Diffuser component

Abstract

A diffuser 620, such as at an inlet or outlet of a motor driven fan or blower, comprises a concertina of material 610 in a ring and having a central axis 615. The concertina comprises a series of axia

Description

BACKGROUND Diffusers are commonly used in fluid flow applications to change the direction of a flow of 5 fluid. A diffuser may typically be found at the inlet or the outlet of a motor driven fan or blower. Known diffusers generally have a plurality of guide vanes supported between a central axis and a surrounding outer support. SUMMARY 10 The present invention provides a diffuser comprising a concertina of material arranged in a ring and having a central axis, wherein the concertina of material comprises a series of axially extending fins, wherein each fin extends between a peak and a trough of the concertina of material, and wherein the peaks and troughs curve in a circumferential direction with respect to the central axis of the diffuser. The ring of concertina material is 15 advantageous as the diffuser may be positioned around other items thereby providing packaging efficiency. The peaks and troughs of the concertina of material lean in opposite circumferential directions when viewed from one end of the diffuser. This arrangement is useful for 20 changing the direction of a fluid flow. Each peak of the concertina of material may optionally have a first side and a second side when viewed from one end of the diffuser, wherein: each fin located on each first side of each peak have the same dimensions and / or geometry as each other; each fin located on 25 each second side of each peak have the same dimensions and / or geometry as each other; and the fins located on the first sides of the peaks have different dimensions and / or geometry to the fins located on the second side of the peaks. The fins may have a curved radial profile. In one example, each peak and / or trough 30 comprises a curved circumferential profile, or a pointed circumferential profile. 09 10 25 Optionally the concertina of material may be located within a tubular surround. Surrounding the diffuser with a tubular member can reduce stresses on the connecting ends of the concertina of material. The concertina of material may optionally surround a tubular member. 5 The diffuser may be configured to heat a flow of fluid as it passes through the diffuser in use. This is advantageous as the diffuser may fulfil the dual purpose of heating and diffusing a flow of fluid. 10 In one example, the diffuser comprises an induction coil located within or around the concertina of material. This allows for the diffuser to be used as an inductive heating element if the diffuser is made of metal. In another aspect, the present invention provides a motor assembly comprising a diffuser as 15 described above. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A shows a schematic illustration of a skiving machine; 20 Figure IB shows a schematic illustration of a first process step using the skiving machine of Figure 1A; Figure IC shows a schematic illustration of a second process step using the skiving machine of Figure 1A; 25 Figure ID shows a schematic illustration of a third process step using the skiving machine of Figure 1A; Figure 2A shows a schematic illustration of a first process step in an alternative skiving 30 operation; 09 10 25 Figure 2B shows a schematic illustration of a second process step of the alternative skiving operation; Figure 2C shows a schematic illustration of a third process step of the alternative skiving 5 operation; Figure 2D shows a schematic illustration of a fourth process step of the alternative skiving operation; 10 Figure 2E shows a schematic illustration of a fifth process step of the alternative skiving operation; Figure 2F shows a schematic illustration of a sixth process step of the alternative skiving operation; 15 Figure 2G shows a schematic illustration of a seventh process step of the alternative skiving operation; Figure 3 shows a schematic illustration of a skived component made by the alternative 20 skiving operation od Figures 2A to 2G; Figure 4 shows a schematic illustration of an alternative skiving machine; Figure 5 shows a schematic illustration of an alternative configuration of cutters; 25 Figure 6A shows a schematic illustration of the fin profiles of a skived component; Figure 6B shows a schematic illustration of the fin profiles of an alternative skived component; 30 Figure 6C shows a schematic illustration of the fin profiles of another alternative skived component; 09 10 25 Figure 7A shows a schematic illustration of cutter configuration in which the tip angle varies along the length of the cutter; Figure 7B shows a schematic illustration of an alternative cutter configuration in which the 5 tip angle varies along the length of the cutter; Figure 7C shows a schematic illustration of a further cutter configuration in which the tip angle varies along the