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AMC REG 385-100 - Chapter 24
CHAPTER 24
MANUFACTURE OF CASTABLE COMPOSITE
PROPELLANT ROCKET MOTORS
24-1. Introduction. This chapter prescribes safety requirements
that are intended to reduce the probability of injury or property
damage during the manufacture and loading into rocket motors of
castable composite propellants. For the purpose of this chapter,
composite propellants are those which consist of a mixture of
fuels, binders, and oxidizers with or without other ingredients.
This also applies to colloid propellants when they are used as
ingredients in composite propellant compositions.
24-2. Operational Shields. The design of operational shields
be
consistent with the provisions of Chapter 25 and DA PAM 385-64,
and take into account the quantity of propellant involved,
confinement that may be present, and the potential initiation
hazard involved. In addition to the hazards outlined in Chapter
14, the following hazards may be encountered in the processing of
composite propellants:
a. Propellant detonation.
b. Unconfined propellant fires.
c. Pressure vessel failure with fragmentation.
d. Pressure vessel failure without fragmentation.
24-3. Facility Layout.
a. Batch mixing and associated operations shall
be performed
in buildings used exclusively for that purpose. Small mixers
(ó
50 gallons capacity) may be located in buildings containing other
operations, provided the mixer is in a separate bay with
operational shields that protect all other operations and
unrelated personnel from the mixing operation.
b. In planning the location of new facilities
that are
intended initially for 1.3 materials, due consideration should be
given to the possibility that 1.1 explosives may be processed in
future operations.
24-4. Explosive Hazard Classification of In-Process Materials.
a. Prior to propellant manufacture, efforts
shall be made to
determine the hazard classification of the individual raw
materials, the uncured propellant, and the cured propellant.
This effort consists of classifying the materials by analogy or
previous test data, or by conducting appropriate tests, such as
those specified in TB 700-2 for propellant characterization.
However, caution must be used as small scale tests may not
accurately reflect the hazard classification of in process
materials when quantities are increased or confinement exists.
b. In the absence of above data, the following
hazard
classifications shall be used for operations involving 1.3
propellants:
OPERATION
HAZARD
CLASSIFICATION
(1)
Organic oxidizer preparation (including
screening and grinding)
1.1
(2)
Inorganic oxidizer preparation
(including screening and grinding)
1.3
(3)
Pre-mix preparation
1.1
(4)
Propellant mixing
1.1
(5)
Propellant casting
1.3*
(6)
Propellant curing
1.3
(7)
Propellant finishing
1.3
(8)
Rocket motors during finishing
1.3
(9)
Finished motors in assembly areas
1.3
(10)
Finished motors during temperature
conditioning, physical measurements,
painting, packaging, etc.
1.3
(11)
Rocket motors in static test stands
1.1
* Casting operations involving propellants containing more than
88% solid constituents and/or composed of particles less than
15 microns in diameter are assigned an explosive hazard
classification of 1.1.
c. If testing reveals that only the uncured
propellant is
detonable, casting and curing operations must be considered 1.1
explosive hazards. If testing reveals that only the cured
propellant is detonable, curing and subsequent operations must be
considered 1.1 explosive hazards.
24-5. Oxidizer Processing. a. General. (1)
All oxidizer
process equipment shall be bonded and grounded.
(2) Screening, blending, grinding
and mechanized drying
operations shall be conducted remotely for organic oxidizers, and
should be conducted remotely for inorganic oxidizers.
(3) Since oxidizing materials are
corrosive to many of the
metals used in process equipment, preventative maintenance
schedules shall be followed closely.
(4) Many organic lubricants are
incompatible with strong
oxidizing materials and may form sensitive or explosive compounds
when allowed to mix. Oxidizer preparation operations shall be
designed to avoid inadvertent contamination of the oxidizer with
organic lubricants.
(5) The use of wood or other porous
materials in the
construction of an oxidizer facility shall be minimized, and if
use is unavoidable, such materials shall be coated with
impervious fire retardant paint. Copper alloys can form
sensitive compounds when exposed to oxidizers such as ammonium
perchlorate, and should not be used in oxidizer processing
facilities.
