Background Art Single and multi-deck conveyor dryers for reducing the moisture content of various materials, including rigid and semi-rigid material in sheet form, such as green veneer, wet plasterboard, fiberboard, perlite, and bagasse mat and the like are known. In these types of dryers, material to be dried is conveyed through a dryer chamber assembly which may be formed by a plurality of juxtaposed dryer sections.

These dryer sections may be substantially similar and include a fan for circulating heated air to a dryer chamber through which the material is conveyed. In prior art dryers of this type, a plurality of elongate nozzles are positioned above and below the conveyors that transport the material.

The nozzles include a plurality of ports which direct the heated air towards impinging contact with the material being dried. The nozzles are typically a four sided housing and are tapered in an effort to promote uniform discharge of air through the ports along the entire length of the nozzle.

Although the prior art nozzles have performed satisfactorily, it has been found that non-uniform drying may still occur in the material due to non-uniform discharge of heated air by the nozzles.

Disclosure of Invention The present invention provides a new and improved method and apparatus for drying rigid and semirigid sheet material. The present invention is disclosed in connection with a veneer dryer and includes an improved nozzle construction which provides enhanced drying of the material conveyed through the drying chamber that forms part of the dryer.

In one embodiment of the invention, a veneer dryer is disclosed that includes at least one drying chamber having an input end and an output end and defining a path of movement between the ends for material to be dried. The movement of the material along the path of movement is provided by at least one conveyor. A plurality of upper and lower nozzles is arranged above and below the conveyor and are operative to direct air into impinging contact with upper and lower sides of the material, as it is being conveyed through the drying chamber.

According to one feature of the invention, the nozzles are tapered in a longitudinal direction such that the ratio of the cross section of an inlet end of the nozzle and the cross section of a terminal end of the nozzle is preferably equal to or less than 7.5625 and greater than 5.04. In a more preferred embodiment, the ratio is substantially 7.5625.

According to a feature of the invention, the upper and lower nozzles are arranged in pairs with one nozzle of a pair including a plurality of discharge ports that are in an offset relationship with respect to a plurality of discharge ports formed on the other nozzle of the pair.

According to another feature of the invention, the nozzles have at least first and second configurations.

These first and second nozzles are preferably similar in construction, except for the positioning and location of discharge ports. In the preferred embodiment, the discharge ports of the first nozzle are in an offset relationship with respect to the discharge ports of the second nozzle.

According to another embodiment of the invention, a method is provided for enhancing the drying performance of existing veneer dryers. According to this embodiment, a plurality of nozzles are removed from an existing veneer dryer. At least some of the removed nozzles are replaced with first nozzles which each first nozzle including a plurality of discharge ports for directing air into impinging contact with material passing through a drying chamber forming part of the veneer dryer. The other of the removed nozzles are replaced with second nozzles that each have a plurality of discharge ports that are in an offset relationship with respect to the plurality of discharge ports forming part of the first nozzles. To further enhance performance of the veneer dryer, the first and second nozzles are installed into a drying chamber in a paired relationship.

In the preferred and illustrated embodiment, the extent of offset between the discharge ports of the first nozzle and the discharge ports of the second nozzle is not greater than the lateral distance between adjacent discharge ports of a given nozzle.

Additional features of the invention and a fuller understanding will become obtained in reading the following detailed description made in connection with the accompanying drawings.

Brief Description of Drawings Figure 1 is a side elevational view of a dryer constructed in accordance with the preferred embodiment of the invention; Figure 2 is a top plan view of the dryer shown in Figure 1; Figure 3 is a sectional view of a dryer section as seen from the plane indicated by the line 3-3 in Figure 2; Figure 4 is a fragmentary, side view as seen from the plane indicated by the line 4-4 in Figure 3; Figure 5 is a fragmentary, side view as seen from the plane. indicated by the line. 5-5 in Figure 3 ; Figure 6 is a fragmentary view as seen from the plane indicated by the line 6-6 in Figure 4; Figure 7 is a fragmentary view as seen from the plane indicated by the line 7-7 in Figure 5; Figure 8 is a top view of a pair of drying nozzles constructed in accordance with the preferred embodiment of the invention; Figure 8A is an enlarged, fragmentary view of the drying nozzle shown in Figure 8; Figure 9 is a perspective view of one of the nozzles shown in Figure 8; Figure 10 is a fragmentary, end view of a nozzle as seen from the plane indicated by the line 10-10 in Figure 9; Figure 11 is a fragmentary, end view as seen from the plane indicated by the line 11-11 in Figure 9; Figure 12 is a fragmentary, sectional view showing the construction of air discharge ports which form part of the improved drying nozzle ; Figure 13 is a fragmentary, end view of an alternate embodiment of the nozzle shown in Figure 9; and, Figure 14 is another view of the alternate nozzle construction shown in Figure 3 with a bottom closure plate attached.

