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Abstract

Abstract. Mechanical Engineering Issues Sushil Sharma, NSLS-II Project

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Abstract

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  1. Abstract Mechanical Engineering Issues Sushil Sharma, NSLS-II Project The NSLS-II storage ring requires multipoles and dipoles of unprecedented field quality in order to achieve its performance goals of high brightness and beam stability. Many mechanical engineering issues were encountered in producing the magnets of such high field quality within the constraints physical envelops and interface requirements. These mechanical engineering issues are described as they were encountered during the various phases of the project, namely, lattice design, conceptual designs, specifications, interface requirements, magnet production and assembly, and magnet transportation. Some technical solutions and recommendations that were developed in resolving these issues are also discussed. *Work performed under auspices of the United States Department of Energy, under contract DE-AC02-98CH10886

  2. Mechanical Engineering Issues Sushil Sharma ME Group Leader – ASD/NSLS-II April 11-12, 2012

  3. Outline Mechanical design, engineering and production issues related to: • Lattice and magnet types • Conceptual designs • Specifications • Interfaces: girders, utility, vacuum chambers • Magnet Production: stacking and bonding • Magnet Reassembly • Magnet Transportation

  4. Lattice and Magnet Types NSLS-II Lattice • The Lattice should be finalized early. Sufficient spaces should be allocated between the magnets. • The magnet types should be optimized. Multiple magnet types impact on: • Design effort • Contractual effort • Suppliers’ support • Girder assemblies • Schedule remediation plans • Spares

  5. Conceptual Designs - 1 NSLS-II Segmented-Pole Designs, December 2006 Segmented-Pole Construction • Segmented-pole , or half-yoke constructions • Half-yoke construction for sextupoles requires removable mid pole. • Meeting field quality requirements with removable mid pole has been challenging. • The magnets must have sufficient iron to avoid magnetic saturation and to make them structurally robust. NSLS-II Removable Mid-pole Design, June 2008

  6. Conceptual Designs - 2 • Secondary machining (EDM, milling or profiling) should be a requirement even if the magnets are procured as per specifications. • Soleil Magnets were precision stamped but mating surfaces for some magnets had to machined precisely (grinding). • The inclusion of nose pieces (solid or laminated) and end plates need to be clearly specified and taken into account in terms of magnetic length, field quality, field matching and mechanical interferences. Quadrupole Nose Pieces 35-mm Dipole

  7. Magnet Specifications Issues • A lack of clarity on magnet specifications affects design, production, testing, acceptance, and leads to unnecessary paperwork (DVRs, DRs, Waivers, etc.) • Missing tolerances on specifications (max, min, range). • Missing or imprecise specifications : • Reproducibility (definition, first-articles/production). • Magnet-to-magnet variation of yoke lengths. • Current (I) range for field harmonics. • Specification on derived rather than primary quantity (integrated field vs magnetic length). • Over-constrained specifications (pressure drop, flow, temperature rise) • Stringent specifications (thermal switch resistance, natural frequencies). • Specifications not enforced (weight density of the yokes). • Avoid using “or equivalent” in the specifications.

  8. Vibration Specification - 1 Horizontal Motion • Magnets’ stability specification – 25 nm (rms, 4-50 Hz) • Girder-assembly natural frequency should be > 30 Hz. • The girder natural frequency is affected by the magnets’ natural frequencies.

  9. Vibration Specification -2 The girder-assembly resonant frequencies do not change significantly when ωn (magnet) > 2 ωn(assembly).

  10. Water Flow Specification • (6-10 oC) temperature-rise specification with an inlet temperature of 29.4 oC insures heat removal by cooling towers. • Only one supplier provided a flow restrictor to meet the (6-10 oC) temperature-rise specification. • The flow restrictor started clogging within a few hours. It was decided to use thin tube flow restrictors between the magnets and the magnet headers. The temperature rise specification was waved. • The hole in the copper conductor could have been smaller Flow Restrictors Flow Restrictor Location

  11. Girder Interface Base Plates and Mounting Hardware Pre-assembly of a Girder • The interface to the girder (magnets’ baseplate, size and locations of the mounting holes, slots for water connections) need to be precisely defined in the interface control drawings. Frequent interference checks are necessary. • Base plates and mounting hardware should take into account alignment, stability and transportation requirements( 4 oversize rods, flat nuts, small gap between the nuts). Base Plate, Corrector Magnet

  12. Utility Interface Manifold connections for dis-assembling a quadrupole. • Recommendation of Accelerator Advisory Committee: No forces should be applied to the magnets (such as in making water connections) after the magnets are aligned by vibrating wire. • Girders are equipped with magnet headers. • The manifold material should have been uniquely identified (PEEK). APS Water Connections

