FIELD OF THE INVENTION

The invention is directed to a mandrel assembly and a method for painting of an inner surface of a drum plug/closure.

BACKGROUND OF THE INVENTION

Conventional mandrel assemblies for polymer coating the inner surface of drum plugs are composed of a hollow mandrel having a circular base and a cylindrical sidewall, mounted on a rotatable drive shaft. The drum plug is placed inside the mandrel chamber for painting. A series of mandrel assemblies are fitted on the conveyor of a conventional polymer spray machine for automatic spray coating of drum plugs. During spray painting, the inner surface of the drum plug is evenly painted due to the plug rotating with the rotation of the drive shaft and the mandrel.

The above-described conventional spray-painting operation often results in deposit of polymer on the exposed rim of the plug collar, lower surface of the plug collar and the plug external wall. This is undesirable since the drum contents could be contaminated on contact with the polymer coating deposited on the said surfaces when the plug is put to use to seal the drum. Further, deposit of polymer on the collar rim and lower surface of the plug collar could lead to ineffective sealing of the drum. Rather than incurring additional expenditure in stripping the polymer coating from the affected surfaces of the drum plug, the present invention provides an effective and economical way to prevent deposit on polymer coating on said areas.

US 7,604,700 B2 provides a stent mandrel for partially covering a stent during an application of coating composition and a method for supporting a stent during the application of the coating.

US 9,364,349B2 relates to a system and method of applying a coating to a medical device. The coating apparatus include a mandrel having a lengthwise axis and an exterior surface, the exterior surface of the mandrel defining a plurality of channels disposed parallel to the lengthwise axis, the mandrel configured to rotate around the lengthwise axis; and a spray head configured to direct a stream of material at the mandrel.

US 4,436, 574A relates to a radial mandrel for building tires, bands, laminated products and coils. A radial mandrel is provided having a plurality of alternating and interfitting large and small segments mounted on a pair of cones, said cones moving the segments radially inwardly and outwardly between a contracted and expanded position.

KR101309451B1 relates to a mandrel cap for forming a hose that can be used for cutting and non-cutting. The cap body has a stepped surface formed along an inner circumference.

None of the prior art discussed hereinabove provide a solution to the problem solved by the present invention or have features disclosed by the present invention. The prevent invention provides an improved mandrel assembly employing a mandrel cap, gaskets and magnets to seal off all surfaces other than the interior/upper surface of the plug, which surface is required to be painted. During a painting operation employing the mandrel assembly of the present invention, only the inside of the plug is exposed to paint as the assembly partially covers the drum plug. With this arrangement, the surfaces of the plug that are engaged when sealing a drum and the surfaces of the plug which may come in contact with the drum contents, are sealed off from the polymer coating/paint, thus ensuring that the contents of the drum are not compromised by paint and the drum is effectively sealed. The present invention may be used in a spray-painting operation or in any alternative method of painting the drum plug.

OBJECTS OF THE INVENTION

It is an object of the invention to partially cover the drum plug during plug painting.

It is an object of the invention to over the problem of paint material being deposited on surfaces of drum plug which are contactable with the drum contents when the drum plug is in use for sealing a drum.

It is another object of the invention to prevent the contamination of the contents of a drum due to contact with paint material, thus saving costs.

It is yet another object of the invention to aid in improved torque retention and effective sealing of the drum by avoiding deposit of paint material on the surfaces of the plug that are engaged when sealing a drum, thereby saving costs due to leakage of drum contents.

It is a further object of the invention to provide for an improved mandrel assembly that is simple to manufacture and easy to operate.