(6) Flexible connections (socks)
in pipes and duct systems
through which oxidizers are conveyed shall be fabricated of fire-
retardant materials that are chemically compatible with the
oxidizers. The pipes or duct systems shall be made electrically
continuous. Flanged connections shall be used in lieu of
threaded joints wherever practicable.
(7) Objects such as jewelry or
pens that may be
accidentally introduced into grinders should not be permitted
into oxidizer preparation facilities. All tools should be
accounted for by the use of tool checklists or shadow boards.
b. Drying operations. (1) The maximum
safe temperature for
drying each type of oxidizer shall be established and shall not
be exceeded at any point in the drying operation.
(2) If the dryer is capable of
exceeding the maximum safe
temperature of the oxidizer being dried, dual thermostatic
controls shall be used to prevent overheating.
c. Screening operations. (1) Screening
equipment shall be
constructed to prevent the oxidizer from being subjected to
pinching, friction, or impact as a result of metal-to-metal
contact. Systems should be designed for continuous removal
particles less than 15 microns, if practical.
(2) Rooms in which screening operations
are conducted
shall be cleaned as necessary to prevent hazardous accumulations
of dust.
d. Grinding operations. (1) Impact-type
mills shall not be
used to grind organic oxidizers.
(2) Oxidizers shall be passed through
a screen and a
magnetic separator immediately prior to entering a grinder or
pulverizer in order to assure removal of extraneous material.
Screen openings should be the smallest that permit free flow of
the oxidizer.
24-6. Preparation of Fuel Compositions. a. Equipment
design
and handling methods shall minimize formation and accumulation of
dust.
b. Compatibility of materials shall be established
and
controls incorporated to preclude the mixing of materials at a
time or in a manner that would result in sensitive compositions.
c. Due to the susceptibility of metal powers
to ignition
from electro static discharge, all dumping, screening, weighing,
and handling equipment should be bonded and grounded. Assure
the
continuity to ground for spatulas, scoops and other tools used to
dump, measure or stir metal powders.
d. Positive measures shall be taken to exclude
moisture from
metal powder operations. Waste metal powders should be immersed
in a compatible nonreactive liquid until disposed.
e. The introduction of an inert gases into
process equipment
in order to reduce oxygen content should be considered as a means
to prevent dust explosions.
f. Objects such as jewelry or pens that may
be accidentally
introduced into mixers should not be permitted into fuel
preparation facilities. All tools should be accounted for by
the
use of tool checklists or shadow boards.
24-7. Mixing of Fuel Compositions and Oxidizers. a.
Facilities
and Equipment.
(1) Mixer facilities shall be provided
to provide the
maximum vent space consistent with the structural integrity of
the facility. The use of wood or other porous materials in the
construction of an mixing facility shall be minimized, and if use
is unavoidable, such materials shall be coated with impervious
fire retardant paint.
(2) Quick-acting detection and
delivery deluge systems
should be installed in the facilities to cover points of
operation. These systems should be interlocked with the mixer
control circuits to prevent mixer operation when deluge system is
inoperative.
(3) Propellant mix bowls shall
be provided with
lightweight covers to prevent materials from dropping into the
mixer. The cover design shall allow adequate venting in the
event of an ignition in the mixer.
(4) The gear housing of vertical
mixers shall be sealed or
purged with an inert gas during mixing operations to prevent
contamination by dust from the mixing bowl.
(5) Blades and other moving parts
of mixers shall be non
destructively tested for cracks, crevices and other imperfections
prior to first use, and continued inspections shall be made on a
regular basis.
(6) Nuts, bolts, and other hardware
on mixers, monorail
systems, or in other locations that could loosen and fall into a
mixer shall be effectively secured.
c. Mixing operations. (1) All materials
introduced into
the mixer during mixing operation shall be done so remotely.
The
mixing cycles shall be completely remote controlled.
