US3341087A - Method and apparatus for forming liquid drops - Google Patents

Description

S. N. ROSIN ETAL Sept. 12,1967

METHOD AND APPARATUS FOR FORMING LIQUID DROPS 2 Sheets-Sheet 1 Filed Oct. 16, 1963 Sept. 12, 1967 s. N. ROSIN ETAL METHOD AND APPARATUS FOR FORMING LIQUID DROPS Filed Oct. 16, 1963 2 Sheets-Sheet United States Patent 3,341,087 METHOD AND APPARATUS FOR FORMING LIQUID DROPS Sebastian Nicholas Rosin and Derek Worrnald, London, England, assignors to Rosin Engineering Company Limited, London, England, a British company Filed Oct. 16, 1963, Ser. No. 316,652 Claims priority, application Great Britain, Oct. 19, 1962, 39,715/ 62 9 Claims. (Cl. 222-422) This invention relates to a method and apparatus for forming and dispensing discrete liquid drops from a main liquid body, and is particularly useful in the production of pellets or pastilles from fusible materials. I

Various methods and types of apparatus are known for this purpose, and one known apparatus comprises a nozzle having a cylindrical bore in which is positioned a conical needle. The needle is stationary during the dripping operation but its position may be altered so as to increase or decrease the cross sectional area of the annular space between the needle and the nozzle bore thereby adjusting both the speed of drop formation and the quantitative output. Another known method of drop forming comprises maintaining a constant level of the liquid in a container, leading the liquid to the upper end of at least one tube mounted in the bottom of the container and causing a piston to reciprocate within each of the tubes with a gap between each tube and its piston through which liquid flows, with the lower end of each piston projecting beyond the lower end of its tube so that drops become detached from the pistons according to the frequency of the reciprocation at each upwardly directed movement of the piston. The dimensions of the nozzle passageway and of the movable piston allow a continuous flow of the molten material through the nozzle when the piston is stationary.

This latter method of drop dispensing is, however, limited in its volumetric output per nozzle and also in its speed of piston reciprocation (e.g. about 350 r.p.m.). It has been found that above these limits of output and rate of reciprocation, drop formation becomes diflicult to control or fails to take place.

Furthermore, if uniformity of drop size is desired from a plurality of such nozzles operating together, the cross sections of the pistons and passageway bores are required to be accurate to within extremely narrow tolerances since the nature of the continuous annular flow is such that slight inaccuracies in these dimensions are greatly magnified in the resulting size of drop and cause flooding.

It is an object of the present invention to provide a method and apparatus by which uniformly sized drops may be dispensed from a liquid source at higher volumetricoutputs and speeds of reciprocation than those heretofore attainable and it is a further object of the invention to provide such apparatus to be capable of operating with liquids of widely varying viscosities. As mentioned above, the invention is particularly useful in the production of pellets or pastilles and this is commonly effected in a machine (hereinafter referred to as a pastillating machine) of the type in which drops of liquid are dispensed via one or more liquid drop dispensers from a liquid reservoir onto a surface, which, if a molten material is used, may be cooled, for example on a cooled conveyor band, cooling cylinder, cooling plate or the like. Alternatively, the solidification may be effected by polymerization, gelling, drying, etc. Consequently, it is a further object of the invention to provide an improved pastillating machine which is capable of attaining higher volumetric outputs and speeds of reciprocation than hitherto known types.

The presentmethod of forming and releasing a succes- 3,341,987 Patented Sept. 12, 1967 sion of discrete liquid drops from a main body of liquid comprises admitting liquid from the main body into a passageway having an open outlet end at a location remote from the open outlet end and applying pulsations to the liquid entering the passageway, thus decelerating the liquid in the passageway and causing drops to be released from the open outlet end.

The invention further consists in a method of forming and releasing a succession of discrete liquid drops from a main body of liquid through an open ended passageway which receives liquid from said main body through port means located remote from said open end, comprising reciprocating plunger means in association with the passageway between an inner position in which the port means are at least partially open and an outer position in which the plunger means remains remote from said open end, the plunger means being eifective to decelerate the liquid in the passageway during a part of each reciprocation, the combined effect of which deceleration and of the momentum of the liquid towards said open end, causes a drop to form and separate from the liquid in the passageway and to be released from the open end.

