Abstract:
Method for manufacture of links designed to be interconnected to form a conveyor and including the following steps; mold a body of the link of rigid low-friction material with said body being provided with projections protruding from one of its faces, and hot-mold on at least part of said face cooled to hardening a high-friction malleable material for formation of a skidproof covering with the high-friction material during molding striking said projections and being injected at a temperature higher than the softening temperature of the rigid material in such a manner as to cause plastic deformation of the projections that originate undercuts with the deformed projections upon completed molding remaining incorporated in the high-friction material to create a mechanical interconnection between the covering and the rigid body.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a conveyor consisting of an indefinite sequence of interconnected links having a nonskid top surface for support of the objects to be conveyed. This invention also relates to a method for manufacture of the conveyor links.  
         [0003]     2. State of the Prior Art  
         [0004]     The problem of making conveyor belts or chains suited to running along appropriate guides and that at the same time have a skidproof support surface on which are arranged the objects to be conveyed in the horizontal plane or in a sloped direction relative to said plane has long been known in the conveyor field.  
         [0005]     To solve this problem, conveyors consisting of an indefinite sequence of interconnected modular members like chain links to which is applied a covering of malleable skidproof material on the entire surface or partially thereon have been proposed. The members or links are made of rigid thermoplastic material and are provided with undercuts designed to receive in engagement a portion of the malleable material to anchor the skidproof covering to the conveyor belt. For example, in patent No. EP 0 523 810 it is proposed to form a reticulate structure on which is molded the malleable material and that is then fastened to the modular member of the conveyor. The reticulate structure is made of a material suited to being welded (for example with an ultrasonic weld) to the material used to make the modular members making up the conveyor. This solution, while avoiding the use of sophisticated and costly molds for forming the undercuts, implies a sequence of molding and welding steps that make the conveyor manufacturing process slow and uneconomical.  
         [0006]     According to the conventional and well known methods of overmolding malleable or thermoplastic materials, it could be thought to hot mold the malleable material forming the covering directly on the rigid link of the conveyor without the latter having undercuts for anchoring the covering. To do this, it is necessary to use malleable material compatible with the rigid material of the linked modular-member body to obtain a link effect by thermal effect. However, the most suitable rigid thermoplastic materials to be used for making the modular members of the conveyors are not generally compatible with the rubbery substances that have good skidproof properties. In addition to this, even with compatibility between the two materials the fastening realized does not ensure satisfactory and safe mechanical resistance so that the skidproof covering could detach itself in the long term from the body of the link during use of the conveyor. It is clear that unreliability of this type is a considerable disadvantage.  
         [0007]     In addition, to obtain a strong link with the interface between the two materials it is to be hoped that the surface of the body of the link at least reach softening with resulting alteration of its dimensional characteristic and deterioration of the quality obtained in molding. The general purpose of this invention is to remedy the above mentioned shortcomings by making available a conveyor having a skidproof surface economical and simple to manufacture.  
         [0008]     Another purpose of this invention is to make available a conveyor that would ensure a firm and steady fastening of the skidproof portion to the modular linked members forming the conveyor.  
         [0009]     Another purpose of this invention is to make available a method for manufacture of linked members of a conveyor that would be fast and economical.  
       SUMMARY OF THE INVENTION  
       [0010]     In view of this purpose it was sought to provide in accordance with this invention a conveyor including an indefinite sequence of interconnected links with said links including a low-friction body of rigid material to which is applied a covering of more malleable high-friction material to form a supporting surface for the objects conveyed and characterized in that the covering is hot-molded on one face of the rigid body from which protrude projections with said projections covered with high-friction material with melting temperature higher than the softening temperature of the rigid material being deformed irregularly to form undercut members that are incorporated by the high-friction material to create a mechanical interconnection between the covering and the rigid body of the link.  
         [0011]     Again in accordance with this invention it was sought to realize for manufacture of links designed to be interconnected to form a conveyor a method including the following steps: 
        mold a body of the link of rigid low-friction material with said body being provided with projections protruding from one of its faces, and     hot mold on at least part of said face cooled to hardening a malleable material with high friction for formation of a skidproof covering with the high-friction material during molding striking said projections and being injected at a higher temperature than the softening temperature of the rigid material in such a manner as to cause plastic deformation of the projections that originate undercuts with the deformed projections upon completed molding remaining incorporated in the high-friction material to create a mechanical interconnection between the covering and the rigid body.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     To clarify the explanation of the innovative principles of this invention and its advantages compared with the prior art there is described below with the aid of the annexed drawings a possible embodiment thereof by way of non-limiting example applying said principles. In the drawings:  
         [0015]      FIG. 1  shows a top view of a portion of a conveyor in accordance with this invention,  
         [0016]      FIG. 2  shows a partial view of a modular member of the conveyor of  FIG. 1  before application of the layer of skidproof material,  
         [0017]      FIG. 3  shows a view of the modular member cross-sectioned along surface III-III of  FIG. 2  before the layer of skidproof material is molded,  
         [0018]      FIG. 4  shows the cross-section of  FIG. 3  after molding of the layer of skidproof material,  
         [0019]      FIG. 5  shows a cross-section view of the link along plane of cut V-V of  FIG. 2  before molding of the skidproof covering,  
         [0020]      FIG. 6  shows a view of the link at the beginning of the molding step of the skidproof covering material in cross section along plane of cut VI-VI of  FIG. 2 , and  
         [0021]      FIG. 7  shows a view of the link cross-sectioned along plane of cut V-V of  FIG. 2  after molding of the skidproof covering. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     With reference to the figures,  FIG. 1  shows a section of a conveyor including a series of modular linked members  11 ,  12  mutually interconnected to form a conveyor belt designed to move in the direction indicated by the arrows along a purposeful guide (not shown in the figure).  
