Insertion block for the formation of a hook field on an injection-moulded object, and a moulded object comprising a hook field of this type

Abstract

Object molded in thermoplastic material in any shape having an outer surface from which protrudes at least one hook in one piece with the molded object, in particular a hook field, the molded object and the hook(s) having been formed by injection molding, each hook comprising a base part and a head or hooking part protruding from the base part and being delimited by first and second lateral surfaces each extending on the outer surface of the molded object, being separated from each other by an intermediate surface forming the edge of the hook, the curve sections, defined by the intersections of at least one of the first and/or second lateral surfaces with planes which are in parallel with the base plane from which the hook protrudes and which are at given distances h from this base plane, have a curvature which varies as a function of the distance h, the curvature of the curve section for h=0 (the base plane and said parallel plane merging) being greater than the curvature of at least one curve section for a distance h substantially corresponding to a level of the head of the hook.

Claims

1. An insertion block intended to be disposed in a mould for forming an object to be moulded to form a hook field in one piece with the moulded object, comprising at least one first plate, having on its upper edge at least one cut-out having a shape complementary to a series of hooks and issuing out of the two opposite lateral surfaces of the plate and of its upper edge, and at least two second plates sandwiching the at least one first plate therebetween, to form a cavity having said shape complementary to said series of hooks, delimited by lateral walls formed by the two second plates and issuing out of the upper edge of the first plate via an opening, the plates being clamped together, characterized in that the plates are fixed to each other by a diffusion bonding process, and in that there is formed in at least one of the plates at least one auxiliary recess which is intended to form, when the plates are against each other, at least one aeration channel communicating on the one hand with at least one part of the at least one cavity and on the other hand with the exterior of the insertion block formed by the plates disposed one against the other, wherein the aeration channel(s) has/have a stepped cross-section formed by a first part having a small cross-section and a second part having a larger cross-section than the small cross-section, wherein the small cross-section is intended to effect the communication with the head part of the cavity having a shape complementary to the hooks such that air can pass into this cross-section but not thermoplastic material, and the large cross-section permits quick venting of the air which passes from the small cross-section into the large cross-section, itself in contact with the outside.

2. An insertion block intended to be disposed in a mould for forming an object to be moulded to form a hook field in one piece with the moulded object, comprising at least one first plate, having on its upper edge cut-outs having a shape complementary to a series of hooks and issuing out of the two opposite lateral surfaces of the plate and of its upper edge, and at least two second plates sandwiching the at least one first plate therebetween, to form a cavity having said shape complementary to said series of hooks, delimited by lateral walls formed by the two second plates and issuing out of the upper edge of the first plate via an opening, the plates being clamped together, characterized in that the plates are fixed to each other by a diffusion bonding process, and in that there is formed in at least one of the plates at least one auxiliary recess which is intended to form, when the plates are against each other, at least one aeration channel communicating on the one hand with at least one part of the at least one cavity and on the other hand with the exterior of the insertion block formed by the plates disposed one against the other, wherein the cross-section of the aeration channel(s) is flared, starting with a small dimension, in communication with the cavity, through which air can pass but not injected thermoplastic material and finishing with a large dimension permitting quick venting of the air.

3. An insertion block intended to be disposed in a mould for forming an object to be moulded to form a hook field in one piece with the moulded object, comprising at least one first plate, having on its upper edge at least one cut-out having a shape complementary to a series of hooks and issuing out of the two opposite lateral surfaces of the plate and of its upper edge, and at least two second plates sandwiching the at least one first plate therebetween, to form a cavity having said shape complementary to said series of hooks, delimited by lateral walls formed by the two second plates and issuing out of the upper edge of the first plate via an opening, the plates being clamped together, characterized in that the plates are fixed to each other by a diffusion bonding process, and in that there is formed in at least one of the plates at least one auxiliary recess which is intended to form, when the plates are against each other, at least one aeration channel communicating on the one hand with at least one part of the at least one cavity and on the other hand with the exterior of the insertion block formed by the plates disposed one against the other, wherein the at least one auxiliary recess is formed in the at least one first plate.

