US3538838A - Fume evacuation system for an etching machine - Google Patents

Description

United States Patent 1 3,538,838

[72] Inventor Charles Ray Hillhouse 1,254,725 1/1918 Pennock 98/1 15 Aurora, Missouri 2,415,471 2/1947 Dorfan 98/1 15 [211 App]. No. 783,854 2,544,769 3/1951 Sperry 98/115 [22] Filed Dec. 16, 1968 3,106,927 10/1963 Madwed 98/115 [45] Patented Nov1ol97o rimar Exami erWilliam J.W e [73] Assignee TasopeLlmited 5 & Powell y Aurora, Missouri a corporation of Missouri [54] FUME EVACUATION SYSTEM FOR AN ETCHING MACHINE Claims 7 Drawing Figs ABSTRACT: The fume evacuation system ncludes a tank for an etchant bath, the tank housing rotating paddles WhlCll [52] [LS-Cl 98/33, agitate the etcham bath, throwing it into Contact with the 98/115 workpiece causing a fume blanket to form above the etchant [51] Int. Cl F34f 13/00 l L The tank includes from and rear hollow sidewalls [50] Field ofSearch 98/33,ll5, vided with air inlet vents admitting fresh from the HSLH- mosphere, and an exhaust outlet vent serviced by an exhaust fan. Fresh air is drawn from the inlet vents over the etchant [56] References cued bath, replacing the exhausted fumes. Switching means actuate UNITED STATES PATENTS the paddles and the exhaust damper in sequence, so that the 1,085,742 2/1914 Leffel 98/115 lid may then be safely opened after etching.

5 26 5Z 11%; k", 55' f: r: /Z\ -1\ i i I I l I a 1 ii 5 ii l. l E i 5 2i 5: 5: l is i 0 L: i f

I I I Q4 55 32 L 1 a a,

Patented Nov. 10, 1970 Patented 3Nov. 10, 1970 Sheet Q of 2 Q Q )4: nae/Mi sy FUME EVACUATION SYSTEM FOR AN ETCI'IING MACHINE BACKGROUND OF THE INVENTION This invention relates generally to fume evacuation systems for etching machines, and in particular, to an evacuation system for exhausting the fumes resulting from the chemical reaction between an acid etchant and the workpiece-coating agent.

The use of acid in etching processes results in the creation of fumes and, particularly in a closed etching machine, these fumes accumulate unless a ventilation system is provided suitable for their evacuation. Before the advent of the socalled powderless etching process in the early l950s, it was customary to disperse the cumulative fumes by continuous ventilation systems and a variety of such systems were devised.

Powderless etching which speeds up the etching process, presented a particular problem in this respect, because an excessive amount of ventilation tended to cause the etching bath to evaporate. Rather than risk the loss of the etchant from evaporation, etching machines using the powderless process were, in general, fitted with a simple vent pipe usually leading to a central venting system in which a fan was often installed.

The problem as it related to the powderless etching process became aggravated with the recent development of new additives to form the protective filming agent. These additives speed up the etching process but require the use of much larger quantities of etching acid than was the case with heretofore usual powderless etching baths. Thus, much greater quantities of objectionable fumes were created, and yet the same objection to continuous ventilation, the evaporation of the etchant bath, remained.

The problem of evaporation is further aggravated in those etching systems in which the etchant bath is agitated in one way or another during the etching process.

SUMMARY OF THE INVENTION This fume evacuation system works at full effectiveness for a short duration substantially in sequence with the etching cycle. The short duration of the fume evacuation cycle results in a minimum loss of the etchant by evaporation. The structural arrangement of the air inlet venting and the fume outlet venting further assists in reducing evaporation of the etchant to a minimum.

The fume evacuation system includes a closeable tank for an etchant bath, the tank having agitating means therewithin, operatively agitating the etchant bath and throwing it into contact with the workpiece, whereby a fume blanket is created above the nominal etchant level. Air inlet vent means disposed above the etchant bath level communicates with the tank. An exhaust means evacuates the fumes, the exhaust means including-outlet vent means also disposed above the etchant bath level. Switching means operatively interconnect the agitating means and the exhaust means, and actuate the agitating means and the exhaust means in that sequence to evacuate the fume blanket.

