CZ31085U1 - An axial fan blade of a hybrid structure - Google Patents

Description

The fan blades, made mostly of steel (structural steels of classes 13, 14, 15) or aluminum alloys (Al-Cu-Si, Al-Si, Al-Zn-Mg and Al-Mg), are characterized by certain specific properties.

The blades are characterized by a relatively high weight, requiring an adequately dimensioned bearing in the impeller hub, which in turn increases the weight of the entire set disproportionately. The high weight of the blades and impeller causes an increase in the polar moment of inertia of the entire rotating system, which is an unfavorable factor, especially in operating modes with rapid speed changes, which increases the acceleration and deceleration times of the system. Complications associated with high weight are also impaired the possibility of handling especially large blades, eg during their assembly, replacement, balancing, repairs, etc.

Characteristic properties of metal blades are relatively demanding production and high production costs given by the purchase price of input materials / semi-finished products, high energy demands on processing, expensive machinery and final processing of semi-finished products with a significant proportion of machining and manual finishing.

Metal shovels are usually made:

a) Casting with subsequent machining

b) Forging with subsequent machining

c) Machining from metallurgical semi-finished products

d) Welding from rolled semi-finished products

The most common technology for processing aluminum alloy blades is sand casting, gravity casting into metal molds or die casting. Steel blades are most often made by forging or welding.

In all cases, these are relatively expensive manufacturing technologies, especially when combined with machining operations, which are often necessary to achieve the desired geometric accuracy. After machining or welding operations, tool traces need to be smoothed, requiring a high proportion of manual and therefore expensive work.

A frequent finishing operation for casting vanes is the repair of defects such as typically surface thinning, shrinkage, slag, sand sites, depressions, bubbles or porosity.

Forgings, internal cavities and cracks are the most common defects in forgings.

Defects, if noticeable and accessible from the surface of the part, are usually repaired by hand grinding with subsequent sealing.

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The production of metal blades by casting, forging and welding requires costly metallurgical and machinery equipment (melting furnaces, holding and dosing furnaces, refractory casting molds, presses, hammers, etc.) and is energy and environmentally burdensome.

Resume:

- Advantages of metal blades are high mechanical resistance and durability, good temperature resistance and relatively easy repair. With good surface protection, metal blades are characterized by high durability and low maintenance.

- Metal blades are characterized by a high weight with all the consequences of rotor and fan operation.

- Due to the high initial investment in machine and fixture facilities, the metal version of the blades is the optimal solution for medium and large production runs.

b) Wood-composite and wooden blades

This category includes both pure wood and so-called wood-composite blades, consisting of a wood core provided with a composite reinforcing element, mostly in the form of an outer laminated shell.

The blades are mostly made of ash, beech or laminated wood, or combinations of these materials and are characterized by certain specific characteristics:

The low specific gravity of the starting material is essential; in the case of the application of ash wood, it is the lowest of the material variants mentioned herein. This results in favorable dynamic properties of the rotor, especially low polar moment of inertia of the whole rotating system.

The production of wood blades and cores of wood-composite blades usually consists in gluing the semi-block from the blanks of selected, aged wood and then machining the block to the desired shape. Machining is performed on copy milling machines, single-purpose NC machines or universal multi-axis CNC milling machines. Machining is usually followed by manual finishing of the surface to smooth the tool marks. In the case of wooden blades, the surface is finally treated with an impregnation and varnishing system.

The cores of wood-composite blades are provided with a composite shell usually by hand laminating eg glass (carbon, aramid, etc.) and thermosetting (epoxy, polyester, etc.) binder. As in the case of wooden blades, the surface is finished by sealing, grinding and painting.

Alternatively, the laminate-composite shell may be made by wrapping the blade core with a dry reinforcing fabric followed by injection of a polymeric binder in an airtight sealed form (Resin Transfer Molding method). In this case, it is advantageous to apply a surface pre-gel to the mold, thereby avoiding a lengthy surface treatment.

