Air Dryer Equipment

Abstract

An air dryer for automatically drying mass production items after their being processed through wash and rinse sections. The dryer includes an air knife capable of directing a concentrated uniform blast of air at the production items being dried as they pass through the air knife section of a conveyor line.

Description

This invention relates to the automatic drying equipment for drying production items as they pass on a conveyor line through different processing stations, and is more particularly concerned with the air knife section of power wash cleaning systems, such as are used in fabricating printed circuit boards, or the like.

During the power wash cleaning operation, the production item being transported by a conveyor passes through a plurality of wash and rinse sections. The wash and rinse operations are accomplished using appropriate chemicals.

It is necessary in the production of equipment with high reliability to thoroughly dry such equipment. The drying equipment forces drafts of hot air against the conveyor transported items. However, there is a limit on the time and temperature of the hot air being directed against the printed circuit boards. If these limits are exceeded, then there's danger of damaging the components of the printed circuit boards. Further, any chemical residue remaining on the board could adversely effect the components.

Therefore, to expedite the drying processes, air knives are used at the onset of the drying process. More particularly, the air knife directs filtered stream of air against the production items to be dried such as printed circuit boards. The stream of air, if properly directed, removes most of the superfluous liquids adhering to the boards after the wash and rinse processes to thereby minimize residue and thereby enable the convection drying process to be accomplished with less caloric input.

A major problem in the past has been to j provide a uniform stream of air across the entire printed circuit board as it passes through the air knife. In the past the air knife has terminated at a cylindrical chamber having apertures therein through which a stream of air passes onto the printed circuit board passing juxtaposed thereto. To obtain the desired result, it is necessary that the air enter the terminating chamber a a relatively high pressure. Due to the high pressures, it has been virtually impossible to obtain a uniform stream of air from the cylindrical chamber.

One end of the air knife terminating chamber is closed. The other end is connected to duct work bringing the air from the air prime mover, such as a centrifugal pump or the like. The air, upon striking the closed end of the chamber is forced back into the chamber and sets up pressure peaks and valleys in the chamber as the returning air intermingles with the forward moving stream of air. Thus, at some apertures there is practically no air pressure at all, and consequently, no air flow; while at other apertures there is high pressure and a large amount of air flow. The large amount of air flow at these apertures set up turbulences which further disturb the flow of air and create unsymmetrical pressure and flow patterns. Attempts have been made to provide uniform air flow by varying the size of the apertures. Such attempts have not proved successful.

In practice, portions of the printed circuit board passing juxtaposed to the air knife chambers are not subjected to the concentrated flow of air from the air knife. Thus, portions of the printed circuit boards remain laden with droplets of liquid as the printed circuit boards pass into the hot air convection dryer. Therefore, the drying operations of present day equipment are faulty and in need of improvement.

Accordingly, an object of the present invention is to provide new and unique power wash cleaning systems wherein the products being processed are thoroughly dried and wherein practically no residual trace of the cleaning chemical remain on the products.

A related object of this invention is to provide power wash cleaning systems wherein thorough drying occurs without subjecting the products being processed to danger from hot air dryers operating at a temperature or for a time duration that may be injurious to the items being dried.

A related object of this invention is to provide a new and unique air knife.

Still another object of this invention is to provide air knives providing uniform air flow over the entire surface of the products being processed.

Yet another object of this invention is to provide air knives having air knife chambers which are not cylindrically shaped.

Yet another object of this invention is to provide air knives having air knife chambers that have polygonal cross sections.

Still another object of this invention is to provide air knives wherein the air knife chambers are rectangular parallelepipeds having apertures along one of the longitudinal vertices of the rectangle.

Yet another object of this invention is to provide air knives having terminating chambers that, are wedge shaped with apertures at the angular meeting point of the biased planes. The apex of the angle is the part of the chambers closest to piece parts being processed.

A preferred embodiment of the power wash cleaning system comprises a plurality of wash and rinse stations followed by an air knife station. The air knife station leads into a hot air dryer station. The air knife station comprises an air prime mover pump that includes a fan and scroll of arcuate compartment leading into ducts. The ducts terminate in a pair of spaced apart, oppositely disposed air knife chambers. The chambers are wedge shaped in part with a series of apertures along the apecies of the wedges.

As the products pass through the space between the chambers on a mesh or screen, they are subjected to a continuous, uniform, strong stream of air against both sides of the products which removes droplets of the wash and rinse fluid from the product passing therethrough.

The airflow is extremely uniform and because of the shape of the chambers, they can be positioned a minimum distance from the printed circuit boards or the like. The proximity of the product being processed and the lack of turbulence in the chambers maximizes the drying effect of the drying station while minimizing the exposure of the components of the printed circuit boards to the deleterious effects of heat and residue.

