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c. D. PRATT sfm.
Filed April 20. 1944
Jm-aes vA. FARR
Patented Dec. 31, 1946
Carl D. Pratt and James A. Farr,’ Tamaqua,‘ Pa.,
assignors to Atlas Powder Company, Wilming
ton, Del., a corporation of Delaware
cApplication April 20, 1944,,S‘erial No. 531,888
10 Claims. (01. 102-24)
an improved sheath for an explosive cartridge.
Another object of the invention is the pro
or about ‘1/1" and therebetween in thickness have
usually been found most desirable.
Since thesheath dimensions are not readily
varied, sheath weight is 'most e?ectively altered
by means of change in sheath density. Many
following description.
sirable that the sheaths be‘ readily susceptible
The present application relates to sheathing
for explosives.
An object of the invention is the provision of
sheathing compositions heretofore proposed
vision of an improved sheathing composition for
have not been susceptible for preparation of
an explosive cartridge.
sheaths of suf?ciently varying densities.
A further object of the invention is the pro
The sheaths prepared according to the present
vision of an improved sheathed explosive.
Still another object ‘of the invention is the 10 invention are characterized by extraordinary
?exibility of density control.
provision of a sheath for an explosive cartridge,
Usually it is desired that sheaths be prepared
which sheath has improved volume and weight .
as self-sustaining units which will hold their
shape before they are placed around explosive
'A still further object of the invention is the
provision of a sheath for an explosive cartridge, 15 cartridges. It is then important that the sheaths
be sui'?ciently strong and rigid to withstand
which sheath is sturdy and yet can be cut easily. >
rough handling. At the same‘ time, it is de
Other objects will become apparent from the
to cutting without crumbling when part car
Most explosives, when ?red, produce .a hot
?ame. In gaseous ,and dusty locations, this 20 tridges' are to be used.
?ame is a source of danger; for it may initiate .
_ an explosion in the surrounding atmosphere.
It has been known for some time that this
Many of the sheathing compositions prepared
prior to the present invention haverequired the
inclusion of undesirable bonding agents. Some
have employed adhesive organic materials which
danger may be reduced if explosive cartridges
are sheathed in compositions containing ?ame 25 are troublesome to use and which produce sticky
compositions giving considerable difficulty in
suppressing chemicals. The ?ame suppressing
loading. Other bonding materials which have
chemicals employed operate, it is believed, to re
been necessary in prior compositions have caused
duce the ?ame temperature ‘or to prevent the
the compositions to set up into brittle sheaths
?ame from reaching mine dust or gases. Prob;
30 which cannot be readily cut; and, in some cases,
ably both of these effects occur.
such sheaths have been so-hard that the force
Many materials which decompose with’the
of the explosion, instead of disintegrating the
absorption of heat or which have high speci?c
heats have been used as flame suppressing chem
' icals in sheathing materials.
Such materials as
hydrated salts such as hydrated magnesium sul
phate, borax, and gypsum, iron ?lings, alkali
halides, such as sodium ?uoride, sodium chlo
ride, and potassium chloride, magnesium car
bonate, and sodium bicarbonate have been em
sheaths into a powder so that the flame sup
pressing chemical may act, has merely broken
35 them into large pieces which ?y off uselessly.
Sheaths bonded in other ways have permitted
passage of a knife but have crumbled away on
Sheaths of the present invention when com
40 pressed, as by ordinary tamping, during forma
tion‘may be made upwithout the inclusion of
bonding agents and yet form entirely satisfac~
positions usually require di?erent weights of
tory sturdy sheaths. When sheaths of this in
sheathing composition and often'these weights
vention are prepared with looser packing pro
should be within rather narrow limits, if op 45 cedures, firm. and strong sheaths which may be
timum e?ects are to be obtained. If the- sheaths
readily out without crumbling may be prepared
are too heavy, the explosive eiliciency is unduly
with the inclusion of inorganic binding agents
lowered while if they are too light there is in
such as are described hereinafter.
sufficient‘ ?ame suppression. For best results,
Some sheaths suggested prior to this invention
however, sheaths should be made co-extensivef 50 have contained organic substances, as filler ma
in length with the sheathed cartridges and
1 terials for example. Such substances being com
usually it is preferred to avoid a wide variety of
bustible have, to the extent of their presence, desheath wall thicknesses both from a point of view
feated the ?ame suppressing function of the
Explosive cartridges of di?erent sizes and com;
of ease of manufacture and from a consideration.
oi’ convenience of use.
sheaths. - sheaths of this invention may be pre
Sheath walls about %" 55 pared Without the inclusion of organic materials.
strength was good. The dry sheath was ?rm and
When sheathing materials are loaded to form
coherent sheaths they are usually mixed with
water to permit proper sheath formation. The
strong, readily cut, and weighed 100 grams.
