FR2663961A1 - Needling method and machine for carrying it out, especially for short mineral fibres - Google Patents

Abstract

A nap (3) is needled on its two faces by two needling heads (6a, 6b). The two heads (6a, 6b) are offset relative to one another in the longitudinal direction of the nap. The needles (8) of each head (6a, 6b), which are driven in a vertical reciprocating movement, penetrate into the nap to a depth at most equal to its thickness (and greater than half this thickness), the nap being supported by a conveyor (41a, 41b) which is itself supported by a bearing surface (53a, 53b). Since the needles have barbs directed towards their base, portions of fibres are returned towards the inside of the nap during each retraction movement of the needles, thereby increasing the cohesion of the nap. The conveyors (41a, 41b) drive the nap by adhesion. Application to the needling of short and/or brittle refractory inorganic fibres, such as rock wool, which can be used for the insulation of boilers, pipework, etc.

Description

 The present invention relates to a method for needling, in particular the needling of short and brittle inorganic fibers.

 The present invention also relates to a machine for implementing this method.

In known needling machines, a needling head or needle holder board is driven by an alternating movement orthogonal to a continuous web of a nonwoven fibrous product traveling through the machine so that the needles periodically penetrate the web , at a rapid rate, which causes a binding effect of the fibers of the ply and considerably increases the cohesion of the latter. The shape of the needle ends (in the fork, with barbs directed towards the tip of the needle, ...) plays a role in the cohesion obtained and also in the external appearance of the final product: curly appearance, "flat" appearance,
The cohesion effect is improved by using two needle-holder boards, instead of one, these boards being arranged on either side of a region of the path of the sheet to be treated, and being driven by symmetrical alternative movements. compared to the tablecloth. Current needling machines are generally designed according to this last principle, the two needle holder boards operating simultaneously.

Experience shows that needling machines
known do not allow pass to switch properly
certain fibrous products such as those containing
short and / or brittle inorganic fibers such as
rock wool (formed from molten stone with
additives), alumina fibers, fly ash (fibers
recovered from burnt coke), ... In other words,
it is impossible to sufficiently improve the cohesion of
these products by a needling performed according to the
known technique.

 The invention is based on the surprising discovery that the effective needling of such products was made possible by a process according to which an incomplete needling is carried out on each side of the sheet one after the other.

More specifically, the subject of the present invention is a method for needling a continuous web of fibers in which
- the fiber sheet is moved in its longitudinal direction
- During the aforementioned movement of the ply, the needles of one of two needling heads are reciprocated briefly and repeatedly into each successive region of the ply, through each of its faces, by a reciprocating movement of said needles heads directed transversely to said sheet,
characterized in that in each region of the water table
- the needles of one of the needling heads are first penetrated through a first face of the ply to a depth less than the thickness of the ply, while the second face of the ply is supported by a first support surface;
- Then, the other needling head is penetrated through the second face of the ply to a depth at most equal to the thickness of the ply, while the first face of the ply is supported by a second surface d 'support.

The present invention also relates to a needling machine allowing the implementation of the above method, comprising
- Means for setting the sheet of fibers in motion in its longitudinal direction
- two needling heads, arranged on either side of the ply, carrying needles directed transversely to the ply
means for communicating to the needling heads an alternating movement directed transversely to the ply in order to periodically penetrate the needles into the ply, characterized in that
the means for communicating an alternating movement to the needling heads are such that the depth of penetration of the needles into the web is at most equal to this thickness
- the two needling heads are offset longitudinally with respect to the ply; and
- Facing each needling head, the machine has a bearing surface capable of supporting the face of the ply opposite the head.

 Thanks to the invention, it is now possible to carry out the needling of nonwoven webs (also called "matts") of short fibers, these fibers being able to be as short as 25 mm. The fact that these fibers are brittle is not an obstacle to needling according to the invention. The inorganic fibers mentioned above, and in particular rock wool, can therefore be advantageously needled by a machine according to the invention.

 The invention thus makes it possible, in particular, to produce a sheet of refractory inorganic fibers which can be used as a thermally insulating lining for boilers, various pipes, etc.

 The machine according to the invention can also treat sheets of fibers of usual composition and length, which is of interest both from the point of view of the versatility of the machine and the possibility of treating "mixed" products.

Other features and advantages of the invention will appear in the following description of a non-limiting embodiment, made with reference to the accompanying drawings, in which
- Figure 1 is a schematic sectional view through the median vertical plane of a needling machine according to the invention;
- Figure 2 is a view similar to Figure 1 showing the needles of the needling heads in the position of penetration into the web to be treated; and
- Figure 3 is an elevational view of a needle usable in the needling machine of Figure 1.

