SU1212830A1 - Extrusion head for treating polymeric materials - Google Patents

Description

The invention relates to the processing of plastics and can be used to produce tubular blanks of articles from thermal plasters.

The aim of the invention is to improve the performance of extrusion by providing an equal-speed yield of processed plastic.

On ,, fig. 1 shows schematically an extrusion head, a section along the central axis; in fig. 2 is a section A-A in FIG. one; on; FIG. 3 - flow curve of the processed plastic in logarithmic coordinates.

The extrusion head comprises a housing 1 with an opening 2 for feeding the melt. In case 1, a mandrel 3, a matrix 4 and a pressure wheel 5 are placed.

Between the housing 1 and the mandrel 3 are formed sequentially located annular collector 6 and retaining channel 7. Dorn 3 and matrix 4 are mounted with the formation of the forming gap 8. Wall 9 of housing 1 on the section of the retaining channel 7 is made in the form of a round cylinder, and the surface profile of the mandrel 3 on This area is formed by a radius vector, which is determined by the formula

 d g 1LO

V li Ii + iir by. t

 M (2h + l) - 180 °

ix

2 (n + r)

/ 1Ф- ° - /) n-fl | --MrT

 1 ° A J

where p is the radius vector of the curved line forming the profile of the mandrel 3; d - inner diameter of the housing 1 on

plot retaining channel 7; D is the average diameter of the annular collector;

R is the average radius of the contour of the cross section of the annular collector 6; A p-polar angle formed by a radius vector p with a polar axis extending from the center of a circle with a diameter d of a normal axis of the head in a section corresponding to the location of the central axis of the molten plastic feed hole; ho-height of the retaining channel in cross section,

the corresponding E is the average length of the retaining channel; n is the average tangent of the slope of the flow curve of the plastic being processed in logarithmic coordinates.

The operation of the extrusion head is as follows.

The processed plastic through the opening 2 is fed into the annular collector 6 and distributed around the perimeter of the extrusion die, enters the retaining channel 7 and through the forming gap 8 exits as a tubular billet, which is used

five

It is, for example, for further forming of pipes, tubular films, blown products, and insulating covers. To the forming gap 8 by means of transitional parts forming intermediate channels, the nozzles of ring granulating heads (not shown) can be docked. The pressure in the annular manifold 6 decreases as the distance from the melt supply hole 2 increases.

plastic and reaches a minimum in the cross section of the collector 6, opposite to the hole 2, i.e. the maximum of the pressure corresponds to the value of the polar angle, measured from the polar axis OT, and the minimum, as shown in Fig. 2. The compensation of the pressure drop in the annular collector 6 is achieved by profiling the cylindrical surface of the mandrel in the section of the retaining channel 7 in accordance with the ratio given, which ensures equal resistance on different trajectories of the system in the ring collector - retaining channel while the volumetric flow of the plastic is equal on all trajectories x and ensures uniform feeding of the forming gap 8 without any adjustments, regardless of the extrusion speeds.

Profiling the surface of the mandrel 3 in the area of the retaining channel 7, i.e. the choice of its geometry is made taking into account the brand of plastic being processed and the extrusion temperature.

Dorn surface profiling. It is necessary to determine the profile of the cross section of the mandrel in the area of the retaining head of the extrusion head having

.. the following defining dimensions of the annular collector and the retaining channel: the inner diameter of the body in the section of the baffled channel cm, the average diameter of the annular collector cm, the average radius of the contour of the cross section

0 ring collector R 1.6 cm, the height of the retaining channel in the section corresponding to the location of the hole for feeding the molten plastic, i.e. at, h () 0.25 cm, average length of the retaining channel, 0 cm. The indicated average values are found after preliminary processing of the geometrical parameters of the head channel, at which small technological elements of the manufacture of its parts (rounding, measuring for measuring dimensions, transitional radii, etc.), and the head channel is dimensioned schematically in accordance with its main sections, namely: an annular collector, a retaining channel forming a gap.

5 The extrusion head must ensure the uniformity of the yield of low density polyethylene processed at a temperature of 180 ° C.

0

five

0

The mean tangent of the inclination angle a on the flow curve is preliminarily determined, for which it is approximated by a straight line (segment CZ in Fig. 3).

Find t that

  0.61.

The lengths MZ and CM are determined directly from FIG. 3. This approximation is possible because the flow curves of plastics used in the production of products by extrusion, in many cases coincide with or are well approximated by straight lines.

Substituting the original values in the above ratio, we obtain

„D I 1jiD ..

 2 (n + l)

rd (3n + l) l, jm Jg ° mp +,

) -l

-o, bw

 , 70-15,24 (1- / 1 - J | QO /) -

When calculating the current values of the radius vector p, it is possible to substitute any values of the polar angle cp in the range from 0 to 360 ° C. For convenience, the construction of the cross section of the mandrel in the section of the retaining channel is set by a uniform division of the specified range.

The results of the calculation of the profile of the surface of the mandrel shown in the table.

ten

15

20

25

Making the substitution of the selected values of f in the equation for p, find the corresponding values of this radius vector. At the same time, the table shows the heights of the retaining channel h in the sections corresponding to the angles cf and characterizing the geometry of the retaining channel, and these values are defined as

h -f- P P The dimensions given in the table determine the cross-sectional profile of the mandrel in the section of the retaining channel and the height of the retaining channel corresponding to the initial data and allowing the mandrel and retaining channel to have the required geometry, ensuring uniformity of the molten plastic output through the forming gap. The fabrication of a mandrel with the required cross-sectional profile can be carried out on a copy milling machine using a copy machine made in accordance with the data in the table.

The supporting channel of such a geometry provides full compensation for the pressure drop in the collector channel, and the extruded plastic uniformly feeds the forming gap. This ensures an increase in the dimensional accuracy of the products and an increase in the extrusion productivity, the possibility of producing products with a minimum deviation from the specified dimensions is realized, which results in saving plastic.

Claims (1)

EXTRUSION HEAD FOR PROCESSING POLYMERIC MATERIALS, comprising a housing with a hole for supplying a melt, a mandrel and a matrix located in the housing, the housing and the mandrel being mounted to form an annular collector, retaining channel and forming gap, characterized in that, in order to increase the extrusion performance by providing an equal-speed output of the processed material, in the section of the retaining channel, the surface profile of the DBRNA is formed by a radius vector of variable magnitude, determined by the following relationship: _{n =} d._i ¹ ____ у ^р 2 tho ² ^ ¹ 2 (n + l) lR ^{7ff: FlX} [8_ (3η + 1) 1 ^Π _ / j _ Д ° °. _{/ g} + 11zht ^{X l} 4 (2h + l) ^JU '180 ^{o / J} where p is the radius vector of the curve line forming the mandrel profile, cm; d is the inner diameter of the housing on the plot of the retaining channel, cm; D is the average diameter of the annular collector, cm; R is the average radius of the contour of the cross section of the annular collector, cm ·, φ is the polar angle formed by the radius vector p with the polar axis g passing from the center of the circle with a diameter d normal to the axis of the extrusion head in the section corresponding to the location of the central axis of the feed hole molten plastic; h ₀ —height of the retaining channel in the section corresponding to ψ = 0, cm; £ is the average length of the retaining channel, cm; it is the average tangent of the slope of the flow curve of the processed plastic in logarithmic coordinates.