Note: Descriptions are shown in the official language in which they were submitted.
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"PROCESS FOR PRODUCTION OF THERMAL SHOCK TUBE,
AND PRODUCT THEREOF"
The present Patent refers to a process for production of a thermal
shock tube and product thereof, applied as signal transmission
device for connecting and initiating explosive columns, or as a filame
conductor, usually complemented by a delay element or used as a
delay unit, which uses a pyrotechnic mixture with low sensitivity to
ignition by shock or friction, with low toxicity, which generates a
spark with superior thermal performance, said process having the
possibility of continuous and separated dosing of the individual non-
active components, in conjunction with the formation of the plastic
tube, making the process safer, and with a more accurate dosing,
and said product maintaining the advantages of the current
pyrotechnic shock tube relative to the shock wave propagating tube:
larger transmission sensibility and sensitivity, propagation even with
cuts or holes in the tubes and low risk transport classification, and
presents additional advantages: use of low toxicity components, use
of ordinary, low cost, low adhesiveness polymers, generation of a
spark that propagates through knots, closed kinks or tube
obstructions, and resistance to failure by attack of components of
hot explosive emulsions.
Since the beginning of the decade of 1970, low energy signal fuses
known commercially as "non-electric detonators" or "shock tubes",
are broadly applied for connecting and initiating explosive charges in
the mining and quarry sector. Such devices, marketed with brands
like NONEL, EXEL, BRINEL, etc., came to substitute electric
blasting caps ignited by metallic wiring, and represented a revolution
in the market of detonation accessories, due to its easiness of
connection and application, and to the intrinsic safety against
accidental ignition by induction of spurious electric current.
Currently, the processes and products that use high explosives as
components (hereinafter referred to as "conventional shock tube")
are the following:
1) American patent US 3,590,739 is the original reference for
conventional shock tube. It describes a process of plastic extrusion
forming a circular tube with outer diameter varying from 2.0 to 6.0
mm and inner diameter varying from 1.0 to 5.0 mm, where it is
continually introduced a secondary explosive powder, such as HMX,
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RDX or PETN, in its inner periphery, at the same time in which the
tube is formed, the resulting product known as a non-electric shock
tube, marketed with trade names such as NOVEL and EXEL. When
initiated by a primary explosive blasting cap, conventional shock
tube generates a gaseous shock wave with a signal transmission
speed ranging from 1,800 to 2,200 m/s. Further improvements
include the addition of aluminum to increase specific energy and
utilization of ionomeric polymers, like SURLYN, to increase
adhesiveness of the powder;
2) American patent US 4,328,753 describes a conventional
shock tube in two layers, the inner layer made of a polymer which
provides adhesiveness to the explosive powder mixture, and the
outer layer made of a polymer which provides mechanical strength,
being the most suitable inner polymer SURLYN and the outer
polymer polypropene, polyamide or polybutene. This product was an
improvement over the original NOVEL tube, as SURLYN alone is
expensive and has a low resistance to external damage;
3) European patent EP 027 219, and its continuations-in-part US
5,317,974 and US 5,509,355 describe a single-layer shock tube,
and its method of manufacture, in which the polymer is Linear Low
Density Polyethylene (LLDPE) with minor quantities of an adhesive
promoter, and the tube is made by extrusion of a tube with outer and
inner diameters greater than that of final tube, and then the tube is
stretched in order to orientate LLDPE molecules, making a final tube
with greater tensile strength. All claims are for a minor amount of an
adhesion promoter in the polymer formulation, as it is well
recognized in the art that powders have a low adherence to LLDPE.
In spite of its claims, the best conventional shock tubes continue to
be made in two layers, and the inner layer continue to be SURLYN,
as even a low dislodgement of bad-adhered explosive powder leave
to failures in signal propagation by discontinuities in powder layer or
by concentration of loose powder in the lower parts of the tube
during field application;
4) American patent US 5,166,470 describes a single-layer tube of
LLDPE similar to that of EP 027 219, in which an additional thin
layer of an hydrophilic polymer, like Polyvinyl Alcohol (PVA), is
deposited by passing the plastic tube through a solution of polymer
in, e.g. water, and drying the solvent. The aim is to make the tube
less permeable to the hydrocarbons present in emulsion explosive.
