METHOD AND APPARATUS FOR CONTOUR CUTTING OF PLASTIC PRODUCTS

Abstract: Apparatus for contour cutting of a number of uniform plastic products from a block of starting material by means of a plurality of parallel filaments heated by an electric current, provided with a work table (3) that is movable in a horizontal direction for receiving at least part of a block of starting material, a supply conveyor (21) and a delivery conveyor (22), a number of vertical columns (2), a horizontal U-shaped framework that is mounted between two horizontal support­ ing beams (4), which framework is provided with a number of parallel cutting filaments and is movable up and down in a vertical direction along the columns (2), driving means (16) for the working table, driving means (11) for the supporting beams with the U-shaped frame, and means for imparting a synchronous oscillating movement of each of the filaments in the U-shaped frame in their long direction.

Description: PROCESS AND APPARATUS FOR CONTOUR CUTTING OF PLASTIC PRODUCTS, AND IMPROVED CONTOUR-CUT PRODUCTS The invention relates to a process for contour cutting of a number of uniform plastic products from a block of starting material, using a plurality of filaments disposed in parallel to one another and heated by an electric current, the starting material being given a movement in at least one direction. For contour cutting of products from a block of foamed plastic starting material such as, for instance, polyurethane or polystyrene, in particular for insulating purposes, use is made of electric filaments for cutting the starting material into the desired shape. Thus, it has already been proposed to manufacture several products simultaneously from a block of starting material by means of a number of filaments disposed in parallel to one another. The filaments in question are, however, mounted rigidly in a framework through which the product is moved, whereby a number of parallel cuts are made through the starting material so as to obtain plate-type products. It is also known that different shaped products can be cut successively from a block of starting material using an endless cutting wire rotating on discs, such that the framework in which the cutting wire has been mounted is given a movement in one direction and the product to be cut a movement at right angles to the former movement. This arrangement, however, permits processing of only one product at a time whilst the use of a framework within which the cutting wire must rotate requires a clearance above the starting material at least as high as the material to be processed. It is the object of the present invention to provide an improved process of the type specified in the introduction, an apparatus to be used for the application of such a process and, thirdly, an improved product obtained by means of this process and/or such an apparatus. To this end, it is proposed according to the invention, using a process of the type specified in the introduction, to give the filaments mounted in parallel an oscillating movement running in their long direction for enhancement of the cutting effect and, in addition, to impart to the block of starting material a programmed reciprocating movement that is substantially parallel to the plane of the filaments, whilst a corresponding programmed reciprocating movement is imparted to the filaments that is substantially at right angles to the plane in which these have been mounted. By means of such a correspondingly programmed combination of movements, a plurality of virtually identical products, depending on the number of filaments used, are obtained from a single block of starting material, the said products being formed simultaneously. Hitherto, in contour cutting use was made of a rotating cutting wire mounted under sufficient pre-stress to obtain as straight a cut as practicable. Admittedly, it is known that several filaments mounted in parallel can be used for cutting the starting material into slabs, but filaments so used undergo deflection so that is is impossible to obtain products that are true to shape in the event of deviations from a cut projected in one plane. By imparting an oscillating movement to the filaments, the cutting effect is enhanced whilst, in addition, a virtually straight cut is obtained, making contour cutting feasible. The appearance and the structure of the surface of the cut product will tell whether an oscillating filament has been used, because in that case on the one hand the surface will be firmer and contours virtually identical over the entire width of the product owing to the absence of a perceptible deflection of the filament, while on the other hand the surface is formed more smoothly under the influence of the filament and exhibits a closed structure, quite unlike a product formed with a mechanically operating cutting wire. An apparatus for the application of such a process according to the invention is provided with a work table movable substantially in horizontal direction for receiving at least a part of a block of starting material, and with a drive mechanism for the work table operated according to a programme, a number of substantially vertical columns, a U-shaped framework movable up and down in a vertical direction along the vertical columns and substantially disposed in a horizontal plane, in which frame a number of filaments have been mounted in parallel to one another for cutting of a plastic material, a drive for moving the U-shaped framework in a vertical direction along the columns according to a certain programme corresponding with the programme for the horizontal displacement of the work table, and a drive for synchronous oscillating movement of each of the filaments in their long direction. Such an apparatus can be of limited vertical