US3407732A - Electrical detonator - Google Patents

Description

Oct. 29, 1968 R. PRZYBYLIK ET AL 3,407,732

ELECTRICAL DETONATOR Filed March 8, 1967 BAP/06E 6 8 0 U W U WW H m6 l m 56 HP P% we MR 5 um M1 MM Z AM 1 1 i Q A A V United States Patent ELECTRICAL DETONATOR Ria Prz'yliylik, Tarnowskie Gory'nl; Piastowsks'; 16, Poland, and Wiktor Zalachowski, Krupski Mlyn ul. Mickiewicza 3, Poland t 1 Filed Mar. 8,1967, Ser.- No. 621,536 Claims priority, application Poland, Mar. 8, 1966, e 113,388

5 Claims. (Cl. 10228) ABSTRACT OF THE prsctofsuizs Wire bridg detonator including a plurailty of wires of different diameter, to give different delay times.

Known electric'delayed action millisecond detonators give desired delays at firing, due to the location in the detoi'iatorshell of a'dela'y element, which is placed between the, ignition-headand the ignition .primary said de-. lay element being the'characteristicelement of detonators of this type. Such delay element consists for-a tube filled with a retarding mass, which burns at a determined velocity.

The delay time from the moment of switching on of current to the moment of the detonation is usually adjusted by an adequate length of the tube with the retarding mass. A delayed action detonator can be manufactured as a series by adjustment of lengths of the respective tubes.

In the known millisecond detonators, the time intervals between detonators of a series are generally about 25 or or more milliseconds. The smallest technically obtainable limit of interfire time between particular detonators of this type is about 20 milliseconds.

The above generally described process for manufacturing detonators is very difficult from the technological point of view due to the necessity of precise maintenance of technological parameters in the production of the delay mass and the delay elements. Even the smallest divergences in technological process may result in a great undesired scatter of delay times in the detonators.

In another more simple technical solution, the detonator is constructed without separate delay elements and the retarding mass is pressed into the shell directly onto its ignition primer. However, the delayed-action detonators of this type are not safe in methane and coal dust environment and so they are not fit for use in coal mining.

There are also known delayed-action detonators wherein the desired delays are obtained by means of faster or slower burning ignition masses, located in the ignition heads of detonators. For each detonator in the series the ignition head includes another kind of ignition mass. The manufacturing process of such detonators is also complicated, due to the difficulty of preparing successful ignition masses for detonators with longer delays. On account of this, this latter process is used for making detonator series consisting of only four detonators which is not sufiicient for the requirements of present mining works.

An object of the invention is the provision of a cheap and con-structionally simple delayed-action detonator.

The construction of delayed-action electrical detonators of milliseconds order is based, according to the invention,

on a new concept in reference to the theory of the ignition of electrical bridge detonators.

The detonators according to the invention are not provided with special delay elements and their ignition heads contain the same. ignition mass for each delay time. The desired delays are obtained by the application of ignition heads, provided with resistance wires of different thick-.

ness for different delay times.

It is commonly known that in electrical bridge detonators, a current impulse causes an incandescence of the resistance wire which bridges the electrodes of the head and simultaneously ignites the head ignitionmass. This impulse is called the ignition impulse and its magnitude to a high degree is dependent on the diameter of the resistance wire involved.

By maintaining other parameters constant, the dependence of ignition impulse on the thickness of wire is given by the formula:

(l) I=K.d where I=impulse of ignition, K=a constant depending on various other parameters d=diameter of the resistance wire.

It is also known that the current impulse is:

where i=current intensity (in this case of the current which fires the detonator) t=time of current passage from the moment of switching on of the detonator to the moment of ignition of the head (ignition time).

From the Formulas 1 and 2 it follows thati.e., the ignition time is proportional to fourth power of resistance wire diameter and inversely proportional to the second power of current intensity. With constant current intensity, the thicker the resistance wire the longer will be the ignition time of head and the reaction time of the whole detonator.

On this formula is based the new concept of the delayedaction electric detonator series of the invention. Such detonator series according to the invention may include an optional number of detonators practically (e.g., from a few to twenty) with diiferent delays, in which the firing delays of particular detonators are predetermined on the basis of the above formula.

The detonators according to the invention are to be connected in parallel. However, parallel connection required careful wiring of shooting lines on account of the limited possibility of control of electric circuit resistance.

As a source of electric current for firing such a detonator series, direct current or industrial current is used. Long-acting electrodynamic igniters of adequate power are also suitable.

The delay time between the separate numbers, as well as the delay range of the whole detonator series can be optionally adjusted within large limits by changing the intensity of current, omitting some of the delay times, or by adding additional ones to the series.

The detonator of the invention can incorporate a wide variety of designs. One such design which can be improved according to the invention appears in Sewerage and Sewage Treatment by Harold E. Babbitt, Sixth Edition, John Wiley & Sons, Inc., p. 183 (chapter entitled Construction of Sewers).

As shown in the drawing, the detonaator may include a metal shell in which are loaded a sulphur filling layer 12.

Patented Qct. 29, 1958 3 a sulphur plug 14, an ignition charge 16, a priming charge 18 and a base charge 20. Bridge 22 is located in ignition charge 16. The bridge 22 consists of a plurality of wires of different diameter, wires 24 and 26 being illustrated by way of non-limitative example. These wires are connected in parallel with DC. source 28 via switch 30. A selector switch 32 is provided to select the wire to be effective.

It is to be understood that the drawing is illustrative only as various other structures can be employed to embody the improvements of the invention. Thus, for example, the invention also envisages a plurality of individual detonators each provided with a wire of different diameter, the detonators being used separately or being connected in parallel.

The advantage of the detonators according to the invention is their simple construction. Due to this fact, the manufacture of these detonators is easy and much cheaper than for those which contain conventional delay elements. Moreover, the possibility of obtaining very short intershoot time delays of millisecond order between the detonators is now possible according to the invention.

Examples DetonatorNo 1 2 3 4 5 6 7 8 Diameter otwireln microns 10(1 The said detonators were connected in parallel. When fired by using various sources of current, they have shown delay times as follows:

at-407,732.. J .J i

What is claimed is:

1. Detonation apparatus comprising ignition means and, in said means, a plurality of electrically conductive bridge. wires of different cross-sections to elfect dilferent delays.

2. Apparatus as claimed in claim 1, wherein said'means is a single ignition charge and said wires are embedded in said charge, comprising means to apply electrical current to a selected one of said wires.

3. Apparatus as claimed in claim 1, wherein said means includes a plurality of charges and said wires are respectively embedded in said charges.

BEN AMI ABORCHELT, Primary Examiner. V. R. PENDEGRASS, Assistant Examiner.

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