The general disadvantage of wood and wood-composite blades is the relatively low mechanical and air-conditioning resistance in operation and a high proportion of skilled handwork in production. The technology is suitable for piece production and less demanding applications.

c) Shovels of composite materials

It is meant products made of composites based on polymer matrix and fiber reinforcement with high modulus of elasticity. Composite fan blades are characterized by certain specific characteristics that can be summarized as follows:

The blades excel in low weight and high stiffness resulting from low density and high modulus of composite material.

The low weight of the blades is associated with favorable polar moment of inertia of the rotor, with the high values of modules the high values of the natural frequencies of the blade (see Table), which is a favorable factor for the resonant behavior of the blade in operation.

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Low viscosity epoxy, polyester or vinyl ester binder systems are frequently used as composite matrices, the fiber reinforcing phase being composed of glass, carbon, aramid, or hybrid fabrics of various bonds.

Wet contact lamination and infusion technologies predominate in manufacturing technologies. A considerable percentage of blades have recently been made by pressing from prepregs. The blades are either classic, ie. rib-girder, glued construction or shell-sandwich with foam filling of the blade cavity.

As follows from Table l (Pompe. Vilém ... [online]. 2010 [cit. 2017-01-19]. Available from http://www.csm-kompozity.wz.cz/Pompe_OS_2010_vl.pdf) Comparing the key parameters of the model blade made in different material variants, composite materials are the optimal choice for the construction of this type.

material version of the blade blade weight m [kg] polar moment of inertia J _p [kg.m ² ] First natural frequency f [Hz] steel 94.1 309.8 26.0 aluminum alloy 32.8 107.9 26.3 composite carbon / epoxy 11.4 30.6 31.8 ash wood 9.7 31.7 22.5

The standard process for preparing and manufacturing composite vanes consists of several steps:

(a) Structural design. Aerodynamic, strength and dynamic design is most often performed using the finite element method (FEM) using the appropriate software. The design must also include a modal analysis of the composite structure, consideration of the long-term environmental impact and the incorporation of protective elements (protection against impact and abrasion damage, anti-icing measures, etc.).

b) Fixing the geometric shape of the blade is followed by the production of the parent model. The mother model is made of hardwood (alder, maple, beech), special polymer block materials or metal. Models are made by machining, followed by manual finishing according to templates and gauges. The surface finishes with a perfect finish.

Note: In terms of cost, the acquisition of the model and its subsequent formation, due to the high demands on precision and the resulting laboriousness, represents a significant initial investment, which constitutes a substantial proportion of the input cost of producing a blade.

c) Design and production of the mold. The mold made of composite material is an optimal solution for the required low production volume. The composite mold is made by molding - imprinting the parent model after the previous modeling of the separating surface. The mold itself is usually made by a wet contact lamination method or by a vacuum-infusion method. In addition to the mold, it is necessary to design and manufacture a number of single-purpose auxiliary products (forming tools, cutting and storage templates, etc.).

The parent model, the form and the auxiliary products must be obtained for each stage of series production, ie also for piece production. In order to achieve profitability, the manufacturer is forced to translate the high costs associated with this into the price of the product in the form of depreciation. In the case of single-piece and small-series fan production, this factor is particularly negative. The proportion of depreciation of the parent model, production forms and ancillary products in the cost of production is inversely proportional to the volume of production and represents a decisive share (70 to 90%) of the product price.

Generally, the activities related to the technical preparation of the composite blade production are not only characterized by high demands on the amount of skilled handwork, but are also very time consuming. The on-going technical preparation time of composite blade production from order to first piece production actually takes three months or more and requires initial investment of the order of

-3EUR 31085 Ul in millions of CZK. Quickly mastering this low-cost process is an important factor that can be critical to winning a contract in a competitive environment.

Existing solutions provide little room for improving production profitability. Reducing the costs of technical preparation of the production and the production of the blade can be achieved only by implementation of innovative design, new materials and production processes.

