FAN BLADE AND METHOD OF MAKING SAME

Abstract

 In known fan blade has a base body (2; 12) with a front edge (7; 17), which front edge is at least partially formed by an edge complementary member (6). In order to provide a fan blade for use in environments with dust-containing or droplet-containing gases, which is has a long service life, so that the downtimes of the plant are reduced, it is suggested that a round groove (5) runs in and along the front edge (7; 17), and in that the edge complementary member is formed as a round bar (6) which is inserted in the round groove (5).

Description

Technological background

[0001] The invention relates to an improvement in the blades of fans for sucking in and discharging dust-laden gases.

[0002] More particularly, the invention relates to a fan blade having a base body with a leading edge formed at least in part by an edge complementary member.

[0003] In addition, the invention relates to a method of manufacturing a fan blade, comprising the following process steps:

(a) providing a blade base body having a leading edge bounded,

(b) providing an edge complementary member,

(c) creating a recess extending along the leading edge, through which at least a portion of the leading edge is removed,

(d) Inserting the edge complementary member into the recess.

[0004] In exhaust systems in metal or glass processing, the petrochemical industry or steel production, fans (also referred to as "ventilators") are often used to draw in and discharge dust-laden gases. In these processes, dust particles or liquid droplets are entrained by the air and come into contact with the fan blades. These fan blades generally move at a very high peripheral speed, so damage to these blades occurs over time. Here, the wear on the leading edge of the blades is particularly high and determines their service life. Therefore, a variety of countermeasures have already been proposed to minimize wear on the leading edges of fan blades.

State of the art

[0005] To reduce wear, traditionally, the leading edge of the fan blade was hardened with a hardbanding of chromium carbide. When used in an environment charged with dust particles, the technical service life of the blade reinforced in this way is quite short, e.g. about 10 days. After that, the fan must be dismounted and re-hardbanding must be performed on the blade in the repair facility, which takes about 3 days.

[0006] Alternatively, the use of fan blade protection systems that utilize metallic caps attached to the leading edge of each blade is well known. The metal caps absorb the impact energy upon collision with the dust particles or liquid droplets and serve as sacrificial material in favor of the fan blade behind them. The caps wear out and must be replaced periodically. To do this, the cap must be removed and the underlying blade material repaired as needed. A new cap is then connected to the fan blade.

[0007] US 4,738,594 A describes a fan blade including blade protection and a method for its manufacture according to the generic art as mentioned above. The fan blade is designed for an axial fan. It comprises a base body made of steel or aluminum in a conventional manner. The base body has a leading edge covered with a leading edge cover member connected to the base body by screws. The leading edge cover member is made of stainless steel and includes a top side leading edge cover and a bottom side leading edge cover, each of which is formed into the desired shape by press molding. The leading edge of the base body is cut along its entire length to form a notch that extends along the leading edge and whose width is constant. An edge complementary member adapted to the geometry of the leading edge is inserted into the notch, and its upper and lower sides are welded to the leading edge covers. For example, the edge complementary member is made of a hard sintered body of metallic boron, a sintered body of a metal carbide such as tungsten carbide, or a sintered body of an inorganic oxide such as aluminum oxide. Welding to the leading edge covers is done by electron beam welding. The weld beads, which extend upward and downward, are then removed by polishing, and the leading edge covers and the edge complementary member are coated with hard chrome as required.

Technical task

[0008] The edge complementary member can be manufactured by cutting from a block of material. As this is extremely difficult with hard materials, such as a hard metal, it is alternatively proposed that a suitable powder is pressed into the desired shape and then sintered to produce an edge complementary member.

[0009] However, both of these methods require a great deal of time and material. The production of the blade leading edge protection using the known process requires numerous post-processing steps and complex tooling, which is associated with further significant production costs.

[0010] The fan blade known from US 4,738,594 A is intended for an axial fan. These often are operated at comparatively low rotational speeds. In various applications, however, high rotational speeds are required, resulting in high demands on the mechanical strength of the fan blades. For these applications, radial fans are often used.

[0011] The invention is therefore based on the task of specifying a method for manufacturing a fan blade which makes it possible to simplify and accelerate the manufacturing process for the leading edge protection and thereby keep the manufacturing costs low.

[0012] In addition, the invention is based on the task of providing a fan blade for use in environments with dust-containing or droplet-containing gases, which is characterized by a long service life, so that the downtimes of the plant are reduced, and which can also be used for radial fans.

