US2983062A - Etching apparatus - Google Patents

Description

May 9, 1961 B. F. SMITH ETCHING APPARATUS 4 Sheetsheet 1 Filed July 25, 1957 INVENTOR.

I M y 9, 1961 B. F. SMITH 2,983,062

ETCHING APPARATUS Filed July 25, 1957 4 Sheets-Sheet 2 May 9, 1961 B. F. SMITH ETCHING APPARATUS 4 Sheets-Sheet 3 Filed July 25, 1957 INVENTOR.

CHE

V/ n/n// Y y 9, 1961 B. F. SMITH 2,983,062

- ETCHING APPARATUS Filed July 25, 1957 4 Sheets-Sheet 4 INV EN TOR.

United States Patent ETCHING APPARATUS Bernard F. Smith, Appleton, Wis., assignor to Doro (Zerporation, Appleton, Wis., a corporation at Wisconsin Filed July 25, 1957 Ser. No. 674,071

1 Claim. (Cl. 41--9) One of the problems encountered inthe etching of such plates is the large amount of time involved in the etching operation (meaning the period or periods during which the acid is removing the undesired metal from between the printing areas). Another problem is that in most etching operations the etching has to be carefully watched and controlled by a person highly skilled in the art of etching or engraving printing plates, and must be accomplished in successive bites separated by inspectionand powdering steps.

Another difliculty resides in the fact that in the ordinary plate etching operation, in spite of the utmost skill and care used by the operator, there is always the danger of excessive undercutting or overhang which causes cleaning difficulties and also, trouble in the preparation of stereotype plates by the use of a mat or matrix, as in newspaper work.

The object of the present invention is to provide an improved process and apparatus for, etching a plate in a single bite, in a matter of a few minutes orless, in a simple and efficient manner to the required depth without the use of highly skilled,;highly paid operators.

A further object is to provide a'process and apparatus which will etch a printing plate so as to have lands with sloping edges so that it may be used' efliciently for newspaper or stereotype Work, and, in general, to provide a process and apparatus for producing an etched plate of the character indicated.

According to one phase of the present invention, a special arrangement is used for making contact between a supply of etching fluid and a plate which isto be etched by the fluid. According to another phase of'the invention, adestructible, etchable link is inserted in a chain of mechanical elements. When this chain is interrupted by the disabling of the link, the etching of the plate is arrested. The link is subjected to the action of the same bath of etching fluid under the same conditions as the plate, and is disintegrated by the etching fluidso that Figure 2.is a plan view of the etching apparatus shown in Figural;

Figure 6 is an elevational view of a reversing cam follower pin used in the portion ,of the'apparatus shown 1 in Figure 3;

Figure 7 is a schematic sketch of the electrical circuit 7 used to operate the etching apparatus shown in the Figures 1 to 5; and

Figure 8 is a representation of one type of etchable link which may be used in the etching apparatus disclosed herein.

The apparatus herein disclosed provides for immersing a plate in a bath of etching fluid and rotating the plate in the fluid in alternately opposite directions for a limited period while it is immersed.

After the destructible link previously referred to is I disabled, the plate is lifted out ,of the bath of etching fluid and then promptly immersed in a wash water bath' to wash off any adhering etching fluid from the plate; 1

As will hereinafter becomemore apparent, the etching equipment shown in the drawings includes, generally,

a base 11 having a post. bearing housing 13 adjacent one end for rotatablyi supporting a cam shaft frame 15. A boom frame 17 is pivotally supported near the top" end of the cam shaft frame 15; A'supporting arm 19 is connected to the boom frame 17 adjacent the right end thereof. At the lower end of the supporting arm 19 a disc or spider 21'is rotatably mounted. A plate 23 to be etched is carried on-the face of the disc-or spider 21. A partitioned tank 25, made of ceramic ware or other non-corrosive material, is. provided in which the with an etching fluid in which the plate 23 is preferably small clamping section 41 and a main section 43 whicha0 a a clamped to the upperiend of the shaft33 by tightening Figure 3 is an enlarged cross-sectional view taken along line 3-3 of Figure 2; a r