Best Mode for Carrying Out the Invention Figures 1 and 2 illustrate the overall construction of a jet veneer dryer that includes apparatus constructed in accordance with a preferred embodiment of the invention.

Those having skill in the art will recognize a"jet veneer dryer"to be the type of dryer which is used to reduce the moisture content of, or dry, sheet material, such as wood veneers, pulpbpard, plasterboard, fiberboard, perlite board, and the like. The material to be dried is introduced at a "wet end"10 of the dryer, is conveyed through a drying chamber assembly 12, ultimately exiting the apparatus at a "dry end"14.

A detailed explanation of the workings of a dryer of the type shown in Figures 1 and 2 can be found in U. S.

Patent No. 5, 603, 168, which is owned by the present assignee and is hereby incorporated by reference. It should be understood, however, that the present invention, which can be adapted to the specific dryer disclosed in the 168 patent, can also be adapted to other types of dryers.

Referring to Figure 1, in the illustrated dryer, four vertically spaced conveyers 40a, 40b, 40c, 40d carry the material to be dried through the dryer chamber 12. The conveyors may be chain driven. The conveyors and the drive system for the conveyors do not form part of the present invention and are considered conventional. The direction of travel of the material, through the dryer, is indicated by the arrow 42 in Figure 2.

As is conventional, the dryer assembly 12 is formed by a plurality of juxtaposed, drying sections or units 16, all of which may be substantially identical. Figure 3 illustrates the construction of a dryer section 16. Each dryer section includes an air circulation fan 22 for recirculating air in a circular path indicated by the arrows 24. The circular path 24 is transverse to the path of movement of material through the section which is indicted in Figure 2 by the arrow 42.

In general, the fan 22 forces air through a heat source (indicated generally by the reference character 44 in Figures 2 and 3) which may be a gas fired burner, steam coil, etc. The heated air travels to a nozzle inlet chamber 36 which delivers air to inlet ends of a plurality of lower and upper nozzles 52,54 arranged in confronting pairs and which are positioned within an internal drying chamber 38 defined by the dryer section 16. Each pair of nozzles 52,54 directs the heated air towards the material that is traveling between them. The lower nozzle 52 directs heated air to the underside of the material whereas the upper nozzle 54 directs heated to the topside of the material.

As explained above, the material to be dried is carried through the dryer on power driven conveyors. In the illustrated embodiment, there are four conveyors which are indicated generally in Figure 3 by the reference characters 40a, 40b, 40c, 40d. Each conveyor passes between associated pairs of nozzles 52,54. In the illustrated dryer, the nozzles 52,54 are constructed in accordance with a preferred embodiment of the invention. The construction of the nozzles is generally shown in Figures 8 and 9.

According to the preferred embodiment, and referring to Figure 4, the upper nozzles in a drying section 16 are laterally spaced, and are arranged in lateral pairs indicated by the reference character 54, 54'. Similarly, the lower nozzles are also arranged in pairs, the nozzles of a pair being designated by the reference characters 52, 52§.

Referring to Figures 8 and 9, the nozzles 52, 52', 54, 54'are preferably similar in construction. In general, each nozzle has a tapered, box-like construction. Referring also Figure 10, each nozzle includes a pair of spaced apart side walls 60, an air discharge plate 62 and a nonperforate closure wall 64 spaced vertically from the air discharge plate 62. The air discharge plate 62 includes a plurality of discharge ports 62a (to be described). The air discharge plate 62 and closure wall 64 span the side walls 60 and thus define a four sided housing.

Because the side walls 60 are tapered, the vertical spacing between the air discharge plate 62 and closure wall 64 gradually decreases from an inlet end 66 to a terminal end 68 of the nozzle. In accordance with the invention, the rate of taper of a nozzle housing is chosen so that the flow rate of heated air through the discharge ports 62a is substantially uniform along the length of the nozzle.

Referring to Figure 8, a lateral pair of nozzles 52, 52'is illustrated. In the preferred embodiment, the air discharge plate 62 includes three staggered, lateral rows 71a, 71b, 71c of air discharge ports 62a. The ports 62a direct heated air, received at the inlet end 66 of the nozzle into impinging contact with the material traveling over the nozzle 52.

The adjacent nozzle 52'also includes three staggered rows 71a', 71b', 71c'of discharge ports 62a, but as can be seen in Figures 8 and 8A, the three rows 71a', 71b', 71c'of ports defined by the nozzle 52'are also slightly offset with respect to the rows 71a, 71b, 71c, 71d of ports defined by the nozzle 52.