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Hot Diesel fuel is particularly aggressive to LLDPE, and prolonged
contact of the tube with hot, Diesel fuel-based emulsions causes
failure in signal propagation. PVA protective skin is fragile and does
not adhere to the LLDPE, and so a pretreatment with a cleaner (like
chromic acid), with hot air or with an adhesion promoter (like
Vinamul EVA copolymer) is necessary.
A further development in the low energy transmission fuses was the
invention of tubes that make use of pyrotechnic mixtures inside the
tube, in substitution for high-explosive-containing powders.
Currently, some of the processes and products with pyrotechnic
mixtures, hereinafter referred as "pyrotechnic shock tube", are the
following:
1) Brazilian patent PI 8104552, from the applicant of the present
patent, is the original reference for the pyrotechnic shock tube. It
describes a process of plastic extrusion forming a circular tube of
outer diameter raging from 2.0 to 6.0 mm and inner diameter
ranging from 1.0 to 5.0 mm, where it is continually introduced a
powder of pyrotechnic mixture of lC2Cr207 + AI or Mg, Fe203 + AI or
Mg, or Sb~03+ AI or Mg, Sb205 + AI or Mg or 02 + AI or Mg, in its
inner periphery, at the same time in which the tube is formed, the
resulting product being denominated pyrotechnic shock wave tube,
marketed with trade name BRINEL. When initiated by a primary
explosive detonator, such tube generates an aluminothermy reaction
without gas releases, and develops a plasma for energy
transmission;
2) American Patent US 4,757,764 describes a non-electric
system for control of a initiation signal in blasting operations using a
plastic tube with pyrotechnic delay mixtures adhered in its interior,
particularly using low speed reactions, in much smaller speeds than
that of the conventional shock tubes and detonating cords, with the
aiming of using predetermined lengths of tube for obtaining a fast
delay time in the milliseconds range, in substitution to the
conventional delay element. The blasting caps connected to the
plastic tube are necessarily instantaneous, without delay elements
into the cap, and so there was no concern of the inventor in
optimizing the thermal action of a spark, nor in eliminating toxic
components, nor in guaranteeing the crossing through restrictions in
the tube, nor in reducing the sensibility of the mixture to friction and
mechanical shock, not even with the adhesiveness of the mixture to
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the tube, nor with the resistance to the attack by hot hydrocarbons
from the emulsion explosive. It is evident, by the patent's descriptive
report, and for all of the examples, that its use as a delay element is
limited to the range of tens of milliseconds, not being adequate for
most of the delays used in field practice.
There is a variety of other low energy fuses advanced in patents, or
in commercial use, and all other applications are here incorporated
as a reference.
Signal transmission tubes are usually complemented with the
insertion of a delay blasting cap in its tip, such cap made of a metal
cap containing two layers of explosive powder pressed inside, the
bottom layer being a secondary high explosive, and the upper layer
being a primary, flame-sensitive explosive, complemented by a
delay element consisting of a metallic cylinder containing in its
interior a compacted column of powdery pyrotechnic delay mixture
and, frequently, an additional column of pyrotechnic mixture
sensitive to the heat generated by the tube's shock wave.
The process for manufacture of conventional shock tube, as well as
the resulting product, presents the following disadvantages:
a) The production of the tube loaded with explosives (RDX, HMX or
PETN are toxic and dangerous) offers risks both of accidental
explosions as in handling toxic products, demanding special care
and protection in the production line. The fact of using molecular
explosives impedes the dosing of non-active components during the
extrusion of the tube;
b) In the conventional shock tube, the reaction products are
basically hot gases which, when leaving the final extremity of the
tube, expand themselves with loss of heat, such heat loss inhibiting
the ignition of the pyrotechnic delay mixture. Slower delay powders
are particularly insensitive to the shock tube output. It is necessary
either to add an additional column of sensitive pyrotechnic mixture to
give continuity to the explosive train or to use pyrotechnic mixtures
more sensitive to heat and with larger column length. As a
consequence, the final product has larger production costs, and the
processing and handling of the pyrotechnic mixture offers larger
accidental ignition risks;
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c) The adherence of crystalline explosives (RDX, HMX or PETN) in .
