A sucker rod fatigue test gripper based on misaligned cylindrical surface clamping

Abstract

The invention discloses a sucker rod fatigue test clamp based on clamping of offset cylindrical surfaces, comprising a clamp A plate and a clamp B plate connected by fasteners, the two being fixed in a relatively fitting manner to form a clamping head, a clamping portion and a clamping tail of the clamp; when the clamping portion is a small cylindrical surface, its equivalent stress is greater than that of the clamping on the entire cylindrical surface, and it is more likely to undergo plastic deformation. Compared with the clamping surface in which the entire cylindrical surface is used, when the sucker rod is staggered on the small cylindrical surfaces, it is clamped by the mutually offset small cylindrical surfaces, and its deformation presents a spiral shape, thereby increasing the friction coefficient and making it easier to clamp, that is, under a smaller preload force, the sucker rod can be tightened without plastic deformation of the clamping device and the sucker rod.

Description

Technical Field

[0001] The present invention relates to the technical field of sucker rod detection, and particularly relates to a sucker rod fatigue test holder based on misaligned cylindrical surface clamping. Background Art

[0002] The sucker rod is an important device in the rod pumping system and bears the load transfer movement between the pumping unit and the sucker rod pump. Due to the alternating load it bears, the main failure mode is fatigue failure. During the use of the sucker rod, it is under alternating stress. Fatigue performance tests on the sucker rod are not required in routine quality inspections and supervision spot checks. However, fatigue performance is an important indicator reflecting the comprehensive performance of the sucker rod. Surface quality, hardened layer depth, and tensile strength are the key indicators affecting fatigue performance. Based on routine physical and chemical property inspections, fatigue performance tests are carried out on long-term suppliers by means of regular spot checks, which serve as the basis for selecting preferred manufacturers and tender procurement.

[0003] Fatigue test parameters: sine wave, tension-tension load, load ratio R = 0.1, test stress 540 MPa, number of cycles 1×10 6 . When using type I, couplings are used at both ends to clamp with the testing machine. When using type II specimens, the rod bodies are directly clamped with the testing machine at both ends. Among them, type II specimens can better illustrate the quality of this batch of sucker rods. However, when conducting fatigue performance tests on type II specimens, a clamping device is required to clamp the ends of the sucker rod. However, due to the complex load conditions at the clamping part of the sucker rod, it often fractures first, rather than the specimen fracturing due to fatigue failure, resulting in the failure of the fatigue test.

[0004] Currently, the "tooth-shaped fixture" is used to clamp the rod body in fatigue tests, which destroys the uniformity and continuity of the rod body. The crack sources formed due to local stress concentration all originate from the clamping part between the "tooth-shaped fixture" and the rod body surface and the "thick in the middle and thin at both ends" test structure. Due to external factors in the test, the test is invalid. A total of 79 fatigue tests have been carried out, and 20 tests are effective, with a success rate of only 25.3%. Summary of the Invention

[0005] The present invention provides a sucker rod fatigue test holder based on misaligned cylindrical surface clamping. This holder changes the clamping method of the fatigue test, can reduce invalid tests, and improve the success rate of the fatigue test.

[0006] To achieve the above purpose, the technical solution of the present invention is as follows:

[0007] A sucker rod fatigue test holder based on misaligned cylindrical surface clamping includes a clamping holder A plate and a clamping holder B plate connected by fasteners. The two are fixed in a relatively fitting manner to form a clamping head, a clamping part, and a clamping tail of the holder;

[0008] The clamping plate A and clamping plate B of the described gripper have heads and tails with relatively symmetrical structures; the outer surfaces of their heads are all flat, and the inner surfaces are all provided with clamping grooves matching the sucker rod. The clamping head formed by their fitting clamps the sucker rod; the outer surfaces of their tails are all semi-conical platforms, and the inner surfaces are all provided with clamping grooves matching the sucker rod. The clamping tail formed by their fitting clamps the sucker rod;