length of the cutter; 10 Figure 7D shows a schematic illustration of a still further cutter configuration in which the tip angle varies along the length of the cutter; Figure 8A shows a schematic illustration of the cutting edge profile of a straight edged cutter; 15 Figure 8B shows a schematic illustration of the cutting edge profile of a wavy edged cutter; Figure 8C shows a schematic illustration of the cutting edge profile of a curved edged cutter; 20 Figure 9A shows a schematic illustration of the fin profiles of a skived component similar to Figure 6A; Figure 9B shows a schematic illustration of the fin profiles of an alternative skived 25 component; Figure 9C shows a schematic illustration of the fin profiles of another alternative skived component; 30 Figure 9D shows a schematic illustration of the fin profiles of a further alternative skived component; 09 10 25 Figure 9E shows a schematic illustration of the fin profiles of a still further alternative skived component; Figure 10 shows a schematic illustration of a process for making a ring shaped component; 5 Figure 11 shows a schematic illustration of a skived component made with a curved edge cutter; Figure 12 shows a schematic illustration of a ring shaped item made from the skived 10 component of Figure 11; Figure 13 shows a schematic illustration of a plurality of skived components made with a curved edge cutter; and 15 Figure 14 shows a schematic illustration of an alternative skiving machine. DETAILED DESCRIPTION In the description that follows, all references to up, down, in, out, vertical, horizontal and the like are with reference to the orientation of the Figures. It will be understood that this is 20 not intended to be limiting and that any suitable orientation may be used in practice. Figure 1A shows a schematic illustration of a skiving machine 10 comprising a fixture 12 for holding a billet of material 20 in place during a skiving operation. In the example shown, the fixture 12 comprises a first support 13a and a second support 13b between 25 which the billet of material 20 is held. The skiving machine 10 comprises a first cutter 14a and a second cutter 14b which are located on opposite sides of the billet of material 20. An actuator (not shown) is provided to move the billet of material 20 with respect to the cutters 14a, 14b. In one example, the supports 13a, 13b comprise rolling supports that operate to progressively move the billet of material 20 with respect to the cutters 14a, 14b. 30 Figure 1A illustrates the skiving machine 10 in an initial configuration just before the skiving operation begins. In this initial configuration, the billet of material 20 has been 09 10 25 positioned in a starting position in the fixture 12, but the skiving operation has not yet begun. Figure IB shows a first process step of the skiving operation in which the actuator has 5 moved the billet of material 20 upwardly with respect to the cutters 14a, 14b by a predetermined incremental amount, and the first cutter 14a has moved horizontally inwardly from its starting position to form a first cut 22 in the billet of material 20. It will be understood that the billet of material itself may move upwardly with respect to the vertical position of the cutters 14a, 14b. Alternatively or additionally, the cutters 14a, 14b 10 may move downwardly with respect to the billet of material 20 which may remain stationary. The formation of the first cut 22 results in the formation of a first sliver of material 23 which has a free edge 24 at its first end 25, but which remains attached to the billet of 15 material 20 at its second end 26. The thickness of the sliver of material is determined by the relative incremental distance that the billet of material moves with respect to the vertical position of the cutters 14a, 14b. Figure IC shows a second process step of the skiving operation in which the first cutter 20 14a has moved outwardly away from the billet of material 20, the billet of material 20 has again moved upwardly with respect to the cutters 14a, 14b by a predetermined incremental amount, and the second cutter 14b has moved horizontally inwardly from its starting position to form a second cut 32 in the billet of material 20. The formation of the second cut 32 results in the formation of a second sliver of material 33 which is connected to the 25 second end 26 of the first sliver of material 23 at its first end 35, and which remains attached to the billet of material 20 at its second end 36. Figure ID shows a third process step of the skiving operation in which the second cutter 14b has moved outwardly away from the billet of material 20, the billet of material 20 has 30 again moved upwardly with respect to the cutters 14a, 14b by a predetermined incremental amount, and the first cutter 14a has again moved horizontally inwardly to form a third cut 42 in the billet of material 20. The formation of the third cut 42 results in the formation of 09 10 25 a third sliver of material 43 which is connected to the second end 36 of the second sliver of material 33 at its first end 45, and which remains attached to the billet of material 20 at its second end 46. 