US3715076A

US3715076A - Method and apparatus for spraying powdered thermoplastic substances

Info

Publication number: US3715076A
Application number: US00136936A
Authority: US
Inventors: T Kenderi
Original assignee: HAJTOMU ES FELVONOGYAR
Current assignee: HAJTOMU ES FELVONOGYAR; HAJTOMU ES FELVONOQUAR
Priority date: 1971-04-23
Filing date: 1971-04-23
Publication date: 1973-02-06
Anticipated expiration: 1990-02-06
Also published as: FR2130989A5; CH556691A; BE765071A

Abstract

POWDERED THEMOPLASTIC SUBSTANCES ARE SPRAYED IN HEATED FORM AGAINST A SUBSTRATE, BY ENTRAINING THE POWDER COLD IN A GAS STREAM, AND EJECTING THE GAS STREAM FROM A NOZZLE IN THE FORM OF A FLAT CLOUD. THE CLOUD IS CONFINED BETWEEN A PAIR OF FURTHER GAS STREAMS AND IS HEATED ON THE WAY TO THE SUBSTRATE. HEATING MAY BE EFFECTED BY PASSING THE CLOUD SANDWICHED BETWEEN ITS CONFINING STREAMS, BETWEEN A PAIR OF OPPOSED ELECTRIC HEATING ELEMENTS. ALTERNATIVELY, HEATING MAY BE EFFECTED BY HEATING THE CONFINING STREAMS THEMSELVES, PARTICULARLY IF THE CONFINING STREAMS ARE FLAMES EMERGING FROM A BURNER.

Description

Feb. 6, 1973 r.

KENDERI

3,11%076 METHOD AND APPARATUS FOR SPRAYING POWDERED THERMOPLASTIC SUBSTANCES Filed April 23, 1971 In venlor 7700,? Aim/05x? 35% raw A Horn 9 y:

United States Patent 3,715,076 METHOD AND APPARATUS FOR SPRAYIN G POWDERED THERMOPLASTIC SUBSTANQES Tibor Kenderi, Budapest, Hungary, assignor to Hajtomu es Felvonogyar, Budapest, Hungary Filed Apr. 23, 1971, Ser. No. 136,936 Int. Cl. 1305b 1/24, 1/28; C23c 7/00 US. Cl. 239-8 14 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method and apparatus for the spraying of powdered substances, particularly of thermoplastic powdered substances.

' Numerous methods and devices are conventional for the spraying of thermoplastic powdered substances, all of which serve for the production of coatings on various surfaces. The gravest and most important disadvantage exhibited by the conventional devices resides in the fact that the uniform and reliable heating of the appropriate amount of spray powder, as well as the uinform metering thereof in the desired quantity, especially after there has been an interruption and resumption of the spraying procedure, are not ensured. Furthermore, the spray nozzles of the devices known heretofore do not ensure a uniform thickness of the coating, and the width of the spray jet cannot be varied without expanding additional energy. Additionally, there is the disadvantage in the conventional devices that they are unsuitable, without some change in the equipment, for the intermittent or continuous spraying not only of powdered substances exhibiting a high melting point but also of those exhibiting a low melting point. A further disadvantage resides in the fact that, in these devices, the transition from one type of powder to another, and the cleansing of the device, can be conducted only with difiiculty and only after re-assembling the device.

In the conventional spraying methods and apparatus, the metered powder is sprayed in the shape of a cone; and consequently, it is impossible to ensure the uniform heating of the powder or the uniform layer thickness of the coating. The devices provided with such nozzles, although suitable for purposes of backfill welding, are unsuitable for the production of a corrosion-resistant coating requiring a uniform layer thickness over a large surface area.