[0009] Both the clamping plate A and clamping plate B of the described gripper are provided with fixing holes in the middle, and clamping grooves are provided on the inner surfaces. Small-diameter clamping cylindrical surfaces and large-diameter clamping cylindrical surfaces are arranged alternately on the clamping grooves; the diameter of the small cylindrical surface is several millimeters smaller than the diameter of the clamped sucker rod, and the diameter of the large cylindrical surface is several millimeters larger than the diameter of the clamped sucker rod; among them, the small-diameter clamping cylindrical surface of the clamping plate A is opposite to the large-diameter clamping cylindrical surface of the clamping plate B, and the small-diameter clamping cylindrical surface of the clamping plate B is opposite to the small-diameter clamping cylindrical surface of the clamping plate A.

[0010] The described fixing hole matches the bolt, and the bolt passes through the fixing holes of the clamping plate A and clamping plate B and is fixedly connected to the nut.

[0011] A spring washer is also provided between the nut and the clamping plate B.

[0012] The length of the small-diameter clamping cylindrical surface is less than the length of the large-diameter clamping cylindrical surface; one small-diameter clamping cylindrical surface is opposite to one large-diameter clamping cylindrical surface; the small-diameter clamping cylindrical surfaces and large-diameter clamping cylindrical surfaces on the same side are arranged at intervals;

[0013] The diameters at both ends of the clamping groove are equal to the diameter of the sucker rod.

[0014] The diameter of the described small cylindrical surface is 2 - 5 millimeters smaller than the diameter of the sucker rod, and the diameter of the large cylindrical surface is 2 - 5 millimeters larger than the diameter of the sucker rod; the length of the small-diameter clamping cylindrical surface is 1 / 3 - 1 / 2 of the length of the large-diameter clamping cylindrical surface.

[0015] The number of small-diameter clamping cylindrical surfaces arranged on the clamping plate A is the same as or different from the number of small-diameter clamping cylindrical surfaces arranged on the clamping plate B (2).

[0016] The arrangement of the offset cylindrical surfaces of the described clamping plate A and clamping plate B is as follows:

[0017] Three small-diameter clamping cylindrical surfaces are arranged on the clamping plate A: surface I, surface J, and surface K. Large-diameter clamping cylindrical surfaces are arranged between surface I and surface J, and between surface J and surface K;

[0018] Two small-diameter clamping cylindrical surfaces are arranged on the clamping plate B: surface I and surface J, and large-diameter clamping cylindrical surfaces are arranged at both ends thereof;

[0019] The I cylindrical surface, J cylindrical surface and K cylindrical surface of the A plate of the clamp are respectively opposite to the large cylindrical surface of the B plate of the clamp. When the I cylindrical surface, J cylindrical surface and K cylindrical surface of the A plate contact the sucker rod to be clamped, the large-diameter clamping cylindrical surface of the B plate of the clamp does not contact the sucker rod.

[0020] The I surface and J surface of the B plate of the clamp are opposite to the large cylindrical surface of the A plate of the clamp. When the I surface and J cylindrical surface of the B plate contact the sucker rod to be clamped, the large-diameter clamping cylindrical surface of the A plate of the clamp does not contact the sucker rod.

[0021] A cylindrical pin for positioning and centering is also provided between the A plate and the B plate of the clamp.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The clamping device can simultaneously meet the requirements that the sucker rod does not slip when subjected to the pull-pull load and no plastic deformation occurs on the surface of the sucker rod and the clamping device. The present invention can meet the minimum yield strength of 793 MPa for the strength check of H-class sucker rods, that is, the structure of changing the clamping of the "tooth-type fixture" to the "bolt clamping + staggered cylindrical surface clamping" of the clamping device can meet the clamping requirements of the fatigue test.

[0024] When the clamping part is a small cylindrical surface, its equivalent stress is greater than that of the clamping on the entire cylindrical surface, and plastic deformation is more likely to occur. Compared with the entire cylindrical surface as the clamping surface, when the sucker rod is staggered on the small cylindrical surface, the use of the mutually staggered small cylindrical surfaces for clamping results in a spiral-shaped deformation, increasing the friction coefficient and making it easier to clamp. That is, under a smaller pre-tightening force, it can meet the requirements of clamping the sucker rod and no plastic deformation occurs on both the clamping device and the sucker rod.

