US2790201A - Apparatus for manufacturing pellets from fusible materials - Google Patents

Description

April 1957 H. EILBRACHT ET AL 2,790,201

APPARATUS FOR MANUFACTURING PELLETS FROM FUSIBLE MATERIALS Filed June 14, 1955 FIGI INVENTORS'Z ANS EILBR'ACHT MANFRED HAEBERLE BY 0.1.2. I

% @o-v-Z I ATT YS APPARATUS FOR MANUFACTURING PELLETS FROM FUSIBLE MATERIALS Hans Eilhracht and Manfred Haeberle, Mannheim, Germany, assignors to Badische Anilin- & Soda-Fabnk Aktiengeselischaft, Ludwigshafen (Rhine), German Federal Republic Application .iune 14, 1955, Serial No. 515,458

Claims priority, application Germany June 19, 1954 7 Claims. (Cl. 18-2.4)

This invention relates to an improved method and to an improved apparatus for the production of pellets from fusible materials such as waxes, dyestuffs and other products of the chemical, pharmaceutical and food industry.

Fusi'ole materials are often sold in the form of pellets which are obtained by cooling drops of the molten material, for instance, on cooling surfaces, such as cooling plates, cooling cylinders or cooling belts. Heated dripping pans provided with perforations or nozzles or little tubes on their bottom side are used to produce the molten drops. The dripping velocity mainly depends on the viscosity, the surface tension of the melt, the level of the melt in the pan, the size of the perforations of the dripping devices and the frictional resistance in the dripping device.

A common feature of all of these dripping devices is that the flow of the molten material through the perforations per time unit must be kept below a certain value to obtain individual drops because at a higher value an uninterrupted stream of the molten material is formed instead of melt drops.

A well known dripping device shown in Fig. 1 consists of a nozzle a having a cylindrical opening or perforation b and a conical nozzle needle 0. The nozzle needle is stationary during drop formation. By raising or lowering the needle 0 to a different fixed or stationary position, the space between the needle and'the side of the nozzle passageway is increased or diminished, whereby the speed of the drop formation is changed. When little tubes are used to provide a nozzle passageway for the dripping devices, the height of these tubes may be modified to vary the velocity of the drop formation.

It is, however, disadvantageous that each nozzle or tube of such an apparatus must be adjusted individually by hand and frequently requires regulation. A further disadvantage arises in the clogging of the dripping devices so that they must be frequently cleaned.

It is an object of this invention to provide an improved method and an improved apparatus for manufacturing pellets from fusible materials, in particular from fusible organic materials.

Another object of the invention is an improved dripping device for waxes, dyestuffs, plastics, and pharmaceuticals.

Other objects and advantages of the invention will be apparent by reference to the following description and the accompanying drawings, in which Fig. 1 represents a prior art dripping device as previously described;

Fig. 2 is a sectional elevation of the invention;

Fig. 3 is an enlarged sectional the device shown in Fig. 2; and

Fig. 4 is an enlarged view of a modifiedform of dropforming piston provided by the invention.

In accordance with this invention a heated molten material which is normally solid at room temperature is passed through a nozzle while moving a piston back and a device provided by elevation of a portion of hire States Patent 0 forth within the nozzle opening so as to interrupt the continuous flow of the molten material through the nozzle.

It is advantageous to arrange one or several of the nozzles on the bottom of a melting pan. The perforations or openings of the nozzles and the reciprocal movement of the piston within the nozzle opening should be preferably in a vertical direction. When the piston of such a nozzle stands still a stream of the molten mass flows through the nozzle. By the upward movement of the piston the flow of the melt is retarded so much that the melt stream leaving the nozzle is interrupted in drops. The drops flow downwardly on the surface of the piston and leaves the piston at its lower end. The downward movement of the piston causes an acceleration of the melt stream. The melt drops are cooled'in the conventional way, for instance, on rotating cooled steel plates or cooled steel cylinders or cooled metal belts.

The dimensions of the nozzle openings and of the piston are so adjusted that the piston does not prevent the gravity flow of the molten material when the piston and the nozzle stand still, with respect to one another. Only the forces produced by the friction of the relative movement of the piston and nozzle lead to the interruption of the molten stream and to the formation of drops. The form and the size of the piston and of the nozzle opening may be varied. Preferred are circular openings and pistons with a cylindrical cross-section. As a rule, nozzles having a diameter for instance between 4 and 10 mm. or more are used. The piston to be employed in such nozzle openings should preferably have a dimension of for instance between 2 and 5 mm. or more. Advantageously, the piston may be arranged'in the center of the nozzle opening in order to provide a space of uniform crosssection. As a rule, nozzles having a length of for instance between 20 and mm. are used. The pistons are longer than the nozzle passageways and their upper part is connected with a device to move them. The lower side of the pistons may have an elongation so as to bring the interrupted melt flow very close to the cooling device.

