Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CO-EXTRUDED SHOCK TUBE
The present invention relates to a low-energy fuse or shock
tube for propagating a percussion or impact wave within and along
the tube for activation of a detonator. More particularly, the
present invention relates to a mufti-layer tube that is co-
extruded, wherein the innermost layer has adhesive affinity for a
reactive material and a wall thickness of less than about 0.3
millimeter. The outer layers) has abrasion and cut resistance,
and an optional outermost layer may be resistent to degradation
from contact with either ultraviolet rays or liquid organics. By
"co-extrusion°' is meant forming the tube and its layers in a
continuous, simultaneous operation through an extrusion element as
is known in the art.
The invention comprises a method of manufacturing a low-energy
shock tube comprising the steps of: (a) heating two or more
materials to their respective desired extrusion temperatures; (b)
co-extruding the materials to form a layered plastic tube having at
least an inner layer with an inner surface and an outer layer, the
inner surface of the inner layer having an adhesive affinity for a
reactive material and the inner layer having a thickness of less
than about 0.3 millimeter and the outer layer having abrasion and
cut resistance; (c) feeding a reactive material to the inner
surface of the inner layer as it is being co-extruded with the
other layer or layers to form a thin layer of the reactive material
on the inner surface; and (d) optionally cooling the co-extruded
tubing to or below its solidification temperature and/or stretching
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the tube after i.t has been co-extruded to obtain the desired
surface density of the reactive material, to increase the axial
orientation of molecules of the plastic materials and thereby
increase the tensile strength of the tube and to attain the desired
inner layer thickness. The invention further comprises a shock
tube whose inner layer has a wall thickness of less than about 0.3
millimeter.
FIG. 1 is a transverse cross section of a preferred embodiment
of a tube according to the present invention.
FIG. 2 is a flow diagram of the process steps involved in the
method of the present invention.
Reference to FIG. 1 shows a shack tube 1 in accordance with
the present invention having an inner layer 2 with an inner surface
3 having an adhesive affinity for a reactive material 3b. The
inner layer preferably has an adhesive property of at least 5.5
g/m2 for the reactive material, which preferably is in powdered
form. The inner layer 2 preferably is selected from the group
consisting of SURLYN, ethylene/acrylic acid copolymers, ethylene
vinyl acetate and other plastics and adhesives. In its final form,
either as extruded or after stretching, the wall thickness of the
inner layer 2 is less than about 0.3 millimeter.
An outer layer 4 is shown having a greater wall thickness than
that of inner layer 2. This preferably provides for greater
tensile strength and increased abrasion and cut resistance. The
outer layer 4 preferably is selected from the group consisting of
polyethylene, polyethylene blends 'with ionomer, polypropylene,
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polybutelyne, nylon and other polyolefins. This outer layer 4
preferably has a tensile strength of at least 35 MPa. An optional
outermost layer 5 is shown that preferably provides protection from
ultraviolet rays and/or chemicals such as organic liquids. A
problem with shock tubes heretofore has been their susceptibility
to degradation upon exposure to ultraviolet rays and/or organic
liquids that are commonly found in blasting agents that the shock
tube often contacts during application in the field. By reducing
the wall thickness and thus the cost of the inner layer 2 and by
co-extruding the layers, such optional outer layer 5 can be added
without making the finished product overly expensive. The optional
outermost layer 5 preferably selected from the group consisting of
linear low, medium or high density polyethylene, polyester,
polyvinylidene chloride and mixtures thereof.
The final surface density of the reactive material 3b on the
inner surface of the inner layer can be varied as desired as known
in the art. Typically, at least 2.7 g of reactive material per m2
of the inner surface is desired. If the tube is stretched, the
initial surface density before stretching may not be significantly
changed after stretching, since the inner diameter may be reduced
as the tube length is increased. The reactive material preferably
is a powder mixture of such materials as PETN, RDX, HMX, powdered
aluminum or other fuels and mixtures thereof.
Reference to FIG. 2 illustrates the method of the present
invention. The inner layer material is extruded by an extruder 6
through the crosshead die 9. Simultaneously, the outer layer
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material is extruded by extruder 7 also through crosshead die 9.
Crosshead die 9 is configured as known in the art so as to regulate
the f low of the extruded materials and to position the material
from extruder 6 internal and concentric to the material from
extruder 7 thereby forming the two-layered tube configuration as
the materials simultaneously exit from crosshead die 9.
Optionally, a third, ultimate outer layer material can be fed to
crosshead die 9 from extruder 13. Simultaneously with the feeding
of the inner and outer layer materials from extruders 6 and 7,
reactive material, preferably in powder form, is fed by reactive
material feeder 8 through crosshead die 9 and to the inner surface
of the inner layer to thereby coat the same.
The layer materials that are extruded through extruders 6 and
7 are pre--heated to their respective desired extrusion
temperatures, and optionally, the two-layered tube exiting from
crosshead die 9 is passed through a cooler 10, such as a water
bath. Further optionally, the co-extruded tube may be stretched
through stretcher 11 for purposes previously described. Stretcher
11 may comprise two pulleys, one which takes tubing from the
crosshead die 9 and then acts as a brake or anchor for a second
pulley which operates at a faster rate and thus stretches the
tubing between the two pulleys. Still further optionally, the tube
may be wound on a take-up reel l2 by conventional means or
otherwise gathered or collected as desired:
The invention can be further described by reference to the
following examples.
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CA 02075738 1999-OS-18
Example 1. A co-extruded tube was formed by heating SURLYN to
a temperature of about 230°C and extruding it by means of a 1-inch
single screw extruder through a crosshead die while simultaneously
heating linear low density polyethylene to a temperature of about
220°C and extruding this material by means of a 1.5-inch single
screw extruder through the same crosshead die. The SURLYN material
formed the inner layer. The co-extruded tube that exited from the
crosshead die had an outside diameter of 3.0 mm and an inside
diameter of 1.1 mm. The ~URLYN* inner layer had a uniform wall
thickness of 0.05 mm. The tube was cooled to a temperature of
about 25°C and then wound on a take-up reel.
Example 2. A co-extruded tube was formed using the same
extruders and inner and outer layer materials employed in Example
1 above. In this example, however, a differently sized crosshead
die was used. The result was a two-layered tube having an outside
diameter of 4.5 mm and an inside diameter of 2.1 mm. After cooling
to a temperature of about 30°C, the tube was then stretched so that
its outside diameter was reduced to 3.0 mm and its inside diameter
was reduced to 1.2 mm. The final wall thickness of the SURLYN
inner layer was 0.25 mm. This stretched tube had a much higher
tensile strength than the tube produced in Example 1. The
increased tensile strength was the result of orientation of the
plastic molecules by the stretching process.
While the present invention has been described with reference
to certain illustrative examples and preferred embodiments, various
modifications will be apparent to those skilled in the art and any
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* Trade-mark
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modifications are intended to be within the scope of the inTrention
as ,set forth in the appended claims.
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