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(11) | EP 3 222 604 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 153(4) EPC |
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| (54) | PROCESS FOR PRESSING DELAY ELEMENTS FOR NON-ELECTRIC INITIATORS |
| (57) "PROCESS FOR PRESSING DELAY ELEMENTS FOR NON-ELECTRIC INITIATORS" refers to improvements introduced into the process for pressing delay elements used
in non-electric initiators for explosives in general and explosive accessories in
particular, produced to provide the accurate firing time (delay time) for continuation
of the explosion sequence as programmed by detonation engineering, an optimized process
which obtains bulk density regularity and homogeneity of the pressed material, providing
the advantages of decreasing firing time variability, greater repeatability and precision
of the delay mixture dosage, and less height variation. |
[0001] The present patent refers to improvements introduced into the process for pressing delay elements used in non-electric initiators for explosives in general and explosive accessories in particular, produced to provide the accurate firing time (delay time) for continuation of the explosion sequence as programmed by detonation engineering, an optimized process which obtains bulk density regularity and homogeneity of the pressed material, providing the advantages of decreasing firing time variability, greater repeatability and precision of the delay mixture dosage, and less height variation.
[0002] As the technical means connected to manufacturing delays nonelectric primers are well known, currently, one of the best delay pressing processes for non-electric initiators takes place in the following sequence:
- a) Firstly, the operator fills a spare mold with 50 zamak injected empty tubes of suitable length for the delay time to be manufactured;
- b) Then, operator fills the delay mixture container, according to the time to be manufactured. Operator also fills the lead azide dosing funnel and the PETN dosing funnel, which remain within a room behind the concrete wall of the press room;
- c) The operator programs in the control panel the number of delay mixture doses corresponding to the delay time to be produced;
- d) Filling of dosing compartment is made through automatic conveyance from the compartment to the power loading room, which is isolated from the press and the operator by the concrete wall and the steel safety door. In order to perform the automatic refill of the delay mixture, the safety door automatically opens, the compartment on position with the dosing nozzle closed is conveyed by a pneumatic cylinder to the refilling room, the door closes, and the 10 funnels of the compartment are automatically filled with the delay mixture.
- e) When a set of doses is completed, the compartment moves until aligning with the bottom of the delay mixture hopper. In an automatic way, a pneumatic device shakes the compartment for some seconds, for the granules to fill the dosing funnels. The compartment begin to move towards the position of return to pressing section, in order to, when it passes close through the Celeron plate (a low friction engineering material), the compartment dosing funnels becomes filled with the proper volume of granules and delay mixture.
- f) The correct volume is transferred to the zamak tube positioned and aligned on the bottom of the compartment; and
- g) The dosed tubes are transferred to the powder pressing sector, where a punch compacts the powder into the tube with a single operation, therefore obtaining the delay elements.
[0003] The lead azide dosage process is carried out as follows:
- A) The rotary cylinder containing 10 holes in row corresponding to a line of the pallet containing the delay elements is in a position that the holes are contacting the holes of the hopper (funnel) in conductive rubber;
- B) A pneumatic vibrator vibrates during two seconds the cylinder so all the dosing holes are filled with granulated lead azide. The cylinder then turns 180 degrees, in the indicated direction, pouring the volume corresponding to 60 - 80 mg of lead azide over the alignment funnel, and from it to the interior of delay element, on the delay mixture;
- C) The rotary cylinder returns to its original position, and the pallet then advances to the next row. Such process is repeated until 5 rows of 10 elements are with elements filled with 60 to 80 mg of azide;
- D) Afterwards the pallet goes through an conveyor belt to the PETN dosing and pressing bay, which is in the same room, however separated from the azide hopper and protected by a half concrete wall;
- E) A PETN hopper with the same azide dosing system then dispenses over the loose lead azide powder approximately 50 mg of PETN;
- F) an horizontal pneumatic cylinder positions the pallet with the first row of 10 elements aligned with a set of 10 vertical punches similar to the final compaction set of the delay mixture;
- G) The punches then descend over the PETN load, driven by the vertical pneumatic cylinders, compacting the PETN load. Note that, in this process, the lead azide load is not directly compacted, but remains encapsulated between the delay mixture load and the PETN load. This process ensures higher efficiency for PETN starting from azide, resulting in azide loads much lower than the conventional in delay fuzes, in addition to represent increased safety in the process.