The invention still further consists in a method of forming and releasing a succession of discrete liquid drops from a main body of liquid through an open-ended passageway having port means communicating with the main body of liquid, comprising reciprocating plunger means in co-operation with the passageway between an inner and an outer position to cause the flow of liquid through said port means to be shut off or throttled, and so controlled,

1 the plunger means also creating drop forming pulsations through the liquid in the passageway whereby drops are formed, at the same frequency as the plunger means reciprocates, as the liquid issues from the open end of the passageway.

The invention still further consists in a drop forming device comprising a nozzle having an internal passageway adapted to receive liquid from a main liquid body via port means, reciprocable plunger means, and means for reciprocating the plunger means in co-operation with the nozzle, between an inner and an outer position to repeatedly shut off or throttle the flow of liquid through said port means thereby controlling the supply of liquid to the passageway, the plunger means also being effective to create drop forming pulsations through the liquid in the passageway, whereby drops are formed, at the same frequency as the plunger means reciprocates, as the liquid issues from the open end of the passageway.

The invention still further consists in a pastillating machine having one or more drop forming devices according to the preceding paragraph.

The invention will be described by way of an example, with reference to the accompanying drawings in which:

FIGURE 1 is a sectional elevation through the reservoir tank of a drop dispenser.

FIGURES 2 to 6 show alternative forms of drop dispenser to that shown in FIGURE 1, and

FIGURE 7 is side elevation, partly in section, of a pastillating machine showing one of a number of drop dispensers positioned therein.

FIGURE 1 shows a liquid drop dispenser mounted at the base of a molten liquid reservoir tank 1 for dispensing a succession of liquid drops from the reservoir tank, for example, onto cooling surface where the drops solidify to form pastilles.

Each drop dispenser comprises a nozzle generally indicated by 3, lower portion 6 of which is provided with an internal passageway 4 and means, for example an external screw thread 5 for attaching the nozzle in a vertical position to the base of the reservoir tank 1. The internal nozzle passageway 4 may be of any convenient cross section, but a cylindrical bore is preferred. The configuration of the nozzle 3 is such that when screwed into the tank, only its lower end projects therefrom while upper portions 9 and 7 extend into the reservoir to be immersed in the liquid. The upper portion 7 is provided with port means consisting of one or more liquid admitting ports 8 formed in its wall at or near the bottom of the tank and these may be of any desired number and form. Above the ports and co-axial with the passageway 4, guide means 9, which may be integral with, or an extension to, the nozzle, are provided for pulsating means consisting of a reciprocable plunger 10 (shown at or towards the bottom of its stroke) which is connected at its upper extremity to a reciprocating means. The following description refers to a cylindrical passageway and plunger but it is appreciated that the description is also applicable to other configurations of the passageway and to other pulsating means, e.g., a disc or plate partly or fully covering and uncovering suitable port means, e.g., not entering the passageway or a plunger having a conical tip which reciprocates in the port of the nozzle.

The plunger 10 comprises a cylindrical rod, the diameter of which has a sliding fit within the upper portion of the nozzle 3 so as to substantially prevent an annular flow of liquid between the plunger and the surrounding nozzle wall above the ports. For example, the ratio of plunger diameter to the internal diameter of the portion of the nozzle in which the plunger reciprocates may be of the order of 0.97 to 1.

The reciprocation means may for example take the form of an eccentrically driven cross-bar into which the plunger is screwed, and it is arranged by suitable adjustment of the plunger in the cross bar so that the active lowermost surface 11 of the plunger within the upper portions 9 and 7 of the nozzle may reciprocate between an extreme upper position at or-above the top of the ports and an extreme lower position at, above or below the bottom of the ports, but, it is generally preferred to operate with the plunger travelling from a position above the top of the ports to a position just below the ports at the bottom of its stroke. If the plunger movement, produced by an eccentric drive, is not suitable, it may be replaced by cam action. In this case, the duration of the plunger reciprocation may be less than the duration of the cycle.

