JP2007239675A - Centrifugal blower reducing stress concentration at joint part of blade plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce stress concentration at a joint part of a blade plate in a centrifugal blower having a backward facing impeller. <P>SOLUTION: A cut-out part having a predetermined shape is provided in an end fringe part of the blade plate in the vicinity of a connection part with a shroud to reduce stress concentration at the joint part of the blade plate. A shape of the cut-out part is composed of side wall parts being parallel for each other and a curved bottom part connecting both of side wall parts mutually. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a centrifugal blower having a rear-facing impeller that is used as a ventilation facility in various air supply / exhaust, painting facilities, dust collectors, factories, and the like.

The rear impeller of the centrifugal blower has the exit portion of the blade plate facing in the radial direction, the exit angle of the blade plate is facing backward (30 ° to 60 °), and is molded in a curved shape from the inlet portion to the outlet portion. The slats are welded or riveted to equal thickness main and side plates. Further, the main plate is welded or riveted to a hub formed to form a flow path at the impeller inlet. In addition, an annular portion called a shroud is connected to the outer edge of the impeller by welding or the like at the inlet of the impeller to facilitate the introduction of air into the impeller.
JP 2001-82383 A JP 2000-310197 A

  Stress concentration accompanying the rotation of the impeller tends to occur at the connecting portion between the blade plate and the shroud, and the blade plate and the shroud are often separated or broken. In order to prevent this and to reduce the size and performance of the impeller, each blade is bent (Patent Document 1) or the thickness of the blade is increased (Patent Document 2). It is set as the structure which adds a reinforcement rib in the middle. In this case, however, the weight and material cost of the impeller are increased. In addition, the increase in the weight of the impeller leads to an increase in the inertia weight of the impeller, the startup time during fan operation becomes longer, and the problem that it cannot be started with a general-purpose motor torque, and in the general-purpose motor overload protection device, There is a problem that starting failure occurs due to malfunction. Furthermore, there is a problem that it becomes uneconomical in terms of resource saving and energy saving by using a special motor or a motor overload protection device in order to make the blower startable.

  Therefore, according to the present invention, in the rear impeller of the centrifugal blower, a notch portion having a predetermined shape is provided at the edge of the blade plate near the connection portion with the shroud. The shape of this notch part is composed of side wall parts parallel to each other and a curved bottom part connecting the both side wall parts to each other. It has a shape that does not.

  The depth of the notch is in the range of 2 to 3 times the distance from the connecting portion between the blade and the shroud to the notch, and the curvature radius of the curved bottom is the stress concentration factor of the notch. It is determined to be within the range of 2.5 to 3.5. Further, the distance from the connection portion between the blade plate and the shroud to the cutout portion is determined so as not to affect the motion performance and to reduce the stress concentration acting on the connection portion between the blade plate and the shroud.

  Since the centrifugal blower of the present invention is configured as described above, the stress flow distribution at the impeller inlet connection portion is changed, and the stress concentration on this portion can be reduced. Therefore, it is not necessary to examine the thickness of the blades in order to withstand the stress concentration, and sufficient strength can be maintained with the wall thickness of the conventional impeller. As a result, the weight of the impeller keeps the inertial mass low, eliminating problems associated with conventional products such as insufficient starting torque and malfunctioning of the motor overload protection device, as well as energy savings. Thus, an economic effect can be obtained.

  One embodiment of the impeller of the centrifugal blower of the present invention is shown in FIG. The rear impeller 1 includes a blade blade 2, a shroud 3, an impeller disk 4, and an impeller hub 5. The blade 2 is provided with a notch 6 at the outer edge near the joint with the shroud 3.

については、次のような式１の関係が成り立つ。 The shape of the notch 6 includes a side wall 7 that is parallel to each other and a curved bottom 8 that connects both side walls to each other. 2A, 2B, and 2C show the basic shape of the notch and its modification. Notch depth d, and distance from blade to shroud connection to notch

With respect to, the following equation 1 holds.

In addition, the curvature radius ρ of the curved bottom is determined so that the stress concentration coefficient α of the notch is in the range of 2.5 to 3.5. Equation 2 shows the relationship between the applied stress σA at the inlet connection between the blade and the shroud and the notch depth d. However, σ ₀ indicates the acting stress at the inlet connection portion between the blade and the shroud when there is no notch.

  The degree of stress concentration reduction due to the influence of the notch depth d is shown in FIG. 3 as a stress concentration reduction graph. Furthermore, FIG. 4 shows the degree of stress concentration between the impeller having a predetermined notch in the blade and the conventional impeller according to the present invention. Thus, even if the plate thickness of the blade is reduced by about 25 to 30% compared to the conventional case where there is no notch, the acting stress σ at the inlet connection portion of the blade and the shroud can be reduced to 30 by providing the notch. Reduced by ~ 40%.

  Since the blower of the present invention is configured as described above, in the centrifugal blower having the rear impeller, when the blade plate is welded or riveted to the main plate and the side plate of equal thickness, the stress concentration applied to the joint portion is compared. Since it can be reduced by a simple configuration, it can be applied to a wide variety of uses as a relatively large variety of air supply / exhaust, painting equipment, dust collectors, factory ventilation equipment, and the like.

It is a sketch of one Example of the impeller of the centrifugal blower of this invention. The basic shape (A) of the notch part of this invention and modification (B), (C) are shown. It is a graph which shows the reduction degree of the stress concentration by the influence of the notch depth d. It is a graph which compares and shows the degree of the stress concentration of the impeller which provided the predetermined notch part in the braid | blade, and the conventional impeller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Backward impeller 2 Blade blade 3 Shroud 4 Impeller disk 5 Impeller hub 6 Notch

Claims (2)

A centrifugal blower in which a notch having a predetermined shape is provided at a peripheral edge of a blade plate in the vicinity of a connection portion with a shroud to reduce stress concentration on a joint portion of the blade plate in a rear impeller of the centrifugal fan. The shape of the said notch part is a centrifugal blower of Claim 1 which consists of a side wall part mutually parallel, and the curved bottom part which connected this both side wall part mutually.

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