(2) All materials shall be screened
prior to entering the
mixer. Where the physical characteristics of the material
preclude screening, other methods such as magnetic separators or
nondestructive testing should be employed to segregate foreign
material and preclude their entry into the mixer.
(3) Oxidizers shall be introduced
into mixers after the
fuel-binder compositions to minimize the probability of the
mixture undergoing a deflagration to detonation transition if an
ignition occurs during mixing.
(4) Clearances between blades and
mixer bowls shall be
established as the maximum clearance consistent with quality and
process requirements, and should provide for deflection of shafts
and wear in journal and bearing areas. Blade clearance shall
be
checked at sufficient intervals to assure adequate clearances.
The openings in screens shall always be smaller than the blade to
bowl clearances.
(5) Frequent inspections and changing
of the packing gland
material shall be accomplished to preclude a build-up of oxidizer
and fuel in the packing gland area. Packing materials and
lubricants shall be compatible the oxidizer, fuel and propellant.
Temperatures in the propellant mass shall be monitored to detect
significant temperature rises due to wear or exothermic
reactions.
(6) Vertical mixer bowls used as casting
cans or transport
hoppers shall be non destructively tested at frequent intervals
to detect possible damage of weldments between the bowl and bowl
jacket. Blade to bowl measurements shall be made and compared
to
previous values to determine if warping has resulted from
handling.
(7) Spilling or splashing of propellant
during discharge of
mixers shall be avoided. Operators shall be so positioned during
discharge operations that direct, unblocked routes of rapid exit
will exist for emergency use.
24-8. Casting Composite Propellants. a. General. The
three
most common methods of casting are bayonet casting, in which the
propellant is introduced into the top of the motor through hoses;
bottom casting, in which the propellant is forced by pressure up
through an opening in the bottom of the rocket case; and vacuum
casting, in which the propellant is passed through a slit plate
into a rocket motor case enclosed in a vacuum bell. High strength
cases are also used as vacuum bells.
b. Casting Facilities. Casting facilities
should be
constructed of lightweight materials and shall be designed to
provide the maximum vent area consistent with the structural
integrity of the facility. They shall be designed so that
operating personnel have unblocked escape routes at all times.
Escape chutes to the outside should be provided from work
platforms.
c. Casting Equipment. (1) All casting vessel
assemblies
shall be designed to preclude internal cracks, crevices, corners,
pockets, and any internal configurations which could subject
propellant to initiation from impact, friction, or compression.
(2) Lids shall be secured to pressurized
casting vessels
in a manner which will withstand the rated pressures of the
vessels. Frequent tests and inspections shall be made to assure
that the clamp or assembly device is functioning properly.
(3) Pressurized casting vessels
shall be capable of
withstanding at least twice the maximum allowable working
pressure to which the can will be subjected. Periodic
hydrostatic tests (1-1/2 times the working pressure) of such
casting vessels should be performed at maximum intervals of six
months. At five-year intervals, vessels should be
hydrostatically tested at twice the working pressure.
Hydrostatic tests (at twice the working pressure) should be made
after any alteration, report of incident of abuse, mishandling.
or dropping A log of tests performed should be maintained for
each vessel.
(4) A blowout disk, designed to
blowout at 120 percent of
the vessel's maximum allowable working pressure, shall be
provided.
(5) The internal welded seams shall be
inspected frequently
by approved methods of weld examination.
(6) Casting vessel support fixtures,
such as legs, shall be
attached in such a manner that routine handling will not cause
damage to the casting vessel internal surface. They shall be
proof tested initially at 111 percent of the total weight to be
supported and periodic tests and inspections conducted
thereafter.
(7) Vibration equipment attachments shall
be designed to
prevent frictional heat generation on the vessel structure which
contains propellant.
(8) Threaded connections shall not be
permitted in piping,
valve connection, or any part of the casting vessel charging or
discharging system. Casting piping and manifold systems shall
not be joined with threaded connections. They should be pressure
tested at 1-1/2 times the maximum casting pressures. Methods
of
attachment for casting piping and manifold joints shall provide
positive fastening to eliminate failure of mating parts when
pressurized.
