本科毕业论文---螺杆式压缩机外文翻译.doc
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1、英文原文Screw CompressorsThe direction normal to the helicoids, can be used to calculate the coordinates of the rotor helicoids and from x and y to which the clearance is added as:, , (2.19)where the denominator D is given as: (2.20) and serve to calculate new rotor end plane coordinates, x0n and y0n,wi
2、th the clearances obtained for angles = /p and respectively. These and now serve to calculate the transverse clearance 0 as the difference between them, as well as the original rotor coordinates and .If by any means, the rotors change their relative position, the clearance distribution at one end of
3、 the rotors may be reduced to zero on the flat side of the rotor lobes. In such a case, rotor contact will be prohibitively long on the flat side of the profile, where the dominant relative rotor motion is sliding, as shown in Fig. 2.29. This indicates that rotor seizure will almost certainly occur
4、in that region if the rotors come into contact with each other.Fig. 2.29. Clearance distribution between the rotors: at suction, mid rotors, and discharge with possible rotor contact at the dischargeFig. 2.30. Variable clearance distribution applied to the rotorsIt follows that the clearance distrib
5、ution should be non-uniform to avoid hard rotor contact in rotor areas where sliding motion between the rotors is dominant.In Fig. 2.30, a reduced clearance of 65 m is presented, which is now applied in rotor regions close to the rotor pitch circles, while in other regions it is kept at 85 m, as was
6、 done by Edstroem, 1992. As can be seen in Fig. 2.31, the situation regarding rotor contact is now quite different. This is maintained along the rotor contact belt close to the rotor pitch circles and fully avoided at other locations. It follows that if contact occurred, it would be of a rolling cha
7、racter rather than a combination of rolling and sliding or even pure sliding. Such contact will not generate excessive heat and could therefore be maintained for a longer period without damaging the rotors until contact ceases or the compressor is stopped.2.6 Tools for Rotor ManufactureThis section
8、describes the generation of formed tools for screw compressor hobbing, milling and grinding based on the envelope gearing procedure.2.6.1 Hobbing ToolsA screw compressor rotor and its formed hobbing tool are equivalent to a pair of meshing crossed helical gears with nonparallel and nonintersecting a
9、xes. Their general meshing condition is given in Appendix A. Apart from the gashes forming the cutter faces, the hob is simply a helical gear in which.Fig. 2.31. Clearance distribution between the rotors: at suction, mid of rotor and discharge with a possible rotor contact at the dischargeEach refer
10、red to as a thread, Colburne, 1987. Owing to their axes not being parallel, there is only point contact between them whereas there is line contact between the screw machine rotors. The need to satisfy the meshing equation given in Appendix A, leads to the rotor hob meshing requirement for the given
11、rotor transverse coordinate points and and their first derivative.The hob transverse coordinate points and can then be calculated. These are sufficient to obtain the coordinate The axial coordinate , calculated directly, and are hob axial plane coordinates which define the hob geometry.The transvers
12、e coordinates of the screw machine rotors, described in the previous section, are used as an example here to produce hob coordinates. he rotor unit leadsare 48.754mm for the main and 58.504mm for the ate rotor. Single lobe hobs are generated for unit leads :6.291mm for the main rotor and 6.291mm for
13、 the gate rotor. The corresponding hob helix angles are 85 and 95. The same rotor-to-hob centre distance C = 110mm and the shaft angle = 50 are given for both rotors. Figure 2.32 contains a view to the hob.Reverse calculation of the hob screw rotor transformation, also given in Appendix A permits th
14、e determination of the transverse rotor profile coordinates which will be obtained as a result of the manufacturing process. These ay be compared with those originally specified to determine the effect ofFig. 2.32. Rotor manufacturing: hobbing tool left, right milling toolmanufacturing errors such a
15、s imperfect tool setting or tool and rotor deformation upon the final rotor profile.For the purpose of reverse transformation, the hob longitudinal plane coordinatesand andshould be given. The axial coordinate is used to calculate , which is then used to calculate the hob transverse coordinates:, (2
16、.21)These are then used as the given coordinates to produce a meshing criterionand the transverse plane coordinates of the “manufactured” rotors.A comparison between the original rotors and the manufactured rotors is given in Fig. 2.33 with the difference between them scaled 100 times. Two types of
17、error are considered. The left gate rotor, is produced with 30um offset in the centre distance between the rotor and the tool, and the main rotor withFig. 2.33. Manufacturing imperfections0.2 offset in the tool shaft angle . Details of this particular meshing method are given by Stosic 1998.2.6.2 Mi
18、lling and Grinding ToolsFormed milling and grinding tools may also be generated by placing in the general meshing equation, given in Appendix A, and then following the procedure of this section. The resulting meshing condition now reads as: (2.22)However in this case, when one expects to obtain scre
19、w rotor coordinates from the tool coordinates, the singularity imposed does not permit the calculation of the tool transverse plane coordinates. The main meshing condition cannot therefore be applied. For this purpose another condition is derived for the reverse milling tool to rotor transformation
20、from which the meshing angle is calculated: (2.23)Once obtained, will serve to calculate the rotor coordinates after the “manufacturing” process. The obtained rotor coordinates will contain all manufacturing imperfections, like mismatch of the rotor tool centre distance, error in the rotor tool shaf
21、t angle, axial shift of the tool or tool deformation during the process as they are input to the calculation process. A full account of this useful procedure is given by Stosic 1998.2.6.3 Quantification of Manufacturing ImperfectionsThe rotor tool transformation is used here for milling tool profile
22、 generation. The reverse procedure is used to calculate the “manufactured” rotors. The rack generated 5-6 128mm rotors described by Stosic, 1997a are used as given profiles: x(t) and y(t). Then a tool rotor transformation is used to quantify the influence of manufacturing imperfections upon the qual
23、ity of the produced rotor profile. Both, linear and angular offset were considered. Figure 2.33 presents the rotors, the main manufactured with the shaft angle offset 0.5 and the gate with the centre distance offset 40 m from that of the original rotors given by the dashed line on the left. On the r
24、ight, the rotors are manufactured with imperfections, the main with a tool axial offset of 40 m and the gate with a certain tool body deformation which resulted in 0.5 offset of the relative motion angle . The original rotors are given by the dashed line.3Calculation of Screw Compressor PerformanceS
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