GB2067672A

GB2067672A - Centrifugal blower impeller

Info

Publication number: GB2067672A
Application number: GB8002039A
Authority: GB
Original assignee: Mercantile Oy AB
Current assignee: Mercantile Oy AB
Priority date: 1980-01-22
Filing date: 1980-01-22
Publication date: 1981-07-30
Also published as: GB2067672B

Abstract

The front and/or back plate of the impeller consists of a center disc 3 and a radially outer ring of smaller thickness than the center disc and formed of segments 4 which are first welded to the center disc 3 and thereafter radially to each other so that the segments are subject to tensile stress and the center disc to compressive stress. <IMAGE>

Description

SPECIFICATION Impeller in a centrifugal blower The present invention relates to an impeller in a centrifugal blower, the front and/or back plate of the impeller being made up of a center part and a radially outer part attached to it and having a material thickness smaller than that of the center part. The front and back plates of the impeller are plate disks. In rotating plate disks, stresses increase towards the hub. The stresses are tensile.

Obtaining a disk of even strength by reducing its thickness towards the periphery is previously known. Likewise, the manufacture of impellers by welding is part of current technology.

Furthermore, prestressing of structures is used in both construction technology and mechanical engineering, as is also prestressing by means of welding. It is also known that different stresses prevail in different parts of the impeller of a blower, and owing to the aerodynamic form it has not been possible entirely to even out these stresses by varying the thickness of material.

Prestressing of the structure is in this case the only usable method by which stress peaks can be lowered. Several attempts have been made. In one structure the front plate is tied to the hub by means of tensing bars, which are prestressed. The characteristics that attempts of this type have in common is that they require additional parts which result in additional costs, limit the blower's uses and lower the performance of the blower. In the case mentioned, the tensing bars increase the noise produced by the blower and lower its efficiency. The lowering of stress peaks achieved by these means is quite modest.

The present invention eliminates the above disadvantages. The characteristics of the invention are given in the accompanying claim.

The technical solution according to the invention combines, in a novel and original manner, the techniques known per'se. Four substantial advantages are gained by dividing the outer ring (rings) into segments: 1. Prestressing of the structure is possible without affecting the performance of the blower.

2. The prestressing can be performed without increasing the manufacturing cost. No additional parts are required, and the welding costs do not increase immoderately, since rather large impellers in particular must usually be made from several parts in any case. On tha other hand, owing to the division into segments, the waste of material can be reduced to such an extent that the total costs are even lowered, especially when using material more expensive than normal steel.

3. As an additional advantage of the prestressing of the impeller, the outer part of the front and back plates can simultaneously be made lighter. Owing to the high manufacturing costs the general use of this structure, known to be advantageous, has not been possible in blowers.

4. Prestressing can be performed within the framework of normal production without separate tools, measuring devices, etc. The method is highly secure in terms of manufacturing techniques. There is no risk of a release of the prestressing by the loosening of the tightening members, for example.

If the outer parts of the disk are assembled from ring segments which are welded to the center part and thereafter radially to each other, a tensile stress is produced in the ring segments and a compressive stress in the center part. By a suitable selection of the number of joints and the thicknesses of material, it is possible, by conventional welding techniques, to construct impellers which have a constant stress throughout the front and back plates during operation. This allows considerably higher peripheral velocities and pressures than those achieved using nonprestressed impellers.

One preferred embodiment of the invention is described below with reference to the accompanying drawing, but without limiting the invention to this embodiment.

Figure 1 of the drawing depicts the back plate of the impeller as a plane representation and Figure 2 depicts a sectioned side view of this plate. Figure 3 depicts the waste material produced in the manufacture of a known outer ring of the impeller, and Figure 4 depicts the waste material produced in the manufacture of ring segments according to the invention.

The ring segments 4 have first been attached by welding to the periphery of the center part 3 of the back plate mounted on the hub 1 of the impeller according to Figures 1 and 2. Thereafter these ring segments 4 have been welded radially to each other, and thus tensile stress is effective in the ring segments 4 and compressive stress in the center part 3.

The shading in Figure 3 shows the waste material produced in the manufacture of a prior known whole outer ring of an impeller, and the shading in Figure 4 shows the water material produced in the manufacture of ring segments according to the invention, the waste being considerably less than in the case of Figure 3.

1. A centrifugal-blower impeller the front and/or back plate of which consists of a center part and a radially outer part which has been attached to the center part and has a smaller thickness of material than the center part, characterized in that the said outer part has been made of ring segments attached by welding to the periphery of the center part, having first been welded to the center part and thereafter radially to each other so that the ring segments are subject to tensile stress and the center part to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Impeller in a centrifugal blower The present invention relates to an impeller in a centrifugal blower, the front and/or back plate of the impeller being made up of a center part and a radially outer part attached to it and having a material thickness smaller than that of the center part. The front and back plates of the impeller are plate disks. In rotating plate disks, stresses increase towards the hub. The stresses are tensile. Obtaining a disk of even strength by reducing its thickness towards the periphery is previously known. Likewise, the manufacture of impellers by welding is part of current technology. Furthermore, prestressing of structures is used in both construction technology and mechanical engineering, as is also prestressing by means of welding. It is also known that different stresses prevail in different parts of the impeller of a blower, and owing to the aerodynamic form it has not been possible entirely to even out these stresses by varying the thickness of material. Prestressing of the structure is in this case the only usable method by which stress peaks can be lowered. Several attempts have been made. In one structure the front plate is tied to the hub by means of tensing bars, which are prestressed. The characteristics that attempts of this type have in common is that they require additional parts which result in additional costs, limit the blower's uses and lower the performance of the blower. In the case mentioned, the tensing bars increase the noise produced by the blower and lower its efficiency. The lowering of stress peaks achieved by these means is quite modest. The present invention eliminates the above disadvantages. The characteristics of the invention are given in the accompanying claim. The technical solution according to the invention combines, in a novel and original manner, the techniques known per'se. Four substantial advantages are gained by dividing the outer ring (rings) into segments:

1. Prestressing of the structure is possible without affecting the performance of the blower.

2. A centrifugal-blower impeller constructed and adapted to operate substantiaily as hereinbefore described, with reference to, and as shown in, Figures 1, 2 and 4 of the accompanying drawings.

The ring segments 4 have first been attached by welding to the periphery of the center part 3 of the back plate mounted on the hub 1 of the impeller according to Figures 1 and 2. Thereafter these ring segments 4 have been welded radially to each other, and thus tensile stress is effective in the ring segments 4 and compressive stress in the center part

3.

1. A centrifugal-blower impeller the front and/or back plate of which consists of a center part and a radially outer part which has been attached to the center part and has a smaller thickness of material than the center part, characterized in that the said outer part has been made of ring segments attached by welding to the periphery of the center part, having first been welded to the center part and thereafter radially to each other so that the ring segments are subject to tensile stress and the center part to compressive stress.