dimensions, because the U-shaped framework need only be raised sufficiently high for a block of starting material to be passed underneath. Preferably, use is made of a work table of considerable length, for instance 4 metres, which enables the customary starting material, i.e. a block with a length of 12 metres, to be cut in three passes. The surface of the work table is preferably provided with recesses into which the filaments can drop in their bottommost position, so that after one cut in a vertical direction the block of starting material can be moved forward for contour cutting of the second portion of the block of starting material. It is preferred to employ four colomns disposed in a rectangle for supporting the U-shaped frame, with a counterweight fitted on each column for a virtually perfect balanced suspension of the locally supported part of the U-shaped frame. This set-up ensures that the time lag for the drive is equal in both directions of travel and that it makes no difference for the precision in shaping of the products to be cut whether the U-shaped frame moves down or up during the cutting. It has been found that by gripping every filament with the aid of a tension spring between two parallel tension bars and mounting these tension springs alternately on either of the tension bars invariably one half of the filaments will move in one direction and the other half in the opposite direction, when the tension bars are moved synchronously in opposite directions. The forces exerted by the filaments in their long direction on the block of starting material are thereby virtually compensated, so that this block will not be displaced or distorted under the influence of the cutting forces. Further particulars of the invention also become apparent from the following description of an embodiment of apparatus according to the invention. In the drawings: Figure 1 is a schematic side view of an apparatus accor ding to the invention; Figure 2 is a top view of the same apparatus; Figure 3 is a detailed top view of a U-shaped frame; Figure 4 is an end view on IV-IV in figure 3; Figure 5 is a sectional view on V-V in figure 3; Figure 6 depicts a section along the line VI-VI in figure 3 on an enlarged scale; and Figure 7 shows a few products. The apparatus depicted in Figure, l comprises a base frame 1 on which four vertical columns 2 have been mounted in a rectangle. Enclosed within the columns is a work table 3. In the long direction of the apparatus a supporting beam 4 has been provided at both ends. These supporting beams are suspended on vertical carrier heads 5 which can be moved along the columns 2. Each of the carrier heads 5 is connected through a chain 6 and a sheave 7 with a counterweight 8. The load of this counterweight 8 is chosen such that it virtually compensates the load of the framework with supporting beams and any other components fitted to it weighing on each carrier head 5. Each of the carrier heads 5 can be displaced in a vertical direction by driving means - not shown in the drawings - moving synchronously for each carrier head, such as a screw spindle with nut. All these driving means are linked together for the four columns by means of drive shafts 9 and 10 in the longitudinal and crosswise direction, respectively. A drive motor is denoted by 11. Obviously, more drive motors may be applied, provided a vertically uniform displacement of the carrier heads is ensured. The columns are connected together at the top by means of structural shapes 12 and 13, respectively. Each of the supporting beams 4 is provided at the location of a vertical column 2 facing the carrier head with a coupling flange 14 for the attachment of the U-shaped framework to be discussed below. On the base frame 1, a screw spindle 15 with driving motor 16 has been mounted underneath the work table 3. This screw spindle meshes with a nut incorporated into a support 17 underneath the work table 3. By means of schematically shown carrier wheels 18, the work table 3 rests on guiding tracks 19. The motor 16 enables the work table 3 to be moved to and fro over a distance of about two metres. The left-hand portion of the work table in Figure 1 is provided wtih a number of rollers 20 which allow of telescopic movement relative to a stationary supply conveyor 21. On the right-hand side, the work table 3 terminates above a delivery conveyor 22. By a combined drive through the motors 11 and 16, any desired movement can be realized of the work table 3 in a horizontal direction and of the supporting beams 4 with the parts mounted in between to be describe hereinafter in a vertical direction. Optionally, these drives may be operated under numerical control. Figure 3 is a top view of a substantially U-shaped frame consisting of two longitudinal bars 30 connected by a cross bar 31. Each bar 30 is provided with two coupling flanges 32 to permit mounting between the supporting beams 4 by means of the coupling flanges 14 mounted thereon. The longitudinal bars 30 are of the box type and each provided with a fan with motor 33 for the supply of cooling air to each bar 30. At the side of each bar 30 a rocker arm 35 has been fitted. The rocker arms 35 move synchronously in opposite directions. On top of the rocker arm 35 a support 36 is provided for tension bars 37. A filament 40, a tension spring 41 and two terminal pull cables 42, 43 are invariably mounted between the two tension bars (see figure 6). As the bars 37 move away from one another, the increased distance will be accommodated by an elongation of the tension spring 41. In the embodiment according to figure 6, the bottommost filament 40 will then move to the left. A large number of wires, say 50, have been stretched between the two rocker arms 35 in the manner indicated, such that the tension