| Acquisition Program: | PMS 415 - Littoral Warfare Weapon, ACAT III |
Objective: | Develop a low-permeability coating for nitrile rubber and nylon-reinforced nitrile rubber pressurized components. The coating must be pliable enough to conform to the shape of the nitrile rubber component as it expands/contracts due to fluctuations in differential pressure across the rubber. The coating must also withstand exposure to seawater for long periods (up to one year) and survive a minimum of 33 years.
| Description: | The TOMAHAWK Capsule Launching System (CLS) is being leveraged for integration of the Littoral Warfare Weapon (LWW) on SSGN and SSN 688I/Virginia Class Vertical Launch System capable platforms. The CLS includes a nylon-reinforced nitrile rubber fly-through cover. During stowage of the capsule in the submarine, the fly-through cover can be exposed to seawater. The fly-through cover must seal the capsule interior, which houses a missile, from the external environment. Since the nitrile rubber is permeable, and the humidity inside the capsule must be maintained below a specified threshold, a mylar-tin-mylar low permeability barrier must be installed over the nitrile rubber cover. These mylar-tin-mylar barriers are expensive, easily damaged, and present potential debris concerns after missile launch. A new low-permeability coating applied to the nitrile rubber would allow the fly-through cover to maintain the humidity within the capsule below required limits and eliminate the need for the mylar-tin-mylar barrier.
| | PHASE I: Identify an existing or develop a new coating for nitrile rubber that significantly decreases its permeability. Laboratory testing to demonstrate and quantify the permeability reduction will be required. Material testing to demonstrate the durability of the coating when the nitrile rubber is expanded/contracted and to quantify the amount of expansion that can be attained without damage to the coating will also be required.
| | PHASE II: Develop a process for applying the coating identified/developed during Phase I to the TOMAHAWK CLS nylon-reinforced nitrile rubber fly-through cover. Apply the coating to a small number of CLS fly-through covers. Conduct pressure cycling on the fly-through covers to demonstrate coating pliability and durability. Conduct permeability testing on the fly-through cover material with and without the coating to quantify the permeability reduction, both before and after pressure testing. Conduct testing of the coating to determine its longevity in a seawater environment.
| | PHASE III: Support integration of the developed coating into the TOMAHAWK CLS fly-through cover development for Littoral Warfare Weapon application. This coating, upon meeting Navy requirements, could also be transitioned into various other programs (i.e.: encapsulated UAVs) that require nitrile rubber membranes with low permeability.
PRIVATE SECTOR COMMERCIAL POTENTIAL/
| | DUAL-USE APPLICATIONS: The low permeability coating would be available for numerous commercial applications for which nitrile rubber (and potentially other elastomers) are not currently suitable due to their permeability. Examples include packaging materials and pressure vessels.
| References: | 1. Joint Cruise Missiles Project, Capsule Closure Assembly, Rev H, Drawing No. JCM-14051
| | Keywords: | Low permeability; Coating; Pliable; Nitrile rubber; Nylon; Fly-through cover |
Questions and Answers: |
Q: 1. Can you provide the nitrile rubber manufacturer(s) and/or grade used in the capsule launching system (CLS)?
2. What species (e.g. water vapor, oxygen, etc) is the mylar/tin/mylar barrier attempting to keep out of the CLS?
3. For the species in Q2, what are the required permeability rates? At what temperatures?
4. What strain (% elongation) is required for the CLS barrier coating?
5. Any there any relevant MIL-SPECS, drawings, etc. that you can provide?
6. For each of the following coating requirements, do you have any specifications? If so, please provide them.
- Thickness
- Temperature
- Pressure
- Chemical Resistance
- Mechanical Properties (tensile, elongation)
- Adhesion to Nitrile Rubber
- Abrasion Resistance
- Dielectric Properties
- Lifetime
7. Of those requirements listed in Q6, which one(s) are the most important and why?
8. Are there any requirements that were not listed in Q6 that should have been? |
A: 1. Nitrile Rubber IAW MIL-R-6855, CL I, Grade 60; Nylon Fabric IAW
MIL-C-20696, Type II. For additional information, see reference material
which should be posted to the SBIR website.
