O-shaped ring hot oil aging test clamp and use method thereof
By using a bottom-up, layered exhaust channel and spring plug structure design, the problem of air retention in the hot oil aging test fixture is solved, thereby improving pressure stability and test efficiency and simplifying the operation process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-30
- Publication Date
- 2026-03-17
AI Technical Summary
Existing hot oil aging test fixtures are prone to trapping air when loading medium oil, leading to abnormally high internal pressure, which affects the accuracy of O-ring life assessment. Furthermore, the exhaust structure design is complex and costly.
A bottom-up, layered exhaust channel structure is designed to utilize the characteristic that air density is less than that of oil. Air is discharged through a central channel and a lateral diversion method, and a spring and plug structure is used to achieve a seal, simplifying the operation process and avoiding air residue.
It improves the repeatability and pressure stability of the test, reduces the test cost and operational complexity, is suitable for batch testing, and improves test efficiency.
Smart Images
Figure CN121678503A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of O-ring life assessment technology, specifically to an O-ring hot oil aging test fixture and its usage method. Background Technology
[0002] O-rings are elastic sealing elements with a circular cross-section, widely used in modern industrial systems due to their simple structure and reliable sealing performance. O-rings are typically made of polymer materials such as rubber, polyurethane, silicone, and fluororubber, and can achieve effective sealing in both static and dynamic environments. Their working principle involves the combined action of the elastic pre-compression force generated during assembly and the system medium pressure to prevent liquid or gas leakage. They are particularly prominent in applications such as hydraulics, pneumatics, machining, automotive manufacturing, petrochemicals, and aerospace.
[0003] While O-rings are renowned for their simple structure and reliable performance in industrial applications, their material properties dictate that they will gradually age and fail over time, thus limiting their service life. O-rings are mostly made of rubber-based polymers, which are affected by factors such as temperature, pressure, media, light, and oxidation during long-term service. This leads to molecular chain breakage or increased cross-linking, ultimately causing problems such as increased hardness, decreased elasticity, and surface cracking. These aging effects gradually weaken the sealing performance and may even lead to leakage, affecting equipment safety and efficiency. Under normal conditions, O-rings used properly at room temperature can last for several years, but their lifespan will be significantly shortened in high-temperature, highly corrosive, or frequently moving environments.
[0004] To better assess and predict the lifespan of O-rings, accelerated calendar life testing has been widely implemented and has become an important tool in seal reliability research. Common accelerated testing methods include thermo-oxidative aging, hot oil aging, and high-temperature static compression. These methods artificially apply conditions more stringent than actual operating conditions to shorten the testing cycle and accelerate the material aging process. Among these, hot oil aging testing is widely used. It can simulate the actual operating conditions of oil-loaded equipment such as hydraulic and fuel systems. Using specific lubricating oils or hydraulic oils, the O-rings are immersed in high-temperature and high-pressure environments to realistically replicate actual operating conditions and evaluate their resistance to media and sealing retention capacity. This makes the test results more engineering-significant. Combining the data obtained from accelerated testing, technicians can use life prediction models to calculate the calendar life of O-rings under normal operating conditions, thus providing a scientific basis for seal selection, maintenance planning, and safety design.
[0005] During hot oil aging tests, oil pressure must be applied through the test fixture according to actual operating conditions. However, a prominent problem in the test implementation is that directly loading the medium oil to the specified pressure inevitably traps a certain volume of air within the test fixture cavity. When the test enters the high-temperature stage, the trapped air in the fixture causes an abnormal increase in internal pressure due to thermal expansion, subjecting the O-ring to an unexpected stress environment. This additional pressure accelerates the material's compression deformation and stress relaxation, leading to a shorter life prediction result. On the other hand, the oxygen in the trapped air will react with the O-ring material in an oxidation reaction, causing the degree of thermo-oxidative aging to exceed normal operating conditions, thus exaggerating the material's aging rate. Therefore, passively trapping air in the fixture will cause the experimental results to deviate from actual service conditions, thereby affecting the scientific assessment of the O-ring's life and reliability.
