MODIFICATION
66 -- DESIGN AND FABRICATE VACUUM CHAMBER
- Notice Date
- 9/16/2003
- Notice Type
- Modification
- Contracting Office
- NASA/Langley Research Center, Mail Stop 144, Industry Assistance Office, Hampton, VA 23681-0001
- ZIP Code
- 23681-0001
- Solicitation Number
- 1-LAH-23044
- Response Due
- 9/23/2003
- Archive Date
- 9/16/2004
- Point of Contact
- Marie W. Hamann, Contract Specialist, Phone (757) 864-2258, Fax (757) 864-7709, Email Marie.W.Hamann@nasa.gov - Lionel E Nadeau, Contract Specialist, Phone (757) 864-2434, Fax (757) 864-8863, Email Lionel.E.Nadeau@nasa.gov
- E-Mail Address
-
Email your questions to Marie W. Hamann
(Marie.W.Hamann@nasa.gov)
- Description
- THIS NOTICE CONSTITUTES AMENDMENT NO. 1 TO THE COMBINED SYNOPSIS/RFQ FOR Design and Fabricate Vacuum Chamber. Companies shall acknowledge all amendment(s) in their quote. This notice serves as the official amendment to subject synopsis/RFQ and a written amendment will not be issued. The purpose of this amendment is to post questions and answers and to extend the response date to 9/23/03. The due date for receipt of offers is extended to 9/23/2003. 1. The choice of materials is described as Alu or SS which are supposed to be non-magnetic (2.3). As SS contains substantial amounts of Fe still, it has a residual magnetic property of 1.01 at least. Aluminum is non-magnetic. If that is what they need, the choice of material is going to be Alu. Magnetic properties of 300-series stainless steels are acceptable. Material selection between aluminum and stainless steel should be based on lower weight and structural performance, not non-magnetic properties. 2. We have discussed stiffener ribs while at the same time keeping the weight under 800lbs while at the same time trying to accomodate the fixture holes (2.14). That is difficult to say the least. But we can accomplish all of the above by going to a fairly thick material Alu. The deflection then is about 2 mm in a worst case scenario in the center of any given plane. Please verify if that is alright with them. Maximum deflection of 0.075 inches (1.9 mm) on all six walls is acceptable. 3. If the chamber needs to be made from Aluminum (as concluded above) we have to use either surface hardened aluminum CF flanges or stainless flanges with aluminum weld-neck. Both are pricey. If non-magnetism is an issue, the all-aluminum flanges should be used. Then however life expectancy of the knife edge is an issue as it rolls-over after 5-10 uses. But as indicated, they are willing to use Viton seals. If they are however, and as we are using lots of O-rings anyhow, the ISO flange standard may be a better choice. These can be made from Alu without a problem while sealing well and repetitively. Cost reductions will amount to a few thousand Dollars. Please advise Magnetic properties of stainless steel CF flanges is not a problem. All equipment except for the windows have already been purchased with CF flange design, so ISO flange standard is not an option. 4. Just a comment: In drawing "Aft Vac Chamber Wall", there is a DN 50 (3.38") CF flange designated. We advise against using this flange diameter as there are discussions about phasing out this one from the standard. If there is an application tied to that, that may be a different matter. But if there is choice..... The equipment to attach to this specific CF flange has already been purchased in the flange size shown. 5. What bakeout temp do they request for certification ? Bakeout should be performed at 250 degrees F to remove adsorbed water molecules. 6. Is the chamber heated during the process ? What are the operating temps ? The chamber will only be indirectly heated by the process being conducted within it. The equipment to be installed within the chamber has an operating temperature not to exceed 200 degrees F, so the chamber will not exceed this temperature. The process will not be run continuously, so internal temperatures are expected to remain well below 200 degrees F on a routine basis. 7. How often do they remove the top cover ? ( We would suggest bolted closure, as they keep the sides "cleaner" in terms of design and generally provide a better seal. They are also allowing us to maximize the opening of the top. ) The top cover will only be removed for permanent installation of the positioning system into the bottom of the chamber, and for any maintenance that cannot be accomplished through the side doors. A bolted closure for the top is acceptable. The requirement for a removeable top may be eliminated from the specifications provided that the two side access doors are designed to allow for installation of the positioning system. The positioning system measures 32.3 inches (in the fore-aft direction on the sketches) by 27.4 inches (in the right-left direction on the sketches) by 21.6 inches in height, and weighs approximately 100 lbs. The side access doors shall still be hinged and interchangeable. 8. Yesterday, we have talked about the door frames being "outside" of the chamber, in order to maximize the door opening. Today we have stumbled accross the "24 x 24 or better" remark in the word doc (2.7) while at the same time calling for a maximum opening in the top (2.6). My comment yesterday did not take that in account. In this case, the door frames will have to be "internal" and the top cover frame external. See answer to previous question. My engineer has reviewed your specifications and has informed me that the chamber cannot be build to the specifications. It you design the chamber to the safety factor of 2 based on material yeild strengh that the weight will be more like 2000 lbs. Material selection between aluminum and stainless steel should be based on lower weight and structural performance. Factors of safety of less than 2 shall be specified. Most chambers designed today are based on a maximum deflection rate of between .050" to .100" in order for the chamber to handle the 14.7 lbs per square inch pressure pushing on the outside of the chamber. If you do not use enough material to handle this load, then the welds will start to crack over time. This chamber may see a duty cycle of 3 vacuation/repressurizations per day, on average. The chamber should be designed to avoid weld cracking due to this cyclic pressurization. Maximum deflection of 0.075 inches (1.9 mm) on all six walls is acceptable. 9. As the chamber is intended to be portable, and as light as possible, but at the same time, minimally deflected under vacuum, we would like to know if the user has a maximum deflection value in mind, and if it is the same for all sides. Maximum deflection of 0.075 inches (1.9 mm) on all six walls is acceptable. 