General description of the invention

[0013] With respect to the fan blade, this task is solved by a fan blade having the features of claim 1.

[0014] The leading edge protection of the fan blade according to the invention is characterized in particular by the fact that a round groove runs in and along the front edge of the fan blade, and that the edge complementary member is designed as a round bar which is inserted in the round groove.

[0015] The round groove forms a longitudinal groove in the former leading edge of the base body of the fan blade. In cross-section, it encloses a segment of a circle and the groove bottom forms an arc of a circle. The edge complementary member is designed as a round bar with a radius approximately matching that of the round groove (the radius of the round bar may be slightly smaller than that of the round groove). The round bar forms the new leading edge of the fan blade. Due to its round shape it is somewhat less efficient in terms of flow mechanics than would be a sharp edge; however, round bars are easy to manufacture and are often even commercially available with the appropriate diameter as inexpensive semi-finished products and staple goods. And because of their simple round and non-complex shape, they exhibit high wear resistance, thus extending the service life of the fan blade.

[0016] The round bar is made of a wear-resistant material, preferably stainless steel, titanium carbide and, particularly preferably, tungsten carbide.

[0017] Tungsten carbide is characterized by a particularly high hardness of up to 2300 HV, and it is stable in air up to about 600°C. Round bars of tungsten carbide are commercially available. The round bar is preferably a solid rod.

[0018] Titanium carbide is characterized by a particularly high hardness of up to 4000 HV, and it is stable in air up to about 800°C.

[0019] The manufacturing costs are further reduced if the round bar is cylindrical - i.e. not conical.

[0020] The manufacturing effort is further reduced if the base body is made of a metal plate with a constant thickness d.

[0021] Such metal plates are also easy to manufacture and are often commercially available with the appropriate thickness as low-cost semi-finished products and staple goods, such as metal plates made of steel, aluminum or titanium.

[0022] One of the end faces of the metal plate forms the leading edge of the fan blade. The round groove for receiving the round bar is machined into this end face. The ratio between the outside diameter D of the round bar and the plate thickness d is preferably to be selected in the following range: 0.7·d < D < 1.1 d, and most preferred: 0.8·d < D < 1.05·d.

[0023] In the simplest case, the outer diameter of the round bar is the same as the thickness of the metal plate. A preferred diameter range of the round bar is for example 10 to 20mm, more preferably 12 to 16mm If necessary, it is suitable for completely covering the face of the metal plate. Smaller outside diameters are basically usable; however, they lead to initially higher wear of the base body (metal plate) in the area of the free, unprotected end face. Larger outer diameters are also conceivable in principle; however, they cause unnecessary weight and adversely affect the flow mechanics of the fan blade.

[0024] In a preferred embodiment, it is provided that at least a portion of the top surface of the base body is covered with an anti-wear layer.

[0025] The wear protection layer helps to extend the service life of the fan blade. It preferably has a thickness in the range from 1mm to 10mm, and consists of a base metal in which hard materials are incorporated which contain niobium, tungsten and/or vanadium, and which are present at least in part in the form of carbides, nitrides, borides, silicides or mixed phases thereof, especially chromium carbide or boron carbide.

[0026] Mixed phases are, for example, carboborides, carbonitrides and the like, which often have an even higher hardness than the simple components from which they are derived.

[0027] With regard to the method, the above-mentioned technical task is solved by a method having the features of claim 9.

[0028] The method of manufacturing the fan blade according to the invention is characterized in particular by the fact that a round groove is produced in the leading edge of a base body, and that a round bar is provided as an edge complementary member and inserted into the round groove.

[0029] The round groove forms a longitudinal groove in the former leading edge of the base body. It is created, for example, by cutting, drilling or sandblasting, and in the simplest case by milling. In cross-section, it forms a depression in the shape of a segment of a circle, with the bottom of the groove forming an arc of a circle.

[0030] The edge complementary member is designed as a round bar with a radius approximately matching the round groove; the radius of the round bar can be somewhat smaller than that of the round groove. The round bar is fixed in the round groove, preferably by soldering, and forms the "new" leading edge of the fan blade. Round bars are easy to manufacture and are often even commercially available with the appropriate diameter as inexpensive semi-finished products and stacked goods. And due to their simple round and non-complex shape, they exhibit high wear resistance, thus extending the service life of the fan blade.

