GB2312023A - Centrifugal fan - Google Patents

Abstract

A centrifugal fan has three parts. The first part 12 has a plurality of slots 22. The second part 11 has a shroud, a plurality of fan blades 20 and a boss 15 for mounting the fan. The fan blades of the second part locate within the slots of the first part. The first and second parts are moulded plastics material and the third part 13 is a hollow metal rivet which passes through the boss 15 and joins the first and second parts 11, 12 together while providing a metal insert for the boss 15 adapted for mounting on a shaft.

Description

CENTRIFUGAL FAN IMPELLER This invention relates to fans and in particular, to a centrifugal fan for use in or with small sized motors such as fractional and subfractional horsepower motors.

There are two basic types of fans, axial flow fans where the airflow is maintained in a single direction and centrifugal fans in which the direction of airflow is abruptly changed by 90" as the air passes through the fan. Each type of fan has its advantages and disadvantages and the present invention has particular application to shrouded or two part centrifugal type fans.

The centrifugal fan is arranged to be mounted on a shaft of a motor or similar to rotate with the shaft to draw air into the fan in an axial direction and expel the air radially.

The fan comprises a plurality of fan blades extending in a radial fashion between two radially extending plates or sides. At least one of the plates has an opening about the shaft forming the inlet of the fan and at least one of the plates has a boss for mounting the fan to the shaft.

The fan described so far is typical of prior art centrifugal fans with the boss mounting directly onto the shaft. While this is satisfactory for many applications, for some applications, the contact between the shaft and the boss of the fan may not be sufficient, for example, when the motor is required to operate under extreme temperature changes, e.g., A00C to 1 500C. When the fan is made of plastics material, in particular, thermosoftening material and the motor is operated under high temperature conditions or subjected to stall loading, the shaft may become sufficiently hot to cause the material of the boss to soften allowing the fan to slip on the shaft.

This problem is overcome by the present invention by providing a metal insert in the boss of the fan for mounting on the shaft thereby having a metal to metal contact between the shaft and the fan with good contact between the metal insert and the boss of the fan.

In addition, the fan is most economically made by injection moulding plastics material but due to the limitation of the moulding die, it must be made in two parts. Typically, these parts are joined together by gluing which is messy and time consuming or by welding, e.g., ultrasonic welding which is expensive. This may be avoided by using the metal insert to join the two parts together.

Accordingly, the present invention provides a fan comprising a plurality of fan blades located between two radially extending side members, at least one side member having an opening defining an inlet for the fan and at least one side member having a central boss wherein the central boss has a metal insert arranged to be mounted on a shaft to - cause the fan to rotate with the shaft.

Preferably, the metal insert is attached to both side members.

Preferably, the metal insert is a hollow rivet.

Preferably, both side members have a central opening through which the rivet passes to secure the two side members together and to the rivet.

Preferably, the side members and the fan blades are moulded plastics material and the fan blades are moulded integrally with one of the side members.

Preferably, the fan blades are formed integrally with the side member having the opening defining the fan inlet.

Preferably, the side member integral with the fan blades is also integral with the central boss.

Preferably, the other side member not integral with the fan blades has a plurality of slots in which the fan blades locate. The slots support the free sides of the blades to increase the rigidity of the blades without the need to glue or weld the blades to the other side member.

A preferred embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a plan view of the preferred fan embodiment; Figure 2 is a sectional elevation of the fan of Figure 1; Figure 3 is an enlarged detail of part B of Figure 2; Figure 4 is an exploded sectional view of the fan of Figure 1; Figure 5 is an assembled isometric view of the fan from above; Figure 6 is an assembled isometric view of the fan from below; - Figure 7 is an exploded isometric view of the fan from below; and Figure 8 is an isometric view from below of one part of the fan of Figure 7.

Figure 1 is a view of the preferred fan 10 viewed from above, looking at the inlet 14 to the fan. In this view, it can be seen that the fan is circular with a central opening forming the air inlet 14. Within the air inlet 14, a central boss 15 for mounting the fan onto a shaft is visible. The boss 15 has a metal insert in the form of a hollow metal rivet 13.