The tank includes opposed, sidewalls. The inlet vent includes aperture means located in one of the sidewalls, and the outlet vent means includes aperture means located in the other of the sidewalls. Each hollow sidewall includes an inner wall and an outer wall. The inlet vent means includes an aperture disposed in the outer wall and an offset aperture disposed in the inner wall, the hollow sidewall providing a passage intercommunicating between ofiset apertures.

The air inlet vent means includes an air scoop means disposed on the outer face of the outer wall which directs air into the outer wall aperture. The inner wall includes a cover spaced inwardly therefrom and disposed in overlapping relation with the air inlet aperture in the inner wall to provide a peripheral air gap transverse to the axis of the air inlet aperture The outlet vent means includes an outlet vent pipe, and the peripheral gap has an annular area at least as great as the area of outlet vent pipe.

The exhaust means includes an exhaust fan, and a damper plate disposed in the outer vent pipe, the plate beingactuated to an effective open position substantially at the end of the etching cycle.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the etching machine with the lid in an open position;

FIG. 2 is a plan view of the etchant bath tank of the etching machine;

FIG. 3 is a front elevational view of the etchant bath tank;

FIG. 4 is aside elevational view of the etchant bath tank;

FIG. 5 is an enlarged fragmentary cross-sectional view taken on line 5-5 of FIG. 2 through the rear sidewall, (a view on line 5'5' taken through the front sidewall would be similar);

FIG. 6 is an enlarged fragmentary view in cross section taken on line 6-6 of FIG. 2 through the front sidewall, (a view on line 6'-6' taken through the rear sidewall would be similar); and

FIG. 7 is a line diagram showing a representation of the electrical switching.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now by characters of reference and first to FIG. I, it will be understood that the etching machine generally indicated by numeral 10 includes an operational cabinet 11 i a hydraulic ram 17 and has a structural arrangement which rotates and lowersthe lid 15 so that the etching workpiece 20, disposed on the underside thereof, is downwardly facing in the closed position and upright in the open position, the open position being shown in FIG. 1. t

The etching machine 10 includes a false front 21, having a hinged access panel 22. The false front 21 is shown in phantom outline in FIGS. 2 and 5, but omitted for clarity in FIGS. 3 and 4.

As stated above, cabinet 11 consists essentially of the etchant bath tank 12, disposed above the refrigerating unit 18. FIGS. 2, 3 and 4 are respectively plan, front, and side elevational views of the etchant tank 12 extracted, as it were, from the operational cabinet 11, and lid 15 and the linkage as sembly 16 are omitted for clarity.

The etchant tank 12 includes a hollow, front sidewall 23 having inner and outer walls 24 and 25 respectively, and a hollow, rear sidewall 26 having inner and outer walls 27 and 28 as shown in FIGS. 5 and 6. Single thickness lateral sidewalls 30 and 31 extend between the front and rear sidewalls 23 and 26. The etchant tank 12 also includes a bottom wall 35 which is downwardly sloped toward a drain 36 located at the center of the bottom wall 35.

The lateral sidewalls 30 and 31 and the outer walls 25 and 28 of the front and rear walls 23 and 26 respectively, include an upper, U-shaped portion which provides a peripheral seating ledge 32 for the peripheral rim 19 of the lid 15.

The front and rear outer walls 25 and 28 respectively are outwardly turned at the lower ends to provide elongate seating lips 33 and 34 as shown in FIGS. 4 and 5.

The etchant tank 12 houses a paddle assembly which includes a plurality of shaft-mounted paddle units 40 and 41, each of which is journaled at its ends into the front and rear sidewalls 23 and 26. Access to the journaling in the front sidewall 23 is by access panel 22.

The paddle units 40 and 41 have axes of rotation somewhat above the level of the etchant bath 42. When rotated, the paddle units 40 and 41 constitute an agitating means throwing etchant upwardly onto the workpiece 20. It is the reaction of the acid etchant 42 on the protective filming agent with which the workpiece is coated, that is principally responsible for the objectionable fumes developed within the closed etchant tank 12.

The venting of the tank to disperse these fumes is located in the front and rear sidewalls 23 and 26. Except for the number of apertures employed, the structural arrangement of the air inlet vent means in both the front and rear sidewalls 23 and 26 is essentially the same, and for this reason, the same reference numerals have been utilized to indicate corresponding parts except that, on the drawings, those parts located on the rear sidewall 26 include a prime mark.