plastic tubes is low, demanding special manufacturing processes
and the use of special, expensive, polymers, usually ionomeric
polymers as SURLYN, in order to minimize the concentration of
loose powder in portions of the tube and to avoid portions without
loading. Lack of adherence of LLDPE is particularly noteworthy. It is
significant that the best known commercial brands continue to use a
two layer tube, with SURLYN as the inner layer, in spite of the
efforts to improve polymer adhesiveness by changes in polymer
formulation;
d) Conventions( shock tube loading lacks sufficient critical mass and
critical diameter to properly propagate a shock wave by classical
detonation theory. The finding of the late Dr. Persson, inventor of the
original shock tube, was that the shock wave is continuously
sustained by dust explosion of the explosive powder dislodged by
deformation of the plastic duct caused by the shock wave behind the
reactive front. Due to this feature, conventional shock tube fails if
there is a cut or a close restriction in the inner duct, dispersing the
shock wave. In field practice, in case of unexpected cuts, stretching,
knots, holes, or closed kinks, the tube could fail to propagate;
e) Conventional shock tube is sensitive to the effect called in the
industry "snap, slap, and sfioof': it could happen unexpected ignition
if the tube is stretched causing rupture, in particular conditions of
mechanical energy release, as recognized in an article presented in
the 28th. Annual conference of the 1SEE, Las Vegas, 2002, and in
all catalogs and technical bulletins of conventional shock tubes. The
article and technical bulletins of some commercial shock tubes are
incorporated here as references.
f) Conventional shock tube is classified for transport purposes as an
explosive in many countries, what results in additional costs and
difficulties for transport, mainly after the increase in dangerous
products regulations due to the fight against terrorism;
g) Conventional shock tube presents failure in propagation after
prolonged underwater exposure above 2 bar pressure, often found
in field practice, due to the hydrophilic characteristics of the
ionomeric resins like SURLYN;
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h) Tubes manufactured with SURLYN alone have a (ow tensile
strength, and a low resistance to abrasion, kinks, knots, etc.,
demanding co-extrusion of an additional outer layer of polyethylene.
Although, this process does not avoid the use of expensive
SURLYN;
i) Conventional explosive powders lack sufficient activation energy
to propagate in case of contamination of the tube interior by hot
hydrocarbons (most likely Diesel fuel) from explosive emulsions.
Polymers, including LLDPE, are quite susceptible to aggression.
Minor quantities of adherence-improving additives, most likely EVA
copolymers, are even more subject to attack by volatile fractions of
Diesel oil. An additional skin of hydrophilic polymer like PVA is
needed, but abrasion resistance of the skin, in the rough
environmental conditions found in field practice, is remarkably bad,
causing removal of the skin and failures. The author performed a
series of tests of PVA-covered tubes, and the low adherence of the
skin was proved;
j) According to the specifications published by the manufacturers,
Conventional shock tube speed of deflagration ranges from 1,800 to
2,200 m/s, or within 10% of a mean speed of 2,000 m/s. This
relatively broad range interferes with the accuracy of the delay
element timing. American patents 5,173,569, 5,435,248, 5,942,718,
and Brazilian patent P19502995, from the author, all use shock tube
as initiator of electronic delay blasting cap. Such caps are
characterized by a highly accurate electronic delay element.
However, the timing error of a certain length of tube is added to the
intrinsic timing error the electronic circuit. In a typical tube length of
21 m, as used in open pit mining, the error would be within + / - 1
ms, while the intrinsic error of the electronic circuits is typically
within + / - 0.1 ms;
k) Conventional shock tube deflagration generates substantially
gaseous reaction products, sustaining a shock wave that quickly
disperses most of the released thermal energy, through expansion
of the gases when leaving the tip of the tube. For this reason,
conventional shock tube output is unable to ignite low flame-
sensitive delay mixtures, demanding an additional, highly flame-
sensitive, igniter element for ignition of the slower delay elements.
Highly flame-sensitive mixtures are usually also highly sensitive to
mechanical shock, friction and electrostatic discharge, increasing
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the accidental risks. The additional element increases the
manufacturing costs;
Pyrotechnic shock tube, as foreseen in the Brazilian patent P!
