2x8.4m TELESCOPE
July 31, 1997
|
LBT PROJECT 2x8.4m TELESCOPE |
|
July 31, 1997 | ||
INDEX:
0 - INTRODUCTION.
1 - SUPPLY DESCRIPTION.
2 - LIST OF ENCLOSED DRAWINGS.
3 - ACCEPTANCE TESTS.
4 - DELIVERY.
The present specification covers the detail design, construction, machining, vacuum testing, partial mechanical integration, and preparation for delivery to the pre-erection workshop of the two mirror cells (M1 Cells) for the two 8,4 m primary mirrors of the LBT telescope.
The LBT telescope has been designed with the concept of performing the aluminizing of the primary mirrors on board the Elevation Mount, using thus the mirror cell as the closing structure of the aluminizing equipment, positioning on top of it the upper bell jar complete with the cryo-pumps and aluminizing hardware. The complete operation shall be done with the mirror in vertical position, i.e. with the telescope horizon pointing.
Completed the vacuum acceptance test, the cells shall be transported to the telescope preassembly shop and assembled on the telescope including suitably designed dummies of the M1 and the Cassegrain instruments (having mass and centre of gravity equivalent both to the instrument and the electromechanical accessories for the M1 support), so that to equilibrate the EL Mount in the final working conditions. For this purpose the dummies shall be designed to be fixed and supported using some of the existing bores for the final equipment.
The LBT Project includes also the construction of one Dummy Cell, because the construction schedule of the second mirror and its integration in the cell. This schedule predicts the completion of the second mirror later than the first light of the telescope equipped with the first mirror. As described in the Technical Specification N. 401a009/C, the Dummy Cell shall be identical in structural stiffness, mass and centre of gravity to the M1 cells of the present specification, of course including also the possibility of being completed with the dummy of the M1, the dummy of the instruments and all the mechanical and electric control auxiliaries.
1.1 - Shop Drawings, planning and technical documentation.
This is the first activity to be performed by the Manufacturer and shall be performed according what specified in the "Statement of Work", attachment A of the RFP
1.2 - Structural requirements and Surfaces protection.
Construction of the steel structure consisting of plates and profiles of standard structural steel Fe 420 quality, welded with the proper procedures and accuracy to generate the minimum deformations of the M1 cell shape and to obtain a vacuum tight assembly. Before machining, the structure must be stress relieved with normal thermal treatments or, not being available sufficiently large furnaces, with mechanical vibration systems.
The most constraining requirements of the cells structure are the geometrical accuracy for obtaining the machining of all the flanges within the demanded dimensions and tolerances, respecting at the same time the design thickness of all parts; at the same time the positioning of all the reinforcing ribs and beams of the top plate must be sufficiently accurate to create no interference problems with the force actuators supporting the M1, having a very small design clearance.
For the above reasons, we recommend to evaluate carefully the possibility of making tests and gain of experience in building and machining the dummy cell before starting the present ones, being the only way to verify, with some sample bores and a suitable template of the actuators, the ability of matching the structural tolerances(that for some actuators are smaller than 10 mm).
It is mandatory for the Manufacturer specifying in the offer the construction procedure foreseen, specially the number of heat or vibration treatments to be carried on between the pre-machining and the final one, if any shall be foreseen.
Another series of pieces of structure that must be positioned within tolerance (±1 mm), are the interface plates with the relevant bolts holes between the M1 cell bottom and the Elevation structure (rolling sector inside and diagonal outside), as quoted on the interface drawing 721a011/D .
