US 3182970 A
Description (OCR text may contain errors)
May 11, 1965 A. IVANOFF STIRRERS OR MIXERS Filed NOV. 3. 1961 FIG.8
INVENTOR ALEXANDER IVAN F ATTORN Y United States Patent 3,182,970 STRS 0R MIXERS Alexander Ivanoit, Greenwich, Conn, assignor to Hayward Tyler & Company Limited Filed Nov. 3, 1961, Ser. No. 150,046 10 Claims. (Cl. 259-95) This invention relates to liquid mixing devices of the kind comprising an oscillating impeller having vanes which extend along the axis of oscillation and project outwardly from it.
The normal construction of impeller used in devices of this kind merely pushes to and fro the liquid in the vicinity of the impeller, with the result that liquid more distant from the impeller is not thoroughly or uniformly mixed.
The present invention provides a device of the kind above mentioned which is operable to produce a unidirectional continuous flow of liquid through the impeller, resulting in efficient and uniform mixing of the liquid.
It is an object of the invention to provide a liquid mixing device of the kind above referred to in which means are provided for amplifying the rotary oscillations applied to the shaft so that the impeller has an increased amplitude of oscillation.
To attain the purpose, the shaft which carries the impeller is flexible in torsion and it is oscillated at a frequency substantially equal to the resonance frequency of oscillation of the system comprising the impeller, the shaft and liquid lying between the vanes of the impeller.
Further features of the invention are based on the discovery that three factors exert an influence on the estab lishment of continuous flow, namely the amplitude of oscillation, the number of vanes and the ratio of the axial length of the vanes to the diameter of the impeller, and that an increase in any one of these factors favors the establishment of continuous flow.
It is, however, undesirable to oscillate the impeller through a large angle because of the excessive vibration which is caused and of the increased danger of seals collapsing.
In accordance, therefore, with a further feature of the present invention, in a device of the kind referred to, having an impeller which is open ended, that is an impeller in which fluid can flow at both ends of the impeller through the gaps between the radial edges of adjacent vanes, the ratio of the axial length of the vanes to the diameter of the impeller is not less than 2/5 and the product of this ratio and the number of vanes is not less than with an impeller so constructed, it is found that continuous flow can be established by oscillating the impeller through a minimum angle of 5".
If the impeller is closed at one end by a shroud which fills the gaps between the radial edges of adjacent vanes, the van s behave as half vanes of double length and in consequence, for continuous flow to be established with a minimum amplitude of oscillation of 5, the minimum value of the said product is 2.5.
By maintaining the ratio of the axial length of the vanes to the diameter of the impeller at a minimum value of 2/5, the required number of vanes is kept small. Preferably the value of the said ratio is approximately 1:1.
Thus, for example, in an open ended impeller having six vanes the length of each vane being equal to the impeller diameter, the value of the said product is 6 1=6. Again, if there are twelve vanes, the length of each being 42% of the impeller diameter, the value of the product is 12 .42=5.04.
For an impeller having an end shroud, with siX vanes equal in length to half the impeller diameter, the value of the product is 6 .5=3.
Some preferred constructions in accordance with the invention are described below, by way of example, with reference to the accompanying drawings, in which:
FIGURE 1 is a part sectional elevation of a mixing pump in accordance with the invention;
FIGURE 2 is a view on the line BB of FIGURE 1;
FIGURE 3 is a view on the line AA of FIGURE 1;
FIGURES 4 and 5 are elevation and plan views, respectively, of a different form of impeller from that shown in FIGURES l and 2;
FIGURE 6 is a plan view of another form of impeller;
FIGURES 7 and 8 are sectional elevation and plan views, respectively, of yet another form of impeller; and
FIGURES 9 and 10 are sectional elevation and plan views, respectively, of a further form of impeller.
The pump shown in FIGURES 1 to 3, inclusive, comprises an impeller 12 secured to the lower end of an impeller shaft 13 extending through an opening in the top wall 14 of a mixing vessel 25, and supported outside the vessel by a support frame 15. The shaft is coupled to an electric motor 16, also mounted on frame 15, by a a linkage 17 which converts the continuous rotary motion of the output shaft of motor 16 into oscillating motion of the impeller shaft (and thus of the impeller), about the axis of the impeller shaft.
The impeller 12 comprises six radial vanes 20 secured to the impeller shaft 13. This impeller is open ended and the pattern of flow through the impeller is indicated by the dotted lines designated 'F. The greater part of the flow from the impeller is in a radially outward horizontal direction, although some flow, nearthe upper and lower ends is radially upwardly, and downwardly, respectively.
