Machining method of hydrodynamic pressure groove o

The processing method of the fluid dynamic pressure groove on the end face of the mechanical seal ring

1 introduction

when the contact mechanical seal is in operation, the contact surface of the moving ring and the static ring should generate heat by friction. For the system with high PV value, the friction heat causes high temperature on the sealing surface, which will increase wear and thermal deformation; When the temperature exceeds a certain value, the lubricating film vaporizes, and friction and wear intensify; If the temperature greatly exceeds the allowable use temperature of the material, the sealing ring may have melting, gluing or hot cracking and other faults, resulting in shutdown, huge economic losses or environmental pollution. Therefore, it is necessary for the contact mechanical seal to use the hydrodynamic effect to improve the bearing capacity of the seal, reduce friction, wear and leakage, improve the reliability of the seal and prolong the service life of the seal. The usual way to make use of the hydrodynamic effect is to open a certain shape of hydrodynamic groove on a sealing surface of the friction pair. Under the action of these flow grooves, ordinary contact seals become hydrodynamic non-contact seals. These grooves can play the role of hydrodynamic lubrication, make the sealing face out of contact, and also play the role of sealing to prevent leakage. According to the working conditions, working parameters and application requirements of mechanical seals, the launder can be designed into different plane shapes and cross-sectional groove shapes. Plane graphics include herringbone groove, splay groove, spiral groove, arc groove, straight groove, etc., and cross-section grooves include trapezoidal groove, square groove, V-shaped groove, inclined bottom groove, etc. Launders can be divided into two categories according to their depth: one is shallow, with a depth of μ M magnitude; One is deep groove, with the depth of mm. The sealing mechanism of shallow grooves is hydrodynamic effect, while the sealing mechanism of deep grooves is thermal hydrodynamic mode effect or hydrodynamic cushion effect. The geometric parameters of the launder have a great impact on the sealing performance, such as groove depth, groove number, groove diameter ratio, inlet angle and groove surface roughness, which are directly related to the opening force, leakage, stiffness to leakage ratio, end face temperature rise, friction coefficient and other sealing performance parameters. μ The depth difference of M-level shallow flow trough is only a few μ M, the leakage will change greatly, so the accurate design and processing of dynamic pressure groove directly affect the quality of mechanical seal. At present, China's mechanical seal industry has made great progress. Domestic mechanical seal products are running on some large or key equipment, and some have replaced imported products, which have been running for more than 5 years. However, in order to further improve the grade of mechanical seal products, a lot of work must be done from the aspects of design, materials, technology and so on. For example, the processing of hydrodynamic pressure groove on the end face of seal ring is one of the prominent problems

2 sealing material

the performance of sealing material is directly related to the processing of dynamic pressure groove. In general, the hard rings of friction pairs are made of WC Cemented Carbide. WC Cemented Carbide is a good sealing material because of its high hardness, good wear resistance and high strength. However, with the development of industry, the performance requirements of mechanical equipment are higher and higher. The working conditions may be high pressure, high speed, high temperature, etc., and the sealing medium may be highly corrosive or contain abrasive particles. In these cases, WC Cemented Carbide is not an ideal sealing material. The working conditions of high parameters put forward new requirements for the development of mechanical seals. This kind of phenomenon is called subordination, especially the quality of hard materials as friction pairs should reach higher standards, such as wear resistance, corrosion resistance, mechanical strength, heat resistance, self lubrication, air tightness, machinability, and the matching materials have no excessive wear and electrochemical corrosion. SiC ceramics meet almost all the above requirements. It is a new hard sealing material developed and put into use in recent years. It is increasingly selected as a friction accessory material in mechanical seals in various industrial sectors such as chemical industry, oil refining, papermaking, automobile, atomic energy, aviation, aerospace and so on. It can be said that in order to adapt to the development of mechanical seals, new sealing materials will continue to be developed

3 processing method of fluid dynamic pressure groove on the end face of sealing ring

dynamic pressure groove of sealing ring has been more and more used in non-contact mechanical seals. However, the shape of dynamic pressure groove is complex, the structure is fine and high precision, and the roughness requirements are also strict. Especially, the sealing rings processing dynamic pressure groove are mostly hard materials, so the processing of dynamic pressure groove is very difficult, and the conventional mechanical processing method is almost powerless. Therefore, People have explored a variety of methods, mainly including the following:

3.1 photolithography (chemical corrosion)

first coat the workpiece to be etched with a photosensitive adhesive film, and then place the prepared negative film on it. After exposure, development, coating a protective layer, and then etching in the etching solution, the required dynamic pressure groove can be obtained. This method is acceptable for grooving on bronze. When grooving on cemented carbide, the quality of the grooved shape is not high because the adhesive film cannot withstand the long-term corrosion of the etching solution at a higher temperature

3.2 EDM (electric etching)

this method uses the method of two electrode discharge to etch the material to be removed in the dynamic pressure groove. The key of this method is to make the discharge head. The structure of the end face of the discharge head is the same as that of the dynamic pressure groove on the end face of the sealing ring, but the pattern is prominent. The seal ring and the discharge head are powered on as two electrodes respectively. When the two end faces contact, discharge occurs, and the material at the dynamic pressure groove on the end face of the seal ring is etched away. However, this method requires good dielectric performance, and the end face of the discharge head and the end face of the seal ring should be parallel, so as to achieve the effect of uniform discharge, otherwise the depth of each groove will be difficult to guarantee. The disadvantage of this method is that it is difficult to machine the discharge head; The efficiency of electric etching is too low, otherwise the loss of discharge head is large; High processing cost; The effect is not good; At the same time, the micro cracks caused by the surface stress produced by EDM will reduce the strength of the material