Surfaces protection cycle. As during the M1 aluminizing the inside of the cell is exposed to 10-2 Torr vacuum, the suggested cycle is as follows:
a) - assemble and weld the structure. To be decided by the Manufacturer
if with intermediate steps of heat treatments and pre-machining or
with one only step.
b) - Final stress relieving treatment.
c) - Machining of all flanges, surfaces and holes.
d) - Protection of all the machined surfaces for the following sand blasting
and painting.
e) - Near-white metal blast cleaning according with the Steel Structure
Painting Council Specification SP-10, or SA 2.5 ISO 8501 -
1:1988/SS055900:1988
f) - Apply Bostik Finch Cat - a - Lac 463-6-5, or approved equal, as a
primer, 100 µ thickness.
g) -After the completion of the vacuum tests and the integration of the
Cassegrain bearings and driving units, apply a top coat of Bostik
Finch Cat - a - Lac 463-3-100, CA-118, or approved equal, in
accordance with manufacturer's recommendations for surfaces to be
exposed to vacuum, 125 µ thickness.
h) - For all the external surfaces, being the same the cycle but not having
the exposure to vacuum, the manufacturer shall submit the type of
paint agreed with the Supplier, taking into account that the
demanded functional requirements are 25 years service life (two
months continuous salt exposure during shipping).
1.3 - Machining and Transport requirements.
1.3.1. - Machining requirements. See DWG. 721a001/D -
Top Plate detail, General view.
After having considered the machining problems for the flanges and the top plate, that means a lathe with the rotating table able to accommodate a piece of about 9,5m diameter, one has to position the cell on a Numerically Controlled milling machine or an equivalent gantry and execute the boring and milling operations on the top plate concerning the fixation of all the supports for the mirror and its ventilation system.
The most complex problem is the one concerning the milling of the planes for the hard points fixed base and the boring of their reference pins, because these are located inside the cell plenum, under the top plate and their vertical distance and radial position must be in tolerance with the machined top plate surface and flanges centre.
As indicated on the dwg. 721a007/A, we have foreseen the possibility of cutting the necessary holes to allow the milling and boring operations of the inside supports surfaces after the top plate flat machining on the lathe; completed the operation, the openings previously made must be closed by welding suitable plates and further locally grinding, so to restore the initial surface.
Completed the above operation, in the top plate must be executed all the bores and slots according the dimensions quoted on the dwg. 721a004/D, 721a006/A, 721a008/D, 721a009/C. We are speaking of about 3000 holes, a good part of which - the ones concerning the force actuators and the static mounts - are requested to be positioned with reference to the centre of the cell with a tolerance lower than 0,5 mm from the nominal value, so it is necessary that the machining is done on a Numerically Controlled machine in one only positioning; if necessary to reposition one time the cell because of the maximum travel of one axis of the machine, it shall be granted safe machined alignment references to reposition the piece.
All the small tapered holes for the fixation of the static supports and the jet ejectors can be drilled separately with a template centred in each main hole; the holes for the bolts supporting the actuators boxes must be bored on the Numerically Controlled machine because they are the real reference for the actuators axis position and have no possibility of further adjustment.
All the external flanges for inspection, conditioning air inlet and electrical utilities must be carefully machined, bearing in mind that every opening shall be closed with a vacuum tight flange when preparing for the mirror aluminising.
As already mentioned in the dummy cell specification, it is important defining carefully machining procedure and achievable tolerances for the six lateral removable interface plates and consoles for the clamping of the bell jar.
1.3.2. - Transport -
For taking into account the needs of the transport of these large single pieces it has been included in their design the possibility of applying two lateral bearings to allow the rotation of the unit , presenting it in every angle between horizon and zenith, according to the road and trucks exigency. At the charge of the Manufacturer it is only demanded the construction and machining of the fixation flange for the bearing support.
1.4 - Supply Limits -
The Manufacturer shall receive, at the charge of the P.O., the two bearings supporting the derotator/instrument and the cable chain support structure, the driving units for the above groups along with the remote controlled locking devices for the rotator/instrument, as illustrated on the dwg. 674a005/B and 674a006/B.
At the charge of the Manufacturer is the supply of the gear and pinions driving the rotator/instrument and the pinion for the cable chain support, plus the flange for the fixation of the locking devices supporting the rotator/instrument; all these items shall be pre-erected and tested in rotation with the M1 cell in horizontal position.
