design of a support system for the vertical beam transfer ... · for the vertical beam transfer...
TRANSCRIPT
Design of a support system for the vertical beam transfer lines of the ELENA project
September 2016
Author: Kristiyan Bozhkov
Supervisors: Antti Juhani Kolehmainen Diego Perini
CERN Summer Student Report 2016
Page 1 of 15
Table of contents
1. Introduction .................................................................................................................................... 2
2. Support system requirements ....................................................................................................... 3
3. First design ...................................................................................................................................... 3
4. Simulation results for the first design ........................................................................................... 5
4.1 Deformation and stress results for the girder ....................................................................... 5
4.2 Deformation and stress results for the alignment table....................................................... 6
4.3 Static structural analysis of the vessels ................................................................................. 7
4.3.1 FE model ......................................................................................................................... 8
4.3.2 Overall deformation results ........................................................................................... 9
4.3.3 Mechanical properties of the quadrupole, the U-shaped plates and the pins ............ 9
4.3.4 Stress results ................................................................................................................. 10
5. Second design ............................................................................................................................... 12
6. Simulation results for the second design .................................................................................... 13
6.1 Overall deformation results ................................................................................................. 13
6.2 Stress results ......................................................................................................................... 13
7. Conclusion .................................................................................................................................... 15
8. References .................................................................................................................................... 15
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1. Introduction During my stay in CERN as a summer student I was introduced to work in the engineering department
and more precisely in the group of mechanical and materials engineering.
My work was in relation with the ELENA (Extra Low ENergy Anti-proton) project which is a new
accelerator currently being built inside the anti – proton decelerator. ELENA is an upgrade of the Anti-
proton Decelerator (AD) at CERN and is devoted to special experiments with physics using low energy
anti-protons. ELENA will increase the number of useful anti-protons by about two orders of magnitude
and will allow to serve up to four experiments, ATRAP, ALPHA, ASACUSA and AEGIS, simultaneously
with anti-protons of reduced energy from 5.3 MeV to 100 keV.
The reduction of the energy is carried out by small ring of circumference 30.4 m where the anti-
protons travel. Then they are sent through the beam lines to the experiments. The ring and the rest
of the beam lines can be seen in figure 1.
Most of the design for all supports and components for the horizontal lines is already done and
engineers and technicians are currently installing them for the first phase of ELENA, the ELENA ring.
My task during my stay in CERN was to create and design the support of the two vertical lines that are
going towards the ATRAP experiment. They are surrounded in red in figure 1 and better represented
(by zooming and hiding some of the parts) in figure 2.
Figure 1 – ELENA lines
Figure 2 – Vertical lines and quadrupole
Welded jaw
connectors
Measurement
equipment
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2. Support system requirements The support system must be able to carry the supported equipment on its place, with no change to its
position, during the life-time of the decelerator. The life-time is expected to be 20 years. The system
must be able to resist the gravitational load and the forces resulting from the pressure differences
between the atmospheric pressure and the Ultra High Vacuum inside the equipment.
The support system must allow the equipment to be aligned within ±0.2 mm with respect to the
theoretical beam line. The support for the two vertical beam lines can be the same.
The support system must allow the thermal expansion resulting from the bake-out (heating the
equipment up to 250 °C on the internal surfaces) to occur without any damages to the equipment or
to the support system. When temperature returns to ambient, around 20 °C, the equipment must
return to its original position.
No fixation of the support system might be placed on the roof or on the walls of the tunnel hosting
the beam line. When looking downstream on the beam line, the right-hand-side of the beam line must
be left free for passage.