         [0023]     The member (or link)  11  includes a rigid body  15  designed to run on the guide that identifies the conveyor belt path. The rigid body  15  forms the interconnection arms  17  between adjacent modular members. These arms  17  have a hole designed to receive a horizontal pin (not shown) that interconnects the modular members to allow them to rotate mutually in accordance with prior art solutions. The rigid body  15  of the link is realized from rigid low-friction materials (for example, thermoplastic resins) to favor the non-deformability and running of the conveyor belt on the associated guides and allow dragging engagement, for example opposite the toothed wheels in the conveyor system for dragging of the belt.  
         [0024]     On the upper part of the rigid body  15  is applied a covering  16  of high-friction material designed to form the support surface for the objects to be conveyed on the belt. The covering  16  is made up in two parts for each modular member as shown in the figures but could be realized in a single piece or several parts. The material used for realizing the covering  16  could be a malleable material with high deformability and with behavior similar for example to rubber or elastomer.  
         [0025]     In accordance with this invention the covering  16  is hot-molded on the rigid body  15  of the link. It is noted however that the high-friction malleable materials used for forming the covering  16  are incompatible with the materials used for molding the rigid body  15 . By ‘incompatible’ is meant that the two materials do not bind with each other with heat treatment or welding (ultrasonic or thermal). Therefore, on the upper face of the rigid body  15  are made multiple projections (indicated by reference numbers  19 ,  20 ,  21 ,  22 ,  23 ,  24 ) over which is molded the malleable material forming the covering  16 . At the time of hot molding of the covering  16  the projections are deformed plastically due to the effect of the heat transmitted by the malleable material that strikes them at high temperature.  
         [0026]     The deformation takes place if the temperature of the malleable material during injection is higher than the softening temperature of the rigid material forming the body  15  of the link. The speed of the injection step carried out in accordance with the prior art, and the relationship between the mass of malleable material  16  and the mass of the rigid material of the body  15  are such that the thin projections  19  are subject to softening and major deformation due to the viscous friction with the injected mass while the body  15  of the link with flat continuous surface does not undergo appreciable deformation or alteration.  
         [0027]     Deformation entails formation of undercut members that remain incorporated in the material forming the covering  16  allowing realization of a mechanical interconnection between the rigid body  15  and the covering  16 .  
         [0028]      FIG. 2  shows partially the rigid body  15  of a modular member of the conveyor before molding of the covering  16 . From the upper face of the rigid body  15  extend two thin ribbings  19  parallel to the greater extension of the modular member. Opposite each interconnection arm  17  is made another projection  20 ,  21 ,  22 ,  23 ,  24  that extends transversely to the ribbing  19  in the direction of the corresponding interconnection arm  17 . This procedure allows improving the anchorage of each portion of the covering  16  and in particular if the latter is shaped to extend at least partly above the interconnection arms  17 .  
         [0029]     A small cylinder  60  is made opposite the point of injection of the malleable material. The cylinder  60  has the function of breaking the flow of the malleable material injection to allow directing this flow toward all the projections to be deformed without the molten malleable material remaining still too long near the point of injection to cause formation of a cavity in the rigid body at that point.  
         [0030]     The rigid body  15  can also include one or more through holes  30  ( FIG. 2  shows two of them). These holes  30  in one embodiment of this invention are realized opposite projections  20  and  24  and are designed to be filled with malleable material when it is molded on the rigid body  15 .  
         [0031]      FIG. 3  shows a cross section of the rigid body  15  along the surface III-III (shown in  FIG. 2 ). In said figure the rigid body  15  is shown before the covering  16  is molded on it. It is noted in particular how the ribbing  19  and the projections  22 ,  23  extend vertically from the rigid body  15 . This procedure allows realizing the molding of the rigid part in a simple and economical manner with no need of using costly and sophisticated molds for formation of the undercuts. In addition, by deforming the ribbings starting from their vertical position the undercuts necessary for realizing the desired mechanical interconnection between the rigid body  15  and the skidproof covering  16  are easily obtained.  