[0006] To avoid trapping unnecessary air during hydraulic pressure application, venting structures can be added. However, venting structures often compromise the integrity of the seal, creating new leakage risks. Under high temperature and pressure conditions, venting devices must also possess resistance to temperature, pressure, and media corrosion, placing extremely high demands on design and manufacturing, thus increasing the difficulty of production and maintenance.
[0007] Therefore, the current common method for venting is to first evacuate the cavity of the test fixture, and then load the medium oil to the specified oil pressure. This approach can mitigate the adverse effects of the sealed air to some extent, but it also has drawbacks: firstly, the high vacuum requirement increases the difficulty of the test; secondly, the medium oil will contaminate the vacuum pump, requiring replacement during the test, increasing the test cost; and thirdly, the medium oil vaporizes under vacuum conditions, leading to unstable test conditions that may affect the test results. Summary of the Invention
[0008] To address the shortcomings of existing technologies, the present invention aims to provide an O-ring hot oil aging test fixture and its usage method. This fixture can effectively eliminate air in the fixture without vacuuming, thereby eliminating test interference. It simplifies test procedures, saves test costs, and improves test accuracy, providing technical assurance for the validity of calendar life test results.
[0009] Specifically, the present invention provides a method comprising the following steps: An O-ring hot oil aging test fixture includes a base, several intermediate plates stacked vertically on the base, and a top cover disposed on the top of the intermediate plates. The base, intermediate plates, and top cover are detachably connected and together constitute the fixture shell. An oil passage hole is opened in the fixture housing along the vertical direction. The top and bottom of the oil passage hole are respectively provided with a detachable first seal and a second seal. The second seal includes a sealing gasket, a second plug and a spring. The oil passage hole has a second step. The top of the spring abuts against the second step and the bottom abuts against the second plug. The sealing gasket is fixed in the oil passage hole and located below the second plug. When the second plug abuts against the sealing gasket, it can seal the bottom of the oil passage hole. When the intermediate plate is attached to the adjacent base, intermediate plate or top cover, a transverse channel is reserved between the two to form a test cavity that can accommodate the O-ring to be tested. The oil in the oil passage can enter the test cavity through the transverse channel.
[0010] Furthermore: the first sealing element includes a first plug and a first set screw, the oil passage hole is provided with a first step, the first plug is located above the first step, when the first plug abuts against the first step, it can seal the top of the oil passage hole, and the first set screw is threaded to the top of the upper cover to abut against the upper part of the first plug.
[0011] Furthermore, the second seal also includes a third plug and a second set screw. The third plug is located below the sealing gasket. When the third plug abuts against the lower part of the sealing gasket, it can seal the bottom of the oil passage. The second set screw is threaded to the bottom of the base and is used to abut against the lower part of the third plug.
[0012] Furthermore, at least four threaded holes are provided at the same position in the base, the middle plate, and the top cover, and the base, the middle plate, and the top cover are fixedly connected by a number of screws corresponding to the number of threaded holes.
[0013] Furthermore, the first, second, and third plugs are all steel spherical plugs.
[0014] Furthermore, the inner diameter of the oil passage hole is 1~2mm.
[0015] Furthermore, the spring is made of 302 stainless steel, 316 stainless steel, or Inconel alloy.
[0016] Furthermore, the surface roughness Ra of the contact surfaces between the base, the middle plate, and the top cover is ≤1.6μm.
[0017] A method for using an O-ring hot oil aging test fixture includes the following steps: S1: Install the O-ring to be tested into the test chamber, and fix the base, intermediate plate and top cover together with screws; S2: Remove the first plug, the second plug, and the third plug; S3: Loosen all screws to release air from the fixture housing; S4: Continuously inject oil into the bottom of the oil passage through the pressurizing device to expel the air from the clamp housing; S5: Observe until there are no bubbles in the oil overflowing from the joint of the clamp housing, then tighten all screws. S6: Observe until the oil overflowing from the top of the oil passage hole is free of air bubbles, and seal the top of the oil passage hole with the first sealing element; S7: Continue injecting oil until the preset test pressure requirement is met; S8: After stopping the oil injection, the bottom of the oil passage hole is sealed by the second seal. At this time, the spring returns to its original position, causing the second plug to abut against the upper part of the sealing gasket to ensure stable oil pressure inside the fixture housing. S9: Turn the fixture shell over and place it in a high-temperature environment with the top cover facing down for a hot oil aging test.