Figure 4 is an enlarged end view, partially in section, taken along line 44 of Figure 1; a

Figure 5 is an enlarged cross sectional view taken along the line 5--5 ofFigure 1;

post or shaft 33 'is rotatably fitted within the bearing 35' ward movement of shaft 33. Amotor bracket 39 isfitted j 1 ab ont theupper end of the shaft 33. As may be seenin 'about'its pivot to liftthe. plate 28. out; of and place' itinto fully immersed during the actual etching operation. Afi ter the etching operation, the: boom frame'17 pivots,'lifts 1 thedisc 21 and the plate 23 out of the etching bath and 'places the disc and plate in a rearward Washingj'se'c- 1 tion 29 of the tank 25 which is filled. with wash water so that any etching fluid adhering to the plate 23 may b'etwashed off. Instead' of submerging the plate 2 3. in; a washing solution, a shower or spray of washing fluid may be used. After the washing operation the disc 21 and plate Z3' are lifted out of the wash water by the pivoting of the boom frame 17 so that the. plate 23 may, be removed from the disc 21.

Referring now more particularly to'the drawings, the base 11' is of fabricated constructionhaving a'flat horizontal platform 3i and verticalsupporting-members 32 p Which'aresuitably connected'together. The base ll-s'up-i ports various of the partsof the etching equiprnent i Adjacent the left end of the base 11Jis the post-bearing housing 13 which is secured to the base ll by 'bolts.. A;v

of the post-bearing housing. 'A ring clamp 37 is providedat the lower portion of the shaft 33 to prevent any up; f

Figure 5, the motor bracket 39 includes two sections;

provides a base for amain drivemotor 45. ."I'he two sections,41- and 43, of the motor bracket-39am securely up on screws 471which pulltheftwo sections 41 and 43' together The main drive motor 45 is mounted on the main section 43 of the motor bracket 39; This motorisprovi cled V to rotate the etching apparatus aboutthe shaft 3'3 in a I l predetermined manner and to pivot the boom frarne 17*? the tank 25 me predetermined manner. whichishere inafter set forth ingreater detail. A gearjspeed reducer 49 is connected to the shaft of the motor 45 sot-hatfther speed of the output shaft 51 of the speed reducer is sub stantially lower than the speed of the shaft of the motor 45.

The cam shaft frame includes a pair of upright frame members 53. The lower end of each of the frame members 53 is secured along the sides of the motor bracket 39 by bolts 55 so that the frame members 53 extend vertically upward in spaced relation to each other. The frame members 53 are provided with suitable bearings 57 and a cam shaft 59 which extends horizontally between the frame members 53 is journaled in these bearings. A lift cam 61 is securely mounted on the cam shaft 59 between the frame members 53. This cam 61 is generally circular except for a projecting cam portion 61a. As the lift cam 61 rotates the cam surfaces effect the pivoting of the boom frame 17 up and down in a predetermined manner about a pivot pin 79. On the cam shaft 59 and on each side of the lift cam 61 (Figure 4), a swing cam 65 is mounted. This swing cam is also secured to the cam shaft 59 and, therefore, the cam shaft 59, the lift cam 61 and the swing cam 65 rotate as a unit. A cam follower bracket 69 is securely mounted on the post bearing housing 13. A pair of cam followers 71 are mounted on the bracket 69 for rotation about vertical axis. As the swing cam 65 rotates, the cam surfaces 67 engage the followers 71 and effect the swinging back and forth of the motor bracket 39, and the other portions of the apparatus secured to the bracket, about the axis of the post 33.

In order to impart rotary motion to the cam shaft 59, a sprocket 73 is secured to an end of the shaft. This sprocket 73 is drivingly connected to a sprocket 75 on the output shaft 51 of the speed reducer 49 by a chain 77. Therefore, when the main drive motor 45 is operating, the cam shaft 59, the lift cam 61 and the swing cam 65 are rotated.

