EP1510292A2

EP1510292A2 - Reinforcing frame for abrasive discs

Info

Publication number: EP1510292A2
Application number: EP03028542A
Authority: EP
Inventors: Giuseppe Maternini
Original assignee: Davide Maternini SpA
Current assignee: Davide Maternini SpA
Priority date: 2003-08-29
Filing date: 2003-12-11
Publication date: 2005-03-02
Also published as: EP1510292A3; ITBO20030502A1

Abstract

The frame for abrasive discs includes a one-piece gridlike structure, obtained by molding of a material which can be molded by injection.

The frame (1) includes a plurality of concentric and substantially thread-like circumferential elements (2), which are disposed, at predefined distances one from another, between an inner edge circumferential element (3) and an outer edge circumferential element of the (4). The frame (1) includes also a plurality of radial elements (5,6), substantially thread-like and extending for predetermined lengths and with predetermined angular distances. Each of said radial elements (5,6) is connected to at least a part of the circumferential elements (2) in the region of relative intersection points (7).

Description

The present invention relates to the production of abrasive discs for grinders (sandpapering machines), lapping machines or cutting tools, of the type including a rotating disc.
In particular, the invention concerns a support frame made of plastic material, aimed at being embedded in an abrasive disc, which can be used on the above mentioned machines or tools.
It is known that abrasive discs used on grinders, lapping machines or cutting tools including rotating discs, are composed of a mixture of granular abrasive material and a suitable binding material, usually epoxy resins.
The disc has a central hole for mounting it on the hub of the machine.
Each disc is formed in suitable molds and left therein for the time necessary to aggregate and harden the resin.
In order to improve the mechanical characteristics of the discs and to avoid breaking or detachment of parts thereof, when the discs in use are brought to rotate very quickly, the discs have one or more inner reinforcing frames.
The reinforcing frames are produced with a circular substantially grid-like or crossed structure, whose diameter is slightly smaller than the diameter of the discs for which they are aimed. The frames are arranged perpendicular to the discs axes.
The reinforcing frames have also a central hole, corresponding to the central hole of the discs.
The frames are embedded in the mixture inside the mold during the disc formation.
If the disc is very thick, there can be two or more frames, arranged at different levels inside the disc.
Currently, the frames are obtained by shearing, beginning from a pile of sheets of grid-like material.
The sheets are usually obtained by threads of glass fiber, crossed at 90°, and soaked in the resin, which is the binding agent for the abrasive material of the discs.
Sheets of paper are introduced between the sheets of grid-like material, in order to help stabilizing the sheets and to avoid the mixing up of different layers.
During the production of abrasive discs, the reinforcing frames are picked up by suitable means together with the sheet of paper connected thereto.
Obviously, the sheet of paper must be removed before the frame is put into the mold.
The above described frames present some drawbacks.
First of all, during the shearing operations, the edges of the frames are often chipped and folded in the shearing direction.
In this way, the edges of adjacent frames can interlace and the frames may get hooked to each other, at least partially along the respective circumferences.
Therefore, when the frames are picked up to be introduced into the mold, more than one frame can be taken, with the relative sheets of paper therebetween.
This leads either to putting two or more frames into the mold, or to erroneous positioning of at least one of the frames.
In all cases, the obtained abrasive disc cannot be used and must be rejected.
Moreover, the resistance of the so obtained frame to the stresses, to which the abrasive disc is subjected during its use, is not as good as desired.
In fact, substantially radial stresses, resulting from the centrifugal force, act on the disc due to the nominal rotation speed, which is often high, and substantially tangential stresses occur, which result from the action of the piece being worked on the disc.
On the contrary, the frame threads are arranged along perpendicular directions, and the so obtained grid is arranged inside the abrasive disc in a random way.
Therefore, the reaction to both radial and tangential stresses is not homogeneous.
The main object of the present invention is to propose a reinforcing frame for abrasive discs, which is capable of reacting in a homogeneous way, to radial and tangential stresses, to which the abrasive disc, into which it is disposed, is subjected.
Another object of the present invention is to propose a frame, in which the edge profile is perfectly defined, and which does not present the above mentioned problems connected to picking up and subsequent positioning in the mold.
A further object of the present invention is to obtain the above mentioned frame with substantially complete elimination of production scraps.
The above mentioned objects are achieved by the features of the independent claim, while preferred features are defined in the dependent claims.
The invention will now be described in more detail with reference to particular, non-limiting embodiments and with reference to the accompanying drawings, in which:

Figure 1 is a top view of a first embodiment of the frame obtained according to the present invention;
Figure 2 is a lateral sectional view taken along the line II-II of Figure 1, in an enlarged scale;
Figure 3 is a top view of a second embodiment of the frame obtained according to the present invention;
Figure 4 is a lateral sectional view taken along the line IV-IV of Figure 3, in an enlarged scale.

