Receptacles – Closures – Removable closure guided in rotary movement
Reexamination Certificate
1999-10-08
2003-04-08
Vidovich, Gregory M. (Department: 3726)
Receptacles
Closures
Removable closure guided in rotary movement
C215S044000, C215S329000, C029S450000, C029S523000
Reexamination Certificate
active
06543636
ABSTRACT:
TECHNICAL DOMAIN
This invention relates to a process for making cans made of a low carbon steel or aluminum alloy, manufactured by deep drawing, drawing and ironing or extrusion, in which the inner wall is covered with a protective coating and which are equipped with a threaded neck designed to fix any type of removable head, for example aerosol spray distribution heads, of the eco-refill type, but also for the attachment of a closing cap.
STATE OF ART
According to standard practice as described in GB 1 445 758, cans with a bottom and a cylindrical wall are manufactured starting from round and flat pieces made of low carbon steel or aluminum alloy, and using deep drawing, drawing and ironing of blanks or backward extrusion (impact extrusion) of slugs. Once formed, these cans are usually varnished on their inner surface, and painted and/or varnished on their outer surface. The open end of the can is then formed to have a cylindrical neck with a smaller diameter, and a strong plastic deformation is then applied by necking.
For practical reasons to facilitate application with a roller or a spray gun, it is better to apply the paint or varnish on the cylindrical surface before necking. The varnish on the inner surface is necessary for many types of applications, in order to prevent contact between the bare metal and the contents of the can. The metallic surface must be well protected throughout the period during which the can is being used and it is important that the inner varnish covers this surface fully and continuously. Prior art includes paints and varnish that remain undamaged during necking.
Since the metal used (low carbon steel or aluminum alloy) is an inexpensive and easy-to-recycle packaging material, it seemed a good idea to develop receptacles onto which aerosol spray distribution heads or covers could be screwed, as is the case for glass and plastic bottles. For example, the receptacle could then be sold full and a screwed cap could be fitted onto it. The user screws and unscrews the distribution head, designed for multiple use, according to his needs. The receptacle could then be refilled, or the consumer could throw it away with the rest of his waste, and it could be taken for recycling.
In order to obtain this type of metallic receptacle satisfying the “eco-refill” principle, it must be possible to make a thread, for example on the neck of the receptacle, in order to participate in the attachment of any type of head. This thread must not damage the varnish layer described above, that has been subjected to necking in order to form the neck, and which must maintain its protective properties in all cases.
In the past, the thread was usually made using internal tooling with a helical impression, acting mainly as a support and shaping mold, and an external tooling acting like one or several rollers. The European patent application EP 0 510 291 (NUSSBAUM) describes a process for making an improved thread, in which the thread(s) is(are) shaped by means of an internal tooling and an external tooling, both toolings being rotated in a coordinated manner such that sliding takes place between the neck material and each tooling. This prevents the neck metal from accumulating and folding in front of the external threading tool and being pushed in the direction of advance of the tooling.
The neck is then cut off on the same device, in other words without having removed the receptacle, leaving a bare surface, in other words unprotected and possibly with burrs, on the edge surrounding the orifice.
Problem that Arises
Even if sliding occurs between the tooling and the neck material, it is impossible to avoid further damage to the varnish. Thus, micro-crazing is observed on the varnish at the thread, both on the outer surface and the inner surface of the neck wall. This crazing makes the can more sensitive to corrosion by the packaged product.
Furthermore, with the can thus obtained, it is impossible to position the distributing head precisely with respect to the edge and the shoulder. It is difficult to control the position of the heads, which has negative consequences both on the leak tightness of the assembly and on its esthetic appearance.
Purpose of the Invention
The process according to the invention is a process for the manufacture of a metallic can comprising at least the following steps:
a) production of a can with a bottom and a cylindrical or shaped wall, for example by deep drawing, drawing and ironing, extrusion or extrusion-drawing, possibly followed by a painting or varnishing deposit on at least the inner surface of the cylindrical wall, followed by a varnish annealing treatment;
b) necking, in order to make a neck on the open end of the can, this step possibly being followed by cutting open end of the neck perpendicular to the center line of the can;
c) use of a ring with a spindle hole and threaded on its outer surface, and sleeve fitting of the said ring so that its spindle hole fits around the neck formed in the previous step, in an operation that will subsequently be called “sleeve fitting”:
and characterized in that it also includes the following step:
d) plastic expansion of the said neck, the outside diameter of the neck being expanded until it is larger than the inside diameter of the spindle hole of the ring when unstressed.
The process is characterized by the use of a ring, for example made of a plastic molded ring (but it could be made of any other material—metallic, machined or die forged, etc.), with a globally toroidal shape, with a cylindrical inner surface that we will subsequently call the spindle hole, and an outer cylindrical threaded surface. The diameter of the spindle hole is slightly greater than the outside diameter of the neck that has just been formed on the can, such that the ring can be sleeve fitted into place freely.
The thread formed on the outer surface of the ring is preferably a standard thread, for example with a
triangular or trapezoidal section, more suitable for precise positioning of the distributor head with respect to the metallic can. The thread obtained in prior art, in other words directly by rolling on the neck, was rounded and consequently imprecise. Furthermore, since rolling is no longer necessary to form the thread, there is no additional damage to the varnish on the inner surface of the neck of the can.
Finally, the choice of a plastic ring together with a distribution head fitted with an attachment skirt also made of plastic, improves the sealing conditions when the said distribution head is put into position by screwing.
A first end of the ring is brought into position facing the can neck that was obtained by necking during the previous step b) and the said neck is then inserted inside the spindle hole in the said ring. This is a relative movement; this sleeve fitting operation may also be made by moving the ring and keeping the can motionless. In this case, this step can be carried out in the same way as the previous and next steps, during the same can clamping phase, in other words these operations may be carried out on the same machine, the cans being placed on a circular rotating table for which the step by step rotation brings them in front of different tools in sequence, each adapted to one of these steps, and themselves installed on a circular tool holder plate. A device of this type has already been described, for example in FR 1 434 177 (LECHNER).
Since precise positioning of the heads to be fixed on the can is required, it is desirable to place the ring precisely on the neck and to create a stop system that gives good positioning at the end of sleeve fitting. The shape of the first end of the ring can be designed so that it is recessed and matches the shoulder of the can. It would also be possible, and preferable, to form a small shoulder on the neck, at a certain distance from the edge of the neck. This distance can be very precise when the shoulder is made at the same time as the end of the neck is cut off (optionally) in step b). The ring also has a surface that stops in contact with the shoulder for
Flecheux Franck
Granger Jacques
Schneider Bernard
Cebal S.A.
Compton Eric
Dennison, Schultz & Dougherty
Vidovich Gregory M.
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