GB2126653A

GB2126653A - A method of assembling spaced discs of a centrifugal impeller

Info

Publication number: GB2126653A
Application number: GB08225419A
Authority: GB
Inventors: Andrew Henry Middleton
Original assignee: British Gas Corp
Current assignee: British Gas Corp
Priority date: 1982-09-07
Filing date: 1982-09-07
Publication date: 1984-03-28
Also published as: GB2126653B

Abstract

A method of assembling spaced members such as discs 1 forming the impeller of a centrifugal air fan comprises the steps of providing a plurality of aligned holes in the discs 1, temporarily holding the discs by means of a jig in the required spaced relationship with the holes aligned and inserting spirally fluted tubes 2 into the aligned holes so that they grip the peripheries of the holes and hold the discs in the spaced relationship, and then removing the jig. When an assembly of spaced discs 1 is incorporated in an air fan, bolts 6 passing through the tubes 2 and nuts 7 clamp the assembly to a back plate 14 which is driven by an electric motor 16. The discs, which are made of plastics or metal, each have a central air inlet opening 5 and are mounted in a casing 17 provided with an air outlet 18. <IMAGE>

Description

SPECIFICATION A method of manufacturing an assembly of spaced members and an assembly manufactured thereby This invention relates to a method of manufacturing an assembly of spaced members and to an assembly of spaced members manufactured by the method.

Such assemblies of spaced members find use in the construction of centrifugal air fans which have one or more series of flat or frusto-conical discs, each series of discs having air inlet opening at or spaced outwardly from their centres and being secured together face to face co-axially with substantially unobstructed spaces between them. Assemblies of spaced disc suitable for use in the construction of centrifugal air fans are usually held together by bolts which pass through the discs and are spaced apart by spacer pieces which surround the bolts between the individual discs. Hitherto the stacks of discs have been built up on locating tubes with spacer pieces between adjacent disc. The locating tubes may then be removed and replaced by the clamping bolts or the clamping bolts may be fitted through the tubes. This form of construction is both time consuming and expensive.Moreover, the presence of the spacer pieces tends to obstruct the air flow through spaces between the discs.

An object of this invention is to simplify the manufacturing of an assembly of spaced members.

According to one aspect of the present invention a method of manufacturing an assembly of spaced members comprises the steps of providing a plurality of aligned holes in the members, temporarily holding the members in the required spaced relationship with the holes aligned, inserting spirally fluted members into the aligned holes so that they grip the peripheries of the holes and secure the members in the spaced relationship, and thereafter removing the temporary holding arrangement.

The spirally fluted members may be spirally fluted pins or spirally fluted tubes.

The assembly of spaced members may comprise a multiplicity of plates arranged substantially parallel to each other and the plates may be from 0.1 mm to 2.0 mm in thickness.

The spaced members may be formed from metal or may be formed from plastics material.

The assembly of spaced members may be temporarily held in the required spaced relationship by a suitable jig.

Preferably the spirally fluted members are driven into the aligned holes in the assembly of spaced members by an axially applied force coupled with rotation at a rate appropriate to the spiral angle of the flutes.

The spirally fluted members may be heated prior to being driven into the aligned holes. The spirally fluted members may be ultrasonically vibrated while being driven into the aligned holes.

The invention also resides in an assembly of spaced members manufactured by the method defined in the seven preceding paragraphs.

According to another aspect of the invention a centrifugal fan comprises one or more series of flat or frusto-conical discs each series of which has air inlet openings at or spaced outwardly from their centres and are secured together face to face co-axially with substantially unobstructed spaces between them, the discs of the or each series being mounted on a carrier having a driving mechainsm by which the carrier can be rotated to rotate the discs about their axis to form an impeller, the discs of the or each series being formed by a spaced assembly manufactured by the method according to said one aspect of the invention.

The centrifugal air fan includes a casing containing the discs and having an air inlet for admitting air, and an air outlet for discharging air, the width of the spaces between adjacent faces of the discs and the speed at which the driving mechanism is capable of rotating the discs being such that the flow of air through the spaces between the discs is laminar.