[0025] When clamping with mutually staggered small cylindrical surfaces, under the condition of constant pre-tightening force, a greater frictional force can be obtained, enabling the clamping device to always clamp the sucker rod. Therefore, the pre-tightening force can be appropriately reduced. While meeting the requirement that the clamping device clamps the sucker rod, no plastic deformation occurs on both the clamping device and the sucker rod, reducing the occurrence of fractures at the fixture and improving the test success rate. Brief Description of the Drawings

[0026] Figure 1 is a schematic structural diagram of the present invention.

[0027] Figure 2 is a schematic sectional view of the present invention.

[0028] Figure 3 is a schematic diagram of the staggered distribution of the clamping surfaces of the present invention.

[0029] Figure 4 is a schematic structural diagram of the A plate of the clamp of the present invention.

[0030] Figure 5It is a schematic structural diagram of the clamping plate B of the gripper of the present invention.

[0031] Figure 6 It is a schematic diagram of the clamping principle of the present invention.

[0032] Figure 7 It is a radial load diagram of the clamped part of the sucker rod.

[0033] Figure 8 It is a schematic diagram of the mechanical model of the sucker rod during clamping.

[0034] Figure 9 It is a schematic diagram of the helix angle during the deformation of the sucker rod during clamping.

[0035] Figure 10 It is a deformation diagram of the finite element analysis result of the clamped part of the sucker rod.

[0036] Figure 11 It is a stress diagram of the clamped part of the sucker rod.

[0037] Among them, 1 is the clamping plate A of the gripper, 2 is the clamping plate B of the gripper, 3 is the connecting bolt, 4 is the nut, 5 is the spring washer, and 6 is the cylindrical pin. Specific embodiments

[0038] The present invention will be further described in detail below with reference to the accompanying drawings. The following is an explanation rather than a limitation of the present invention.

[0039] See Figures 1 - 6 , a sucker rod fatigue test gripper based on misaligned cylindrical surface clamping, including a clamping plate A 1 and a clamping plate B 2 connected by fasteners, and the two are fixed in a relatively fitting manner to form a clamping head, a clamping part and a clamping tail of the gripper;

[0040] The clamping plate A 1 and the clamping plate B 2 of the gripper have heads and tails with symmetrical structures; the outer surfaces of their heads are both flat, and the inner surfaces are both provided with clamping grooves matching the sucker rod. The clamping head formed by fitting tightly clamps the sucker rod; the outer surfaces of their tails are both semi-conical platforms, and the inner surfaces are both provided with clamping grooves matching the sucker rod. The clamping tail formed by fitting tightly clamps the sucker rod;

[0041] Both the clamping plate A 1 and the clamping plate B 2 of the gripper are provided with fixing holes in the middle, and clamping grooves are provided on the inner surfaces. Small-diameter clamping cylindrical surfaces and large-diameter clamping cylindrical surfaces are arranged alternately on the clamping grooves; the diameter of the small cylindrical surface is several millimeters smaller than the diameter of the clamped sucker rod, and the diameter of the large cylindrical surface is several millimeters larger than the diameter of the clamped sucker rod; among them, the small-diameter clamping cylindrical surface of the clamping plate A 1 is opposite to the large-diameter clamping cylindrical surface of the clamping plate B 2, and the small-diameter clamping cylindrical surface of the clamping plate B 2 is opposite to the small-diameter clamping cylindrical surface of the clamping plate A 1.

[0042] The fixed holes described above are matched with the bolts 3. The bolts 3 pass through the fixed holes of the gripper A plate 1 and the gripper B plate 2 and are fixedly connected to the nuts 4.

[0043] A spring washer 5 is further provided between the nut 4 and the gripper B plate.