[0018] Furthermore: the preset pressure is 29 MPa.
[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention adopts a bottom-up, layer-by-layer exhaust channel design, with a structure that passes through the center and diverts the flow to each layer laterally. This allows the oil to fill each test chamber from bottom to top in one go, ensuring that the air in each chamber can be completely pushed out by the oil. It also takes advantage of the fact that air is less dense than oil to ensure that the air in the oil passage is pushed out by the oil, without leaving any local air bubbles, thus improving the repeatability and pressure stability of the test.
[0020] 2. The top outlet of the oil passage designed in this invention can not only serve as an exhaust port, but also, due to its visual design, allow for direct observation of whether the exhaust port is consistently emitting oil, thus visually determining that the air has been completely expelled. This effectively avoids the waste of residual air or oil in the fixture housing.
[0021] 3. The top of the oil passage designed in this invention also serves as an exhaust port and a sealing port, eliminating the need to replace the connector or add a valve. Exhaust and sealing are achieved in one step, reducing operational steps and avoiding potential leaks.
[0022] 4. By designing a spring + second plug structure, the present invention can automatically reset the spring when oil injection stops, pressing the second plug against the sealing gasket to complete the seal and prevent oil leakage. On the other hand, it ensures stable oil pressure inside the fixture housing, which is suitable for long-term constant pressure aging tests.
[0023] 5. By designing a multi-layer intermediate plate structure, this invention can simultaneously test multiple O-rings, improving testing efficiency. Furthermore, the exhaust method is an integral exhaust, where a single exhaust channel can simultaneously exhaust and fill oil into the cavities of multiple sample pieces, significantly reducing the workload of multi-sample testing, improving experimental efficiency, and making it suitable for batch testing. Attached Figure Description
[0024] Figure 1 This is a cross-sectional view of the O-ring hot oil aging test fixture provided by the present invention; Figure 2 This is a diagram showing the state of the O-ring hot oil aging test fixture provided by the present invention during the oil injection process.
[0025] Key reference numerals in the attached drawings: 1. Base; 2. Middle plate; 3. Top cover; 4. Oil passage hole; 41. First step; 42. Second step; 5. Sealing gasket; 6. Second plug; 7. Spring; 8. Transverse channel; 9. O-ring; 10. First plug; 11. First set screw; 12. Third plug; 13. Second set screw; 14. Screw; 15. Hand pump; 16. Fixture housing. Detailed Implementation
[0026] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0027] Example 1 like Figure 1 As shown, the present invention provides an O-ring hot oil aging test fixture, which includes a base 1, a plurality of intermediate plates 2 stacked vertically on the base 1, and a top cover 3 disposed on the top of the intermediate plates 2. The base 1, intermediate plates 2 and top cover 3 can be fixed together by four screws 14 to form a fixture shell 16. An oil passage hole 4 is provided in the fixture shell 16, which is vertically penetrating. The top and bottom of the oil passage hole 4 are respectively provided with a detachable first seal and a second seal.
[0028] When the intermediate plate 2 is attached to its adjacent base 1, intermediate plate 2 or top cover 3, a transverse channel 8 is reserved, forming an annular test cavity that can accommodate the O-ring 9 to be tested. The transverse channel 8 connects the oil passage 4 and the test cavity, so that the oil injected at the bottom of the oil passage can rise in the oil passage and fill the test cavity transversely, providing the pressure required for the test to the O-ring 9 to be tested.
[0029] The first sealing element includes a first plug 10 and a first set screw 11. The top of the oil passage hole 4 is provided with a first sealing cavity with a large diameter. The bottom of the sealing cavity is a first step portion 41. The first plug 10 is placed in the sealing cavity. When the first set screw 11 is tightened, the first set screw 11 abuts against the first plug 10 so that it abuts against the first step portion 41, thereby completing the sealing of the top of the oil passage hole 4.