5 The process described above in relation to Figures 1A to ID repeats such that a first plurality of cuts made by the first cutter 14a are interspersed with a second plurality of cuts made by the second cutter 14b resulting in the formation of a concertina of material 50. The process continues until a desired amount of the billet of material 20 has been skived. The resulting concertina of material 50 is then removed from the skiving machine 10 for 10 further processing. In one example, either of the cutters 14a, 14b is used to cut the concertina of material 50 from the billet of material 20 by cutting the whole way through the billet of material 20. A lubricant or cooling fluid may be used during the skiving process if necessary. 15 The first and second cutters 14a, 14b are illustrated in Figures IC and ID as moving outwardly away from the billet of material between process steps to a position beyond their starting positions as illustrated in Figure 1 A. It will be understood that this is not essential and the cutters 14a, 14b may return to their starting positions, or another position, rather than beyond their starting positions. 20 In the skiving operation described above, the cutters 14a, 14b move linearly in a reciprocating motion towards and away from the billet of material 20 in a direction perpendicular to the direction of movement of the billet of material 20 relative to the cutters 14a, 14b. This is illustrated as horizontal movement of the cutters 14a, 14b in 25 Figures IB to ID. It will be understood that this is not essential and that the cutters 14a, 14b may move in a direction which is not perpendicular to the direction of movement of the billet of material 20 relative to the cutters 14a, 14b. Figures 2A to 2G describe a modified skiving operation in which the first and second 30 cutters 14a, 14b each make two consecutive cuts in the billet of material. Figure 2A is identical to Figure IB such that the billet of material 20 has moved upwardly with respect to the cutters 14a, 14b by a predetermined incremental amount, and the first cutter 14a has 09 10 25 moved horizontally inwardly from its starting position to form a first cut 122 in the billet of material 20. The formation of the first cut 122 results in the formation of a first sliver of material 123 which has a free edge 124 at its first end 125, but which remains attached to the billet of material 20 at its second end 126. 5 Figure 2B shows an intermediate process step in which the first cutter 14a has moved outwardly away from the billet of material to allow the billet of material 20 to move upwardly with respect to the cutters 14a, 14b by a predetermined incremental amount. As shown in Figure 2C, the first cutter 14a then moves inwardly once more to form a second 10 cut 127 which results in the formation of a second sliver of material 128 which has a free edge 129 at its first end 130, but which remains attached to the billet of material 20 at its second end 131. The depth of the first cut 122 is greater than the depth of the second cut 127 such that the second sliver of material 128 forms a rib 174 on the skived component (see Figure 3). 15 Referring now to Figure 2D, the first cutter 14a has moved outwardly away from the billet of material 20, the billet of material 20 has moved upwardly with respect to the cutters 14a, 14b by a predetermined incremental amount, and the second cutter 14b has moved horizontally inwardly from its starting position to form a third cut 132 in the billet of 20 material 20. The formation of the third cut 132 results in the formation of a third sliver of material 133 which is connected to the second end 126 of the first sliver of material 123 at its first end 135, and which remains attached to the billet of material 20 at its second end 136. The second end 131 of the second sliver of material 128 is attached to the third sliver of material 133 at a point between the first 135 and second 136 ends of the third sliver of 25 material 133. Figure 2E shows another intermediate process step in which the second cutter 14b has moved outwardly away from the billet of material to allow the billet of material 20 to move upwardly with respect to the cutters 14a, 14b by a predetermined incremental amount. As 30 shown in Figure 2F, the second cutter 14b then moves inwardly once more to form a fourth cut 147 which results in the formation of a fourth sliver of material 148 which has a free edge 149 at its first end 150, but which remains attached to the billet of material 20 at its 09 10 25 second end 151. The depth of the third cut 132 is greater than the depth of the fourth cut 147 such that the fourth sliver of material 148 forms a rib 174 on the skived component (Figure 3). 