The air inlet vent means in the front sidewalls includes a plurality of apertures 43. An air scoop 44 is welded or otherwise attached to the outer wall 25 and serves to direct air from the atmosphere into the hollow front sidewall 23. it will be observed that the rear air scoop 44' is directly accessible to the atmosphere, but that air enters the front air scoop 44 through the side screens of the refrigeration unit 18 and up behind the false front 21. In the drawings, air flow is indicated by arrows. The air admitted into the hollow sidewall 23 passes through said sidewall 23 to apertures 45. These apertures 45 are disposed in the inner wall 24 and communicate with the interior of the tank 12.

The apertures 45 include a peripheral lip 46 cupped out from the inner wall 24. The peripheral lip 46 includes a plurality of threaded socket portions 37 welded or otherwise attached thereto, to provide for the spaced connection of a cover 48 by means of a plurality of bolts 38. The cover 48 is substantially concentric with the aperture 45 and overlaps the aperture 45 whereby to shield the aperture 45 and prevent ingress of etchant into the interior of the hollow sidewall 23, and to provide an annular gap 49 communicating directly with the interior of the tank 12. As is clear from H6. 6, the cover 48 also overlaps the lip 46 longitudinally, further to facilitate the shielding function. The minimum cross-sectional area of the air inlet vent means along the air flow route is preferably at least equal to the minimum exhaust area. In particular, the peripheral gap 49 is preferably oversize.

it will be understood that the shielding of the apertures 45 and the staggering of the apertures 45 with apertures 43 in the outer sidewall 23 tends to inhibit the outward passage of fumes to the atmosphere during the etching cycle. The exhaust means evacuating the fumes includes a vent pipe 50 having a transition portion i welded or otherwise attached around an outlet vent aperture 52. The aperture 52 extends through the hollow sidewall 26 and is sealed off from the interior of the hollow sidewall 26 by means of opposed side plates 53 and a bottom plate 54 as is clearly indicated in FIG. 5. A butterfly valve 56, constituting a damper means, is located in the interior of the vent pipe 50. An exhaust fan F is connected to the vent pipe 50.

The minimum exhaust vent area of the vent pipe 50 is preferably not greater than the combined area of the inlet apertures 45 and 45 to ensure rapid extraction of the fumes and replacement of clean air within the interior of the tank 12.

The switching arrangement, diagramatically illustrated in FIG. 7, provides that the fan F is operating continuously during the operation of the etching machine 10. The paddle motor P and a damper solenoid D are controlled by a switch S. The switch S provides sequential actuating of the damper solenoid D after the paddle agitation has ceased. in other words, the evacuation cycle substantially follows the etching cycle.

It is thought that the functional advantage of this fume evacuation system have become fully apparent from the foregoing description of parts, but for completeness of disclosure, the operation of the fume evacuation system will be briefly described.

During the etching cycle, the acid etchant thrown against the workpiece reacts with the coating thereon and causes a fume blanket to form above the level of the etchant bath 42. During this period, the damper provided by the butterfly valve 56 in the vent pipe 50 is almost closed. Preferably it is open to only about 10 percent of its fully open position. The exhaust fan is running continuously during this time, withdrawing, however, only a small amount of the fumes. The continuous running of the fan provides a slight exhaust pressure on the fume blanket inhibiting the outward leakage of fumes through the air inlet means. The continuous running of the exhaust fan F has an additional advantage in that it prevents a backup of fumes into the tank 12 after the completion of the principal exhaust cycle and before the machine is turned off. Thus when the closure lid 15 is open, there is no risk of atmospheric pollution from fume backup.

When the etching process is substantially completed and the paddles 41 have ceased their agitating rotation, a solenoid switch indicated by the letter S in FIG. 7 switches open the damper 56 to a fully open position. The exhaust fan F sucks the fume blanket through the vent pipe 51 and, at the same time, sucks in replacement fresh air through the air intake scoops 44 and 44' located on the outer walls 25 and 28 of the front and rear sidewalls 23 and 26 respectively because of the partial vacuum caused in the tank 12.

The fresh air drawn into the air scoops 44 and 44' enters the hollow front and rear sidewalls 23 and 26 through the apertures 43 and exits from the hollow sidewalls through the offset apertures 45 and the annular gap 49 into the interior of the tank 12. The air inlet apertures 45 are located at three of the four corners of the tank l2, and the outlet aperture 52 is located at the fourth corner. Air is thus drawn across the surface of the etching bath en route to the outlet vent pipe 5b which facilitates rapid fume exhaust.

