US3648412A

US3648412A - Plate graining apparatus

Info

Publication number: US3648412A
Application number: US74700A
Authority: US
Inventors: Charles T Hathaway
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-09-23
Filing date: 1970-09-23
Publication date: 1972-03-14
Anticipated expiration: 1989-03-14

Abstract

An apparatus adapted to grain a planar surface of a plate comprising a moving conveyor which carries such plate into and out of contact with moving graining means which operate to impress grit into contact with the planar surface and produce a random roughening thereof.

Description

Hathaway Mar. M, 11972 [54] PLATE GRAINING APPARATUS [56] References Cited [72] Inventor: Charles T. Hathaway, 518 Rancho Lindo UNITED STATES PATENTS ri i Calif- 91722 I 899,236 9/1908 Botz ..51/136 [22] Filed: Sept 23, 1970 2,739,426 3/1956 Kinker et a1. ..51/138 [21] App1.No.: 74,700 Primary Examiner-0thell M. Simpson Attorney-Huebner & Worrell [52] U.S.Cl ..5l/61,51/136,51/328 [57] ABSTRACT [51] Int. Cl. ..B24b 7/12, B24b 21/04, B24b 1/00 An apparatus adapted to grain a planar Surface ofa plate [58] Field of Search ..51/135-147, 328, prising a moving conveyor i h carries such plate into and out of contact with moving graining means which operate to impress grit into contact with the planar surface and produce a random roughening thereof.

11 Claims, 10 Drawing Figures PLATE GRAINING APPARATUS BACKGROUND OF THE INVENTION This invention is particularly adapted to the preparation of aluminum lithographic plates, which are in almost universal use for commercial printing runs of 5,000 to 10,000 copies or more. Regardless of whether stone, zinc, aluminum, paper or plastic plates are used the lithographic process depends on establishing chemically contrasting areas: hydrophilic or water-loving," ink repellent nonprinting areas and oleophilic or ink-loving, ink receptive, printing areas. Raw aluminum generally has or will develop an oleophilic surface so that is is first necessary to provide a completely hydrophilic surface upon the plate by chemical and/or mechanical means. In practice the plate is then made light sensative and portions of this hydrophilic area are selectively converted to oleophilic areas by exposure to light through a photographic negative (or positive) transparency.

This invention is concerned with the essential first stage of converting large area plates from erratically performing surfaces to a very uniform hydrophilic surface.

There are three fundamental existing graining processes, the chemical etching process, the ball graining process and the brush graining process. In the chemical process plates are etched under mild alkaline conditions. The etching removes about 0.0001 to 0.001 inches of the surface eliminating all surface soil and oxidation, exposing fresh metal. The ball graining process was developed for zinc plates in the late 1800s and in the early 1960s was found to be applicable to aluminum as well as to zinc plates. This is a physical operation, involving the rotation of steel, glass, or even wood marbles over the surface of the plate in a graining machine. Water is added and then an abrasive grit material. The actual roughening of the surface of the metal to produce a grain is done by the abrasive grit.

In the brush graining method the plates are passed under rotating brushes and a water slurry of crushed silica to produce a mechanically cleaned and roughened surface.

The chemical etching process reduces the gauge or thickness of the metal slightly, requires numerous chemical baths, and produces an essentially smooth plate which is normally more difficult to control on the printing press and is usually of somewhat shorter run (number of impressions obtainable). The etching process requires a substantial investment in equipment to move the plate from one bath to another, or an even greater investment in equipment to carry a continuous web through a series of chemical baths, rinsing the plates between each bath to avoid carryover from bath to bath. It is susceptible to a great deal of handling loss due to mechanical damage of the plate and due to the total loss of substantial numbers of plates any time the process is interrupted for any reason. This is due to the fact that anywhere from a half an hour to an hour and a half or 2 hours of production material is tied up or in progress at any given time with this system so that any interruption of the process can result in substantial loss of material which at best must be reprocessed and frequently must be totally discarded.

The ball graining method suffers the disadvantage of extremely high labor costs due to the long cycle time and the essentially hand operation of loading the tables, dumping the balls from the tables, cleaning the plates, washing the table and reloading with fresh plates. Although the equipment costs are relatively low for an individual table, many tables are required to produce any significant amount of production.