The offsetting of the ports 62a is best shown in Figure 8A. As seen in that Figure, the discharge ports 62a of a given row, such as row 71c are spaced apart by a distance S.

Similarly, the discharge ports 62a on the nozzle 52'are also spaced a distance S. As can be seen in Figure 8A, the discharge ports 62a on the nozzle 52 are offset with respect to the discharge ports 62a on the nozzle 52'. In the preferred embodiment, the offset is equal to M the port spacing distance which, as seen in the Figure 8A is equal to S/2.

As a result of this offsetting, the heated air discharged by the nozzle pairs 52, 52' (and 54, 54') impinges on the material traveling between the associated nozzles more uniformally resulting in a more uniform drying of the material as it passes through the dryer section. The possibility of hot and cold spots on the material due to the spacing of the ports 62a is substantially reduced.

In the preferred embodiment, the lower nozzles 52, 52' are substantially identical to the upper nozzles 54, 54'. A lower nozzle 52 may be paired with an upper nozzle 54 or an upper nozzle 54', so long as the laterally adjacent lower nozzle, i. e., 52'is paired with the appropriate upper nozzle. So, as an example, if a lower nozzle 52 is paired vertically with a nozzle 54, then the laterally adjacent lower nozzle 52'should be paired with an upper nozzle 54'.

If, on the other hand, the lower nozzle 52 is paired with an upper nozzle 54', then the laterally adjacent nozzle 52' should be paired with an upper nozzle 54. In short, the paired relationship of the upper or lower nozzles 52, 52', 54, 54', should preferably be maintained throughout the dryer section.

Turning now to Figures 6,7, 10 and 11, the structure for supporting each nozzle within the dryer section 16 will be explained. Each nozzle includes a flange 70 formed at the inlet end 66 of the nozzle. The terminal end 68 of the nozzle is sealed by a plate 76 which may be welded to the terminal end of the nozzle. Alternate means for attaching the sealing plate 76 are also contemplated by the invention.

The sealing plate 76, as best seen in Figure 11, mounts a laterally extending pin 78.

In Figures 9 and 10, the flange 70 at the inlet end of a nozzle is shown as being four sided i. e defined by four flange segments 70a, 70b, 70c, 70d. In the preferred arrangement, only the top nozzles (as viewed in Figure 4) have the four flange segments. Due to space constraints, the other nozzles located below the top row have only three flange segments i. e 70a, 70b, 70c.

Referring to Figures 3,6 and 7, the nozzles are removably supported between a pair of vertical side plates 80, 82 which at least partially define the internal drying chamber 38 through which material to be dried travels. The plate 80 includes a plurality of square shaped apertures 84 (shown only in Figure 4), corresponding in size to the cross section of the inlet end 66 of the nozzles 52, 52', 54, 54'.

The apertures 84 are uniformally spaced and located so that the upper nozzles 54 are positioned such that their associated air discharge plates 62 are immediately above an associated conveyor, whereas the lower nozzles are positioned immediately below an associated conveyor. There is a corresponding aperture 84 for each nozzle.

To install a nozzle, the terminal end 68 of the nozzle is inserted through an associated nozzle opening or aperture 84 defined by the chamber wall 80. The nozzle is pushed through the opening until its mounting pin 78 engages a complementally shaped opening 88 (shown in Figure 5) defined in the vertical support plate 82 (which in the illustrated embodiment is on the chain drive side of the dryer section 16). The engagement of the support pin 78 with the side plate 82 (via opening 88) provides-support for the terminal end 68 of a nozzle. The engagement of the support pin 78 with the side plate 82 is best shown in Figure 7.

The nozzle is inserted through its associated opening 84 in the side plate 80 until the inlet flange 70 abuttably contacts structure surrounding the inlet opening. The inlet flange 70 is then secured in position by a clamping arrangement which may be conventional. In particular, and with reference to Figures 4 and 6, the inlet flanges of the nozzles are held against the side plate 80 by vertical, elongate nozzle clamps 86. Each nozzle clamp 86 includes a plurality of holes sized and located to receive an associated nozzle stud 88. The illustrated nozzle stud 88 is conventional and those skilled in the art will recognize it to be similar to an eye bolt, except that the eye opening is in the shape of a square or rectangle. The"eye"is sized to receive a locking wedge 89. To secure the nozzles in position, the nozzle clamps 86 are placed against the side plate 80 with the side flange, segments 706,70c (see Figure 10) clamped between the associated nozzle clamp 86 and the side plate 80. The nozzle stud 88 is inserted through an opening in the side plate 80 (not shown) which is also aligned with an associated opening in the nozzle clamp 86. The locking wedges 89 are then inserted into the"eyes" of the nozzle studs 88 in order to maintain the position of the associated nozzle clamps against the side flange segments of the inlet flanges. The wedge shape causes the locking wedges 89 to exert a clamping force on the nozzle clamps 86 which urges the inlet flanges 70 into a sealing engagement with the side plate 80.