3. First design The design of the supports for the horizontal lines was also introduced to the vertical lines. The system
and its functioning is represented in figure 3. The quadrupoles and the secondary emittance monitor
between them are hidden to better represent the support.
fixed point
Boundary conditions Figure 3 – Support tables
Pins
4 anti-buckling
columns
6 screw supports
4 U-shaped support plates
8 M16x40 bolts fixing the
base plate to the girder
4 M16x137 threaded rods
4 Hex screws M8x60
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The ELENA quadrupoles represent a vacuum vessel supported by four jaw connectors. The connectors
are welded together with the vessel using fillet welds placed on the upper and lower extremity of each
jaw. The jaw connectors are screwed to the U-shaped support plates designed to allow for an elastic
deformation. The support plates can slide on the foot plate thanks to seven-spring bolts and permit
the longitudinal and transversal expansion of the tanks during the bake-out (thermal expansion). Two
additional connectors for supporting the measurement equipment are welded on the other side of
the vessel. The model with component description is shown in Figure 2.
The foot plate, which acts as a common base plate for the two quadrupoles and the SEM, is aligned
on the alignment table thanks to the 6 screw supports and then fixed to it with 4 hex screws
represented in figure 3. Four pins were added to the top “U” shaped plate which allow to avoid the
eventual rotation due to the force coming from the difference of the pressure inside and outside the
vessel, and resulting in axial force in the assembly.
The design of the girder to which the base plate of the alignment table is attached is represented in
figure 4.
Two reinforcement plates are added to each side for more security. The profiles and the reinforcement
plates are screwed to the support as shown on figure 4 (view from below). The safety screw support
is added as an extra security for the base plate attached to the girder.
2 reinforcement
plates
Concrete
2670 mm
Safety screw
support
Figure 4 - Girder
2 profiles 80x240x2670
3 profiles 80x240x170
Support plate
Support plate – view from below
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4. Simulation results for the first design In order to start the simulation, calculation of the different forces was established as shown in figure 5.
4.1 Deformation and stress results for the girder For every simulation a simplified assembly was first created. A remote force of 2100 N (1050 N if
symmetry) was applied on the theoretical axis of the beam lines. Symmetry was also applied to reduce
the simulation time. Results of the simulation of the girder are shown on figure 6.
Figure 5 – Calculation of the applied force
Figure 6 – Simulation results for the girder
Worst case during maintenance
Normal operation
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The stress and the deformation on the girder are significantly small and therefore acceptable, and the
design can be approved. The material is aluminium EN AW 6063 T66 with R0.2% = 200 MPa [1]
4.2 Deformation and stress results for the alignment table For the simplified assembly a small bloc was created to which the base plates were attached. The bloc
is fixed and again a remote force of 2100 N was applied on the axis of the beam lines. Firstly, the plates
were designed to have three rods so the system can be isostatic, thus easier to align. Results for this
design are shown in figure 7.
Top 2 threaded rods
Bottom 2 threaded rods
Figure 7 – Simulation results for the base plates with 3 rods
Figure 8 – Simulation results for the base plates with 4 rods
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On figure 8 are shown the results for the design with 4 rods. The highest stress values 271 MPa and
211 MPa on the bottom threaded rods are due to the edge where the anti-buckling column and the
threaded rod are connected. These values could be a numerical error because a refinement was done
on this particular area and they became bigger. Moreover, each value was applied on one particular
element. For an extra – security the design with 4 threaded rods will be accepted even if the system
will then become hyperstatic.
A small calculation was done to calculate the actual stress on one rod. The following formula was used:
𝜎 =M. e
𝐼𝑦𝑦=
𝐹. 𝑙. 𝑒𝜋
64𝑑4
= 95 𝑀𝑃𝑎
The plates and the anti – buckling columns are made of aluminium EN AW-6082 (T6) and the treaded
rods - stainless steel 316 1.4401. Linear elastic isotropic models of the two materials were
implemented within ANSYS. Mechanical properties only for the stainless steel are shown on table 1
since all the stress is applied on the threaded rods.
Material: Stainless Steel 316 1.4401 [1]
Temperature
20 °C
Poisson
ratio
Elastic
modulus Density Rp0.2 Rp1.0
Tensile
strength
Number - (GPa) (kg/m3) (MPa) (MPa) (MPa)
1.4401 0.29 193 7950 220 260 530-680
4.3 Static structural analysis of the vessels For this simulation an assembly with only the foot plate, the U-shaped supports, the pins and the
vessels was created. First, an atmospheric pressure of 0.1 MPa on the three vessels was applied.