The essence of the technical solution

The essence of the technical solution is a hybrid blade construction, combining composite construction elements based on high-modulus fibers and polymer matrix, with elements created by additive 3D printing technology. (Additive 3D printing is a production method that produces a solid physical object based on a three-dimensional digital model, usually by machine laying a large number of thin layers of material, usually polymer or metal).

The blade construction is formed by a shape-precise, thin-walled, split outer shell, made by the additive 3D printing method, on whose inner (reverse) side are deposited layers of composite, which form the supporting structure of the blade.

The outer shell thus forms the visible and exposed side of the blade, which at the same time serves as a mold for receiving the inner, supporting layers of the composite. The outer shell may be formed of a polymeric material, a fiber or particulate filled polymeric material, or a metal.

For manufacturing reasons, the blade is divided along the leading and trailing edges into two parts: the so-called pressure and so-called suction part. This concept is illustrated schematically in FIG. 2.

In principle, the outer, printed blade shell can be made by any additive printing technology, but the SLS (Selective Laser Sintering) or FDM / FFF (Fused Deposition Modeling) method is most suitable for the application. If the size of the printing chamber does not make it possible to produce (print) the outer shell in one unit, it can be divided into several appropriately large parts connected to each other eg by a suitable mechanical lock Fig. 4.

The deposition of the composite carrier layers on the inner side of the outer shell can in principle be performed in one of the following standard ways:

- wet contact lamination

- vacuum-infusion method

- low temperature prepreg

After the composite support layers have been laid and cured, both paddles are assembled and glued to the leading and trailing edges. The connection can be made, for example, in the manner shown in Fig. 6 (leading) and Fig. 7 (drain).

A metal root insert is placed and glued into the root part before assembly of both parts of the blade.

The basic principle and the main advantage of the technical solution is the fact that the printing of the outer shell eliminates the need to use the parent model and the mold for the production of the blade, which leads to significant cost savings and continuous production time.

The technical solution makes it possible to apply a variety of functionally modified polymers (filled, colored, hydrophobic, reinforced, UV filter, transparent, etc.) for the outer shell. Other functional elements such as heating, cooling, etc. can be more easily integrated into the blade structure. Applying the printed structure to the outer, exposed surface of the blade also increases the toughness of the composite structure and provides better resistance to impact damage and abrasion in operation.

The main benefits of the technical solution are:

(a) the exclusion of parent models from the technical preparation process of blade production

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(b) the elimination of molds and auxiliaries from the production of the blade

c) fast and efficient piece and small series production of blades

(d) significantly shortening the product's production cycle and reducing input costs;

e) application of a thermoplastic polymer or metal to the surface of the blade improves the performance of the article

Clarification of drawings

The technical solution is explained in more detail in the figures, where:

Fig. 1 shows schematically a paddle, which is the subject of the utility model; Fig. 2 shows the separation of the paddle along the leading and trailing edge into the suction and pressure parts; Fig. 3 shows the suction and pressure parts of the outer shell and the carrier composite layer. 5 shows the alignment of the outer shells on the base plates and the method of assembling the blade FIG. Fig. 8 shows the suction part of the outer shell provided with a reinforcing rib. Fig. 9 shows a composite support layer consisting of a matrix and continuous fibers.

Example of technical solution implementation

The axial fan blade of the hybrid structure shown in FIG. 1 is a rectangular plan view and an asymmetrical curved profile.

The blade consists of two parts: tongue I and root 2.

The dimensions of the blade I of the blade are: length 1200 mm, depth 650 mm, maximum profile thickness at the root 50 mm, maximum profile thickness at the tip 16 mm.

The root 2 is of circular cross section with a diameter of 95 mm and a length of 120 mm.

