Woodworking machine, such as a traversing sanding machine

Abstract: On woodworking machines of the traversing type, for example those used for sanding operations, the items (23) are secured on a vacuum conveyor (3). When the items are not perfectly plane, or when the contact surface against the conveyor is small, the holding power is often not sufficient to allow satisfactory processing operations to be effected without the time-consuming use of devices such as clamping tools or the like. In order to overcome this disadvantage, the machine according to the invention is provided with a number of compressed air nozzles (10) which direct a stream of air towards the items (23), whereby there is achieved a hitherto unknown degree of good retention, even of items which have not hitherto been able to be secured by means of air alone. The nozzles (10) are connected to the pressure side (9) of the air pumps (6), and the suction of the conveyor (3) is connected to the pumps' inlet sides (8), thus hereby creating a closed system with good economy. Finally, there is a reduction in the friction of the belt (13) as well as the wear on the supporting plate (18), this being the result of the formation of eddy currents in some grooves (20), which are formed in the plate (18) and through which the air is sucked.

Description: The invention relates to a woodworking machine, such as a sanding machine and as disclosed in the preamble of claim 1. Machines of this type are used especially within the wood-working industry for various forms of finishing operations such as sanding. From US-A-2 877 607 there is known a machine of this type for the sanding and polishing of surfaces in finishing operations, or as a link in a surface-treatment process such as lacquering. For the feeding of the items during the processing in the machine, an endless belt is used which is provided with holes and suction from underneath and functions as a so-called vacuum conveyor on which the items can be secured. The endless belt rests on a support and by suction the contact pressure of the belt on this support is increased. In the known machine the support is provided with longitudinal grooves extending in the direction of motion of the belt. The grooves have a rectangular cross section, and the upstanding walls are at the top provided with shoulders on which the belt can slide. It should also be noted that US-A-4 003 226 shows a machine for removing dust from sheet materials, such as leather. This machine has a support and drive mechanism for moving the sheet material into the machine, whereby the material is sucked to an endless belt which creates the said support and drive mechanism. Above the belt air nozzles are provided which direct air currents downwards at an inclined angle towards the top surface of the material in order to blow away material dust towards suction openings provided above the belt for receiving the dust which has priorly been loosened by means of a rotating brush. This arrangement serves the purpose only of blowing material dust away from the items and is not suited for securing the items to the belt. It is the object of the invention to improve the first mentioned known machine such that a reduction of the wear on the belt and the support can be obtained while at the same time reducing the energy consumption required in order to drive the belt. At the same time the item to be worked on should be pressed down against the belt. This object is obtained by a machine of the initially described kind which machine according to the invention is characterized by the features of the characterizing part of claim 1. By this embodiment air will form whirls in the grooves so that the air is reflected i.a. against the underside of the belt. Hereby the belt is lifted or raised slightly from the plate, whereby friction is reduced quite considerably. This partly reduces the power requirement for driving the belt and partly reduces wear of the belt and the plate. Moreover, it provides a very calm and steady belt motion and conveyor movement, which ensures the best possible processing result. It is advantageous that the total area of the holes in the belt per area unit of the belt is substantially equivalent to the total area of the holes in the plate per area unit of the plate, in that this creates a fair balance between on the one hand a good suction of the item to the surface of the belt, and on the other hand, a suitable reduction of the contact pressure between the underside of the belt and the plate on the other hand. The series of nozzles which are directed towards the belt are connected via channels to the pressure side of the air pump. The retaining power is hereby considerably increased, and thus items which are normally difficult to retain, either because of a curvature in shape or a relatively small contact surface against the belt, can now be effectively secured without risk of being displaced on the belt. This is due particularly to the extra compression which the air discharge exercises on the items, and which can be established without any reduction in the size of the machining chamber or interference with the machining process. Furthermore, this nozzle arrangement does not require any particular energy over and above the loss of pressure which arises as a result of flow resistance in the channels and the nozzles. Moreover, the flow of air directed against the items during processing results in the items being continuously blown clean of dust and fibres, whereby it is not only ensured that the process is optimized but also that the belt is kept completely clean during conveyance, and hereby that the function of the recesses is not disturbed. Finally, this increased flow of air in the working chamber of the machine provides efficient ventilation and cooling, which further contributes towards reducing the wear on machine parts and hereby extends the lifetime of the machine. It is moreover advantageous that the machine is provided with a series of nozzles at both the inlet as well as the outlet end of the belt. The items are hereby blown totally clean after the processing, which means that they can continue directly into a lacquering plant or the like. The invention will now be described in more detail with reference to the drawing, where fig. 1 shows a perspective illustration of a machine partly in section, fig. 2 shows a machine seen in section from the side, fig. 3 shows the machine seen in section from the end, and fig. 4 shows a section of the actual conveyor belt seen in the direction IV-IV in fig. 2. In figs. 1-3 is shown an example of a preferred embodiment of a machine comprising a cabinet 1 consisting of an under-frame on which the movable plane 3 is mounted, plus side portions on which rests an upper part. Between the upper part and the plane 3 there exits a processing chamber 2 in which there is mounted a machining tool (not-shown), so that an item 23 placed on the belt 3 can be processed by the tool in a commonly-known manner during its passage through the machine. As will appear from figs. 1 and 3, in the cabinet 1 there is an air pump 6 in the form of a radial pump mounted in each side. The pump wheel is driven by a motor 7 and is placed in such a way that the air intake 8 and air outlet 9 of the pump 6 face outwards towards the side parts. These side parts have a built-in system of air channels, i.e. a pressure channel system connected to the pressure sides 9 of the pumps 6 and a vacuum channel system connected to their suction sides 8, whereby an almost closed air system is created in the machine, which therefore functions in the most economic manner. The pressure channels open out in two series of nozzles 10 which extend above the belt 3 in a transverse channel 4, which as indicated in fig. 2 can be housed in a front shield 24 which below the nozzles is further provided with a skirt 26 through which the items 23 can be introduced and fed out on the conveyor 3. The nozzles 10 are oriented in such a manner that the air currents are directed downwards towards the items 23 on the conveyor 3, whereby the items are pressed down against and hereby secured on the belt. In the upper part of the machine there is also seen a commonly-known exhaustion system comprising a suction head 5 which, via a commonly-known dust filter, is connected to a suction system which can possibly form part of the closed air system. As shown in fig. 2, the conveyor 3 is built up of an endless rubber belt 13 which runs over two reversing rollers 14 mounted at the ends of the conveyor 3, and which are coupled to a drive arrangement so that the belt 13 can run around the rollers 14. The speed at which the belt 13 moves can be variable for adjustment of the feed during operation. The construction of the conveyor 3 itself is shown in fig. 4. The rubber belt 13 has a plane underside and an upper-side patterned with upwardly-extending ribs 15 which with the same height form a pattern of recesses 16. In each of these recesses 16 there is a hole 17 through the belt 13, thus giving rise to a surface consisting of low pressure chambers as indicated in figs. 1 and 3. The belt 13 is supported underneath by a metal plate 18 which extends at the same level between the reversing rollers 14, so that the belt 13 is supported by the plate 18 during its passage through the machine. The plate 18 is also configured with a number of grooves which extend lengthwise with the direction of movement of the belt, and which have a breadth which corresponds substantially to the largest breadth of the recesses 16. The belt 13 is thus supported only by the raised portions between the recesses 16, as shown in fig. 4. In the wall 19 of the recesses there are also holes 21 for the passage of air through the plate 18. Mounted under the plate 18 there are a number of separating walls 22 which extend down in the plane to a baseplate 25, thus forming a chamber of the desired length under the belt 13. Finally, two pipes or channels 11, see figs. 1 and 2, are mounted transversely to the conveyor 3 and between the separating walls 22, said pipes 11 being connected to the low-pressure channel system in the machine which is connected to the inlet channels 8 of the air pumps 6. The mode of operation of the air system will now be described. Upon start-up of the machine, the drive motor for the reversing rollers 14 is activated, whereby the belt 13 is driven around. The air pumps 6 are also started, whereby compressed air is fed through the nozzles 10 over the belt. At the same time, air is sucked out through the recesses 16 via the holes 17 in the belt 13, through the holes 21 in the plate 18, through the openings 12 in the longitudinal channels 11, and also through the suction nozzles 5 in the processing chamber 2. Hereafter, the not-shown processing tool can be started and the machine is ready for operation. An item 23 placed on the belt 13, see figs. 3 and 4, will now be secured on said belt, in that the item will shut off the supply of air from outside to some of the recesses 16, and will also be pressed downwards by the downwardly-directed stream of air from the nozzles 10. At the same time that the item 23 is thus better secured than with the hitherto-known vacuum conveyors, said item will be blown clean while being fed into as well as out of the machine. The suction system inside the processing chamber 2 ensures that the dust-laden air is constantly exhausted and cleaned during operations before it is again fed back to the channel system. The suction at the recesses 16 is effected further via the groove-formed channels 20, where it should be noted that the air creates eddies in these grooves, so that the air is reflected towards among other things the underside of the belt 13. The belt 13 is hereby lifted or eased slightly away from the plate 18, whereby the friction is quite considerably reduced. This reduces not only the power required for driving the belt, but also the wear on the belt and the plate. Moreover, this also results in a very smooth and uniform conveyor movement, and thus a feeding of the item which ensures the best possible processing result.