SUMMARY OF THE INVENTION

The invention entails a mandrel assembly comprising a mandrel and a mandrel cap mounted thereon, for providing selective coating of surfaces of a drum plug by partially covering the drum plug. The mandrel assembly prevents deposit of paint material on the surfaces of the plug that are engaged when sealing a drum and on the surfaces of the plug that are contactable with the drum contents. One or more magnets are provided on the circular base of the mandrel and at intervals on a skirting adjoining the external wall of the mandrel. The mandrel cap is hollow, cylindrical, open at the top and bottom and is mounted over the mandrel to cover the mandrel partially. When a plug is disposed inside the mandrel assembly for painting, the magnets exert pulling force on the plug bottom and the mandrel cap to clamp the plug collar between gaskets provided on the mandrel and the mandrel cap. This leads to sealing off of the plug collar rim, thus partially masking the drum plug and exposing only an internal surface of the plug to paint. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a top perspective view of a drum plug and a conventional mandrel.

Fig. 2 is a top perspective view of the drum plug disposed in a conventional mandrel for painting. Fig. 3 illustrates the front sectional view of a drum plug in a conventional mandrel assembly during painting, depicting the undesirable deposit of paint on the plug collar rim.

Fig. 4 is an exploded view of the mandrel assembly of the present invention, showing the components in order of arrangement for painting of a drum plug.

Fig. 5 is a top perspective view of the assembled mandrel assembly of the present invention with the drum plug disposed within.

Fig. 6 is a top plan view of the mandrel of the present invention.

Fig. 7 is an exploded perspective bottom view of the mandrel cap of the present invention.

Fig. 8 is a front sectional view of the mandrel assembly showing the components in order of arrangement.

Fig. 9 is a front sectional view of the assembled mandrel assembly.

Fig. 10 is a perspective sectional view of the assembled mandrel assembly of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

As used herein, the term "about" shall be interpreted to mean "approximately" or "reasonably close to" and any statistically insignificant variations therefrom.

As used herein, the term "at least" indicates that a number or amount is the smallest or the minimum that is possible and that a greater number or amount is possible.

As used herein, the terms "comprising" "including," "having," "containing," "involving," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. The terms "preferred" and "preferably" refer to embodiments of the invention that may afford certain benefits, under certain circumstances

In an embodiment, the aspects and embodiments described herein shall also be interpreted to replace the clause "comprising" with either "consisting of" or with "consisting essentially of" or with "consisting substantially of".

As used herein, "substantially" refers to a degree of deviation that is sufficiently small so as to not measurably detract from the identified property or circumstance. The exact degree of deviation allowable may in some cases depend on the specific context. The use of "substantially" is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result. As used herein, "adjacent" refers to the proximity of two structures or elements. Particularly, elements that are identified as being "adjacent" or "proximate" may be near or close to each other without necessarily contacting each other. The exact degree of proximity may in some cases depend on the specific context.

As used herein, the term 'sheath' indicates a close-fitting casing.

As used herein, the term "paint" includes any type of suitable coating material and the term "drum plug" includes any similarly configured closure.

The use of any and all examples provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed.

Fig. 1 illustrates a conventional mandrel (1) and a drum plug (2). The drum plug has an external wall (3), a base (6) and a collar (4) with a collar rim (5).

As seen in Fig. 2, in a conventional mandrel assembly when the drum plug (2) is placed inside the mandrel chamber, the plug collar (4) merely rests on the upper surface of the mandrel sidewall (7). During a paint operation, the mandrel rotates by means of a rotatable drive shaft coupled to its base. As seen in Fig. 3, in a conventional mandrel assembly, a paint source (23), for example, a spray gun may deposit polymer coating on the rim (5) of the plug collar (4). Further, polymer coating may enter a space between the plug collar (4) and the mandrel sidewall (7) due to the drum plug (2) being loosely fitted into the mandrel (1). This could result in polymer coating being deposited on the lower surface of the plug collar (4) and on the plug external wall (3), leading to ineffective sealing of the drum and also contamination of the drum contents by the polymer coating. The objective of the present invention is to prevent the undesirable deposit of coating material on the surfaces of the drum plug that are engaged in sealing of a drum and on the surfaces of the drum plug that are in communication with the contents of the drum when the drum plug is in use. The mandrel assembly achieves this objective by preventing paint deposit on the plug collar rim, lower surface of the plug collar and plug external sidewall.