In Fig. 2 the pellet-forming device illustrated comprises a container 1 adapted to receive a thermoplastic or other meltable substance 2 which is maintained in a molten condition by means of steam pipes 3 in the bottom of the container 1. A float 4 provided with a rod 5 indicates the level of the melt 2. A pipe 6 is connected to a source of supply for the molten material. I

The pistons 7 are each connected to a cylindrical soft iron disc 8 which is magnetically attracted by the magnetic forces of the electromagnet generally shown at 9. The electromagnet 9 consists of a soft iron core 10 and a coil 11. The screw devices 12, 12 are provided to adjust the height of the magnet 9.

The nozzles 13 are provided with a cylindrical bore or passageway 14. Each of the pistons 7 is provided with a stop member 15 at which is mounted a spring 16.

The pistons 7 are mounted above a cooling belt 17 which is cooled from beneath by means of a pipe 18 which is perforated to provide a spray of cooling water 19.

In operation the pistons 7 are drawn upwardly by the magnetic attraction of the magnet 9 for the soft iron discs 8. When the magnet 9 is demagnetized the spring 16 causes the pistons 7 to move downwardly again. The rapidity of the movement can be controlled by the rapidity of the magnetization and the demagnetization of the magnet 9. Drops of the molten material are formed'in the openings or passageways 14 and the individual drops fall on to the belt 17. In a preferred embodiment of our invention the piston moves down to a point'close above the belt. With this constructive embodiment of the piston the molten material carried down by 'the'piston is deposited. on the belt when the piston has reached its lowermost position and the drop is formed when the 3 piston moves upwards again. The belt 1 7 is moved at a suitable rate to carry the drops away from the dropforming device. Instead of the belt 17 a disc or other "suitable'carrier device can be employed.

I-tis alsopossible toenlarge or toreduce certainpa'rts of the piston. There may'beused, for :example, pistons havingthe lower part enlarged in the formof'aball ora disc-20 as'shown in Fig. 4. Such enlarged parts maybe so arranged that they lie in the mouth of the nozzle while the-piston is in -the upper dead point. By var ing-the dimensions of the free space "between the sides of the nozzle passageways and the pistons, the size of the drops and the dripping velocity can be markedly changed. The frequency of the piston movement has a great influence on the drop size and ahigh frequency of the piston movement leads to small drops while a low frequency tgives large drops. The speed of the drop formation may be changed for a given dimension of the nozzle opening and .of'the piston diameter by varying the frequency of the piston movement and to a lesser extent by changing the heights of the stroke. As a rule, the piston should be moved for instance from mm. to 50 mm. with a frequency from about .150 'to'about 250 .movementsper minute, each frequency including a back'and forth movement.

The movement of'the piston can be efiected individually or commonly by eccentric discs or aperiodic magnetic field, pneumatically, or by other known devices. The downward movement may beaccelerated by a spring.

Several pistons can be fixed on a common soft iron core while using a periodic magnetic field for their movement. This soft iron core is periodically lifted by themagneticfield. The downwardmovement is effected by the weight of the movable parts or by a spring. The pistonscan also be individually fixed on a soft iron core.

It is advantageous to .use nozzles with different frequencies ifa rotating plate is used as a cooling device. In .suchcasc thefrequencyrof-the piston movement should be higher toward the external parts of the rotating plate and lower toward the internal part of the rotating plate to obtain a uniform charge ofsthe cooling plate. Cooling belts and cooling cylinders require :only one frequency for-the movement of the nozzle pistons.

The term piston used to .describe this invention includes plugs, stamps, rods, sticks and similar forms "of moving members having a smaller cross-section than the nozzle passageway. The expression pellet encompasses beads, pearls, balls and similar particles obtained from melt drops which are usually flattened to *a certain extent while cooling and solidifying.

The following example illustrates a particularembodiment of the invention but theinvention is not restricted .to this example.

Example A wax-like polyethylene having a 'molecular'weight of about 5,500 determined by the method of K. Ueberreiter, .H. J. Orthmann and O. Sorge Die makromolekulare Chcrnic 8, 1952, page2l, isnrolded and formed into pellets in two similar apparatus, one of them (Apparatus I) having the old dripping device according to Fig. 1, and the other (Apparatus H), a new dripping device schematically shown in Fig. 2, showing in Fig. 3 a nozzle 13 having a circular passageway 14 with a diameter .of 5 mm. and a length of 50 mm. The piston 7 has a diameter of 2 mm. and is moved with 'afrequency of 200 reciprocatory movements per minute. In both types of apparatus the melt level is 60 mm. and the polyethylene melt is kept at a temperature of 230 C. having at this temperature a viscosity of 7C 'cst. 'The dripping device of Fig. 1 is adjusted to maximum velocity. Within 1 hour 400 grams of polyethylene pellets are obtained with Apparatus I.

