US 2602417 A
Description (OCR text may contain errors)
July 8, 1952 H.IV. e. MEDCALF 2,602,417
. DUSTING CABINET Filed Aug. ,16, 1949 3 Sheets-Sheet l w w" "I" \I wi l h Inventor A I C Attorney July 8, 1952 H. v. e. MEDCALF DUSTING CABINET s Sheefs-Sheet 2 Filed Aug. 16, 1949 Inventor A ltornaey July 8, 1952 H. v. G. MEDCALF DUSTING CABINET 3 Sheets-Sheet 5 Filed Aug. 16, 1349 I Inventor v i Attorney Patented July 8, 1952 UNI E -STATE TE O CE ,1. .7 a 72,602,417 1 v 1 DUSTING CABINET I I Henry Victor George Mcdcalf, New Cross, London, England, assignor to Hunter-Penrose Limited, London, England, a British company Application'August 16, 1949,,Serial No. 110,494 In GreatBritain October 21, 1948 1 This invention relates to dusting cabinets, especially to those intended foruse in the application of dragons blood to photographic plates.
In the'preparation of printing plates of zinc or other metal carrying a' photographic image the plate is immersed in an acid bath for a very short time to produce a relief image in the plate, it is then dried and covered with dragons blood, bitumen, chalk'or other well-known media in powderform, which is afterwardsbrushed, with the result that a layer'of powder remains on'the surface'of the image. The powder also forms a seal along the edges of the image in contiguity with the plate. A plate so treated is then heated to fuse the powder which then becomes acidresisting, and protects the image as awhole so that further immersions in acid baths may be freely effected to' increase 'the relief without danger of the'acid destroying the detail of, or undercutting the image.
Cabinets have heretofore been proposed for the process of dusting photographic images comprising a hood, in the bottom of which is a tray containing a dusting medium, for example dragons blood, and at the back a fan is provided which extracts from the hood any powder in suspension in the atmosphere above the tray.
The main object of the present invention is to prevent theoccurrence of blow-back in the hood which may occur when filters arranged behind the) extract fan become sufliciently clogged to permit a pressure build-up -in the air duct with the result that a sudden blow-back occurs across the hood, covering the operator with the powder.
- A furtherobject ofthe invention is to maintainan even extraction from the hoodso'that any powder in suspension is carried away from the atmosphere immediatelyin front of the operator, and at the same time to provide a qui escent atmosphere in thelocality of the tray,
A dusting cabinet. for use inthe application of dragons blood to photographic plates'constructed according to the present invention, comprises a hood enclosing a dusting tray, the hood at the- The invention also comprehends a dusting 3 Claims. (Cl. 118309) 2 a cabinet comprising a hood open at the'front of the cabinet and having closing side walls, and a tray at the base of the hood extending from the front to a false back, which false back'rises in streamline form to the'front of the hood at the upper part, the false back having an elongated opening extending nearly to the side walls of the hood, said elongated opening being disposed above the level of the tray; so that a suction effect applied to'the opening entrains therethrough all the air in'the hood above the tray, leaving the locality of the tray'in a substantially quiescent atmosphere, the opening being connected by ducting passing between the false back and the actual back of the hood into the cabinet .to a filter chamber therein, to which chamber an exhaust fan is fitted, so that only filtered air passes through the fan.
By employing constructions according to the invention the air extracted may be conveyed by ducting outside the building in which the cabinet is used.
Preferably, the ducting is connected to a horizontal partition separating a dust collecting compartment, providedwith a removable collecting drawer, from the filter chamber, and the: filter chamber includes a pluralityof tubular elements closed at the topand opening throughgthepartition into the collecting compartment. I I
In order that the invention: may be more clearly understood, a preferred embodiment will-now be described with reference to the accompanying drawings which show a hood surmounted'on a cabinet which is divided by a vertical partition, so that in the front of the cabinet are drawers in which materials used in the photo-engraving industry, for example dragons blood, can be stored, and at'the back of the partition the cabinet comprises a filter chamber, in 1 which drawings: c
Figure 1 is a side elevation, Figure 2 is a plan and Figure 3 a front elevation of the dusting cabinet, 1 Figure 4 is a vertical section thereof the line IV-IV of Figure 2, and j Figure 5 is a sectional plan taken on the line V-V of Figure 3.
In the drawings like references designate similar parts. I
The dusting cabinet-illustrated comprises a hood 1 having an opening 2 at the front of the cabinet bounded at the bottom by a shelf 3, at the sides by inwardly directed flanges 4 emanating from side walls 5 and at the top by the-downwardly curved part 5 of thehood.
taken on 1 In the vertical wall a of the false back is a O elongated opening l2 disposed above the tray so that a suction effect applied to the opening entrains therethrough all the air in the hood above the tray, leaving the locality 'of the tray in a substantially quiescent atmosphere,
The opening l2 communicates with ducting l3 located between the false back I and the actual back of the hood I leading to a filter chamber l4 housed within a cabinet [5 on which the hood structure is mounted. An exhaust fan I6 is fitted to the filter chamber so that only filtered air passes to the fan. v i s The cabinet comprises front and rear walls I1, 18 and the side walls 5 of thehood extend downwardly to form side walls to. the cabinet of which they fioor is indicated at I9., The cabinet-is divided by a vertical partition 20 and at the front thereof drawers 2! are mounted on the upper part and a cupboard 22 in th lower part. At the rear of the vertical partition 20 and on the floor I9 is set the filter chamber l4 so that the inlet thereto indicated at 23 is in alignment with the ducting [3.