The bolted joints between the U-shaped support plates and the jaw connectors were replaced by
bonded contacts. Exception makes the contact between the top U-shaped support and the top
connectors – it was replaced by “no separation”, to be able to evaluate the stress transmitted on the
pins. The contact between the pins and the support plate with the connector is also bonded.
The contacts between the U-shaped supporting plates and foot plate were considered as “no
separation” to allow a limited sliding. Again, exception makes the top supporting plate – the contact
is bonded because the supporting plate cannot slide the longitudinal direction (figure 3). Since the
other three U-shaped plates can slide the longitudinal direction, the boundary conditions were
considered as symmetric and symmetry was applied to simplify the model. The foot plate is considered
as fixed.
In order to model the welds between the jaw connectors and the vessels, face to face and edge to
face contacts were defined (figure 9). They restrain the relative rotation of the vessel around the weld
that simulate the real behaviour of the welds. The edge to face contacts are considered as bonded
and the face to face contacts as “frictional” with a coefficient of friction f = 0.7 (between stainless
steels [4]). The rest of the contacts between the components were generated automatically and set
as bonded.
F – Force on one rod =2100
4= 525 𝑁
𝑙 – length of the rod = 73 𝑚𝑚
𝑒 – Radius of the rod = 8 𝑚𝑚
𝐼𝑦𝑦 – moment of inertia with
Table 1 – Mechanical properties of St. steel 316 at 20 °C
Page 8 of 15
4.3.1 FE model In order to simplify the model and use advantageous shell elements, the internal surface of the tanks
was extracted and 3 mm thickness was assigned. A geometry cleaning was done to prepare the FE
model. Some simplifications were made. The unnecessary holes and non-essential components were
removed. The bolted joints between the support plates and welded connectors were replaced by the
bonded contacts between the faces.
The mesh for the quadrupoles (Figure 10) was generated with focus on the region with welded joints
between the vessels and the connectors. The most critical regions were refined to capture the stress
triggered by the vertical load of 2100 N on the centre axis of the vessels. The top U-shaped plate was
also refined because it’s fixed and therefore it triggers some stress.
no separation contact face to face contact -
frictional
edge to face contact -
bonded
Figure 9 – Contacts
U-shaped plates
3 mm
3 mm
3 mm
2 mm
0.5 mm
2 mm
1 mm
1 mm
15 mm
Figure 10 – Meshed equipment with refinement
Sym
met
ry
Page 9 of 15
4.3.2 Overall deformation results A maximum deformation of 0.65 mm is obtained for the installation. As shown on figure 11 the
deformation is propagated through the whole assembly. Therefore, a conclusion can be drawn that
the equipment is rigid enough. During normal operation, a force of 270 N is applied (case 3). The
deformation is, as expected, smaller – 0.26 mm (figure 12). Before integrating the vertical equipment
this displacement should be first discussed with the equipment responsible.
4.3.3 Mechanical properties of the quadrupole, the U-shaped plates and the
pins All components of the quadrupole, including the jaw connectors, are made of the stainless steel
1.4429 (316LN), the U-shaped plates of stainless steel 1.4301 and the pins of hardened martensitic
stainless steel, grade C1, class 110. Linear elastic isotropic model of these materials was implemented
within ANSYS. The mechanical properties of these materials for 20˚C were needed in order to calculate
the stresses due to the vertical load of 2100 N.