4. The insertion block as claimed in claim 1, wherein the second plates are plates without cut-outs.

5. An insertion block, intended to be disposed in a mould for forming an object to be moulded to form a hook field in one piece with the moulded object, comprising at least one first plate, having on its upper edge at least one cut-out having a shape complementary to a series of hooks and issuing out of the two opposite lateral surfaces of the plate and of its upper edge, and at least two second plates sandwiching the at least one first plate therebetween, to form a cavity having said shape complementary to said series of hooks, delimited by lateral walls formed by the two second plates and issuing out of the upper edge of the first plate via an opening, the plates being clamped together, characterized in that the plates are fixed to each other by a diffusion bonding process, and in that there is formed in at least one of the plates at least one auxiliary recess which is intended to form, when the plates are against each other, at least one aeration channel communicating on the one hand with at least one part of the at least one cavity and on the other hand with the exterior of the insertion block formed by the plates disposed one against the other, wherein the diameter of the equivalent cross-section of the opening for communication between the cavity and the aeration channel is between 110.sup.2 mm and 410.sup.2 mm.

6. The insertion block as claimed in claim 1, wherein the second plates have at their edge at least one second plate cut-out for forming a second series of hooks and when the second plates are disposed against the at least one first plate, the second plate cut-out forms a second plate cavity that is offset with respect to the cavity of the first plate, the first plate forming a wall for the second plate cavity and the second plates each forming a wall of the cavity of the first plate.

7. An insertion block, intended to be disposed in a mould for forming an object to be moulded to form a hook field in one piece with the moulded object, comprising at least one first plate, having on its upper edge at least one cut-out having a shape complementary to a series of hooks and issuing out of the two opposite lateral surfaces of the plate and of its upper edge, and at least two second plates sandwiching the at least one first plate therebetween, to form a cavity having said shape complementary to series of hooks, delimited by lateral walls formed by the two second plates and issuing out of the upper edge of the first plate via an opening, the plates being clamped together, characterized in that the plates are fixed to each other by a diffusion bonding process, and in that there is formed in at least one of the plates at least one auxiliary recess which is intended to form, when the plates are against each other, at least one aeration channel communicating on the one hand with at least one part of the cavity and on the other hand with the exterior of the insertion block formed by the plates disposed one against the other, wherein the pressure applied to the stacked plates during the diffusion bonding process is so high that the walls of the cavities formed in said plates are deformed.

8. The insertion block as claimed in claim 7, wherein the walls of the cavities have a camber which evens out the opening towards the bottom of the cavity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) One embodiment of the invention, given solely by way of example, will now be described with reference to the drawings, in which:

(2) FIG. 1 is a side view of a plate of an insertion block;

(3) FIG. 2 is a perspective view of an insertion block in accordance with the invention formed of a stack of plates shown in FIG. 1, wherein plates without cavities have been interposed between said plates;

(4) FIGS. 3A and 3B are top views of one part of the stack of plates of FIG. 2, before and after diffusion bonding respectively;

(5) FIG. 4 shows a moulded object having a hook field, the moulded object and the hooks being in one piece and obtained by injection moulding in a mould in which the insertion block has been disposed beforehand to form the hook field;

(6) FIG. 5 shows a perspective view of a hook of a hook field obtained using a moulding insert in accordance with one embodiment of the invention;

(7) FIG. 6 is a cross-sectional view taken along line A-A of FIG. 5;

(8) FIG. 7 is a cross-sectional view taken along line B-B of FIG. 5;

(9) FIG. 8 is a cross-sectional view taken along line C-C of FIG. 5;

(10) FIG. 9 is a cross-sectional view taken along line D-D of FIG. 5;

(11) FIG. 10 is a cross-sectional view in the base plane P0 of the hook;

(12) FIG. 11 shows a perspective view of a hook of a hook field obtained using a moulding insert in accordance with another embodiment of the invention; and

(13) FIG. 12 shows a perspective view of a hook of a hook field obtained according to yet another embodiment of the invention.