In the impeller shown in FIGURES 4 and 5, the radial vanes 243A are capped b a shroud plate 21, which confines the flow near the upper end of the impeller to a substantially horizontal direction. The mass flow through this impeller is approximately half that obtained with the impeller shown in FIGURES l and 2, but continuous flow is nevertheless achieved. The flow pattern is substantially the same as that produced by one half, say the lower half, of the open ended impeller.
The impeller shown in FIGURE 6 also has six vanes 20B, but these vanes are arranged in diametrically opposed groups of three. This impeller produces aflow which is similar in the elevational view to that shown in FIGURE 1, but in the plan View the flow, as shown, is radially outwards in diametrically opposite directions. If desired this impeller can be provided with an end shroud 21A serving a similar purpose to the shroud plate 21 shown in FIGURES 4 and 5.
FIGURES 7 and 8 illustrate another form of impeller in which the vanes 26C are surrounded by a cylindrical shroud 22. attached to the outer edges of the vanes. This shroud confines the flow to directions substantially parallel with the axis of the impeller.
A modified version of the last described impeller is shown in FIGURES 9 and 10, and comprises, in addition to a cylindrical shroud 22A, an annular shroud 23. In this case the material flows through the central opening in the end shroud 23 towards the lower end of the impeller and leaves the impeller in a' direction generally parallel to the impeller axis.
In each of the open ended impellers illustrated in the FIGURES 1, 2 and 6 to 10 inclusive, there are six vanes whose axial length is equal to the impeller diameter, that is, dimension B (FIGURE 1) is equal to dimension A (FIGURE 2). i
The impeller shown in FIGURES 5 and 6 has six vanes whose axial length is equal to half the impeller diameter.
The actual form of impeller for a given application will in general depend on the general pattern of flow required (having regard to the shape of the mixing vessel), and the attitude and position of the impeller within the vessel. For example, if a generally horizontal flow is required with the impeller shaft vertical, one of the impellers shown in FIGURES 1, 4 and 5 or 6 would be chosen. But if a horizontal flow was required with the impeller shaft horizontal, an impeller producing axial flow, such as those shown in FIGURES 7, 8 and 9, 10 would be used.
Each of the impellers illustrated can conveniently be manufactured in two halves of welded or cast construction clamped together on the impeller shaft.
Referring once more to FIGURES l and 3, the above mentioned support frame comprises a support tube 30 secured at its foot to a base plate 31 which in turn is detachably mounted on the top wall 14 of the mixing vessel. The impeller shaft 13 extends upwardly through the tube 30 and at its upper end is supported in a pair of silentblock bearings 32, 33 mounted in a bearing block 34 fixed to the upper end of the support tube. These silentblock bearings each consist of inner and outer concentric bushes with a body of soft plastic material filling the annular clearance between them. The plastic material is bonded to both bushes and seals the said clearance while permitting relative angular movement between the bushes.
The impeller shaft 13 is formed with a collar 36 to whose cylindrical surface a sealing tube 37 is clamped by a clamping ring 38. The sealing tube, which of course completely surrounds the impeller shaft is also clamped, by a clamping ring 39, to the outer cylindrical surface of a flanged bush 40 whose flange is secured to base plate 31. This tube is flexible in torsion and thus permits oscillation of the impeller shaft whilst forming a fluid tight seal between the shaft and the opening in the top wall of the mixing vessel. The sealing tube may be plain or may take the form of a bellows whose corrugations are at right angles to the impeller shaft, or at a more acute angle, or in the form of a spiral.
Preferably, and as shown, the impeller shaft 13 is in two portions, upper and lower, which are clamped together by a split bush coupling 41 which can be released to permit removal of the lower portion of the shaft, together with the impeller, from the upper portion.
The electric motor 16 is mounted on a platform 42 attached to the upper end of the bearing block 34, and the output shaft of the motor is coupled to the impeller shaft by the above mentioned linkage 17, which is best seen in FIGURE 3 comprising a pair of arms 43, 44 pivotally connected to form a knee joint 46. Arm 43 is secured to the impeller shaft, in between the bearings 32, 33 and arm 44 is pivotally connected to an eccentric 47 carried by the motor shaft.
From a consideration of FIGURE 3 it will be seen that as the motor shaft rotates continuously, the impeller shaft will be made to oscillate about its own axis.