Each disc of the or each series of discs may have a single central opening, the discs being secured by the spirally fluted members to a back plate which forms the carrier.

Alternatively, the discs of the or each series of discs may be secured by the spirally fluted members to a back plate which forms the carrier, the spirally fluted members being located within a central portion of the discs, each disc being provided with a number of separate openings spaced apart angularly around the central portion.

The casing may have an outer part in the form of a volute extending around the outer peripheries of the disc and terminating in an opening which provides the air outlet, the air inlet being provided by a central axial opening formed in an end face of the casing adjacent the opening or openings in an end disc of the adjacent series.

The driving mechanism may be provided by an electric motor, and the width of each gap between the discs may be arranged to give a desired air throughput and pressure rise for a predetermined speed of rotation of the motor.

The volute form of the casing may be arranged to produce a constant static air outlet pressure.

The invention in both its aspects will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a sectional side elevation of the centre part of an assembly of spaced members in accordance with the invention; Figure 2 is a fragmentary sectional side elevation, similar to Figure 1, but showing an alternative form of spiral fluted member; Figure 3 is a sectional side elevation of a centrifugal air fan incorporating an assembly of spaced members of the kind shown in Figure 1; Figure 4 is a sectional elevation of the centrifugal air fan shown in Figure 3 taken on the line lV-lV in that Figure; Figure 5 is a sectional side elevation of another centrifugal air fan incorporating an assembly of spaced members of the kind shown in Figure 2; and Figures 6 and 7 are end views respectively of two forms of discs suitable for use in the centrifugal air fan shown in Figure 5.

Referring in the first instance to Figure 1, the assembly comprises a multiplicity of plates or discs 1 arranged substantially parallel to each other in a spaced relationship and secured in this position by a plurality of spirally fluted tubes 2.

Each disc 1 has a central opening 5 which is surrounded by holes 4 into which the spirally fluted tubes 2 are inserted. The assembly is clamped between two rings 8 by bolts 6 which pass through the spirally fluted tubes 2 and are secured by threaded nuts 7.

In the method of manufacture in accordance with the invention the multiplicity of discs 1 is temporarily held in the required spaced relationship by a jig (not shown) so that the holes 4 are aligned and the central openings 5 are aligned. The spirally fluted tubes 2 are then inserted into the aligned holes 4 so that they grip the peripheries of the holes 4 and secure the disc 1 in the spaced relationship. The jig which originally held the discs 1 is then removed.

The spirally fluted tubes 2 are driven into the aligned holes 4 by an axially applied force coupled with rotation at a rate appropriate to the spiral angle of the flutes. The spirally fluted tubes 2 may be ultrasonically vibrated while being driven into the aligned holes. Typically, the discs 1 would be 0.5 mm in thickness and spaced 1.0 mm apart and may be formed from metal.

In an alternative assembly shown in Figure 2 spirally fluted pins 11 replace the spirally fluted tubes. In this assembly the spirally fluted pins 11 are also effective to secure the assembly to an end ring 12. The discs 1 may be formed from plastics material and the spirally fluted pins 11 may be heated before being driven into the aligned holes 4. Alternatively the pins 11 may be ultrasonically vibrated while being driven into the aligned holes.

The discs 1 are secured in the required spaced relationship by two factors, namely, the friction between the disc material and the pins 11 or tubes 2, and the geometric "quarrel" which arises if the discs 1 try to move axially along the pins 11 or tubes 2. If the discs were held by one pin 11 or tube 2 only, the pin or tube could be "unscrewed" by rotating the discs 1 relative to the pin or tube.

However, when two or more pins 11 or tubes 2 are used, the second and third pins or tubes prevent rotation of the disc and thus prevent unscrewing.

Referring now to Figures 3 and 4, the centrifugal air fan is of the single stage kind which comprises an assembly of discs 1 similar to that shown in Figure 1 and each of which has a central opening 5 represented by dotted lines in Figure 3.

The discs 1 are secured in a spaced relationship by spirally fluted tubes 2 in the manner previously described. The assembly of discs 1 is secured to a back plate 1 4 by bolts 6 which pass through the spirally fluted tubes 2 and are secured by threaded nuts 7. The back plate 1 4 is mounted in cantilever fashion on a shaft 1 5 which is driven by an electric motor 1 6.