As indicated above, the staggered rows of ports 62a defined, for example, on the nozzle 52 are slightly offset with respect to the staggered rows of ports defined by an adjacent nozzle 52'. In the preferred embodiment, this offsetting is obtained by offsetting the position of the discharge ports formed in the discharge plate 62 as compared to the discharge plate 62'forming part of the nozzle 52' (see Figures 8 and 8a). In an alternate arrangement, the offsetting can be obtained by offsetting the actual position of an adjacent nozzle. As indicated above, in a typical application, a nozzle is inserted through its associated opening 84 in the side plate 80 until the inlet flange 70 abuts the side plate. In the alternate arrangement, a spacer can be used between the inlet flange 70 and side plate 80 to slightly offset the overall lateral position of a nozzle in order to achieve offsetting of the discharge ports. Alternately, the inlet flange 70, formed on the inlet of a nozzle, can be. moved slightly to achieve the same offset position of the nozzle within the chamber 38. It should be noted here that those skilled in the art will recognize that minor changes in the mounting/clamping arrangement will have to be made to accommodate the alternative offset arrangements described above.

At least two types of constructions for the nozzles are contemplated by the present invention. In the construction shown in Figure 10, the side plates 60, the air discharge plate 62 and closure plate 64 are formed from a single sheet of material that is formed into the desired shape. The longitudinal edges of the sheet of material are joined using a pittsburgh joint 90 (which is considered conventional and best shown in Figure 11). Alternately, the nozzle may be of a two piece construction in which side plates 60'and air discharge plate 62'are formed from a single sheet of material. As seen in Figure 13 the three plates 60', 62' are formed in a U-shaped configuration in which the side plates 60'define the legs of the U. A closure plate 64'is made from a separate piece of material and includes bent flanges that are used to fasten the closure plate 64'to the side plates 60'.

The configuration of an individual air discharge port may be conventional. As seen in Figure 12, in the preferred embodiment, each air discharge port defines a semi-spherical shape or dimple the protrudes out of the plane of the plate.

The port 62a includes a solid spherical segment 94, and a discharge opening 96 that directs the heated air at an angle indicated by the vector line 97. The overall shape of the port 62a is spherical as indicated by the phantom circle 98; the vector line 97 may be substantially radial with respect to the circle 98.

As indicated above, the nozzle is tapered and, in particular, the cross section of a nozzle decreases from its inlet end 66 to its terminal end 68. It has been found that to achieve optimum performance, the nozzle cross sectional area should taper in such a way that the cross sectional area of the nozzle is reduced by at least 8. 7% of the nozzle inlet area for every 10% along its length. Using this relationship, it has been determined that the ratio of the inlet cross sectional area to the cross sectional area at the terminal end'of the nozzle should be in the range of 7.5625 and greater than 5.04. In the preferred embodiment, the width of the nozzle is substantially constant for its entire length. For a nozzle of constant width it has been determined that the ratio of the vertical distance between the discharge plate 62 and the closure plate 64 at the inlet end, to the spacing of the same plates at the terminal end 68 should be in the range of 7.5625 and greater than 5.04.

Based on this relationship and empirical data, for a nozzle having a plate spacing (between the discharge plate and closure plate) at the inlet of 7. 5625" the spacing of these plates at the terminal end should be less than in2". In a more preferred embodiment, the spacing at the terminal end for this nozzle should be about 1"and ideally it should be based on the relationship discussed above. However, the cost of manufacturing a nozzle with a spacing at the terminal end may be prohibitively expensive making the 1" spacing a more commercially viable embodiment of the invention.

In the preferred embodiment, the nozzles 52, 52'are paired in a side-by-side relationship and are also paired in a vertical relationship with corresponding nozzles 54, 54'.

It should be noted that the invention does contemplate other arrangements for the nozzles 52, 52', 54, 54'. For example, a plurality of nozzles 52 can be positioned in a side-by- side relationship followed by a plurality of nozzles 52' positioned immediately adjacent the plurality of nozzles 52.

Similarly, a plurality of nozzles 54 may be positioned together followed by a plurality of nozzles 54'.

Although the invention has been described with a certain degree of particularity, it should be understood that those skilled in the art can make various changes to it without departing from the spirit or the scope of the invention as hereinafter claimed.