The invention relates to a blower of the displace¬ ment type, comprising a stationary outer cylinder and an inner cylinder eccentrically rotatably mounted in rela¬ tion to the outer cylinder, a stationary shaft arranged concentrically in the outer cylinder, and a number of vanes which are individually rotatably mounted at one end thereof on the stationary shaft and have the other end thereof adjacent the inside surface of the outer cylinder and between the ends thereof are pivota ^' lly and displaceably mounted in the inner cylinder, each vane at said other end thereof sealing against the inside surface of the outer cylinder. The object of the invention is to provide a reliable and silent blower of the type referred to herein and at the same time to simplify the manufacture of such a blower so that the manufacturing costs can be reduced. In order to achieve this object the blower of the invention has obtained the characteristics appearing from claim 1, and there is provided a method in manu¬ facturing the blower in accordance with claim 6.

For a closer explanation of the invention an embodi¬ ment thereof will be described in more detail , reference being made to the accompanying drawings in which FIG. 1 is a plan view of the blower, FIG. 2 is a central vertical sectional view of the blower,

FIG. -3 is a cross-sectional view of the blower, and FIG. 4 is a cross-sectional view of the inner cylinder during the manufacture thereof. The blower comprises an outer cylinder with a cylindrical wall 10 and end walls 11. The end walls are clamped against the end edges of the cylindrical wall, said edges being received by annular grooves in one side

of the end walls, by means of tie rods 12 and nuts 13 engaging said rods. A shaft 14 is arranged concentrically in the outer cylinder and is fixedly mounted to the right hand end wall 11 as seen in FIG. 2, by a split lock ring 15 being mounted in an annular groove 16 in the shaft 14, and being clamped against the inside surface of the end wall by a shaft nut 17 which is engaged with the outside surface of the right hand end wall and is locked by means of a lock washer 18. The shaft 14 thus stationarily mounted is provided with an eccentrically arranged ^" bear¬ ing housing 19 at the left hand end thereof as seen in FIG. 2, which receives a ball bearing 20. By means of this ball bearing said end of the shaft 14 is supported on a pin 21 which forms part of a shaft 22 rotatably mounted by means of a ball bearing 23 in a socket 24 on the left hand end wall 11. The ball bearing 23 is clamped between a lock ring 25 and a shaft nut 26 and is sealed by means of a bearing cover 27 mounted to the socket 24 by means of screws 28. The shaft 22 shall be connected by means of a belt transmission or similar device to a drive motor for operating the blower.

A flange 30 is formed on the shaft 22 and an end wall 32 of an inner cylinder is mounted by screws 31 on this flange, said inner cylinder also comprising a cylindrical wall 33 and a further end wall 34. Said latter end wall is rotatably mounted by means of a ball bearing 35 on the right hand end wall 11 of the outer cylinder as seen in FIG. 2. The cyl i ndri cal _. all 33 comprises three identical sections each forming a cylindrically curved surface 36 and having two axially extending edge portions 37 angled towards the centre, which are made thicker than the rest of the related section. In each portion 37 a cylindrically curved bearing -surface 38 is formed in the edge surface of the related portion. Between adjacent edge surfaces of two

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sections following one upon the other of the cylindrical wall 33 of the inner cylinder a vane 39 is pivotally and displaceably mounted by means of two bars 40 of a resistant material having good bearing properties, e.g. coal fiber reinforced polytetraf1 uoro ethylene. The bars 40 have a cylindrically curved bearing surface engaging the bearing surface 38, and a flat bearing surface engaging the vane 39.

Each vane 39 is individually rotatably mounted to the stationary shaft 14 by means of two rings 41 and associated ball bearings 42. Accordingly, there are totally six rings and ball bearings of this kind. Each vane has a foot 43 which is connected by means of screws 44 to the ring 40. The ball bearings located at the right hand end of the shaft 14 as seen in FIG. 2 are clamped between the lock ring 15 and a cup spring 45 engaging a lock ring 46 inserted in an annular groove in the shaft, spacer rings 47 being located between the ball bearings and between the lock ring 15 and the adjacent ball bearing as well as between the cup spring 45 and the adjacent ball bearing. Since the lock ring 15 can be removed and the shaft 14 is of uniform thickness with turned-down annular grooves arranged therein for re¬ ceiving the lock rings, the manufacture of the shaft is simple and the mounting of the ball bearings can be done easily when the lock ring 15 has been removed. The three ball bearings located at the left hand end of the shaft 14 as seen in FIG. 2 are connected to the respective vanes thereof but otherwise can be displaced freely on the shaft 14 such that they can move on the shaft at thermal length changes of the vanes, should such changes occur.

In the end wall 34 of the inner cylinder there is provided ^' for each pair of bars 40 a recess 48 with a compression spring 49 arranged therein, which exerts a

pressure on the bars 40 so that these bars are held in engagement with the other end wall 32 of the inner cyl ι nder.

Each vane 39 has at the outer end thereof a flange 50 projecting longer at one side of the vane than at the other side thereof. The shorter projecting portion of the flange should be at the side of the vane which is the leading side when the vanes are rotating in the intended direction indicated by the arrow 51 in FIG. 3. The flange 50 may be curved as the inside surface ofrthe outer cylinder and the surface thereof facing said inside surface is slightly spaced from the surface when the blower is in a cool condition. The gap can be of the order 0.2 mm. Possibly, this surface of the flange 50 can have axially extending grooves causing turbulence and thus an improved seal between the vanes and the outer cylinder. When the blower is operating and the temperature thereof increases, the gap between the flanges 50 and the outer cylinder will decrease due to the thermal expansion of the vanes, such that said gap will be substantially no more than half the gap existing when the blower is in the cool condition. For accurate adjustment of the gap exchangeable shims can be arranged between the feet 43 and the rings 40. The end walls 32 and 34 of the inner cylinder can have ci cumferential ly extending grooves at the circum¬ ferential surface thereof for sealing between the circum¬ ferential surface of the end walls 32 and 34 and the end walls 11 of the outer cylinder at 52. Preferably, the outer cylinder is made of steel while the inner cylinder is made of aluminium as are the vanes.