In the example of FIGURE 1, the arrangement of the ports 8 and nozzle passageway is such that when the plunger 9 is in the extreme upper (or inner) position, liquid is freely admitted to the passageway, and that with certain exceptions, of which an example will be given, the plunger, on its downward movement (or movement towards its outer position), cover the ports so that the flow of liquid to the passageway is either throttled or interrupted. During the period in which the ports are uncovered, with each plunger reciprocation, the liquid which flows through them into the passageway corresponds to the average volume of the drop formed. Hence, the cross-sectional area of the ports have to be dimensioned to suit this requirement and generally has to be increased for larger outputs and more viscous liquids.

The dimensions of the port and passageway may be such that for a given liquid the plunger speed when covering the ports is less than the speed of the liquid flow through the passageway. In this case the plunger, in its downward movement, decelerates the liquid in the passageway. This process continues until on its return stroke the plunger again uncovers the ports. This deceleration of the volume of liquid upstream of the drop assists and speeds up the process of drop formation and its separation from the liquid in the passageway. For more viscous liquids it is preferred that the arrangement be such that during part of the return stroke of the plunger there is a reversal of the forward flow in the passageway.

The dimensions of the port and the passageway may, on the other hand, be so chosen in relation to the plunger or equivalent pulsating means that during the downward movement of the latter an impulse is transmitted to the liquid in the passageway. In this case the deceleration only begins when towards the end of the downward stroke.

It has been found that by continuously reciprocating the plunger in this manner, liquid drops can be rapidly formed and released from the open end of the passageway, and a single discrete drop is formed for each plunger reciprocation.

For a given volume output, it is possible to vary the size of each drop by adjusting the rate of reciprocation of the plunger, a greater rate of reciprocation giving more, but smaller drops, while conversely, a slower rate of reciprocation produces fewer but larger drops with the same overall volumetric output.

The apparatus has been satisfactorily operated at frequencies of the order of 1,000 reciprocations (and hence 1,000 drops) per minute, and is considered to be capable of operating at frequencies in excess of this.

It should also be appreciated, that the length of stroke of the plunger is another variable capable of adjustment since this, together with plunger velocity, influence the size of drop formed. Thus for a particular port area, one satisfactory port configuration is a narrow circumferentially extending slit, since this provides maximum liquid supply for minimum plunger movement, which enables short plunger strokes and consequently high frequencies of reciprocation and drop formation to be employed. Alternatively, the ports can be of circular cross section and there may be one port or a number of ports.

As examples, the following are suitable values for the dimensions of a liquid drop forming apparatus constructed according to the invention, when used under the cond1t1ons shown, the mventron however in no way being lumted to these ranges of values:

Example Example Example I II III Tert. Dimethyl Product butyl Pitch terephphenol thalato Operating temperature, C. 217 Viscosity, centistokes 2. 5 240 0. 84 Surface tension, dynes/orn. 20-30 30 Head of liquid, cm 14. 5 7. 5 Rate of reciprocation of plunger,

strokes/min 400 600 500 Output per nozzle, kg./hr 3. 2 l7 3. 3 Volume per drop, cc... 15 40 103 Nozzle details:

Dia. of passageway, mm 3. 97 6. 35 3. 97 Dia. of plunger, mm 3. 83 6. 25 3. 83 Die. of port, mm. 1. 59 5. 6 0. 97 N0. and form of ports 1 1 Z 2 1 1 Length of passageway below ports, mm 19. 6 17 33 Length of plunger stroke, mm. 7 14.5 5 Distance of plunger tip below bottom edge of port at bottom of stroke, rnm 5 1 a 8 1 Round hole. 2 Round holes. 5 Above port.

It will be seen from the table that in Examples I and II the lower face 11 of the plunger 10 in its extreme upper position is above the port means, and in its extreme lower position is below the port means so that the plunger itself operates as a valve on the port means. In Example III the plunger operates wholly above the level of the port means and the plunger induced flow of the liquid past the port means may throttle or inhibit the flow of liquid through the port means into the passageway. In all three cases, the reciprocation of the plunger has the function of transmitting longitudinal pulsations through the liquid in the passageway which assists the rapid separation of the emerging drops.