Material: Stainless Steel 1.4429, 1.4301 and C1 110 [1] [3]
Temperature
20 °C
Poisson
ratio
Elastic
modulus Density Rp0.2 Rp1.0
Max
allowable
stress
Tensile
strength
Number - (GPa) (kg/m3) (MPa) (MPa) (MPa) (MPa)
1.4429 0.27 196 7950 280 320 213 550-700
1.4301 0.29 200 7900 230 260 173 540-750
C1 110 0.3 200 7850 820 - - 1100
Figure 11 – Total deformation –
case 1 – 2100 N
Table 2 – Mechanical properties of St. steel 1.4429 and 1.4301 at 20 °C
Figure 12 – Total deformation –
case 3 – 270 N
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4.3.4 Stress results
Figure 13 – Overall stress intensity
Figure 14 – Welded connector – back view
Figure 16 – Welded connector – front view Figure 17 – Stress intensity for the pins
Figure 15 – Stress intensity for the top vessel
Figure 18 – Stress intensity for the support plate
Page 11 of 15
The main stresses are concentrate on the top weld connector because it’s attached to the top U-
shaped plate which is fixed to the plate. The results for this connector are shown in figure 14 and 16.
Numerical singularities were observed as a result of the contacts that replace welds.
The stress on the support plate (figure 18) is distributed around the edge of the plate and there could
be some plasticization but it should not affect the whole installation. The peak values of the stress are
due to the edge effect, where the foot plate is connected, and do not affect the overall strength of
the structure.
High stress values were also found for the pins (figure 17) and on the holes where they are attached
to the connector (figure 16). To be able to calculate the actual stress on the pins a new simulation was
performed without the pins. A bonded surface was considered between the support plate and the
welded connector. By extracting the axial forces, the global force was then calculated as follows:
𝐹 = √𝐹𝑧2 + 𝐹𝑦
2 = 1138 𝑁
Stress results for the vessel where the connector is welded are shown in figure 15. The stress found
at the bottom left part of the vessel is a little bit higher than the elastic limit of this material – 280
MPa. Multiple simulations were done to check carefully the stress on the vessel and the welds of the
jaw connectors. A calculation of the stress on the welds was done by creating a coordinate system on
the weld (45° between the edge and the Y axis) and by extracting forces on every direction and
referring to the EN welding code [5]:
𝜎𝑤𝑒𝑙𝑑 = √𝜎┴2 + 3(𝜏┴
2 + 𝜏||2) ≈ 14,5 𝑀𝑃𝑎
During the thermal expansion, the temperature is rising up to 250 °C. The yield strength of the material
of the vessels (stainless steel 316LN 1.4429) is descending down to 155 MPa at that temperature. The
conclusion is that the obtained stress value is not a numerical singularity since it’s applied on multiple
elements as shown on figure 15. Some plasticization can arise on the vessel in this particular area. The
welds will sustain the load on the equipment but since the structure is twisting they may penetrate
the vessel and small fractures or fissures can occur.
The welds were therefore seen as a risky part to support the vessels. A supporting was planned to be
connected to a part robust enough itself to resist the load – the uppermost flange. The final decision
was to create a new design which will replace the top U – shaped support plate fixed to the foot
plate.
Material: Stainless Steel 1.4429 [1]
Temperature
250 °C
Poisson
ratio
Elastic
modulus Density Rp0.2 Rp1.0
Max
allowable
stress
Tensile
strength
Number - (GPa) (kg/m3) (MPa) (MPa) (MPa) (MPa)
1.4429 0.27 196 7950 155 183 122 -
and thus the shear stress also: 𝜏 =𝐹
𝑆𝑝𝑖𝑛= 58 𝑀𝑃𝑎
Table 3 – Mechanical properties of St. steel 1.4429 at 250 °C
Figure 19 –
Coordinating
system on
the weld
Page 12 of 15
5. Second design The second design consisted on creating a more rigid support than the U-shaped support plate. For
this purpose two brackets were created and positioned under the uppermost flange (figures 20 and
21). They were fixed to the foot plate using two supporting plates and one connecting the two
brackets. The holes created on the brackets allow the bolts and the washers, used to close the vacuum
flanges together, to be inserted. The brackets are fixed to the jaw connectors via small plate and three
M8 bolts.