Brush graining is probably the most economical method of production in operation today but suffers a significant disadvantage in that it cannot produce the depth of grain that ball graining can. Furthermore, control of the process is extremely subjective in that the bristles of the brush are constantly being worn in a manner which is difficult to measure or evaluate. The pressure of the bristles against the plate is difficult to control and the distribution of the grit across the plate is also difficult to regulate. In actual practice, it is frequently found that several hours of production time may be lost while an effort is made to find out what combination of brush setting, grit composition, flow rates, r.p.rn., and so on will produce the desired grain. Also, standing waves or vibrations frequently form in the brushes which result in patterns on the plate surfaces and do not produce a uniform hydrophilic finish. The system does have the advantage that it can be and has been adapted to work with coil operations.

SUMMARY OF THE INVENTION The invention preferably includes an endless conveyor upon which untreated or ungrained plates are randomly positioned. A series of graining means such as moving chains, belts, or the like are positioned across the conveyor and normal to the line of travel of the conveyor. As the plates to be grained are moved along the conveyor belt they come in contact with the chains. At the same time, a grit slurry consisting of finely crushed silica or quartz or the like in a liquid suspension is sprayed onto the plate surfaces. The moving chains, belts or the like rub the grit slurry against the plate surfaces imparting a graining finish to the surfaces.

It is an object of this invention to provide apparatus and a method for graining surfaces which is simpler to operate and easier to control than existing graining methods.

It is a further object of this invention to provide apparatus and a graining method which is controllable to produce any desired grain depth, from the very shallow 2 to 5 micron peak to valley grain depth of the brush graining method up to the 10 to 15 micron peak to valley depth of the ball graining method.

The present invention, unlike brush and ball graining methods can be used with any gauge plate.

An additional purpose of the present invention is to provide a graining method which is both more efiicient and less expensive than current graining methods.

As with any of the currently available graining processes, this invention relates only to the first step in the preparation of lithographic plates. Further, chemical "treatment of the plates is essential to provide a long lasting hydrophilic surface. However, these chemical treatments affect the surface on a molecular scale, e.g., 1-50 Angstroms, whereas the treatment of interest in this invention relates to physical structure on a microscopic scale, e.g., 1-10 microns. These chemical treatments are ineffective without exposure of clean freshly grained plate surfaces.

Other objects and advantages will become apparent from the following drawings and description, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a top elevational view of the graining apparatus of this invention;

FIG. 2 is a cross sectional view of the graining apparatus taken along line 2-2 of FIG. 1;

FIG. 3 is a fragmentary, partial cross sectional view of the apparatus taken along line 3-3 of FIG. 1;

FIG. 4 is an enlarged cross sectional view of one graining chain taken along line 4-4 of FIG. 3;

FIG. 5 is a view similar to FIG. 3 illustrating a modification of the invention.

FIG. 6 is a view similar to FIG. 3 and illustrates a modification wherein V-belts are substituted for the graining chains;

FIG. 7 is an enlarged cross sectional view of a V-belt taken along line 7-7 of FIG. 6;

FIG. 8 is a top elevational view of a further modification of the invention;

FIG. 9 is a partial cross sectional view taken along line 99 of FIG. 8; and

FIG. 10 is a top elevational view of still a further modification of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 there is illustrated the graining apparatus of the invention generally designated 12. The apparatus 12 comprises a frame 14 which supports an endless conveyor belt 16. Roller 18 is one of a series of rollers which provide additional support the the belt 16 and which also drive the belt 16. One or more of the rollers 18 may be powered by any suitable motor means (not illustrated) so as to move the conveyor belt 16 in the direction indicated by the large arrow in FIG. 1. Mounted on vertical support posts or

frame extensions

20 and 22 of frame 14 is a grit dispersing means or hollow slurry pipe 24, which extends laterally across the conveyor belt 16 at a height of ap proximately 1 foot above the belt 16 in the preferred embodiment. A hose 26 is connected to slurry pipe or conduit 24 by means of a coupling 28. The hose 26 connects the slurry pipe 24 with a slurry storage tank, not shown. While the structure just defined is preferred, any ,type of appropriate apparatus may be used to distribute a grit slurry.

