|3946454||Apparatus for cleaning the surface of plate-shaped objects by means of at least two brushes|
The present invention relates to a printing plate washing machine comprising a washing section with several rotatable brushes for scrubbing sides of printing plates under application of a rinsing fluid, a drying section for drying the plates, and a conveyor for moving the plates through the washing and drying sections of the machine with the plates in a substantial vertical position and in a largely plane condition.
In the present connection, the term "printing plate" is defined as a generic term for printing plates of different kinds that have form as a sheet or may easily be flattened as a sheet, especially plates made of rubber or synthetic material and for printing relative large surfaces as on cardboard boxes for packing, the plates having elevated or countersunk area for providing the printing pattern.
Today, soft printing plates of rubber or synthetic material as mentioned above are cleaned manually after being used in the printing process, using brush and soap water. This is a hard and time-consuming work requiring a substantial amount of man-power and thus being costly.
A washing machine of the kind indicated in the introduction and especially intended for rigid, flat plates is described in DE 196 05 058 Al. The plates are supported by their lower edge and moved through a washing section with long, cylindrical brushes rotating about their cylinder axes. The rinsing fluid is based on water. Subsequently the plates are dried just by letting them stand in the vertical position for a period. This prior art has the disadvantage that the unidirectional movement of the brushes relative to the plates is not sufficient to clean printing plates of the kind with elevated or countersunk areas, as the brush hairs do not penetrate into all comers in the plate profile as the brush hairs in the movement over the structures of the profile jump over these corners. A washing machine for flat, transported PC-cards is disclosed in US 3946454. This machine comprises rows of rotatable brushes having a mainly plane surface.
The object of the invention is to avoid the disadvantages of prior art.
This is achieved by a washing machine of the kind indicated in the introduction which is peculiar in that the brushing surface of a brush constitutes a mainly plane surface, and that the axis of rotation of the brush is perpendicular to the surface, where the brushes are juxtaposed along rows arranged in mutual parallel lines at least at one side of a printing plate passing through the machine, and where at least one row of brushes is provided with a driving mechanism arranged to cause the brushes in the row or rows to make oscillating rotational movement about the axis of rotation.
Thus the invention provides multiple end-face brushes at each side of a printing plate, and thereby every point on the plate surface is subjected to at least bi-directional brush action when the plate passes each brush row. If the brush rows are staggered as seen in the direction of movement of the plates, the plate surfaces may be subjected to four or more different brushing directions. Thereby an effective cleaning of corners and intricate details of the plate profile is performed.
The arrangement and suspension of the brushes is preferred with the brushes on plastic gear wheels mutually meshing in each row. As plastic gear wheels of e.g. polyoxymethylene or polyethylene may be lubricated by water, this embodiment simplifies the machine when soap water is used as rinsing fluid, the fluid also serving as lubricant for the teeth and suspension of the gear wheels.
A simple way of suspending the gear wheels is indicated in claim 3. Journals and bearings for each brush wheel may thus be avoided.
As indicated in claim 4, the brushes may be embedded directly in the side of each gear wheel in at least one row, the brush area being extended to the teeth of the gear wheels. Thereby overlapping brushing areas for adjacent brushes are attained.
As alternative or supplementing embodiment of the brush arrangement, the machine may comprise elongated brushes, where adjacent, separately rotatable brushes are arranged to sweep overlapping areas. The brushes may either be placed extending diametrally/radially or as chords/tangents to the rotating wheel. In a radial arrangement, two or more elongated brushes may be provided on each wheel. Also, hereby it is easy to obtain a secure overlap between adjacent brushes sweeping the plate surface. Furthermore, the brush components themselves are relatively cheap to obtain as elongated, rectangular brushes are standard products in the brush industry.