A powder spray device is also known wherein the mixing of oxygen or air and fuel gas is effected by means of nozzle bores arranged in parallelism to each other in two concentric circles. In this device, a guide ring connected to the nozzle by a metal bond is employed for varying the flame shape. Due to this metallic connection, the nozzle is strongly heated during operation. In this device, the powder spray nozzle is mounted by means of a fixed and airtight connection provided on the center line of the nozzle. In other words, the nozzle is surrounded on all sides by the flame during operation. Also in this apparatus, a cone-shaped spray jet results which, accordingly, does not ensure that the thus-sprayed powder particles are heated uniformly. The axis of the bores serving for the exit of the gaseous mixture producing the flame is disposed parallel to the axis of the power nozzle; consequently, the lateral expansion of the powder jet is unlimited, with the result that the planar surface to be coated by means of the spray from this nozzle is provided with a non-uniform coating which is thicker in the center.

Still another device is conventional wherein the powder to be sprayed is conducted by the nozzle through a pipe with a heated wall and is plasticized in this manner. In order to prevent flowing of the substance particles emanating from the nozzle on the substrate to be coated, the mouth opening of the nozzle is provided with a number of bores through which unheated gas is admixed with the hot gas jet conveying the molten powder. During operation, the pipe serving for melting the powder must have a temperature which is substantially above the melting point of the powder. Thus, for example when spraying aluminum powder, this temperature is above 900 C. However, at such a high temperature, the gastight seal and the production thereof are plagued with difliculties. Also in this device, the orifice adjoining the end of the heating pipe is fashioned with a circular cross section, or with a different one, for example a basket-shaped cross section, However, a consequence of this shape is that the powder which has been molten or brought to a high degree of plasticity is subjected, after flowing through the round heating pipe, to a forcible change in direction in the basket-shaped mouth orifice; and as a result, the powdered substance adheres to the wall of the mouth orifice.

An object of the present invention is to provide a process and construction of a powder spraying apparatus universally suitable for powder types having a high melting point as well as those having a low melting point, without exhibiting the disadvantages of the above-described devices, and ensuring a uniform and reliable heating of the powder, as well as, after shutoff and resumption of operation, a uniform metering of the powder and a uniform thickness of the coating, without the use of additional energy, and capable of being cleaned easily without disassembly.

The invention resides in that the powdered substance to be sprayed is spread out in a cold condition, with the aid of a cold gaseous stream, in the form of a flat cloud, the thickness of which cloud must be at least twice the granular size of the powder to be sprayed and at most one-eighth inch, the application of the powder to the substrate to be coated being effected by means of the cloud laterally supported by a gaseous stream and shaped as set out above, with simultaneous melting by thermal or electric energy.

Accordingly, this invention is based on the surprising finding that a cloud-like powder stream spread out flat can be heated in quite a short period of time and without the aid of any larger amount of thermal energy, over its entire extent, i.e., from the exit of the powder particles from the discharge orifice of the nozzle until their im pingement on the substrate to be coated, to the desired extent.

In the process of this invention, in contrast to all processes known heretofore, the cloud-like powder jet spread out flat is heated over its entire extent. Heretofore, it was possible to heat sufliciently only the particles which were present on the exterior of the atomizing cone; whereas the powder particles moving in the center of the atomized cone in the largest quantity and at the highest speed could be heated only with difficulty and in an unreliable mannner.

The invention provides not only an apparatus suitable for conducting the process of this invention, equipped with a powder container with a metering unit, but also a spraying device suitable for spraying the metered powder.

An important feature of the apparatus of this invention resides in that the spraying device is provided with a flat or fishtail nozzle, the width of which is at least twice the granular size of the powder to be sprayed and which nozzle is provided with a flat outlet orifice of a length of at most ten inches. Another important feature is that gasconducting bores are arranged on both sides of this outlet orifice and form an angle of about 20 with the midplane or plane of symmetry of the spraying device. Still another noteworthy feature is that energy supply elements are provided behind the outlet orifice of the nozzle, which elements extend along the two longitudinal sides of the powder jet spread out by means of the nozzle and defined laterally by gas jets.

