1.1 flange bolt load

The minimum bolt load required in the preloaded state is given in equation (1).

Wa=3.14DGbpy(1) where: DGD gasket pressing force acts on the center circle diameter, mm; bD gasket effective sealing width, mm; pyD gasket specific pressure, MPa.

1.2 The minimum bolt load required for system operation is shown in the formula

(2) Wp=0.785D2GP+6.28DGbmP(2) where: PD design pressure, MPa; mD gasket coefficient.

When designing flange bolts according to the provisions of GB150D1998 "Steel Pressure Vessels", the larger of Wa and Wp should be selected to determine the bolt design load. The design stipulates that the actual bolt total section should be no less than the required bolt area. In engineering practice, the flange used is a standard flange series that is higher than the engineering pressure value at the time of calculation, and the diameter of the bolt used is also increased accordingly. Therefore, the strength check of the bolts used in the existing standard flanges according to the operating system pressure proves that the bolts have sufficient safety margin in actual operation.

1.3 Additional load on flange bolts

2 additional force Wg test and analysis

2.1 bolt stress test conditions

(1) Test method: For the flange bolts of the same diameter, the stress and strain tests under simulated load are carried out under different pressure, temperature and medium working conditions. Use BX-3 box strain gage, two horizontal and horizontal bridges, externally protected with epoxy resin, tested and calibrated.

Measurement and recording using a UCAMD5B strain gauge.

(2) Experimental pressure: The system pressures are: normal pressure 0.25 MPa, 1.6 MPa, 2.0 MPa, and the bolts used for flanges of the same common diameter DN 50 mm are tested at different temperatures.

(3) Test procedure: Firstly, the stress of the bolt under the pre-tightening state is measured, and then the stress is measured under different system pressures. Finally, according to the operating procedures of the "Interim Provisions on Pressure Plugging Technology", the sealant is injected separately, and the force change of the bolt is measured at the same time. When the final plugging is completed, the force change of the bolt is measured 3 minutes to 4 minutes after the injection of the sealant is stopped.

2.2 bolt stress state

For the simulated leakage points of various working conditions, the plugging with pressure plugging is used to obtain satisfactory sealing effect. Inject the sealant according to the specified order and control the pressure and speed of the sealant, and measure the stress change data of the bolt after the force is applied.

On the basis of the two forces (1) and (2), the stress of the two bolts A and C increases greatly, and the added value is different. Although the strength of the other bolts B and D increases, the stress is not increased. Even the bolt stress values ​​in the same position of individual working conditions are reduced. Among the measured measured stress data, the specific change values ​​are larger and more complicated under the premise of the same growth trend. When the sealant is injected into the injection holes of 2, 3, and 4, the force change state of the bolt is the same as that when the sealant is injected into the injection hole.

2.3 Analysis of bolt stress state

2.3.1 Two bolts A and C increase on both sides of the injection port

Since the sealant enters the sealed cavity at the inlet of the nozzle, under the pressure of the pressure in the system, the sealant entering the cavity accumulates on the top of the cavity at the mouth, and the sealant of 1 is squeezed and bonded. The combination is as a whole, and gradually moves downward until it is filled between the injection holes on both sides of the injection hole (including the gap between the two bolt holes of A and C). In the process of filling 1 injection point section (including crossing the two bolts A and C to the edge of the 2, 3 injection port), the frictional resistance of the sealant to the cavity wall and the filling of the pressing force cause the injection hole to be both sides The bolt tensile stress appears to be the highest value. In addition, the pressure of the injection of the sealant is too high, the pressure is too fast, and the tensile stress of the bolt is increased in proportion to the pressure and speed of the injection sealant. In the extreme case of the test, there was a bolt break accident.

The process of filling and compacting the sealant in the cavity, the force generated on both sides of the injection port is unbalanced due to the difference in the amount of the sealant moving to the sides at the same time. Therefore, the stress values ​​on the bolts on both sides of the injection port are also different.

After the sealing of the 1 section is completed, the injection of the sealant is stopped for 3 min to 4 min, and the tensile stress that the bolt has been subjected to is observed, which is reduced by the data display. This is because although the thrust operation of the injection sealant is stopped, the sealant in the cavity is flowed by the strong extrusion, and there is a balance process of shear stress at normal temperature. If at high temperatures, there is also stress-induced degradation. Explain the balance process of the sealant in the cavity.

2.3.2 The stress increase of the B and D bolts at the far end of the injection port is small.

Because the sealant injected at the 1 injection port has not only flowed to the vicinity of the B and D bolts, but also does not fill the cavity. Therefore, on the bolts on both sides of B and D, the tensile stress caused by the pressing force of the sealant is not directly formed. However, due to the sealant in the A and C sections, the pressing force formed on the cavity is transmitted to the B and D bolts through the flange (assumed to be a non-deformed body), so the bolts on both sides of the B and D also bear Less than the tensile stress of the A and C bolts. In addition, although the pressing force of the sealants of the A and C sections under special stress conditions, the pre-tightening tensile stress that the B or D bolts have been subjected to is temporarily reduced. However, after multiple points are injected separately, the absolute value of the bolt tensile stress is still increased. Not only the whole process of sealing with pressure plugging, the pressing force of the sealant on the inner wall of the cavity is always in a state of change. It also states the importance of the basic principle of multi-point injection that must be applied to the non-stop pressure seal.