Support
plates
Small plate
Connecting plate
Brackets
Pins
Spring
washers stack
Vertical
M8 bolt
Touching
top surface
Figure 20 – Brackets under flange
Figure 21 – Brackets
Figure 22 – Pins and washers
Four pins were also added (figure 22) to the sides of the brackets. Beside them, a spring washer
stack is placed and then tightened with M10 bolts. During the thermal expansion of the vessel, the
pins will retreat and they will return back when the temperature decrease. Two vertical M8 bolts
(figure 22) are screwed to each side through the bracket and tightened till the top surface of the
top jaw connector. The goal is that when a vertical load of 315 N is applied upwards during
maintenance (case 2 – figure 5) the bolt will transfer the vertical load to the bracket and thus to
the connection bracket – flange.
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6. Simulation results for the second design The same mesh was used again. A refinement was done on the new brackets as well on the small
plates connecting the brackets with the top jaw connectors. All bolted joints were replaced again with
bonded contacts. A “no separation” contact was applied between the bracket and the flange.
6.1 Overall deformation results The deformation obtained for the new design is no more than 0.2 mm for both of the cases as shown
on figures 23 and 24. This deformation is due to the atmospheric pressure applied on the vessels.
There is almost no deformation coming from the vertical load (2100 N or 270 N) applied on the
equipment which means that the installation is robust and rigid.
6.2 Stress results The stress is almost equally distributed through the whole assembly. Some numerical singularities
were found again on the welds of the connectors (figure 27). The stress on the vessel was carefully
checked (figure 26) and the highest value found is 95 MPa due to the atmospheric pressure as there
is vacuum inside the quadrupoles. This stress is fully acceptable as the elastic limit of the material is
280 MPa (table 2).
The stress for the small plate, the support plate and the bracket was also checked (figures 28, 29 and
30). The material of these parts is the same as for the U-shaped support plates – stainless steel 1.4301
(table 2). The biggest stress found – 73 MPa, is again completely acceptable.
The final conclusion is that the second design is reliable and acceptable with stresses no bigger than
95 MPa which leaves a large margin of safety factor – 𝑆𝐹 =𝐸𝐿
95≈ 3 for 20 °C and 𝑆𝐹 =
𝐸𝐿
95≈ 1.6 for
250 °C.
Figure 23 – Overall deformation – second
design – worst case - 2100 N
Figure 24 – Overall deformation – second
design – normal operation - 270 N
Page 14 of 15
Figure 29 – Stress – support plate
Figure 26 – Stress on the vessels
Figure 27 – Stress – welded connector
Figure 25 – Overall stress intensity – second design
Figure 28 – Stress – small plate
Figure 30 – Stress – bracket
Page 15 of 15
7. Conclusion The simulations showed that the stress intensity for the quadrupoles and other parts of the second
design during the vertical load of 2100 N is acceptable. The simulations for the other two cases of the
vertical load don’t have significant difference.
The final conclusion is that the second design is reliable but maybe too complicated to be integrated.
Still some design upgrades can be done but the main idea of putting a more rigid support instead of a
U-shaped plate can be approved. Since the interface plate, placed between the top flange and the
sector valve is not yet designed, fixing the support on this part could be a good idea.
I would like to express my gratitude to my supervisors and the design and simulation office, to the
help they provided to me during my internship in the group MME.
I would like to thank also the summer student team for all the effort and good organization making
the summer student program an interesting event.
I also acknowledge all the lecturers and professors for these six weeks of interesting lectures that they
provided to the summer students.
I thank also all the summer students for making this stay a truly valuable experience.
Throughout these months I have gained highly appreciated experience in the designing and simulation
field by strengthening my knowledges in CATIA V5 and ANSYS programs.
8. References [1] https://www.rk-rose-krieger.com/fileadmin/catalogue/profiltechnik/bl_aluprofilsystem_en.pdf - page 470,
appendix
[2] EN 10088-2, Stainless steels. Part 2: Technical delivery conditions for sheet/plate and strip of corrosion
resisting steels for general purposes. September 2005 – Tables 10 and 15.
[3] ISO 3506-1, Mechanical properties of corrosion resistant stainless-steel fasteners – Table 3.
[4] Website http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm#coefficients
[5] Website http://www.mitcalc.com/doc/welding/help/en/welding.htm