US3413955A - Apparatus for coating the interior of a container with a resinous film - Google Patents

Description

Dec. 3, 1968 Filed April 23, 1965 V. J. PATTI APPARATUS FOR COATING THE INTER CONTAINER WITH A RESINOUS P IOR OF A ILM 2 Sheets-Sheet 1 BY a [5/ I ATTORNEYS Dec. 3, 1968 v. J. PATTI 3,413,955

APPARATUS FOR COATING THE INTERIOR OF A CONTAINER WITH A RESINOUS FILM Filed April 23, 1965 2 Sheets-Sheet 2 IN VENTOR. ///l/C/V7 24777 BY I ATTORNEYS United States Patent 3,413,955 APPARATUS FOR COATING THE INTERIOR OF A CONTAINER WITH A RESINOUS FILM Vincent J. Patti, Norridge, IIL, assignor to TRW Inc., a corporation of Ohio Filed Apr. 23, 1965, Ser. No. 450,480 3 Claims. (Cl. 118-55) ABSTRACT OF THE DISCLOSURE Apparatus for coating the interior of a container with a resinous film including a conveyor means, individually driven work holder means which deliver the container to an injecting station where the resinous material is injected into the container, then to a high speed rotation station where the work holder is driven at a high speed to distribute the resinous material as a film along the interior of the container, and finally to a heating station where the container is driven at a lower velocity while the resinous material is being set under the influence of a heating means.

The present invention relates to apparatus for coating the interior of open ended containers with compositions settable by heat. The invention has particular reference to the coating of metal cans which are used as magnetic shields about circuit elements such as coils.

In the past, some attempts have been made to shield the inner walls of the metallic can by lining the walls with a preformed sheet containing a ferromagnetic powder dispersed through a synthetic resin or elastomer. A strip of the preformed material would be inserted into the can in the desired location, and then a-dhesively secured to the walls of the can. This operation was time consuming and expensive, and had its limitations when there was only a very small space available between the exterior of the coil and the inner surface of the can.

The present invention provides a means for coating cans of this type whereby the material can be deposited as an adherent coating along the inner walls of the can. By the process of the present invention, the ferromagnetic material becomes firmly bonded to the interior of the can without the use of adhesives. The magnetic shield which results includes a layer of set resinous material containing the ferromagnetic particles at a heavier concentration at the interface between the coating and the can than exists farther inwardly of the coating. The magnetic shield thus produced reduces the magnetic shorting effect of the can and has been found to significantly increase the Q of the circuit element. The present invention is particularly useful in providing shields for low frequency IF coils which necessitate fairly large physical structures for the coil, and the use of a can which provides only a slight clearance between the interior wall of the can and the outer periphery of the coil.

One of the objects of the present invention is to provide an apparatus for coating the inside of an open ended container with a thermally settable resinous composition, preferably including ferromagnetic particles.

Another object of the invention is to provide an apparatus for continuously applying a coating within the interior of an open ended can structure.

Still another object of the invention is to provide apparatus for the injection and distribution of a resinous composition containing ferromagnetic particles along the inner periphery of a metallic can.

A further object of the invention is to provide an improved apparatus for rapidly and controllably providing a concentration gradient of ferromagnetic particles within a coating of resin deposited inside an open ended magnetic shield.

Still another object of the invention is to provide apparatus for making an improved shield for coils and the like which contains a resinous composition bonded to the inner walls of the container and containing more ferromagnetic particles at the surface abutting the can wall than exist further inwardly of the coating.

The present invention involves first injecting a heat settable resinous composition containing ferromagnetic particles into the open ended container, followed by spinning the container to distribute the resinous suspension by centrifugal force along the inner walls of the container. This centrifugal action also serves to force the relatively heavier ferromagnetic particles closer to the interface of the coating and the can, so that a relatively high concentration of ferromagnetic particle exists at such interface. After the coating has been distributed, the entire assembly is heated so that it reaches a temperature at which the synthetic resinous material is set to a hardened form. This heating is preferably carried out while the container is being rotated at a speed somewhat less than the speed used for the centrifugal distribution of the material, but high enough so that there is no sagging of the coating during heating, and the heating is uniformly applied to all surfaces.

The apparatus described above lends itself readily to automatic operation. In a preferred form of the invention, the apparatus consists of a conveyor carrying a plurality of motors in spaced relation, with work holding means being secured to each of the motors. A container to be coated is mounted in axially snug fitted relation on each of the work holders. and then passed to an injection station where a nozzle is automatically inserted into the container, and a predetermined amount of the resinous composition is injected through the nozzle and into the container. Then, the container moves to an energizing station positioned to energize each of the motors to operate at a high rotational speed so that the composition deposited in the container is distributed along the walls of the container by centrifugal action. Finally, the container with the redistributed resinous material is heated, preferably by means of an open flame, so that the composition is set to a solid form within the container.