(9) Valves through which uncured propellant
flows shall be
designed to prevent compression of propellant between two metal
surfaces (e.g., rubber diaphragm-type valves). These valves
should be cleaned and inspected after each casting operation.
A
positive system to prevent propellant flow shall be incorporated
into the casting system to stop the flow in the event of primary
valve failure .Valve attachments to a non-pressurized casting
vessel shall be equipped with flanged mating surfaces and secured
by positive methods. The use of "quick release" type fittings
shall not be permitted.
(10) Vacuum casting bells shall
be designed to withstand
the conditions under which casting is accomplished.
(11) De-aeration assemblies shall
be designed to prevent
pinching or impacting propellant and for ease of assembly and
disassembly.
d. Casting operations. (1) Pressurization
of casting
vessels shall be performed remotely. Pressure at the casting
vessel shall not exceed the working pressure of the vessel.
Filters shall be installed in air lines to remove water and oil.
Use of safety links is recommended for pressurized casting
vessels to restrain the casting vessel lid in the event the
attachment device fails when pressurized.
(2) Casting vessel handling method
and equipment shall be
designed and operated in accordance with approved standards.
The
vessels shall be restrained to prevent movement should a rupture
of the relief valve occur.
(3) Mechanical insertion and removal
of cores in motors
containing cured propellant shall be accomplished remotely or by
personnel protected by adequate shields or barricades. When
cores are to be inserted mechanically, the equipment should be
designed to prevent metal-to-metal contact between the core and
motor case below the propellant surface.
(4) Loaded motor cases or casting
molds shall be secured
during casting and handled in a manner which will prevent
overturning or spillage of propellant. For large motors, casting
cores shall be secured to prevent movement when loaded motors are
transported in any manner.
24-9. Propellant Curing. a. Curing Facilities and Equipment.
(1) Curing facilities shall be
constructed of lightweight
materials and should be designed to provide the maximum vent area
consistent with the structural integrity of the facility.
(2) The safe temperature for curing
the propellant shall
be established and dual heat controls shall be used to prevent
that temperature from being exceeded.
(3) Heating units or elements shall
be designed to
eliminate any direct contact between the heating unit or element
and the propellant or rocket motor.
(4) Mold supports and other casting
and curing fixtures
shall be designed to avoid rubbing or pinching of thin layers of
propellant between metal surfaces.
(5) Means of pressure relief shall
be provided on closed
pressurized vessels into which motors are placed for curing.
b. Curing Operations
(1) Loaded motor cases or casting
molds shall be handled
or secured so that overturning will be prevented.
(2) Loaded or partially loaded
rocket motors shall be
raised or suspended at minimum distances above floor level. If
tests or experience indicate that rocket motors may ignite upon
dropping, protective measures shall be employed to minimize the
possibility of such ignition.
(3) Core popping (initial release
or separation of case
from propellant) shall be done remotely or from a shielded
location. When the core has been "released", final extraction
of
the core may be accomplished manually. When cores are not
designed with a taper (smaller dimension at forward end),
extraction of the core from the motor cavity shall be done
remotely or from a shielded position.
24-10. Motor Finishing and Assembly. a. Securing motors.
Rocket motors and pressure vessels containing cured propellant
shall be secured in fixtures capable of withstanding the rated
thrust of the assembly (based upon its performance as a rocket
motor with a safety factor of 2.5 to offset shock loads) for
operations involving the possibility of propellant ignition.
b. Threads. (1) Where the design
of a motor case
incorporates internal threads, means shall be provided for
preventing contamination of the threads with propellant.
(2) Whenever possible, the design
of casting and curing
assemblies and fixtures shall exclude internal threads, cracks,
and crevices where propellant may be deposited.
(3) All threads shall be cleaned
and inspected prior to
assembly of component parts.