[0030] The second sealing element includes a spring 7, a second plug 6, a sealing washer 5, a third plug 12, and a second set screw 13. The bottom of the oil passage 4 has a second sealing cavity with a larger diameter, and the top of the second sealing cavity is a second stepped portion 42. The top of the spring 7 abuts against the second stepped portion 42, and the bottom of the spring 7 abuts against the second plug 6. When oil is injected into the bottom of the oil passage 4, the oil pushes open the second plug 6, compresses the spring 7, and the oil flows from bottom to top within the oil passage 4. When oil injection stops, the second plug 6 descends under the influence of gravity and the spring's restoring force, automatically abutting against the upper surface of the sealing washer 5, thus completing the seal at the bottom of the oil passage 4. To further ensure the sealing performance of the bottom of the oil passage 4, after tightening the second set screw 13, the third plug 12, located at the bottom of the sealing washer 5, is pressed tightly by the second set screw, thus abutting against the bottom of the sealing washer 5, serving as another sealing measure for the bottom of the oil passage 4 to ensure no oil leakage at the bottom of the oil passage 4.
[0031] The first plug 10, the second plug 6, and the third plug 12 are all made of steel spherical plugs to ensure a better sealing effect and a longer service life.
[0032] The specific parameters are determined as follows: 1. Size of the vent; The vent hole and the oil outlet at the top of oil passage 4 are primarily designed to allow air to escape, not to allow oil to flow out at high speed. Therefore, the vent hole should be as small as possible while ensuring that air can escape smoothly, in order to avoid oil spraying during operation, which would cause waste and contamination, and to reduce the risk of clogging by contaminants.
[0033] Two calculation methods are given below. The maximum value between the two methods is taken as the design value of the exhaust port.
[0034] 1) Theoretical calculation methods; Airflow rate: ; Oil flow rate (if accidentally turned on): ; in: Qa, Qo are the volumetric flow rates (m³) of air and oil, respectively. 3 / s); Cd: Flow coefficient (usually taken as 0.6 ~ 0.8); A: Cross-sectional area of the vent (m²) 2 A = πd² / 4 (d is the aperture); ΔP: Pressure difference (Pa) before and after the exhaust port; ρa, ρo: Density of air and oil (kg / m³) 3 ).
[0035] Due to the density of oil (such as aviation hydraulic oil) ) is much greater than the density of air (≈ Under the same orifice diameter A and pressure difference ΔP, the outflow velocity of oil is much smaller than that of air (approximately...). (Times). This suggests that it is possible to achieve efficient venting with a very small orifice, and that the flow rate would be much slower once the oil arrives.
[0036] Estimate the required air volume V_air and the estimated evacuation time t to obtain the required airflow rate. .
[0037] Then, the required aperture A is calculated by working backward from the formula.
[0038] 2) Empirical method; In practice, the diameter of the vent hole is determined by a combination of the following factors: ① Prevent blockage: The orifice diameter cannot be too small, otherwise it will easily be clogged by tiny particles or colloids in the oil, losing its venting function. A rule of thumb is that the minimum orifice diameter should generally not be less than 1 mm. This is an important balance between reliability and functionality. Orifices smaller than 1 mm are considered too risky in industrial hydraulic environments.
[0039] ② Operability and splash protection: The orifice diameter needs to be matched to the venting operation method. When venting manually, if the valve diameter is too large, even a slight opening will cause oil to spray out at high speed, making it difficult to control. The effective venting orifice diameter of the valve core end section of a standard manual venting needle valve is usually between 1mm and 2mm. This size ensures effective venting when slightly open, while preventing excessive oil loss when fully open (in case of operational error).
[0040] Standard vent valves have standardized interface thread sizes (such as M5x0.8, M6x1, 1 / 8" NPT, 1 / 4" NPT) and internal passage diameters. For most industrial hydraulic systems (pressure up to 31.5 MPa), vent needle valves with M5x0.8 or 1 / 8" NPT interface threads are the most common choice, as their internal passages are sufficient to meet the venting needs of the vast majority of cylinders and valve blocks.
[0041] ③ System pressure: High-pressure systems have higher sealing requirements and tend to use smaller diameter exhaust valves (such as M5) to reduce the risk of seal failure.