5 Referring now to Figure 2G, the second cutter 14b has moved outwardly away from the billet of material 20, the billet of material 20 has moved upwardly with respect to the cutters 14a, 14b by a predetermined incremental amount, and the first cutter 14a has moved horizontally inwardly to form a fifth cut 162 in the billet of material 20. The formation of the fifth cut 162 results in the formation of a fifth sliver of material 163 which is connected 10 to the second end 136 of the third sliver of material 133 at its first end 165, and which remains attached to the billet of material 20 at its second end 166. The second end 151 of the fourth sliver of material 148 is attached to the fifth sliver of material 163 at a point between the first 165 and second 166 ends of the fifth sliver of material 163. 15 The process described above in relation to Figures 2A to 2G repeats such that a first plurality of cuts made by the first cutter 14a are interspersed with a second plurality of cuts made by the second cutter 14b. In particular, in this example, two consecutive cuts made by the first cutter 14a are interspersed with two consecutive cuts made by the second cutter 4b in a repeating series. 20 Figure 3 shows a schematic view of a concertina of material 170 which comprises a series of fins 171 which each extend between a respective peak 172 and trough 173 of the concertina of material 170, where each fin 171 has an associated rib 174. It will be understood that the concertina of material 50 resulting from the process described above in 25 relation to Figures 1A to ID has a similar configuration but without any ribs 174. It is not essential that consecutive cuts made by the same cutter into the billet of material 20 be of different lengths and in another example the consecutive cuts made by the same cutter may be of the same length. In another example the number of consecutive cuts made 30 by each cutter may differ such that one cutter may make a first number of consecutive cuts on a first side of the billet of material 20, and the other cutter may make a different number 09 10 25 of consecutive cuts on a second side of the billet of material 20. In some examples, one cutter makes a single cut before the other cutter makes a series of consecutive cuts. In the examples described above with reference to Figures 1A to ID and 2A to 2G, the 5 movement of the cutters 14a, 14b is described such that only one of the cutters 14a, 14b moves at any one time. This is not essential and the skiving machine 10 may be configured so that both cutters 14a, 14b are in motion for at least a portion of the operating time. Figure 4 shows a schematic illustration of an alternative skiving machine 200 which is 10 configured to skive a plurality of billets of material 20 at the same time to produce a corresponding plurality of concertinas of material 50 concurrently. The skiving machine 210 is the same in all respects to the skiving machine 10 described above except for the fact that the fixture 212 of the skiving machine 210 is configured to hold a plurality of billets of material 20 next to one another, and the first and second cutters 214a, 214b are of 15 a width suitable to cut all of the billets of material 40 at the same time respectively. The first and second cutters 214a, 214b each have a straight cutting edge 80 although this is not essential as described in greater detail below. Many different skiving machine configurations are possible. In one embodiment illustrated 20 schematically in Figure 5, the dimensions of the first cutter 14a, differ from the dimensions of the second cuter 14b such that tip angle 0a is larger than the tip angle 9b. Figures 6A to 6D show a schematic illustrations of cutter configurations in which the tip angle 9 varies along the length of the cutter (into the page as shown in Figures 6A to 6D). 25 In Figure 6A the tip angle 9i is smaller at the side of the cutter closest to the observer (with reference to the Figure) than the tip angle 92 at the side of the cutter furthest from the observer. This configuration is reversed in Figure 6B such that the tip angle 92 is smaller at the side of the cutter furthest from the observer (with reference to the Figure) than the tip angle 9i at the side of the cutter closest to the observer. 