The covers 48 overlapping the apertures 45 tend to act as baffles, and the passage between the offset apertures 44 and 45 in the front and rear sidewalls 23 and 26 tends to impede any undesirable leakage of fumes to the atmosphere.

It will be understood that the butterfly valve 56 is switched to the fully open position automatically for a specific time period for example, 10 or 15 seconds after the etching cycle as may be set by the operator. The substantial damping of the exhaust means to about 10 percent of full potential during the etching process prevents evaporation of the etching bath at this time. Of course, the exhaust fan F need not run continuously. And as an alternative, the exhaust fan F and the damper means could be actuated and deactuated simultaneously, in sequence with the paddle agitation means, all within the scope of the claims hereunto appended.

I claim:

1. A fume evacuation system for a powderless etching machine comprising:

a. a tank for an etchant bath, the tank including sidewall means extending above the etchant level;

b. agitating means in the tank operatively agitating the etchant bath and causing a fume blanket above the etchant bath level; closure means substantially operatively covering the tank during agitation;

d. air inlet vent means disposed above the etchant bath level and communicating with the interior of the tank;

. exhaust means evacuating the fumes including outlet vent means disposed above the etchant bath level and communicating with the interior of the tank; and switching means operatively interconnecting the agitating means and the exhaust means and actuating the agitating means and the exhaust means in that sequence to substantially evacuate the fume blanket before the opening of the closure.

2. An evacuating system as defined in claim 1, in which:

g. the inlet vent means includes at least one aperture located in the tank sidewall means.

3. An evacuation system as defined in claim 1, in which:

g. the tank sidewall means includes a pair of hollow sidewalls having an inner wall and an outer wall;

h. the inlet vent means includes aperture means located in one of said sidewalls; and

i. the outlet vent means includes aperture means located in the other of said sidewalls.

4. An evacuation system as defined in claim 1, in which:

g. the tank sidewall means includes a hollow sidewall having an inner wall and an outer wall;

h. the inlet vent means includes an aperture disposed in the outer wall and an aperture disposed in the inner wall, said apertures being offset; and

i. a portion of said hollow sidewall provides a passage interconnecting said offset apertures.

5. An evacuation system as defined in claim 4, in which:

j. the inlet vent means includes an air scoop means disposed on the outer face of the outer wall and directing air into the outer wall aperture; and

k. the inlet vent means includes a cover spaced inwardly from the inner wall and disposed in overlapping relation with the aperture in the inner wall to provide a peripheral gap transverse to the axis of the inner wall aperture.

6. An evacuation system as defined in claim 1, in which:

g. the tank sidewall means includes a pair of sidewalls;

h. at least one of the sidewalls is hollow to provide spaced inner and outer walls;

i. said one sidewall includes a pair of communicating apertures spaced in the direction of air flow to provide at least part of the inlet vent means;

j. the other sidewall includes an aperture providing part of the outlet vent means; and

k. the outlet vent means includes an outlet vent pipe communicating with said other sidewall aperture.

7. An evacuation system as defined in claim 6, in which the inlet vent means includes an aperture area, communicating directly with the tank at least equal to the vent pipe area.

8. An exhaust system as defined in claim 6, in which:

l. the exhaust means includes an exhaust fan and damper means disposed in the outlet vent pipe; and y m. the damper means is actuated to the open position, substantially at the'end of the agitating cycle.

9. An evacuation system as defined in claim 1, in which:

g. the sidewall means includes front and rear hollow sidewalls each including an inner wall and an outer wall;

h. the inlet vent means includes aperture means disposed in each of said sidewalls;

i. the aperture means in each hollow sidewall includes an aperture in the outer wall and an aperture in the inner wall, said apertures being offset, and a passage portion intercommunicating said offset apertures in the direction of air flow; and

j. the inlet vent means includes an air scoop directing air into the outer wall apertures and cover means shielding each of the inner wall apertures.

10. An evacuation system as defined in claim 9; in which:

R. the outlet vent means includes an outlet aperture located in one of the hollow sidewalls to draw air across the etchant bath and through that hollow sidewall from the inlet vent means in the other of said sidewalls;

l. the exhaust means includes an outlet vent pipe communicating with the said outlet aperture and an exhaust fan located within the outlet vent pipe; and

m. the exhaust means includes a damper plate controlled by the switching means to be partly open during etching and fully open during exhaust.

Images