 In FIGS. 1 and 2, a frame 1 in the form of a tunnel with a horizontal axis parallel to the plane of FIG. 1 supports the various members of the needling machine, which essentially comprises two needling assemblies 2a, 2b offset in the direction of the path of a sheet to be treated 3, this direction being indicated by the arrow D and being parallel to the axis of the tunnel.

 Each set 2a, 2b comprises a needling head or needle holder board 6a, 6b known in itself, comprising a frame 7a, 7b carrying a number of needles 8, of which only a few are shown on each head. Figure 1, one of them being shown in more detail in Figure 3. The needles 8 are directed perpendicular to the plane path P of the sheet, path which extends in the tunnel formed by the frame. The head 6a is disposed above the path P of the sheet and its needles 8 are directed downwards. The head 6b is arranged under the path of the sheet and its needles are directed upwards.

 The heads 6a, 6b are each subjected to a movable frame 9a, 9b. The frames 9a, 9b are driven in an alternating movement in the direction orthogonal to the plane P, that is to say here vertically.

 To this end, each movable frame 9a, 9b is moved, in a known manner, by a drive system partially shown at 13a, 13b. Each system 13a, 13b comprises in particular a connecting rod 16 articulated on the one hand at the top of the associated movable frame 9a or 9b and on the other hand at an eccentric point of a respective reduction gear 18, itself driven by a drive wheel 21 by means of a belt 23. A device 26 makes it possible to adjust the eccentricity of the point of the wheel 18 where the upper end of the connecting rod 16 is fixed, and thereby the vertical amplitude of the movement of the frame mobile 9a or 9b concerned. The drive system 13a or 13b also includes an oscillating counterweight 28 mounted at the articulation of a toggle joint whose ends are articulated one to the frame 1 and the other at a point on the wheel 18 diametrically opposite the point of attachment of the connecting rod 16. This oscillating counterweight 28 has the function of balancing the main vibrational forces of the corresponding assembly 2a or 2b.

 In addition, the height position of the vertical movement of the head 6a or 6b is adjustable by means of a respective screw-nut system 11.

 Facing each needling head 6a, 6b, there is a table 31 provided with a plate 33 allowing the passage of the needles of the head 6a or 6b, thanks for example to an openwork construction. This tray has the function of retaining the ply during needling, when the movement of the needles of the head 6a or 6b is oriented respectively upwards or downwards.

 Each plate 33 is slightly inclined towards the plane P and downstream. Given the fact that the thickness of the product decreases from the inlet to the outlet of the machine, the needling operation also has a compacting effect. In addition, the parts of the plates 33 coming into contact with the sheet have a smooth surface favoring the sliding of the sheet.

 In accordance with the invention, it is arranged opposite each needling head 6a, 6b, on the other side of the path P of the web with respect to this head, a support structure 41a, 53a and 41b respectively, 53b of the tablecloth. The support structures are substantially rigid with respect to the forces transverse to the plane P.

 In the example shown, each rigid structure comprises a conveyor belt 41a, 41b which, opposite the associated head 6a or 6b, has a face in contact with the ply on the side opposite the needles 8 of this head 6a or 6b, and a other face, opposite the first, which slides on a fixed support surface 53a or 53b relative to the respective cylinders 43a, 44a, and 43b, 44b. The surface 53a, 53b is defined by a table inside the loop formed by the mat 41a or 41b.

 Each bearing surface 53a, 53b has the role of supporting the sheet and the associated mat in a vertical direction when the needles 8 penetrate the sheet.

 In use, the offset adjustment device 26 and the screw adjustment device 11 for the height of each head 6a or 6b for a given position of the corresponding wheel 18 are adjusted in such a way that the needles 8 never pass completely through. the sheet, that is to say never hit the mat 41a or 41b, even when the heads 6a or 6b are in their neutral position closest to the mat 41a or 41b.

 The movement of the ply to be needled takes place in the direction D, in the plane P, which is a horizontal plane in the example shown. This movement is provided, in a manner known per se, by introduction and extraction devices, for example pairs of rollers upstream and respectively downstream of the machine.

 This movement is also obtained by means of two conveyor belts 41 each rotating around two cylinders with parallel axes 43a, 44a, and 43b, 44b. The belts 41a, 41b are driven at a suitable speed, corresponding to that of the aforementioned introduction and extraction devices, by motors 49a and 49b and belts 61 to 64. The external surface of each carpet 41a, 41b which comes in contact with the ply has asperities of a shape chosen so as not to be aggressive with respect to the ply, and in particular, so as not to retain fibers of the ply after separation from it beyond the downstream cylinder. For example, the outer surface of the belts 41a, 41b coming into contact with the sheet, may be constituted by a flexible material and may include cells having a certain suction effect.

