US2581451A

US2581451A - Mixing pump

Info

Publication number: US2581451A
Application number: US115671A
Authority: US
Inventors: Morgan B Sennet
Original assignee: Laval Steam Turbine Co
Current assignee: De Laval Steam Turbine Co
Priority date: 1949-09-14
Filing date: 1949-09-14
Publication date: 1952-01-08
Anticipated expiration: 1969-01-08

Description

Jan. 8, 1952 Filed Sept. '14, 1949 M.B.SENNET MIXING PUMP 4 Sheets-Sheet l FT F l HVVENTOR. MORGAN 5.. SENNET j ATTDRN Y5 M. B. SENNET MIXING PUMP Jan. 8, 19 52 4 Sheets-Sheet 2 Filed Sept. 14, 1949 FIG. 2.

INVENTOR. MORGAN B. SEN/VET ATIORNE s Jan. 8, 1952 M. B. SENNET 1 MIXING PUMP Filed Sept. 14, 1949 4 Sheets-Sheet 5 I INVENTOR. 'F/G. 5. MORGAN B. SEA/N57 AT TORNEYS.

Jan. 8, 1952 I SENNET M 2,581,451

MIXING PUMP Filed Sept. l4. 1949 4 Sheets-"Sheet 4 INVENTOR. F/ 6. Z MORGAN B. SEI VNET ATTORNEYS.

Patented Jan. 8, 1952 UNITED STATES PATENT OFFICE MIXING PUMP Morgan B. Sennet, Trenton, N. J., assignor to i I De Laval Steam Turbine Company, Trenton, I N. J., a corporation of New Jersey Application September 14, 1949, Serial No. 115,671

13 Claims. 1

This invention relates to a mixing pump particularly designed for the effective mixing or kneading of materials of a fluent or viscous type, the pump being of a multiple screw type.

The effective mixing of paints or other suspensions of solid, semisolid, or liquid materials in liquids to provide homogeneous products is generally a rather diflicult and time consuming operation for which ordinary Stirring or other agitation in batches will frequently not suflice to give the desired products. In accordance with the presentinvention the mixture of constitucnts'is subjected to flow through tortuous paths provided between cooperating rotating screws involving kneading action which is extremely effective in producing homogeneity.

In the patent to Montelius 1,698,802, dated January 15, 1929, there is disclosed a type of screw pump which is positive in its displacement characteristics. Positive screw pumps of this type have gone into widespread use and are capable of operating at quite high speeds. A pump of this positive displacement type if fed with a solid-liquid mixture or with a mixture of liquids which are not mutually soluble in the propor tions used will promote mixing to some extent due to therelative motions of the screw surfaces and housing surfaces with respect to the material trapped in the travelling chambers of the pump. However, since the portions of the material are carried through .the pump effectively inthe form of individual slugs of substantially fixed shape from the standpoint of their boundaries the mixing is not particularly effective and, in fact, much of the efliciency of these pumps is due to the fashion in which the liquid is advanced with a minimum rather than a maximum of turbulence imparted thereto.

In the 'Montelius patent referred to above there are discussed the requirements on the relationships between the numbers of threads on intermeshing screws required for the attainment of positive displacement. A violation of these requirements will result in an inherent nonpositive characteristic of a screw pump provided with intermeshing screws even though the thread'shapes are generated in accordance with the principles of the patent, and irrespective of the etiectiveaxial length of the pump which may be defined as the length which involves interis attempting to effect pumping action.

meshing of screws within intersecting bores in I l 2 accordance with departure from the principles established for positive screw pumps and such a non-positive pump is used for the pumping of a mixture with the object of providing homogeneity, more effective mixing is produced than would be produced by a positive screw pump of comparable length provided the pumping takes place against a substantial head. In contrast with a positive screw pump the pumping action of such a non-positive screw pump is dynamic in character, i. e., the material is progressed through the pump by virtue of a propelling action of the screws since no closed chambers are formed and if the pump is stopped the material will fiow from the high pressure end of the pump through the low pressure end. Slippage of the material is accordingly an inherent characteristic of such a non-positive pump: i. e., the ad-' vance of the material pumped is always less than what might be considered the theoretical displacement of the pump involving no retrograde movement of the material relative to the screw threads. The fact that such slippage occurs accounts for the increase in eiiectiveness of mixing, inasmuch as the material, as it is progressed through the pump, has a greater amount of relative slippage with respect to the screws than would be the case in a comparable positive pump of the same effective screwlength.

