FR2680334A1 - METHOD FOR MANUFACTURING CYLINDRICAL PIPES BASED ON WOOD VENEERS, AND PRODUCT THEREFOR. - Google Patents

Abstract

Process for making cylindrical pipes from wood veneers, and resulting product. It consists first of all in making an asymmetric ply comprising "n" cross stacked veneers with at most n - 1 grain veneers parallel to the axis of the final cylinder (CF DRAWING IN BOPI) preferably adjacent, then letting this ply be naturally deform into a tile (4), finally, to be placed between this tile (4) in an assembly press allowing, thanks to an external heating mandrel (5) and a heating wedge (7) in the form of an arc of a circle diameter equal to that of the final cylinder as well as an inner mandrel (8), and to bring it to a shape of perfect cylinder blocked using one or more glued veneer (s) (6). It is particularly suitable for manufacturing formwork pipes, central coil mandrels, reel cores, ventilation ducts and fluid transport pipes.

Description

i

  PROCESS FOR MANUFACTURING CYLINDRICAL PIPES BASED ON

  WOOD VENEERS, AND PRODUCT THEREOF

  The present invention relates to a method of manufacturing cylindrical pipes based on wood veneers. In the current state of the art, by pressing

  around a cylindrical mandrel using two semi-circular molds

  cylindrical, one connects to each other by their longitudinal edges two stacks of veneers glued to

to form more than one cylinder.

  For example, a method currently used in the United States of America is to stack several veneers glued wire to wire, that is to say with their respective wood grain parallel to that of others, and so that this meaning the wire is parallel to the axis of the central mandrel This double parallelism, on the one hand son between them, on the other hand son with the central axis, is necessary to allow sufficient flexibility for forming The two semi molds -cylindriques heated are close together and come tighten the two sets of stacking around the central mandrel: at the beginning the forming is done cold, before the calories from the molds have hardened the glue, then the hardening is done that the assembly forms only one cylinder The two sets of stacking have been made in such a dimension that the sum of their two widths is equal to or slightly greater than the circumference of the central mandrel. tade parallel borders to the axis then be by simple

berthing, either by recovery.

  The cylinder thus obtained, after opening of the two half-molds and disengagement from the central mandrel, has a high flexural strength which makes the fibers work parallel to their yarn, that is to say in elongation where the value is maximum, but a low tensile strength which makes the fibers work perpendicularly to their yarn, that is to say in tearing where the value is minimal In particular, the cylinders thus produced

  do not withstand internal pressures in use.

  The method according to the invention makes it possible, among other advantages, to remedy this drawback. Indeed, it consists of two phases and takes advantage of the anisotropy characteristics of the wood. In the first phase, a "n" folded plywood composed in a non-conventional manner is manufactured in a flat press, thus in a conventional manner because according to a totally asymmetrical stacking, that is to say to say that, unlike the usual composition of a multipli o10 the veneers are symmetrical with each other in relation to the median plane of the whole, the veneers are here totally asymmetrical to each other In the symmetric multiplication to "no folds, the veneers arranged on either side of the median plane are indeed so on the one hand that they are simultaneously simultaneously of the same quality of wood, the same thickness and direction of their parallel wire between them and secondly that their respective wire direction is perpendicular to

  the one or two other directly adjacent veneer (s).

  There will therefore be, in the case where "n" is even, n / 2 veneers with the yarn of the wood fiber parallel to an axis and n / 2 veneers with the yarn of the wood fiber perpendicular to this axis and, in the case where "n" is odd, N + 1 veneers 2 with the yarn of the wood fiber parallel to an axis and N 1 2 veneers with the yarn of the wood fiber perpendicular to this axis b In the asymmetric multiplier at In accordance with this invention, the veneers after sizing are stacked so that when the number "n" of veneers is even, there is at least N + 2 and at most N 1 of them whose 2 direction of the wood fiber yarn is parallel to the axis of the

final cylinder desired.

  when the number "n" of veneers is odd, there is at least N + 1 and at most N 1 of them whose direction of the yarn of the wood fiber is parallel to the axis of the desired final cylinder. the thicknesses and the respective wood qualities of each of the veneers are not necessarily identical two by two and may even be voluntarily different. preferably, the veneers which have a direction of the wire parallel to the axis of the desired final roll are adjacent. Experience has shown that wood is a high anisotropic material which has, for example, the characteristic of having a low shrinkage coefficient of about 0.30% in the longitudinal direction parallel to the fibers and a high coefficient of about 7% in the transverse direction perpendicular to the fibers It also shows that these internal stresses of the wood are directly proportional on the one hand to the density of the wood species

  concerned and secondly to the thickness of the veneer used.

  This means in practice, for example, that at the exit of the press: when the asymmetric multiplier consists of veneers of the same essence, of the same zone in the original tree and of the same thickness, that is to say to say of same quality (to the abstraction near the local heterogeneities of the various veneers implemented), the planar parallelepiped that constitute the veneers glued together undergoes a deformation in tile by a tendency to form a cylinder whose main axis is parallel at the yarn direction of the veneers whose number is between N + 2 and N 1 when 'ln' is even and between N + 1 and N -1 when 'n' is

  odd, that is to say, whose number is the highest.

  when everything else is equal, this tendency is accentuated or attenuated according to the fact that, in the stacking of veneers considered, the thickness or the density of the essence of one or more of them are modified in

one way or the other.