Example 3
water is later dried out so that the sheaths may
be su?iciently ?rm and strong. Many sheathing
Another sheath was prepared as in Example 1 .
except that in this'case a coarser grade of per
lite, 90% of which passed a U. S. Standard No. 8
sieve and 98% was held on all. 8. Standard No.
compositions have required so much water dur
ing formation that they have become obiectiona- _
bly wet and have had insu?icient wet strength,
while other compositions have, on loading, tended
45 sieve. This sheathing mixture also possessed
to ball up or to become lumpy and consequently 10 good wet strength. It was slightly more di?icult
have been di?icult to pack.
to load than the composition of Example 1, but
not objectionably so. It produced a good ?rm
sheath easily cut. weighing 105 grams on drying.
The sheathing compositions of the present in
vention on the other hand take up water in suf
ficient quantities to provide cohesive. self-sus
taining sheaths of good wet strength without be
coming di?icult to load.
Example 4
A sheath was prepared having the proportions
used in Example 2 and by the method of Example
These sheathing materials of the present inven
2. but the coarser expanded perlite was used. The
dried sheath weighed 101 grams and had proper
Expanded perlite, a commercially available .20 ties slightly better than those of the sheath of
tion are prepared with combinations of a flame
suppressing chemical and expanded perlite.
Example 3.
material, is the mineral perlite, a volcanic glass
composed largely of an alkali aluminum silicate,
It is found that sheaths may be strengthened
if some binding agent such as Epsom salts (mag
which has been put through a heating process so
nesium sulphate) is added to the mix.
. that it is expanded into an extremely light cellu
The addition of some ?brous material improves
lar form.
the ?exibility of the sheaths. Short ?bered as
The invention will be described in comiection
bestos is particularly desirable for this purpose.
with the drawing, which is a view, partly in sec
The next two examples show di?erent formu
tion, of a sheathed explosive cartridge.
lations, using Epsom salts and short ?bered
As shown in the drawing, II' is a cylindrical ’
paper shell inside which lies sheathing compo 30 asbestos. which have produced valuable sheaths.
In. each of these examples, the ?ne expanded
sition 13. The ends of shell I l are closed by end
perlite was used and the proportion of water
wads l5 and I1. Lying inside sheathing I8 is an
given is based on the total weight of the other
explosive cartridge made up of paper shell [9, in
ingredients. In each case, the Epsom salts were
closing explosive charge 2|.
dissolved in the water which was mixed with
A sheathed explosive such as that shown in the
the remaining ingredients as in the examples
drawing may be prepared by placing shell it over
above. The sheaths of each of thé following ex
' a solid mandrel which is about the size of the ex- '
amples, however, instead of being tamped, were
plosive cartridge to be sheathed. The sheathing
packed by vibration packing. ‘The mandrel was
composition is then packed between the shell and
the mandrel. Thevmandrel is removed and the 40 ?xed in an upright position on a vibrating table. The paper shell was placed around the mandrel
sheath is dried. Then the cartridge of explosive
' and the sheathing composition was poured in as‘
is inserted in the sheath and the end wads are
the table vibrated. These sheaths all showed ex
fastened in place to produce the ?nished
sheathed explosive.
cellent wet strength and loading characteristics
and all shells produced were found on drying to
Sheathing materials of the present invention
have good ?exibility and to be ?rm, strong sheaths
are also particularly adapted for use in the prep
aration of preformed sheaths, such as are dis
closed in the application of Daniel D. Huy'ett and
Frank S. Pollock, Ser, No. 315,094, ?led January
/. 22, 1940 for "Sheathing tori explosive."
which were easily cut.
Example 5
Expanded perlite ________________________ __
.Short ?bered asbestos ___________________ __
20% of fine expanded perlite, 99% of which
Dried sheaths prepared according to this form
ulation weighed 65 to 70 grams.
Example 6
60 "
Per cent
Sodium bicarbonate ____________________ __,_ 80
Epsom salts _________ __'_________________ __
eter and 8%" long around a mandrel 11's" in
diameter. The material loaded into the shell eas
ily and had good wet strength, as was shown by
the absence of crumbling on removal of the man
Expanded perlite ________ -_- ______________ __
could be easily cut, and weighed 108 grams.
it into an 8 gram heavy paper shell 13/4" in diam
' drel. After the mandrel was removed, the‘ sheath
» was dried at 65° C. It was then ?rm and.strong,_
Epsom salts __________ _.-. ____ _.... _________ __
55 Water
passed a U. S. Standard'No. 12 sieve, was mixed
with 80% of pulverized sodium bicarbonate. The
‘composition was then thoroughly mixed with an‘
amount of water amounting to 10% of the dry.
ingredients. The mixture was loaded by tamping
Per cent
Sodium bicarbonate _____________________ __
‘The following examples illustrate speci?c em
bodiments of the invention.
