FR2669906A1 - Device for transporting (silk) screen printing screens (stencils) on a washing and engraving-removal line - Google Patents

Abstract

The device is installed on a treatment line comprising a washing chamber (1) and an engraving-removal chamber (2) which are arranged one after the other; the device includes at least one transport bar (4, 4') which is driven in a pilgrim-step movement (f) and is adapted for displacing the screens (3, 3') inside the said chambers (1, 2) and for transferring them from the chamber (1) to the chamber (2). Transporation of screen printing screens on a washing/engraving-removal line.

Description

DEVICE FOR TRANSPORTING SCREEN SCREENS
ON A WASHING AND DEGRAVING LINE
The present invention relates to a device for transporting screen printing screens on a washing and degreasing line.

 The screens used in screen printing are formed from a generally rectangular frame, for example aluminum, on which is stretched a porous fabric called "silk". It is generally a polyester canvas with fine perforations; it bears an engraving, or emulsion, which corresponds to the plate to be reproduced by screen printing. The size of the screens is very variable and depends on the intended use; the screens can reach dimensions of 4 x 3 m for printing large advertising posters.

 When a screen printing process is complete, it is necessary to wash the screen to remove all traces of paint. If you wish to keep the screen for the subsequent reprint of the same design, dry it and put it away after washing. On the other hand, if the reprint of the same motif is not envisaged for the future, the emulsion carried by the screen is chemically degraded so as to obtain a virgin silk of any motif, which can be used for a new one. drawing.

 Traditionally, screen washing and unblasting operations are done manually.

 In order to improve the working conditions of the personnel, to reduce the risks linked to solvent fumes and discharges, and to preserve the environment, it has recently been proposed to automate these operations. Thus, an automatic washing and de-greasing line is commercially available, distributed under the trade name "AB a. Buisine s.a". This treatment line includes two cabinets in the form of vertically arranged cabinets. These are two watertight cabinets, quite distinct, but juxtaposed, and located in alignment with each other, the outlet end of the first cabinet being just opposite the inlet end of the second.

 In each enclosure are provided horizontal guide bars which maintain the screens in an approximately vertical position in the center of the cabinet.

 The first enclosure is used for washing screens. Washing consists of spraying solvent on the screens. The nature of the solvent depends of course on the paint which was used at the time of printing. By way of example, mention may be made, as solvents which can be used, of ethyl glycol acetate, ethyl glycol, diacetone alcohol and trimethylbenzene.

 The solvent is sprayed using two sets of nozzles which are each carried by a movable vertical bar. There is a spray bar on each side of the screen. The bars are carried by a carriage animated with a horizontal reciprocating movement, which makes it possible to process the entire surface of the screen, or screens, located in the enclosure.

 Washing residues are collected in trays placed under a grid at the bottom of the cabinet. These residues are then treated, part of the solvent being recycled while the undesirable substances are removed.

 The second enclosure is used for cleaning the screens that have just been washed. This operation comprises several successive phases, namely a rinsing with water, a draining, a spraying of degreasing product, a rest time during which the actual chemical degreasing reaction takes place (intended to eliminate the emulsion). , a spray of water under high pressure and a final rinse with water.

 These different treatments are carried out by means of several sets of spray nozzles which are carried by horizontal bars driven by an alternating vertical movement.

The work sequences are controlled by a programmable controller.

 As a possible degravant product, mention will be made of sodium metaperiodate.

 Degreasing residues are collected in tanks located at the bottom of the cabinet and are then treated by an appropriate system, the water being recycled.

 As an indication, the washing and degreasing times are both of the order of 7 minutes.

 In the known automatic chain, the displacement of the screens inside each of the cabinets, as well as their transfer from the washing cabinet to the degravage cabinet, are carried out by means of a single conveyor which is made up of an endless chain extending all along the line, that is to say traversing the two cupboards.

 The chain supports screens; it is fitted with cleats (pushers) capable of driving the screens in translation, in the vertical position.

 This known transfer device is not satisfactory.

 Indeed, experience has shown that the links in the conveyor chain carry from one enclosure to another a significant amount of product.

 Thus, the solvent collected by the chain in the first enclosure is transferred by the "go" strand of the latter in the second enclosure. It is estimated that the quantity of solvent transported by the chain is approximately equal to that which is transported by the screen itself.

 During the treatment in the degravage enclosure, in particular in the initial rinsing phase, this solvent is collected in the tanks with the other degravage residues. This poses an important problem linked to the subsequent treatment of the residues with a view to recycling the water, since the removal of the solvents is delicate and often incomplete. There is therefore a risk of environmental pollution, and this is why the amount of solvent present in the liquid recovered in the degravage cabinet must be as low as possible.