In accordance with the present invention the mixing effect is very greatly increased by combining a positive pump with a non-positive screw pump in such fashion as to drive the material undergoing admixture in a direction contrary to the direction in which the non-positive pump The positive pump which is used may be of any type to eiTect reverse flow through the non-positive screw pump but, as will hereafter appear, the invention lends itself to embodiment in a simple and highly effective mixer involving the combination of a positive pump and a non-positive pump both of screw type which may be in the same housing and may have common shafting to reduce to a minimum the problem of providing simplicity of drive, provision of proper bearings, small size, etc.

, The invention, however, is not confined to a non-positive screw pump opposing a positive one. Similar effective results may be secured by opposition of a pair of non-positive pumps one of which has a more effective pumping action than the other so as to force the mixture in retrograde direction through the latter. As will appear hereafter various such combinations of pumps may be provided.

The broad object of the invention in providing an effective mixing device has been indicated above. The attainment of this object as well as the attainment of various other objects particularly relating todetails of construction and operation will become apparentfrom the following description read in conjunction with the accompanying drawings, in which:

Figure 1 is an axial section through a mixer illustrating one preferred embodiment of the principles of the invention;-

Figure 2 is a transverse section takenuon': the plane indicated at 2-2 in Figure 1;

Figure 3 is a transverse section taken on the plane indicated at 33 in Figure 1;

Figures 4, 5, 6 and 7 are diagrams which clarify the nature of the flow paths of the types herein involved; and V Figure. 8 is asection similar to Figure 2 but showing anentrance sand/or exit arrangement for the non-positive mixing pump to promote mixing action.

Referring first to Figures 1, 2 and 3, the mixing pump comprises a casin 2 havingan inlet opening 4 and an outlet opening 6. The former may communicatewith a'source of roughly admixed material which is to be transformed into a homo-, geneous mixture, while the latter may communi cate with a receiver- If more than onepass of themixture through the; apparatus is required to -secure the necessaryhomogeneity the receiver and-.source'may bemerged intoone receptacle through which the pump will produce recirculation to proces a batch of material. As will be evident, various circuits external to the pump may beprovided such as are common in connection with other mixers and these circuits form no specialpart of the present invention, vwhichis concerned primarily with what occurs to the mater-ialfrom the entrance 4 and the exit 6.

Liners

8 and 10 contained within the casing 2 provide housings fora positive multiple screw pumpindicatedgenerally at I 2 .and a non-positive multiple screw illustrated generally at [4. A shaft I6 has mounted thereon, or, as shown, cut thereon, a power screw [8 for thepositive pump and 'a power screw fora non positive pump. As specifically indicated inthe drawings each of these screws contain two threads with the threads of the respectivescrews of opposite hands. Meshing with the power screws are so-called idler screws formed oncommonspindles or shafts indicated at 22 and 24. Theidler screws meshing with the screw 3 of. the positive pump are indicated at 26 and 28. The idler screws meshing with the power screw 20 of the non-positive pump and formed on shafts 22 and 24: are indicated atv 3fl and 32. In addition to the

idler screws

30 and 32 there mesh with thescrew 2!! of 'thenonpositive pump another pair of idler screws 34 and -36. As will be evident, to provide meshing the idler screws 30, 32-, 34-and 36 are of a hand opposite that of the idler screws2B and '28.

'Inthe-arrangement illustrated all of the idler screws are of two-thread type and except for their hand all of these idler screws are preferably identical. Both the power screws *and idler screws aredesigned in accordance with 'the'principles set forth insaid Montelius patent so that, when assembly is provided, as indicated in Figure 3 in the case of the positive. pump I2, a conventional region provided by a spacer cylinder 40., the interior 42 of which provides a conduit for the passage of material from the positive pump to the non-positive pump. Bearings of suitable type are provided at 46 and 4B for mounting and taking the end thrusts of the various screws. The

screws have additional mounting in the bores in their housings ,8 and H), the former having two side bores for. thereception of the positive pump idler screws and the latter having four side bores forithenon-positive pump idler screws. The clearances of the screws with their mounting bores are quite small, being exaggerated .in Figureszand 3..

