GB2039630A - Centrifugal fanwheel with replaceable blade covering - Google Patents

Abstract

Each blade is hollow and has an erosion-resistant covering 42 replaceably secured thereto by means of internally threaded, upset-type fasteners 50 inserted and secured in place in countersunk holes formed in the skin 28 of the assembly, and screws 52 turned into the respective fasteners 50 through countersunk holes formed in the liner 42. <IMAGE>

Description

SPECIFICATION Centrifugal fanwheel with replaceable blade liner The invention pertains to the art of centrifugal fan wheels provided with hollow airfoil-shaped blades subject to operation in erosive atmospheres.

It is known to provide liner materials to give erosion protection to hollow airfoil-shaped blades used on centrifugal fan impellers. So far as know, such liner arrangements have in the past been limited to welding the liners directly to the impeller and adjacent components, such as the centerplates, backplates orsideplates; orto bolting such liners, through upstanding flanges at the edges of the liner, to the adjacent centerplates, backplates, sideplates (or shrouds). Since, by welding, the metals are fused together, this severely limits field replaceability of the liners. In an arrangement in which bolting through flanges is used, there is inherently provided metal which protrudes into the airstream and thereby upsets to some degree the smooth flow of gases over the airfoil-shaped blades.It will be recognized, of course, that the very provision of airfoil-shaped blades which are more expensive than solid, single thickness blades is for the very purpose of obtaining smooth efficient airflow and better performance.

Accordingly, it is the principal object of this invention to provide an arrangement for securing a liner to airfoil-shaped blades which does not have the disadvantages of the noted prior art practices.

In accordance with the invention, a centrifugal fanwheel is provided which includes spaced-apart plates, centerplate, backplate, sideplate (or shroud), a plurality of generally hollow, airfoil-shaped blades extending transversely between the plates in spaced-apart relation, each of the blades comprising an inner frame and skin assembly and an exterior liner, the frame and skin assembly including at least a major part of its extent having a construction of ribs covered substantially completely by the skin and welded thereto to provide a rigid integral structure, the skin including a first array of countersunk openings therein, the exterior liner covering the part of the skin having the first array and including countersunk openings in a second array to register with the first array, and means for fastening the liner directly to the skin throughout the area of the arrays, the fastening means including interiorly threaded, upset-type fasteners fastened to the skin with the heads seating in the countersunk openings of the first array, and externally threaded screw fasteners turned into the upset-type fasteners through the openings of the second array to secure the liner in overlying relation to the skin.

The liner is preferably of an erosion resistant alloy and, in accordance with the particularfanwheel and its intended service, the liner may be dimensioned to cover the skin substantially completely, or some lesser part of the skin in accordance with the particular airflow pattern expected in accordance with the fan design.

A preferred embodiment of the invention will now be described, by way of example, with reference to thn Irrnmnin\rinn rErnwinne in whinh - Figure 1 is a partly broken isometric view of one type of single width centrifugal fanwheel to which the invention is applicable but not limited; Figure 2 is an isometric view of a major portion of a blade having a frame and skin assembly; Figure 3 is a broken edge view of one type of airfoil-shaped blade according to the invention; Figure 4 is a cross-sectional view corresponding to one taken along the lines IV-IV of Figure 3; Figure 5is an exploded sectional view of a fastener arrangement (before upsetting fastener) according to the invention; and Figure 6 is a sectional view of a single fastener according to the invention in a final assembled position.

Referring to Figure 1, a single-width, single-inlet centrifugal fanwheel is shown which basically includes a backplate 10, a sideplate 12 axially spaced from the backplate 10, a plurality of airfoil-shaped blades 14 which extend transversely between the plates in spaced-apart relation, the backplate 10 being supported from a shaft 16 through a conventional hub arrangement. The air or gas being handled by a fanwheel of this type flows axially into the opening 18 of the sideplate and is turned and discharged radially from between the blades 14.

While the example shown in Figure lisa singleinlet, single-width fan in which the sideplate is dished, it will be appreciated as the description proceeds that the invention is applicable to other centrifugal fanwheels such as doublewidth, doubleinlet wheels, and with other configurations of the plates of the wheel.

Referring to Figure 2, each blade 14 is generally hollow and basically comprises a frame and skin assembly including a plurality of transverse ribs 20, 22, 24 and 26 from front to rear of the blade, and a top skin section 28 and a bottom skin section 30 which are contoured as shown in Figures 2 and 3 to provide the desired airfoil shape of the blade. As in a typical conventional construction, the skins 28 and 30 may be welded to a solid bar 32 at their front or nose edges and to a relatively narrow rear rib 34 at their rear edges.

Before the blade is assembled to the plate, access to the interior of the blade is readily available between the ribs so that the welds 36 at each of the Tee joints between the welds and skin may be made.

The materials for the frame and the skin assembly may be conventional materials, such as cold-rolled metal.

After the frame and skin assembly has been accomplished, if the blade is to include a tail piece 38, as illustrated in Figure 3, this solid tail piece is built up of the parts generally as illustrated in Figure 3, and is in turn also welded to the stub tail of the blade.

After the blade has been assembled to this extent and all welding and cleaning operations have been accomplished, the hollow blade is secured to the plates 10 and 12 by applying a weld 40 at the Tee joints formed between the top skin 28 and the bottom skin 30 and the facing plates (only the plate 10 being shown in Figure 4).