Claims: Woodworking machine, such as a sanding machine, with a supporting and feeding device (3) for an item (23) during its passage through the machine, and with an endless belt (13) which runs over two reversing rollers (14) and is provided with a rib pattern (15) on its upper side for the formation of evenly-spaced recesses (16), each of which has an air suction hole (17) which via channels (11) is connected to the suction side of an air pump (6), so that an item (23) can be secured on the belt (13) by the vacuum in the recesses during passage through the machine, that the belt (13) slides on a suction box with longitudinal grooves (20) which extend in the direction of movement of the belt, characterized in that the machine is further provided with a series of air nozzles (10) above the conveyor (3), said nozzles (10) being connected via channels (9) to the pressure side of the air pump (6), so that the item (23) is pressed down against the upper surface of the belt (13) by the air, and in that the suction box consists of a plate (18) having grooves (20) with V-shaped cross sections and suction holes (21) through the plate (18) where this plate forms walls (19) for said longitudinal grooves (20). Woodworking machine according to claim 1, characterized in that the total area of the holes (17) in the belt (13) per area unit of the belt (13) is substantially equivalent to the total area of the holes (21) in the plate (18, 19) per area unit of the plate (18, 19). Woodworking machine according to claim 1, charac terized in that the machine is provided with a series of nozzles (10) at both the inlet as well as the outlet end of the belt (13).

Inventors: HUNDEBOL KELD OTTING, HUNDEBOL, KELD OTTING
Applicants: HH PATENT AS, HH PATENT A/S
Application year: 1991
Main classification: B24B41
IPC codes: B27C1, B24B21, B24B7, B24B41