[0042] Calculation of the force that the steel balls (i.e., the first plug 10, the second plug 6, and the third plug 12) need to overcome to seal: The calculation method for the force that the steel ball seal needs to overcome is as follows: First, determine the effective pressure-bearing area (or, for simplicity, calculate using the diameter of the central hole): , where r is the radius of the hole.
[0043] Secondly, the hydraulic pressure P (Pa) generates a driving force F along this area: , where 10 bar (1 MPa = 1 × 10 6 Pa).
[0044] Finally, the spring preload The safety factor is generally taken as 1.2 to 1.5 to ensure that the steel ball is not pushed open under the target pressure.
[0045] Spring 7 Selection: The selection method for spring 7 is as follows: First, obtain the required preload F0. If P_max = 10 MPa, then F ≈ 31.4 N. Taking a safety factor of 1.5, we correct it to 47 N.
[0046] Secondly, spring stiffness 7 Where Δx is the compression deformation of spring 7. The free length L0 and the compressed installation length Lc are determined during the design phase, specifically based on the valve cavity dimensions. Then select k to make .
[0047] Finally, based on the spring stiffness 7 Choose high-temperature and oil-resistant materials, such as stainless steel 302 / 316 or Inconel springs.
[0048] The verification of O-ring 9 and the groove takes into account anti-extrusion / sealing reliability: Unless otherwise specified, the static sealing compression amount is 10% to 30%, depending on the material and hardness.
[0049] Extrusion prevention: If the oil pressure is high, an anti-extrusion ring should be designed on the outside of the O-ring 9 to be tested or the gap should be reduced to prevent the O-ring 9 to be tested from being extruded under high pressure.
[0050] Surface roughness: The sealing surface Ra should be as low as possible, such as Ra≤1.6μm or according to material and experimental requirements, to avoid scratching the O-ring and causing leakage.
[0051] Taking the design of a hot oil aging test fixture for a specific O-ring 9 as an example. The parameters of the O-ring 9 to be tested are shown in Table 1.
[0052] Table 1 This invention also provides a method for using an O-ring hot oil aging test fixture, combined with... Figure 2 As shown, it includes the following steps: S1: Install the O-ring 9 to be tested into the test chamber, and fix the base 1, the intermediate plate 2 and the top cover 3 together with screws 14 to form the fixture shell 16.
[0053] S2: Remove the first plug 10, the second plug 6 and the third plug 12 so that both ends of the oil passage 4 are connected to the outside.
[0054] S3: Slightly loosen each screw 14 to release air from the clamp housing 16.
[0055] S4: Oil is continuously injected into the bottom of the oil passage hole 4 by hand pump 15 to expel the air in the clamp housing 16. The hand pump can better control the oil injected into the oil passage hole 4 and prevent oil waste.
[0056] S5: Observe until there are no air bubbles in the oil overflowing from the joint of the fixture housing 16, then tighten all screws 14. At this point, the air in each test chamber has been basically expelled.
[0057] S6: Observe until the oil overflowing from the top of the oil passage hole is free of air bubbles, indicating that all the air in the oil passage hole has been expelled. Tighten the first set screw 11, and the first set screw 11 will press against the first plug 10 to seal the top of the oil passage hole 4.
[0058] S7: Use hand pump 15 to continuously inject oil until the preset pressure requirement of the test is met. In this embodiment, the preset pressure requirement is 29MPa.
[0059] S8: After the oil injection stops, the second plug 6 is pressed against the upper part of the sealing gasket 5 by gravity and the rebound force of the spring 7 to ensure the stability of the oil pressure inside the clamp housing 16 and seal the bottom of the oil passage hole 4. Then, tighten the second set screw 13 to press the third plug 12 against the bottom of the sealing gasket 5 to further ensure the sealing of the bottom of the oil passage hole 4.
[0060] S9: Turn the fixture housing 16 over and place the top cover 3 face down into the high-temperature aging test chamber for hot oil aging test.
