RU2519604C1 - Pressing method of multi-layered pyrotechnic charges - Google Patents

Abstract

FIELD: blasting operations.

SUBSTANCE: pressing method of multi-layered pyrotechnic charges involves subsequent batch loading to a matrix installed on a tray of different powder compounds, which are pressed with the specified movement force per puncheon travel. Pressing is performed at the speed of 0.5-1.0 cm/s with puncheon pressure equal to: P=P₀·Π_i·[1+(0.10-0.12)·h_i/d_i], where i=1, …, n - number of layers; P₀ - minimum allowable tray pressure; Π - operator of a product; h_i - height of the charge compound layer; d_i - charge diameter.

EFFECT: simple and safe industrial pressing method.

2 dwg, 1 tbl

Description

The invention relates to the field of pyrotechnics, and more particularly to the pyrotechnic production of multilayer charges by pressing.

The level of this technical field characterizes the method of sequential automatic pressing of composite charges in a multi-position rotary device, which consists in the fact that at each position in the matrix portioned powder is loaded, which is compacted by counter movement under the action of cams of coaxial punches (see patent US 3063390, nat.cl. 107-1, 1962).

A feature of this method is that the next portion of the powder is loaded onto the pressed tablet and pressed by applying pressure to the powder through it, which determines additional technological limitations.

In particular, it does not seem technically possible to press a three-layer product due to the spring action of the pressed layers (tablets), which dampens the pressing force, the loss of which must be compensated.

With an increase in the pressing force necessary for compaction of the third layer, the finished tablets can be destroyed, that is, the monolithicity of the multilayer product is not guaranteed to be guaranteed due to the low adhesive bond of the structural components to the monolith, which distorts the predetermined combustion mode of the made puff pyrotechnic charge.

In this case, it is necessary in each case of combining materials and the number of layers in the charge to experimentally establish rheological coefficients depending on the physicomechanical properties of bulk materials, the overall parameters of the multilayer charge and the ratio of the thicknesses of its layers, which is laborious and requires highly qualified technologists and laboratory assistants.

In addition, the process stream for the practical implementation of the method is cumbersome and difficult to regulate.

The described method is limited to the practical pressing of products from two layers.

More perfect is the method of pressing three-layer pyrotechnic charges described in the journal Chemical and Oil and Gas Engineering, No. 11, 2008, pp. 18-21, V.Yu. Arkhangelsky and M.B. Generals "Study of the process of pressing powder materials with a layered internal structure", which is selected according to the technical nature and the number of matching features as the closest analogue of the proposed method.

This article describes a method for pressing a cylindrical multilayer pyrotechnic charge from various powder compositions: igniter, transitional and functional, which have different friction sensitivity and compressibility, bulk density and layer height.

When powdery materials are pressed in a closed die volume in one working stroke of the punch, the pressure decreases nonlinearly towards the pallet due to the action of radial and ring forces due to the limited movement of the material from the inner surface of the die, jamming of adjacent particles, as well as arches and arched effects .

In the known method, an analytical relationship is established between the force parameters of the pressing and the density of the material in the volume of the pressed composite product.

As a result of pressing the multilayer pyrotechnic charge in one stroke of the punch, the products have different densities in height: maximum - at the working surface of the punch in the upper layer, minimum at the opposite end of the pallet in the lower layer, which is a limiting parameter.

Depending on the required height and density of the material in the charge layers, the necessary pressing pressure is set on the punch by calculation.

So, for typical three-layer pyrotechnic charges, the ratio of the height of the charge to its diameter is experimentally limited in the range 1: (1-2), and the relative height of each layer should be less than one.

The known method allows, taking into account the rheological properties of the materials in the layers and certain assumptions, through the tabular values of the specified density and thickness of the structural layers, calculated by a special technique, to determine the maximum pressing pressure of the composite charge in one stroke of the punch.