This construction of the spraying device ensures cooling of the nozzle, since the air sucked in through an opening between the heating head and the nozzle ensures intense cooling due to the injector effect of the powder stream emanating from the spray nozzle. At the same time, this structural design also results in a quieter flow of the flame jets, because with the sunken nozzle construction the marginal vortex produced by the exit of the powder stream does not reach the flame jets.

Due to the fact, in turn, that the powder stream, spread out by the flat nozzle, is surrounded on both sides by energy supply elements behind the fiat outlet orifice of the spray device, it is ensured that it is possible to supply the powdered substances with the thermal energy, as well as with a diflerent type of energy, e.g. electric energy.

According to this invention, the inlet opening of the ejector serving for conveying the powder is arranged on the side of the ejector suction chamber. By this design, the disturbances occurring during start-up and shutoff can be eliminated, since the suction chamber of the ejector cannot become clogged.

Underneath the powder container of the device of this invention, which container is open at the bottom, a metering unit is provided which is controlled independently of the ejector, which unit is positively mechanically operated and is provided with an infinitely variable control. In this manner, this metering device can be operated independently of the ejector at any time with the required amount of power, or the operation can be interrupted or started up again. Due to the fact that this metering unit is provided with an electrically driven vibrating chute, bridging over of the powdered substance is avoided by transmitting vibrations to the system.

With the use of the process or apparatus of this invention, the spraying of the required amount of powder can be conducted with safety; and an additional advantage is afforded by the fact that all powder particles can be heated to the same temperature and that the device is universal, i.e. it is suitable for the spraying of powders of a high melting point, as well as those of a low melting point.

A detailed description of the invention is set forth below with reference to the embodiment illustrated in the drawing, wherein:

FIG. 1 diagrammatically shows the arrangement of the metering unit of the powder spraying device according to the present invention;

FIG. 2 is a fragmentary sectional view of the ejector of the device;

FIG. 3 diagrammatically shows the arrangement of the nozzle of the spraying device according to this invention;

FIG. 4 is a horizontal sectional view of FIG. 3;

FIG. 5 is a view of the nozzle of this invention as a heater outlet orifice according to a modification of the apparatus; and

FIG. 6 is a horizontal sectional view of the embodiment illustrated in FIG. 5.

Referring now to the drawing in greater detail, there is shown a container 1 for the storage of the powder to be sprayed. Container 1 is open so that the powder can be replenished continuously and in a simple manner. The

container 1 is fashioned, in the illustrated embodiment, in the form of a funnel which tapers downwardly and is open at the bottom. The powdered substance to be meterd flows through the lower end of this hopper to the vibrating chute 2. The vibrating chute 2 is actuated by an electromagnet. The feed of the powder present in container 1 can be infinitely varied by means of a rheostat (not shown) independently of the quantity of powder present. By interrupting the current source for the magnet, the powder feed can be interrupted or started up again at any desired instant, or it can be continued for any desired length of time. Underneath the discharge end of the vibrating chute 2, a funnel 3 is provided. On the side of this funnel, an opening 4 is provided which is in communication with the ejector 5, which latter is constantly operated. The powder dropping from the vibrating chute 2 thus passes through the funnel 3 and the opening 4 thereof into the ejector 5, which latter then entrains the powder and feeds the same to the nozzle via the conduit 6. By providing the opening 4 on the side of the funnel 3, instead of the structure generally conventional heretofore, the danger is eliminated that the suction chamber of the ejector 5 will fill with powder when the device is shut off or when an error occurs during operation and thus results in an interruption of the operation of the device.

The spraying head essentially consists of the flat fishtail nozzle 7 and the heater 8, wherein the nozzle 7 is disposed in the longitudinal gap of the heater 8. The powder conveyed through the conduit 6 is transformed, by the nozzle 7, into a finely distributed, cloud-like stream 9 and blown through the heater 8 between the two rows of flames 10 arranged on the right-hand and left-hand sides of the burner '8 as seen in FIG. 4. The oxygen or air required for combustion, as well as the fuel-gas mixture are fed to the burner 8 via the conduit l l.