[0061] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A hot oil aging test fixture for O-rings, characterized in that: It includes a base (1), several intermediate plates (2) stacked vertically on the base (1) and a top cover (3) set on the top of the intermediate plates (2). The base (1), intermediate plates (2) and top cover (3) are detachably connected and together form a clamp shell (16). An oil passage hole (4) is opened in the clamp housing (16) in a vertical direction. The top and bottom of the oil passage hole (4) are respectively provided with a detachable first seal and a second seal. The second seal includes a sealing gasket (5), a second plug (6) and a spring (7). The oil passage hole (4) is provided with a second step (42). The top of the spring (7) abuts against the second step (42), and the bottom of the spring (7) abuts against the second plug (6). The sealing gasket (5) is fixed in the oil passage hole (4) and located below the second plug (6). When the second plug (6) abuts against the sealing gasket (5), the bottom of the oil passage hole (4) can be sealed. When the intermediate plate (2) is attached to the adjacent base (1), intermediate plate (2) or top cover (3), a transverse channel (8) is reserved between them to form a test cavity that can accommodate the O-ring (9) to be tested. The oil in the oil hole (4) can enter the test cavity through the transverse channel (8).
2. The O-ring hot oil aging test fixture as described in claim 1, characterized in that: The first sealing element includes a first plug (10) and a first set screw (11). The oil passage (4) is provided with a first step (41). The first plug (10) is located above the first step (41). When the first plug (10) abuts against the first step (41), it can seal the top of the oil passage (4). The first set screw (11) is threaded to the top of the upper cover (3) to abut against the upper part of the first plug (10).
3. The O-ring hot oil aging test fixture as described in claim 1, characterized in that: The second seal also includes a third plug (12) and a second set screw (13). The third plug (12) is located below the sealing gasket (5). When the third plug (12) abuts against the lower part of the sealing gasket (5), it can seal the bottom of the oil passage (4). The second set screw (13) is threaded to the bottom of the base (1) and abuts against the lower part of the third plug (12).
4. The O-ring hot oil aging test fixture as described in claim 1, characterized in that: At least four threaded holes are provided in the same position in the base (1), the middle plate (2) and the top cover (3), and the base (1), the middle plate (2) and the top cover (3) are fixedly connected by screws (14) of the corresponding number of threaded holes.
5. The O-ring hot oil aging test fixture as described in claim 3, characterized in that: The first plug (10), the second plug (6) and the third plug (12) are all steel spherical plugs.
6. The O-ring hot oil aging test fixture as described in claim 1, characterized in that: The inner diameter of the oil passage (4) is 1~2mm.
7. The O-ring hot oil aging test fixture as described in claim 1, characterized in that: The spring (7) is made of 302 stainless steel, 316 stainless steel or Inconel alloy.
8. The O-ring hot oil aging test fixture as described in claim 1, characterized in that: The surface roughness Ra of the contact surface between the base (1), the middle plate (2), and the top cover (3) is ≤1.6μm.
9. A method of using the O-ring hot oil aging test fixture as described in any one of claims 1-8, characterized in that: It includes the following steps: S1: Install the O-ring (9) to be tested in the test chamber, and fix the base (1), the intermediate plate (2) and the top cover (3) together with screws (14); S2: Remove the first plug (10), the second plug (6) and the third plug (12); S3: Loosen each screw (14) to release air from the fixture housing (16); S4: Continuously inject oil into the bottom of the oil passage (4) through the pressurizing device to expel the air from the fixture housing (16); S5: Observe until there are no bubbles in the oil overflowing from the joint of the clamp housing (16), and tighten all screws (14); S6: Observe until the oil overflowing from the top of the oil passage hole is free of air bubbles, and seal the top of the oil passage hole (4) with the first sealing element; S7: Continue injecting oil until the preset test pressure requirement is met; S8: After stopping the oil injection, the bottom of the oil passage hole (4) is sealed by the second seal. At this time, the spring (7) is reset and the second plug (6) is driven to abut against the upper part of the sealing gasket (5) to ensure that the oil pressure inside the clamp housing (16) is stable. S9: Turn the fixture shell (16) over and place the top cover (3) face down in a high-temperature environment for hot oil aging test.
10. The method of using the O-ring hot oil aging test fixture as described in claim 9, characterized in that: The preset pressure is 29 MPa.