The mandrel assembly (8) of the present invention comprises a mandrel (9) and a mandrel cap (18). The mandrel (9) is modified to meet the objectives of the present invention.

As seen in Fig. 4, 5, 6 and 7, the mandrel (9) of the present invention has a cylindrical mandrel sidewall (12) and a circular mandrel base (13). The mandrel is sized to receive the drum plug (2) in a cavity defined by the sidewall (12) and the base (13). An annular mandrel gasket (10) is fastened to the upper surface (11) of said sidewall. Preferably, gasket (10) is of substantially the same inner and outer circumference as mandrel sidewall (12). The upper face of base (13) is fitted with a magnet holder (14) that is provided with a cavity sized to receive and hold a centre magnet (15) secured within. Preferably, the magnet holder (14) and the centre magnet (15) are positioned at substantially the centre of the mandrel base (13) to enable the magnet to exert a uniform attraction/pulling force on the drum plug (2) disposed within the cavity formed by the mandrel sidewall (12) and base (13). The magnet holder (14) may be welded to the upper face of base (13) and the centre magnet (15) may be embossed into the magnet holder (14) cavity. Any other convenient means of securing the magnet holder and centre magnet may be used. The magnet holder (14) may even be entirely avoided by securing the centre magnet (15) directly to the base (13) at about the centre of the base.

A skirting (16) is provided adjoining the outer circumference of mandrel sidewall (12), said skirting being of sufficient width and thickness to have a plurality of side magnets (17) fixed to the upper face of said skirting. Preferably, the skirting is ring-shaped.

The skirting may be secured to the mandrel sidewall by welding or other convenient means or may form an integrated part of the mandrel sidewall. The skirting (16) may be recessed at intervals to form bores, the side magnets (17) fixed within said bores.

The magnets (15, 17) are of sufficient strength to create pulling force on the drum plug and the mandrel cap, respectively. In a preferred embodiment of the invention, four side magnets (17) are disposed at uniform intervals on the skirting (16) as illustrated in Fig. 6. The number of magnets, their shape, size, strength and positioning may be varied as required. Preferably, high- strength magnets are employed.

Fig. 7 is an exploded perspective bottom view of a cylindrical mandrel cap (18).

Fig. 8 is a front sectional view of the mandrel assembly showing the components in order of arrangement. As seen in Fig. 8, the mandrel (9) is sized to receive a drum plug (2) for painting, the plug (2) placed inside the cavity formed by the mandrel sidewall (12) and base (13). The mandrel (9) is further sized such that the plug collar (4) rests on the mandrel gasket (10) and the plug base (6) is in close proximity to the centre magnet (15), preferably adjacent to it. This proximate positioning aids in enhancing the pulling force exerted by centre magnet (15) on the drum plug (2) when the mandrel assembly is in use.

A rotatable drive shaft (22) is secured approximately at the centre of the lower surface of the mandrel base (13) for providing rotational motion to the mandrel assembly. The mandrel (9) has a central axis running through shaft (22) as seen in Fig.8.

As seen in Fig. 7 and 8, the mandrel cap (18) has a cylindrical cap sidewall (19) and an open top and bottom formed by said sidewall (19), defining a hollow central area. The cap sidewall (19) at its upper end extends radially inward to form an annular cap gasket seat (20).

A ring- shaped cap gasket (21) is fitted against the undersurface of gasket seat (20) as seen in Fig. 7 and 8. The mandrel gasket (10) and the cap gasket (21) may be formed from black nitril or any other suitable material.

The mandrel cap (18) is sized such that the cap gasket (21) is aligned with the mandrel gasket (10), when the mandrel cap (18) is mounted over the mandrel (9) for a paint operation.