 Furthermore, it should also be noted that the "return" strand of the chain carries water which has been collected in the second enclosure, and is therefore transported to the first enclosure. This water may mix with the recycled solvent in the washing chamber and disturb this operation. In particular, it has the drawback of fixing the emulsion, which makes subsequent degravage (in the second enclosure) more difficult.

 The present invention aims to solve these difficulties by proposing a device for transferring screens which, while being simple and robust in design, makes it possible to very significantly reduce the quantity of undesirable substances which are liable to be transported from the washing enclosure. towards the degravage enclosure, and completely eliminating the transfer of the products in the other direction, that is to say from the degravage enclosure to the washing enclosure.

 These various results are achieved in accordance with the invention, thanks to the fact that the transport device comprises at least one transport bar animated by a movement with pilgrim steps and adapted to move the screens inside the speakers and transfer them from the washing chamber to the degreasing chamber. The transport members are therefore members which have a very limited displacement travel, so that they are not capable of carrying an undesirable substance from one enclosure to another. In addition, due to the pilgrim's movement of the bar, that is to say a cyclical movement of ascent, advance, descent, and return, each screen is subjected to a jerky movement which has a dripping effect, also eliminating a large part of the products that adhere to the screen.

 In a preferred embodiment of the invention, there is provided at least one pair of parallel and adjacent transport bars which are each driven by a pilgrim step movement, these two transport bars being arranged side by side and their movements being out of phase so that they support and move the screens in turn.

 Preferably, two pairs (or sets) of transport bars are provided which are placed one inside the washing chamber and the other inside the degravation chamber, these two pairs bars being moved in synchronism and arranged in alignment with each other.

 Thanks to this arrangement, each pair of bars remains constantly inside the enclosure where it is placed, and there is absolutely no substance which can be transported by the transport device from one enclosure to another. .

 In this case, the distance which separates the downstream end of the bars located in the first enclosure from the upstream end of the bars located in the second enclosure is naturally very much less than the length of the screens which are processed, so that the screens can be automatically transferred from the first to the second pair of bars.

 Advantageously, the bars are "L" section profiles, one wing of which, arranged horizontally, supports the base of the screen to be transported. The other (vertical) wing prevents lateral escape from the base of the screen.

 In the case where a pair of adjacent bars working out of phase is used, it is advantageous to give these horizontal wings a baffled outline, so that the raised parts of one of the wings overlap in the cutouts of the wing of the neighboring bar, and vice versa, with the possibility of relative displacement of the two bars in the longitudinal direction.

Thanks to this arrangement, the two juxtaposed wings of the bars are not separated by a gap which would pose problems for supporting a thin screen. On the contrary, the assembly of the two juxtaposed bars can thus adapt to various screen thicknesses.

 According to a particularly advantageous embodiment, the drive mechanism of the transport bar (s) comprises a circular contour cam which supports the bar, this cam being driven in rotation about a horizontal axis which is arranged transversely to the bar and is offset from the axis of the cam. The cam therefore plays the role of an eccentric which, during its rotation, causes the bar to rise and fall.

 In this case, the movement of the bar in the longitudinal direction can be obtained in a simple manner by mounting on this cam a finger whose axis is eccentric relative to the axis of rotation of the cam, this finger engaging in a vertical light formed in a part integral with the bar. The finger therefore plays the role of an eccentric crank pin which, during the rotation of the cam, will cause a longitudinal reciprocating movement of the bar.

 Preferably, for each of the bars, two identical drive mechanisms are provided, one located at the front and the other at the rear of the bar.

 In the case where two pairs of bars are provided, one located in the first enclosure, and the other in the second enclosure, the synchronization of the two drive systems can be obtained by a chain and sprocket transmission from a single motor, the latter as well as the transmission members being arranged outside the enclosures (which protects them from corrosion and facilitates their maintenance).

 Other characteristics and advantages of the invention will appear from the description and the appended drawings which show a preferred embodiment thereof.

On these drawings
- Figure 1 is a schematic side view of a washing and degravage line;
- Figure 2 is a cross section of the washing enclosure
- Figures 3, 4 and 5 are schematic cross sections of two transport bars working in phase shift
- Figure 6 is a cross section showing the drive mechanism of two transport bars
- Figure 7 is a side view corresponding to the broken section plane VIl-VIl of Figure 6
- Figures 8 and 9 are schematic views from above and partial of two transport bars whose horizontal wings have baffles, these two views corresponding to different relative positions of the two bars
- Figures 10, 11, 12, 13 and 14 are schematic detail views, from the side, illustrating the principle of displacement of a screen by means of a pair of transport bars
- Figure 15 is a partial side view showing a possible variant of a transport bar.