Example 1
Short ?bered asbestos _______ ___-_...._. _____ __
Water _-__.' ___________ __~_; _____________ __
",Dried sheaths . prepared Taccording to
formulation weighed 89 to 95 grams.
this ,
While all of the above examples relate to the
use of sodium bicarbonate as a ?ame suppressing
Example 2
chemical, and it is usually preferred that this
A sheath was prepared in accordance with the
procedure of Examplel except that it was com
cient and economically used'?ame suppressing
chemicals, other ?ame suppressing chemicals,
posed of 25% ?ne perlite and 75% sodium bicar
bonate. Loading was again easy and wet
employed in the present invention.
chemical be used, it being one 0! the most e?i
such as those listed hereinbefore, may also be
sheaths of these examples were prepared in the
same manner as that described‘ for Examples 5.
expanded perlite and yet the-advantages of the
present sheathing compositions will be retained.
The Epsom ‘salts binding agent appears to
crystallize in an interlacing needle formation
which assists in making the sheaths cohesive.
and 6 above.
Other similar materials such as plaster of Paris
The following three examples show formula
tions using 70 mesh sodium chloride or powdered
borax as ' ?ame suppressing chemicals.
In each case the ?ne expanded
may also ‘be used as binding agents. These ma
'perlite was used.
terials being hydrated salts have the additional
value of being ?ame suppressing chemicals them
Example 7
Per cent
Sodium chloride- _________________ __._ ____ .._
Sheaths of the present invention may be packed
Expanded perlite ________ s. ______________ __
Short ?bered asbestos"... ________________ __
in any convenient manner. In addition to the
- tamping and vibration packing examples given
Water‘ _____________________ -i __________ __
above, extrusion and pelleting procedures may,
for example, be employed.
v Sheaths prepared from this formulation loaded
well, exhibited satisfactory wet strength and dried
Other ?brous materials than short ?bered as
to form good ?rm sheaths having a weight range
bestos may be used to provide increased ?exibility
in the sheaths of the present invention. For ex»
ample, wood pulp may beused for this purpose.
20 Also sheaths of the present invention may include
any of the numerous binder and ?ller ingredients
of from 71 to 72 grams.
Example 8
Per cent
Sodium chloride ________________________ __
Epsom salts _________________________ __-___.
Short ?bered asbestos ____________ _._Y_.____-__
Expanded perlite_-__'.. ____________________ __
in the art.
What is claimed is:
1. A sheathing composition for explosive car
Water _____________________________ __'____ . l0
tridges comprising a ?ame suppressing chemical
and expanded perlite.‘
sheaths prepared according to this formula
2. A sheathing compositiongfor explosive car
tion loaded easily, showed excellent wet strength
tridges comprising a ?ame suppressing chemical,
and dried to form entirely satisfactory sheaths
expanded perlite. and a binding material.
which were somewhat stronger than the sheaths 30
3. A sheathing composition for explosive car
of Example 7. . These sheaths weighed 82 to 85
tridges comprising sodium bicarbonate and ex
panded perlite.
Example 9
Short fibered asbestos__'_ ________________ _‘
as to loading and as to wet and'dry character
istics. They weighed from 62 to 64 grams.
It will be readily seen that the present inven
tion provides a sheathing material which affords
great?exibility in sheath density since sheath
density may be varied with the amount of ex
panded perlite included, this amount being sub
ject to wide variation for use in di?erent situ
It is round that as little as 2% and as
much as 65% by weight of the dry ingredients
5. A sheathing composition for explosive car
tridges comprising sodium bicarbonate, expand
ed perlite, magnesium sulphate and asbestos
These sheaths were also entirely satisfactory
' ations.
35 ed perlite, and magnesium sulphate.
Expanded perlite____e ___________________ __ , 15
tridges comprising sodium bicarbonate, expand
‘Per cent
4. A sheathing composition for explosive car
of sheaths of this invention may be made up of 50
6. An explosive cartridge sheathed with,a com
position according to claim .1.
7. An explosive cartridge sheathed with a com
’ position according to claim 2.
8. An explosive cartridge sheathed with a com- '
position according to claim 3.
9. An explosive cartridge sheathed with a com
position according to claim 4.
10. An explosive cartridge sheathed with a
composition according to claim 5.
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