With reference to Figures 1 and 2, the reference numeral 1 indicates a frame for abrasive discs obtained according to a first embodiment of the present invention.
An important feature of the frame 1 results from the fact that it is made in one-piece configuration, obtained by known techniques, e.g. by injection molding in a suitable mold having an impression reproducing the frame.
The above mentioned frame 1 is preferably made of a resin or a mixture of thermoplastic resins which are to be injected into the mold.
The resins occupy the inner spaces of the impression and, due to solidifying resulting from cooling, they define an integral body without lack of continuity.
The frame 1 includes a plurality of concentric circumferential elements 2, substantially thread-like, which extend along the whole circumference of the frame 1.
In the illustrated frame 1, the distance between two adjacent circumferential elements 2 is constant.
In any case, the constant distance does not constitute a critical aspect of the invention and it can be modified in relation to the specific needs.
Likewise, the cross-section of the above mentioned circumferential elements 2, which in the example is approximately square, can be different in relation to different constructive choices.
The circumferential elements 2 are situated between an inner edge circumferential element 3 and an outer edge circumferential element 4.
the inner edge circumferential element 3 and the outer edge circumferential element 4 delimit the frame 1, respectively from inside, in order not to interfere with the central hole of the abrasive disc aimed at allowing its mounting on the machine, and from outside, in order to give a continuous and practically non-deformable edge to the frame.
The frame 1 includes also a plurality of radial elements 5, 6, likewise thread-like and with approximately square cross-section, arranged coplanar with the circumferential elements 2.
The radial elements 5, 6 intersect the circumferential elements 2 in the intersection points 7, in order to form the grid.
Due to the above described constructive way, the circumferential elements 2 and the radial elements 5, 6 are integral with one another in the region of the above mentioned intersection points 7 and constitute an integral body.
The radial elements 5, 6 include long radial elements, which extend between the inner edge element 3 and the outer edge element 4, and short radial elements 6, which extend between the outer edge element 4 and an intermediate circumferential element 8.
The short radial elements 6 alternate with the long radial elements 5.
The angular spacing between the radial elements 5, 6 is constant, thus they are regularly spaced apart along the surface of the frame 1.
Since the distance between adjacent radial elements increases going towards the outer edge element 4, the short radial elements 6, disposed therebetween allow to reduce such distance and makes the dimension of the meshes more regular, so as to strengthen the frame 1 structure.
Obviously, for bigger frames 1 and/or for different constructive needs, more than two groups of different radial elements can be provided, without going beyond the protective scope of the present invention.
According to a second embodiment of the invention, shown in Figures 3 and 4, the frame 1 features two gripping areas 9, aimed at facilitating the gripping of the frame by suitable means in order to position it during the abrasive disc obtaining process.
Each of the gripping areas 9 includes a "filled" area obtained in the same material as the frame 1. The filled area does not have the grid-like configuration, but is made as an integral, preferably thicker section.
This area includes at least the surface delimited by two consecutive circumferential elements 2 and by two consecutive radial elements 5, 6.
In the shown embodiment, each area extends along three circumferential elements 2 and three radial elements 5, 6.
In particular, there are three gripping areas 9, spaced apart at regular angular distances.
The surface of the gripping areas 9 from one side of the frame 1 is elevated with respect to the surface of the grid, so as to facilitate the gripping by the suitable means.
The frame 1 obtained in the above described way and applied to an abrasive disc, allows advantageously to make substantially isotropic the reaction to the stresses to which the disc is subjected during its use.
In particular, it increase to the maximum possible value the resistance to the radial as well as to the tangential stresses.
Another advantage of the frame 1 derives from the fact that its outer and inner edges are perfectly defined and continuous.
During the withdrawing of the frame from a pile, this fact prevents the edges from hooking with the edges of the frames situated below and thus it allows the frames to be easily and safely picked up.
A further advantage results from the substantial elimination of the production scraps.
Actually, the molding production reduces the scraps to the ones relative to the mold injection channels, which are irrelevant.
Moreover, the so obtained frame 1 is particularly light and practically non-deformable.

Claims

Frame for abrasive discs, characterized in that it includes a grid-like one-piece structure, obtained by molding and made of a material which can be molded by injection, said frame (1) including a plurality of concentric and substantially thread-like circumferential elements (2), which are disposed at predefined distances one from another, between an inner edge circumferential element (3) and an outer edge circumferential element (4), said frame (1) including also a plurality of radial elements (5,6), substantially thread-like and extending for predetermined lengths and with predetermined angular distances, each of said radial elements (5,6) being connected to at least a part of said circumferential elements (2) in the region of relative intersection points (7).
Frame, according to claim 1, characterized in that said circumferential elements (2) and radial elements (5,6) are coplanar.
Frame, according to claim 1, characterized in that said circumferential elements (2) extend along the whole circumference of said frame (1).
Frame, according to claim 1 or 3, characterized in that the distance between the adjacent circumferential elements (2) is substantially constant.
Frame, according to claim 1, characterized in that said radial elements (5,6) include long radial elements (5), which extend between said outer edge circumferential element (4) and said inner edge circumferential element (3), and short radial elements (6), which extend between said outer edge circumferential element (4) and an intermediate circumferential element (8).
Frame, according to claim 5, characterized in that said short radial elements (6) alternate with said long radial elements (5).
Frame, according to claim 1, characterized in that it includes at least one gripping area (9), constituted by an integral made area of said material, which can be molded by injection, and which extends in a surface delimited by at least two consecutive circumferential elements (2) and by two consecutive radial elements (5,6).
Frame, according to claim 1, characterized in that it features three of said gripping areas (9), which are spaced apart at regular angular distances.