In order to ensure the interchangeability of the nozzle 7, the latter is independent of the heater 8 and is connected to the heater in a suitable manner by heat insulation. In place of heat insulation, it is also possible to provide cooling at this point.

The outlet opening of the nozzle 7 is not disposed flush with the front of the heater "8 but rather is somewhat farther to the rear at a distance therefrom. In the thusdesigned spray head, due to the injector effect of the gaseous stream exiting through nozzle 7, air is sucked in through the gap between the heater 8 and the nozzle and thereby a significant cooling effect is obtained. Due to this construction of the spray head, the flow of the flame jets of the row 10 of flames is also quieter and more uniform since this flow is not aifected by the marginal vortex of the emerging powder jet.

The nozzle 7 is flat, and the width of its orifice is at least twice the diameter of the powder grains to be sprayed, whereas this width must be no larger than It has been found in practice that the length of the mouth orifice of the nozzle 7 must not exceed ten inches.

The outlets of the row 10 of flames on the right-hand and left-hand sides of the burner '8 are disposed at a maximum spacing of 0.4 inch as measured from the edge of the nozzle 7 in the lateral direction. The center. line of each outlet of the row 10 of flames forms an angle of at least 5 and at most 20 with the flow direction of the powder jet 9. I

The outlet orifice of the nozzle 7 is spaced about 0.040.3 inch behind the front of the burner 8.

In operation, the powder container 1 is filled with the powder to be sprayed; thereafter, with the aid of the rheostat (not shown), the amount to be fed is set, and in correspondence therewith, the vibrating chute Zexecutes a shaking motion and thereby conveys the powdered substance from the container 1 along the vibrating chute 2 to the funnel 3 of the ejector 5. The ejector 5 is in continuous operation, whereas the metering of the powder can be interrupted and/or started up again at any desired instant by switching the magnet of the vibrating chute 2 on or 011. Since, in place of the arrangement generally employed heretofore, the opening 4 on the side of the funnel is arranged laterally in the ejector 5, it is impossible for clogging to occur by shutting ofi or erroneous operation of the device, for the suction chamber thus cannot be clogged.

Through the ejector 5, the powdered substance passes via conduit 6 into the nozzle 7; the latter then conveys the powder through its flat opening in the form of a cloud-like, finely distributed powder jet 9, into the space between the rows 10 of flames of the heater 8. During this process, the powder jet 9 is sandwiched between the flame rows 10. The gaseous stream emanating between the flame rows 10 of the heater 8 heats the powdered substance to be sprayed.

The heater -8 of this invention ensures such a surprisingly high degree of thermal efficiency that it is possible to spray not only synthetic resin powders, but, with the use of a gas-air mixture, also powdered aluminum.

The gas pressure relationships can also be selected so that the heater 8 remains untouched by the flame core and thus the burner is kept completely cold during operation and even cools the exiting gaseous stream. Accordingly, it is also possible to avoid any adherence of the powder, and to ensure the spraying thereof without combustion, with safety, without the use of any special measures. An additional advantage resides in that the heating of the cold powder flowing out of the cold nozzle 7 begins in the mixing zone of the combustion gas mixture and the powder jet 9, at a distance of about 0.3-0.4 inch from the front of the heater 8, in the free space or between surfaces serving for heating purposes; consequently, strongly adhering powders such as, for example, powdered synthetic resins, do not adhere anywhere nor produce disturbances in operation.

As is shown in FIGS. and 6, air or another nonflammable gas is allowed to flow, in place of fuel gas,

through the heater 8 and the pipe 11 of the device of this invention; as a consequence thereof, incombustible air emanates from these openings in place of the raw of rflames, which air then prevents the lateral expansion of the powder jet 9. Upstream of the heater 8, the powder jet 9 is sandwiched between energy supply elements 12 in order to transfer thermal or electric energy to the powder jet 9.