2. Water and water vapor.
3. Current MTM barrier is tested IAW ASTM F 372 @ 100 +/- 5 deg F, 95 +/-
5% humidity. 10 samples mean NTE 0.005 US Perms. No single specimen to
exceed 0.010 US Perms. Understand this is a tall order for non-metalic, se
we'd be interested to know how well the proposed solution would perform.
4. A conservative estimate of 25% biaxial elongation near the apex of the
seal assembly is provided. Characterization of the maximum strain that can
be attained by the coated seal assembly without damage to the coating is
required.
5. See reference material which should be posted to the SBIR website.
6.
Thickness - Not to adversely affect fly through cover (CCA) performance.
Temperature - Operational: 28 to 97 deg F; Storage/Stowage: -30 F to 120
deg F
Pressure - Operational Pressure Cycles: 80 cycles between 0 and 80 psid
(external); 80 cycles between 0 and 12 psid (internal); The seal assembly
is pressurized to 120 + 5.0 / - 0.0 psid (external to internal water
pressure for 10 minutes w/o damage), 18 + 1.0 / -0.0 psid (internal to
external air pressure for 10 minutes w/o damage) and 7.2 +/- 0.5 psid
(internal to external air pressure for 10 minutes w/o leakage) during
factory acceptance testing.
Chemical Resistance - Must be resistant to isopropyl alcohol and cleaning
solvents conforming to MIL-D-16791 and MIL-PRF-680 as well as lubricants
conforming to SAE-AMS-G-4343, SAE-AS8660, MIL-PRF-27617 Type III and
DOD-L-25681.
Mechanical Properties (tensile, elongation) - Not available.
Adhesion to Nitrile Rubber - Coating material must not produce loose
fragments during missile launch induced rupture.
Abrasion Resistance - Material must be resistant to accidental impacts
with hand tools or other objects as well as salt deposits, corroded
material or sediment.
Dielectric Properties - Not available
Lifetime - Service Life: 16 yrs minimum, 33 year goal with Seawater
Immersion:74 mo lifetime exposure.
7. They are all important.
8. Not to my knowledge.
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Q: Metal should provide essentially a perfect permeation barrier. Therefore, I believe that the water permeation through the present Mylar/tin/mylar cover is primarily due to edge leakage. Do you have any data relating permeation to temperature at several temperatures, for a single specimen? In principle, this would allow permeation to be differentiated from leakage, because of the different behavior in re temperature change. |
A: 1. We do not that type of data.
|
Q: 1. Can you post a drawing of the part? You have referenced "Joint Cruise Missiles Project, Capsule Closure Assembly, Rev H, Drawing No. JCM-14051" but I have no way to access this drawing.
2. From answers to various questions herein, I surmise that the existing cover is bonded to the NBR base. Does the existing cover extend around the bead, and if so, how is a seal formed between the (presumably metalic mount) and the mylar/tin/mylar coated fly through cover in the vicinity of the bead?
3. Is the existing cover capable of surviving the program of inflation/deflation tests that you mentioned above? |
A: 1. There is a white paper posted to the SITIS website in lieu of the
drawing referenced in the topic.
2. Please see the white paper reference.
3. Yes.
|
Q: 1. I did not understand your answer: "The seal assembly is pressurized to 120 + 5.0 / - 0.0 psid (external to internal sea water pressure for 10 minutes w/o damage), 18 + 1.0 / -0.0 psid (internal to external air pressure for 10 minutes w/o damage) and 7.2 +/- 0.5 psid (internal to external air pressure for 10 minutes w/o leakage) during factory acceptance testing. Operationally, 80 cycles between 0 and 80 psid (external seawater) and 80 cycles between 0 and 12 psid (internal air)"
Please define internal versus external pressure. It is not clear because I believe there is an outer steel hatch in addition to the fly-through cover. What I mean is differential pressure across the fly-through barrier; if I understood correctly, the maximum pressure differential accross the cover is 120 psi, but it is also tested at much lower pressures, which makes no sense to me.
