Theoretical Analyses and Design Guidelines of Oil-Film-Lubricated Mechanical Face Seals with Spiral Grooves

The oil-film-lubricated mechanical face seal is a kind of pure hydrodynamic lubricated noncontacting mechanical face seal with zero leakage. On the basis of systematic theoretical analyses, the design calculation formulas under zero-leakage condition for mechanical face seals with different spiral groove patterns, including double-row spiral grooves such as splay pattern and single-row spiral grooves, are derived. The effects of groove geometry including number of grooves, balance ratio, spring force, rotating speed, and differential pressure on the seal performance are discussed in detail. Finally, the design guidelines of this kind of seal with zero leakage and no wear are put forward. The seals designed according to the guidelines can withstand the pressure disturbance and speed change by means of a slight change of oil-film thickness. Seals developed according to the design guidelines have been tested on a test rig in detail and applied successfully in high-speed turbocompressors of the oil refinery and petrochemical industries.     

Theoretical Analyses and Field Applications of Gas-Film Lubricated Mechanical Face Seals with Herringbone Spiral Grooves

The gas-film-lubricated mechanical face seal is a combined hydrodynamic and hydrostatic seal with positive leakage. Up to now, it has been widely accepted by end, users and builders of high-speed turbo compressors. The groove technology on the sealing face of the seat is one of the core technologies of dry gas seals. This article presents a patented herringbone spiral-grooved gas seal. Its one-dimensional analytical solution and two-dimensional numerical solution methods for the gas-film pressure distribution on the sealing face are presented. Up to now, more than 200 gas seals adopting this groove technology have been applied successfully in high-speed turbo compressors that deal with dangerous process gas in the oil refinery and petrochemical industries. The theoretical analyses and field applications show that gas seals with herringbone spiral grooves are advanced and practicable.     

Critical Balance Ratio of Mechanical Seals

In this paper, several failure modes related to mechanical seal balance ratio are introduced, such as seal face opening, premature wear, dry running, heat checking, blistering, phase stale instability, seal face tilling instability, fluid film instability, inhibition of fluid film formation, fluid film rupture, vaporization and excessive liquid leakage. Formulae for critical balance ratios for these failure modes are presented. Suitable balance ratios can be selected by considering these critical balance ratios. Several examples are given for mechanical seal design and application.     

机械密封的功率消耗试验及测量方法

随着机械密封应用的普及、机械密封的失效已成为石油化工等部门的回转机械（离心泵等）工作不可靠的重要因素,机械密封的端面摩擦不但直接消耗能源,而且,因端面摩擦过度而引起的密封失效泄漏所造成的损失则更大。本文在试验的基础上,研究了机械密封消耗的构成,介绍机械密封摩擦功率的测量方法,对机械密封不同工况不功率消耗的变化进行了分析,提出了降低机械密封功率消耗和改善密封功能,提高机械密封的工作可靠性的途径。     

A Model for Mechanical Seals with Regular Microsurface Structure

A mathematical model is developed to allow performance prediction of all-liquid noncontacting mechanical seals with regular microsurface structure in the form of hemispherical pores. Seal performance such as the equilibrium face separation, friction torque and leakage across the seal are calculated and presented for a range of sealed pressure, pore size and pore ratio of ring surface area. An optimum pore size is found that depends on the other variables and corresponds to maximum axial stiffness and minimum friction torque. Also, a critical pore size is found above which seal failure is possible.     

A New Shaft Sealing Solution for Small Cryogenic Pumps

Commonly scaled cryogenic fluids include liquefied gases such as nitrogen, argon and oxygen, pumped both on site and from road tankers at temperatures approaching — 200°C (392°F). Traditionally, cryogenic sealing has employed conventional contact sealing technology, the seal typically being of a metal bellows design.

However, because most liquefied gases are pumped at temperatures close to their boiling points, vaporization at the sealing interface is a major problem. Dry running causes accelerated face and seat wear and short seal life.

A new type of seal has been developed which combines two critical seal, technologies. It comprises a profiled noncontacting seal face and seal as the primary seal, and a welded metal bellows as the secondary seal, and spring.

The paper will outline the technology employed in solving this cryogenic sealing application. It will describe the equipment and environments that are typically employed, focusing on those issues that are relevant, to the shaft seal. Some examples of operating installation will be given, together with measurements taken from them.     