         [0032]     Advantageously the height of the ribbing  19  is greater than their thickness in order to favor formation of the undercuts when the latter are formed. For example, the ribbings  19  could be higher than 1 mm with thickness a few tenths of a mm.  
         [0033]     Also note in  FIG. 3  the teeth  31  formed in one piece with the rigid body  15  of the modular member and designed to engage for example with a rail guide of the conveyor belt (not shown in the figures). Notice also the holes  25  made in the arms  17  and designed to receive the adjacent link interconnection pins in accordance with what was stated above.  
         [0034]      FIG. 4  shows a conveyor link cross-sectioned in the same manner as in  FIG. 3  after the covering  16  has been hot-molded on the rigid body  15 . Due to the effect of the heat spreading from the malleable material at the time of molding of the covering  16  the projection  22  and the ribbings  19  reach a temperature at which they are plastically deformable. The projections are struck by the flow of malleable material and being made deformable by the high temperature they deviate from the vertical portion to form undercut seats  40 . The malleable material forming the covering  16  engages in the seats  40  and once cooled remains mechanically interconnected with the rigid body  15  of the modular member. It is noted that the rigid body  15  remains nearly undeformed because its mass (and consequently its thermal inertia) is much higher than that of the ribbings and the projections. In this manner, firm and safe anchorage of the covering  16  is realized without noticeably altering the dimensional characteristics and the form of the modular member.  
         [0035]     It is also noted that in  FIG. 4 . that the through hole  30  is filled with malleable material during molding of the latter. This procedure allows further improvement of the anchorage of the covering  16  to the rigid body  15  of the modular member.  
         [0036]      FIGS. 5 and 7  show two views of the modular member  11  cross-sectioned along plane of cut V-V of  FIG. 2  respectively before and after molding of the covering  16 .  FIG. 7  shows well the possible deformations undergone by the two ribbings  19  during hot molding of the portion  16 .  
         [0037]      FIG. 6  shows a link of the conveyor cross-sectioned along plane of cut VI-VI of  FIG. 2  and inserted in the mold just before molding of the covering  16  of high friction material. It is noted advantageously that the lower -half of the mold  39  could be the same part used for molding of the rigid body  15  of the link. This procedure allows hastening the manufacturing process of the conveyor modular member because it is sufficient to replace the upper half of the mold to proceed with molding of the portion  16  without ever removing the rigid body  15  of the lower half of the mold  39  and merely leaving it to cool before proceeding to the following molding at least below the softening temperature of the material.  
         [0038]     In  FIG. 6  the upper half of the mold  38  has already been applied for molding of the covering  16 . Note that the injection channel  37  of the malleable material is arranged in such a manner as to cause the material to flow in temperature opposite the cylinder  60 . Advantageously, the cylinder  60  can project slightly above the ribbings  19  to reduce the cross section of the flow of malleable material between the wall of the mold and the cylinder  60 . This procedure allows increasing the speed at which the flow of malleable material strikes the projections to be deformed. The injection flow is therefore shunted immediately towards the ribbings  19  that heat up until they become plastically deformable. Being struck by the flow of malleable material the ribbings  19  deviate from their vertical position until they form the undercuts  40  shown in  FIG. 7 . It is noted that the flow of malleable material from the center outward can lead to the formation of two undercuts turned in opposite directions as shown. However, in the zones furthest from the injection channel  37  the flows of malleable material could be different to give origin to a chaotic and irregular deformation of the projections of the rigid body of the link. In any case, the mechanical interconnection that was just created between the two materials is such as to ensure a firm and lasting fastening of the covering  16  to the rigid body  15  of the conveyor link member. It is now clear that the preset purposes have been achieved.  
         [0039]     In particular, a conveyor having a skidproof supporting surface whose members can be made rapidly and economically is realized. Indeed, the material forming the skidproof covering is molded directly on the rigid body of the modular member with no need of using any supplementary structure on which is molded the rubber to then be fastened to the link body. In addition, the mold used to make the rigid body of the modular member is very simple and economical because the initial form of the body does not call for any undercut. Indeed, the undercuts are formed only at the time of molding of the covering of malleable material.  
         [0040]     It is noted that the modular member in accordance with this invention can be made without ever removing the piece in work from the lower part of the mold by merely replacing the upper half of the mold to mold the covering of malleable material. This procedure allows considerably accelerating the manufacturing process of the conveyor links.  
         [0041]     In addition, a conveyor ensuring firm and constant anchoring of the skidproof portion to the support surface for the objects is realized. Indeed, the mechanical interconnection between the rigid thermoplastic material and the malleable material forming the skidproof covering ensures a steady fastening between the rigid part and the surface covering supporting the modular member.  
         [0042]     Naturally the above description of an embodiment applying the innovative principles of this invention is given by way of non-limiting example of said principles within the scope of the exclusive right claimed here.  
         [0043]     For example, the projections designed to be deformed at the time of molding of the skidproof covering could have various initial forms and not necessarily those described above.