasket on the piston rod;

(5) Use lubricating grease to lubricate the surface of the gasket or the screw clamping end. 3.2 Tightening of super nuts

Step 1: Tighten the super nut onto the piston rod by hand until the bottom contacts the gasket, then rotate it in reverse by 45 ± 15 °.

Ensure that the main thread is in a completely free state;

Step 2: According to the position shown in Figure 5, use 50% of the rated torque to symmetrically tighten the two sets of screws at positions 1-1 and 2-2;

Step 3: According to the position shown in Figure 6, use 50% of the rated torque to symmetrically tighten the four sets of screws at positions 3-3, 4-4, 5-5, and 6-6 in sequence;

Step 4: Repeat the second step with 75% of the rated torque;

Step 5: Repeat step 3 with 75% rated torque;

Step 6: Repeat step 2 with 100% rated torque;

Step 7: Use 100% rated torque and tighten the remaining screws in a clockwise direction;

Step 8: After all screws are tightened, recheck the tightness of all screws. The final tightening torque requirement is 100% to 105% of the rated torque.

3.3 Disassembly of super nuts

When disassembling the super nut, attention should be paid to gradually removing the torque on each screw, and it is never allowed to remove a certain one at once

The total torque of a screw. Lubricating grease needs to be added to assist in disassembly. Starting from screw 1, loosen each screw by a maximum of 1/4 turn in a circular order (Figure 7), do not loosen it to the point where it is loose. At least three times, completely relieve the pressure on the screws. After all the super nut screws are loosened, the super nut can be removed by hand. During the installation and disassembly process, attention should be paid to preventing scratches on the piston body and piston rod threads. If necessary, heating can be used to promote disassembly speed.

3.4 Maintenance and other precautions

Tighten the super nut according to the correct method, and even after many years of use, its pre tightening force will not loosen. However, we still recommend checking the pre tightening force of the nuts during each inspection and repair. Use a torque wrench that is adjusted to 100% of the allowable tightening torque. It is not allowed to tighten a single screw of the super nut to the rated torque at once. After disassembling the super nut, sometimes it is found that the hard washer has a dent of 0.1% millimeter, which is a normal phenomenon. The hard washer can still be used, just flip it over.

4 Conclusion

The use of super nut structure in reciprocating compressor piston components has obvious advantages. In recent years, many compressors have applied this structure, and there is a trend of super nut structure replacing the original structure in large compressor units. In the future, super nut structure will become a standard design structure for reciprocating compressor pistons, making users safer and more at ease when using reciprocating compressors.