Then an exterior liner which. as illustrated in Figure 3, includes a top liner 42 and a bottom liner section 44, are placed in overlying relation to the skins 28 and 30 and an array of pilot holes is drilled through both the liner and the skins. One pattern of array of the holes is illustrated in Figure 2, the holes 46 indicating those of the first array drilled in the top skin, and those identified as 48 indicating the pattern of the second array drilled in the liner part. Since all these pilot holes are drilled through both the liner and skins together, it will be appreciated that the first array and second arrays of holes will register with each other.

Referring to Figure 5, following the drilling of the pilot holes in the skins and liner, the holes 46 of the skins are countersunk, as illustrated in Figure 5, to accommodate the head of an upset-type fastener 50 with the flat head of the fastener being flush with the exterior face of the skin after the fastener is inserted in place. Likewise, the liner material pilot holes are countersunk as shown in Figure 5 to accommodate the flat head of the screws 52 to be received by the fasteners 50 in the final assembly.

In the assembly of the liner to the blade, all of the fasteners 50 are first inserted into their respective holes 46 of the skin. The fasteners are then upset with special tools to secure them to the blade skins.

Then the liners 42 and 44 are placed on the skins with the array of holes 48 in registry with the holes in the fasteners 50. The screws 52 are then applied through the liner and into the fasteners 50, as shown in Figure 6, to tighten the liners down flush against the skins. This final assembled relationship of the parts around a single hole should be clear from the view in Figure 6.

To secure the liners to the solid tail piece 38, where there is no possibility of using upset-type fasteners because of the solid nature of the tail piece, the same type of pilot holes are drilled, but the solid tail piece is simply tapped and flat head screws 54 are used where there is adequate thickness, and at the extreme tail of the blade, flat head rivets 56 can be used if desired.

The number of parts which together form the complete liner can vary in accordance with whatever seems to be the preferable fabricating practice for a given type of blade. In Figure 3, the liner comprises three basic parts, a nose part 58 which is folded around the nose of the blade, and a top and bottom part 42 and 44, respectively. This particular division of parts may be preferable in some situations in which the nose part tends to erode faster than the major parts 42 and 44. The provision of a separate nose piece 58 may also be preferable in that this particular piece may be coated with a hard, chrome plating surface 60 if desired for a particular type of service.

It will be understood that ordinarily it is desirable to use liner parts which are of erosion-resistant alloy, such as a Haynes alloy 25 or Stellite 68, which are conventionally available sheet alloys. An example of one type of upset-type fastener which is considered satisfactory is a "Unilock" fastener as manufactured by the B.F. Goodrich Company. It will be appreciated that other types of threaded blind hole fasteners may alternatively be used in carrying out the invention.

In some installations, it may not be necessary to completely cover the skins of the airfoil-shaped blades with liner material, depending upon the type of service as well as the particular airflow pattern with a given fan. Thus, with the wheel as shown in Figure 1, it may occur that the erosion tends to be concentrated on that part of the blade closest to the backplate because of the inertia of the erosive particles as they enter the fanwheel axially and are then turned radially. In such a case, and depending upon experience, it may be necessary to line only the part of the blade which is closer to the backplate 10 than the plate 12, or to the centerplate for double width wheels.

From the foregoing, it will be appreciated that the invention with its novel fastening arrangement provides a readily replaceable liner without any protruding flanges to add weight or interrupt the smooth flow of air over the airfoil-shaped impeller blades.

Since these blades are fabricated weldments, allowing no access to opposite sides of top and bottom skins, conventional bolting techniques are precluded. Any holes drilled in welded airfoil-shaped blades are inherently blind by their construction.

Drilling and tapping such impeller blade skins is precluded by the limited thickness of the skins.

Claims (8)

1. A centrifugal fan wheel comprising axially spaced-apart plates, and a plurality of generally hollow, airfoil-shaped blades extending transversely between said plates in spaced-apart relation with respect to each other, each blade comprising an inner frame and skin assembly, and an exterior liner, said frame and skin assembly, over at least a major part of its extent, having a construction of ribs covered substantially completely with a skin and welded to said skin so as to form a rigid integral structure, said skin having a first array of countersunk openings formed therein, and said exterior liner covering the part of said skin having said first array of countersunk openings, and having countersunk openings formed therein in a second array registering with said first array, said liner being fastened directly to said skin with fastening means including internally threaded, upset-type fasteners secured to said skin, said upset-type fasteners being disposed in the respective countersunk openings of said first array and having heads which are seated therein, and externally threaded screws turned into the internally threaded upset-type fasteners through the countersunk openings of said second array so as to secure said liner to said skin in overlying relation with respect thereto.

2. A centrifugal fan wheel according to claim 1, wherein said liner is composed of an erosion resistant alloy.

3. A centrifugal fan wheel according to claim 1 or 2, wherein said liner covers the major part of the extent of said frame and skin assembly substantially completely.

4. A centrifugal fan wheel according to claim 1,2 or 3, wherein said liner covers the part of the frame and skin assembly lying in that portion of the airstream produced by the wheel, when in use, which carries the major loading of erosive particles.

5. A centrifugal fan wheel according to any one of the preceding claims, wherein said upset-type fasteners have flat heads.

6. A centrifugal fan wheel according to any one of the preceding claims, wherein said screws have flat heads seated in the respective countersunk openings of said second array.

7. A wheel according to claim 6, wherein the heads of said upset-type fasteners are of greater diameter than the heads of said screws.

8. A centrifugal fan wheel substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.