The heat settable composition used in accordance with the present invention need not be a thermosetting resin where the chemical setting of the resin is accomplished by the addition of heat. While such thermosetting resins can be used, I prefer to employ a thermoplastic composition which consists of a plastisol loaded with ferromagnetic particles. Such plastisols are dispersions of polyvinyl chloride resin particles in a plasticizer preferably an alkyl phthalate such as dioctyl phthalate, or isobutyl phthalate. Still other families of plasticizers useful for polyvinyl chloride resins include the adipates, oleates, stearates, sebacates, azelates, phosphates, and citrates.

The polyvinyl chloride compositions preferably include stabilizers which prevent any change of properties during processing of the resin. Typical stabilizers for polyvinyl chloride are the barium cadmium carboxy-lates, bariumcadmium complexes, and the like.

A typical polyvinyl chloride plastisol for use in accordance with the present invention has a viscosity of about 600 centipoises at 20 C. before loading with the ferromagnetic particles. The ferromagnetic particles, preferably metallic iiron, constitute about by weight of the final composition, and may range from about 70 to by weight. At too high an iron concentration, the material becomes too hard to feed, while at too low an iron concentration, the desired electrical properties are diminished.

A further description of the present invention will be 3 made in connection with the attached sheets of drawings in which:

FIGURE 1 is a view in elevation of an assembly useful for the purposes of the present invention;

FIGURE 2 is a cross-sectional view taken substantially along the line IIII of FIGURE 1 on an enlarged scale;

FIGURE 3 is a view taken substantially along the line III-III of FIGURE 1; and

FIGURE 4 is a greatly enlarged cross-sectional view of a metallic can coated in accordance with the procedure of the present invention.

As shown in the drawings:

In FIGURE 1, reference numeral indicates generally an assembly for coating the interior of cans to be used for enclosing coils. The assembly 10 includes spaced conveyor chains 11 between which there is supported a plurality of individual drive motors 12 in spaced relation. The chains 11 are driven by means of sprockets 13 and 14, with a plurality of smaller diameter idler sprockets 16, 17 and 18 being arranged within the loop formed by the chains 11.

The entire assembly is supported on a table 19 which also supports a material pump 21 which serves to agitate the dispersion of ferromagnetic particles in the plastisol before being introduced into the coating portion of the apparatus. A motor 22 is mounted above the pump 21 to drive the same. A drain valve 23 is provided to selectively discharge material from the pump 21, and a recirculating line 24 is provided to keep the settable composition circulating at all times when the material is being passed to the coating station.

The coating material is pumped by the pump 21 through a conduit 26 into a metering ejector 27 which feeds an injector coating device generally indicated at reference numeral 28, the coating device being best shown in FIG- URE 2 of the drawings, and including an air cylinder 29 shown in FIGURE 1. The function of the metering ejector 27 is to provide a predetermined amount of coating composition to the injector station where it is injected into the can.

The individual motors 12 are supported on platforms 31 extending between the spaced chains 11. The entire assembly is timed, as by means of a Geneva movement which drives the sprockets 13 and 14 to move the motors 12 individually into the injecting station, then to a high speed centrifuging station, and finally to a flame curing station, the dwell time at each station being only a matter of a few seconds.

Each of the motors 12 has a drive shaft 32 (FIGURE 2) on which there is mounted an arbor 33 of suitable size so that it receives a can 34 in snugly fitting axial engagement against a shoulder 35 formed thereon. The arbor 33 has a pointed nose portion 36 which has the function of assisting the distribution of the material, and shaping the end of the coating as indicated by the beveled surface 37 in FIGURE 4.

The drive system positions the individual cans 34 'in the injecting station in timed sequence. An electric eye 41 and a light source 42 are provided at the injecting station, the light source 42 projecting a beam of light to the electric eye system 41. When this beam of light is interrupted by the presence of a can 34 on an arbor 33, the injecting system is put into operation, the system including a reciprocable carriage 44 carrying a nozzle 46 and insertable into the can through an aperature 47 best seen in FIGURE 4 of the drawings. The aperature 47 is provided in the can 34 to receive an adjusting tool for adjusting the inductance of the coil contained therein when the can is used as a shield for an IF coil.

The reciprocating carriage 44 is secured to a shaft 48 operated by the air cylinder 29. A feed line 49 from the metering ejector 27 delivers a predetermined mass of material through the line 49 and into an axial bore 51 ing exit port 52. The ejector 27 is operated in timed relation to the movement of the cans and the movement of the carriage 44 so that a viscous mass 53 of resin heavily loaded with ferromagnetic particles is deposited in the interior of the can 34. The injection normally takes about 1 to 2 seconds after which the reciprocating carriage is withdrawn by the action of the air cylinder 29.

During the next incremental movement of the conveyor system, when a new can is positioned for injection of the resinous material, the can previously coated is moved to a first energizing station where it is rotated at a high velocity in order to distribute the mass 53 along the walls of the can and completely filling the corners. For this purpose, each of the motors 12 is provided with a pair of feeler arms 56 which extend between the chains 11 and are arranged to engage a pair of spaced bus bars 57. The bus bars make electrical contact with the feeler arms 56 and thereby drive the motor 12 at a sufficiently high velocity to cause centrifugal force to distribute the mass 53 as a fairly uniform coating about the inner wall of the can 34. The actual speed of rotation depends, of course, on the viscosity of the mass 53, and the dimensions of the can 34, but for a can of /2 inch square cross-section, suitable velocities for this step range from about 3,000 to 7,000 r.p.m. To provide an additional gripping on the can at such high rotational velocities, the arbor 43 is provided with a pair of lugs 58 and 59 on opposite sides thereof, the two lugs being pivoted at pivot points 61 and 62, respectively. When the shaft 32 goes up to full rotational speed, the mass of the lugs 58 and 59 is distributed such that their respective nose portions 63 and 64 are urged toward the can and tend to bite in on the can 34, to hold it rigidly against the arbor 33.

The feeler arms 56 of each motor 12 remain engaged with the bus bars 57 so that the coating is distributed within the interior of the cam 34 for a period of time equal to three incremental movements of the chain 11, in the form of the invention illustrated in FIGURE 1. Then, the feeler arms 56 contact a second bus bar 66 which supplies a lower voltage to the motor 12, driving it at a lower rotational speed. This lower speed is sufficient to prevent sagging of the coating 67 along the walls of the can, but is not sufiicient to cause excessive turbulence during the heat treating cycle. The hardening is accomplished by playing open flames from a series of gas burners 68, 69 and 70 at the exterior of the coated cans while the same are being rotated at the lower rotational speed. For a can which is /2 inch square in cross-section, suitable rotational speeds in this stage range from about 1000 to 3000 r.-p.m.

The temperature achieved in the coating through this exposure to the open flame is sufiicient to set the plastisol into a self-sustaining coating. As illustrated in FIGURE 4, this coating 67, due to the centrifugal effects of the spinning operation, consists of a zone 71 having a relatively high concentration of the iron particles, and a zone 72 having a substantially lesser concentration of iron, and consisting primarily of the resinous plastisol.

The apparatus of the present invention can be used to apply coatings of varying thickness in the container, as required. All that is necessary is an adjustment of the amount of coating composition fed to the nozzle 46 by the metering ejector 27.

While the apparatus of the present invention finds particular use for providing a magnetic shield within a metallic container, it should be evident that the apparatus can also be used for insulating cans with a dielectric material containing no ferromagnetic particles.

It should also be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention.

I claim as my invention:

1. An apparatus for coating the interior of a container with a heat settable resinous composition which comprises conveyor means, rotatable work holder means on said conveyor for supporting a container thereon, electrical drive means for rotating each of said work holder means, said conveyor means being arranged to deliver each work holder and the container carried thereby successively through aninjecting station, a high speed rotation station, and a heating station, injecting means at said injecting station arranged to inject a predetermined amount of said resinous composition into each container, a first electrical contact means positioned beyond said injecting station and engageable. by said electrical drive means to rotate said container at a high speed and thereby distribute said resinous composition as a film along the interior'of said container, heating means at said heating station for solidifying the film in said container, second electrical contact means at said heating station engageable by said electrical drive means to rotate said container at a lower speed during the heating thereof by said heating means, each of said electrical contact means consisting of a pair of bus bars and each of said electrical drive means having feeler arms engageable with said bus bars.

2. The apparatus of claim 1 which said conveyor means is driven bylan intermittent drive means so that the container is stopped at said injecting station, said high speed rotation station, and said heating station.

3. The apparatus of claim 1 in which each of said work holders includes centrifugally operable clamping means which serve to clamp onto said container during high speed rotation thereof.

References Cited WALTER A. SCHEEL, Primary Examiner.

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