[0031] The manufacturing effort required to produce the fan blade is further reduced if the base body is made from a metal plate with a constant thickness d.

[0032] Such metal plates are also easy to manufacture and are often commercially available with the appropriate thickness as low-cost semi-finished products and staple goods, such as metal plates made of steel, aluminum or titanium.

[0033] Further advantageous embodiments of the process according to the invention result from the dependent method claims. Insofar as the embodiments of the process indicated in the dependent method claims are similar to the embodiments mentioned in the dependent claims for the fan blade according to the invention, reference is made to the above explanations of the corresponding device claims for supplementary explanation.

[0034] The fan blade according to the invention is particularly suitable for the manufacture of a radial fan.

[0035] Radial fans are mainly used when high air flow rates and thus high fan speeds are required. Damage is particularly easy to occur in this case, which can be prevented or reduced by using fans according to the invention.

Description of preferred examples

[0036] The invention is explained in more detail below by means of preferred embodiments and a patent drawing. In detail, the following is shown in schematic representation

Figure 1

a first embodiment of the fan blade according to the invention for use in an axial fan in a plan view, partially in section;

Figure 2

a second embodiment of the fan blade according to the invention for use in a radial fan in a three-dimensional partial view.

[0037] The fan blade 1 shown in Figure 1 is construed for use in an axial fan. It consists of an elongated base body in the form of a metal plate 2, the entire plane upper side of which is covered with a wear protection layer 3 (Figure 1 shows a free section without the wear protection layer on the left side for better illustration). The metal plate 2 is connected on one of its narrow sides to a connecting piece 4. A round groove 5 is milled into one of the long end faces of the metal plate 2 over its entire length, into which a round bar 6 made of stainless steel is soldered. This end face forms the leading edge 7 of the fan blade 1.

[0038] The metal plate 2 is made of stainless steel. It is cut in fan-shaped plates having a length of 700mm and a maximal thickness of 10mm and a minimal thickness of 5mm at the leading edge.

[0039] The wear protection layer 3 consists of chromium carbide. It covers the entire upper surface of the metal plate 2 and has a thickness of 2mm. It is produced by laser hardfacing.

[0040] Circular groove 5 has a radius of 2.2mm, a depth of 2mm. The round groove 5 thus forms a longitudinal groove along the total length in the former front side of the metal plate 2. In a cross-sectional view the round groove forms a depression in the shape of a segment of a circle, with the bottom of the round groove describing an arc of a circle.

[0041] The round bar 6 is soldered into the round groove 5 over its entire length by means of hard soldering. Its length corresponds to the length of the round groove 5 and its diameter is 4mm. It covers the entire long end face of the metal plate 2 and forms the front edge 7 of the fan blade 1.

[0042] Where the same reference signs are used in Figure 2 as in Figure 1, these designate identical or equivalent components and parts, as explained in more detail above on the basis of the description of the first embodiment of the fan blade according to the invention.

[0043] The fan blade 10 shown schematically in Figure 2 is construed for use in an impeller of a radial fan.

[0044] The radial fan comprises an impeller with a plurality of curved blades 10. Each blade 10 consists of an elongated base body in the form of a curved metal plate 12. The leading edge 17 of the fan blade 10 is provided with a reinforcement member in form of a round solid rod 6 made of tungsten carbide.

[0045] The metal plate 12 has a constant thickness of 15mm and a length L of 210mm and made of steel.

[0046] A round groove 5 is milled into the leading edge 17 over its entire length to receive the tungsten carbide round rod 6. The round rod 6 is brazed into the round groove 5 so that the round bar 6 forms the entire leading edge 17 of the fan blade 10.

[0047] The round groove 5 forms a longitudinal groove in the former front side of the metal plate 12. In a cross-sectional view the round groove 5 forms a depression in the shape of a segment of a circle, with the bottom of the round groove 5 describing an arc of a circle. It has a radius of 7.1mm, a depth of 6mm and a length L of 210mm.

[0048] The round rod 6 is brazed into the round groove 5 over its entire length by means of hard soldering. Its length corresponds to the length L of the round groove 5 and its diameter is 14mm. It covers the entire long end face of the metal plate 12 and forms the front edge 17 of the fan blade 10.