As shown in Figure 2, the fan has two side members 11, 12 forming a base and a shroud which extend on respective sides of fan blades 20. The fan blades may be straight or curved and may extend only radially or radially and circumferentially. The embodiment shown has straight blades 20 which extend radially and circumferentially.

The side members 11, 12 and the fan blades 20 are moulded from plastics material and the blades 20 are integrally moulded with the top side member 11. The top side member 11 also has the central opening defining the air inlet 14 and the central boss 15 through which the metal insert 13 is fitted. The lower side member 12 is substantially planar with a central hole 16. A recess 17 is formed around the central hole 16 on the outer surface to receive a flange 25 of the metal insert 13, more clearly shown in Figure 3. The inner surface of the lower side member has a number of recesses or slots 22 as shown in Figure 7 for receiving the free side edges 21 of the fan blades 20.

An annular groove 28 is also provided to assist with locating the upper side member 11 with respect to the lower side member 12.

As can be seen in Figures 2, 3, 4 and 7, the upper side member 11 is integral with the central boss 15 which is formed in the opening of the inlet 14. This is possible by using the fan blades 20 to connect the outer portion of the upper side member 11 with the central boss 15. This arrangement forms a plurality of windows 23 in the inlet 14, leading to the air passages 24 through the fan defined by the upper and lower side members 11, 12 and the fan blades 20.

The central boss 15 is shaped to assist in changing the direction of airflow. The boss 15 also has a recess 18 in its upper surface as shown more clearly in Figure 3 to accommodate the crimped end 26 of the rivet 13 while still providing an abutment surface 19 needed for accurate positioning of the fan on the shaft of a motor.

In the preferred embodiment, the metal insert 13 is a hollow rivet or ferrule. The rivet has one end preformed with a flange 25 which locates in the recess 17 in the outer surface of the lower side member 12. The rivet 13 passes through the hole i6 in the lower side member 11 and through the hole 27 in the central boss 15. The other end 26 of the rivet 13 is then deformed to fasten the two side members 11, 12 together by flaring the end of the rivet 13 and deforming it out into the recess 18 in the upper end surface of the boss 15. During the deforming step, care is taken to avoid reducing the diameter of the inner bore of the rivet as this size is important for making a good fit between the fan and the shaft.

Figure 8 illustrates the upper side member 11 with integral blades 20 and central boss 15 when viewed from below. The windows 23 between the blades 20 can be seen as can the hole 27 through the central boss 15. Also visible is an annular ridge 29 arranged to be placed in the annular groove 28 of the lower side member 12.

Claims (10)

Claims

1. A centrifugal fan comprising a plurality of fan blades located between two radially extending side members, at least one side member has an opening defining an inlet for the fan and at least one side member has a central boss wherein the central boss has a metal insert arranged to be mounted on a shaft to cause the fan to rotate with the shaft,

2. A fan according to claim 1 wherein the metal insert is attached to both side members.

3. A fan according to claim 1 wherein the metal insert is a hollow rivet.

4. A fan according to claim 3 wherein both side members have a central opening through which the rivet passes to secure the two side members together and to the rivet.

5. A fan according to any one of the preceding claims wherein the side members and the fan blades are moulded plastics material and the fan blades are integrally moulded with one of the side members.

6. A fan according to claim 5 wherein the fan blades are integrally moulded with the side member having the opening defining the fan inlet.

7. A fan according to claim 5 or 6 wherein the side member integral with the fan blades is also integral with the central boss.

8. A fan according to any one of the preceding claims wherein the side member not integral with fan blades has a plurality of slots in which the fan blades are located to support the free sides of the blades.

9. A three part centrifugal fan comprising a first part defining a base, a second part defining a shroud, a plurality of fan blades and a central boss and a third part comprising a hollow metal rivet securing the first and second parts together and providing the central boss with a metal insert adapted for mounting to a shaft.

10. A centrifugal fan substantially as hereinbefore described with reference to the accompanying drawings.