超高速涡轮泵机械密封热弹流润滑特性研究

以超高速涡轮泵用机械密封为研究对象,针对超高速工况下密封界面多场耦合变形行为和热弹流润滑特性不明等问题,建立密封动静环和润滑液膜的耦合数学模型,研究不同转速和密封压力下的密封界面润滑特性和端面变形行为,分析相应的密封性能变化规律。结果表明：超高速工况下密封端面产生沿泄漏方向收敛的液膜间隙,密封动环的高温热变形是主因;随密封压力的增大,液膜间隙的收敛角减小,最大膜厚和泄漏率增大,端面温升明显减小;随着转速的增大,液膜间隙的收敛角、端面温升和泄漏率增大,摩擦扭矩减小。建立的流固热力耦合模型可为超高速涡轮泵用机械密封端面的优化设计提供理论指导。     

Spiral Groove Face Seal Behavior and Performance in Liquid Lubricated Applications

ABSTRACT

A series of experiments was conducted to study the behavior and performance of a spiral groove mechanical face seal in liquid lubricated applications. The seal's ability to contain water from ambient to near saturation conditions was tested. A comparison of experimental results with a numerical solution of the Reynolds equation under isothermal conditions was done. Two-phase and non-laminar flows were observed because of high speed, high temperature and high film thickness. Different lubrication regimes, such as mixed and hydrodynamic, were also reached. The results show that the spiral groove face seal can work for a large operating range with a lower friction factor but a higher leakage than the smooth face seal configuration.     

Comparison of Leakage Performance in Three Types of Gas Annular Seals Operating at a High Temperature (300°C)

Adequate sealing in rotating machinery reduces secondary leakage and results in more efficient and stable systems. Labyrinth seals are most common, although brush seals are popular in specialized applications. The hybrid brush seal (HBS) is a novel design that adds to the bristle brush matrix a number of cantilever pads that rest on the rotor surface. Upon shaft rotation the pads lift due to the generation of a hydrodynamic gas film, and the brushes effectively seal an upstream pressure. Hence, the HBS has no wear and no local thermal distortion effects. This article presents measurements of leakage versus pressure differential obtained in a three-tooth labyrinth, a conventional brush seal, and a hybrid brush seal for operation at high temperature (300°C) and with shaft surface speeds to 26 m/s. The measurements demonstrate that the HBS leaks ～ 31% less than a standard brush seal and is significantly better (～ 68%) than a similarly sized labyrinth seal. As temperature increases, the labyrinth seal leakage decreases because its clearance changes due to the thermal growth of the components. The HBS, on the other hand, shows leakage that is nearly insensitive to air inlet temperature. The measurements demonstrate HBS as a reliable seal technology for use in gas turbines, for example.     

A Condition Monitor For Liquid Lubricated Mechanical Seals

A recently developed condition monitor for liquid lubricated mechanical seals utilizes actively generated ultrasonic shear waves to determine conditions at the sealing interface. A shear wave transducer is mounted on the backside of the non-rotating seal face, and generates waves that propagate toward the sealing interface. The amplitude of the reflected waves indicates whether or not face contact occurs and, if there is contact, the severity of contact. Thus, this monitor is suitable for use with both non-contacting and partially contacting seals. Laboratory tests on a commercial, unbalanced seal demonstrate the effectiveness of the approach.     

Parametric Study of Spiral Groove Gas Face Seals

A finite element analysis for the isothermal flow in spiral groove gas face seals is detailed along with a successive approximation method for the iterative solution of the nonlinear Reynolds equation. Zeroth- and first-order pressure fields are calculated for evaluation of the seal opening force and leakage and the axial stiffness and damping force coefficients, respectively. A parametric study shows the static and dynamic force behavior of a baseline SGFS operating with a large pressure ratio. The recommended geometric parameters presented ensure large static stiffness and damping force coefficients while still allowing for low seal leakage rates. A reduction in the power loss and a significant increase in the seal static stiffness coefficient are unique features of thin seal dams.     

Design methodology for an air-lubricated seal

A methodology to design an air-lubricated piston seal for pneumatic actuators is described. Such a seal permits a small air leakage through a very narrow gap between the seal lip and the counterpart; this air film both avoids contact and ensures lubrication at the seal-counterpart interface thus permitting reduced friction and wear. Subsequently the use of grease could be limited or avoided. A seal geometry equipped with a self-pressurized balancing chamber was designed to make leakage as insensitive as possible to the supply pressure and to the barrel machining tolerances. A prototype was manufactured and tests were carried out.     

机械密封环端面变形研究

本介绍了“机械密封环端面变形研究”课题的初步研究结果。在电算分析中,在端面上引入虚拟的“杆元”,建立了计算密封环端面变形的轴对称模型,分析了密封环的受力变形和受热变形。试验验证之一是在端面上装上引伸片,直观地测定了密封环的变形值,较好的与计算值相符合,试验验证之二是比较了具有不同变形趋势的各种结构的机械密封在高压,高温,高速工况下的性能。     

"零压差零泄漏"液体润滑螺旋槽机械密封性能的实验研究

通过实验方法,研究了内外双螺旋槽机械密封端面简的液膜压力和端面温升。液膜压力直接反映了密封端面的润滑状况,液膜压力开始随转速的增加而增大,当转速较大时,随转速的再增大而下降。正常运转时,端面温升很小。实验研究表明,螺旋槽机械密封能在保持零泄漏的同时,实现端面的非接触。     

Numerical Study of Two-Phase Mechanical Seal Stability

The axial dynamic stability of two-phase mechanical seals has been studied theoretically. A numerical model featuring thermoelastic deformations, asperity contact, and squeeze film effects, was developed and implemented in a computer program to predict the transient behavior of two-phase seals. The governing system of ordinary differential equations is very stiff and is time-integrated using a scheme based on singular perturbation concepts. The model has been used to predict the dynamic behavior of a seal, with axial perturbations initiated from various operating conditions. Both popping open and oscillatory motion have been encountered. Results show that equilibrium points with positive stiffness are stable if the total face coning is positive. However, if the total coning is negative the point is unstable, even if the stiffness is positive. Equilibrium points with negative stiffness are unstable.     