 The screen printing processing line which is represented in FIG. 1 comprises a washing enclosure 1 and a scouring enclosure 2. These are two cabinets in the form of rectangular boxes arranged vertically and fixed to the floor S.

These two boxes are fitted with watertight doors. We have designated by the references 10 and 11 the entry and exit doors of the enclosure 1 respectively and by the references 20, 21 the entry and exit doors of the enclosure 2. The door 11 is located just opposite door 20, the two enclosures being arranged in the extension of one another. The enclosures 1 and 2 have a grid-shaped bottom 12, respectively 22, under which are placed tanks 13, respectively 23 for recovering washing and degreasing residues.

 In the drawings, the screen screens have been designated by the reference 3. These comprise a rectangular frame 30 on which a silk 31 is stretched.

 In each enclosure is arranged a pair of transport bars 4, 4 ′ respectively, only one of which is visible in the side view corresponding to FIG. 1. Each of the pairs of bars 4, 4 ′ is adapted to support the screens in vertical position . Horizontal bars 14, respectively 24, which are fixed laterally to each wall of the cabinets 1, respectively 2, maintain the screens in a roughly vertical position.

 In Figure 1, there are shown two screens 3, 3 'which are being transferred from the first to the second enclosure, the washing operation of these screens having just been completed.

 Each pair of bars 4, 4 ′ respectively is driven by two drive mechanisms 5, 5 ′ arranged at their two ends.

 These drive mechanisms will be described later with particular reference to FIGS. 6 and 7.

 They are controlled by a single motor 6, preferably an electric motor having two possible directions of rotation. The motor output shaft 6 directly controls the mechanism 5 located at the upstream end of the bars 4. This shaft carries a pinion 62 over which passes an endless chain 7 engaged with a pinion 63 which allows the mechanism to be driven 5 located at the downstream end of the bars 4. The mechanism 5 'located at the upstream end of the bars 4' has a drive shaft which is driven from the pinion 63 by means of two pinions 64, 65 connected by a chain 70. This shaft itself drives the control shaft of the second mechanism 5 '(located downstream of the bars 4'), via a sprocket system 66, 67 connected by a chain 7 '.

 The two pairs of bars therefore work in perfect synchronism from motor 6.

 Figure 2 shows in section the washing cabinet 1.

This figure shows how the screen 3 rests on the pair of bars 4, which are designated one 4a and the other 4b, and how it is kept substantially vertical by the guide bars 14.

 This figure also shows two vertical bars 100. These each carry a series of nozzles 101 for spraying solvent. They are mounted on a carriage (not shown) which ensures their alternating movement in the horizontal direction in the cabinet. The movement of the bars 100 is represented by the double arrow H in FIG. 1. In this same figure, there is shown in broken dashed lines a pair of horizontal bars 200 whose alternating movement in the vertical direction is represented by the double arrow V. These bars, located in the cabinet 2, carry a series of spray nozzles used for the degreasing operation.

 The section of the box 2 is quite similar to that of the box 1 shown in FIG. 2, and this is why it was not considered useful to make a representation in section of the box 2.

 The movements of displacement with pilgrim's step (ascent, advance, descent, retreat) of the bars 4 and 4 'have been represented by the arrows f in FIG. 1 while the direction of movement of the screens inside the enclosures and their transfer from one enclosure to another is shown by the arrow F.

 As can be seen more particularly in FIGS. 3 to 5, each of the adjacent bars 4 is a profile, for example made of stainless steel sheet, having an "L" shaped section. The vertical and respectively horizontal wings of the profile have been designated by the references 402 and 403. The upper edge of the vertical wing 402 is inclined outward at an acute angle relative to the vertical. This rim 401 constitutes a chamfer facilitating the positioning of the screen between the two sections 4a, 4b.

The latter have their horizontal wings 403a, 403b facing one another. The assembly of the two profiles therefore has the general shape of a "U" adapted to support the base of a screen.

 As illustrated in FIGS. 3, 4 and 5, the two bars 4a and 4b are subjected to pilgrim step movements having a component of vertical direction, and which are out of phase, so that when the bar 4a rises (arrow ga , figure 4) the other bar 4b goes down (arrow gb), and vice versa.

 The frame 30 is therefore in turn supported on the wing 403a or on the wing 403b.