2. You estimate that the maximum biaxial strain is arroubd 25% at the apex. This is a LOT higher than I would guess, based on the fact that the inflation pressure load is carried by high modulus nylon fibers. I would have expected that biaxial strain on the outer surface of the fly-through cover would be comparable to a truck tire, less than 5%. Can you check this? |
A: 1. The reference material posted to the website should clarify.
2. 25% is a conservative estimate for which we would like to have the coating stay attached to the nitrile part without separation.
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Q: 1. What is the damage problem with current mylar-tin-mylar, is it too brittle, inflexible, easy to tear?
2. Is a coating that includes metalized polymer onto nitrile rubber acceptable?
3. What are the cost metrics for the coating? |
A: 1. The MTM barrier is easily damaged during normal handling and operation. In addition, the missile ruptures the nitrile diaphragm and MTM barrier during ejection from the tube. During this event, the MTM barrier has a potential to become debris and could foul a missile tube hatch seating surface. This condition is undesirable.
2. Metalized polymer is not restricted from use.
3. We do not have any cost metrics for the coating at this time.
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Q: 1. I assume the flexure at the surface of the NBR is biaxial. What is the maximum flexure seen in service?
2. How many strain/release cycles must the part survive? |
A: 1. A conservative estimate of 25% biaxial elongation near the apex of the seal assembly is provided. Characterization of the maximum strain that can be attained by the coated seal assembly without damage to the coating is required.
2. Approximately 165.
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Q: 1. What is the total surface area of the fly-through cover which is exposed to sea water?
2. How long does a non-coated cover maintain adequately low humidity in the missile enclosure? |
A: 1. Approximately 900 square inches.
2. This has not been determined. Exposure of the cover to seawater results in significant swelling, which degrades the functional performance of the cover.
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Q: 1. What method do you use to assess the durability (>33 year required)?
2. Is moisture permaebility the critical issue? Do you requires reduction in oxygen permeability also?
3. Is coating VOC an issue? |
A: 1. Material must be resistant to accidental impacts with hand tools or other objects as well as salt deposits, corroded material or sediment.
2. Moisture permeability is the critical issue. Current MTM barrier (What we want to replace) is tested IAW ASTM F 372 @ 100 +/- 5 deg F, 95 +/- 5% humidity. 10 samples mean NTE 0.005 US Perms. No single specimen to exceed 0.010 US Perms. Also, the on take of seawater via swelling is a functional/structural concern.
3. Yes - The system is ultimately connected via air piping to manned space within the submarine. Materials must be compatible with submarine atmosphere and not cause injury to personnel. Additionally, no cadmium or mercury should be used.
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Q: 1. Must the material being treated be nitrile rubber or can it be an elastomer with equivalent performance properties?
2. What is the form of the nylon reinforcement? Is it a fabric, random mat or other form?
|
A: 1. The nitrile formulation is as follows: MIL-R-6855, CL I, Grade 60.
2. Nylon fabric is MIL-C-20696, Type II.
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Q: 1. The solicitation states the coating must be permeable to a seawater environment, does this also include air, water, etc.?
2. What are the maximum pressures that the nitrile rubber will be exposed to? |
A: 1. Of the mediums listed, seawater permeability is of primary concern.
2. The seal assembly is pressurized to 120 + 5.0 / - 0.0 psid (external to internal sea water pressure for 10 minutes w/o damage), 18 + 1.0 / -0.0 psid (internal to external air pressure for 10 minutes w/o damage) and 7.2 +/- 0.5 psid (internal to external air pressure for 10 minutes w/o leakage) during factory acceptance testing. Operationally, 80 cycles between 0 and 80 psid (external seawater) and 80 cycles between 0 and 12 psid (internal air)
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Q: 1. Please would you provide all of the ASTM reference numbers that are relevant in the testing of the covers in development
2. What type of QA testing would you expect on production covers?
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A: . . . response pending . . . |