3.3 electroplating method

this method is to coat a layer of hard material on the part other than the dynamic pressure groove on the end face of the sealing ring, so as to make the pattern of the dynamic pressure groove. The use condition of this method is that the groove should be shallow first, and then the plated end face must be a material that can be plated, and the coating should be dense, and the bonding strength with the plated surface should be high enough. At the same time, the plated parts should be hung correctly in the electroplating process, otherwise the coating thickness error at different parts will increase, resulting in uneven groove depth, which also destroys the extremely high parallelism of the two end faces of the sealing ring

3.4 sand blasting method

this method first needs to manufacture a sand blasting mask, and the pattern of holes on the mask is the same as the dynamic pressure groove structure. When the mask is placed on the end face of the seal, the parts other than the dynamic pressure groove on the end face are covered, and the materials at the exposed parts are removed by high-energy sand blasting to form a certain depth of dynamic pressure groove. The key technology of this method lies in the selection of mask material, the manufacture of mask, the bonding between mask and seal ring end face, and the mastery of sand blasting technology. The problems of sand blasting method are low manufacturing accuracy, uneven edges of the processed dynamic pressure groove, serious distortion of fine parts such as sharp corners, bad cross-section groove shape, rough sand blasting surface, etc., which will affect the fluid dynamic pressure effect and sealing characteristics of the groove line

3.5 laser processing method

laser processing is a method of industrial thermal processing using the high energy of laser. The practical processing of this method for material removal includes cutting, drilling, dynamic balancing, marking, etc. at this time, the power density of the laser can be as high as 107w/cm2 or more, and any material can be vaporized and melted in a very short time. The process of laser processing the dynamic pressure groove of the sealing ring is actually laser marking, which is a relatively new work. The author has made a deep study of jjg1136 ⑵ 017 specifying that the verification waveform is sine wave entering the ground and achieved good results, so he makes more introductions

laser marking is to use the laser beam to irradiate the surface of the workpiece and engrave the required graphic marks. Carving effect is through the evaporation of surface materials, exposing deep materials. Compared with traditional engraving technology, laser marking has a wide range of applications, and is suitable for processing surfaces of different materials and shapes. It has the characteristics of no mechanical deformation, no pollution, high speed, good repeatability and high degree of automation. It has a wide range of applications in industry, national defense, scientific research and many other fields. In the laser marking method, the scanning method is suitable for the processing of any figure and any batch with physical quality similar to vulcanized rubber without vulcanization. This method is used in this paper. In the scanning marking system, the computer can process the graphics in two ways: dot matrix and vector. After experiments, it is found that the lattice mode is slow and the boundary is not smooth when the graphics are amplified, so we use the vector mode laser marking system [1]. The biggest feature of vector mode is that it uses vectors (square line segments) to represent graphics, and uses the computer advanced graphics system to process graphics. It has the functions of high drawing efficiency, high graphics accuracy, and the ability to arbitrarily enlarge and reduce graphics without distortion and deformation, so it can ensure the speed and quality of laser processing the dynamic pressure groove on the end face of the sealing ring

3.5.1 composition of laser marking system

the laser marking system is composed of laser part, galvanometer scanning head, control system, computer and other parts. The laser part is composed of a solid-state laser and a laser power supply, which is continuously pumped and then acoustooptic Q-switched. The tight supply of working substances in the spot market is nd:yag, with a wavelength of 1.06 μ m。 The scanning head is composed of a galvanometer and a flat field focusing mirror that can vibrate orderly in the X and Y directions. Scribed line width is less than 100 μ m. The resolution is 1.7 μ m. Fully meet the requirements of marking and engraving. The control system controls the whole laser marking system through the control software. Its principle is: the computer of the control system converts the good graphics into electrical signals, and transmits them to the galvanometer and the laser respectively at a certain frequency. Under the control of a series of signals, the galvanometer vibrates orderly in X and Y dimensions, so that the laser points scan the corresponding graphics. At the same time, the laser sends out laser pulses of a certain frequency and energy under the control of electrical signals, Etch the pattern scanned by the laser focal spot on the workpiece. As a high-performance laser marking machine, the control software is very important. The marking control software of this machine is a software with strong functions. It can not only be used for manual programming, but also accept vector graphics processed by some basic drawing software, mainly * PLT vector format file. In addition, the graphical interface of the software is very convenient, which can truly display * Vector graphics of PLT, and you can input commands through the keyboard or menu to select and modify graphics, such as size transformation, moving, rotating mirror image, grouping, etc. at the same time, you can select different process parameters for different graphics on the screen to achieve different levels of engraving. The peripheral computer is used to complete the scanning or programming of laser marking graphics, and Core1DRAW graphics design software is used as a tool of dynamic pressure groove part drawing generation and processing software. The file is * PLT vector format

the main performance parameters of the system are as follows: YAG laser power is 100W; Q modulation frequency range is 1 ~ 50KHz; The output power after modulation is 1 ~ 47w; The diameter of focal spot is 50 ~ 150 μ m； Position accuracy is 0.1% (beam); The accuracy of repeated positioning is ± 25 μ M (workbench); The marking speed is 0 ~ 3000mm/s; Marking range is 114 × 114mm

3.5.2sic ceramic vector laser marking process overview

the marking process is to use a computer to control the scanning galvanometer to make a highly focused laser beam on the workpiece