8104552, from the applicant of the present patent, has the following
disadvantages:
A) Pyrotechnic mixtures use toxic components (K2Cr207, Sb203,
Sb205) and flammable solvents, demanding recycling of the
solvents, handling cares, and appropriate waste disposal;
B) The process of extrusion of the plastic tube includes the dosing of
previously prepared sensitive pyrotechnic mixture, during the
formation of the plastic tube, with safety risks in handling and
process;
C) Like conventional shock tube, pyrotechnic shock tube doesn't
resist to the aggression by the hydrocarbons present in emulsion
explosives, and prolonged exposure leads to failures in propagation;
D) Mixtures of O~ + AI or Mg, were not shown feasible in practice,
due to the loss of gases in the production and use of the product;
E) Mixtures of Fe~03 + Al or Mg, were not shown feasible in practice,
due to the low sensibility of these pyrotechnic mixture to the ignition
stimulus of blasting caps and a high rate of propagation failures. The
fundamental cause proved to be the components high Tammann
temperature;
F) Giving the limitations presented in the items D and E, the only
remaining options were highly toxic, highly friction and shock
sensitive mixture of K2Cr20~, Sb~03, and Sb205 with AI or Mg;
G) The reaction products formed in the aluminothermy reactions,
AIZO3, K20, Sb, antimony oxides, Cr203, necessarily solids by the
limitations in the patents claims, have low thermal conductivity, what
inhibits the ignition of slower, low sensitive delay elements;
H) Like conventional shock tube, powdered pyrotechnic mixture also
presents a low adherence to the tube polymer, particularly in
LLDPE;
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1) Pyrotechnic mixtures are not optimized to allow propagation
through to closed knots, cuts or kinks.
The system for control of a initiation signal in blasting operations
foreseen in the American Patent US 4,757,764 presents the
following disadvantages:
Aa) Like happens in the original pyrotechnic shock tube, the process
also includes the dosing of previously prepared sensitive
pyrotechnic mixture, during the formation of the plastic tube, with
safety risks in handling and process;
Bb) The system makes use of direct tube-to-tube connections for
supplying a time delay exclusively through a predetermined length of
tube, and is limited to fast delays, in the range of tens of
milliseconds, while field blasting operations demand delay timing up
to10s;
Cc) The powdered mixtures, containing no adherence additive in its
formulation, present a low adhesiveness to the tube polymer,
demanding the use of expensive material, like SURLYN or silicone,
as can be seen in all of the examples in descriptive report;
Dd) As the author's aim was a system of delay obtained through a
tube with substantially reduced speed, eliminating the delay
element, and directly igniting the highly sensitive primary explosive
inside the blasting cap, there was no optimization of the thermal
performance of a transmission signal. A !ow speed mixture lacks the
energy to directly ignite slower, fow sensitive delay mixtures, and to
propagate through close kinks, knots or cuts;
"PROCESS FOR PRODUCTION OF THERMAL SHOCK TUBE
AND PRODUCT THEREOF", was developed to overcome the
problems in the process of manufacture and in the performance of
the current shock tubes. The approach is a new one.
The focus of research in previous art was mainly to obtain desirable
characteristics in the polymers that form the tube, but not to optimize
the pyrotechnic mixtures formulation, in order to use ordinary, low
cost polymers. The new approach is also multipurpose, i.e., to
obtain the greatest possible number of desirable characteristics
through the formulation of the pyrotechnic mixture. The process and
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product from this Patent application have the following advantages
over the current shock tubes:
- The thermal shock tube employs an optimized pyrotechnic mixture
with low toxicity;
- The process allows the continuous dosing and mixture of two non-
active components during the extrusion process, this components
been all most practically insensitive to friction and shock before its
mixture, in such way substantially reducing the probability of
accidental initiation in handling, and, even in case of ignition of the
tube during production, causing minimum damages by the
deflagration of a very small amount of mixture;
- The process obtains a safer pyrotechnic mixture more, with smaller
sensibility to friction and mechanical shock, by covering the
oxidizers components with a desensitizing additive;
- Its pyrotechnic mixture obtains an excellent adherence to the
plastic tube, using the same additive, even in low cost, ordinary
polymers, including LLDPE, avoiding tube portions with lack or
excess of charge;
- The product maintains some advantages of the current pyrotechnic
shock tube in relation to conventional shock tube: a larger sensibility
and sensitivity of propagation, propagation to cuts or holes, and low
risk classification for transport;
- The spark of signal transmission is formed so much by gases as by
melted metals, and so it crosses knots, closed kinks or obstructions
in the tube, and presents an optimized heat transport by thermal
conduction and convection, igniting less sensitive, slower delay
columns directly.