In a preferred embodiment of the invention, at least one row is provided with elongated brushes longer than the distance between adjacent axes of rotation of the brushes and with a driving mechanism arranged to cause the elongated brushes in the row to make oscillating rotational movement about a centre position in which the brushes in the row are situated one after another to be mutually parallel and displaced. The angular displacement in the oscillating, rotating movement is so small that the brushhairs only move a short distance on the plate surface before reversing; usually angular displacements are less than 50°. At the point of reversing, the position of the hairs changes from lying bent onto the plate surface in one direction to the opposite direction, and as the hairs reverse, they stand up and exert a greater pressure on the surface. Thereby the brush hairs have the opportunity to penetrate into the corners and intricate details of the elevated or countersunk areas of the surface, and the cleaning effect of the brushes is enhanced considerably.
A further preferred embodiment of the invention as indicated in claim 7 has two rows of brushes arranged opposite to and facing each other and arranged to wash both sides of a printing plate closest to an inlet end of the washing section, where the washing section is arranged with succeeding rows of brushes at one side only for washing the print side of a printing plate, and where the second side opposite to the succeeding rows of brushes is provided with a flat, substantially vertical surface for supporting the printing plate. The two opposite rows of brushes may then clean both side of the plate while the subsequent rows at one side of the passing plate do the further treatment necessary to remove the remaining ink from the profiled and uneven printing surface of the plate. The support plate counteracts the pressure of the brushes at the opposite side.
For pre-soaking dry ink on the printing plate it,may be preferred to design the machine as indicated in claim 8, wherein the rows of brushes in the washing section are preceded relative to the direction of conveyor movement by nozzles arranged for flushing a passing plate with rinsing fluid.
In order to blow off droplets of rinsing fluid, the washing section is succeeded by a drying section provided with nozzles for supplying pressurised air on both side of a passing printing plate. Hereby the plate is sufficiently freed from liquid so that it may air dry in the while before storage or in a storage compartment afterwards.
For easy conveying of soft printing plates, the machine according to the invention is provided with an overhead conveyor with attachment points designed to suspend a printing plate by its edge. Existing attaching means along one edge of the plate may then be utilized for suspending the plates, or special attaching means with clamps may be used.
An embodiment of the washing machine according to the invention will now be described in more detail with reference to the drawing, where
The schematic overview of an embodiment of the invention in Fig. 1 shows a washing facility for soft printing plates of rubber or plastic. The facility comprises a washing machine 3 and a closed-circuit overhead conveyor 1 with not shown attachment means for suspending the plates during conveying and treatment in the facility. The direction of movement of the conveyor 1 is shown with the arrow 2. The level of conveyor 1 is so that the machine may treat plates with vertical dimension of up to 160 cm.
The washing machine 3 is divided into a pre-soaking section 5, a scrubbing or washing section 7 and a drying section 9. The machine is placed in an enclosure 11 for avoiding spray and droplets being dispersed to the surroundings. An inlet 13 and outlet 15 for the moving printing plates are located at each end of the machine. Closures 16 in the shape of flexible means, e.g. rows of hairs meeting at an angle, are provided at the inlet 13, outlet 15 and at the partition 17 between the washing section 7 and the drying section 9, the closures 16 being able to deflect when a printing plate 10 passes but preventing airborne spray and droplets moving through. See also Fig. 2.
The pre-soaking section 5 contains two parallel pipes 19, one at each side of a passing printing plate 10, carrying rinsing fluid used in the process, in this embodiment soap water. At equidistant points, the pipes 19 are provided with outlets or nozzles directed toward the plate 10.
Moving to the washing section 7, the plate 10 is scrubbed simultaneously on both sides by end-face brushes 24 rotating about horizontal axes in rows 23. The brushes 24 are integrated in gear wheels which are drivingly interconnected by gear teeth 34 (see Fig. 3) at the rim of each wheel. The side of the plate 10 facing the viewer on Fig. 2, the front, is a surface with a profiled section while the opposite side, the back, is blank and completely flat. The back of the plate 10 does therefore not require any more scrubbing, and in the following part of the washing section 7 there are no brushes for the back, but instead a support plate 25.
