RU2477220C2 - Method of processing porous extruded article surface layer - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to mechanical surface processing of articles or semis from porous polymer materials, i.e. cellular plastics, extruded in screw extruder. Proposed method may be used in chemical and food industries. Method comprises subjecting extruded article surface layer 5 to mechanical effects at extrusion nozzle outlet 5 to eliminate gas bubbles on, at least, a part of article surface. Said bubbles are punched by one or several piercing tools.

EFFECT: decreased stresses in surface layer, improved structural and technological properties of porous polymer materials.

2 cl, 13 dwg, 3 ex

Description

The invention relates to machining or surface treatment of products or semi-finished products from porous polymeric masses - poroplastics obtained by thermoplastic extrusion in a screw extruder, and can be used in the chemical and food industries.

Until recently, the problem of reducing mechanical stresses in the surface layer was considered only in relation to liquids (see, for example, RF patent No. 21114414, class G01N 13/02, 1998, where a method for reducing the surface tension of liquids is proposed). With the spread of extrusion processing technologies for polymer masses, it became necessary to solve this problem with respect to the extrudate.

Porous polymer masses obtained by extrusion are formed (that is, they are given certain sizes and shapes in the profile) mainly by passing a die - a special shaped nozzle on an extruder. However, the product obtained after passing it is, as a rule, just a semi-finished product called an extrudate, requiring substantial refinement to obtain the final product. Gas bubbles in the outer layer of the product, randomly expanding with a predominance of expansion in the outer, free side, create uncontrolled mechanical stresses in the surface layer of the extrudate, in contrast to inner bubbles more uniformly compressed inside the product. A distortion of its geometric shape occurs both in the transverse and in the longitudinal direction (see Figs. 1 and 2). This complicates the subsequent molding of the extrudate to give it a specific profile, since the existing technology requires considerable effort.

According to existing technology, to obtain the specified dimensions of the final product, the extrudate immediately after exiting the die is subjected to mechanical action by molding using molding devices. Most often, this is a kind of rolling rolls. With the help of the pressure produced by them at the stage of post-extrusion molding, some of the bubbles of the surface layer are deformed, sometimes up to their destruction. To achieve the result — reduction of mechanical stresses in the surface layer of the extrudate — sufficient efforts must be applied, sometimes significant; the fact that post-extrusion molding (calibration) has to be carried out at a time when the semi-finished product has not yet hardened and the bubbles are elastic, so that after compression they tend to return to their original shape. In addition, there are such modes of the extrusion process in which a superporous semi-finished product comes out of the forming die - a foam extrudate that far exceeds the required dimensions, but it is impossible to reduce these sizes directly by reducing the size of the die for technical reasons; it is impossible to achieve this with simple forming devices due to the very large swelling of the extrudate. Usually requires multi-stage molding with great effort, which inevitably increases the cost of the final product. It also weakens the outer layer of the foamy extrudate - making this layer loose. The objective of the proposed method is to reduce the cost of the final product by reducing production costs for molding the final product and improving quality due to the lower degree of deformation of the remaining bubbles.

There is another problem: for the reasons indicated below, it is highly desirable for a porous extrusion prefabricated product to have a denser surface layer with fewer or no pores. The proposed method is aimed at solving these first and second tasks, which more effectively solves the problem of reducing mechanical stresses in the surface layer of the extrudate while creating a hardened surface layer of the product.

The proposed method relates simultaneously to methods for modifying the surface layer of a material (see, for example, RF patent No. 22328548, class C22F 1/04, 2008) and methods of hardening the surface layer of products (see, for example, RF patent No. 2151806, class B23B 1 / 00,2000).

The technical result of the proposed method is to reduce mechanical stresses in the surface layer of the porous extrudate and, as a result, reduce the distortion of the shape of the extrudate before its final molding, improve the structural and operational properties of foams, improve consumer qualities and organoleptics of cereal extrusion products.

The specified technical result is achieved by the fact that in the method of reducing mechanical stresses in the surface layer of the extrudate, which consists in mechanically acting on the specified surface layer after it leaves the die, before or during its formation, in order to eliminate the smaller or most part of the surface gas bubbles throughout or on a part of the surface of the extrudate, said bubbles of the surface layer of the extrudate are punctured with a pricking tool. In this case, the said piercing tool can be set to oscillatory movements transverse to the general direction of the extrudate exit.