spring 41 is alternately attached to either one of the tension bars. In consequence, when the tension bars 37 move outwards, one half of the filaments 40 travel to the left and the other half of the filaments to the right, and when the tension bars move back inwards these filaments will each travel in opposite direction. As the forces exerted by the several filaments are oriented in opposite directions, the resulting force on the material to be processed will be virtually nil. As appears from figure 6 in particular, the hollow bar is provided with discharge openings 45. Cold air supplied flows through these openings and thereby cools the part of the filaments 40 that projects from a block 46 to be cut. For the synchronous drive of the tension bars on the rocker arms 35, reference is made to the terminal view of figure 4. On the end of the rocker arms 35 that is located near the cross bar 31 a lever 50 has been mounted. The tip of this lever rests at 51 on an eccentric 52 which forms part of a short axle provided with a gear wheel 53. The two gear wheels 53 are interconnected by a rubber driving belt 54 which is provided with an internal toothing and which is held under initial tension by means of a movable thrust collar 55. The eccentric shaft mounted on the right-end side in Figure 4 is driven by a motor 56 (see also Figure 3). A synchronous displacement of the two rocker arms is accomplished by the use of a toothed belt. The initial tension of the several springs 41 ensures that the levers 50 continuously lie against the eccentric 52. It has been found that an efficient, vibration-proof drive of the whole can be achieved by maintaining an initial tension for the two rocker arms 35 relative to the U-shaped framework such that the overall tension of the springs 41 is substantially compensated provided that sufficient force is at all times preserved for the levers 50 to lie against the eccentrics 51. Depending on the requisite driving frequency, the initial tension may be adapted. The work table is designed for receiving a block of starting material at least four metres long. It is also possible to process blocks of starting material twelve metres long by running such blocks through the apparatus in three passes. By the application of fifty cutting wires between the two rocker arms, forty-nine pieces can be cut at a time in one vertical movement. This is illustrated in Figure 7, where the dot-dash line represents the contour of a block to be cut. A number of successive cutting wires are denoted by A', N, O. The block to be cut is placed with its foremost boundary line at the desired distance. Next, the cut A'-A is made by a vertical displacement of the U-shaped framework. All the other cutting wires perform a corresponding cut. Then, a combined displacement of the work table in a horizontal plane and of the filaments in the U-shaped frame upwards takes place for the cut A-B and the corresponding cuts of the other filaments. Subsequently, a horizontal displacement is continued in the same direction, whereas the U-shaped frame moves down, so that the cut B-C is carried out. Thereupon, the vertical displacement is continued but the work table inverts the direction of travel for the cut C-D to be made. Next to follow is the cut D-E, upon inversion of the direction of travel of the work table, and then the cut E-F, again requiring inversion of the direction of travel of the work table. Finally, a cut F-G is made, whereupon the U-shaped frame nives down to the indicated G'. In this position the filaments 40 have all come ro rest in local recesses 70 in the work table 3. As the consecutive wire N has in the mean time gone through a corresponding movement along the points A, K, L, G to N', the foremost product has been cut loose with one vertical movement of the U-shaped frame, and as a matter of course so have all the other forty-nine products. Thereupon, the block of starting material can be pushed on to position 60, it being understood that its front will have been profiled in accordance with the contours of the cut products, and subsequently a corresponding number of products can be cut by a substantially upward movement of the U-shaped frame, to be followed by a third series of products made from the block of starting material. It is worth noting that a very sharp cut is obtained by the use of oscillating filaments with hardly any deflection of the filament. As a result, it is possible to produce clear-cut contours over the entire width of the block to be processed, even when acute angles are cut as in the example of Figure 7. In the cutting of angles, therefore, the cutting speed need hardly be reduced, although this is easily done, if desired. In this fashion, products are obtained with a sharply profiled appearance. In this case of thermoplastic starting material, all cells at the surface of cut are.sealed by annealing, affording an extremely smooth appearance, because no dust is formed during cutting which could roughen the surface. It has been found that oscillating contour cutting can be practised not only on thermoplastic synthetics such as polystyrene foam, but also on rigid foam material such as polyurethane. The surface so obtained is smooth and comparable to that produced by mechanical sawing, but without any sawdust being formed. Cutting according to the invention involves a material loss of at most 1 mm, whilst the cutting speed attainable for, say, rigid polystyrene foam may be as much as four metres per minute. The temperature of the filament is set to a value of 80 to 90 "C, but, depending on the resistance of the material to be cut, a higher equilibrium temperature may be reached on account of the friction. An effective straight cut proves to be feasible at an average initial tension of the filaments of 10 kg.