As will be evident from consideration of the figures, a rotation. of the shaft. [6 in'the directionv of the-arrow will causethe positive pump to operate to drive the pumped material from the right toward the left. The non-positive pump I4, on" theother hand,,is so operated as to tend to. drive the material from the left toward the right;

' However, being non-positive this lastpump must yield tothe action of the positive pump so that despite theeffort which it exertsthe material will flowv therethrough from the righttoward the.

pump is provided suchas is commonly used for high speed positive pumping. Desirably the left. From the standpoint of pressures produced it, will be evident that this operation will giverlse to a very high pressurein the space .42...v The overall pressure of the pump from. inlet toroutlet will depend upon the head which is pumped against and which, in most uses of the pump; would be relatively low. The-shaft 6 and the idlers carried. by the shafts .22 and 24 will have a net. thrust toward the right but this is generally relatively low and simple thrust bearing arrangements will suffice to. take care of thisthrus-t. On the other hand, the thrusts on thescrews 3.4.:and 36 will be towardthe left and quite, large softhat as. indicatedthe bearing arrangementat 46 must be of a typesufiicient to. resist this left hand thrust of these screws.

As will beeVident, the non-positive pump will produce an intense turbulence and shearing. mix! ing action, on thematerial passing therethrough since an extreme relative motion of the material with. respect tothe screws is. provided dueto-the fact that thescrews are operating to oppose the flow of material forced by the positive-pump. The mixing action is. greatlyincreased, further? more, by the tortuous .path of the material throughthe non-positive pump To explain this, and. in. particular, the relative characteristicslof differentkinds of non-positive pumps-reference may bemade to Figures 4, 5, 6 and '7' which-respectivelyindicate the characteristics of:opera,- tion of a positive pump having two idlers, a non;- positive :pump having three idlers, a rnon-posi tive pump'zhaving. four idlers,1and a non-positive pump. :h-avingtfive. idlers, in each. case there being apower screw having two threads and idlers each having two threads. v i

The various diagrams of Figures 4, 5; Sand 7 may-berbest understood by considering thatthey represent, from a purely diagrammaticstand point, sections of slightly more than a complete circuit about the power screw in e'achca'se. These diagrams may be best 'understoodby considering the diagram of Figure 6 with reference to Figure 2, the diagram being a development of a section taken on an axial surface just inside the peripheries of the screws along a path. from an about the outer portion of idler 39 to :02, thence to 3:3 about the power screw 20, thence about idler 34 to 11:4 and similarly about the power screw and the other idlers to axial lines as, rs, m1 and x8, and finally back to an. The segmental sections of the power screw are then indicated at P, while the segmental sections of the idler screws are indicated at the Is provided with subscripts corresponding to the various idlers provided. Figures 4, 5 and '7 are sections taken in similar fashion. V

Continuing thereference to Figure 6, the form of pump having four idlers, assume'rotation of the power screw in the direction of the arrow at the top of Figure 6. Under this assumption the inletto the pump will be at the bottom of the figure and the outlet will be at the top of the lengths of the screws this path will be continuously open and will provide a tortuous leakage path from the outlet end of the set of screws to theirinlet end. Furthermore, since the leakage path is duplicated there are, in effect, two parallel leakage paths preventing the pump from operating in a positive fashion. These paths, however,-are so tortuous, as may be recognized particularly by reference to Figure 2, that the pump has a very effective dynamic action and, if of proper length, is capable of producing a quite substantial head.

Consideration may-now be given to the question of proper length of the screws. By length is meant the effective length through which the screws-are in mesh and arealso properly surrounded by the housing to form a closed path.