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

(14) The insertion block 1 shown in FIGS. 2 and 3B is formed of an alternating stack of plates 2 having cut-outs 4 of a shape complementary to the hooks, and plates 3 not having cut-outs of a shape complementary to the shape of the hooks. The plate 2 shown in FIG. 1 is a plate having two lateral faces 5 and an upper edge or field 7 on which cut-outs 4 of a shape complementary to the hooks intended to be formed are formed by spark-machining. When this plate 2 is sandwiched between two plates 3 without cavities in the form of hooks, each cut-out 4 forms, with the walls of the adjoining plates 3, a cavity closed on the sides by two lateral, planar walls formed by the two plates 3 adjoining the plate 2 and this cavity is open at the top by an upper opening forming the base of a hook. Also formed by spark-machining, in the two lateral surfaces 5 of the plate with hooks, are two grooves 8 which will intersect the parts forming the head of the cavity having a shape complementary to that of a hook. Each groove is stepped, having a first part with a small cross-sectional dimension such that only air can pass therethrough and not thermoplastic material, and a second part with a larger cross-sectional dimension which enables the air to be vented more quickly. These stepped channels could also be formed not in the plate with hooks but in the intermediate plates without hook-shaped cut-outs, or simultaneously in the intermediate plates and in the plate with hooks.

(15) Once the plates with cut-outs and the intermediate plates have been formed, they are firmly pressed together and diffusion bonding is performed to obtain a final block in which all of the elements are connected. A thermal processing oven can be used for example, fitted with a cylinder of a Demag press which holds the plates together by means of pressure during the cycle in which the atoms diffuse between the plates (under vacuum or in the presence of an inert gas) under the combined effect of temperature and pressure, the diffusion process permitting a connection between each adjoining plate at the atomic level to obtain in the end a block in which all of the elements are connected. At the end of this process, the plates have undergone a compression of between 0.5 and 8%, preferably between 1 and 4%, in particular about 2% and like the empty parts (the cavities were not affected by this compression) the walls 30 of the cavities 4 in the plate 2 have undergone a deformation which provides them with a camber which evens out from the base or opening towards the bottom or head of the cavity. In practice, this deformation is about 2% with respect to the initial thickness of the intermediate plate 3, but this deformation can vary between 0.5 and 8%, preferably between 1% and 4%. The camber of one of the lateral walls has its concavity directed in a direction opposite to the concavity of the camber of the other lateral wall.

(16) The insertion block of FIG. 2 can thus be disposed in any type of mould for forming an injection-moulded object. The object shown in FIG. 4 can be made for example. A hook field corresponding to the hooks formed by the cavities of the block 1 protrudes from the moulded object and can thus permit fixation thereof. The surface over which the field extends is substantially smaller than the total surface of the moulded object, but it is also foreseeable to provide a moulded object where the majority of the surface is covered by the hook field. Upon forming the moulded object, thermoplastic material is injected into the mould in which the insertion block has been inserted beforehand substantially at the location where the hook field which will form one piece with the moulded object is intended to be formed. This thermoplastic material will enter the cavities of the insertion block and, owing to the presence of the aeration channels, will then reach the bottom of the hooks, pushing out the air into the channels.

(17) FIGS. 5 and 6 show hooks as obtained in accordance with the invention. Each hook 10 is delimited by two lateral, substantially planar and parallel surfaces 11 and 12 and by an intermediate surface 13 adjoining the two surfaces 11 and 12. The intermediate surface 13 is delimited by the upper edges of the two planar surfaces, from the bottom of the hook on the right to the bottom of the hook on the left, passing through the tip thereof. The intermediate surface 13 forms the upper edge of the hook. These three surfaces thus delimit the hook which comprises a rod or base part 14 and a head part 15 protruding from the rod part. At the level of the lower part of the base or rod, the transition between each lateral surface and the intermediate surface is formed by a line such that the surfaces form an angle therebetween, in particular a right angle, whilst at the level of a part of the head, for example in the upper part, the transition between the lateral surfaces and the intermediate surface is smooth, i.e., curved. Thus, the shape of the cross-section of the hook at A-A of the head is itself formed, as shown in FIG. 6, of four straight lines 16 connected together by curved parts with large curvatures 17. Based on the location where the cross-section is taken, a cross-section which has all of its corners rounded, or only one or two or three of its corners, is possible.