Experimentally, in laboratory conditions, the researchers obtained acceptable results of pressing three-layer pyrotechnic charges.

However, for industrial mass production, the known method is complicated, since the shop technologist does not have tools and a mathematical model for practical use in the manufacture of different multilayer pyrotechnic charges with different physical and mechanical properties.

The disadvantage of this method is the possibility of ignition of the compositions during pressing due to the different sensitivity of the structural pyrotechnic compositions of the layers to friction, as well as the poor quality of the product due to the different compressibility of the constituent powders, which determines the complexity of its practical use in serial production.

The technical problem to which the present invention is directed is to simplify the method of pressing multilayer pyrotechnic charges of the required quality, suitable for safe industrial use in serial production.

The required technical result is achieved by the fact that in the known method of pressing multilayer pyrotechnic charges, containing a batch sequential filling in a matrix mounted on a pallet, various powder compositions that are pressed with a given movement force in one stroke of the punch, according to the invention, the pressing is carried out at a speed of 0.5 -1.0 cm / s with a pressure on the punch equal to:

P = P ₀ · Π _i · [1+ (0.10-0.12) · h _i / d _i ], where

i = 1, ..., n is the number of layers;

P ₀ - the minimum allowable pressure on the pallet;

Π is the product operator;

h _i is the height of the composition layer in the charge;

d _i is the diameter of the charge.

Distinctive features of the proposed technical solution allow engineering mathematical dependence on the given geometric parameters of the multilayer charge (relative height of each layer, their quantity) to establish the necessary technological parameters of pressing (speed and pressure on the punch, with limited pressure on the pallet), which is sufficient for serial production production in the manufacture of various pyrotechnic charges from the required number of layers of structurally different powder compositions.

The factor 0.10-0.12 of the relative layer height (h _i / d _i ) is the quantitative equivalent of the product of the external friction coefficient and the lateral pressure coefficient when pressing at a speed of 0.5-1.0 cm / s, taking into account the compressibility of the pyrotechnic compositions of bulk materials .

It was experimentally established that the external friction coefficient for igniter, reinforcing, color-flame, spark-ignition, etc. pyrotechnic compositions during pressing at a speed of 0.5-1.0 cm / s does not noticeably change, therefore, the specified product of the coefficients in the operating range of pressing pressures from 150 up to 250 MPa remains almost constant for the main groups of pyrotechnic compositions and is in the range of 0.10-0.12.

Thus, the pressing pressure on the punch is directly determined analytically from the values of the minimum allowable pressure on the pallet and the height of each layer, in particular for three:

P = P ₀ · (1 + 0.2h ₁ / d) · (1 + 0.2h ₂ / d) · (1 + 0.2h ₃ / d).

Therefore, each essential feature is necessary, and their combination is sufficient to achieve a novelty of quality that is not inherent in the signs of disunity, that is, the technical problem posed in the invention is solved not by the sum of the effects, but by a new effect of the sum of the attributes.

The essence of the invention is illustrated by the following.

To ensure a given density of each pressing layer, it is necessary to set the maximum pressing pressure, which is determined by calculating the stresses and density by volume of the multilayer pyrotechnic bulk prefabricated product.

The calculation of the pressure on the punch is reduced to a phased analysis of the equilibrium conditions of each of the layers of the material, starting from the bottom layer. The equilibrium equation for the elementary layer of the lower composition has the form:

$$-({\sigma }_{z_{\mathrm{one}}}+d{\sigma }_{z_{\mathrm{one}}})\mathrm{<figure-callout\; id="2"\; label="\pi \; r"\; filenames="00000015.png"\; state="\{\{state\}\}">\pi \; </figure-callout>}{r}^{}{}^2+{\sigma }_{z_{\mathrm{<figure-callout\; id="2"\; label="one\; \pi \; r"\; filenames="00000015.png"\; state="\{\{state\}\}">one\; </figure-callout>}}}\pi r^{}{}^2+\mathrm{<figure-callout\; id="2"\; label="\tau "\; filenames="00000015.png"\; state="\{\{state\}\}">\tau </figure-callout>}2\pi rd{z}_{\mathrm{one}}=0(\mathrm{one})$$