Near the upper end of the cam shaft frame 15 a horizontal boom pivot pin 79 is secured between the frame members 53 and the boom frame 17 is pivotally mounted on this pivot pin. As may be seen in Figure 3 the boom frame 17 has a depending leg 81,011 to the left side of which is mounted a bearing 83 which engages the pivot pin 79. At the lower end of the depending leg 81 a cam roller 85 is mounted so as to rotate on a horizontal axis. This cam roller 85 engages the cam surfaces of the lift cam 61, and as the lift cam 61 rotates the boom frame 17 is rocked about the pivot pin 79.

The boom frame 17 is of fabricated construction and includes a flat platform 87 and vertical side pieces 89. At the left end of the boom frame 17 a disc drive motor 91 and a geared speed reducer 91a are mounted. This motor is provided to rotate the disc 21. A reversing housing assembly 18 is also mounted on the boom frame 17. The reversing housing assembly 18 is provided to alternate the rotation of the disc 21 in a manner which will become apparent as the description progresses and for reasons which are hereinafter set forth.

The reversing housing assembly 18 includes a housing 93 which encloses various of the moving parts of the assembly 18. The assembly 18 includes an elongated barrel cam 95 having smaller diameter end portions 95a which are suitably journaled in bearings 97 adjacent the ends of the housing 93. The axis of this cam 95 is in line with the axis of the shaft of the disc drive motor 91. The barrel cam 95 projects through the left end of the housing 93 and is drivingly connected to the output shaft 91b of the geared speed reducer 91a through a conventional flexible coupling 99. Since some thrust in a direction along the axis of the barrel cam 95 is exerted, thrust ball bearings 101 are also provided adjacent the ends of the barrel cam 95. The barrel cam 95 has continuous threadlike grooves 115 therein. These grooves 115 provide a guideway for a cam follower 109.

A nut block 103 which travels back and forth on the barrel cam 95 is mounted on the barrel cam 95. The nut block 103 has a cylindrical hole 105 therein through which the barrel cam 95 passes. The nut block 103 has another cylindrical hole 107 therein which has its axis perpendicular to the axis of hole 105. A reversing cam follower pin 109 is rotatably fitted within the cylindrical hole 107. The pin 109 has a lower narrow section 110 (Figure 6) having a semi-circular notch 111 therein giving the narrow section 110 two leg portions 113. The two leg portions 113 of the narrow portion 110 fit over the barrel cam 95 into thread-like grooves 115 in the barrel cam.

As the barrel cam 95 rotates the narrow section 110 remains in the grooves and travels down to one end of the threaded portion of the barrel cam 95 whereupon the grooves are so constructed that the narrow section 110 so engages the grooves 115 that the follower pin 109 reverses direction and moves to the other end of the barrel cam-95 where it again reverses direction. The cam follower pin 109, as well as the nut block 103 in which the follower pin 109 is positioned, thus move back and forth, in a direction parallel to the axis of the barrel cam 95, on the barrel cam, as the barrel cam rotates. This type of reversing direction mechanism resembles the so-called level wind mechanism used on most bait casting fishing reels. The upper portion of the nut block 103 carries an oil cup 117 so that the follower pin 109 and cam 95 are kept well lubricated. The disc drive motor 91 is in operation for substantially the entire etching operation and, accordingly, the barrel cam 95 is rotating for substantially the entire etching operation. In one commercial embodiment the disc speed was 39 rpm. and the disc reversed its direction of rotation after 3 /3 revolutions.

Near the left end (Figure 3) of the reversing housing assembly 18 a horizontal shaft 119 is positioned between the sides of the housing assembly 18. This shaft 119 is secured in brackets 121 which are fastened to the housing 18. A ratchet 123 is mounted on this shaft 119. In a similar manner, near the right end of the housing 13 a horizontal shaft 125 is positioned. A ratchet 127 is mounted and keyed on this shaft. An endless chain 129 drivingly connects both of the ratchets 123 and 127. This endless chain 129 is securely fastened to the nut block 103 and, therefore, as the nut block 103 moves back and forth on the barrel cam 95 the chain 129 moves back and forth and causes the shaft 125 to rotate first in one direcion and then in the reverse direction. The shaft 125 extends through the housing 18 and a pulley 131 is fastened on the shaft 125 outside of the housing 18.