In the above examples and part of the description it has been tautly assumed for the sake of clarity that the liquid flows by gravity into the passageway and that the plunger is moving in a substantially vertical direction.

' This is in many cases the simplest and best arrangement.

But it will be appreciated that the flow of liquid through the ports could be effected by means other than gravity and that due to the rapidity of reciprocation and the momentum of the drops issuing from the open end of the passageway there is no necessity to release them vertically downward.

Vertically downward release may indeed become a definite disadvantage when pastillating at a high rate of output and when the drop size is large and the liquid viscous. The time required for full drop formation increases with drop size and the viscosity of the liquid, which means that, particularly at high outputs, the distance between the nozzle and the cooling surface has to be increased to ensure clear separation of successive drops before impact on the cooling surface. This is undesirable as this also increases the speed of impact which, combined with the inevitably larger band speeds, leads to undesirably flattening and elongation of the pastilles and other faults.

Hence, it is advantageous under such conditions to eject the drops in the horizontal direction or even slightly upwards. The center line of the nozzle should be generally parallel to the surface of the cooling band and the vertical distance between this center line and the band surface as small as convenient.

If under such conditions where the speed of the band is adjusted to the velocity of the drops leaving the nozzle, it will be appreciated that such an arrangement would have many advantages.

(1) Firstly, the distance through which the drop would travel from the nozzle before impinging on the cooling surface could be lengthened without any inconvenience. As the drop would travel parallel to the cool surface it Would lose more heat before impinging on it than in a vertical descent through the same distance. This results normally in the formation of a sink which improves the shape of ultimate pastille.

(2) Secondly, the speed at which the drop would impinge on the surface would be independent of the forward speed and, therefore, could be much smaller. This results in less flattening and elongation of the drop on impact.

(3) Thirdly, the angle at which the drop would impinge is very small which again results in an improvement of the pastille shape.

Furthermore, it may be convenient to eject the drops from the nozzle in the opposite direction to the travel of the band. In this arrangement, advantage (1) above is apparent and also, the tail of the drop tends to collapse into the dropbody on impact with the band so that a tailed pastille is avoided.

As heretofore described, the drop forming apparatus includes a passageway 4 of constant cross section, but the cross section may be varied along the length of the passageway.

Various other modifications are also possible, within the scope of the invention, for example, the plunger instead of co-operating with the ports from within, as shown in FIGURE 1, may be constructed in the form of a sleeve 12 as shown in FIGURE 2 fitting around the upper portion of the nozzle and co-operating with ports 13 externally. The upper end of the sleeve is closed and connected to the reciprocating means by a rod 15. Alternatively, the sleeve, as shown in FIGURE 4, may have a port or ports 17 formed in its walls, to co-operate with nozzle ports 18, or, as shown in FIGURE 3, the nozzle ports may be eliminated, and only a sleeve port or ports 16 used.

In these alternative constructions the area of the forward face of the plunger is larger than the cross sectional area of the passageway. The larger plunger displacement, therefore, leads under otherwise identical conditions to a larger forward velocity of the liquid in the passageway than in the arrangement of FIGURE 1. Hence, if a posi- 6 tive impulse is to be imparted to the liquid in the passageway during the downward movement of the plunger, the constructions of FIGURES 2 to 4 are preferred.

The plunger may also be in the form of a disc 34 (see FIG. 5) or a cone 35 (see FIG. 6). In these cases, the opening at the top of the passageway 4 forms the port means.

FIGURE 7 shows a section of a pastillating machine in which vessel 1 may be heated by electrical or other means e.g., an outer jacket 31 through which a heating fluid is circulated. The liquid product is fed into this vessel through pipe 20, with the flow into the vessel being adjustable by a valve 21 which is generally automatically controlled.

The nozzles 3 are screwed into the base of this vessel.

The plungers 10 are carried by a reciprocating plunger bar 22 which, at each end, is fixed to a guide pillar 23 passing through brass sleeve bearing 24. These pillars are coupled by self aligning bearing bushings 25 to connection rods 26 driven by two eccentric self aligning bearings 27 on a rotating shaft 28. This shaft is driven :by a variable speed gear 29 which allows the rate of reciprocation of the plungers to be varied. This gear 29 is driven by a motor 30 running at 1440 rpm. for example.