- радиус пресс-инструмента (пиротехнического заряда); $${\sigma }_{{}_{z_1}}$$

- нормальное напряжение, действующее по оси z (в направлении прессования) на уплотняемый материал первого слоя.Where $$r=\frac{d}{2}$$

- radius of the press tool (pyrotechnic charge); $${\sigma }_{{}_{z_{\mathrm{one}}}}$$

- normal stress acting along the z axis (in the pressing direction) on the material to be sealed in the first layer.

The shear resistance τ in such processes can be represented in the form: τ = α ₀ (ν) + f (ν) σ. The quantities α ₀ and f are functions of the sliding velocity ν.

, при z₁=0 , имеет вид $${\sigma }_{z_1}=\left(p_0+\frac{{\alpha }_{01}}{{\xi }_1{\alpha }_{11}}\right)\exp \left(\frac{2f_1}{\gamma }{\xi }_1{z}_1\right)-\frac{{\alpha }_{01}}{{\xi }_1{f}_1}$$

.The solution of this equation, taking into account the boundary conditions $${\sigma }_{z_{\mathrm{one}}}=p_0$$

, for z ₁ = 0, has the form $${\sigma }_{z_{\mathrm{one}}}=\left(p_0+\frac{{\alpha }_{01}}{{\xi }_{\mathrm{one}}{\alpha }_{\mathrm{eleven}}}\right)\exp \left(\frac{2f_{\mathrm{one}}}{\gamma }{\xi }_{\mathrm{one}}{z}_{\mathrm{one}}\right)-\frac{{\alpha }_{01}}{{\xi }_{\mathrm{one}}{f}_{\mathrm{one}}}$$

.

Since the self-adhesive component of the external friction forces α _{0 is} quite small compared to the deformation component, its effect on the stress state of the material can be neglected.

Given that the relative thickness of the layer in pyrotechnic charges is usually less than unity, the exponential term of the obtained solution can be expanded in the Taylor series and the solution can be simplified without significantly reducing the calculation accuracy. In this case, the pressure at the boundary of the first and second layer will be equal to:

. $$\sigma H_{\mathrm{one}}=p_0\left[\mathrm{one}+f_{\mathrm{one}}{\xi }_{\mathrm{one}}\frac{H_{\mathrm{one}}}{d}\right]$$

.

Solving equation (1) for each layer, it is possible to calculate the pressing pressure for the entire multilayer pyrotechnic charge from n compositions:

, где p₀ - давление прессования, необходимое для получения нижнего слоя с заданной плотностью и высотой, $$\frac{H_i}{d}$$

- относительная высота i-го слоя пиротехнического состава, f_iξ_i - произведение коэффициента внешнего трения на коэффициент бокового давления. Экспериментально установлено, что это произведение в рабочем диапазоне давлений прессования от 150 до 250 МПа остается постоянным (фиг.1) и для основных групп пиротехнических составов находится в пределах от 0,10 до 0,12. $$p=p_0{\displaystyle \prod _{i=\mathrm{one}}^n\left[\mathrm{one}+f_i{\xi }_i\frac{H_i}{d}\right]}$$

where p ₀ is the pressing pressure necessary to obtain the lower layer with a given density and height, $$\frac{H_i}{d}$$

is the relative height of the ith layer of the pyrotechnic composition, f _i ξ _i is the product of the external friction coefficient and the lateral pressure coefficient. It was experimentally established that this product in the operating range of pressing pressures from 150 to 250 MPa remains constant (Fig. 1) and for the main groups of pyrotechnic compositions is in the range from 0.10 to 0.12.