As stated above the impeller is so constructed that continuous, flow can be achieved with an amplitude of oscillation of as little as 5. However it is preferred to use a larger angle than 5 so that a larger mass flow through the impeller is established. In practice an angle of 15 has been found satisfactory, since it produces a satisfactory mass flow without introducing excessive mechanical problems. In the embodiment shown in FIGS. 1, 2 and 3 the impeller is oscillated through an angle of 15". This is achieved by making the shaft or both the shaft and the vanes flexible and oscillating the upper end of the shaft through an angle of less than 15. This flexibility of the shaft and, if applicable, the vanes is so adjusted that the natural frequency of oscillation of the system, including the inertia of the liquid lying between the blades of the impeller, is close or equal to the resonant frequency, and in this way an increase in the amplitude of the impeller is obtained. Such an increase in amplitude can of course be obtained for other resultant amplitudes of oscillation of the impeller. For example, if the impeller is to be oscillated through its minimum angle of 5, the shaft is oscillated through an angle of less than 5.
The motor 1-6 experiences an oscillating reaction and is preferably mounted on bearings or resilient mounts to minimise vibration.
While the mixing pump has been described as being in an upright position, it will be understood that it can Operate just as well in any other attitude. Thus, whereas the usual requirement is for the shaft to extend vertically through the top wall of a mixing vessel, the pump can equally well be used with its shaft passing into a mixing vessel through a vertical or inclined side wall.
In a modified form of pump, generally similar to that described, the sealing tube arrangement is replaced by a third silent block bearing whose outer member is sealed in the opening in the top wall of the vessel and whose inner member is secured to the impeller shaft, say just above the split bush coupling 41, so that the length of the impeller shaft is somewhat reduced. For some applications of course it is not necessary to seal the impeller shaft to a wall of the mixing vessel in any way.
1. A liquid-mixing device comprising a vessel adapted to contain a liquid to be mixed in the vessel, a rotary shaft flexible in torsion, mounting means supporting said shaft in a position extending into the vessel, an impeller secured to one end of the shaft for immersion of the impellet into liquid contained in said vessel, said impeller including a plurality of vanes radially extending from the axis of the shaft, and oscillating rotary drive means coupled to a part of said shaft spaced apart from said impeller for oscillating said part through an angle of rotation and at a frequency substantially equal to the resonant frequency of oscillation of the system comprising the impeller, the shaft and liquid lying between said vanes.
2. A device as claimed in claim 1 wherein said impeller comprises a cylindrical shroud coaxial with the said shaft and surrounding the vanes for closing the gaps between the outer edges of adjacent vanes.
3. A device as claimed in claim 1 wherein said impeller comprises a plate disposed transversely to said shaft and having a centrally disposed opening surrounding the shaft and overlying the inner portions of the radial edges of adjacent vanes at one end of the impeller, said plate closing the gaps between the outer portions of the radial edges of said vanes at one end of the impeller.
4. A device as claimed in claim 1 wherein said vanes are arranged in diametrically opposed groups such that the gap between two pairs of adjacent impellers are greater than the gaps between the remaining pairs.
5. A liquid mixing device comprising a vessel adapted to contain a liquid to be mixed in the vessel; a shaft flexible in torsion; mounting means supporting the shaft in a position extending into the vessel; an impeller secured to the shaft and immersed in said liquid, said impeller comprising a plurality of vanes extending along the axis of the shaft and projecting outwardly therefrom, the ratio of the axial length of said vanes to the diameter of the impeller being not less than 2/5, and the product of the number of vanes and said ratio being not less than 5, with some of said liquid lying between said vanes; and oscillating drive means coupled to a part of said shaft spaced from said impeller for oscillating said part through an angle and at a frequency substantially equal to the resonant frequency of oscillation of the system comprising the impeller, the shaft and the liquid lying between said vanes; whereby operation of said drive means causes said impeller to oscillate through a greater angle than said first-mentioned angle, said greater angle having a minimum value of 5.
6. A liquid mixing device as claimed in claim 5 wherein a shroud plate is disposed transversely of the shaft closing rigid.
is at least as great as 1:1.
8. A device according to claim 5, whereinsaid part of 5 the shaft is flexible, the remaining part of the shaft being 9. A device according to claim 5, wherein said vanes are flexible.
10. A device as claimed in claim 1 wherein a shroud plate transverse of the shaft closes oneend of the impeller vanes, the other end being open, the minimum ratio of the axial length of said vanes to the diameter of the impeller being 2/5 and the minimum product of the number of vanes and the ratio being 2.5.
References Cited by the Examiner UNITED STATES PATENTS Bolton 259-101 Brown 259-434 Lundahl 259134 Thompson 259-134 Morehouse 68132 Wahl 259-128 Wenger 259-10 1 Clark 259-134 Examiners.