[0049] Onto one of the plane surfaces of the metal plate 12, which is the front surface in operation of the radial fan, a wear protection layer 3 is applied. It consists of chromium carbide and has a thickness of 3mm. The wear protection layer 3 covers the entire front surface of the metal plate 12. It is produced by arc buildup welding.

[0050] The method of manufacturing the fan blade according to the invention is explained below by way of example with reference to Figure 2.

[0051] A blade base body is produced by cutting a commercially available rectangular metal plate 2 at an angle on one of its short sides and bent into the required curved shape. A round groove 5is milled on one of the opposite short sides.

[0052] The round rod 6 of tungsten carbide is brazed into the round groove 5 over its entire length (i.e. not just at points), which then forms the leading edge 17 of the fan blade 10. All fan blades of the impeller for the radial fan are manufactured in the same way and mounted on the impellers axis of rotation.

[0053] The service life of the fan blade, the leading edge of which is reinforced with the tungsten carbide rod, is increased by a factor of about 5 (from about 10 days to about 50 days) compared with the state of the art, in which the leading edge is provided with a hardband layer of CrC of comparable thickness. The reduced downtime of the plant thus leads to considerable cost savings.

Claims

1. Fan blade having a base body (2; 12) with a front edge (7; 17), which front edge is at least partially formed by an edge complementary member (6), characterized in that a round groove (5) runs in and along the front edge (7; 17), and in that the edge complementary member is formed as a round bar (6) which is inserted in the round groove (5).

2. Fan blade according to claim 1, characterized in that the round bar (6) is made of stainless steel, hard metal, titanium carbide and particularly preferably tungsten carbide.

3. Fan blade according to claim 1 or 2, characterized in that the round bar (6) is cylindrical in shape.

4. Fan blade according to one or more of the preceding claims, characterized in that the base body is made of a metal plate with (2; 12) constant thickness d.

5. Fan blade according to claim 4, characterized in that the round bar (6) has an outer diameter for which applies: 0.7·d < D < 1.1 d, preferably:
0.8·d < D < 1.05·d.

6. Fan blade according to claim 4 or 5, characterized in that the metal plate (2; 12) is made of steel or of aluminum.

7. Fan blade according to one or more of the preceding claims, characterized in that at least part of a plane surface of the base body (2) is covered with a wear protection layer (3).

8. Fan blade according to claim 7, characterized in that the wear protection layer (3) has a thickness in the range from 1mm to 10mm, and which consists of a base metal in which hard materials are incorporated which contain niobium, tungsten and/or vanadium, and which are present at least in part in the form of carbides, nitrides, borides, silicides or mixed phases thereof.

9. Method of manufacturing a fan blade (1; 10), comprising the following method steps:

(a) providing a blade base body (2; 12) having a leading edge (7; 17),

(b) providing an edge complementary member (6),

(c) creating a recess (5) extending along the leading edge (7; 17) through which at least a portion of the leading edge (7; 17) is removed,

(d) inserting the edge complementary member (6) into the recess (5), characterized in that said recess is formed as a round groove (5), and in that a round bar (6) is provided as an edge complementary member and is inserted into the round groove (5).

10. Method according to claim 9, characterized in that a round bar (6) made of stainless steel, hard metal, titanium carbide and particularly preferably tungsten carbide is provided.

11. Method according to claim 9 or 10, characterized in that a round bar (6) of cylindrical shape is provided and the round bar (6) is fixed in the round groove (5) by soldering.

12. Method according to any one of claims 9 to 11, characterized in that a base body made of a metal plate (2; 12) of constant thickness d is provided, the round bar (6) having an outer diameter D for which applies:
0.7·d < D < 1.1·d, preferably: 0.8·d < D < 1.05·d.

13. Method according to one or more of the preceding claims 9 to 12, characterized in that a wear protection layer (3) is applied to a plane surface of the base body (2; 12).

14. Method according to claim 13, characterized in that the wear protection layer (3) is applied with a thickness in the range of 1mm to 10mm, and consists of a base metal in which hard materials are incorporated which contain niobium, tungsten and/or vanadium, and which are present at least partially in the form of carbides, nitrides, borides, silicides or mixed phases thereof.

15. Use of a fan blade (10) according to one or more of the claims 1 to 8 or of the fan blade (10) manufactured by a method of one or more of the claims 9 to 14 for producing a radial fan.

Drawing