Comparison of Gasket Materials
Brandonite® 1200-60A
Vs.
Class III Buna-N Material (MIL Spec G-15624F)
March 19, 2008
Prepared by:
Dr. Xiujun Wang
Director of Polymer Technologies
Globe Composite Solutions, Ltd.
254 Beech Street
Rockland, MA 02370
www.globecomposite.com
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I.
Executive Summary
Globe Composite Solutions, Ltd. (GCS) manufactures 92-inch diameter gaskets for
missile tube muzzle hatch seals aboard US nuclear submarines. These gaskets are made
with Brandonite®1200-60A, a high performance polyurethane compound material
designed to replace previously specified Class III Type Buna N material (MIL Spec. G15624F). Over the past ten years, the performance of Brandonite®1200-60A material has
been flawless: no gasket made with Brandonite®1200-60A material has failed in service
due to physical or mechanical failure.
Brandonite®1200-60A is a liquid castable material which combines the properties of high
tensile strength and elongation with outstanding elasticity and excellent resistance to
seawater, oils, chemicals and UV degradation. Additionally, Brandonite®1200-60A
tensile strength is 100% greater, weighs 23% less and has similar elongation, Shore
hardness and compression set properties as Class III Type Buna N.
II.
Background
In the mid-1990s, there was an increase in the incidence of fraying and/or extrusion
damage to the edges of missile tube muzzle hatch gaskets with the Ohio-class SSBN
nuclear submarine fleet. This was a major concern since there was a high incidence of
failure which caused leaking or flooding inside Trident missile tubes. At that time, the
gaskets were manufactured using Mil-G-15624F Type III Buna-N rubber material
(copolymer of butadiene-styrene).
Sixty-four samples of Mil-G-15624F Type III Buna-N rubber material gaskets were
tested and the review found that gaskets made of Mil-G-15624F Type III Buna-N rubber
material would degrade over time and failed to meet the physical specifications and
dimensional requirements for this application.
In pursuit of a resolution to these performance problems, alternative materials were
investigated. The choice of a polyurethane-based material was made based on the
previous results obtained and the outstanding performance of polyurethane materials used
on Seawolf-class submarines. These materials demonstrated excellent survivability in the
ocean environment. A series of tests according to the specifications of Mil-G-15624F
were conducted and it was concluded that GCS Brandonite®1200-60A high performance
polyurethane compound material, then specified as G4317-05, had the combination of
properties best suited to resolve failure problems previously observed with Buna-N
materials. Since then, GCS, as a primary supplier, has continuously manufactured 92inch diameter polyurethane gaskets for the US Navy and its contractors according to the
specifications EB-4224(1) that was established between GCS and General Dynamics
Electric Boat.
III.
Development of Brandonite®1200-60A
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Brandonite®1200-60A is a polyurethane compound material based on MDI Polyether
chemistry. It combines the properties of high tensile strength and elongation, outstanding
elasticity, and excellent resistance to seawater, oils, chemicals and UV degradation. Its
certification for use in the 92-inch diameter missile tube muzzle hatch seal underwent
several major review milestones.
Brandonite®1200-60A was initially developed in 1997 by Globe Rubber Works, Inc.,
whose assets were purchased by GCS in 2004. At that time, six full-sized gaskets made
from this material were installed on the Ohio-class submarine SSBN 743 (Louisiana) for
sea trials. After minor modifications to the physical dimensions of the gasket, the second
set of sea trials demonstrated that hatches fitted with Brandonite®1200-60A gaskets
functioned properly. Additionally, the static compression load for these gaskets, as
measured in a laboratory fixture, was comparable to that for the original Buna-N gasket.
During the sea trials, the gaskets discolored slightly, which is attributable to UV
exposure. This caused problems with closing operations of the hatches due to higher
compressive loading stiffness. In early 1998, 21 separate UV improvement formulae
were incorporated into the compound material formula to improve UV resistance. A
test of UV stability was conducted by NMMEL and included completion of Mil-G15624F UV light aging on Brandonite®1200-60A. This test also evaluated: the effects of
color pigments and UV inhibitors on physical performance; the effect of reduced gasket
height on sealing performance; compatibility of Brandonite®1200-60A with silicone
lubricant; and, 48-hour “creep” evaluation requested by NAVSEA 03W14.
Additional tests were also performed in the following areas:
1.
2.
3.
4.
Hydrostatic Pressure Sealing: Using 7 Inch Diameter Gasket Fixture
Static Load vs. Deflection: Using 7 Inch Diameter Gasket Fixture
Cyclic Loading: Using 7 Inch Diameter Gasket Fixture
ASTM D 624: Tear Strength of Conventional Vulcanized Rubber and
Thermoplastic Elastomers
5. ASTM D 471, Rubber properties: Effects of Liquids
After conducting these tests, it was concluded that Brandonite®1200-60A polyurethane
compound material, incorporated with specific pigments and UV inhibitors, resolved the
effects of discoloration and was the most suitable material for solving fraying or
extrusion-type damage observed with Buna-N materials.