Based on the foregoing, the pressure on the punch when pressing multilayer pyrotechnic charges should be taken equal to:

$$p=p_0{\displaystyle \prod _{i=\mathrm{one}}^n\left[\mathrm{one}+\frac{(0.1...0.12)H_i}{d}\right]}$$

Studies of the dependences of the external friction coefficient on speed for the main groups of pyrotechnic compositions: color-flame, force, thermobaric, lighting and aerosol, showed that with an increase in the shear rate of the mixture relative to the external boundary, the friction coefficient initially decreases to a minimum value and then monotonically increases (Fig. 2 )

In the working speed range, the approximation of this dependence can be represented in the form of a polynomial of the second degree with an accuracy sufficient for technical calculations:

f = αν ² -b _ν + c, where f is the external friction coefficient, ν is the shear rate of the composition relative to the matrix walls (pressing speed); a, b and c are empirical coefficients.

и $$\frac{d^{2}f}{d{\nu }^2}>0$$

, то естьObviously, the work of external friction forces during pressing of the ith layer will be minimal at a pressing speed corresponding to the minimum value of the external friction coefficient. This condition is satisfied when at some point of the function $$\frac{df}{d\nu }=0$$

and $$\frac{d^2\mathrm{<figure-callout\; id="2"\; label="f\; d\; \nu "\; filenames="00000015.png"\; state="\{\{state\}\}">f\; </figure-callout>}}{d{\nu }^{}}>0$$

, i.e

$$\{\begin{array}{c}\frac{df}{d\nu }=2\alpha \nu -b=0\\ \frac{d^2\mathrm{<figure-callout\; id="2"\; label="f\; d\; \nu "\; filenames="00000015.png"\; state="\{\{state\}\}">f\; </figure-callout>}}{d{\nu }^{}}=2a>0\end{array}$$

.From these conditions it follows that the speed at which the work of external friction forces is minimal will be equal to $$\nu =\frac{b}{2a}$$

.

When choosing the pressing speed of a multilayer pyrotechnic charge from n layers, one should choose the minimum value of ν for the ith layer. Considering that the minimum values of the external friction coefficient for the main groups of pyrotechnic compositions used are in the range from 0.5 to 1.0 cm / s, the pressing speed of the multilayer pyrotechnic charge should be taken within the specified limits.

Comparative data on the density and height of the layers for three-layer pyrotechnic charges with a diameter of 15 mm, pressed by the sequential pressing method and the proposed, are shown in the Table.

Table Layer number Structure Layer height mm The average density of the composition in the layer according to the method of the prototype, g / cm ³ The average density of the composition in the layer according to the proposed method, g / cm ³ one Igniter 2 1,918 1,918 2 Transitional four 1,922 1,925 3 Color flame 9 1.935, 1.94

As can be seen from the above data, the relative deviation of the density of the proposed method does not exceed 0.5%, which suggests that the proposed method, allowing to significantly improve performance, does not reduce the quality of charges.

A comparative analysis of the proposed technical solution with identified analogues of the prior art, from which the invention does not explicitly follow for a pyrotechnic specialist, showed that it is unknown, and taking into account the possibility of using the method of pressing multilayer pyrotechnic charges in serial production on existing equipment, we can conclude eligibility criteria.

The method according to the invention has been successfully tested in laboratory conditions on the whole practical variety of puff charges and can be recommended for use in serial enterprises of the industry.

Claims (1)

A method of pressing multilayer pyrotechnic charges, containing a batch sequential filling in a matrix mounted on a pallet of various powder compositions that are pressed with a given movement force in one stroke of the punch, characterized in that the pressing is carried out at a speed of 0.5-1.0 cm / s with punch pressure equal to
P = P ₀ · Π _i · [1+ (0.10-0.12) · h _i / d _i ], where:
i = 1, ..., n is the number of layers;
P ₀ - the minimum allowable pressure on the pallet;
Π is the product operator;
h _i is the height of the composition layer in the charge;
d _i is the diameter of the charge.

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