The assembly of discs 1 is mounted in a casing 17, the outer part of which forms a volute extending around the outer peripheries of the discs 1 and terminating in an air outlet 18. The shaft 1 5 extends through a bearing 19 at one end face of the casing 17 and the other end face of the casing is provided with an air inlet opening 20.

Referring finally to Figures 5 to 7, the centrifugal air fan is of the single stage kind which comprises an assembly of discs 1 similar to that shown in Figure 2 and each of which has a central opening 5 represented by dotted lines in Figure 5.

The discs 1 are secured in a spaced relationship and to back plate 14 by spirally fluted pins 11 in the manner previously described. Each disc 1 is provided with a number of separate openings 21 represented by dotted lines in Figure 5 and of the shapes shown in Figures 6 and 7 spaced apart angularly around the central opening 5. The assembly of discs 1 is provided with a casing 1 7 similar to that described with reference to Figures 3 and 4.

The width of the gaps between the discs 1 forming an assembly will depend upon the required air throughput and pressure rise, and in a particular construction of air fan in accordance with the invention, an electric motor 1 6 with a supply frequency of 50 cycles per second, gave an impeller speed of approximately 3000 rpm. It was found that with this speed of rotation a suitable width for the gaps is between 2 mm and 0.25 mm and preferably from 1 mm to 0.5 mm.

In operation, air flows into inlet opening 20, through the central opening 5 or openings 21 (as the case may be) and then centrifugally outwards through the series of discs 1 to emerge at the volute air outlet 1 8.

It will be appreciated that fans of this kind may readily be made to have two separate stages by having a first series of annular discs fixed to a carrier plate (as before) and then by having a second carrier plate, also without any central opening, spaced from said first series of discs and carrying a second series of annular discs.

The two series of discs and their respective carrier plates are rotated as a unit and are enclosed within a casing having a volute surrounding the second series of discs and an annular chamber surrounding the first series of disc. In operation, air flows in to an inlet opening at the side of the casing adjacent said first series of discs and flows outwards through the first series of discs which form a first stage. This air flows into the annular chamber and thence inwards through a space between adjacent series of discs. that is to say. between the front disc of the second series and the carrier plate of the first series. The air from the first stage then enters the opening or openings of the second series of discs and flows outwards through the spaces between these discs, which form a second stage, and into the volute.

Further series of discs separated from the previous series by plates without any central openings may be added to form a fan of any number of stages.

For ease of construction all of the discs 1 are preferably flat, but for some purposes it may be desirable for them to be frusto-conical. In this case, the smaller the angle of conicity the greater will be the frictional loss of head by the flow through the fan.

Since the flow between the discs 1 is laminar, the energy imparted to the air is independent of the surface finish of the discs, and thus smooth surfaces which do not retain dust can be employed.

In known bladed type impeller fans, precise constant air pressure is generally unnecessary in their design. However, because in a centrifugal type friction fan with which the present invention is concerned the air flow through the impeller is somewhat critical in respect of the outlet pressure it 'sees', it is desirable to design the casing 1 7 as a constant static pressure diffuser using the following mathematical relationship in the design.

Thus, referring to Figure 3 or Figure 5,

Where: r=radius of discs volute depth b at volute length x a=volute width (constant) b=volute depth x=volute length (i.e. distance around volute from exit: (x=O at outlet) vO=velocity of air flow at outlet depth of volute at outlet q=volume flow increase per unit length of volute f=Fanning friction factor Such a volute as well as collecting the flow from the periphery of the impeller also diffuses it to some extent, that is to say, the flow velocity reduces as it progresses around the volute, and thus the pressure tends to increase. However, this increase in pressure is arranged just to off-set the loss in pressure that occurs as a result of friction against the volute walls, which is described in the equation above through the Fanning friction factor, f.