A clamp 133 is attached to the underside of the boom frame 17 near the right end thereof. This clamp 133 holds the supporting arm 19 so that it extends downward from the boom frame 17. At the lower end of the arm 19 is positioned a horizontal rotatable shaft 135. A pulley 137 is securely mounted on the shaft 135 and the disc 21 which holds the plates'23 is also secured to this shaft. The pulleys 131 and 137 are drivingly connected by a pulley belt 139. Therefore, since the shaft 125 alternately rotates in reverse directions, the shaft 135 and the disc 21 also alternate in their direction of rotation.

A bracket 159 to which a destructible link 157 is connected is attached to a lower section of the supporting arm 19. The destructible link 157 is also connected to a connecting rod 161. The destructible link, therefore, is a member which connects various of the mechanical elements of the apparatus. This destructible link is of a material which is attacked by the etching solution, and when the link has disintegrated it no longer connects the connecting rod 161 and the bracket 159.

For operating the etching equipment, various operating mechanisms are provided. The lift cam 61 with itsassociated cam follower 85, the swing cam 65 and its associated cam followers 71, the barrel cam 95 and its associated cam follower 109, the main drive motor 45 and the disc drive motor 91 have already been described. In order that these items of 'the apparatus operate in a predetermined sequence and at predetermined times other pieces of apparatus are also provided.

A schematic diagram illustrating various parts of the apparatus and their electrical connections are shown in Figure 7. The electrical circuit is provided to operate the etching mechanism as follows: When the apparatus is in the stopped position both the main drive motor 45 and .the disc drive motor 91 are stopped. The boom frame17 has been pivoted so that the disc 21 is positioned above the etching. solution. The plate 23 to be etched is attached with the back of the plate to the face of the disc and a destructible link is connected in the apparatus. When the apparatus is started both of the motors operate. The main drive motor '45 operates to lower the boom frame 17 so that the plate to be etched is immersed in the etching solution. The main drive motor 45 then stops. The disc drive motor91, however, continues in operation and the disc 21 continues its rotating in alternate directions in the etching solution.

When the destructible link is cut through by chemical reaction with the etching fluid this again starts up the main drive motor45 and its operation lifts the disc 21 out of the etching solution, swings the boom frame 17 about sothatthe disc 21 is brought above the washing section of the tank and then lowers the disc into the washing section of the tank. After a predetermined time in the washing section the boom frame 17 is pivoted to lift the disc out of the wash water'and the frame is swung about its starting position in which the disc is above the etching solution, In'this position both motors stop and the etched plate 23 may be removed from the disc 21.

One electrical circuit for accomplishing the etching op eration set forth above is illustrated in Figure 7. Other electrical circuits, however, may be provided. The illustratedcircuit includes fourparallel circuits A, B, Cand D and terminals 179 and 181 connected to a suitable source of electrical power (not illustrated) for operating the motor. Referring to this figure of the drawings the numeral 45 designates a schematic representation of the main drive 'motor 45 and the numeral 91 designates a schematic representation of the disc drive motor 91. A

starting push button 139 and a stopvpush button 141 are provided in the circuit. When the start push'button is pin165 which is secured to an upper portion of the boom frame 17 by a bracket 167. Another arm 169 of the bell crank 163 is connected by a wire 171, or other sub stantially nonstretchable material to a lever 173 which operates the switch 155.