- The thermal shock tube resists to the environmental exposure to
marine Diesel oil present in the hot explosive emulsions, maintaining
functionality even after 72 hours of exposure at high temperature (65
°C for 24 h + 40 °C for 48 h in pure marine Diesel);
- Thermal shock tube has a propagation speed accuracy within +/-
1,67% from the mean speed, i.e., an error of +/- 20 m/s in 1,200
m/s, adding to electronic delay detonators only +/- 0.3 ms of error in
a 21 m long tube.
FIELD OF THE INVENTION
Invention is based on the knowledge the inventor possesses of the
production and use of the pyrotechnic shock tube BRINEL, from the
applicant, complemented by research for additional objectives:
- Substitution of poisonous components of the pyrotechnic mixture;
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- Improvement in the adherence of the mixture to the inner surface
of the tube;
- Desensitization of the mixture to shock and friction;
- Decrease in the handling risks of pyrotechnic mixture;
- Substitution of manufacturing processes for the pyrotechnic
mixtures that used labor-intense working, including grinding and re-
crystallization with dangerous solvents, and handling of bulk,
sensitive, pyrotechnical mixture by automated, risk-free, and
environmentally-safe processes;
- Generation of a an optimized spark with excellent heat transfer by
conduction and convection without dispersion of heat by gas
expansion;
- Production of a tube with functionality after exposure to hot, Diesel
oil-based explosive emulsions up to 65°C for 3 days.
One of the fundamental concepts for the understanding of the
obtained inventive effects was described by the Russian chemist
Tammann. According to his theory, the vibrationai energy needed to
start an oxidation-reduction reaction among solid substances is
largely available at the temperature equivalent to half the melting
point of the substance, in the absolute scale (K). This temperature of
Tammann explains why certain components make pyrotechnic
mixtures quite sensitive to heat to flame and mechanical shock,
while other ones are quite difficult to start an propagate. As
example, mixtures of powdered aluminum, whose temperature of
Tammann is 193°C and ferrous-ferric oxide, Fe304, whose
temperature of Tammann is 632°C are particularly difficult to start
and propagate, while mixtures of powdered aluminum and
potassium chlorate, whose temperature of Tammann is only 47,5°C,
is especially dangerous. One of the invention bases is to obtain
enough activation energy to warranty the initiation and propagation
of the pyrotechnic reaction even with the contamination of the
interior of the tube by hydrocarbon fuel coming from explosive
emulsion, such contamination decreasing the enthalpy pyrotechnic
reaction. As low-Tammann temperature substances adequate to
take part of the pyrotechnic mixture can be mentioned potassium
perchlorate, potassium chlorate, antimony trisulfide, sulfur,
potassium nitrate, ammonium perchlorate, sodium chlorate, or any
substance whose temperature of Tammann is adapted to this
purpose. The invention is also based, without being limited to this, in
the observation that a pyrotechnic reaction that generates products
with high thermal conductivity and thermal convection coefficient,
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will allow a better propagation continuity, and will ignite delay
elements with greater thermal efficiency, allowing the use of smaller,
slower delay columns without additional ignition elements. As
interesting oxidation-reduction reactions, we have:
8 AI + 3 Fe304 ~ 4 AI203 (solid) + 9 Fe (liquid) or,
2 AI + Fe203 ~ AI203 (solid) +2 Fe (liquid)
where the melted metallic iron supplies an excellent heat transfer, so
much by thermal conduction as by convection. Another observation
in which the invention is based is that the simgle generation of solid
or liquid products will not allow the propagation through knots, kinks,
restrictions, etc. it is necessary that enough gas volume would be
generated to allow the elastic expansion of the polymer around the
fold or restriction, forcing the crossing of the spark. However, this
gas volume cannot be excessive, otherwise there will be the
dispersal of the solid and liquid products of the spark in the tip of the
tube, combined with the gaseous expansion, what will provoke the
loss of the thermal energy necessary for ignition of the delay
element. Examples of appropriate components for gas generation
are antimony trisulfide, potassium perchlorate, potassium nitrate,
sodium nitrate, ammonium perchlorate, sodium perchlorate, etc.