By considering the contacts between the screws it will be found that, first assuming a symmetrical arrangement of the idlers about the power screw, 9. complete circuit of the power screw by the liquid to follow a leakage path will be required if the effective length of the pump, as above deffined, is given by the following equation:

in which, assuming a single power screw,

-' M is the minimum effective length of mesh and enclosure of the screws to insure that liquid passing from outlet to inlet must make at least a complete circuit of the power screw;

P is the pitch, equal to the lead of each screw divided by the number of its threads;

N is the number of idlers; V

m is the number of threads on each idler;

. up is the number of threads on the power screw; and, l' Wis the axial width of the top of the power screw.

If the minimum effective length is less than this, it will'happen that in some positions of the screws a path may be found from'outlet to inlet which will make less than a complete circuit of the powerscrew. This possibility is undesirable giving not only an absence of full effectiveness of the screw arrangement in terms of producing maximum head for a given speed of operation, but will also give rise to pulsations by virtue of the less effective pumping action whenever the screws attain a configuration which gives the shorter path just mentioned.

As an application of the foregoing formula, the following tabulation indicates the: values of M for pumps having a single power screw carrying two threads and two, three, four and five idlers, respectively, each carrying two threads:

The assumption of a minimum effective pump length for a symmetrical array of idler screws applies, however, to an asymmetrical array, since it will be found that, if an asymmetrical array is used, the minimum length would have to be greater than that given by the above formula to avoid a leakage path in certain positions of the screws which would provide less than a complete circuit of the power screw. Actually, symmetrical arrays are most desirable to avoid the existence of unbalanced lateral thrusts on the screws.

Attention may now be given to Figures 4, 5 and 7 which indicate the nature of the paths or chambers existing when two, three and five idlers, respectively, are used.

Figure 4 is provided only for completeness of the systematic disclosure. It represents a positive pump comprising a power screw of two threads meshing with two idlers of two threads each, this being the positive pump illustrated in Figure 1. If the path CD is noted, it will be seen that it starts andends in the same groove position. Accordingly, it does not extend axially and this path represents a closed chamber making the pump positive. The expression given for M, however, still applies and in this case has a significance that the effective length of the pump should be as indicated in the foregoing tabulation to-insure that thepump will actually be positive.

Referring to Figure 5, which shows a three idler arrangement it will be noted that the path EF, corresponding generally to the path AB of Figure 6, completes a circuit of the power screw in the next lower groove below the startin groove E. Since the value of M for this pump is less than for the four-idler pump, and only a single pathis provided, it will be evident that for given screw dimension and for given speed of operation a greater head may be produced with the threeidler arrangement than with the four-idler arrangement with, however, a reduction in capacity.

The five-idler arrangement is illustrated in Figure '7, the free leakage path being indicated at GI-I. It will be noted that this path makes a circuit of the power screw dropping to the third groove below its beginnin at the end of this circuit. This means that there will be three parallel paths running through the screws, the additional two paths, for example, passing through G and G". As pointed out in Montelius Patent 1,698,802 a positive pump is provided by a power screw having one thread meshing with a single idler screw having two threads. From this construction a non-positive pump may be derived merely by adding another idler of the two thread type; Numerous other non-positive pumps may be. derived by departure from the conditions given in said Montel-ius Patent 1,698,802. for positive screw pumps.

It may be noted that the. formula given above for M applies to such. pumps in general provided with a single power. screw, and from this there maybe determined the minimum-effective pump length forgbest utilization of..any such screw arrangement.

It will also be evident that non-positivescrew pumps may be derived'from positive screw pumps merely be decreasing'the circumferential extents of the threads of the power or idler screws so as to afford clearances which will prevent complete closures of pockets which would normally exist in positive pumps, though this modification is not recommended since it permits play between the screws and weardue to impact unless timing gears are added.

In all the cases referred to above effective mixing can be attained by causing flows to take place in directions opposite the flows through a nonposi't'ive pump.

It will also be evident that imposing reverse flow through a non-positive pump maybe secured by causing two non-positive screw pumps to buck each other if one is of a typeiproducing a dynamic propelling characteristic in-iexcessof that of the other. As an. example, a 3-idler pump of the type diagrammed in Figure 5 may be arranged tov oppose the flow through a i l-idler pump of the type illustrated in.Figure 6; In this, case for the same or comparable lengthsof the pump 3 the 3-idler pump will overcome the 4-idler pump so as to. enforce a reverse flow throughthe latter. At the same time a considerable degree-of admixing action will occur in the 3-idler pump due to slippage therein. The arrangement may also be reversed so that a i-idler pump overcomes a 3-idler pump by making the screws ,of the former sufficiently long.