Horizontal support brackets

30 and 32 extend outwardly from frame 14. These

brackets

30 and 32 are at approximately the same height or level as the conveyor belt 16. An electric motor 34 is mounted on bracket 32. A drive shaft 36 extends from motor 34 and is joumaled in a bearing mount 38. A gear wheel 40 is mounted on drive shaft 36 near motor 34. A drive shaft 42 extends between and is supported by two bearing mounts 44 and 46 respectively. Shaft 42 lies parallel to drive shaft 36. A gear wheel 48 is mounted on shaft 42 and meshes with gear wheel 40. Therefore, when motor 34 is energized and turning shaft 36 in a clockwise direction, the meshing of gears 40 and 48 will cause shaft 42 to rotate in a counterclockwise direction. In other words, the

shafts

36 and 42 will always rotate in opposite directions.

A pair of parallel,

free turning shafts

50 and 52 are positioned upon bracket 30 and mounted in bearing mounts 54, 56, 58 and 60, respectively. Pulley wheels 62 are mounted on

shafts

36 and 42 and are affixed thereon by any appropriate means such as by set screws or welds. Idler pulleys 64 are mounted on

shafts

50 and 52 and may be affixed thereto or may be free to rotate independently of the

shafts

50 and 52.

Graining means or elongated grit engaging elements generally designated 65, such as an endless chain 66 formed of articulated links 67 are mounted around pulleys 62 and 64 as can best be seen in FIG. 1 so as to extend horizontally across conveyor belt 16.

Thus, when the drive shaft 36 of motor 34 rotates in a clockwise direction those chains 66 mounted on the pulleys 62 of drive shaft 36 and the pulleys 64 of drive shaft 50 will also rotate in a clockwise direction. Concurrently, those chains 66 mounted on the

pulleys

62 and 64 affixed to

shafts

42 and 52 respectively, will be rotated in a counterclockwise direction.

In operation the plates 68 to be grained are placed upon the conveyor belt 16 near roller 18 either randomly or at predetermined intervals by hand or by a machine (not shown). As the plates 68 pass under slurry pipe 24 the slurry mixture 69 of crushed silica and water is sprayed onto plates 68 from nozzles or apertures 70 located at intervals along the bottom of pipe 24. The plates 68, with the slurry mixture spread across their upper surfaces, are then passed underneath the lower sections 72 of chains 66. As the chains 66 are drawn across the surfaces of plates 68 the silica grit particles 73 are forced into the relatively soft metal so as to impart the desired grained or roughened finish to the plate surfaces 68. The grained plates 68 then pass through a series of wash baths and chemical treatment baths (not shown) which complete the process of imparting a uniform hydrophilic surface to the plates 68.

In the preferred embodiment illustrated in FIG. 1 through FIG. 4, pulleys 62 and 64 all lie in substantially vertical planes, and the endless chains 66 thus have substantially vertical orbits. It is envisioned, however, that the

pulleys

62 and 64 could be mounted in a horizontal plane parallel to and slightly above the plane of the conveyor belt 16. Chains 66 would then rotate in a horizontal orbit and both sides of the chains 66 would contact plates 68 and belt 16.

Additionally, while the grit engaging elements 65, as illustrated, extend substantially laterally across conveyor belt 16 in a direction normal to the line of travel of conveyor 16, it is anticipated that the grit engaging elements 65 could be placed so that they extend parallel to the line of travel of conveyor 16. This could be accomplished by suspending the means imparting a horizontal shifting of the chains 66, that is, the motor pulley and shaft assemblies, above the conveyor.

The frame 14 includes gutters or

drain channels

74 and 76 along both sides of the conveyor belt 16 where excess grit slurry 69 can collect. These

channels

74 and 76 may be angled downwardly slightly from one end of the frame 14 to the other end thereof to facilitate draining of the grit slurry 69 so that it may be recycled. It should be understood that more than one slurry pipe 24 may be used and that such slurry pipes 24 may be positioned directly over the endless chains 66.

