GB2039558A - Production of a plastics material square mesh net by extrusion and traction - Google Patents

Abstract

The process consists of extruding a first set of threads (5) parallel with the extrusion axis, extruding from the same head a second set of threads (6) skew to the first set and intersecting the latter to form a tubing, passing said tubing over a mandrel (7) immersed in a cooling bath, cutting the tubing parallel with and along the first set of threads (5), and subjecting the web thus produced to a uniform traction in the same direction (P) of extrusion and/or in a transverse direction (P'). <IMAGE>

Description

SPECIFICATION An improved process for the production of webs of extruded plastics material square mesh net through the combination of extrusion and traction This invention relates to an improved process for the production of webs of extruded plastics material square mesh net through the combination of extrusion and traction.

As used herein, the term "web" is meant as relating to indefinite lengths of extruded net defined by longitudinal parallel edges, the spacing of which defines the web width. By the term "square meshes", such meshes are meant as defined by threads parallel with the web edges crossing with threads transverse to the web, the structure of these meshes substantially comprising four threads crossing with one another substantially at 90 , of which one pair is parallel with and the other pair is transverse to the web development.

Among the various known processes for the production of extruded square mesh net, the process as described and claimed in the Italian Patent No.

857,021 is the process that has provided the most satisfactory results. Essentially, such a known process consists of extruding a net tubing comprising two sets of threads, none of which is parallel with the extruding direction, cooling such extruded net tub- ing, slipping said tubing on a mandrel of circular cross-section, rotating the net tubing as it is fed about the axis of said mandrel, cutting the net tubing along a pair of threads of the same set helically wound about said mandrel, removing the web so obtained tangentially of the mandrel surface and inclined relative to the axis of the latter in line with said helicoidal pattern, and conventionally biaxially drawing or stretching the web.

Such a solution requires the use of a quite complex and also cumbersome apparatus since the production of webs of substantial width would require to mount a mandrel of considerable length integral with the bottom of the cooling liquid tank in axial alignment with the extruder head.

A further disadvantage is the necessity of providing at least another back roller to move the web back to the extruding direction in orderto make the apparatus as compact as possible for the final biaxial drawing or stretching step.

It is the object of the present invention to provide a process for the production of extruded square mesh net webs, which comprises simplified steps over the conventional ones.

It is another object to provide a process enabling to use for its accomplishment apparatuses which are per se known and can be relatively simply made and allowing the starting thereof in a simple and rapid way.

These and further objects of the invention will become apparent to those skilled in the art when considering the following description and claims.

A process according to the invention comprises the steps consisting of: (a) extruding from a conventional extruder head a first set of threads parallel with the extruding axis; (b) extruding from said extruder head a second set of threads skew to the first set and intersecting the latter to form joining knots and provide a net tubing; (c) slipping said net tubing on a gauging mandrel immersed in a cooling bath, so that said first set of threads is arranged longitudinally of the axis of said mandrel and said second set is arranged slantwise of said axis; (d) cutting said net tubing parallel with said first set of threads; and (e) subjecting the web so obtained to uniform suitable traction in such an extruding direction, coincident with the axis of said web, and/or in a transverse direction.

The improved process according to the invention will be more clearly understood from the foilowing description with reference to the accompanying drawings, in which: Figure 1 shows as a whole an apparatus for carrying out the process according to the invention; Figure 2 shows the arrangement taken by the two sets of threads in a length of web just after the longitudinal cutofthe net tubing; Figure 3 is an enlarged view of a knot for the length shown in Figure 2; Figure 4 shows the arrangement of the two sets of threads in a length of web after longitudinal traction; Figure 5 is an enlarged view of a knot in the length of Figure 4; and Figure 6 shows the arrangement of the two sets of threads in a web length also in completion of a possible transverse traction.

Referring to the above figures of the accompanying drawings, a convention extruder head generally shown at 1 and comprising a stationary die 2 and a rotating die 3 (rotating, for example, in the direction of arrow N), extrudes a net tubing 4 formed of a first set of th reads 5 produced by stationary die 2 and a second set of threads 6 produced by rotating die 3.

This tubing 4 so produced is slipped on a stationary gauging mandrel 7 of circular cross-section, located in register with extruder head 1 and just below the level L of a cooling liquid, for example water, intended for causing consolidation of said tubing 4. As well known, said mandrel 7 is effective to give a uniform configuration to the tubing during consolidation step.