IV.
Brandonite®1200-60A Physical Properties
GCS Brandonite®1200-60A polyurethane compound material has superior tensile
strength and elongation properties when compared with Mil-G-15624F Type III Buna N
rubber material. Brandonite®1200-60A also has a significantly lower specific gravity,
which is ideal for applications where weight consideration or part handling is a factor.
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Table 1: Summary of Brandonite®1200-60A Physical Properties
Properties
Specific Gravity
Shore Hardness
Young’s Modulus
Tensile Strength
Elongation at Break
Tear Strength
Compression Set, Method B
Temperature Range
ASTM Method
ASTM D 792
ASTM D 2240
ASTM D 412
ASTM D 412
ASTM D 412
ASTM D 624
ASTM D 395
Units
sp gr 23/23 OC
A Scale
Psi
Psi
%
lb/inch
%
Typical Value
1.080
60
172,000
3,000
400
200
30
-20ºF to 200ºF
Chemically, Buna-N or Nitrile rubber material is a copolymer of butadiene and
acrylonitrile. Acrylonitrile content varies in commercial products from 18% to 48%. As
the Nitrile content increases, there is an increased resistance to petroleum-based oils and
hydrocarbon fuels, but a decrease in low temperature flexibility.
Table 2 lists
specifications of Mil-G-15624F Type III Buna-N rubber(2), along with polyurethane
compound material Brandonite®1200-60A:
Table 2: Mil-G-15624F Type III Buna N Rubber vs. Brandonite®1200-60A
Properties
Tensile strength, psi minimum
Ultimate elongation, percent,
minimum
Shore A hardness, maximum
Specific gravity, maximum
Compression set, percent,
maximum
V.
Mil-G-15624F
Type III Buna
N Rubber
1,550
400
Brandonite®
1200-60A
3,000
400
100% greater
Same
50
1.400
30
60
1.080
30
20% harder
22.8% lighter
Same
Comparison
Applications
Brandonite®1200-60A is versatile and liquid-castable. It can be used to produce large
parts with significantly lower tooling costs when compared to traditional compressionmolded rubber products. GCS processes this material in a unique way which
significantly reduces the presence of voids and increases the uniformity of the material as
well. Since the material is liquid-castable, one-piece gaskets or seals can be made in
virtually any size without the risk of compromising strength along knit-lines or
compression zones.
Brandonite®1200-60A can be modified to increase or decrease certain physical properties
such as tensile strength, rebound, durometer or elongation. It is mold and fungi resistant,
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which makes the material ideal for marine, agricultural, tropical and water/sewage
treatment applications and is available in FDA and non-FDA approved grades.
Summarized below is a general comparison of Brandonite®1200-60A with Buna N
rubber material:
Table 3: Comparison of Brandonite®1200-60A with Buna N Rubber
Property
Tensile strength
Tear Resistance
Abrasion Resistance
Compression Set
Elongation
Weight/Specific Gravity
Ozone Resistance
UV Resistance
Hydrolytic Stability
Durability/Weathering
Low Temperature Resistance
Moldability
Mold/Fungi Resistance
Rebound
Durometer Range
Higher Temperature Service
Diesel/Gasoline Resistance
Brandonite®
1200-60A
Excellent
Outstanding
Outstanding
Good
Excellent
Excellent
Outstanding
Outstanding
Excellent
Excellent
Outstanding
Excellent
Outstanding
Excellent
Outstanding
Fair
Fair/Good
A few obvious uses for this material include:
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VI.
Custom-molded shapes
Diaphragms
Access hatch gaskets and seals
Water pump gaskets and seals
Storage tanks gaskets and seals
Aircraft gaskets and seals
Deep-sea gaskets and seals
Water/sewage treatment gaskets and seals
Marine gaskets and seals
Bladders
Conclusion
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Buna N Rubber
Good
Fair
Good
Good
Good
Good
Fair
Poor
Excellent
Fair
Excellent
Fair
Poor
Good
Good
Good
Outstanding
For the last decade, GCS has advanced polyurethane processing technologies and has
constantly improved product performance and consistently provides high-quality
products. GCS has been able to provide US Navy (and its purchasing departments and
contractors) with thousands of 92-inch Brandonite®1200-60A polyurethane gaskets.
There has not been a single incident of in-service physical or mechanical failure. This is
primarily due to the superior physical properties of Brandonite®1200-60A as well as the
processing and molding capabilities of Globe Composite Solutions.
VII.
Reference
1. “General Requirements for the Procurement of Polyurethane Material”, Specification
No. EB-4224
2. “Rubber Gasket Material, 50 Durometer hardness”, Mil-R-15624E
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