The length of the wire 171, the link 157, and the con necting rod 161 are predetermined so that when the link is inserted into the apparatus as shown in Figure l the bell crank 163 pulls on the wire 171 to pull the arm 173 of the switch 155 to the right thereby moving the switch 155 to open position. With the switch 155 open, the link and switch mechanism 153 shown in Figure 7'is open and any flow of current through circuit B would have to be 1 through the limit switch 149 which is operated by cam 145. The arm 173 of the switch, however, is spring moved to its circuit closing position the apparatus starts 1 its operation. The stop push button 14-1is provided so that'the apparatus may be stopped at any stage of the etching operation. A limit switch 1-49 which is operated by a cam 145 on the cam shaft 59 is provided in circuit B. As may be seen from Figure 4 this limit switch 149 is mounted on a bracket 147 which is attached to one of the frame members 53 of the cam shaft 15'. limit switch' 143 mountedon'the bracket 147 is also pro vided. This limit switch 143 is operated by a cam 151 which is secured to an extension of the cam shaft'59; Connected'in parallel with the limit switch 149is a destructible link and switch mechanism, 153, of which the switch 155 is schematically illustrated in Figure 7. As

may be seen from Figure l of the drawings the'destructible link and switch mechanism 153 includes a switch 155 and the link 157,.

v p The link 157 is the link which maintains operative con- Another tact between the plate-23 and the etching fluid. The link .157 is made of a material which is acted upon by the etching fluid so as to disable this link by the eating away of the metal-by chemical'actio'n of the metal of the link with the etching solution. One form of link is shown in Figure 8. This liiuk' is relatively flat and has holes 157a adjacent-the ends for hooking'the link to the apparatus. The link is coated over sections 15% with a material which is inert to the'etching fluid, leaving a small bare piece of metal'157c exposed to the-action of the etching solution. Other types of strips or other shapes of metals may obviously housed in the apparatus. The lower end of the link 157 is securely attached to a bracket 159 which is fastened to the suppcrting arm 19. The upper end of biased to return the lever 173 to the'left, thereby closing the switch .which would permit current to flow through circuit B regardless of the position of the limit switch 149. This spring biasing is provided by a spring 175 which has one end attached to the lever arm 173 and the-other end attached to a post 1'77 which is attached to the boom frame 17. Other forms of spring biased switches may also be used., I

' The operation of the main drive. motor 45, therefore, depends upon whether or not the destructible link and switch mechanism 153'is open or closed and whether the limit switch 149 is open or closed. The operation of the etching equipment also depends upon the operative position of the limit switch 143 which is operated the cam 151.

I The etching equipment with the circuit illustrated in Figure 7' is operated in the following manner. In the stopped position, both the drive motor 45 and the disc drive motor 91 are ofi. The boom frame 17 is positioned that the disc 21 is brought above the level of the liquid in the tanks 25 to the position as indicatedby the dotted I lines in Figure 1. While the apparatusis in 'thisposia tion' the plates 23 are secured to thedisc 2 1 of the appa- Before the plate 23 has been attached ,to'the disc ratus. 21', the plate is prepared for etching by any suitable process, for example the customary photoengraving process.

. While the apparatus is in this position a destructible link 157 is connected to the bracket 159 attachedto. a lower portion of the supporting arm. 19. .The other end r or" the link is connected to the relatively thin connecting rod 161 which issecured to one arm of the bell crank:163., Pivoting of the bell. crank about its pivot 165 pulls the lever 173 of the switch 155, positioned on top of the boom frame assembly 17, to its rightmost positionasina :dicated in Figure l, in which positionthe switch 155 is opened. The start push button 139 is then closed, therey by beginning operation of-both of the motors 45 and 91g. As the lift cam 61 rotates, the boom frame17 pivots aboutthe pivot pin79, lowering the disc 21 and. plate 23 into the etchingfluid until they are completelyUim-f mersed in the etching fluid insection 27 of the tank 25. As;herebefore mentioned,the operation of the main drive motor 45 depends upon the position of the switch" 155 and the limit switch149; Since the switch 155 is 59 so thatthe limit switch 149 is maintainedin closed position and current is flowing through circuit 'I'he, main drive. motor 45 is therefore operating andthe- 'raised J 9 portion 61a of the lift cam 61 passes the'roIIerSSQand' pivots the boomframe 17 1 about pivot P1111379; until the-'1 The upper end of the connecting rod 161 is'secured i I i i 7 disc 21 and plates 23 to be etched are completely immersed in the etching fluid in the forward section 27 of the tank 25. The cam 145 at this time opens limit switch 149 whereupon the main drive motor 45 is shut off.