In the embodiment shown, the three brush rows 27,28,29 subsequent to the first row 23, are all provided with elongated, rectangular standard product brushes 31 fastened on gear wheels 33, see Fig. 3. In the first and the third rows 27,29 as seen in the direction of travel of the plates 10, the brushes 31 are situated diametrally on the wheels 33, causing the axis of rotation to pass through a part of the brush 31 itself, and in these rows 27,29 the wheels 33 are rotating continually as in row 23. The brushes 31 overlap the area swept by neighbouring wheels and are angularly displaced in relation to adjacent wheels 33 as indicated on Fig. 2. The lowermost wheels 33a and 23a, respectively, are driven by not shown electric motors.
Soap water is supplied to the washing process through nozzles distributed on pipes 22 extending in parallel with the rows 23,27,28,29, see Fig. 1. A suitable detergent for the printing ink concerned is selected for making the soap water together with a foam inhibiting agent.
The suspension of the gear and brush wheels in the rows 23,27,28,29 is shown on Figs. 3 and 4, which by example show the arrangement in rows 27 and 29, but where the principle of suspension also apply to rows 23 and 28. Two rails 41 are fastened to the not shown frame of the machine, having longitudinal, mutually facing slits that accommodate annular, laterally projecting flanges 43 of the gear wheels 33. All wheels are made of high density polyethylene which has very low coefficient of friction when flushed with water or soap water. The soap water is distributed over the wheels so that gear teeth 34 and the adjoining surfaces of slits and flanges 43 are lubricated.
The middle row 28 has the brushes 31 fastened tangentially on the gear wheels 33 and alternately displaced so that they do not interfere. The reason for the tangential position of the brushes 31 is that only translational movement of brush hairs is desired which is possible when the axis of rotation does not pass through the brush 31 itself. The movement in the row 28 is oscillating rotation about a middle position shown on Fig. 2 so that the whole surface of the plate 10 is swept, the oscillation caused by a "rocker" mechanism known per se and shown in principle with the wheels 35 and 36 interconnected by a rod 37, where the motor-driven wheel 36 is rotating continually while the wheel 35 perform oppositely directed angular motions. Thereby the brushes 31 perform similar movements, the extremes of which are shown in Figs. 5a and 5b. The reversion of rotation of the wheels in row 28 causes the brush hairs to change their position as shown in Figs. 6a-c, where the arrow 45 indicates the direction of relative movement of the brush 31. In Fig. 6a, the brush hairs are drawn along the plate surface while deflecting to raised portions 47. Fig. 6b shows the situation immediately after reversing the direction of brush movement, and here the hairs tend to stand up, some buckling, while pressing hard on the plate surface. Now the hairs have possibility of penetrating into the corners at the foot of the raised portions 47, thereby cleansing the ink remaining here. Fig. 6c shows the situation when the brush movement is continued in the same direction as in Fig. 6b.
After passing through the closure 16, the plate 10 moves into the drying section 9 and passes between parallel pipes 49 conducting pressurised air and provided with a number of air outlets 51. The discharged air blows off any free liquid and drops from the plate surfaces, and after passing through the outlet 15 of the machine, the plate 10 is sufficiently dry to be stored, especially if the liquid temperature is held slightly elevated compared to ambient air temperature.
The washing machine is provided with a tank 21 for collecting used soap water under the pre-soaking and washing sections 5,7. In other embodiments, the tank 21 may also extend under the drying section 9 for collecting fluid blown off the plate 10. The soap water is recirculated to the pre-soaking and washing sections through a not shown piping system including pumps. No filtering systems is necessary for the rinsing fluid in the present application of the invention, and the soap water is just exchanged when too dirty.
As shown on Fig. 2, the different features for treating the plate 10 are arranged obliquely in order to facilitate the introduction of the vertical leading edge of the printing plate in each section or through the closures 16.
The form and arrangement of brushes 24,31 may be varied in other embodiments of the invention. Hence the disc-like brushes 24 may be applied in more or all the rows in the washing section 7, and the same applies to the elongated brushes 31. The oscillating brushes in row 28 may also be of the disc type 24. More or less number of rows may be used in the washing section, and the centres of rotation of brushes in adjacent rows may be staggered to avoid uniform treatment caused by the brush sweeping pattern.