[0044] The length of the small-diameter clamping cylindrical surface is less than that of the large-diameter clamping cylindrical surface; one small-diameter clamping cylindrical surface is opposite to one large-diameter clamping cylindrical surface; the small-diameter clamping cylindrical surfaces and the large-diameter clamping cylindrical surfaces on the same side are arranged at intervals;

[0045] The diameters at both ends of the clamping groove are equal to the diameter of the sucker rod (H surface, L surface).

[0046] The diameter of the small cylindrical surface is 2-5 mm less than the diameter of the sucker rod, and the diameter of the large cylindrical surface is 2-5 mm larger than the diameter of the sucker rod; the length of the small-diameter clamping cylindrical surface is 1 / 3-1 / 2 of the length of the large-diameter clamping cylindrical surface.

[0047] The number of small-diameter clamping cylindrical surfaces arranged on the gripper A plate 1 may be the same as or different from the number of small-diameter clamping cylindrical surfaces arranged on the gripper B plate 2.

[0048] The arrangement of the misaligned cylindrical surfaces of the gripper A plate 1 and the gripper B plate 2 is as follows:

[0049] Three small-diameter clamping cylindrical surfaces are arranged on the gripper A plate 1: I surface, J surface, K surface, and large-diameter clamping cylindrical surfaces are arranged between the I surface and the J surface and between the J surface and the K surface;

[0050] Two small-diameter clamping cylindrical surfaces are arranged on the gripper B plate 2: I surface, J surface, and large-diameter clamping cylindrical surfaces are arranged at both ends thereof;

[0051] Among them, the I cylindrical surface, J cylindrical surface, and K cylindrical surface of the gripper A plate 1 are respectively opposite to the large cylindrical surfaces of the gripper B plate 2. When the I cylindrical surface, J cylindrical surface, and K cylindrical surface of the A plate contact the sucker rod to be clamped, the large-diameter clamping cylindrical surfaces of the gripper B plate 2 do not contact the sucker rod;

[0052] The I surface and J surface of the gripper B plate 2 are opposite to the large cylindrical surfaces of the gripper A plate 1. When the I surface and J cylindrical surface of the B plate contact the sucker rod to be clamped, the large-diameter clamping cylindrical surfaces of the gripper A plate 1 do not contact the sucker rod.

[0053] A cylindrical pin 6 for positioning and centering is further provided between the gripper A plate 1 and the gripper B plate 2.

[0054] Specific embodiments are given below.

[0055] During the fatigue test, when the gripper clamps the sucker rod, the gripper should meet two requirements:

[0056] 1) Always clamp the sucker rod;

[0057] 2) The sucker rod will not break.

[0058] Refer to the appendix Figure 1 , a sucker rod fatigue test holder, which consists of a holder A plate 1, a holder B plate 2, a connecting bolt 3, a nut 4, a spring washer 5 and a cylindrical pin 6; during the fatigue test, two sets of sucker rod holders with the same structure are used to clamp the two ends of the sucker rod respectively.

[0059] Refer to Figure 2 and Figure 3 , the holder A plate 1 and the holder B plate 2 have an inner surface and an outer surface. The inner surface is close to the sucker rod, and the outer surface is far from the sucker rod.

[0060] Refer to the appendix Figures 4 - 6 , there are two kinds of cylindrical surfaces, small and large, on the inner surfaces of the holder A plate 1 and the B plate 2. The diameter of the small cylindrical surface is equal to the diameter of the clamped sucker rod, and the diameter of the large cylindrical surface is several millimeters larger than the diameter of the clamped sucker rod, and it does not contact the sucker rod.

[0061] Specifically, the I surface, J surface and K surface of the holder A plate 1 are opposite to the large cylindrical surface of the holder B plate 2, that is, when the I surface, J surface and K surface contact the clamped sucker rod, the large cylindrical surface of the holder B plate 2 does not contact the sucker rod.