30 In Figure 6C the tip angle 02 is smaller at the edge of the cutter furthest from the observer (with reference to the Figure) than the tip angle 0i at the edge of the cutter closest to the 09 10 25 observer. Furthermore, the cutting edge 80 of the cutter is slanted such that the horizontal extent X of the cutter (with reference to the Figure) increases into the page from Xi to X2. This configuration is reversed in reversed in Figure 6D such that the tip angle 0i is smaller at the edge of the cutter closest to the observer (with reference to the Figure) than the tip 5 angle 02 at the edge of the cutter furthest from the observer, and the horizontal extent X of the cutter (with reference to the Figure) decreases into the page from Xi to X2. In another example, the horizontal extent X of the cutter may vary with width of the cutter such that the cutting edge 80 has any desired profile (when view from above) such as 10 curved, stepped, wavy etc. This may be applied to a cutter having a fixed tip angle 0 across the width of the cutter, or to cutter having any of the variations described above with reference to Figures 6A to 6D. Furthermore, the profile of the billet of material (when viewed from above) may optionally be machined to conform to the profile of the cutter. For example, cutters with a concave curved cutting edge 80 (when viewed from above) 15 may be used to skive a billet of material having convex curved profile (when viewed from above). Figures 7A to 7C show a schematic illustration of different cutting edge profiles. For the avoidance of doubt, referring to Figure 1A for reference, the cutting edge profile is the 20 vertical variation of the cutting edge looking into the page. The cutting edge profile 580a shown in Figure 7A is that of a straight cutter having no vertical profile variation. An example of a straight cutting edge profile 80 is illustrated in Figure 4. Figure 7B shows a wavy cutting edge profile 580b and Figure 7C shows a curved cutting edge profile 580c. 25 It will be understood that any of the cutter variations described above can be used in any combination as desired. Furthermore, it is not necessary for the cutters 14a, 14b to be orientated in a horizontal plane (with reference to Figure 1A), and one or both of the cutters 14a, 14b may be orientated at an angle with respect to the horizontal (with reference to Figure 1 A). 30 Schematic illustrations of the effect of differing the tip angles of the cutters 14a, 14b is are shown in Figures 8A to 8C. In Figure 8A a concertina of material 350a produced by a 09 10 25 skiving machine 10 having first and second cutters 14a, 14b with equal tip angles is shown. The concertina of material 350a comprises a series of fins 371a which each extend between a respective peak 372a and trough 373a of the concertina of material 350a. As illustrated in Figure 8A, the peaks 372a of the concertina of material 350a point vertically upwards and 5 the troughs 373a of the concertina of material 350a point vertically downwards. Figures 8B and 8C show schematic illustrations of example concertinas of material 350b, 350c that may be produced by a skiving machine 10 having first and second cutters 14a, 14b with unequal tip angles. In Figure 8B the peaks 372b of the concertina of material 10 350b lean in a first direction 375, and the troughs 373b of the concertina of material 350b lean in a second direction 376. In Figure 8C the peaks 372c of the concertina of material 350c lean in the second direction 376, and the troughs 373c of the concertina of material 350c lean in the first direction 376. 15 Figures 9A to 9E show a schematic illustration of the effect that varying the cutting parameters by which the cutters 14a, 14b make the cuts has on the profile of the fins of the concertina of material (where cutting parameters include speed, depth and length of cut). Figure 9A shows fins 471a having a straight profile made by passing the cutters 14a, 14b through the billet of material 40 using cutting parameters which do not vary during the 20 duration of the cut. Figure 9B shows fins 471b having a first curved profile made by passing the cutters 14a, 14b through the billet of material 40 using a first cutting parameter variation, and Figure 9C shows fins 471c having a second curved profile made by passing the cutters 14a, 14b through the billet of material 40 using a second cutting parameter variation. The first cutting parameter variation produces curved fins 471b which result in 25 peaks 472b and troughs 473b with pointed profiles, whereas the second cutting parameter variation produces curved fins 471c which result in peaks 472c and troughs 473c having a more curved profile. Figures 9D and 9E show further examples of fin profiles achievable by variation of the 30 cutting parameters. In Figure 9D, the cutting parameter variation produces curved fins 47Id which result in a concertina having a shark-fin like profile. In Figure 9E, the cutting 09 10 25 parameter variation produces curved fins 47 le which result in a concertina having a shark-fin like profile oriented in the opposite sense to Figure 9D. It will be understood that the cutting parameter variations used to make any particular cut 5 can be selected as desired and it is not necessary that the same cutter parameters be used for consecutive cuts made by the same, or different, cutter. In addition, variation of cutter parameters may be used in conjunction with cutters of differing dimensions and or geometries to achieve peak / trough ‘lean’ in conjunction with curved profile fins. 10 Figure 10 shows a method of making a ring shaped item from a billet of material 20 which has been skived into a concertina