The inner circumference of the gasket seat (20) is sized to define an aperture such that the upper surface of the drum plug (2) is sufficiently exposed to paint, when the plug is disposed within the mandrel assembly (8). Preferably, the inner circumference of the gasket seat (20) is substantially equivalent to the inner circumference of the mandrel (9).

As seen in Fig. 9, the mandrel cap (18) has inner circumference sufficient to sheath the mandrel sidewall (12) when said cap is mounted over the mandrel (9), the mandrel sidewall and the cap sidewall being positioned concentric and proximate to each other.

The mandrel (9) and the mandrel cap (18) in combination form the mandrel assembly (8) of the present invention and may be formed from mild steel, any kind of alloy steel or other suitable material that responds to magnetism.

The mandrel cap (18) is sized to partially encase the mandrel (9) when mounted thereon. Further, the mandrel cap (18) is sized such that the cap sidewall (19) is proximate to side magnets

(17), when the mandrel cap (18) is mounted over the mandrel (9). Preferably, the outer diameter of the mandrel cap is substantially equivalent to the outer diameter of the skirting (16). Preferably, the cap sidewall (19) is positioned directly above side magnets (17), the lower end of the cap sidewall in close proximity to the side magnets. This positioning optimizes the pulling force exerted by side magnets (17) on the mandrel cap (18).

The attraction force exerted by side magnets (17) additionally prevents the mandrel cap

(18) from being dislodged during rotation of the mandrel assembly. In the preferred embodiment of the invention, the skirting (16) is provided proximate to mandrel base (13) enabling the mandrel cap (18) to sheath a substantial portion of the mandrel sidewall (12) which in addition to preventing paint deposit on particular areas of the drum plug, also aids in stabilizing the mandrel cap and preventing its dislodgement during rotation of the assembly.

As seen in Fig. 9 and 10, during a painting operation, the drum plug (2) is disposed inside the mandrel assembly (8) of the present invention. The plug (2) is loaded into the mandrel (9) cavity with the plug collar (4) resting upon the mandrel gasket (10) as seen in Figs. 9 and 10. When the mandrel cap (18) is mounted over the mandrel (9), the cap gasket (21) is aligned with the mandrel gasket (10). Further, the plug collar (4) is caught between the mandrel gasket (10) and cap gasket (21). Thus disposed, the plug base (6) is proximate to the centre magnet (15).

In this position, the mandrel cap (18) sheaths the mandrel sidewall (12) partially and a lower end of said cap sidewall is proximate to and preferably directly above side magnets (17).

The centre magnet (15) exerts attraction force on the drum plug (2), pulling the plug, causing the plug collar (4) to be pressed against mandrel gasket (10). Simultaneously, the side magnets (17) exert attraction force on the mandrel cap (18), pulling said cap, causing the cap gasket (21) to press against the plug collar (4) and mandrel gasket (10). Thus, gaskets (10, 21) are compressed together, clamping the plug collar (4) therebetween and sealing off the plug collar rim (5).

When the mandrel assembly is actuated, a rotational motion is supplied to the drive shaft (22) resulting in rotation of the mandrel assembly and the drum plug disposed within. The paint source (23) is actuated to commence painting. Sealing off of the collar rim (5) ensures that in addition to said rim, the lower surface of the plug collar (4) and the plug external wall (3) are also shielded/masked from the paint source (23).

The assembly (9) therefore facilitates the deposit of paint material only on the inside of the plug thereby providing selective painting of surfaces of the drum plug. The inner surface of the drum plug is evenly painted due to the plug rotating with the rotation of the mandrel assembly.

Use of the mandrel assembly ensures that the surfaces of the drum plug (2) that are engaged in sealing a drum, for example, the plug collar rim (5) and the lower surface of the plug collar (4), are not contaminated by paint material. Further, the plug external wall (3) which may come in contact with the drum contents, is also protected from contamination by paint, thereby protecting the integrity of the drum contents. Thus, the drum is effectively sealed and the contents are not compromised.

While the above description and drawings are illustrative of the principles of the present technology in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the present disclosure.