[0062] The I surface and J surface of the holder B plate 2 are opposite to the large cylindrical surface of the holder A plate 1, that is, when the I surface and J surface contact the clamped sucker rod, the large cylindrical surface of the holder A plate 1 does not contact the sucker rod. The outer surface C surface of the holder A plate 1 and the holder B plate 2 is a plane, which is used to contact the clamping block of the fatigue testing machine and bear the clamping force of the fatigue testing machine.

[0063] When clamping the sucker rod, there is a gap of several millimeters between the holder A plate 1 and the holder B plate 2.

[0064] See Figure 6 , the holder is divided into upper and lower parts, and the two parts are connected by bolts to clamp the sucker rod. The gap between the two parts of the fixture is Δ, and a total of 4 bolts are used to clamp the sucker rod. The strain parts of the sucker rod are connected by bolts to clamp the sucker rod. The gap between the two parts of the fixture is Δ, and a total of 4 bolts are used to clamp the sucker rod. The sucker rod is placed between the holder A plate and the holder B plate, and the holder A plate and the holder B plate are connected by bolts, and the bolts are tightened to clamp the sucker rod. When tightening, the cylindrical pin is used for positioning to ensure the centering of the holder A plate and the holder B plate. After both sets of holders clamp the sucker rod, it is installed on the fatigue testing machine.

[0065] Sucker rod load distribution

[0066] The load distribution on the sucker rod is as shown in Figure 7 . According to the working requirements of the fixture, it is necessary to ensure that the sucker rod is in a clamped state. Therefore, it is required that the frictional force is greater than the maximum test load F max , that is, when F f ≥F max . Therefore, the uniform pressure should satisfy

[0067]

[0068] Simplify the distributed pressure into a concentrated force, and the mechanical model of the sucker rod is as shown in Figure 8 . The x-axis represents the axial direction of the sucker rod.

[0069] As can be seen from Figure 8 , when using the staggered cylindrical surfaces to clamp the sucker rod, the deformation of the sucker rod is similar to a helix. Therefore, the friction coefficient at this time should be the equivalent friction coefficient f v , and its magnitude is

[0070]

[0071] In the formula, f v is the equivalent friction coefficient; α is the angle between the tangent of the sucker rod deformation and the plane perpendicular to the axis of the sucker rod, as shown in Figure 9 .

[0072]

[0073] It can be seen from the above formula that under the condition of constant pre-tightening force, a larger frictional force can be obtained to ensure that the fixture always clamps the sucker rod.

[0074] When the sucker rod is clamped, its overall deformation diagram is as shown in Figure 10 , and the stress distribution of the sucker rod is as shown in Figure 11 .

[0075] As can be seen from Figure 11 , when the sucker rod is staggered on the small cylindrical surface, its deformation presents a spiral shape, increasing the friction coefficient. Therefore, this structure shows from both the principle and the finite element analysis that the gripper clamps the sucker rod for the fatigue test of the sucker rod.

[0076] The sucker rod is placed between the gripper A plate 1 and the gripper B plate 2. The gripper A plate 1 and the gripper B plate 2 are connected by bolts, and the bolts are tightened to clamp the sucker rod. When tightening, use the cylindrical pin for positioning to ensure the centering of the gripper A plate and the gripper B plate. After both sets of grippers clamp the sucker rod, install it on the fatigue testing machine. The C surfaces of the gripper A plate 1 and the gripper B plate 2 are in contact with the clamping blocks of the fatigue testing machine and bear the clamping force of the fatigue testing machine.

[0077] Specific trial experiments: The fatigue test clamping device of the present invention was cumulatively applied for 7 times in fatigue tests, among which 5 times were successful, and the success rate was 71.4%. The success rate of the test was increased by 46.1% compared with that of the "tooth-shaped fixture", and good application effects were obtained in the test.