- H) After the complete production cycle of all 50 elements, the pallet (mold), is positioned at front of the punches to be withdrawn by the operator; and
- I) The pallets are conducted to the delay fuze press.
[0004] This current process presents disadvantages, inconveniences and limitations of the delay element, which presents variation in apparent density of the powder, height variation, and firing time variation.
[0005] "PROCESS FOR PRESSING DELAY ELEMENTS FOR NON-ELECTRIC INITIATORS", object of the present patent, was developed to overcome the disadvantages, inconveniences, limitations and technical issues of the referred up-to-date process by means of improvements that achieve bulk density homogeneity and regularity of the compressed material, bringing advantages of reducing the variability of firing time, greater repeatability and accuracy for dosing delay mixtures and lower height variation.
[0006] The process of the present patent provides the following novelties:
- I. Preliminary powder compaction with special inner punch in dosing funnel is performed, achieving greater precision of power dosage measure in dosing plate, with excellent homogeneity and regularity of compressed material density;
- II. Final compaction of powder in delay element is made into pads that are compacted one above the other, maintaining the bulk density homogeneity and regularity of the material;
- III. Vibration in powder dosing is not necessary.
[0007] The process of the present patent solved the following problems that the current process not addresses:
- 1. The bulk density varies throughout the column height, addressed by means of preliminary compaction and final compaction of powder;
- 2. The press requires greater pressing effort, addressed by means of preliminary compaction; and
- 3. Variation of firing time, addressed by means of preliminary compaction and final compaction of powder.
[0008] For a better understanding of the present patent, the following figures are found attached hereto:
Figure 1., which shows the schematic drawing of the mixture metering device in its stage 1:
Figure 2., which shows the schematic drawing of the mixture metering device in its stage 2:
Figure 3., which shows the schematic drawing of the mixture metering device in its stage 3: and
Figure 4., which shows the schematic drawing of the mixture metering device in its stage 4.
[0009] According to the referred figures, the delay element pressing process of the present patent is executed in the following sequence:
[0010] With the dosing funnels with powder delay mixture, with lead azide and with PETN previously filled, the spare molds (M) with injected empty zamak tubes (T) are filled, the number of successive dosages of delay mixtures corresponding to the firing time to be produced is programmed in the control panel, complemented with the following operations:
Stage 1: The holes of dosing plate (1-B) are aligned with the bottom of the dosing funnel (1-A) filling the holes with the necessary quantity of powder delay mixture (3);
Stage 2: The preliminary compaction punch (1-C) descends compacting the powder (3) in the holes, thus obtaining the compacted powder cylindrical pellet;
Stage 3: The dosing plate (1-B) moves close to bottom of the dosing funnel (1-A) and the table (2-A), leaving a compacted-powder cylindrical pellet (3-A) of constant volume aligned with the pressing mold (2-C) and the final compaction punch (2-B);
Stage 4: The final compaction punch (2-B) compresses the compacted-powder cylindrical pellet (3-A) obtaining compressed powder (3-B) of delay mixture inside the zamak tube; and
Stage 5: The logical controller of the press then performs successive dosages and transfers/compactions of the delay mixture pellet, as much as programmed for each tube, in multiple pressings, until completing the total number of elements.
Stage 1: The holes of dosing plate (1-B) are aligned with the bottom of the dosing funnel (1-A) filling the holes with the necessary quantity of powder delay mixture (3);
Stage 2: The preliminary compaction punch (1-C) descends and compact the powder (3) in the holes, thus obtaining the compacted powder cylindrical pellet (3-A);
Stage 3: The dosing plate (1-B) moves close to bottom of the dosing funnel (1-A) and the table (2-A), leaving a compacted-powder cylindrical pellet (3-A) of constant volume aligned with the pressing mold (2-C) and the final compaction punch (2-B);
Stage 4: The final compaction punch (2-B) compresses the compacted-powder cylindrical pellet (3-A) obtaining compressed powder (3-B) of delay mixture inside the zamak tube; and
Stage 5: The logical controller of the press then performs successive dosages and transfers/compactions of the delay mixture pellet, as much as programmed for each tube, in multiple pressings, until completing the total number of elements.