The inlet 23 leads under a horizontal partition 24 constituting the floor of the filter chamber. Below the floor is a drawer 25 supported ona shelf 26 and the drawer extends beyond the floor into the inlet 23 so that inlet 23 leads into the drawer. The floor 24 has openings 27 over each of which 'is superimposed a filter bag 28 constituted by a cotton fabric tube held against the floor and against a top wall 29 to the filter chamher in any suitable manner.
Thus the fan draws air from the filter chamber and delivers it through an outlet 30 from the chamber into the space surrounding the chamber whence it passes through an exhaust port 3| in the rear wall 18 of the cabinet, over which port a guard 3la is arranged said guard having a foraminous panel 3 lb through which exhausted air passes.
When the fan 16 operates, air laden with dragons blood or other powdery material in suspension, is sucked into the ducting l3 and passes into'the collecting compartment constituted by the removable drawer 25 wherein the major part of the load in the form of dust is deposited. The air is'then forced to make a sharp turn upwardly into the tubularfiltering elements 28 formed with cabinet.
One side wall of the cabinet is provided with a door 32 ('see'Fig. 1) giving access to the filterin: elements, this door being countersunk within 4 the side wall of the cabinet so as to accommodate a sealing panel 33 covering the drawer 25.
The false back to the hood is of parabolic form, as it rises from the back to the top of the hood, thereby giving a streamline form for the entering air to the elimination of eddies, whilst'the bottom; edge of the elongated; opening is sufiiciently "high above thetray to leave undisturbed the dragons blood in the tray by the air currents flowing through the hood, thereby a substantially quiescent atmosphere is obtained in the locality of the'tray.
. -It will the observed, therefore, that the body of moving-air within the hood is of tapering form from front to rear and extends for the width of the hood, so that efiective movement of the wholeof the body of air continually occurs from the front to the back in contra-distinction to a moving body of air in a conical or trumpet form, which is engendered by the employment of a fan at the back of the'hood to the accompaniment of eddying at the front of the side walls, particularly in the vicinity of the tray.
The opening 12 may be covered by gauze or other foraminous material.
' By the present invention a simple but very effective dusting device especially for usein the application of dragons blood to zinc-plates is produced, in which efficient evacuation of dust-laden air continually occurs and blow-backs into the hood are eliminated, jmoreover, considerable economy is achieved by complete, recovery of the powder-brushed from the plates, whilst there can be no escape of powder in its passag through the'cabinet;
The filtering elements may be embraced by a light-frame (not shown) slidably mounted in the cabinet and provided with a handleextending through the cabinet wall so that clinging powder may be shaken from the elements from time to time toensure the efficiency of the elements.
1. A dusting cabinet for use in the application of dusting powder to photographically prepared printing plates, comprising a hood open at the front and having walls enclosing the rear, top and sides thereof, a dusting tray at the base of said hood extending from front to rear thereof, said hood having an elongated aperture extending at least over" the greater part of the width ofthe rear wall of the hood at a level above the said tray, a fan for applying suction to said aperture, whereby dust in suspension in the said hood can be sucked up through said aperture over substantially the entire width of the hood without disturbing the air immediately above the said tray, a filter chamber interposed between said fan and said hood, a dust collectingcompartment comprising a removable collecting drawer below said filter chamber, the floor of said chamber being constituted by a horizontal partition separating'saidchamber from said drawer, tubular filtering elements within said chamber, said elements being closed at one end and opening out at the opposite end through said partition into said collecting drawer, a duct connecting said aperture by way of said collectingdrawer with said filter chamber, and an exhaust conduit leading from said filter chamber.
2. A dusting cabinet according to claim 1, having a false back to the said hood disposed in spacedrelation to the rear wall of thehood, the said elongated aperture being located in the said false back and the said duct extending initially through the space between the false back and the rear wall of the hood.
3. A dusting cabinet according to claim 1, hav- 111g a false back to the said hood disposed in spaced relation to the rear wall of the hood, the said elongated aperture being located in the said Ialse back and the said duct extending initially through the space between the false back and the rear wall of the hood, said drawer extending be- I yond said chamber, and said duct enclosing the part of the drawer extending beyond the said chamber.
HENRY VICTOR GEORGE MEDCALF.
REFERENCES CITED The following references are 01' record in the file of this patent:
UNITED STATES PATENTS Number Name Date Leiman Mar, 28, 1916 Leiman Mar. 3, 1925 Dobinson Dec. 31, 1929 Guenst Sept. 12, 1933 Naugler Jan. 25, 1938 Bell Feb. 9, 1943 Antrim Sept. 4, 1945