 Figures 6 and 7 show a preferred embodiment of a control mechanism of the bars 4a and 4b.

 Each of the "L" bars 4 is fixed by appropriate means, for example using screws, not shown, on a square plate 40, the vertical wing of which has an elongated opening, or lumen, 41 arranged vertically. Its horizontal wing is supported on a cam 50 having the shape of a disc of axis Y. This cam is integral with a shaft 54 of horizontal axis X perpendicular to the longitudinal direction of the bars. The axis Y of the cam is eccentric with respect to the axis X which constitutes the axis of rotation of the cam. The shaft 54 is guided in rotation in a fixed bearing 53.

 In FIG. 6, the parts used to drive each of the transport bars 4 have been designated by the same references. However, the reference has been assigned to the references relating to the parts used to drive the bar 4a, and of the index b those which are used for training the bar 4b.

 One of the two shafts 54, in this case the shaft 54a, is connected via an appropriate coupling 61 to the output shaft 60 of the electric motor 6. The latter rotates at constant speed. The discord cam 50 is integral with a small cylindrical rod, or pin, 51a which passes through the lumen 41a of the part 40a supporting the bar 4a. The diameter of the rod 51a is slightly less than the width of the opening 41a. Similarly, the cam 50b carries a rod 51b passing through the lumen provided in the part 40b. The ends of the rods 51 located beyond the light they pass through are in a central space substantially perpendicular to the gap separating the two horizontal wings 403a, 403b. These ends penetrate with some play in holes formed in a connecting piece 52, these holes being diametrically opposite with respect to the axis X.

 The part 52, which will therefore rotate around the axis X will transmit the movement of the cam 50a (which is directly driven in rotation by the motor 6) to the cam 50b.

The axis of the rods 51 has been designated by Z. The axes Xa, Ya and
Za on the one hand and Xb, Yb and Zb on the other hand are coplanar. Of course, each rod 51 rotates relative to the connecting piece 52 (around the axis Z) during the movement.

 The two cams therefore rotate in the same direction with an angular phase shift of 1800.

 Thus, when one of the transport bars is raised while advancing, the other descends while reversing, and vice versa.

 Figures 10 to 14 illustrate the mode of movement of a screen 3 by means of a pair of bars.

 The rotation (continuous) of one of the discs 50 is represented by the arrow.

 In FIG. 10, one of the bars 4, which carries the screen, is in its extreme high position, at a maximum height h relative to the axis of rotation X). The pin 51 is then also in its high position, at the top of the light 41.

 The rotation of the cam 50 continuing, the bar 4 begins to descend while the finger 51, pressing against one of the edges of the elongated opening 41 moves the part forward (to the right of the figures) 40 and, correspondingly, the bar 4 which is integral with it (see FIG. 11). At the same time, the other bar, the outline of which is shown in broken dashed lines, is subjected to an upward recoil movement.

 Then the bar 4 begins to retreat during its descent, while the other bar, in a combined movement of advance and ascent, arrives at a level higher than that of the bar 4 (Figure 12).

 It is the other bar which then takes care of transporting the screen 3 further, over a certain distance (Figures 13-14).

 The screen is therefore supported and moved in turn by each of the constituent bars of the pair.

 Means are provided for causing the automatic opening of the watertight doors 11 and 20 when a screen 3 '(see FIG. 1) arrives near the exit door 11 of the enclosure 1.

 As already mentioned above, the two busbars 4 and 4 'work in synchronism, which means that the bars of each set which are located on the same side (left or right) lift and s 'lower at the same time. It will also be recalled that the downstream end of the bars 4 is very close to the upstream end of the bars 4 ', the distance between these ends being very substantially less than the length of the screens 3, so that the transfer of the screens from one enclosure to the next is done in a gentle way.

 During this transfer, the two pairs of bars 4 and 4 'each remain confined in their enclosure 1, respectively 2, so that they do not participate in any way in the transfer of solvent from enclosure 1 to enclosure 2. The only possibility solvent transfer is done by the screens themselves.

 However, as already mentioned, the movement with pilgrim steps has the effect of shaking the screens during their transport, which achieves a certain drainage of the screens and reduces the amount of solvent that they are capable of transporting.

 Under normal working conditions, there is no possibility of transferring products in the other direction, i.e. water taken from enclosure 2 to enclosure 1.

 However, it is advantageous to provide a motor 6 having a possible double direction of rotation, which allows the screens to be moved in the opposite direction if necessary.