of material 50 using any skiving method described above. After the concertina of material 50 has been removed from the skiving machine 10, it is wound around a mandrel 500 so that the peaks 572 of the concertina of material are located radially outwardly of the troughs 573 of the concertina of material. The two free 15 ends of the concertina of material are fixed together by any suitable method such as welding, brazing or adhesion, and the resulting ring shaped item 550 is removed from the mandrel 500. It will be appreciated that if the concertina of material 50 has been produced so that the peaks and troughs lean in opposite directions (as illustrated in Figures 8B and 8C), the peaks of the ring shaped item 550 will lean in a first circumferential direction, 20 while the troughs will lean in the other. One example use for a ring shaped item 550 is in the production of an inductive heating element 560. As illustrated in Figure 10, the ring shaped item is placed within a retainer 552 which is sized to hold the ring shaped item 550 in compression so as to reduce the 25 stress on the peaks and troughs of the ring shaped item 550 as well as on the connection between the ends of the concertina of material 50. An induction coil 554 is placed inside the ring shaped item to produce an inductive heating element 560. It is not essential that the ring shaped item 550 is located within a retainer 552 and the retainer 552 may be omitted if desired. Furthermore, in any case, the induction coil 554 may surround the ring 30 shaped item 550 rather than being located within the ring shaped item 550. 09 10 25 Any suitable material may be used to fabricate the ring shaped item 550, the induction coil 554 and the retainer 552. In one example the ring shaped item 550 comprises stainless steel, aluminium or copper. The concertina of material 50 may be coated with an electromagnetic material such as nickel or a nickel-chromium alloy before or after it is 5 formed into the ring shaped item 550. Figure 11 shows a schematic illustration of a concertina of material 600 which has been skived from a billet of material 20 by a pair of cutters having a curved edge such as curved edge 580c shown in Figure 7C. As shown in Figure 11, the fins 671 of the concertina of 10 material 60 are curved. In one example, the billet of material 20 is machined before the skiving process begins so that the top surface of the billet of material 20 conforms to the shape of the cutter. Figure 12 shows a ring shaped item 610 which has been made from the concertina of 15 material 600 by winding the concertina of material 600 around a mandrel so that the peaks 672 of the concertina of material are located radially outwardly of the troughs 673 of the concertina of material. Because the fins of the concertina of material 600 are curved, the peaks 672 and troughs 673 of the ring shape item 610 curve in an anticlockwise circumferential direction with respect to a central axis 615 of the ring shaped item 610 20 when viewed along the axis from the direction 617 illustrated. The ring shaped item 610 may be employed as a diffuser 620 to alter the direction of a flow of fluid as it passes through the diffuser 620. If desired, the diffuser 620 may be placed within a retainer (not shown) which is sized to hold the diffuser 620 in compression 25 to reduce stress on the peaks 672, troughs 673 and on the connection between the ends of the concertina of material 600. In another example, an induction coil (such as the induction col 554 of Figure 10) may be located within the diffuser 620, or may surround the diffuser 620, to form a diffuser which 30 is capable of heating the flow of fluid as it passes through the diffuser 620. A diffusing inductive heating element such as this can be usefully employed at the exit of a motor driven air blower or fan for example. 09 10 25 In a further example, a non-inductive method of heating the flow of fluid passing through the diffuser 620 may be employed such as a resistive heating element which may be configured to heat the fluid flow directly, or which may be configured to heat the material 5 of the diffuser 620 so that heat is passed to the fluid flow via the diffuser 620 as the fluid passes through the diffuser 620 in use. Figurel3 shows a schematic view of a plurality of concertinas of material 600 arranged side by side. Such an arrangement may be produced by skiving a plurality of billets of 10 material 20 arranged sided by side using a pair of cutters in an arrangement similar to that shown in Figure 4 with each cutter having a waved cutting edge profile configured to cut a curved sliver of material from each billet of material 20 to produce the plurality of concertinas of material 600. Each concertina of material 600 may then be further processed in any desirable way including formation into a diffused 620. 