(4) Assembly of threaded components
shall be accomplished
by remote control with personnel protected by adequate shielding
if a possibility of propellant contamination exists.
c. Mandrel removal. Operations involving
mandrel removal
shall be conducted remotely.
d. Machining non-case-bonded propellant grains.
Propellant
grains that are not case-bonded should be machined to the extent
necessary before they are loaded into motors.
e. Igniter Insertion.
(1) The following requirements
apply where the design of a
motor makes it necessary to insert the igniter within the
manufacturing line:
(a) The supply of igniters
at the insertion station
shall be the minimum consistent with safe and efficient
operation.
(b) If removal of the
shorting clip is required by the
process, the igniter shall remain shorted until immediately prior
to insertion.
(c) Process storage
facilities for igniters shall be
vented to the atmosphere and designed to withstand the effects of
an incident involving all igniters within.
(2) Electrical continuity tests
for igniters installed in
motors shall be performed remotely from other operations.
24-11. Environment and General Practice. a. Tool Design.
(1) Where propellant may come into
contact with equipment
during processing, all metal-to-metal surfaces shall be avoided.
There shall be no threads, cracks, crevices, or blind holes in
metal parts that may contact the propellant during casting or
finishing operations. Teflon-coating metal surfaces such as
molds and mandrels will generally prevent the propellant from
adhering.
(2) Recommended materials for hand
tools include the
following: aluminum, oil-resistant Neoprene, beryllium-copper
alloy, ANSI 300 stainless steel, and tempered steel (for cutting
tools such as X-acto knives). Steel cutting tools shall not be
allowed to cut through the propellant to the metal. For example,
during small sample cutting, the cutting board should be covered
with a Teflon sheet.
(3) Tool design or selection shall
incorporate safety
considerations such as tool speed control, use of non sparking
metals in contact with or close proximity to the propellant,
provision of limit switches to prevent over-ranging of tool and
possible metal-to-metal contact, explosion proofing of machinery,
use of effective coolant where necessary, effective dust and chip
removal, ease of cleaning, and provision for adequate grounding.
The deluge system shall provide for the quenching water to be
directed at the area where the cutting or machining is occurring,
since it is the likely point for ignition to occur.
b. Manual Operations
(1) Manual operations shall only
be allowed when the
propellant is well characterized and it is not feasible to
conduct the operation remotely.
(2) Safety goggles shall be worn,
and additional shielding
shall be provided where feasible. Whenever possible, the
operator shall not face the hazardous source directly. Fire-
retardant clothing shall be worn, avoiding any type of
encumbrances. Protective gloves shall be used when they do not
hinder the manual operation.
(3) Tooling should be designed
so that cutting pressure
can be applied to the tool with only one hand. For certain
operations, it may be necessary to use the other hand to assist
in guiding the tool to regulate the depth of cut, prevent
pinching of the propellant, or avoid metal-to-metal contact.
(4) Such tools as specifically
designed cutters can be
used for manual trimming, although final trimming may be more
safely done by hand when the operation is closer to metal walls.
(5) Parts shall never be forced
to fit, as this may
indicate that propellant has worked in between mating parts.
Threads and bolt holes should be protected against propellant
contamination by such measures as covering with masking tape when
operations on them are not being done.
(6) For highly hazardous manual
operations such as hand
trimming of motors, a second, qualified individual shall be
present or available in the event of an accident. The second
individual can also be used to verify the adequacy or completion
of critical operational procedures.
c. Remotely Controlled Operations. (1)
For extremely
hazardous propellants and/or configurations of motors, remotely
controlled operations using power-driven equipment shall be
required.
(2) Automated warning systems and
television monitors
shall be used to monitor potential trouble spots. Direct line-
of-sight viewing, unless appropriately shielded, shall not be
allowed. The sound of the operation should also be monitored
to
catch unusual sounds that could indicate potential problems.
(3) Adequate safety precautions such
as barricades,
flashing lights, chains, or interlocks shall be used to prevent
operators from entering rooms during equipment operations.