Claims

1. A sucker rod fatigue test gripper based on misaligned cylindrical surface clamping, characterized in that, It includes a clamp A plate (1) and a clamp B plate (2) connected by fasteners, and the two are fixed in a relatively fitting manner to form a clamping head, a clamping part and a clamping tail of the clamp; The clamp A plate (1) and the clamp B plate (2) have symmetrically structured heads and tails; the outer surfaces of their heads are both flat, and the inner surfaces are both provided with clamping grooves matching the sucker rod, and the formed clamping head clamps the sucker rod; the outer surfaces of their tails are both semi-conical platforms, and the inner surfaces are both provided with clamping grooves matching the sucker rod, and the formed clamping tail clamps the sucker rod; Both the clamp A plate (1) and the clamp B plate (2) are provided with fixing holes in the middle, and the inner surfaces are provided with clamping grooves, and small-diameter clamping cylindrical surfaces and large-diameter clamping cylindrical surfaces are arranged alternately on the clamping grooves; the diameter of the small cylindrical surface is several millimeters smaller than the diameter of the clamped sucker rod, and the diameter of the large cylindrical surface is several millimeters larger than the diameter of the clamped sucker rod; among them, the small-diameter clamping cylindrical surface of the clamp A plate (1) is opposite to the large-diameter clamping cylindrical surface of the clamp B plate (2), and the small-diameter clamping cylindrical surface of the clamp B plate (2) is opposite to the large-diameter clamping cylindrical surface of the clamp A plate (1); The length of the small-diameter clamping cylindrical surface is less than the length of the large-diameter clamping cylindrical surface; the small-diameter clamping cylindrical surfaces and the large-diameter clamping cylindrical surfaces on the same side are arranged at intervals; The diameters at both ends of the clamping groove are equal to the diameter of the sucker rod; The arrangement of the misaligned cylindrical surfaces of the clamp A plate (1) and the clamp B plate (2) is as follows: There are three small-diameter clamping cylindrical surfaces arranged on the clamp A plate (1): surface I, surface J, and surface K, and large-diameter clamping cylindrical surfaces are arranged between surface I and surface J and between surface J and surface K; There are two small-diameter clamping cylindrical surfaces arranged on the clamp B plate (2): surface I and surface J, and large-diameter clamping cylindrical surfaces are arranged at both ends thereof; Among them, the I cylindrical surface, the J cylindrical surface and the K cylindrical surface of the clamp A plate (1) are respectively opposite to the large cylindrical surfaces of the clamp B plate (2). When the I cylindrical surface, the J cylindrical surface and the K cylindrical surface of the A plate contact the clamped sucker rod, the large-diameter clamping cylindrical surface of the clamp B plate (2) does not contact the sucker rod; The I surface and the J surface of the clamp B plate (2) are opposite to the large cylindrical surfaces of the clamp A plate (1). When the I surface and the J cylindrical surface of the B plate contact the clamped sucker rod, the large-diameter clamping cylindrical surface of the clamp A plate (1) does not contact the sucker rod; The fixing hole matches the bolt (3), and the bolt (3) passes through the fixing holes of the clamp A plate (1) and the clamp B plate (2) and is fixedly connected to the nut (4).

2. The sucker rod fatigue test gripper based on misaligned cylindrical surface clamping according to claim 1, wherein A spring washer (5) is also provided between the nut (4) and the clamp B plate.

3. The sucker rod fatigue test gripper based on misaligned cylindrical surface clamping according to claim 1, characterized in that, The diameter of the small cylindrical surface is 2 to 5 millimeters smaller than the diameter of the sucker rod, and the diameter of the large cylindrical surface is 2 to 5 millimeters larger than the diameter of the sucker rod; the length of the small-diameter clamping cylindrical surface is 1 / 3 to 1 / 2 of the length of the large-diameter clamping cylindrical surface.

4. The sucker rod fatigue test holder based on misaligned cylindrical surface clamping according to claim 1, wherein, The number of small-diameter clamping cylindrical surfaces arranged on the clamp A plate (1) is the same as or different from the number of small-diameter clamping cylindrical surfaces arranged on the clamp B plate (2).

5. The gripper for sucker rod fatigue test based on misaligned cylindrical surface clamping according to claim 1, characterized in that, A clamping plate (1) and a clamping plate B (2) of the gripper are also provided with a cylindrical pin (6) for positioning and centering.

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