  In a variant of the process, any synthetic film, for example a paper impregnated with phenol-formaldehyde resin, may be added to the composition of the stack either on the side intended to become the concavity of the tile or on the other side. will constitute a tight and hard skin having participated, if the direction of its own constituent fiber was well implemented, the deformation in

desired tile.

  The dimensions of the veneers used will have been chosen so that the width "L" of the flat panel

  thus manufactured is equal to the development of the desired cylinder.

  This width "IL" must therefore be equal to the value "D" of the final diameter that multiplies the number "l T", ie L = 3.1416 x D. During the second phase, it is sufficient to place the open cylinder obtained in an assembly press This assembly press consists of a simple heating inner mandrel which does not need to be cylindrical but perhaps only flat with two reactive ends and an external heating mandrel with the necessary condition and sufficient to be effective is to be a circular arc of diameter equal to that of the cylinder to be manufactured: this outer mandrel will be accompanied by a possibly heating wedge of equal curvature placed symmetrically at the diametrically opposite end of the press. effect of bringing the two outer mandrels closer so that the two edges of the plywood parallel to the longitudinal axis of the tile, guided by the heating mandrel of adequate curvature, are brought together They come together to form a perfectly cylindrical shape, helped by the simultaneous action of the opposite wedge. Care should be taken to place at the level of the curved heating mandrel, parallel to the generatrix of the final cylinder, inside or outside, is one or more veneer (s) glued (s) of length equal to that of said final cylinder is a piece shaped glue; a second identical plating may also be placed outside or inside if the final use of the cylinder does not oppose it. The hot pressing thus produced makes it possible to obtain a definitive closure of the desired cylinder. be balanced, we can stick, on the diametrically opposite side, using the wedge that is there for this purpose, inside or outside an assembly

identical to the previous one (s).

  This gives a cylinder which has the advantage, while having a sufficient bending strength thanks to the (x) plating (s) whose direction of the wire is parallel to the main axis, to have a high tensile strength thanks to the (x) plating (s) whose direction of the wire perpendicular to the axis of the cylinder is such that an internal pressure will work the fiber elongation, that is to say

  say with maximum resistance values.

  In a variant of the method, it is possible to use the heating wedge placed on the diametrically opposite side of the first outer mandrel, not to bond a balancing, but to associate two asymmetric multiplies that are deformed into tiles. This is of interest when one is limited in press width flat, to be able to manufacture cylinders of larger diameter For example if the flat press has a width of 1500 mm can only achieve cylinders whose maximum diameter is equal to 1500 mm / 3.1416 therefore a little less than 50 centimeters; on the other hand, if two multiplis can be associated, cylinders with a maximum diameter of 2 × 1500 can be produced in this case, ie approximately

3.1416

1 meter.

  The attached drawings provide a better understanding of the invention: FIG. 1 represents the first phase of

  manufacture, that is to say the planar asymmetric multiplier.

  Figure 2 shows, in section, the second phase of manufacture, that is to say that of the cylinder itself in

  an assembly press specially designed for this purpose.

  Figure 3 shows, in section, a variant of the

process.

  With reference to FIG. 1, bonded wood veneers (1) are associated whose direction of the wood grain is parallel to their largest dimension in the plane, to a smaller number of glued veneers (2) whose direction of yarn is perpendicular to that of the two previous ones According to a variant, it will be possible simultaneously to associate a paper impregnated with synthetic resin (3) whose direction of the fiber, if it is known, will preferably be placed

  parallel to that of the fiber of the veneers (1).

  The assembly is placed in a hot press flat, at a sufficient pressure and the time required for the resins to be well polymerized At the opening of the flat press, the plane parallelepiped obtained is released and placed in the ambient atmosphere. variations in temperature and humidity, and, in general, the release of the internal stresses resulting from the asymmetry of its constitution and the large difference in tendency to dimensional variations thus caused between the two axes of its plane cause the natural deformation of the parallelepiped into a tile (4) The deformation will be even more pronounced if the thicknesses and / or densities of some

  veneers (1) are superior to those of veneers (2).

  With reference to FIG. 2, the tile (4) is placed in an assembly press so that the open part of the tile (4) faces the heating outer mandrel (5) which is shaped like arc whose radius of curvature is equal to half the diameter of the

final cylinder desired.

  One or more glued veneer (s) or a glue-shaped part (6), optionally lined (s) with an impregnated paper identical to the preceding, are placed (s) along the mandrel (5) preferably with the direction of its fibers perpendicular to the axis of the cylinder A shim (7) of equal curvature is located symmetrically, that is to say at

  the diametrically opposite end of the press.

  An inner mandrel (8), of dimension at most equal to the value of the desired final diameter, is designed such that

  how it can react to the pressures of the outer chucks (5) and (7).