.The .pellets have a diameter of about 5.5 mm. and an average weight of 0.048 gram. The distance between the pellets on the cooling surface is 12 mm. Within thesame 4 period of time Apparatus 11 produces 1900 grams of polyethylene pellets having a diameter of 10 mm. and an average weight of 0.19 gram. The distance between the pellets on the cooling surface in this case is about 1.5 mm.

The output of the apparatus with the new dripping device was therefore about five times higher than that of. the apparatus with the commonly used dripping device. By varying the dimensions of the nozzle opening and of the piston and increasing'thefrequency of the piston move 'ment, the efficiency of the new device can be further increased.

It is an essential advantage of this this invention that it is not necessary to adjust 'each dripping device individually while using an apparatus with several nozzles. The pistons may be secured to a common suspension device and may be commonly moved up and down. No clogging of the nozzlesoccurs and the level of the melt in themelting pan has only a slight influence on the drop formation. The output of a nozzle according to this invention is about five to ten times higher than that of nozzle of the type shown in Fig. 1. At the same time, a much denser charge of the cooling devices is achieved.

The inventionis hereby claimed as follows:

1. An apparatusffor pelletizing fusible materials comprising a nozzle, apiston within the opening of said nozzle, the dimensions of said nozzle opening and of the piston being such that there is a space between the sides of the nozzle openingand the piston which allows a continuous How of a molten material through the nozzle openings when the piston and the opening stand still with respect to one another and causes individual drops to form when the piston and the nozzle opening are moved with respect to one another when a molten material is flowing therethrough, means to supply said molten material to said nozzle, and means to move said piston and said nozzle opening one with respect to the other while said molten material is being supplied to said nozzle.

'2. An apparatus for pelletizing fusible materials comprising a nozzle a piston within the opening of said nozzle, the dimensions ofsaid nozzle opening and of the piston being 'such that there is a space between the sides of the nozzle opening and the piston which allows a continuous flow of a moltenmaterial through the nozzle openings when the piston and the opening stand still with respect .to one another.andcausesindividual drops to form when thep'is'ton and the nozzle opening are moved with respect to one another when a molten material is flowing therethrough, means tosupply said molten material to said nozzle, and means to move said piston in said nozzle opening while said molten material is being supplied to said nozzle.

3. An apparatus for pelletizing fusible materials comprising a nozzle and amovable piston within the opening of said nozzle, the nozzle perforation having a diameter between about 4 and about 16 mm., the piston having a diameter of between about 2 and about 5 mm., and the piston being secured to a moving device capable of moving the piston back and forth in the nozzle opening with a frequency between about and 250 piston movements per minute.

4. apparatus 'for pelletizing fusible materials comprising a nozzle, a reciprocable piston extending through said nozzle, thedimensions of said nozzle opening and of the piston being-suchthat there is a space between the sides of the nozzle opening and the piston which allows a continuous .flowof. amol-tenmaterial through the nozzle openingswhen the piston and the opening stand still with respect to one another and causes individual drops to form when the piston and the nozzle opening are moved with respect to one another when a molten material is flowing therethrough, means to supply said molten material to .said nozzle, and means to reciprocate longitudinallysaid piston-insaidnozzle, a portion of-said piston extending from the discharge :end of the nozzle during the entire reciprocal cycle.

5. An apparatus for pelletizing fusible materials comprising a nozzle, a reciprocable piston extending through said nozzle, the dimensions of said nozzle opening and of the piston being such that there is a space between the sides of the nozzle opening and the piston which allows a continuous flow of a molten material through the nozzle openings when the piston and the opening stand still with respect to one another and causes individual drops to form when the piston and the nozzle opening are moved with respect to one another when a molten material is flowing therethrough, means to supply said molten material to said nozzle, means to reciprocate longitudinally said piston in said nozzle, a portion of said piston extending from the discharge end of the nozzle during the entire reciprocal cycle, and a drop-receiving member movable transversely of said piston movement to carry the drop away from said piston, said drop-receiving member positioned close to the end of said piston at its outermost extension from said nozzle.

6. The apparatus of claim 5 wherein said drop-receiving member is provided with cooling means to facilitate solidification of the drops deposited thereon.

7. An apparatus for pelletizing fusible materials comprising a nozzle, a reciprocable piston extending through said nozzle, the dimensions of said nozzle opening and of the piston being such that there is a space between the sides of the nozzle opening and the piston which allows a continuous flow of a molten material through the nozzle openings when the piston and the opening stand still with respect to one another and causes individual drops to form when the piston and the nozzle opening are moved with respect to one another when a molten material is flowing therethrough, means to supply molten material to said nozzle, and means to reciprocate longitudinally said piston in said nozzle opening while said molten material is being supplied to said nozzle.

References Cited in the file of this patent UNITED STATES PATENTS 1,938,219 Eckerbom Dec. 5, 1933

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