It is known that gas-filled, under internal pressure greater than the external, elastic body is usually called a bubble. If its shell is strong enough, then it is able to resist an external force tending to reduce its volume, in proportion to the elasticity of the shell and its strength. During the extrusion of porous polymer masses, the extrudate emerging from the die also represents many such bubbles. Therefore, if we need to radically reduce the volume of the shell with minimal effort, it is necessary to release gas from the shell. The most affordable and energy-efficient way to do this is to use a point-wise, bubble-destroying shell of the bubble that literally eliminates or destroys the bubble.

Thus, piercing the bubbles of the surface layer of the extrudate with a pricking tool is the most affordable and energy-efficient way to remove them from the surface layer of the extrudate.

Giving the said piercing tool transverse with respect to the general direction of the extrudate exit oscillatory movements significantly enhances the effect of removing bubbles from the surface layer of the extrudate.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 schematically shows a longitudinal section of the exit of the extruder with the extrudate emerging from its die; figure 2 is a cross section of the extrudate along aa of figure 1; figure 3 - stabbing tool with one and several points; figure 4 is a cross section of the extrudate on BB of figure 3; figure 5 - stabbing tool in the form of a barrel-shaped roller; figure 6 - stabbing tool in the form of an endless tape; Fig.7 - stabbing tool in the form of a rotating disc with spikes; in Fig.8 is a view of the piercing tool of figure 7 along arrow G; figure 9 is a stabbing tool in the form of pointed spikes radially mounted on the axis; figure 10 is a view of a piercing tool of figure 9 along arrow D; figure 11 - options for moving the tips relative to the extrudate; in Fig.12 - the process of forming several rotating rollers with fixed on their lateral surface points; Fig.13 is a cross-section along BB of figure 12.

As shown in figures 1 and 2, the polymer mass 1 extruded from the extruder 2 through the die 3 is converted into a porous extrudate 4 with a distorted geometric shape in both the transverse and longitudinal directions. This is because the gas bubbles 5 in the surface layer of the product, randomly expanding with the prevalence of expansion in the outer, free side, create uncontrolled mechanical stresses in the surface layer of the extrudate 4, in contrast to the internal bubbles 6, more uniformly compressed inside the product.

A method of reducing mechanical stresses in the surface layer of the extrudate 4 consists in mechanically acting on said surface layer after it leaves the die 3, before or during its formation, in order to eliminate less or more surface gas bubbles 5 on all or part of the surface of the extrudate.

In accordance with the purpose of the invention - method - these bubbles 5 of the surface layer of the extrudate are punctured with a pricking tool.

A device is proposed to reduce mechanical stresses in the surface layer of the extrudate 4 (Fig.3-11). The device is designed to eliminate less or more of the surface gas bubbles 5 on the surface of the extrudate 4 and is based on the principle of mechanical action on the surface layer of the extrudate.

In accordance with the purpose of the invention, a device for reducing mechanical stresses in the surface layer of the extrudate (Figs. 3-11) 4 is made in the form of a piercing tool located at the exit of the extruder so that the tips of the tips of the piercing tool interact with the surface layer of the extrudate 4 and provided piercing of said surface gas bubbles 5.

As shown in FIGS. 3 and 4, said piercing tool may be a fixture 7 (7a) with one or more fixed tips 8.

Also, the indicated piercing tool (Figs. 3-5, 11, 12) may be a device including one or more rotating rollers 9, 10 with points 8 fixed to their side surface. As shown in Fig. 5, the roller may be barrel-shaped or another profile.

The specified piercing tool (Fig.6) may be a device that includes one or more endless ribbons 11, worn on the rollers 11A and 11b. The endless tape 11 is provided with points 8 fixed on its outer surface.

The pricking tool (Figs. 7, 8) can be a device that includes one or more disks 13 mounted on the axis 12 with radially pointed spikes 14 made on the periphery of the disk.

The pricking tool (6, 9, 10) can be a device that includes one or more sets of pointed spikes 16 radially mounted on the axis 15. In our example of such a device in FIGS. 9 and 10, each set of pointed spikes 16 includes two radially opposite mounted spike.

The proposed method of reducing mechanical stresses in the surface layer of the extrudate, carried out by means of one or more of the described piercing tools, is performed as follows (see Fig. 3, 4, 6, 11, 12).