10. A related issue to making it light is stiffeners. Normally, on a box this size, we would not rely on wall thickness for strength, but rather on external stiffening elements (beams). Are there locations (other than at the actual flanges) where such beams would interfere with external equipment? No. 11. Another related issue is the internal support for hardware. These are shown as blind-tapped holes in the inside walls of the chamber, minimally 3/8 or 1/2" deep. This impacts minimum wall thickness, and points toward excessive total weight. We would like to suggest that these mounts be, instead, small, thick plates that are welded to the chamber surfaces. The mounting surfaces would then move inboard by a corresponding amount, which either would or would not be a problem for the user. Opinion? Small thick plates welded to the chamber surfaces for mounting purposes are acceptable, provided that the plates do not exceed 1 inch in height for the top mounted hardware (wire feeder), and provided that the height of the chamber be adjusted to the thickness of the plates added to the bottom of the chamber (for the positioning system). The positioning system mounted to the bottom of the chamber drives the height of the chamber, so if that has been raised within the chamber, the distance top of the chamber needs to be compensated accordingly. The wire feeder at the top of the chamber does not require any compensation for the overall chamber height. 12. The doors. As described, the doors are minimally 24x24, but the viewport locations on the drawings require at least 30 3/4" in one dimension, which amounts to the full dimension of the chamber side. Since both doors are to be interchangeable, the minimum door size is, perhaps, 31x24. This causes some severe structural problems in trying to make a lightweight box, as there is no available flange space unless the door flanges protrude above the top and bottom, or the box itself is somewhat larger. Then, of course, there is a problem with a full-opening top. If operational access to the chamber can be made exclusively by using the doors, we might propose eliminating the removable top from the spec. In fact, if we knew the maximum dimension of objects and hardware that had to transfer in and out, or be installed, we could propose a significantly different basic design. The requirement for a removeable top may be eliminated from the specifications provided that the two side access doors are designed to allow for installation of the positioning system. The positioning system measures 32.3 inches (in the fore-aft direction on the sketches) by 27.4 inches (in the right-left direction on the sketches) by 21.6 inches in height, and weighs approximately 100 lbs. The side access doors shall still be hinged and interchangeable. 13. Weld certification. This is normally not supplied on non-pressure vessels. Leak test data is taken to be sufficient. Can we drop the former? No. Weld inspection and certification is still required. 14. Non-magnetic construction. Note 2.13 shows concern about magnetic thread inserts. Concern for such tiny fields is somewhat unusual in an e-beam tool operating at x-ray producing voltages. If we correctly remember a possibly related prior solicitation for the e-beam hardware, we understand that this is a high resolution, high positional accuracy application, that may, indeed have unusual requirements on residual fields. If this is the case, we may need to suggest more exotic methods of construction, and materials. We have some experience with this, but need to know if there is a field specification, roughly at or below the Earth's own field. The user may also need to consider the effects of nearby equipment, such as the attached pump. Magnetic properties of stainless steel anywhere in the chamber, including threaded inserts and CF flanges, are not anticipated to cause problems with interference with magnetically steering the beam. 15. The solicitation restricts chamber weight to 800 pounds (ref paragraph 2.5). In the statement of work, there is reference to tapped holes in the chamber wall. Size preferred 1/4-20 x 1/2" deep. This requires a chamber wall thickness in excess of 1/2". Weight of a chamber of 1/2" exceeds the required weight. If one were to opt for the alternate 6-32 x 3/8 deep, that would require a 1/2" wall thickness also (reference paragraph 2.14). Is the 800 pound requirement realistic? Note also that the handholds specified for carrying the chamber (paragraph 2.10)imply that it will be manually carried. Is that requirement realistic? Location of tapped holes is flexible to allow for aligning with stiffeners. This would permit using a thinner minimum wall thickness thereby lowering overall weight. The system may be manually moved on casters, thus handholds are requested for ease of positioning. 16. To achieve the required weight, it may be necessary to use non-flat sections for the doors. Would it be acceptable to have the viewports on short tubes, only long enough to allow the use of the non-flat sections. This approach would be acceptable. Viewport tube length should be minimized to allow maximum visibility into the interior of the chamber. 17. There is a bracket that is shown on the top cover. It seems to be very close to the inside chamber wall. If the top is to be removable, the chamber will have to be made up to 3" larger to accommodate it. That makes the chamber larger and hence heavier. Can the bracket be redesigned? The bracket can be redesigned if necessary. Provisions are still required to allow for hard mounting this hardware (a wire feeder) to the top of the chamber near the corner as shown in the sketches provided. Please answer the following questions: 17. Are the dimensions shown on the PDF file inside chamber dimensions only? Yes. 18. If yes, can there be structure intruding into the inside of the chamber? Yes. Structure may intrude into the inside of the chamber on the four side walls and to the top of the chamber, provided that the structure does not exceed 1 inch in height for the four side walls or the top, and provided that the height of the chamber be adjusted to the thickness of the structure added to the bottom of the chamber (for the positioning system). The positioning system mounted to the bottom of the chamber drives the height of the chamber, so if that has been raised within the chamber, the distance top of the chamber needs to be compensated accordingly. The design has attempted to minimize the chamber size as tightly yet allows installation of the positioning system within the chamber. The positioning system measures 32.3 inches (in the fore-aft direction on the sketches) by 27.4 inches (in the right-left direction on the sketches) by 21.6 inches in height, and weighs approximately 100 lbs.
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