 The supports of the axes of the cylinders 43a, 44a 43b, 44b supporting the belts 41a and 41b are connected to the frame 1 by means of screw-nut systems 48, making it possible to adjust the position of each belt in the direction perpendicular to the plane P, c that is to say vertically in the example.

 The path P of the sheet is flat and continuous through the two assemblies 2a and 2b, the forward speeds of the two belts being equal. In other words, the active face of each belt 41a, 41b is substantially in the extension of the sliding face of the fibers on the plate 33 of the other needling assembly.

 The offset of the two heads 6a, 6b relative to each other in the direction D is greater than the length L of needling of each head.

 Each region of the sheet therefore performs a path greater than L to pass from one head 6a to the other head 6b.

 The axis of the downstream cylinder 43a of the assembly 2a and the axis of the upstream cylinder 44b of the assembly 2b are substantially in the same plane perpendicular to the plane P.

Thus, the belts 41a and 41b pinch the web between them in its path of passage from one to the other of the subassemblies 2a, 2b, and the web is entrained by adhesion at least on one face throughout its passage through the machine .

 The machine comprises an additional roller 66 whose axis is in the same plane perpendicular to the plane P as the axis of the downstream roller 43b of the downstream assembly 2b. On leaving the machine, the ply is entrained between the mat 41b, located above it, and the additional roller 66 entrained in the opposite direction to the roller 43b.

 Figure 3 shows a needle 8 usable in the machine described above. This needle has, at its periphery, in a penetration area 56, small points or barbs 57, directed towards the base of the needle.

 The method according to the invention will be described on the occasion of the description of the operation of the machine above with reference to FIGS. 1 and 2.

 To clarify the ideas, it is assumed that a sheet of non-woven fibers, also called matt, of determined thickness, for example 50 mm, must be needled, these fibers being made of rock wool, that is to say of short, brittle inorganic fibers.

 We start by adjusting the relative positions of the different parts of the machine. One can for example operate as follows. The height position of the belts 41a and 41b and that of the plates 33 is adjusted by means of the adjustment systems 48 and 38 respectively, so that the vertical distance between the surfaces facing the carpet 41a, 41b and of the associated plate 33 corresponds to the thickness of the matt along its path in the machine.

 The amplitude of the vertical movement of the movable frames 9a and 9b is then adjusted to a value which must be substantially greater than the desired penetration in the matt plus a distance corresponding to the thickness of the plate 33, so that the needles are released of the ply for most of the time, which allows the ply to advance between two strikes by the needles 8. For this adjustment, the eccentricity of the upper attachment point of the connecting rod 16 is acted on by means of the adjusting device 26.

 Finally, the dead center of the needling heads 6a, 6b closest to the plane P is adjusted by means of the adjustment system 11, so that the needles 8 penetrate the desired depth into the sheet, for example 40 mm.

 It only remains to adjust the speed of advancement of the matt and the frequency of the reciprocating movement of the heads, these two quantities being linked to each other, most often in a proportional manner, which is the case of the described embodiment. The corresponding adjustment system, well known in itself and not shown in the drawing, allows the two quantities to be adjusted simultaneously. By way of example, we can retain a frequency of 300 strokes / minute, corresponding to a speed of advance of the matt close to 1 meter / minute.

 The different settings of the needling machine being made, the mattress is introduced into the assembly 2a in the direction D and the motor members are actuated by moving the belts 41a, 41b and the needling heads 6a and 6b.

 A first region of the matt is first needled by the head 6a, the needles of which penetrate, during the movement of the head towards the plane P, into the upper surface of the matt, which is supported by the carpet 41a and the surface of support 53a. Then, without having passed through the matt, the needles take a directed movement away from the plane P and emerge from the matt.

 When the region of the matt thus needled on the upper side reaches between the plate 33 and the conveyor belt 41b of the second needling assembly 2b, the needles 8 of the second head 6b likewise penetrate, in a non-traversing manner, into the lower surface of the matt, then come out, completing the needling of the matt region considered.

 FIG. 2 represents the phase of the process in which the needles of the needling heads 6a, 6b are at their maximum of their penetration into the matt, that is to say that the end points of the needles are very close to the external surface matt without reaching it.

 Due to the shape of the needles 8, the movement of exit of the needles brings portions of fibers towards the face of the matt pressed against the plate 33, which increases the cohesion of the matt.

 In what precedes, it was considered that the penetration depths of the needles were identical in each of the two surfaces of the matt, which allows constructive and adjustment simplifications.

But this is not an absolute obligation and the two depths could be different.

 According to an advantageous embodiment of the method, the penetration depth must be between 50% and 98% of the thickness of the matt.