The surface layer of the extrudate 4, extruded from the extruder 2 through the die 3 and consisting of gas bubbles 5, is subjected to mechanical action in order to eliminate a smaller or larger part of these bubbles on all or part of the surface of the extrudate. The elimination of these bubbles is carried out by piercing them with one of the above or several pricking tools described above. Rotating stitching tools can be rotated either by gripping them with a moving extrudate or by an electric drive.

At least one of the mentioned piercing tools can be set transversal with respect to the General direction of the extrudate 4 oscillatory motion. Oscillatory movements (see Fig. 11) can be set to any of the used pricking tools and in the direction of the transverse line that cuts the center line of the extruder and extrudate at a right (arrow E) or acute (arrow E ₁ ) angle.

As mentioned above, the porous product exiting the die 3 of the extruder 2 — the extrudate 4 without the use of pricking tools, is too large and uneven in diameter and is difficult to mold. With the interaction of pricking tools with at least part of the surface of the extrudate 4, its cross-sectional dimensions decrease, molding is facilitated, the final dimensions of the product are obtained more accurately, and the surface is smoother. On its surface, intermittent or continuous traces of piercing elements are possible depending on the pressure of the devices on the extrudate, the magnitude of the piercing elements and the nature of the impact.

Example 1. To obtain a surface layer with a minimum number of bubbles on a part of the surface of the porous extrudate (see figure 3) set the piercing tool so that it is in contact with this part of the surface of the extrudate. As this tool passes by, the surface of the extrudate in contact with it, exposed to the tips of the tool, is freed from a certain number of bubbles. By selecting a tool, you can set the required surface quality or the corresponding pattern.

Example 2. To obtain a dense surface layer with a minimum number of bubbles on the entire surface of the porous extrudate, piercing tools with the number and size of piercing elements (tips), commensurate with the number and size of the bubbles of the extrudate, are installed along the perimeter of the cross section of the extrudate (see FIG. 4) . You can, for example, use two types of pricking tools from the number described above: 1) fixtures 7 and 7a with several fixed tips 8 and 2) rollers 9 and 10 with tips 8 fixed to their side surface, total four tools. When passing through these devices in this part of the perimeter, most of the bubbles of the surface layer can be destroyed, creating a semblance of a dense crust of various patterns.

Example 3. To obtain a dense surface layer with a minimum number of bubbles on a part of the surface of the porous extrudate, two pricking tools are installed on both sides of the extrudate cross-section (see Fig. 6) - an endless tape 11 with tips 8 on top, and a tool in the form of a radially bottom mounted on the axis 15 of the pointed spikes 16, shown in Fig.9 and 10. When passing through these devices in these sections of the perimeter, a certain part of the bubbles of the surface layer can be destroyed, creating a similar e dense crust of various patterns on both sides of the extrudate.

After this operation, less effort is required for subsequent or simultaneous molding. With an increase in the number of piercing elements in the device, a situation occurs when their number is comparable to the number of bubbles in the outer layer (the outer layer is conditionally the layer to which the piercing elements penetrate) and practically no bubbles remain on the extrudate section perimeter section, resulting in the formation of bubbles dense layer of the processed material.

Thus, due to the application of the proposed method, the elimination of a part, more or less, of the bubbles weakens the chaotic and excessive force stresses on the surface of the extrudate, reduces its geometric dimensions before possible further molding, or creates a denser surface layer of the material.

The scope of the method and device is the extrusion of porous polymers for household purposes (polystyrene, foam, rubber, etc.) and for food purposes (soy, cereal, etc. food polymers). For example, this invention enables the hardening of the outer layer of foams, thereby improving their structural and operational properties. Possible puncture marks can be used both for decorative and for identification purposes, as well as to increase adhesion. The denser surface of cereal extrusion products prevents the rapid penetration of moisture inside them, thereby improving consumer qualities - organoleptics, facilitating and simplifying the consumption and storage of these products.

Information sources

RU 2114414, G01N 13/02, 1998;

RU 2151806, B23B 1/00, 2000;

RU 2328548, C22F 1 / 04,2008.

Claims (2)

1. A method of treating a surface layer of a porous extrudate, comprising mechanically acting on the surface layer of the extrudate before the final molding of the product to remove surface gas bubbles, at least on a portion of the surface layer of the extrudate by piercing with one or more pricking tools immediately after the extrudate leaves the die. 2. The method according to claim 1, characterized in that at least one of the aforementioned pricking tools is given oscillatory movements transverse to the general direction of the extrudate exit.

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