Furthermore, two similar. non-positive pumps of the same type, from the standpoint of num- .bers of screws and threads, maybe arrangedto oppose. each other if they are of diiferent lengths so'that the longer of them willproduce a head greater than the shorter.

Similar results may also be secured by the opposition of screw pumps of the same or different types having different pitches" of'their threads so that one of them may overcome the action of the other. As will be evident, avery great variety of screw pumps may be combined to attalnmixing actions in accordance with the principles of the invention. While the opposition of a pair; of screw pumps is particularly desirable in carrying-out the in vention, it may be noted that it" is'thereverse flow through a non-positive pumpwhlchis-particularly responsible for eifective mixing;- the pump which produces the reverse flowithrofugh' the mixing pump has primarily only thefunction of producing that flow and, consequentlylmaybe replaced by other positive pumps. or by such nonrpositive pumps as may-be capable of. producing the reverse flow as described. When-,1 as usual,

viscous materialsare being mixedit may bend-ted that the non-positive screw. pumps which. have been described actually, are capable of. producing very substantial heads and,; consequently,; the pump which enforces reversefiowmust; becapable, of producing, even .greaterheads. Another screw pump. isv particularly.applicable for this purpose and, furthermore: the use of aspair of screw pumps; results. .in the practical: advantage entrance to the. screws of the non-positive pump,

and. .exit therefrom takes place axially, i.e.,;.the ends of .athe screws are completelyopentoaenq trance =and-exit chambers. An augmented mixing.

action may. be produced in; accordance-.withtthe arrangementillustrated in Figure 8 which applies to: bothzthe entrance and .ex-itends-of the screws. In this modification, the ends of thescrewssmay be .confined and entrance of the mixture tosthe screws andexitafrom the screws may be provided through. radially extending openings Elsi-n, the ends: otthe-houslng 50 for the screws IDA- 3 113 32"., 34" and536" which correspond to the similarly numbered screws inFigures .1 and 2. vIt will be evidentthat the screw threads will cut across such openingszandqaccordingly effect a chopping actionz onthe entering or leavingmixtura. If the pump is operating at high speed, this chopping action is, particularly efiective to produce a breaking up of any agglomerates 01 solid material or concentration of liquid droplets, which may existdn the .mixture. The screws should ..desirablybe :of .such lengths exceeding the.mini mum. effective lengths discussed above so.-- that theopenings v52 at the entrance and exit-are spacedby more than this effective. length;

What I claim.- and desire. to protect by Letters Patent is:

1.2111119. mixing device, in combination; anon; positivemultiple screw pumpincluding a power serew=andatleast zone idler screw,., a second multiple. screw pump including a power screw andat. leastone. idler screw, said power screws being ooaxiallyemounted and. rotating together and said idler screws being coaxially-mounted androtating together, said pumps having a-common housing. and said second pump being cons structedand arranged to force afl-uent mixture through the first mentioned pump in a. direction opposing-the-pumping action of the-first mene irioned pump. 7

2.1 In amixing device, .in combination, a anonpositive multiple screw pump including a power screw and at least one, idler screw, a second-positivermultiple screw pump; including a power-screw andatleast one: idler; screw,,said power screws being coaxially mounted and. rotating together and said idler screws being coaxially mounted and rotating together.,-.said pumps havinga'common housing, and said second pump-being constructed and arranged ,to forcea fluent mixture through the first mentioned pump-in a direction opposing the pumping'action oi. the firstgmentioned pump;

3. Ina mixing--device,1 in combination, anion-'- positiv e multiple screw pump including a power screw having two threads and at least three, idler screws, each having two threads, asecond multiple screw pump-including apowerscrew having two threads. and at least twoidlerscrews; each having two threads, said power screws belng scos axially. mounted and rotating, togethenzand each of said idler screws of the second mentioned pump being coaxial. with',.and rotatingrwith, a corresponding idler :screvr of the first, mentioned pump, said second pump being constructedand arranged to force a fluentmixture .throught..-the