An inlet box 53 is provided at one side of the outer cylinder, and an outlet box 54 is provided at the d ametrically opposite side. In the cylindrical wall 10 of the outer cylinder, an inlet opening 55 is provided

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between the inlet box 53 and the interior of the outer cylinder, th ^" e inlet box being provided with an air inlet socket 56 preferably provided with an air filter. Between the outlet box 54 and the interior of the outer cylinder an outlet opening 57 is provided, the outlet box being provided with an outlet socket 58 ^* for connec¬ tion to the apparatus to which pressurized air is to be supplied from the blower. The inlet and outlet boxes preferably have an oblique wall 58 in order that a favourable flow pattern will be obtained in the boxes. Moreover, the openings 55 and 57 are chamfered at the inner side thereof at 59 in order to reduce the noise level when air is flowing through these openings. Also the short portion of the flanges 50 of the vanes 39 contributes to the reduction of the noise level .

The operation of the blower is well known. When the shaft 22 is driven in order to rotate the inner cylinder 32, 33, 34 in the direction of the arrow 51 , the volume of the cavities defined by the vanes 39 between the outer and inner cylinders, will increase when passing the inlet opening 55, for the admission of air from the surroundings. Then, the air will be forwarded to the diametrically opposite side where the volume of the cavity decreases again while the forwarded air is being forced through the outlet opening 57 so as to be passed through the outlet box 54 and the socket 58' to the apparatus to which pressurized air is to be supplied from the blower. It will be seen from FIG. 3 that the position of the vanes 39 in relation to the inner cylinder will vary, and due to the fact that the inner cylinder has edge portions 37 angled towards the centre, there are longitudinal grooves 60 in the outside surface of the inner cylinder, receiving the flanges 50 when the vanes and the inner cylinder take the relative position shown for the upright vane in FIG. 3. This arrangement

promotes the efficiency of the blower.

The blower can be provided with conventional devices for lubricating the balil bearings. However, it is not necessary to lubricate the bearings formed by the bars 40 if they are made of coal fiber reinforced polytetraf1 uoro ethylene, because this material has a low friction combined with high wear resi stance.

The invention relates to an advantageous method in the manufacture of the blower described. Considering first the outer cylinder, it has previously been common practice to provide a welded shoulder 61, FIG. 1, on the outer cylinder in order to replace the tie rods 12 by bolts at the inlet and outlet boxes, respectively, said bolts being screwed into the shoulders. In the blower of the invention, the shoulders have been maintained, but also at this place tie rods are used which pass freely through the shoulders as well as bushings 63 extending through the inlet and outlet boxes, respectively. The shoulders have been maintained, because they are useful at the machining of the cylinderical wall 10 of the outer cylinder. This cylindrical wall is made of steel sheet which is bent to cylindrical form and welded, rough machining then taking place. After annealing (removal of stress) the cylindrical wall is finished at the ends and the inside surface thereof in one setting-up by the cylindrical wall being clamped in the lathe by means of said shoulders 62. It is a great advantage that the bolts otherwise screwed into the shoulders, have been eliminated in the present case, because the outer cylinder previ¬ ously has been deformed by tightening these bolts, disturbing the fit between the outer and inner cylinders. Also the manufacture of the inner cylinder may cause problems-. However, these problems are avoided by util- izing the method of the invention as shown in FIG. 4.

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The sections forming the cylindrical wall 36 of the inner cylinder are provided with angular fittings or rails 64 on the inside surface thereof, said fittings or rails being connected to the thick edge portions 37 by means of screws 65. Steel bars 66 which are cylindrical and have the same outside diameter as the bearings formed by the bars 40, are located between the sections engaging the bearing surfaces 38 as shown in FIG. 4. Then, the sections are clamped against the steel bars by means of tie bolts 67 extending through the angular fittings 64. The cylindrical wall thus obtained then can be set up in a lathe by using an expanding tube chuck the_jaws of which are indicated at 68 in FIG. 4 in order that the cylindrical wall can be turned on the inside surface as well as the end surfaces thereof in a single setting-up. When the turning has been done the steel bars 66 and the angular fittings 64 are removed and as will be easily understood the sections forming an inner cylinder manufactured in this way, will be associated with each other and will have a predeter¬ mined position in the cylinder.

The blower of the invention can of course be used for any purpose, but it is particularly well suited for the operation of an infrasound generator of the kind described in the Swedish patent application 7905616-4. Such sound generators are operated intermittently when they are used for cleaning furnaces, heat exchangers and the like: peri odi ca.'ly the sound generator is operated at full power and between these periods it is operated at reduced power not in order to produce an effective infrasound but in order to keep the movable elements of the device for supplying pressurized air moving such that the starting difficulties otherwise arising due to dust coating on these elements will be eliminated. In that case the blower preferably is driven by a two-speed motor.

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Then, a relief valve of a known construction should be provided in the outlet box 54 to relieve the back pressure if the blower starts with the feed unit of the infrasound generator in a closed position and this unit does not start immediately.

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