During this entire period, however, the disc drive motor 91 is operating and when earn 145 has moved to a position opening limit switch 149, whereupon main drive motor 45 stops, the disc drive motor 91 remains in operation. Therefore, with the disc 21 and plates 23 fully immersed in the etching solution and the disc drive motor 91 operating, the disc 21 rotates in one direction and then reverses its direction, as controlled by the previously described reversing housing assembly 15. This reversing of the direction of the disc 21 while submerged in the etching solution prevents an uneven etching as a result of one-way relative movement of the plate 23 and the etching solution. The plates etched in this manner have the edges of the printing areas or lands in the shape of fillets and exhibit no overhang.

Since the link 157 is of a material which is acted upon by the etching solution, and since the link 157 is immersed in the etching solution, the metal of the link disintegrates due to what appears to be chemical reaction with the etching solution. When the link disintegrates, the biasing spring 175 pulls the lever 173 of the switch 155 to the left (Figure 1) to its closed position, whereupon the main drive motor 45 is again put into operation. In one commercial embodiment the link disintegrated in 47 seconds and accordingly the etching operation was accomplished in approximately 47 seconds.

As the lift cam 61 and the swing cam 65 rotate, the cam surface 61a of the lift cam 61 engages the roller 85 on the boom frame 17 and pivots the boom frame 17 about the pivot pin 79 to lift the disc 21 out of the etching bath. The lift cam 61 and the swing cam 65 are designed and relatively positioned on the cam shaft 59 so that when the lift cam 61 has lifted the disc 21 out of the etching solution, the cam surfaces 67 of the swing cam 65 come into play and swing or pivot the cam frame 15 about the post 33 to place the disc 21 over the washing section 29 of the tank 25. This position is shown'by the dotted lines in Figure 2. As the cams continue to rotate, the came surface 61a of the lift cam passes the roller 85 and the disc 21 is accordingly lowered into the washing section 29.

After a predetermined time in the washing section 29 where the disc 21 and plates 23 are rotated while submerged in wash water, the lift cam 61 again pivots the boom frame 17 about the pivot pin 7? and lifts the disc 21 out of the washing section 29. The swing cam 65 may again come into operation and pivot the cam frame 15 forward to the position indicated by the solid lines in Figure 2. At this point in the operation, the cam 151 on the cam shaft 59 opens the switch 143 and both of the motors, 45 and 91, stop. With the disc 21 positioned above the etching solution, as indicated by the dotted lines in Figure 1 and the solid lines in Figure 2, the plates 23 fully etched may be removed therefrom.

The preparation of the plates preliminary to the etching operation, and the composition of the etching solution have not been described in great detail since the apparatus of this invention may be used to etch the plates which have been subjected to various types of preliminary treatment in various types of etching solution. The apparatus of the present invention, however, is specifically suitable for use in the process as described in US. Patent No. 2,916,363, issued December 8, 1959 of Lester H. Doro.

The destructible link 157 controls the amount of time which the plate 23 remains in the etching solution since the motor 45 does not operate to lift the plate out of the etching solution until the link 157 is disabled by disintegrating as a result of chemical reaction with the etching solution. When the line 157 has been disintegrated the connecting rod 161 is no longer held down and the biasing spring 175 pulls the lever 173 of the switch 155 to its closed position, whereupon the motor 45 starts and the lift cam 61 lifts the plate 23 out of the etching solution. Since the link 157 and the plate 23 are both acted upon by the same etching solution the amount or depth of etching is positively controlled by the link used in the apparatus. In the event that a link which is rapidly disintegrated is used, the period of contact between the etching solution and the plates is low. On the other handin the event that a link which is only slowly disintegrated by the etching solution is used, the period of contact between the etching solution and the plate will be greater.