Another knowledge taken into account as base for the invention is
that certain products present lubricating properties and superficial
adherence properties, what reduces the sensibility to the friction and
mechanical shock of the mixture, and provides adhesiveness even
to difficult polymers like pure LLDPE. Examples of such products
are: talc (magnesium and aluminum hydrosilicate) and graphite.
Another objective of the invention is to obtain an unpublished
process in that the mixture of the oxidizers and additive is done in
separate from the fuels or reduction agents, and that the final active
mixture is obtained in the own plastic extruder, in an automated,
continuous or semi-batch process, so that just a very small amount
of pyrotechnic mixture is formed at any instant, minimizing the risks
and effects of an accidental ignition of the tube during the industrial
production. Another aspect taken as base for the invention is that, to
propagate through eventual cuts or holes accidentally done in the
tube during field application, the spark should be constituted so
much by products of high heat transfer, as by gaseous products, in a
way to happen both the heat transfer to allow the continuity of the
pyrotechnic signal transmission as to allow the mechanical impulse
for releasing of the spark for the open portion of the tube.
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The development of the optimized formulation for the thermal shock
tube was accomplished by several practical tests. For these tests,
formulations of powdered pyrotechnic mixtures were dosed by
spraying in the inner diameter of melted pure LLDPE in a extruder,
the tube was cooled, and stretched to obtain a 3.1 mm outer
diameter, 1.4 mm inner diameter flexible tube. Conventional
SURLYN shock tubes, obtained from a major manufacturer, as well
as prior art pyrotechnic shock tubes from the applicant, were
sampled and tested as a comparison.
For better understanding of the examples the tests are described as
follows:
1) Speed of propagation test: A tube portion with a measure length
of 5 m is put among two optical sensors linked to a precision
chronometer. When the tube was ignited, the light of the spark,
when passing by the first sensor, starts the time counting, and, when
passing by the second sensor interrupts the time counting. The
propagation speed is obtained dividing 5 by the time counted in
seconds;
2) Kink propagation test: In 10 samples, the tube spark should
propagate through 10 closed 1 ~0° folds spaced by the same
distance. This smallest distance among the following: 1 m, 50 cm,
30 cm, 20 cm, and 10 cm in which all 10 samples propagate
completely, without failure, is recorded as "minimum distance
between kinks";
3) Tight knot propagation test: a 1 m long tube sample is single-
knotted in its middle section, and the tube extremities are hold by a
hydraulically-driven traction device, with a loading cell attached to
measure the tensile strength to which the knotted tube is submitted.
The tube is ignited, and the maximum load in which five successive
samples propagate through the knot is recording. The higher is the
maximum load, the better is the ability of the tube in propagating
through tight knots which could accidentally be made in field
application. This test was performed for single-layer shock tubes, as
well as for double-layer (LLDPE and SURLYN) conventional shock
tube, for comparison;
4) Low energy detonating cord initiation: 100 samples of 1 m long
tubes are connected to a line of detonating cord with a core loading
of 2 grams/m of PETN, through a "J" type connector, and the .line of
detonating cord is initiated. The number of tubes which failed to
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propagate is recorded as "percentage of failures in initiation by 2
grams /m detonating cord";
5) Mechanical Shock Sensibility: A sample of the pyrotechnic
mixture powder is submitted to a know weight falling hammer, free-
failing from a certain height. The energy in that 5 successive
samples deflagrate is calculated by the formula E = m.g.h, where m
is the mass of the weight in free fall, g is the local acceleration of
gravity, and h is the minimum height for ignition;
6) Slower delay sensibility: a delay element of 8.3 seconds delay
time, with a 24 mm long column of pressed delay powder, containing
slow delay mixture, without any additional layer of igniting mixture, is
placed at the end of a PVC hose of 6 mm outer diameter, with
variable length, with the tip of a 1.0 m long thermal shock tube,
aligned in the other extremity. When the thermal shock tube is
ignited, the spark should cross the free space from the hose interior
and start the delay element. The larger the length of the hose in
which the elements always ignited, the better will be considered the
thermal performance of the spark. The largest hose length for
ignition in 5 successive samples is recording as "sensibility of the
slow delay element";
7) Tube-to-tube "air gap": a 3 m long thermal shock tube is
transversally cut at the middle length and their half tubes are moved
away with a measured spacing, maintaining there alignment through
an aluminum guide in "half-pipe°' format. The largest distance in than
the spark, when crossing the free gap among the tube portions,
initiate the second portion in 5 successive samples, is recording as
"all-fire air gap";
8) Initiation after exposure to the hot explosive emulsion: 30
samples of 12 m long thermal shock tube, with the extremities
sealed by a rubber plug and a crimped aluminum cap, as usual in
the industry, are dipped in 65°C hot bulk explosive emulsion with
marine Diesel oil as fuel, and the recipient is placed in a lab stove at
65°C for 24 hours. After this period, the stove has its thermostat
lowered for 40°C, and the samples stay in the emulsion for more 48
hours, totalizing 72 hours of exposure. The tubes are ignited and the
percentage of failed tubes is recorded as "failures after exposure to
the hot emulsion";
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9) Adherence of the mixture to the tube: 10 tube samples 5 m long
are weight in an analytical scale with and accuracy of 0.0001 g.