The electronic equipment needed to drive the motors shall be supplied by the P.O.
Last items being part of the supply of the M1 cells are the temporary flanges for the vacuum test (one set for every cell complete with the relevant O-ring and fixation bolts), according the dwg.721a017A.
2 - LIST OF ENCLOSED DRAWINGS.
Dwg. 721a011/D - Interface between Cell and EL structure -
Dwg. 721a012/D - Mirror Cell - Assembly -
Dwg. 721a014/B - Mirror Cell - Detail Sect. GG -
Dwg. 721a015/B - Mirror Cell - Detail Sect. CC - DD - View N P Q R -
Dwg. 721a016/A - Mirror Cell - Detail Sect. EE - FF - HH -
Dwg. 721a001/D - Top Plate details - General view -
Dwg. 721a010/A - Top Plate details - Reinforcing ribs -
Dwg. 721a008/D - Top Plate details - Actuators drilling pattern -
Dwg. 721a007/A - Fixed points actuators support machining -
Dwg. 721a004/D - Top Plate details - Jet Ejectors drilling pattern -
Dwg. 721a006/A - Top Plate details - Static Mounts drilling pattern -
Dwg. 721a009/C - Top Plate details - Air Nozzles drilling pattern -
Dwg. 674a005/A - Support and Drives for Instruments and Rotators -
Dwg. 674a006/A - Details locking devices positioning -
Dwg. 674a008/A - Fixed support for adaptive optics -
Dwg. 674a009/A - Fixed support for adaptive optics - SECT. A - A -
Dwg. 721a017/A - M1 Cell structure - Details of vacuum flanges -
3 - ACCEPTANCE TESTS.
a) - Dimensional Test-
Every M1 cell shall be checked and dimensionally verified on the same numerically controlled milling machine where it shall be completed; at the same time, with a proper template supplied by the P.O., it shall be verified that all the force actuators shall be properly assembled in their machined position without interference with the top plate reinforcing ribs.
After the integration of the Gregorian bearings, gear and drives for the Gregorian Instruments/Rotators, it shall be carried on functional and dimensional tests with the locking devices assembled on their flanges.
b) - Vacuum leakage test -
Being intention of the P.O. to tender for the supply of the aluminising bell jar at the same time of the M1 cells construction, it will be possible performing, in the M1 cells Manufacturer workshop, the acceptance of each piece after a satisfactory vacuum test. The objectives of the tests are to determine that no external leaks exist at the level of 8x10-8 atmosphere per cubic centimetre/sec; and to verify that the entire volume can be evacuated to a pressure of 10-5 Torr with a 64000 liter/second diffusion pump (or equivalent).
Being the bell jar and the three M1 cells part of the same Request for Quotation, the Manufacturer shall specify in his offer if he has the necessary equipment and experience to perform the vacuum test, with the Representative of the P.O. only witnessing; in the opposite case shall be at the charge of the P.O. supplying the necessary equipment and organising the test, of course with all the necessary assistance of the Manufacturer.
4 - DELIVERY.
For the two M1 cell, complete of all the described accessories, it is demanded the delivery ex works, loaded on truck, ready for transport at the charge of the P.O. to the pre-erection workshop of the telescope.
Doc_info_start
Title:Technical Specification for M1 Cells Structure
Document Type: Technical Specification
Source:ADS Italia Srl
Issued by:W.Gallieni
Date_of_Issue:07-31-97
Revised by:W.Gallieni
Date_of_Revision:07-31-97
Checked by:W.Gallieni
Date_of_Check:07-31-97
Accepted by:
Date_of_Acceptance:
Released by:
Date_of_Release:
File Type:MS-WORD 6
Local Name:
Category:Telescope Azimuth Platform
Sub-Category:General Telescope
Assembly:Technical Documentation
Sub-Assembly:Technical Specification for M1 Cells Structure
Part Name:
CAN designation:401a015
Revision:G
Doc_info_end