The heater 8 provided for ensuring the lateral expansion of the powder jet 9 can also be entirely omitted in certain cases, in which case the powder jet 9 exiting from the nozzle 7 is then immediately supplied with the required thermal or electric energy by the energy supply elements 12.

In view of the foregoing, it will be evident that all of the initially recited objects of the present invention have been achieved.

Although the present invention has been described and illustrated in connection with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit of the invention, as those skilled in this art will readily understand. Such modifications and variations are considered to be within the purview and scope of the present invention as defined by the appended claims.

Having described my invention, I claim:

1. A method for spraying powdered thermoplastic substances onto a solid substrate, comprising entraining the powdered substance in a cold gaseous stream, projecting said stream from an outlet opening in the form of a flat cloud against a said substrate, projecting a pair of gaseous streams from outlet openings that are on opposite sides of and forward of the first-mentioned outlet opening, laterally confining the projected stream between said pair of gaseous streams, sucking air between said pair of gaseous streams from behind and on opposite sides of said first-mentioned outlet opening, and applying heat to opposite sides of said fiat cloud while confined between said pair of streams.

2. A method as claimed in claim 1, in which said heating is effected by heating said pair of streams.

3. -A method as claimed in claim 1, in which said heating is effected by passing said projected stream between opposed heating means.

4. A method as claimed in claim 1, in which the thickness of said projected stream is from twice the diameter of the powder particles to be sprayed, up to about inch.

5. A method as claimed in claim 4, in which the breadth of said cloud is not more than ten inches.

6. A method as claimed in claim 1, and directing each of said pair of streams towards said projected stream at an angle of 5 to 20.

7. A method as claimed in claim 1, in which said pair of streams are flames.

8. Apparatus for spraying powdered thermoplastic substances onto a solid substrate, comprising a spray nozzle having an elongated flat outlet opening, means to feed to said nozzle and out said outlet opening a stream of powdered thermoplastic substance in the form of a flat cloud of particles entrained in a relatively cold gas, means to direct streams of gas from opposite sides through further outlet openings at an acute angle against opposite sides of the flat cloud of particles emerging from said nozzle thereby to confine said flat cloud between said streams, said outlet opening of said nozzle being to the rear of said further outlet openings, means to suck air forwardly between said further outlet openings and on opposite sides of said nozzle outlet opening, and means to heat said fiat cloud between said streams.

9. Apparatus as claimed in claim '8, said nozzle having a width not more than 10 inches.

10. Apparatus as claimed in claim 8, said streams being directed against said flat cloud at an angle of 5 to 20.

11. Apparatus as claimed in claim 8, said heating means comprising a burner from which :said streams emerge as flames.

12. Apparatus as claimed in claim 8, said heating means comprising a pair of heating elements between which said cloud passes between said nozzle and said substrate.

13. Apparatus as claimed in claim 8, said feed means including an ejector having an inlet opening for powdered substance horizontally to the side of the ejector thereby to avoid clogging of the ejector with said powdered substance.

14. Apparatus as claimed in claim 13, said feed means comprising a vibratory conveyor feeding to a hopper which in turn feeds to an ejector by which said particles are entrained in a gas stream.

References Cited UNITED STATES PATENTS 2,673,121 3/1954 Brennan 239-81 2,900,138 8/1959 Strate 239-85 X 2,418,533 4/1947 Walker 239-422 2,721,147 10/1955 Sullivan 1 17-105.1 2,746,883 5/1956 Powers 117105.2 X 3,449,145 6/ 1969 Bloom et a1 117-46 FS FOREIGN PATENTS 658,353 1/ 1965 Belgium t. 239-85 533,391 11/1956 Canada 239-79 554,208 6/ 1943 Great Britain 239-81 1,111,995 7/ 1961 Germany 239-79- 921,924 11/ 1954 Germany 239-422 629,417 3 1963 Belgium 2 39-85 ROBERT S. WARD, JR., Primary Examiner U.S. Cl. X.R.