Claims

1. A method of manufacturing an assembly of spaced member comprising the steps of providing a plurality of aligned holes in the members, temporarily holding the members in the required spaced relationship with the holes aligned, inserting spirally fluted members into the aligned holes so that they grip the peripheries of the holes and secure the members in the spaced relationship, and thereafter removing the temporary holding arrangement.

2. A method as claimed in Claim 1, wherein the spirally fluted members are spirally fluted pins.

3. A method as claimed in Claim 1, wherein the spirally fluted members are spirally fluted tubes.

4. A method as claimed in the preceding claim, wherein the assembly of spaced members comprises a multiplicity of plates arranged substantially parallel to each other.

5. A method as claimed in Claim 4, wherein the plates are from 0.1 to 2.0 mm in thickness.

6. A method as claimed in any preceding claim, wherein the spaced members are formed from metal.

7. A method as claimed in any one of Claims 1 to 5, wherein the spaced members are formed from plastics material.

8. A method as claimed in any preceding claim, wherein the assembly of spaced members is temporarily held in the required spaced relationship by a suitable jig.

9. A method as claimed in any preceding claim, wherein the spirally fluted members are driven into the aligned holes in the assembly of spaced members by an axially applied force coupled with rotation at a rate appropriate to the spiral angle of the flutes.

10. A method as claimed in Claim 9, wherein the spirally fluted members are heated prior to being driven into the aligned holes.

1 A method as claimed in Claim 9, wherein the spirally fluted members are ultrasonically vibrated while being driven into the aligned holes.

12. An assembly of spaced members manufactured by the method claimed in any one of the preceding claims.

13. A centrifugal air fan comprising one or more series of flat or frusto-conical discs each series of which have an air inlet openings at or spaced outwardly from their centres and are secured together face to face co-axially with substantially unobstructed spaces between them, the discs of the or each series being mounted on a carrier having a driving mechanism by which the carrier can be rotated to rotate the discs about their axis to form an impeller, the discs of the or each series being formed by a spaced assembly manufactured by the method claimed in any one of Claims 1 to 11.

14. A centrifugal air fan comprising one or more series of flat or frusto-conical discs each series of which have air inlet openings at or spaced outwardly from their centres and are secured together face to face co-axially with substantially unobstructed spaces between them, the discs of the or each series being mounted on a carrier having a driving mechanism by which the carrier can be rotated to rotate the discs about their axis to form an impeller, and a casing containing the discs and having an air inlet for admitting air, and an air outlet for discharging air, the width of the spaces between adjacent faces of the discs and the speed at which the driving mechanism is capable of rotating the discs being such that the flow of air through the spaces between the discs is laminar, and the discs of each series being formed by a spaced assembly manufactured by the method claimed in any one of Claims 1 to 11.

1 5. A centrifugal air fan as claimed in Claim 1 3 or Claim 14, wherein each disc of the or each series of discs has a single central opening, the discs being secured by the spirally fluted members to a back plate which forms the carrier.

1 6. A centrifugal air fan as claimed in Claim 13 or Claim 14, wherein the disc of the or each series are secured by the spirally fluted members to a back plate which forms the carrier, the spirally fluted members being located within a central portion of the discs, each disc being provided with a number of separate openings spaced apart angularly around the central portion.

1 7. A centrifugal fan as claimed in any one of Claims 13 to 16, comprising a casing having an outer part in the form of a volute extending around the outer peripheries of the discs and terminating in a opening which provides the air outlet, the air inlet being provided by a central axial opening formed in an end face of the casing adjacent the opening or openings in an end disc of the adjacent series.

18. A centrifugal fan as claimed in any one of Claims 13 to 17, wherein the driving mechanism is provided by an electric motor, and the width of each gap between the discs is arranged to give a desired air throughput and pressure rise for a predetermined speed of rotation of the motor.

19. A centrifugal fan as claimed in Claim 1 7 or Claim 18, wherein the volute form of the casing is arranged to produce a constant static air outlet pressure.

20. A method of manufacturing an assembly of spaced members substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.

21. An assembly of spaced members substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.

22. A centrifugal air fan constructed and arranged to operate substantially as hereinbefore described with reference to Figures 3 and 4 or Figures 5 to 7 of the accompanying drawings.