It should also be understood that the embodiment illustrated in FIG. 1, which includes four chains, two of which rotate in a clockwise direction and two of which rotate in a counterclockwise direction, is so shown for purposes of clarity and simplicity. Additional chains may be used without departing from the spirit of the invention. It is believed that a moderate number of chains, 15 for example, which can be driven at speeds well in excess of feet per minute, can completely grain or roughen plates on a conveyor belt moving at rates in the range of l to 10 feet per minute. The chains travel in alternate clockwise and counterclockwise directions so that the plates 68 and the grit slurry 69 will not all be pulled to the same side of the conveyor belt 16 and to insure a random roughening.

There is a suflicient degree of slackness in the chain sections 72 so that the individual chain links 67 are free to adjust to the inherent thickness and contour variations of the plates being grained. This freedom to adjust to various contour and gauge variations means that the invention is capable of handling different gauge plates at the same time and without elaborate or time consuming equipment modifications.

There are several factors which may influence the depth of the grain imparted by the apparatus of this invention. These factors include grit particle size, conveyor belt speed, chain loop speed, chain link weight, and chain wear. Referring to the latter factor, after the chains have been in use for a period of time the edges of the chain links 67 will wear down or flatten somewhat, as seen in FIG. 4, thereby creating more surface area to press the grit particles 73 into the plate surface. Recent tests have indicated that the process is substantially less sensitive to variations in chain link mass or grit particle size than originally expected. It now appears that the principal variable is actually the hardness of the chain link metal itself. A hard steel chain will give grain depths of 6 to 8 microns with either fine or coarse grit and with either heavy chain or light chain while a soft surface such as rubber or leather will give a depth of 4 microns over the same broad range of chain weight and grit size.

In FIG. 5 there is illustrated a modification of the invention wherein the grit engaging elements or chains 66 include a rubber hose 79 which surrounds the chains 66'. Because the rubber hose 79 is softer than the chains 66', the grit particles 73 are not pressed into the plate 68 with as much force or as deeply as is done by the chain links 67 of FIGS. 1 through 4, resulting in a shallower grain.

FIGS. 6 and 7 illustrate a further modification of the grit engaging elements 65 of the invention wherein these elements comprise rubber V-belts 66". As seen in FIG. 7, the V-belts 66" are frustoconical in cross section. As with the modification shown in FIG. 5, the V-belts 66" are relatively soft and do not press the grit particles 73 into the plate 68 with as much force as do the chains 66, thereby imparting to the plate 68 a shallower grain than would normally be obtained by using exposed chains 66 as the grain effectuating elements.

FIG. d illustrates a further modification of the invention wherein the grit engaging elements 65' comprise cylindrical graining bars 80. Motor 34 mounted on frame bracket 32 is connected to an offset crank shaft 82. Connecting bars M, which are mounted on and free to rotate about the offset subshafts 86 of crank shaft 82, are connected to bars 80 at one end thereof by means of pivot pins 99. Bars M lie laterally across conveyor 16. The opposite ends 90 of bars 80 are reduced slightly in diameter and extend into sleeves 92, which are mounted on L-frame member 94 of frame bracket 30. Helical springs 96 may be coupled to the reduced diameter end portion 90 of graining bars $0 and to sleeves 92 by means of spot welds or other appropriate methods. These springs operate to urge or draw graining bars 90 away from crank shaft 82 and toward frame member 94. In operation plates 68 placed upon conveyor belt 116 pass under graining bars Ml. As motor 34 rotates, crank shaft b2 and the bars 80 move laterally and reciprocally normal to the direction of travel of belt 16 pressing grit particles 73 into plates 68.

in FIG. 110, a drive wheel 98 of motor 34 is connected to reciprocating bar 100 by means of coupling bar 1102. Reciprocating bar 1100 is supported in slide bearings 11M mounted on frame bracket 32. Stationary frame member 94' is mounted parallel to reciprocating bar 100 and frame bracket 30. Both reciprocating bar we and stationary frame member 94 include a series of eyes or hooks lilo. Grit engaging elements 65" include chains 108 which are hooked or otherwise fastened to the eyes 106 of reciprocating bar 100 and frame member 94' so that chains 108 lie laterally across conveyor belt 16. When motor 34 is activated so as to move reciprocating bar 100 back and forth in a line parallel to the direction of travel of conveyor belt 16, chains 1108 move or whip eccentrically upon conveyor belt 16. As with the other modifications of the graining means 65 the chain links 67' operate to press grit particles 73 into plates 68 thereby graining the plates.