While the destructible link may be made of a sample of any metal which is chemically attacked by the etching solution so as to disintegrate it, the link is preferably made of a sample of substantially the same material as the plates to be etched. When the same material as is used in the plates is used for the link, the amount of etching done on plates in subsequent etching operations may be varied by changing the thickness or width of the link. For example, when a long period of etch is desired in a subsequent etching operation, a thicker link should be used; and, likewise, if the amount of etching desired is less, then a thinner link should be used. Once a correlation is established between the size of a link and the depth of etch on the plate it is a simple matter to select the proper link for the desired depth of etching; and the desired depth of etching on the plate will be effected regardless of whether or not there has been a change in the concentration of the active constituents of the etching solution, or a change in temperature, or a change in any of the other variables which ordinarily affect the rate of etching by the etching solution. The apparatus is capable of reproducing the depth of etch very accurately since the link is acted upon by the same etching solution that is etching the plates and, for example, if the etching solution were weaker than in a previous etching operation, the link would not be acted upon as rapidly by the weakened etching solution and, therefore, the time of etching would automatically be increased. The link therefore automatically integrates the various variables which normally affect the etching operation and which previously gave variations in the resultant etch.

In a commercial embodiment using magnesium alloy plates and magnesium alloy destructible links, it has been found that to produce 55 screen halftone etching a link approximately 3 inches long, 4 inch wide and 0.023 inch thick should be used. For 65 screen halftone results the link should be 0.020 inch thick;for screen halftone, 0.016 inch thick; for screen halftone, 0.014 inch thick; for screen halftone, 0.011 inch thick; and for 133 screen halftone, 0.004 inch thick. For line engraving to 0.008 inch depth, a link 0.026 inch thick givm this depth of etch; for line engraving to 0.016 inch depth, a link0.032 inch thick; and for line engraving to 0.21 inch depth, a link 0.037 inch thick. Other thicknesses of links for other etches may readily be determined.

The process and apparatus of this invention is also capable of accurately reproducing the desired depth of etch. For example, using links approximately three inches long, inch wide and 0.0215 inch thick, with the links coated with an acid resistant paint except for an area inch by 4 inch approximately in the center of each link (area 1570 of Figure 8), the length of the etching period varied only plus or minus one percent from the desired length of etching period.

Although shown and described in relation to a specific arrangement of specific pieces of apparatus, it should be understood that various changes of the described process and apparatus may be made which are Within the teachings of the invention and which do not depart from the spirit or scope of the claim. For example, the operation of the etching equipment has been described as beginning and ending with the disc 21 positioned above the etching solution in tank 25. The apparatus,

9 however, could function so as to begin and stop the operation with the disc 21 positioned above the washing section of the tank 25. Other modifications within the scope of this invention can be made by one skilled in the art.

I claim:

Etching equipment comprising a base, a frame mounted on said base, said frame being rotatable with respect to said base about a vertical axis, a boom pivotally mounted on said frame for pivoting about a horizontal axis, means attached to said boom to which a plate to be etched is attached, cam means on said frame for pivoting said frame on said base and for pivoting said boom on said frame in a predetermined sequence so as to lower said plate into a supply of etching fluid, a means interconnecting said link and said plate, whereby said link is adapted to be contacted by said etching fluid as an incident to making contact between said fluid and said plate, and which link is arranged to maintain operative contact between said plate and said etching fluid, said link being adapted to be chemically disintegrated and thus disabled by a limited period of contact between the etching fluid and the link, said cam means on said frame being interconnected to and biased against said link, whereby breakthrough of said link by chemical disintegration actuates said cam means to raise the plate out of said supply of etching fluid by pivoting said boom about said horizontal axis and then pivoting said frame on said vertical axis and subsequently lowering said plate into a supply of washing fluid.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,983 O62 May 9 1961 Bernard F. Smith certified that'error appears in the above numbered pat- 5 Patent should read as It is hereby tion and that the said Letter ent requiring cqrrec corrected below.

Column 5, line 51, after "shaft." insert M frame "line" read link column 7 line '14, for

Signed and sealed this 26th day 01. September 1961., v

(SEAL) Attest: v ERNEST W. SWIDER DAVID L. LADD Commissioner of Patents Attesting Officer USCOMM-DC

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