On the leading edge 5 and the trailing edge 6, the blade tongue 1 is divided into a so-called pressure part 4 and a so-called suction part 3. Both the pressure part 4 and the suction part 3 consist of two rigidly connected layers, namely the outer shell 7 of the suction part 3 and the outer shells 9 of the pressure part 4 formed by the additive 3D printing method and the inner backing layers of the composites 8 and 10 formed by the fiber composite 15. Both the blade part - the pressure part 4 and the suction part 3 - are glued to the leading edge 5 and trailing edge epoxy adhesive 18 (FIGS. 6 and 7). The outer shell 7 of the suction part 3 and the outer shell 9 of the pressure part 4 are provided with a system of reinforcing ribs 11 on the outer, face surface. The zebra 11 are rigidly but detachably connected to the surface of the outer shells 9 and 7 in the manner shown in FIG. The reinforcing ribs 11 are also formed by the additive 3D printing method, simultaneously with the printing of the outer shells 9 and 7. The ribs 11 serve to shape stabilize the outer shells 9 and 7 during manufacture and are separated after production. Copies of the outer shells 9 and 7, including the ribs H, have a constant thickness of 1.5 mm and are made using the Selective Laser Sintering (SLS) printing technique of Polyamide PA12.

The fiber composite backing layers jsou5 consist of an epoxy matrix 17 reinforced with continuous carbon fibers 16. The internal backing layers of the composites 8 and 10 consist of a plurality of individual layers arranged to transfer the mechanical stress of the blade. In the root 2 an aluminum alloy root insert 14 is embedded and glued in between the pressure part 4 and the blade suction part 3.

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The impression of the outer shell 9 of the pressure part 4 and the impression of the outer shell 7 of the suction part 3 are aligned and fixed over the ribs 11 on the base plates 12 and 13 during manufacture of the blade.

The process of manufacturing the blade can be summarized in the following steps:

1. Production of the two parts of the outer shell 7 and 9 in a 3D printer using the SLS (Selective Laser Sintering) method, including the ribs ii- If the dimensions of the workspace of the printer do not allow printing in one piece, it can be assembled from multiple segments connected (an example of the shape lock is shown in Fig. 4).

2. Align and fix the printout of the outer shell 9 of the pressure part 4 on a flat base plate 12.

3. Analogously: aligning and fixing the printout of the outer shell 7 of the suction part 3 on a flat base plate 13.

(Note: The base plates 12 and 13 serve to shape stabilize the outer shell 7 and the outer shell 9 before sticking the blade).

4. Laying the carrier layers of the composites 8 and 10 by the wet lamination method on the inside of the prints of the outer shell 7 and 9.

5. Cure the layers of composites 8 and 10 at 60 ° C for 24 hours.

6. Gluing the pressure part 4 and the so-called suction part 3 of the blade with epoxy glue 18,

7. Cure adhesive J8 at room temperature for 24 hours.

8. Separation of base plates 12 and 13.

9. Cutting of reinforcing ribs 1L

Claims (5)

PROTECTION REQUIREMENTS An axial fan blade of hybrid construction, characterized in that it consists of a tongue (1) and a blade root (2), wherein the blade tongue (1) is divided into a pressure part (5) and a trailing edge (6) at the leading edge (5). 4) and a suction part (3), wherein the pressure part (4) and the suction part (3) consist of two rigidly connected layers, namely the outer shell (7) of the suction part (3) and the outer shell (9) of the pressure part (3). 4), formed by the additive 3D printing method and from the inner backing layers of the composites (8) and (10), consisting of a fiber composite (15) with an epoxy matrix (17) reinforced with continuous carbon fibers (16). The blade according to claim 1, characterized in that the two parts of the blade, the pressure part (4) and the suction part (3), are adhered to the leading edge (5) and the trailing edge (6) by epoxy adhesive (18). A scoop according to claim 1, characterized in that the outer shell (7) of the suction part (3) and the outer shell (9) of the pressure part (4) are provided with a system of reinforcing ribs (11) on the outer face. the ribs (11) are firmly but releasably connected to the surface of the outer shells (9) and (7). The blade according to claim 1, 2 and 3, characterized in that base plates (12) and (13) are used to stabilize the outer shell (7) and outer shell (9) before gluing, which are separated after the product has been made. The blade according to claim 1, 2, and 3, characterized in that in the root (2) an aluminum alloy root insert (14) is inserted and glued in between the pressure part (4) and the blade suction part (3).