(18) The cross-section B-B of the hook of FIG. 5 and shown in FIG. 7 has the same type of shape as that of the cross-section A-A of FIG. 5, but the rounded corners 17 have a greater radius of curvature than that of the rounded corners 17 of FIG. 5.

(19) The cross-section C-C at the level of the base, shown in FIG. 8, has sharp-edged, i.e., non-rounded, corners, forming a sort of turning point. However, the two curve sections 20 and 21 which correspond to the intersection between the respective lateral surfaces 11 and 12 and the plane parallel to the base plane P0 and to the distance he from this plane are curved having their concavity towards the exterior of the hook and opposed to each other.

(20) Similarly, the cross-section at the level of the base plane, shown in FIG. 10, has sharp-edged, i.e., non-rounded, corners forming a sort of turning point. However, the two curve sections 22 and 23 which correspond to the intersection between the respective lateral surfaces 11 and 12 and the base plane P0 are curved, having their concavity towards the exterior of the hook and opposed to each other. The curvature or concavity of the section 22 is greater than that of the section 20 and that of the section 23 is greater than that of the section 21. Similarly, at the level of the head, the sections 24 and 25 corresponding to the cross-section along line D-D are substantially straight, their concavity thus being zero and therefore less that that of the sections 20 and 21.

(21) The thickness e0 at the level of the base plane is less than the thickness at the level of the plane C-C which itself is less that the thickness eDD at the level hd of the plane D-D.

(22) In the hook field of the moulded object of FIG. 4, the hooks are arranged in rows and columns, which are in particular perpendicular to each other.

(23) The thermoplastic moulding material can be selected from polyolefins, polyamides, TPEs, etc.

(24) In the case of FIG. 5, the cavities of the corresponding insertion block have an opening towards the aeration channel which has a small cross-section, and in particular is only present on one side of the head. This results in some degree of braking for the material which is not able to perfectly fill the corners of the cavities, and thus in rounded shapes for the head at the corners of the cavity.

(25) In contrast, as shown in FIG. 11, in the case where the opening has a larger cross-section and in particular extends over virtually all of the bottom of the head, the corners are well formed and the hook does not have a rounded shape, or only has a slight rounded shape.

(26) In the case where the opening between the moulding cavity and the aeration channels is very large and where furthermore the viscosity of the material permits an extremely fluid flow, the thermoplastic material is able to surge into this opening and protrude into the channels. In such a case, and as shown in FIG. 12, the hook will comprise at the level of its head a development 40 created by this infiltration of the thermoplastic material in the passage opening towards the aeration channels of the moulding cavity. Often in this case, the transition between the lateral surfaces and the intermediate surface will be formed with a sharp edge or corner over the entire extent from left to right of the hook of the intermediate surface. The cross-section without a sharp edge or corner will be formed in particular at the level of the development.

(27) To show the gradient of curvature of the lateral surface of the hook (i.e., that at the level of the head the curvature is virtually zero or at least less than the curvature at the level of the base of the hook, the following test can be used:

(28) The hook field of the moulded object must be inclined by 15 with respect to the horizontal, the inclination being effected around an axis in parallel with the intersection of the transverse plane and of the base plane of a line of hooks.

(29) The hooks must be observed using a microscope having a magnification of at least 150, for example the variable pressure, Hitachi S 3200N Scanning Electron Microscope, high vacuum observations and secondary electrons after Au/Pd metallization.

(30) In order to be able to observe a hook in the middle of the hook field, the hooks surrounding it can be cut using a razor blade.

(31) Cross-sections which are substantially rectangular are shown. However, they can also be simply substantially quadrilateral by cutting with the blades not at 90 with respect to the plane of the plates but sloping.