 In the embodiment of the transport bars shown in FIGS. 8 and 9, the wings 403 have a baffled outline composed of slots 46 (parts in relief) and cutouts or notches (recessed parts) 45. The notches 45 have a length substantially greater than the slots 46, which allows the relative displacement of the two bars in the longitudinal direction during their movement with pilgrim steps; in FIG. 9 the arrows fa and fb illustrate this relative movement (advancement of the bar 4a and retraction of the bar 4b). Of course, the dimensioning of the slots and notches is chosen to allow play greater than or equal to the amplitude of the relative longitudinal displacement of the two bars 4a, 4b. The presence of these baffles ensures good seating for the screens, even if their frame has a small width, while leaving between the two bars openings of sufficient size to allow good flow of treatment residues down the cabinet.

 In the absence of baffles, the gap separating the two bars - which must be sufficient to allow a good flow of residues - would risk posing difficulties in maintaining a thin screen in the central position.

 The width of a screen is very variable; it generally falls within a range between 20 and 70 mm, and it is important that the transport device can adapt to the different widths of screens without having to resort to adjustments.

 As shown in FIG. 15, it may be advantageous to provide catchy reliefs on the horizontal wings 403 such as transverse ridges 404, reducing the risks of the screen sliding relative to the transport bars.

 As an indication, the speed of rotation of the motor 6 will be of the order of 30 revolutions per minute, and the mechanism 5 will be designed to ensure advancement of the screens at an average speed of the order of 5 centimeters per second.

 Instead of providing a transport device using a pair of movable bars, with movement of pilgrim steps out of phase with each other, it would be possible to use a single movable bar, cooperating with a fixed bar. In this case, the forward speed would naturally be halved.

 It would also be possible to provide more than two movable bars with pilgrim steps, for example three bars with phase-shifted movements of 1200.

 Finally, instead of providing a mechanism for actuating bars of the mechanical type, such as with cam and eccentric pin, provision could be made for actuation by jacks operating in square cycle.

Claims (10)

 1. Device for transporting screen printing screens on a washing and degravage line, this line comprising an enclosure (1) for washing and an enclosure (2) for degravage arranged one after the other, characterized by the fact that it comprises at least one transport bar (4) animated by a movement with pilgrim steps and adapted to move the screens (3) inside said enclosures (1, 2) and to transfer them from the 'washing enclosure (1) to the degravity enclosure (2).  2. Device according to claim 1, characterized in that it comprises at least one pair of parallel transport bars (4a, 4b) each animated by a movement with pilgrim steps and arranged side by side, their movements being out of phase so that they support and move the screens in turn.  3. Device according to claim 1, characterized in that it comprises two pairs (4, 4 ') of transport bars according to claim 2, placed one (4) inside the enclosure of wash (1) and the other (4 ') inside the degravage enclosure (2), these two pairs of transport bars being moved in synchronism and arranged in alignment with each other .  4. Device according to one of claims 1 to 3, characterized in that the (or) bars (s) of transport (4) are sectional sections in "L" including a wing, arranged horizontally, supports l screen (3) to be transported.  5. Device according to claims 2 and 4 taken in combination, characterized in that the horizontal wings of the two transport bars (4a, 4b) have a baffle contour, the raised portions (46) of one s' nesting in the cutouts (45) of the other, with the possibility of relative displacement in the longitudinal direction.  6. Device according to one of claims 1 to 5, characterized in that the mechanism (5) for driving the (or) bar (s) of transport (4) comprises a cam (50) with circular outline which supports the bar (4), this cam (50) being rotated about a horizontal axis (X) which is arranged transversely with respect to the bar (4) and is eccentric with respect to the axis (Y) of the cam.  7. Device according to claim 6, characterized in that said cam (50) carries a finger (51) whose axis (Z) is eccentric relative to the axis (X) of rotation of the cam (50) , this finger (51) engaging in a vertical slot (41) formed in a part (40) integral with the transport bar (4).  8. Device according to claims 2 and 7 taken in combination, characterized in that the cam (50) and eccentric finger (51) drive mechanisms of the two parallel bars (4a, 4b) are connected by a transmission member movement (52) which provides a phase shift at 1800 between the movements of the two bars.  9. Device according to claim 8, characterized in that there is provided a drive mechanism (5) at the two ends of the (or) bar (s) of transport (4), the two mechanisms being moved synchronism from a common motor (6).  10. Device according to claims 3 and 9 taken in combination, characterized in that the drive of the bars (4) located in the washing enclosure (1) and the drive of the bars (4 ') located in the release enclosure (2) are produced from a single motor (6), via a chain and pinion transmission, the motor and these transmission members being arranged outside said enclosures (1, 2).