A cutting element, such as a rotary blade 8 driven by a motor 9, cuts said tubing 4 just downstream of mandrel 7 parallel with the first set of th reads 5, and the web 4' thus obtained is drawn or pulled in the extruding direction H by a pulling unit 10, externally of the cooling liquid tank, after back movement or return through a roller 11 immersed in said tank.

It should be noted that said unit 10 and back roller 11 are on the same vertical plane containing the center line of extruder head 1, which minimizes the transverse room space of the apparatus.

As particularly shown in Figure 3, owing to rotation of die 3, each of the knots 12 formed at the crossing of threads 5 and 6 will be deformed, so that the lengths of threads 5 in close proximity of such a knot assume patterns A-B and C-D straying from the extrusion axis X-Y, and threads 6 assume pattern E-F inclined by an angle a relative to the horizontal.

The structure of web 4' provided from the cut of tubing 4 in the section between blade 8 and unit 10 is shown in Figure 2, where a substantially longitudinal pattern for threads 5 can be seen, while the pattern for threads 6 is inclined by the above mentioned angle a relative to the horizontal.

The web 4' of unit 10 enters a hot bath 13, for example water, is moved back by a roller 13', and passes through a second pulling unit 14. Finally, the web is wound up as a roll in the direction of arrow G.

The speed of rotation of unit 14 is higher than that of unit 10 according to a ratio which depends on the speed or rate of extrusion and which can be calculated time by time depending on the type of plastics material being processed, extruder head used, and other parameters as determined from experience, but readily achievable by those skilled in the art.

The web length 4" immersed in bath 13 is thus subjected to a uniform tractive action in the direction of axis X-Y, shown by arrows F in Figure 4, causing a traightening moment M (Figure 3) for threads 6 due to a torsional motion of knots 12, so that, as shown in Figure 5, the lengths A-B, B-C and C-D of threads 5 are arranged coincident with the extrusion axis X-Y, and threads 6 are oriented transversely of said axis X-Y, said web 4" taking the structure shown in Figure 4, which is evidently a square mesh structure.

After softening in warm bath or atmosphere, said web 4" is subjected to a uniform tractive action in the direction of arrows P' (transversely of direction P) to take a possible final structure, shown in Figure 6, where the meshes have a square configuration. As apparent, the tractive action in direction P' will vary according to the type of desired mesh, for example square (as shown in Figure 6), or rectangular with the major axis directed transversely of the web development, or also by suitable ratios of the tractive actions P and P', with the major axis directed in the same direction of the web development.

From the foregoing it clearly appears that the proposed process allows to operate with conventional type of apparatuses, requires a gauging mandrel of minimum length which, in case, may be also directly mounted on a fixed portion of the extruder head, enables to obtain webs, the width of which is directly proportional to the active circumference of the extruder head and mandrel, and not last, the web development during the several processing steps is contained on a single vertical plane which, in addition to afford the above mentioned reduction in transverse room space of the apparatus and greater simplicity of the latter, prevents the web from being subjected to useless and detrimental twists.

Claims (5)

1. An improved process for the production of extruded plastics material net webs of square meshes, characterized by comprising the steps consisting of: (a) extruding from a conventional extruder head a first set of threads parallel with the extrusion axis; (b) extruding from the same extruder head a second set of threads skew to the first set intersecting the latter to form joining knots and provide a net tubing; (c) slipping said net tubing on a gauging mandrel immersed in a cooling bath, so that said first set of threads is arranged longitudinally of the axis of said mandrel, and said second set of threads is arranged slantiwise with respect to said axis; (d) cutting said net tubing parallel to said first set of threads; and (e) subjecting the web thus produced to a uniform tractive action in the same direction of extrusion, coincident with the axis of said web, and/or in a transverse direction.

2. A process according to Claim 1, characterized in that said uniform tractive action in the direction of extrusion is effected just downstream of the extrusion step after web softening.

3. A process according to Claim 2, characterized in that said tractive action is effected in the direction of the web axis, so as to cause a straightening moment in the second set of threads as a result of a torsional motion of the joining knots of the threads of said second set with the threads of the first set, said torsional motion being due to said uniform traction in the direction of the web axis.

4. A process according to Claim 3, characterized in that the length of softened web is subjected to a tractive action exerted by pulling units operating at differentiated speed, said differentiated speed depending on the desired rate of extrusion and straightening moment.

5. A process for the production of extruded plastics material net webs of square meshes sub stantially as described herein and with reference to and as illustrated in the accompanying drawings.