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How to connect large industrial fan blades

Update:11-01-2020
Summary:

Large industrial fans, because of the longer blade leng […]

Large industrial fans, because of the longer blade length and heavier blades, make the root connection of the blade to withstand greater loads, the size of the blade root structure is large, and the blade root is the weak link of the overall structure, and there are many failure modes of the connection, and Strength prediction is difficult, so the root connection of the blade is critical.

At present, there are three main ways of connecting the roots of industrial fan blades on the market: T-bolts, embedded bolts, and implanted bolts.

T-bolt connection is to make a circle of bolt holes uniformly in the circumferential direction perpendicular to the end surface of the root, and to make a round nut hole in the radial direction perpendicular to the bolt hole at the corresponding orientation of the bolt. One end of the double-headed screw is connected to a round nut and the other end is connected to a bearing mounted on the hub. The double-headed bolt and nut form a T-shaped structure, so this connection is called a T-bolt or cross-bolt connection. This is a reference. Connections for large power generation windmill designs. Since the bolt holes and round nut holes are made after the blade is formed, the drilling accuracy is also guaranteed by the equipment. There is no need to consider root connection issues during the production of fan blades, nor will it be caused by curing shrinkage during the blade manufacturing process. It affects the accuracy of the root connection, so the manufacturing of the blade is relatively simple, which is especially suitable for companies that produce industrial fan blades in an assembly line.

Embedded bolt connection, consisting of embedded bolt sleeve and double-headed screw. The outer surface of the embedded bolt sleeve has wavy or toothed annular protrusions, and the surface is sandblasted to improve the cleanliness and roughness of the surface. Before use, the groove is filled with a continuous glass fiber bundle. Because the root of the blade is formed by bonding two semi-cylindrical molds together, the accuracy of mold clamping also directly affects the accuracy of bolt connection. The end face of the blade root of the embedded bolt connection is generally no longer trimmed, and the flatness is guaranteed by the flatness of the mold end face after molding and mold clamping. Therefore, the manufacturing of the embedded bolt connection places higher requirements on the rigidity of the mold root, the manufacturing accuracy and structural rationality of the embedded bolt positioning tooling, as well as the mold clamping accuracy and manufacturing process of the blade mold, which also increases the quality of the blade The probability.

Implanted bolt connection is to make axial connection bolt holes on the end surface of the blade root according to requirements. Steel connection anchors are implanted into the axial connection bolt holes and bonded with epoxy adhesive. However, this method makes the steel connection anchor unable to be replaced. An improved method is to implant a connector similar to the embedded bolt sleeve in the axial connection bolt hole, and then use a double-headed screw to connect with the host.

Compared with the embedded bolt connection, the T-bolt connection has the advantages of simple root ply structure, convenient manufacturing and short mold time, but the shortcomings of round nut holes will weaken the strength of the blade root, which determines the maximum number of bolts. Not as many as other connection methods, limiting the application on large blades. The embedded bolt connection technology has the following advantages:

1. Shortened process flow. Embedded bolts are manufactured when the blades are formed, without the need to go to the next job for drilling like the T-bolt connection, which reduces circulation and shortens the production cycle.
2. Reduce the investment of special punching equipment required for high precision, and no special punching station is needed, reducing the floor space.

3. To avoid the problem of weakening the strength of the root caused by the horizontally rounded screw holes of the blade root caused by the T-bolt connection. Under the same root diameter, the number of bolts can be effectively increased to increase the connection strength. This advantage determines that although there are many shortcomings in the embedded bolt connection, it will be more and more applied as the leaf shape continues to increase.

The embedded bolt connection technology has the following disadvantages, which requires special attention when designing and manufacturing:

1. The dimensions and tolerances of the embedded bolt connection and the flatness of the blade root connection end face are determined by the positioning of the embedded bolt sleeve during the blade manufacturing process, which is difficult to adjust later.

2. The positioning of the embedded bolt sleeve must also consider the air tightness during the vacuum infusion process of the blade. If it is not handled properly, air leakage will easily occur, resulting in product quality problems that require maintenance or even scrap. The problem that the positioning bolts of the bolt sleeve cannot enter the resin cannot be removed.

3. It increases the difficulty of manufacturing and quality control of the blade root.

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