  13. Magnet – Vacuum Chamber Interface - 1 Beam Aperture 25mm x 76 mm ~ 280 mm ~ 3m Exit Port Machined Profile Ante Chamber • Machining of the chambers’ grooves: • 2-mm gap between the pole faces and the chamber. • 4-mm gap between the coils and the chamber. • 10-mm extra length on each side. • Can vacuum chambers be designed with ante chamber on the in-board side? Installed Vacuum Chamber

  14. Magnet – Vacuum Chamber Interface - 2 Exit Port Girder No. 6 Girder No. 4 • C-Type magnet spacers are not optimum for magnet re-assembly. • A better spacer design is possible by optimizing the design of the exit port: • Reduce the diameter of the exit-port tube. • Reduce the gap between the exit-port tube and the spacer blocks. • Simplify exit port of chamber no. 6. LBL - New Sextupole Exit-Port Tube

  15. Stacking Fixture and Bonding Issues - 1 Ref: C. Spencer, Magnet Lecture 2, Guanajuato, 2012 FE Analyses – Pressure in psi Separately Moving End Plate Equal Tension on 9 Tie Rods ( ) • Stacking fixture should be able to apply uniform pressure (3 – 6 MPa) on the stack of laminations. 3 MPa is the recommended pressure, but a higher pressure results in better pressure uniformity. • The stacking fixture without tie rods allows more flexibility in distributing the pressure. • The stack should be compressed after each bundle of ~ 200 mm of laminations. Tension in Central Rods = 3 x Outer Rods

  16. Stacking Fixture and Bonding Issues - 2 • Stack shrinkage (~ 5 mm/m) in oven due to compression and oozing out of the epoxy coating (~ 7 μm thick). The Belleville washers stacks should be designed to take this shrinkage into account . • Uniform pressure is difficult to achieve in a curved dipole. • For epoxy curing, ThyssenKrupp recommends a soak time of 2 hours at 160°C, or 1 hour at 180°C. A thermal analysis is recommended to establish the expected temperature profile in the yoke. Belleville Washers - Stacking Load-Deflection Curves Dipole Stack - Thermal Analysis FE Analyses: by V. Ravindranath

  17. Magnet Reassembly - 1 NSLS-II Wide Sextupole NSLS-II Wide Quadrupole Mating Surfaces • Reassembly specifications should be clearly defined and verifiable. • Avoid bending deformations and frictional sliding. The spacer blocks should be under compression. • Avoid multiple mating surfaces. • Mating surfaces should be machined precisely. Preferred Spacer Block

  18. Magnet Reassembly - 2 Bolting Sequence and Specifications: • NSLS-II magnets experience higher deformations under a horizontal force than a vertical force. • Spacer blocks will prevent deformations under a vertical force. • Applying vertical force first will increase the friction between horizontal mating surface. • By keeping horizontal force one-half the vertical force, the probability of horizontal sliding is reduced. FE Analyses: by V. Ravindranath Lifting from Top Lugs Recommended Bolt Torques (NSLS-II): Vertical: 50-60 N.m Horizontal: 25-30 N.m Anti-seize lubricant such as Kema RG-100 Design the interface without horizontal bolts !

  19. Magnet Reassembly -3 NSLS-II Quadrupole (BINP) NSLS-II Wide Sextupole NSLS-II Normal Sextupole • Magnets should be structurally robustto insure reproducibility of the magnetic field. • C-clamps were removed from NSLS-II normal sextupoles – they adversely affected the repeatability. • FE analyses showed that the spacer bars can significantly stiffen the magnets, thus improving reproducibility. FE Analyses: by V. Ravindranath

  20. Magnet Transportation - 1 FE Analyses: by V. Ravindranath Smax=0.36 MPa Smax=0.34 MPa Gravity Deformations Additional Plates – 27 mm Thick Gravity Stresses • Micro-fissures were discovered in the yokes of the 35 mm dipoles. • Under its self-weight the maximum normal tensile stress (Smax ) =0.36 Mpa. • Adding extra top and bottom plates were not effective. • The magnet feet are removed during transportation. • The maximum change in the pole gap, ~ 10 μm. ΔGap

  21. Magnet Transportation - 2 Smax=0.46 MPa Smax=0.14 MPa FE Analyses: by V. Ravindranath Lifting from Top Lugs Lifting from Bottom Lugs • Lifting the magnets from top lugs produced less stresses than the less-optimally placed bottom lugs. • Bottom lugs were subsequently removed.

  22. Team Work BINP Director’s Office Roller Machine at BINP BINP Workshop No. 8 Dipole Lamination Peeling-Off

  23. Acknowledgement Thanks to all magnet teams.

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