Afterwards, the interior of the tubes is flushed by compressed air
with a flow rate of 0.3 Nm3/minute for 2 minutes, to remove the non-
adhered powder. The tube is weighed again and the weight is
recorded. The interior of the tubes is washed with a flow of sodium
hydroxide aqueous solution for dissolution of the aluminum and
perchlorate, and dragging of iron oxide and talc, eliminating the
adhered powder. The empty plastic tube is weighed. After
determination of the tube's inner diameter the superficial area is
calculated and, by difference, the free powder load by area rate, the
adhered powder load by area rate, and the percentile rate of free
powder mass by total powder mass are calculate.
Tests results are consolidated and summarized in the Table 1.
According to the test results in Table 1, the formulation
AI/Fe30~/KC104/Talc in the respective percentiles 40/27.5/31.5/1.0
presented the best performance. A high content of aluminum fuel
with 65% Al, with a corresponding lower speed of 750 m/s, means
an insufficient spark perfiormance in the propagation through kinks
and knots, and a very low sensibility of the slow delay element. On
the other hand, a very low aluminum fuel content as in the
formulation 30/32.5/36.5/1.0, will generate a very high gaseous
volume, dispersing the spark products at the tube tip, reducing the
sensibility of the slow delay element and the "all-fire air gap". It is
proved also the effect of the talc in improving the adherence of the
mixture to the tube and in decreasing the mixture shock sensibility.
Based in the accomplished research and in the practical tests it can
be concluded that the optimized formulation for the thermal shock
tube is composed by:
- 32% to 60% of powdered aluminum. Another powdered fuels or
reduction agents able to generate a high temperature spark, such as
magnesium, silicon, boron and zirconium could be used;
- 15% to 35% of powdered ferrous-ferric oxide - Fe304. Another
substances that in oxidation-reduction reaction generates products
of high thermal conduction and convection, such as ferric-oxide -
Fe203, ferrous oxide - FeO, cobalt oxide, cupric oxide - Cu0 and
cuprous oxide - Cu20 could be used;
CA 02538734 2006-03-10
WO 2005/028401 PCT/BR2004/000178
- 20% to 40% of potassium perchlorate - KCIO~. Another substances
of low temperature of Tammann, able to lower the energy of
activation of the pyrotechnic reaction and to generate enough
gaseous volume to propagate through kinks, knots, or tube
restrictions such as potassium chlorate, potassium nitrate,
ammonium perchlorate, sodium perchlorate, sodium perchlorate,
sulfur and antimony trisulfide;
- 0.5% to 3.0% of talc. Another substances able to promote
adherence and to reduce shock and friction sensibility, such as
graphite, could be used.
The components of the pyrotechnic mixture formulation can have
combined characteristics, in other words, the same substance
component can have more than a function as mentioned above at
the same time.
The characteristics of the components of the formulation can be
applied to conventional shock tubes, individually or combined, with
the aim of optimizing them to obtain a better performance, a higher
safety in production and a decrease in the environmental and
occupational health risks.