15 It will be understood that in the description above, all references to variations and alternatives in the dimensions, geometry and use of cutters 14a, 14b apply also to variations and alternatives in the dimensions, geometry and use of cutters (such as the cutters 214a, 214b of Figure 4) which are configured to cut a plurality of billets of material 20 20 at the same time. Figure 14 shows an alternative skiving machine 700 comprising a fixture 712 for holding a billet of material 720 in place during a skiving operation. The fixture 712 comprises a fixed portion 713a and a rotating portion 713b to which the billet of material 20 is attached. The 25 skiving machine 700 comprises a single cutter 714. During the skiving operation, the billet of material is positioned in the correct position for a first cut to be made into a first side 721 of the billet of material. After the first cut has been made, the cutter 714 is withdrawn away from the billet of material 20 and the billet of 30 material is rotated 180 degrees by the rotating portion 713b of the fixture 712. A second cut is then made into the second side 722 of the billet of material. The process is repeated until the desired amount of the billet of material 20 has been skived. The fixture 712 may 09 10 25 be used to increment the relative height of the billet of material with respect to the cutter 714. Alternatively or additionally, the cutter 714 may move relative to the fixture 712. The cutter 714 shown in Figure 13 has a straight cutting edge 780. However, it will be understood that the cutting edge of the cutter 714 may be of any suitable configuration 5 such as curved. It will be appreciated that the billet of material 20 may be cut from any series of directions. For example, the rotating portion 713b of the skiving machine 700 may rotate the billet of material 20 by 90 degree increments so that a first plurality of cuts are made from a first 10 orientation with respect to the billet of material, a second plurality of cuts are made from a second orientation with respect to the billet of material, a third plurality of cuts are made from a third orientation with respect to the billet of material, and a fourth plurality of cuts are made from a fourth orientation with respect to the billet of material. In another example the billet of material may be rotated by 120 degrees such that a first, second and third 15 plurality of cuts are made from different orientations with respect to the billet of material 20. The skiving machine 10 described above with reference to Figures 1A to ID may also be used to cut from different orientations by providing cutters arranged at the desired orientations with respect to the billet of material 20. 20 It will be understood that any number of consecutive cuts may be made by the same cutter to any desired depth regardless of tip angle, cutting speed variation, cutting edge profile or skiving machine type. For example, a concertina of material having ribs 170 as illustrated in Figure 3 may be made by any shape of cutter on any type of skiving machine described above. 09 10 25

Claims

1. A diffuser comprising a concertina of material arranged in a ring and having a central axis, wherein the concertina of material comprises a series of axially extending fins, wherein each fin extends between a peak and a trough of the concertina of material, and 5 wherein the peaks and troughs curve in a circumferential direction with respect to the central axis of the diffuser, wherein the peaks and troughs of the concertina of material lean in opposite circumferential directions when viewed from one end of the diffuser.

2. A diffuser according to claim 1, wherein each peak of the concertina of material 10 has a first side and a second side when viewed from one end of the diffuser, wherein:each fin located on each first side of each peak have the same dimensions and / or geometry as each other;each fin located on each second side of each peak have the same dimensions and / or geometry as each other; and15 the fins located on the first sides of the peaks have different dimensions and / orgeometry to the fins located on the second side of the peaks.

3. A diffuser according to claim 1 or 2, wherein the fins have a curved radial profile.20 4. A diffuser according to any one of claims 1 to 3, wherein each peak and / or troughcomprises:a curved circumferential profile; ora pointed circumferential profile.25 5. A diffuser according to any one of claims 1 to 4, wherein the concertina of materialis located within a tubular surround.

6. A diffuser according to any one of claims 1 to 5, wherein the concertina of material surrounds a tubular member.

307. A diffuser according to any one of claims 1 to 6, wherein the diffuser is configured to heat a flow of fluid as it passes through the diffuser in use.LO CXI8. A diffuser according to claim 7, comprising an induction coil located within or around the concertina of material.5 9. A motor assembly comprising a diffuser according to any one of claims 1 to 8.

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