The above enumerated and other features and objects of this invention will now be explained in detail with the aid of the accompanying drawings, wherein:

FIG. 1 is a plan view of a typical power wash cleaning system utilized in processing printed circuit boards after they are automatically soldered;

FIG. 2 is a pictorial view of the air knife and hot air dryer stations of the power wash cleaning system of FIG. 1;

FIG. 3 is an exploded pictorial view showing that part of the duct work leading from the scroll to the air knife chamber;

FIG. 4 is a pictorial view of a preferred air knife compartment;

FIG. 5 is a plan view of the bottom one of a pair of horizontally mounted air knife chambers showing the apertures as they appear to the products passing thereover; and

FIG. 6 shows two alternative shapes for the air knife chambers.

In the power wash cleaning system 11 of FIG. 1, a pair of wash stations 12 and 13 are shown. The wash stations are followed by a rinse station generally indicated at 14. The drying station comprises the air knife section generally indicated as 16, followed by the hot air dryer section generally indicated as 17. The goods are either hand carried and loaded onto the power wash and cleaning system of FIG. 1, or brought there by a continuous conveyor belt from another processing station such as an automatic fluxer and soldering station.

In the plan view of FIG. 1 there is shown an initial exhaust air duct 18 in a hood 19. The exhaust duct aids in removing the vapors resulting from the soldering process. There is, of course, sufficient room between the hood 19 and the meshed carrier or conveyor belt 21 for passage of the printed circuit boards.

Each of the wash and rinse stations may be separately controlled by controls such as the control boxes 22, 23 and 24 associated with the wash and rinse stations 12, 13 and 14, respectively. Similarly the air knife and dryer stations 16 and 17, respectively are controlled using controller 26.

Wash sections and rinse sections generally comprise horizontally disposed spaced apart apertured pipes for directing streams of fluids at the products being processed sas they pass therebetween. The conveyors are usually of the continuous type and are seen at the ends of the power wash cleaning system 21 and 27. Generally speaking, the fluids, except for the rinse section wherein in a typical situation clean hot water is used, are recirculated. The plumbing for recirculating the washing fluid is schematically shown at 28 and 29. The hot water input and drain are schematically indicated at 31. Certain pertinent portions of the air knife are indicated at 16. For example, the fan and scroll compartment of the air prime mover are generally indicated as 32. The intake is filtered and the filter is schematically indicated at 33. The ducts coupling the scroll to the chamber duct work are schematically shown as 34.

Certain pertinent portions of the hot air dryer are indicated at 17. For example, the power input to the hot air dryer is indicated at 36. The ducts indicated at 37 are for directing the hot air through a dryer hood 38.

A portion of the meshed carrier 41 carrying printed circuit boards such as boards 42 and 43 through the power wash cleaning system is graphically depicted in FIG. 1.

FIG. 2 pictorially shows the air knife 16 and dryer station 17 of FIG. 1. As can be seen, both stations include a section of the base tank 44 which contains the endless conveyor system. Component parts of the air knife station are the previously mentioned filter 33 at the intake to the fan and scroll compartment 32. The scroll compartment comprises, for example, an intermediate compartment effectively directing the air from the air prime mover, such as a fan, into the ducts. Only a portion of the scroll is shown, since scrolled compartments are well known to those skilled in the art. The pump and scroll compartments are located between plates 46 and 47. The filter 33 is shown as a double filter comprising sections a and b. The filter is held onto plate 46 by means such as threaded fastener 48 passing through circular plate 49 to retain filters 33a and 33b juxtaposed and abutting the entrance of the air intake entrance (not shown) to the pump and scroll 32. The plates 46 and 47 are held together with threaded fasteners such as threaded fastener 51 passing through both plates. A bushing 52 between the plates maintains a set distance between the plates sufficient for the passage of duct 53 located at the end of the scroll.

Duct 53 terminates at flange 54a. A first and a second knife chamber 57, 58, spaced apart and horizontally disposed traversing the conveyor or carrier are provided. The first air knife chamber 57 is shown positioned above the carrier and is attached to flange 54b. The second air knife chamber is attached to the flange 54b through duct 61.

The chambers themselves are generally shown as rectangular parallelepipeds having apertures at the vertex of one of the longitudinal angles such as apertures 62 in the chamber 58 and apertures 63 in the compartment 57. The chambers are positioned so that the apertures are as close as possible to the printed circuit boards passing therebetween.

Air is forced through the filter 33 A and B at the intake of the prime mover and through the fan and the associated scroll through duct 53 attached to air knife chamber ducts 61 and to 59, through the chambers 58 and 57 and through the apertures at the vertices of the longitudinal angles to strike the bottom and top of the printed circuit boards passing the spaced apart chambers. It should be understood, of course, that the printed circuit boards could be held vertically rather than horizontally, and then the air knives would then be oriented to apply a uniform stream of air in the horizontal direction to strike the components and the boards to drive excess moisture therefrom.