 The frequency of the reciprocating movement of the heads can vary, depending on whether the fibers are more or less brittle, between 100 and 700 cycles per minute approximately.

 The shape of the needles 8 can be quite varied.

However, when it comes to needling relatively brittle fiber matts, it is preferable to use, in the range of conventional needling needles, fine or medium needles, since experience has shown that relatively needles large ones can cause many fiber breaks.

 The invention allows the needling of matts composed of very varied refractory inorganic fibers which may be, in addition to rock wool, carbon fibers, quartz fibers, silica fibers, alumina fibers, fly ash, ...

 Of course, the invention is not limited to the example which has just been described, and many modifications can be made to it without departing from the scope of this invention.

Claims (17)

 1. Method for needling a continuous web of fibers (3), in which  - the fiber sheet is moved, in its longitudinal direction  - During the aforementioned movement of the ply (3), one makes penetrate briefly and repeatedly in each successive region of the ply, through each of its faces, the needles (8) of a respective one of two heads of needling (6a, 6b) by an alternating movement of said heads directed transversely to said ply (3),  characterized in that in each region of the water table  - The needles (8) of one of the needling heads (6a) are first penetrated through a first face of the ply to a depth at most equal to the thickness of the ply, while the second face of the sheet is supported by a first bearing surface (41a)  - Then, the other needling head (6b) is made to penetrate through the second face of the ply to a depth at most equal to the thickness of the ply, while the first face of the ply is supported by a second bearing surface (41b).  2. Method according to claim 1, characterized in that between the moment when one makes one of the heads penetrate through a first face of a region of the sheet and the moment when one makes penetrate the 'other head in the second face of the same region of the web, the web is shifted longitudinally by a distance at least equal to the longitudinal dimension (L) of the first needling head (6a).  3. Method according to one of claims 1 or 2, characterized in that penetrates each needling head (6a, 6b) in at least half the thickness of the web.  4. Method according to claim 3, characterized in that each needling head penetrates a depth between 50% and 98% of the thickness of the web.  5. Method according to one of claims 1 to 4, characterized in that the frequency of the reciprocating movement of the needling heads is between 100 and 700 cycles per minute.  6. Method according to one of claims 1 to 5, characterized in that the bearing surfaces (41a, 41b) are displaced in the direction of movement of the ply.  7. Method according to claim 6, characterized in that the bearing surfaces (41a, 41b) are used as a means of driving the sheet by adhesion.  8. Method according to one of claims 1 to 7, characterized in that each region of the ply is clamped between the two bearing surfaces (41a, 41b) in its path from the first head (6a) to the second head (6b).  9. Method according to one of claims 1 to 7, characterized in that a matt of relatively short and / or brittle fibers, in particular refractory inorganic fibers such as: rock wool, carbon fibers, fibers quartz, silica fibers, alumina fibers, fly ash.  10. A needling machine for a web or matt of nonwoven fibers comprising  - Means for setting the sheet of fibers in motion in its longitudinal direction  - two needling heads (6a, 6b), arranged on either side of the ply, carrying needles (8) directed transversely to the ply  means for communicating to the needling heads an alternating movement directed transversely to the ply in order to periodically penetrate the needles (8) in the ply,  characterized in that  - The means for communicating to the needling heads (6a, 6b) an alternating movement are such that the penetration depth of the needles in the web is at most equal to the thickness of the latter  the two needling heads (6a, 6b) are offset relative to each other in the longitudinal direction of the ply, and  - Facing each needling head (6a, 6b) the machine has a bearing surface (41a, 41b) capable of supporting the face of the ply opposite the head.  11. Machine according to claim 10, characterized in that the needles (8) of the needling heads (6a, 6b) have barbs (57) directed towards the base of the needles.  12. Machine according to one of claims 10 and 11, characterized in that it comprises means (11,26) for adjusting the penetration depth of the needles (8) in the web.  13. machine for needling a sheet of fibers according to one of claims 10 to 12, characterized in that the bearing surface facing each head is constituted by a surface of a mat (41a, 41b) participating in the of the tablecloth.  14. Machine according to claim 13, characterized in that said surface of the carpet has roughness.  15. Machine according to claim 13, characterized in that said surface of each drive belt (41a, 41b) is defined by a flexible material comprising cells.  16. Machine according to one of claims 13 to 15, characterized in that the two belts (41a, 41b) partially overlap so as to pinch the web in a region between the two needling heads (6a, 6b ) relative to the direction of advancement of the web.  17. Machine according to one of claims 13 to 16, characterized in that each belt (41a, 41b) in the active region of its path slides on a rigid support surface (53a, 53b) which is opposite the head corresponding needling (6a, 6b).