2.3.3 The necessity of controlling the pressure and speed of the sealant injection The minimum thrust value required for the sealant to enter the sealed cavity from the outlet of the high pressure injection gun through the injection valve can be clearly displayed on the pressure gauge of the high pressure oil pump outlet. If this thrust is exceeded, it proves that the thrust and speed of the sealant entering the cavity exceeds the actual need.

This unnecessary thrust, which forms a harmful overload tensile stress on the bolt. Therefore, in the operation of injecting the sealant, the injection pressure and speed should absolutely be controlled. In the test, the bolt was plastically deformed due to overload until it broke, which occurred without controlling the injection thrust.

2.3.4 Bolt stress reduction after plugging During the entire plugging operation, the clamp and flange bolts are subjected to additional stress due to the pressing force of the sealant. Moreover, the stress on all bolts is generally an additional growth phenomenon. However, after the plugging, the peak stress of the bolt which occurs after stopping the injection of the sealant for a period of time is related to the physical properties of the sealant itself.

After being affected by external heat, the thermosetting sealant exhibits a melting state from a viscoelastic body (having a certain hardness) at normal temperature to an extreme fluidity as the temperature rises, and then excessively increases to a curing stage in which the strength and hardness are increased. During these changes, the volume of the sealant has a process of expansion and contraction.

After the test plugging is completed, after a period of time, the original stress of the bolt is reduced, which is related to the shrinkage characteristics of the sealant. For the basic performance requirements of the sealant, the ratio of volume expansion to shrinkage should be minimized, and it is also one of the key technical indicators to measure the quality of the sealant. In addition, it is also related to the operation technique of injecting the sealant. If the sealing operation is completed and the sealing agent is completely filled in the cavity and the pressing force reaches the sealing requirement, the expansion and contraction amount of the sealing agent can be reduced, and the change of the bolt stress is correspondingly reduced. .

3 conclusions

3.1 Application of non-stop pressure sealing technology to the total load formed by the original flange bolts, still make the screw in the safe operating range, therefore, this technology can ensure the safety of the flange bolts in the pressure sealing and sealing operation.

3.2 The additional stress generated by the extrusion of the sealant can be controlled within a reasonable and necessary range by reducing the unnecessary additional stress by performing the plugging operation construction method indicated in the operating procedure.

3.3 should pay attention to the metal material properties of the flange bolts. For the sealing of low temperature working conditions, bolt breakage caused by low temperature brittleness should be taken.

3.4 Before performing the sealing operation, the bolt condition should be inspected in detail. The inspection contents include: 1 bolt material; 2 bolt corrosion condition. For bolts with severe corrosion, overloaded bolts should be replaced or strengthened before the plugging operation; 3 bolt working temperature. All bolt materials shall not exceed the allowable temperature range of the corresponding materials listed in GB150.

3.5 After the sealing operation is completed, the bolts must not be tightened.

3.6 In order to ensure the safe application of non-stop pressure sealing technology, the provisions of the listed sealing operation must be strictly implemented.

Deep Groove Ball Bearing

Deep groove ball bearings are the most common type of rolling bearings.
The basic type of deep groove ball bearing consists of an outer ring, an inner ring, a set of steel balls and a set of retaining frames. There are two types of deep groove ball bearings: single row and double row, and the deep groove ball structure is also divided into two structures: sealed and open, open means that the bearing does not have a sealed structure, and the sealed deep groove ball is divided into dustproof seal and oil-proof seal. The dust seal cover is made of steel stamping, which simply prevents dust from entering the bearing raceway. The oil-proof type is a contact oil seal, which can effectively prevent the grease in the bearing from escaping.
The type code for single row deep groove ball bearings is 6, and the code for double row deep groove ball bearings is 4. Its structure is simple, easy to use, is the most common production, the most widely used type of bearing.
How it works
Deep groove ball bearings are mainly subjected to radial loads, but can also bear both radial loads and axial loads. When it is only subjected to radial loads, the contact angle is zero. When the deep groove ball bearing has a large radial clearance, it has the performance of angular contact bearing, can bear a large axial load, the friction coefficient of the deep groove ball bearing is very small, and the limit speed is also very high.
Bearing characteristics
Deep groove ball bearings are the most commonly used rolling bearings. Its structure is simple and easy to use. It is mainly used to bear radial load, but when the radial clearance of the bearing is increased, it has the performance of a certain angular contact ball bearing, and can bear the combined load of radial and axial directions. When the speed is high and thrust ball bearings are not suitable, they can also be used to bear pure axial loads. Compared with other types of bearings with the same specifications and dimensions as deep groove ball bearings, this type of bearing has a small friction coefficient and a high ultimate speed. However, it is not resistant to impact and is not suitable for bearing heavy loads. [2]
When the deep groove ball bearing is mounted on the shaft, the axial displacement of the shaft or housing can be limited within the axial clearance range of the bearing, so that it can be positioned axially in both directions. In addition, this kind of bearing also has a certain self-aligning ability, when it is inclined to 2′~10′ relative to the bore of the shell, it can still work normally, but it has a certain impact on the bearing life.
Structure and classification
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Bearing construction
Deep groove ball bearings have a simple structure and are easy to achieve high manufacturing accuracy compared with other types, so they are convenient for mass production in series, and the manufacturing cost is also low, and they are extremely commonly used. In addition to the basic type, there are various variant structures of deep groove ball bearings, such as: deep groove ball bearings with dust covers, deep groove ball bearings with rubber seals, deep groove ball bearings with stop grooves, deep groove ball bearings with large load capacity with ball notch, and double row deep groove ball bearings

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Hebei Fangqiang bearing manufacturing Co., LTD , https://www.fangqiangbearing.com