海洋平台油气混输泵轴端密封改进设计与试验研究

针对某海洋平台油气混输泵轴端机械密封在运行过程中存在的失效问题，分析其产生的原因，并对其结构进行改进设计。对改进后机械密封进行实验室台架性能试验，分析不同弹簧比压条件下密封性能随压力的变化和密封端面磨损状况，以及不同端面设计宽度下密封性能随压力和转速的变化。结果表明：减小弹簧比压能略微降低密封端面摩擦功率，但会增大泄漏风险；减小端面宽度能有效提升润滑不良条件下的端面密封性能。确定密封优选设计参数，并对密封样机进行100 h型式试验。试验结果表明，改进后密封端面摩擦功率基本稳定，波动较小，泄漏量满足标准指标要求，验证了该密封结构改进的合理性、优选设计参数的有效性和运行工况的适应性。     

A Numerical Model of a Reciprocating Rod Seal With a Secondary Lip

A numerical model of an elastomeric reciprocating hydraulic rod seal, with both a primary and a secondary lip, has been developed. It is applicable to cases in which the stroke length is significantly larger than the seal width. Coupled fluid mechanics, contact mechanics, and deformation analyses are applied to each lip. Mass conservation and the pressure of the intervening fluid couple the two lips to each other. The leakage, the film thickness distribution, the fluid and contact pressure distributions, and the friction force are predicted for both the outstroke and the instroke for a typical seal, operating with mixed lubrication.     

Seal-Inlet Disturbance Boundary Condition Correlations for Rotordynamics Models,Part 2: Assessment

Nearly all seal rotordynamics models were forced to assume that the seal-inlet swirl velocity disturbance boundary condition components (W _1C and W _1S ) are zero. The companion (Part 1) paper employs an extensive parametric study to develop a complete set of widely applicable seal-inlet disturbance boundary condition correlations that will alleviate this shortcoming. The benefits of using the new seal-inlet boundary condition correlations were assessed by implementing them into a CFD-perturbation model. Two widely different test cases were employed. Case 1 is a test of the correlations for large upstream chambers using a simple liquid smooth-plain seal, and Case 2 is a test for small, as well as radial injection, upstream chambers using a complicated gas labyrinth seal. For both cases, consistently improved agreement with measurements was obtained for the options with non-zero W _1C and W _1S compared to the option with W _1C = W _1S = 0. Specifically, the correlation set using the W _1C -profile option gave a clearly better prediction of the effective damping and the cross-coupled stiffness than did the set using the W _1C -bulk option for the higher spin speed case of the challenging gas labyrinth. For the smooth-plain liquid seal case, the correlations with the W _1C -profile and W _1C -bulk options gave nearly the same level of agreement with measurements.     

Ultrananocrystalline Diamond Film as a Wear-Resistant and Protective Coating for Mechanical Seal Applications

Mechanical shaft seals used in pumps are critically important to the safe operation of the paper, pulp, and chemical process industry, as well as petroleum and nuclear power plants. Specifically, these seals prevent the leakage of toxic gases and hazardous chemicals to the environment and final products from the rotating equipment used in manufacturing processes. Diamond coatings have the potential to provide negligible wear, ultralow friction, and high corrosion resistance for the sliding surfaces of mechanical seals, because diamond exhibits outstanding tribological, physical, and chemical properties. However, diamond coatings produced by conventional chemical vapor deposition (CVD) exhibit high surface roughness (R_a ≥ 1 μm), which results in high wear of the seal counterface, leading to premature seal failure. To avoid this problem, we have developed an ultrananocrystalline diamond (UNCD) film formed by a unique CH₄/Ar microwave plasma CVD method. This method yields extremely smooth diamond coatings with surface roughness R_a = 20–30 nm and an average grain size of 2–5 nm. We report the results of a systematic test program involving uncoated and UNCD-coated SiC shaft seals. Results confirmed that the UNCD-coated seals exhibited neither measurable wear nor any leakage during long-duration tests that took 21 days to complete. In addition, the UNCD coatings reduced the frictional torque for seal rotation by five to six times compared with the uncoated seals. This work promises to lead to rotating shaft seals with much improved service life, reduced maintenance cost, reduced leakage of environmentally hazardous materials, and increased energy savings. This technology may also have many other tribological applications involving rolling or sliding contacts.     

GY70型机械密封基本性能试验及其分析

对GY70型机械密封的基本性能进行了试验研究,得出了弹簧比膻、介质压力以及转速对机械密封泄漏量和摩擦功耗的影响规律。试验研究发现,运行中的机械密封仔在一个最佳的密封工况点,通过对弹簧比压的调节与控制,可以实现这一工况．