Printing – Stenciling – Stencils
Patent
1992-07-09
1994-09-20
Burr, Edgar S.
Printing
Stenciling
Stencils
1011271, 1011281, B05C 1700
Patent
active
053479254
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus for solder or conductive paste printing, with a frame for the clamping of an etched, milled or laser-cut printing plate made of metal or plastic, which is secured to at least two oppositely disposed sides of the frame, with the help of mounting apertures and bolts.
For small formats, this type of apparatus has, up to now, been constructed such that the relatively thin printing plate, typically with a thickness of a few tenths of a millimeter, has mounting apertures which are threaded upon bolts of the frame, the printing plate then being affixed with beams which are secured to the frame using threaded bolts.
When greater accuracy is required, or for larger formats, the printing plates have been secured to a printing screen which then is cut away in the region of the printing plate and subsequently mounted into a printing frame.
Both kinds of connection between the printing plate and the frame are such that a change of the printing plate requires a substantial effort, wherein the frame must be removed from the "printing bench", and after the replacement it must be again returned to its position.
The aim of the invention is to provide an apparatus in which a change of printing plate can be undertaken without each time having to remove the frame and then replace it in position.
According to the invention, this aim is attained in that one of the two opposed frame sides is constructed as a tie beam which is moveable with respect to the other side of the frame, the tie beam--in order to mount the plate, and guided by resiliently mounted guide bolts hingedly connected thereto--being displaceable with respect to an abutment which is located at a fixed distance to the other side of the frame; and further in that, along each of the two sides of the frame, and in the working plane of the frame which receives the plate, a support band for the plate is provided, the support band having distributed therealong a plurality of bolts provided with heads, by means of which plates of different thicknesses can, with the help of a spacer shim, be placed in the working plane and secured to the respective frame sides, wherein the bolts are directed inwardly into the space enclosing the frame.
By the displacement of the tie beam, the printing plate can be tensioned or relaxed. When in the relaxed condition, the new construction makes is possible for the printing plate with the mounting apertures to be removed from above, with a new printing plate being inserted, without having to remove the frame from the printing bench.
Advantageously, the support bands are made of thin sheet steel, having an elasticity which, during printing, makes possible an acceptable placement of the printing plate on the material to be printed.
In order to prevent the plate from being incorrectly inserted into the frame, it is advantageous to provide, at least for one of the support bands, a distribution of the bolts which is unsymmetrical with respect to the mid-plane extending perpendicular to the support bands. For the displacement of the tie beam it has been found appropriate for the beam to be shaped as a hollow extrusion, in which is inserted, in the longitudinal direction as a tensioning means, a tube which can be loaded through a check valve with a pressure medium, for example, air. Advantageously, the tube has a rectangular section, as well as a reinforced forward wall and side walls which, in the relaxed condition are folded in the manner of bellows.
A quite exact positioning of the printing plate with respect to the frame, and an avoidance of internal tensions and warping of the printing plate, is facilitated by providing, a bolt in the mid-plane of each side of the frame, with a corresponding mounting aperture in the plate, in order to provide a centering and position-establishing faculty wherein the diameters of the bolt and aperture closely match one another, while the remaining mounting apertures are formed as oblong openings surrounding the corresponding bolts with play. A uniform tension over the entire
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Burr Edgar S.
Hilten John S.
PRSS - Maschinen AG
Squire William
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