The present patent can be better understood by the following
figures:
FIGURE 1: shows the block diagram of the process for production of
the thermal shock tube;
FIGURE 2: that shows the thermal shock tube spark, leaving the
tube tip;
FIGURE 3: that shows, as comparison, the basically gaseous
products of a conventional shock tube (prior art) when leaving the
tube tip;
According to FIGURE 1, the process for production of thermal shock
tube has the following sepuence:
a) The oxidizers and the adherence promoter and desensitizing
additive are previously and thoroughly mixed, forming mixture I;
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WO 2005/028401 PCT/BR2004/000178
16
b) Mixture I is fed in a dosing silo, and the f uels are fed another
dosing silo;
c) The balanced proportions of mixture I and fuels are continuously
dosed through two parallel dosing thread type devices or through
vibratory dosers or any other conventional weight or volume
microdosing mean, endowed with electric motors with frequency
controller or any other conventional controller in control loop with the
plastic tube extruder, such balanced doses continuously reaching a
roll homogeneizer-mixer with a bottom screen, making the final
sensitive pyrotechnical mixture, small quantities, such bottom screen
connected to the extrusion ring of the plastic tube exfiruder;
d) In parallel to the making of the pyrotechnic mixture a melted
polymer is extruded through the extruder ring forming a plastic tube,
at the same time in that happens the dosing, by gravity, of the final
pyrotechnic rnix~ture inside the plastic tube being formed, obtaining
the thermal shock tube.
Additional steps of processing could include tube cooling, stretching
of the tube to obtain tensile strength, therrt~al treatment of the tube,
and other techniques conventional in the plastic processing area,
without loss for the invention teachings.
The final product, thermal shock tube, uses conventional plastic
tube, such as E~r'A, F~3LYETHYLEi~E, LLf3FE or ~URLY(~i, with
outer diameter ranging from 2.0 to 6.0 mm and inner diameter
ranging from 1.0 to 5.0 mm and containing 5 to 40 mg/m of
pyrotechnic mixture adhered to its internal walls;
FIGURE 2 shows the thermal shock tube spark when leaving the tip
of the tube during propagation, such drawing representing a high
velocity photograph of the tube spark, where can be seen the high
temperature solid and melted products (1), such products including
highly thermal conductive and convective melted iron, the gaseous
products (2), responsible for the melted jet projection at the tube tip.
FIGURE 3 shows, for comparison, conventional shock tube (prior
art) basically gaseous products, when leaving the tip of the tube
during propagation, such drawing also representing a high velocity
photograph of the tube flame, where can be seen the basically
gaseous products (1 ) being dispersed by gas expansion at the
tube's end. These comparative photographs clarify why conventional
shock tube fails to propagate trough cuts and does not have the
ability to ignite low sensitive delay columns.
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17
TA~L~ 9 - FracticaE 1'es~s Pesults
FormulationSpeed Minimum Wight Low energyShock Slower ail-
fireInitiationAdherence
of gap knot after of
propagationbetween propagationdetonatingSensibilityDelay air exposurethe
mixture
kinks gap to to
in
kink propagation cord Sensibility the hot the tube
initiation (% of
test explosivefree
powder)
emulsion
Al 65% 750 Failure 3 f B% 9.2 8 cm 80 25% 5
mls at any kg N mm
FesOa distance
17%
KCIOQ
17%
Talc
1.0%
At 50 1170 1 m 8 f Zero 9.2 16 cm 100 zero 3.8
% m!s kg N
Fe309
mm
24.5%
KCIOQ
24.5%
Talc
1.0%
AI 40% 1260 30 cm 11 f Zero 9.2 22 cm 120 zero 4.0%
mls kg N
Fe30Q mm
27.5%
Kcia4
37.5%
Talc
1.0%
A130% 1290 30 cm 12 f Zero 9.2 5 cm 15 15% 3.2%
m!s kg N
Fe30a mm
32.5%
KGIOq
36.5%
Talc
1.0%
AIlKzcrz071000 Failure 3 f Zero 3.8 8 cm 100 30% 18.3%
m!s at any kg N
Standard distance mm
for
the
pior-
art
pyrotechnic
shocktube
Mixture2000 1 m 2 f zero 3.8 Fails 90 not not
m!s fig N to mm
HMXlAI ignite, performedperformed
even
Standard at zero
for
the distance
convention
al shock
Tube
single
la er
Mixture2000 50 cm 8 f zero 3.8 Fails 10 not not
m!s kg N to mm
HMXlAI ignite, performedperformed
even
Stendard of zero
for distance
the
convention
al shock
Tube
double
layer