The drops fall on to a moving steel conveyor band 32 which is cooled by water sprays 33 on the underside.

This invention is not to be confined to any strict conformity to the showings in the drawings but changes and modifications may be made therein so long as such changes and modifications mark no material departure from the spirit and scope of the appended claims.

We claim:

1. A method of dispensing a liquid in the form of a continuous series of discrete drops of uniform size from a container of the liquid including a nozzle having an axial passageway communicating with the interior of the container and having an unobstructed outlet opening and including a reciprocable plunger cooperating with the nozzle to control the flow of liquid therethrough comprising the steps of moving the plunger toward and away from the nozzle so as to cause a drop to be dispensed from the outlet opening during each cycle of plunger operation, and maintaining a volume of the liquid being dispensed within the nozzle passageway at the unobstructed outlet end thereof at all times during the cycle of plunger operation so that each drop of liquid is dispensed by causing it to separate from the body of liquid maintained within the nozzle passageway.

2. A method according to claim 1 wherein the volume of liquid maintained at all times within the nozzle passageway is at least equal to about one drop.

3. A method according to claim 1 wherein the flow of fluid from the container into the nozzle passageway is completely obstructed by the plunger during a portion of each cycle of plunger operation.

4. A method according to claim 1 wherein communication between the container and the nozzle passageway is maintained at all times during each cycle of plunger operation.

5. In apparatus for dispensing a liquid in the form of a continuous series of discrete drops of uniform size including a container for liquid to be dispensed, nozzle means in the wall of the container having an inlet opening communicating with the interior of the container through which liquid to be dispensed is received into the nozzle means and having an axial passageway communicating with the inlet opening, and a reciprocable plunger cooperating with the nozzle means inlet opening and having an end movable axially with respect to the nozzle passageway between a first extreme position spaced from the inlet opening and a second extreme position adjacent to the inlet opening to control the flow of liquid into the nozzle passageway, the improvement comprising a tubular extension of the nozzle means forming an unobstructed axial extension of the passageway therein extending a substantial distance beyond the second extreme position of the end of the plunger and terminating in an unobstructed outlet opening so as to retain a selected volume of the liquid within the passageway after each drop has been dispensed from the outlet opening thereof.

6. Apparatus according to claim 5 in which the tubular nozzle extension provides a passageway volume beyond the second extreme position of the end of the plunger at least equal to that of about one drop of the liquid dispensed by the apparatus.

7. Apparatus according to claim 5 wherein the crosssectional shape of the plunger end is the same as that of the nozzle passageway.

8. Apparatus according to claim 7 wherein the nozzle means includes an inwardly extending portion within the container, the plunger end being slidably guided therein, the inlet opening comprising an aperture in the wall of the inwardly extending portion.

9. Apparatus according to claim 5 wherein the plunger end forms a hollow sleeve and the nozzle means includes an inwardly extending portion guided within the hollow sleeve.

References Cited UNITED STATES PATENTS ROBERT F. WHITE, Primary Examiner.

WALTER A. SCHEEL, Examiner.

J. SHEA, J. R. HALL, Assistant Examine-rs.

Claims (1)

1. A METHOD OF DISPENSING A LIQUID IN THE FORM OF A CONTINUOUS SERIES OF DISCRETE DROPS OF UNIFORM SIZE FROM A CONTAINER OF THE LIQUID INCLUDIG A NOZZLE HAVING AN AXIAL PASSAGEWAY COMMUNICATING WITH THE INTERIOR OF THE CONTAINER AND HAVING AN UNOBSTRUCTED OUTLET OPENING AND INCLUDING A RECIPROCABLE PLUNGER COOPERATING WITH THE NOZZLE TO CONTROL THE FLOW OF LIQUID THERETHROUGH COMPRISING THE STEPS OF MOVING THE PLUNGER TOWARD AND AWAY FROM THE NOZZLE SO AS TO CAUSE A DROP TO BE DISPENSED FROM THE OUTLET OPENING DURING EACH CYCLE OF PLUNGER OPER-

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