After the roughening of plates 68, the residue of grit 69 is removed by conventional means and the plate is then ready for further conventional processing to prepare it for lithographic use.

While the invention described herein is primarily intended for use in the lithographic process, it should be understood that the process is applicable to the treatment of other surfaces where a roughened or grained appearance is desired, as with frosted glass, light diffusers, matte finished plastic drafting media, and burnished decorative metal panels.

Although I have herein shown and described my invention in what l have conceived to be the most practical and preferred embodiment it is recognized that departures may be made therefrom within the scope of my invention.

What is claimed is:

1. An apparatus adapted to roughen a planar surface of a plate wherein a roughing agent in the form of a grit is used in cooperation with said apparatus comprising:

a conveyor supporting frame assembly;

an endless conveyor belt supported by said assembly in a manner presenting a generally horizontal portion adapted to receive and move said plate;

motor means associated with said belt adapted to drive said belt;

dispersing means adapted to disperse grit on said planar surface during travel of said plate on said belt; and

a plurality of elongated grit engaging elements overlying said generally horizontal portion of said conveyor belt and said planar surface, said elements possessing sufficient weight to gravitationally bear upon the grit deposited on said planar surface;

means imparting a horizontal shifting of said elements while in contact with such grit to impress the grit against the planar surface and produce a random roughening thereof.

2. An apparatus for graining planar surface as defined in claim 1 wherein:

said dispersing means comprises a tubular conduit mounted on said frame assembly so as to extend laterally across said conveyor belt, and said conduit includes apertures spaced therealong to release said grit onto said planar surface.

3. An apparatus for graining planar surfaces as defined in claim 1 wherein:

said conveyor supporting frame assembly includes at least one parallel gutter disposed along said frame assembly adapted to receive excess grit during the roughening of said planar surface.

d. An apparatus adapted to roughen a planar surface as defined in claim ll wherein:

said elongated grit engaging elements comprise an endless chain of articulated chain links.

5. An apparatus adapted to roughen a planar surface as defined in claim 4 wherein:

said endless chain is enclosed in a rubber tubing.

6. An apparatus adapted to roughen a planar surface as defined in claim 1 wherein:

said elongated grit engaging elements are rubber flexible,

resilient belts. 7. An apparatus adapted to roughen a planar surface as defined in claim ll wherein:

said grit engaging elements include cylindrical bars which extend laterally across said conveyor belt and said means imparting a horizontal shift to said elements comprising a motor driven offset crankshaft imparting alternately reciprocating lateral movement of said bars across said conveyor belt. d. An apparatus adapted to roughen a planar surface as defined in claim ll wherein:

said grit engaging elements include articulated chain lengths and said horizontal shifting means comprises a motor driven reciprocating bar mounted on said frame assembly substantially parallel to the line of travel of said conveyor belt and a stationary bar mounted on said frame assembly laterally opposite and parallel to said reciprocating bar;

one end of said chain lengths being fastened to said reciprocating bar and the other end of said chain lengths being fastened to said stationary bar, whereby when said reciprocating bar is activated said chain lengths horizontally whip.

9. An apparatus adapted to roughen a planar surface of a plate wherein a roughing agent in the: form of a grit slurry is used in cooperation with said apparatus comprising:

a conveyor supporting frame assembly;

motor means associated with said belt adapted to drive said belt;

dispersing means adapted to disperse said grit slurry on said planar surface during travel of said plate on said belt; and

a plurality of endless chains formed of articulated links lying normal to the line of travel of said conveyor and overlying said generally horizontal portion of said conveyor belt and said planar surface, said chains representing a section possessing sufficient weight to gravitationally bear upon the grit slurry deposited on said planar surface;

drive means adapted to rotate said chains imparting a horizontal shifting thereof while in contact with such grit slurry to impress the grit slurry against the planar surface and produce a random roughening thereof.

10. An apparatus as defined in claim 9 wherein:

the planar surfaces of a plurality of plates may be simultaneously grained.