  When closing the press, the action of the curved mandrel (5) naturally causes the closing of the multipli (4) according to a perfect cylinder of diameter equal to the value of the ratio of its width divided by the number T = 3.1416 ; the assembly being held by the mandrel (7) The pressure obtained by the contact between the mandrel (5) and the mandrel (8) and the corresponding temperature are maintained for the time necessary for the polymerization of the bonding of the assembly ( 6): this causes the sealing of the

multiplied closed in press.

  When the press is opened, a hose is released

perfectly cylindrical.

  If it is desired that the cylinder be balanced around its main axis, at the beginning of the operations, a second assembly (9) identical and in position

  diametrically opposed to the assembly (6).

  In a variant of the method, and with reference to FIG. 3, it is possible to place, no longer a single tufted multiplier, but two tuiled multiplies, of equal widths and such that their sum is itself equal to the developed of the desired final cylinder. Their edges will be welded using a

assembly (9).

  As a first nonlimiting example and with reference to FIG. 2, a cylinder 2500 mm in length, with a diameter of 400 mm and with a wall thickness of 3.3 mm is produced with a laminated formophenolic inner surface. produced in a flat press having trays of a little more than 2500 mm long and 1300 mm wide an asymmetric multiplied panel with two veneers (1) and a veneer (2) of 1.15 mm thick each, 2500 mm long and 1256 mm wide and one sheet of phenolic impregnated paper (3) with a grammage per m 2 adapted to the needs and dimensions in the plane of 2500 mm and 1256 mm The realization of the cylinder will be carried out in the special press by means of a mandrel (5) of radius of curvature equal to 200 mm using a joining assembly (6) of 2500 mm long having a thickness and a width adapted to the need, associated with a

  sheet of paper impregnated with the same dimensions in the plane.

  An assembly (9) identical to the assembly (6) will be

preferentially implemented.

  As a second nonlimiting example and with reference to FIG. 3, a cylinder 2500 mm in length, with a diameter of 900 mm and a wall thickness of 3.3 mm, with a formophenolic laminated outer surface is manufactured. in the flat baler having trays slightly over 2500 mm long and 1300 mm wide two 5-ply asymmetric plywood panels with two veneers (2) and three veneers (1) each 1.15 mm thick as well as 2500 mm long and 1413 mm wide These two multiplis will then be assembled in the special press with the help of

  assemblies (6) and (9) of suitable jointing.

  The method according to the invention makes it possible to manufacture cylindrical pipes that can be used in various applications such as: hollow cylinder formwork, lost formwork or remaining in place and participating in the decoration of solid abutments, mandrel of coils, for example paper reels, heart reel for cable winding, wire, etc., air duct, piping for transporting fluids (grains, powders)

various, etc.).

Claims (8)

  1 / A method for manufacturing cylindrical pipes based on wood veneers, characterized in that in a first phase is carried out in a flatbed heating press one or two asymmetrical multipli (s) may include on one or both sides a or more sheets impregnated with synthetic resin, having a number ni of previously glued and stacked veneers crossed such that when "n" is even there is at least N + 2 and at most N 1 2   veneers (1) whose yarn direction of the wood fiber is parallel to the axis of the final cylinder while preferably being adjacent to each other and when "n" is odd there is at least N + 1 and at most N 1, that this multiplier 2   is deformed in tile (4) at the press exit and that in a second phase this or these two tile (s) (4) are placed in an assembly press allowing, thanks to a heating external mandrel (5), a heating inner mandrel (8) and a heating wedge (7), to bring the one or two tile (s) to a perfect cylinder shape and to block it by means of one or two assemblies (6) and (9) consisting of one or more glued veneers or a shaped part   glued and arranged inside or outside.   2 / A method according to claim 1, characterized in that the outer heating chucks (5) and (7) are shaped circular arc diameter equal to that of the cylinder to be manufactured. 3 / A method according to claim 1, characterized in that the inner heating mandrel (8) has a length equal to the inner diameter of the desired final cylinder and two convex ends rounded in a circular arc of smaller diameter and at most equal to that of the cylinders to manufacture.   4 / A method according to claims 1 to 3, characterized in that the asymmetric multiplier realized in the   first phase has its width, or smaller dimension in the plane, equal to the development of the desired final cylinder.   / Method according to claims 1 to 3,   characterized in that the two asymmetric multiplies made in the first phase have their width, or smaller dimension in the plane, each equal to half of the developed final cylinder desired.   6 / Method according to one of claims 4 or 5,   characterized in that all or part of the veneers (1) have a   thicker than veneers (2).   7 / Method according to one of claims 4 or 5,   characterized in that all or part of the veneers (1) are of gasoline (s) of higher density than that (s) veneers (2).   8 / Method according to one of claims 6 or 7,   characterized in that the film or sheets impregnated with resin   are located on the inner surface of the cylinder.   9 / Method according to one of claims 6 or 7,   characterized in that the film or sheets impregnated with resin   are located on the outer surface of the cylinder.   / Method according to one of claims 6 or 7,   characterized in that one or more sheets impregnated with synthetic resin are located on the two inner surfaces and external cylinder.   11 / Cylindrical pipe manufactured according to one of claims 1 to 10.