Claims: CLAIMS 1. A process for contour cutting of a number of uniform plastic pro ducts from a block of starting material, using a plurality of fila ments disposed in parallel to one another and heated by an electric current, the starting material being given a movement in at least one direction, characterized in that the filaments are given an oscillating movement in their lon direction for enhancement of the cutting effect, that the block of starting material is given a pro grammed reciprocating movement that is substantially parallel to the plane of the filaments, whilst a corresponding programmed recipro cating movement is imparted to the filaments substantiaaly at right angles to their plane of mounting. 2. Apparatus for the application of the process according to claim 1, provided with a work table that is movable substantially in a hori zontal direction for receiving at least a part of a block of starting material, also provided with a drive mechanism for the work table operated according to a programme, a number of substantially verti cal columns, a U-shaped framework movable up and down in a vertical direction along the vertical columns and disposed substantially in a horizontal plane, in which frame a number of filaments have been mounted in parallel to one another for cutting of the plastic ma terial, a drive for moving the U-shaped framework in a vertical direction along the columns according to a certain programme corresponding with the programme for the horizontal displacement of the work table, and a drive for a synchronous oscillating movement of each of the filaments in their long direction. 3. Apparatus according to claim 2, characterized in that it is provided with four vertical columns disposed round the work table in a rectangle for supporting and guiding the U-shaped frame, each column being provided with a drive for the vertical displacement of the part of the frame supported by that column, whilst the drives of all four collumns are connected together for a synchronous drive, each column also having a counterweight fitted to it for virtually complete counterbalancing of that part of the weight of the U-shaped frame with components mounted on it which is borne by the approp riate column. 4. Apparatus according to either one of claims 2 and 3, characterized in that each filament is connected to a tension spring such that filament and tension spring are invariably stretched between two tension bars mounted in parallel to one another within the U shaped frame, which tension bars can be moved synchronously to and fro in opposite directions for imparting a reciprocating movement to the filaments, whilst the tension spring fitted to successive filaments is preferably attached alternately to one tension bar and the other. 5. Apparatus according to claim 4, characterized in that the tension bars can be driven in opposite directions, because they have each been fitted on a rocker arm mounted on each of the two parallel bars of the U-shaped frame, both of these rocker arms being pro vided near the cross bar of the U-shaped frame with a pre-tensio ning device and a lever, which lever is caused by the forces by the filaments with tension springs and the pre-tensioning device to rest against an eccentric, whilst the eccentric shafts on both sides of the U-shaped frame can be driven by means of a common driving motor and a toothed belt. 6. Apparatus according to any one of claims 2 to 5, characterized in that the work table is provided with a great number of grooves made in crosswise direction for receiving the filaments in the bottommost position of the U-shaped frame. 7. A product cut in at least two directions following a contour, mani festly made with use of the process according to claim 1 and/or by means of an apparatus according to any one of claims 2 to 6, such that the product's contours are substantially identical over its entire width and that the surface has a smooth, sealed structure.

Inventors: VAN DIJK, HENDRICUS JOHANNES MARIA
Applicants: GEBR. VAN DIJK B.V.
Application year: 1983
Main classification: B26F3
IPC codes: B26F3, B26D1