The air coming from the apertures is focused by the shape of the chambers 57 and 58 contiguous to the apertures and flows forcefully through the apertures. In addition, it has been found that the angular shape proximate to the apertures avoids the turbulence in the air caused by the air bouncing off a closed end of the chamber and interfering with the incoming air.

The air knife chambers 57 and 58 are joined to the ducts by means such as male threads 64 and 66 on circumferential portions at the duct ends of the chambers. Matching female threads are located at the circumferential sections 67 and 68, respectively, of the ducts 59 and 61. Naturally, pipe threads are used to prevent air leakage at the coupling of the ducts and the air knife chambers. Also, the threads enable orientation of the chambers so that the aperture portions of the chambers are directly opposite each other, directing the air most efficiently at the circuit boards.

As shown in FIG. 2 the combined air knife and hot air dryer section includes a biased drain sheet 67 to enable excess moisture to flow to the drain. It is biased to gravitationally force the excess moisture to the drain. Immediately after the air knife section, a hood 68 is provided leading from duct work 69 for directing heated air through the duct work and onto the printed circuit board.

Because of the efficiency of the air knives shown and described herein, the drying job is more efficiently executed.

FIGS. 4 and 5 are exemplary showings of the air knife chamber such as air knife chamber 58 having a series of apertures 62 therein at one corner thereof.

FIG. 6 at A, B and C show different embodiments of the cross-sections of different embodiments of the air knife chambers 58. The cross-section of air knife chamber of FIG. 6 A, for example, has two sections 71 and 72 which are at an angle to each other but are separated by an aperture such as aperture 73. The bottom of the chamber 74, however, is flat so that the configuration of the air knife chamber of FIG. 6A is triangular or wedge shaped with a polygonal cross section.

FIG. 6 B shows the cross-section of the shape of the chamber 58 shown in FIGS. 4 and 5.

FIG. 6 C shows the angular sections 71, 72 separated by the aperture 73 and wherein the bottom of the chamber is also angularly disposed and comprised of sections 76 and 77 joined together at angle 78. FIG. 6 C is very similar to FIG. 6 B except for the difference in the angles.

In operation, then, articles of manufacture, such as printed circuit boards are transfered from the automatic soldering operation to the power wash cleaning system where it first passes underneath an exhaust duct on a conveyor whose beginning is shown at 21. The printed circuit board then passes through a sprinkler wash section comprised of a plurality of overhead and bottom sprinklers that thoroughly sprinkle a washing solution onto the boards.

The rinse section generally uses hot water which is also sprinkled from the top and the bottom with a multiple sprinkler arrangement. After the rinse section, the article of manufacture passes through air knife chambers. The present system using the air knife having a parallelepiped chamber provides a uniform stream of air to drive excess moisture and fluid from the article of manufacture prior to the hot air dryer station.

While the principals of the invention were described above in connection with the specific apparatus and application, it is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention.

Claims

We claim:

1. An air knife for use in directing a uniform stream of air against an article to be dried,

said air knife comprising a rectangular parallelepiped shaped chamber,

a series of apertures along one of the longitudinal angular corners of said parallelepiped shaped chamber, and

means for supplying air under pressure to said chamber at an angle to said apertures so that said air is uniformly dispersed through said apertures at products to be dried passing proximate to said apertures.

2. A power wash cleaning system for processing articles of manufacture,

said system comprising wash stations for washing said articles,

means for drying the articles of manufacture after the washing,

said drying means comprising air knife means for directing a stream of air at said articles,

said air knife means comprising a chamber,

said chamber having a polygonal cross section,

said chamber having a series of apertures for directing the air uniformly against the articles of manufacture passing proximate thereto,

means for supplying air under pressure into said chamber, and

said apertures being at one of the longitudinal meeting points of two sides of the said chamber.

3. The power wash cleaning system of claim 2 wherein the means for supplying air to the chamber includes coupling means for joining the means for supplying air to the chamber,

said coupling means comprising an air entry opening at one end of said chamber,

said opening surrounded by a pipe threaded section,

said means for supplying air under pressure comprising pump means,

air filter means at the input to said pump means,

said pump means discharging into a scroll compartment,

said scroll compartment discharging into duct means, and

the end of said duct means being aligned with the longitudinal axis of said chamber and having mating pipe threads for receiving said pipe threaded section of said chamber.

4. The power wash cleaning system of claim 2 wherein said chamber is a parallelepiped comprising side walls and a pair of end walls,

an opening at one of said end walls for coupling said chamber to said means for supplying air,

said air chamber being closed at the other of said end walls, and

said apertures being along the junction of a pair of said side walls of said chamber.

5. The power wash cleaning system of claim 2 wherein said apertures are of varied sizes.

6. The power wash cleaning system of claim 2 wherein said apertures are of the same size.

7. The power wash cleaning system of claim 2 wherein said apertures are the same size and are evenly spaced.