1111. The method of graining the planar surface of a plate adapted to be further processed to form a complete lithographic plate including the steps of:

selecting a metal plate of appropriate hardness and size having a generally flat planar surface;

positioning said plate on a moving conveyor with said planar surface exposed upwardly;

such grit slurry to impress the grit within said grit slurry against the planar surface and produce a random roughening thereof, and removing said grit slurry from said plate t l l I t

Claims

1. An apparatus adapted to roughen a planar surface of a plate wherein a roughing agent in the form of a grit is used in cooperation with said apparatus comprising: a conveyor supporting frame assembly; an endless conveyor belt supported by said assembly in a manner presenting a generally horizontal portion adapted to receive and move said plate; motor means associated with said belt adapted to drive said belt; dispersing means adapted to disperse grit on said planar surface during travel of said plate on said belt; and a plurality of elongated grit engaging elements overlying said generally horizontal portion of said conveyor belt and said planar surface, said elements possessing sufficient weight to gravitationally bear upon the grit deposited on said planar surface; means imparting a horizontal shifting of said elements while in contact with such grit to impress the grit against the planar surface and produce a random roughening thereof.

2. An apparatus for graining planar surface as defined in claim 1 wherein: said dispersing means comprises a tubular conduit mounted on said frame assembly so as to extend laterally across said conveyor belt, and said conduit includes apertures spaced therealong to release said grit onto said planar surface.

3. An apparatus for graining planar surfaces as defined in claim 1 wherein: said conveyor supporting frame assembly includes at least one parallel gutter disposed along said frame assembly adapted to receive excess grit during the roughening of said planar surface.

4. An apparatus adapted to roughen a planar surface as defined in claim 1 wherein: said elongated grit engaging elements comprise an endless chain of articulated chain links.

5. An apparatus adapted to roughen a planar surface as defined in claim 4 wherein: said endless chain is enclosed in a rubber tubing.

6. An apparatus adapted to roughen a planar surface as defined in claim 1 wherein: said elongated grit engaging elements are rubber flexible, resilient belts.

7. An apparatus adapted to roughen a planar surface as defined in claim 1 wherein: said grit engaging elements include cylindrical bars which extend laterally across said conveyor belt and said means imparting a horizontal shift to said elements comprising a motor driven offset crankshaft imparting alternately reciprocating lateral movement of said bars across said conveyor belt.

8. An apparatus adapted to roughen a planar surface as defined in claim 1 wherein: said grit engaging elements include articulated chain lengths and said horizontal shifting means comprises a motor driven reciprocating bar mounted on said frame assembly substantially parallel to the line of travel of said conveyor belt and a stationary bar mounted on said frame assembly laterally opposite and parallel to said reciprocating bar; one end of said chain lengths being fastened to said reciprocating bar and the other end of said chain lengths being fastened to said stationary bar, whereby when said reciprocating bar is activated said chain lengths horizontally whip.

9. An apparatus adapted to roughen a planar surface of a plate wherein a roughing agent in the form of a grit slurry is used in cooperation with said apparatus comprising: a conveyor supporting frame assembly; an endless conveyor belt supported by said assembly in a manner presenting a generally horizontal portion adapted to receive and move said plate; motor means associated with said belt adapted to drive said belt; dispersing means adapted to disperse said grit slurry on said planar surface during travel of said plate on said belt; and a plurality of endless chains formed of articulated links lying normal to the line of travel of said conveyor and overlying said generally horizontal portiOn of said conveyor belt and said planar surface, said chains representing a section possessing sufficient weight to gravitationally bear upon the grit slurry deposited on said planar surface; drive means adapted to rotate said chains imparting a horizontal shifting thereof while in contact with such grit slurry to impress the grit slurry against the planar surface and produce a random roughening thereof.

10. An apparatus as defined in claim 9 wherein: the planar surfaces of a plurality of plates may be simultaneously grained.

11. The method of graining the planar surface of a plate adapted to be further processed to form a complete lithographic plate including the steps of: selecting a metal plate of appropriate hardness and size having a generally flat planar surface; positioning said plate on a moving conveyor with said planar surface exposed upwardly; spreading a grit slurry over said entire planar surface; activating elongated grit engaging elements overlying said conveyor and said planar surface, said elements possessing sufficient weight to gravitationally bear upon the grit slurry spread on said entire planar surface to impart a horizontal shifting of said elements while in contact with such grit slurry to impress the grit within said grit slurry against the planar surface and produce a random roughening thereof, and removing said grit slurry from said plate.