-.firs,t mentionedpump in a direction -opposi-ng 4. In a mixing device, in combination, a nonpositive multiple screw pump including a power screw having two threads and at least three idler screws, each having two threads, a second positive multiple screw pump including a power screw having two threads and two idler screws,

each having two threads, said power screws being coaxially mounted and rotating together, and each of said idler screws of the second mentioned pump being coaxial with, and rotating with, a corresponding idler screw of the first mentioned pump, said second pump being constructed and arranged to force a fluent mixture through the first mentioned pump in a direction opposing the pumping action of the first mentioned pump.

5. In a mixing device, in combination, a nonpositive multiple screw pump including a power screw having two threads and four idler screws, each having two threads, a second multiple screw pump including a power screw having two threads and at least two idler screws, each having two threads, said power screws being coaxially mounted and rotating together, and each of said idler screws of the second mentioned pump being coaxial with, and rotating with, a corresponding idler screw of the first mentioned pump, said second pump being constructed and arranged to force a fluent mixture through the first mentioned pump in a direction opposing the pumping action of the first mentioned pump.

6. In a mixing device, in combination, a nonpositive multiple screw pump including a power screw having two threads and four idler screws, each having two threads, a second positive multiple screw pump including a power screw having two threads and two idler screws, each having two threads, said power screws being coaxially mounted and rotating together, and each of said idler screws of the second mentioned pump being coaxial with, and rotating with, a corresponding idler screw of the first mentioned pump, said second pump being constructed and arranged to force a fluent mixture through the first mentioned pump in a direction opposing the pumping action of the first mentioned pump.

7. In a mixing device, in combination, a nonpositive multiple screw pump including a power screw having two threads and four idler screws, each having two threads, a second positive multiple screw pump including a power screw having two threads and two idler screws, each having two threads, said power screws being coaxially mounted and rotating together, and each of said idler screws of the second mentioned pump being coaxial with, and rotating with, a corresponding idler screw of the first mentioned pump, said two power screws being of opposite hands, said second pump being constructed and arranged to force a fluent mixture through the first mentioned pump in a direction opposing the pumping action of the first mentioned pump.

8. In a mixing device, in combination, a nonpositive multiple screw pump including a power screw and at least one idler screw, means for driving said pump, and a second pump for forcing a fluent mixture through the first mentioned pump in a direction opposing the pumping action of the first mentioned pump.

9. In a mixing device, in combination, a non positive multiple screw pump including a power screw and at least one idler screw, means for driving said pump, and a second positive pump for forcing a fluent mixture through the first mentioned pump in a direction opposing the pumping action of the first mentioned pump.

10. In a mixing device, in combination, a nonpositive multiple screw pump including a power screw and at least one idler screw, means for driving said pump, and a second positive multiple screw pump including a power screw and at least one idler screw for forcing a fluent mixture through the first mentioned pump in a direction opposing the pumping action of the first mentioned pump.

11. In a mixing device, in combination, a nonpositive multiple screw pump including a power screw and at least one idler screw, a second multiple screw pump including a power screw and at least one idler screw, said pumps having a common housing and a common drive shaft, and said second pump being constructed and arranged to force a fluent mixture through the first mentioned pump in a direction opposing the pumping action of the first mentioned pump.

12. In a mixing device, in combination, a nonpositive multiple screw pump including a power screw and at least one idler screw, a second positive multiple screw pump including a power screw and at least one idler screw, said pumps having a common housing and a common drive shaft, and said second pump being constructed and arranged to force a fluent mixture through the first mentioned pump in a direction opposing the pumping action of the first mentioned pump.

13. In a mixing device, in combination, a non positive multiple screw pump including a power screw and at least one idler screw, means for driving said pump, and a second multiple screw pump including a power screw and at least one idler screw for forcing a fluent mixture through the first mentioned pump in a direction opposing the pumping action of the first mentioned pump.

MORGAN B. SENNE'I.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS