Method of processing containers

Abstract

A method of processing industrial steel containers of the types having a threaded opening for reception of a closure member wherein a synthetic plastic closure member is threadedly engaged to such opening and a coating is applied to the exterior of the container. The closed container is then subjected to an elevated temperature for curing the container coating whereupon the finished container is ready for shipment to the end user container filler.

Parent Case Text

This application is a continuation-in-part of application Ser. No. 318,926 filed Dec. 27, 1972, now abandoned.

Description

BACKGROUND OF THE INVENTION

In the steel container industry and particularly that segment of the industry involved in the manufacture of 55-gallon steel drums there has been a longstanding problem having to do with the painting of such drums in the most economical manner. More explicitly, the practice has evolved of painting such drums as the last step in the manufacturing process for the purpose of protecting the drum exterior against corrosion and enhancing its overall appearance.

The provision of one or more threaded openings in the container has complicated this practice in requiring a cover for such openings to prevent the entry of paint within the container during the coating operation. For various reasons it has frequently not been practical to apply a gasketed metal closure to the opening which will withstand the elevated paint curing temperatures and thus equipping the drum for shipment to the end user. As a result, in such instances, resort has been had to placing a temporary cover of some type over the opening solely to protect the drum interior during the painting and curing operation which cover is then replaced with a permanent gasketed closure prior to shipment. This arrangement leaves much to be desired, however, from the standpoint of economy due to both the cost of the temporary closure and the additional labor factor involved.

The invention method improves over these relatively costly prior art practices in the application of a closure member, molded of heat resistant synthetic plastic material, to a threaded container wall opening. The closed container is then passed through a painting operation and subsequently subjected to the elevated temperature of a paint curing oven. The closure interacts with the threaded container wall opening so that inadvertent dislodgement during handling is prevented while at the same time permitting the consequent build up of internal pressure within the container to vent past the closure, thus avoiding damage to the container. The fully assembled and finished container is then readied for shipment to the filler customer.

It is accordingly a primary object of the invention to provide a new method of processing steel shipping containers.

Another object is to provide a new labor saving method of plugging and painting steel shipping and storage drums.

Other and more detailed objects will be in part pointed out and in part obvious as the description of the invention taken in conjunction with the accompanying drawing proceeds.

In that drawing:

FIG. 1 is a part elevational part schematic view of the container and process steps of the invention;

FIG. 2 is a part sectional part elevational view of the container closure assembly;

FIG. 3 is a top plan view of the container closure assembly;

FIG. 4 is an enlarged sectional view showing the closure plug in venting position.

Considering first the container with which the method of the invention is concerned, FIG. 1 shows a steel shipping container 1 such as a 55-gallon drum commonly used in the shipping and storage of industrial products. The head of the drum 1 is provided with a pair of diametrically opposed closure assemblies 2 which, although differing in size, are of basically the same design. As shown in FIGS. 2 and 3 the closure assembly 2 is constructed by forming the wall 3 of the container 1 outwardly in a shallow octagonal embossment 4 which surrounds a vertically extending cylindrical neck 5. A closure flange 6, having an internally threaded cylindrical wall 7 surrounded by a laterally extending octagonal base 8, is nested within the above described container wall formation. An unthreaded upper end portion of the flange wall 7 is formed outwardly in a rounded bead 9 overlying the uppermost end of the container wall neck 5. Any leakage path between the container wall 3 and the flange 6 is sealed off by an annular gasket 10 compressed between the flange base and the overlying container wall.

The manufacture of the container 1 is now complete with the exception of closing the threaded flange openings and performing the drum painting operation. It is this final process operation with which the invention herein disclosed is primarily concerned. As pointed out above, heretofore, in certain applications there has been lacking a satisfactory method of closing the flange openings and painting the container without resorting to a relatively costly handling operation. This has been overcome in the present instance by inserting a threaded closure plug 11 within the flange neck 7 prior to the coating operation. The plug 11 is injection molded of nylon synthetic plastic material, Monsanto 21X being a nonlimiting example, and is formed with an externally threaded cylindrical sidewall 12 closed off by a base wall 13 adjacent the lower end thereof.

A circumferential lip 14 is formed at the uppermost end of the plug sidewall 12 extending radially outwardly beyond the plug thread and provided with a lower corner 15 adapted to create an integrally molded sealing gasket upon contacting the flange bead 9. As an alternative, a separate sealing gasket can also be affixed to the plug sidewall beneath the lip 14 if so desired. A pair of wrench engaging lugs 16 are formed interiorally of the plug sidewall as clearly seen in FIG. 4.

Threaded engagement of the plug 11 within the flange 6 is effected by means of the unaided hand since a finger tightening or seating of the plug is adequate to bring the lip edge 15 in contact with the flange bead 9. This degree of tightening is sufficient to protect against the entry of the paint coating spray within the container and also to prevent inadvertent dislodgement of the plug through processing vibration. The plugged container is then conveyed to the container coating operation which, most commonly, applies a coating of paint such as an acrylic lacquer to the drum exterior, including the closure assemblies. Next the painted container is conveyed into a paint curing oven wherein the entire container is subjected to an elevated curing temperature. During the curing cycle the resultant expansion of air within the container must be vented to the exterior to prevent damage to the container. As shown in FIG. 4, the plug 11 reacts to an excessive build up of internal pressure by permitting the passage of air past the thread interengagement and into communication with one or more of the minute voids created by the surface irregularities at the line contact between the flange bead 9 and the corner 15 of the plug lip.

The container exits from the curing oven in finished condition for subsequent shipment to the filler end user. As a precautionary measure prior to shipment, the plug 11 may be torqued down into sealing position with a suitable wrench so as to assure against backing off of the plug during handling and shipment. The above described process greatly improves over previously practiced methods of utilizing a separate closure member for closing off the container interior during the painting operation. The invention thus discloses a simple novel method of closing off the flange opening with a heat resistant plastic plug wherein painting and baking of the container can be efficiently carried out without having any detrimental effect on either the container or the closure assembly.

Claims

Having described my invention what I claim as new and desire to secure by Letters Patent is:

1. The method of coating steel containers having an internally threaded container wall opening comprising the steps of threadedly engaging a self-gasketing closure plug integrally molded of synthetic plastic material within said container wall opening, applying a torque value to said plug less than the torque value required to seal the plug against the container wall, applying a coating to said container exterior, subjecting said coated container to an elevated temperature curing cycle for curing said coating and allowing said container to cool down for handling and shipment with said plug maintaining said thread engagement.

2. The method as in claim 1 and applying a sealing torque to said plug prior to shipment.

3. The method of coating steel containers having an internally threaded container wall opening comprising the steps of threadedly engaging a closure plug molded of synthetic plastic material within said container wall opening, applying sufficient torque to said plug to bring an unthreaded portion of said plug into contact with said container wall while permitting said container to vent past said plug, applying a coating to said container exterior, subjecting said container to an elevated temperature curing cycle for curing said coating and allowing said container to cool down for handling and shipment with said plug maintaining said thread engagement.

4. The method as set forth in claim 3 and subjecting said coated container to a curing cycle having an approximate minimum temperature of 325.degree.F for an approximate minimum duration of 10 minutes.

5. The method of coating steel containers having an internally threaded container wall opening comprising the steps of threadedly engaging a closure plug molded of synthetic plastic material within said container wall opening, seating said plug within said opening with sufficient torque to prevent loosening of said plug from vibration while permitting said container to vent past said plug, applying a coating to said container exterior, subjecting said coated container to an elevated temperature curing cycle for curing said coating and allowing said container to cool down for handling and shipment with said plug maintaining said thread engagement.