Metal deforming – By use of closed-die and coacting work-forcer – Cup or shell drawing
Reexamination Certificate
2001-05-15
2002-12-10
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of closed-die and coacting work-forcer
Cup or shell drawing
C072S366200
Reexamination Certificate
active
06490904
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A MICROFCHE APPENDIX
Not applicable.
FIELD OF THE INVENTION
The present invention relates to an apparatus and method of forming and shaping a metal can blank to a geometric configuration most suitable to contain pressurized liquids, such as carbonated beverages. More particularly, the present invention relates to a novel and improved double action bottom former capable of operating at a high cyclic rate for a sustained period of time with appreciable capability to repeatedly form and shape can bottoms of a specified thickness.
BACKGROUND OF THE INVENTION
It has been conventional in the prior art to form and shape the bottom wall of cans using a bottom former assembly generally comprising an inner die and an outer die circumferentially positioned thereabout. Often the prior art describes the inner die as the dome plug and the outer die as the clamp ring, both of which cooperate with the functioning of the ram generally made part of the bodymaker. As the ram carries a metal can blank for contact with the domer assembly, the clamp ring engages the bottom portion of the metal can blank radially outward from the area to be formed with an inwardly-protruding dome. Subsequently, as the ram fitted with the metal can blank resiliently travels with the clamp ring, the dome plug is engaged to form the desired dome profile of the bottom wall of the can blank. It is generally desirable to set the ram forward of the end of the stroke of the ram to generate overtravel thereof to ensure bottoming out of the ram for complete formation of the inwardly-protruding dome and desired thickness of the bottom wall of a can.
Preferably, the clamp ring and dome plug are resiliently held in a longitudinal working position as the ram travels to and within the bottom former assembly. A number of prior art references teach the resilient positioning of the clamp ring and dome plug through configuration of the bottom former assembly with mechanical springs acting alone or in conjunction with a reservoir having pressurized fluids contained therein. For instance, U.S. Pat. No. 4,790,169 issued to Johansson et al. describes therein the use of springs for both the clamp ring and the dome plug and U.S. Pat. No. 4,930,330 issued to Weishalla, which is presently owned by the Assignee of the present invention, describes therein the use of a fluid actuator for resilient positioning of the clamp ring and a plurality of urethane springs for resilient positioning of the dome plug.
Although Weishalla adequately provides for adjustability of the forces acting on the clamp ring, which provides for greater output capabilities in some instances, there continues to be problems associated with the control of such forces acting thereon to shape and form metal can blanks without substantial failure during high cyclic operation.
The Assignee of the present invention has discovered that in some instances the bottom of the metal can blank has a tendency to split at the periphery thereof as the production rate substantially increases from approximately 300 to 500 containers per minute. This occurrence is mainly attributed to the ability to adequately control the forces acting on the clamp ring as the bottom of the can engages thereto. Generally, the ability to control the forces acting on the clamp ring is limited in part or related to the operating components responsible for resilient positioning of the clamp ring, such as a pressurized medium acting on a movable piston, as seen in Weishalla, or a spring of known physical properties or characteristics, as seen in Johansson et al.
In the attempt to provide a satisfactory solution to the problem, the pressure reservoir or chamber is generally optimized or increased in size to the extent of alleviating the pressure buildup on components generally responsible for resilient positioning of the clamp ring. By allowing for gas expansion, and thus reducing the pressure buildup on the resilient-positioning components, the clamp ring is permitted to adequately engage the bottom of the metal can blank for noticeable reduction in failure rates even during high cyclic operation, while improving the bottom former's ability to form can bottoms having thinner walls. However, the ability to increase the effective volume of the pressure chamber may be limited or not possible due to the design or configuration of those components comprising the typical bodymaker. In attempt to circumvent these design limitations, the art teaches modification of the bottom former assembly to include a surge tank or canister that is in hydraulic communication with the pressurized reservoir. However, in most instances, pressure buildup will continue to occur given the means in which the surge tank is joined with the pressure reservoir, which often only includes a pipe or a hose having limited capacity to effectively transfer fluid to and from the surge tank and back into the pressurized reservoir within the short cycle time generally allowed in such operations.
The Assignee of the present invention also observed in the art substantial mechanical failure of components generally comprising the bottom former assembly. Mechanical failure of mechanisms responsible for resilient positioning of the clamp ring and dome plug generally arise as the ram is inadvertently overextended during high cyclic rates or is configured to overextend to ensure bottoming out of the ram for complete formation of the inwardly-protruding dome. Generally, the art teaches configuration of the ram to overextend in order to exert an adequate amount of force to form the can bottom of specified wall thickness. As a consequence of an excessive overextension of the ram, the components generally responsible for resilient positioning of the dome plug, as well as other components comprising bodymaking equipment, prematurely wear necessitating immediate replacement as they can no longer meet the close tolerances required for adequate formation of the can bottom. Under other operating environments where the ram is not overextended, the spring responsible for the resilient positioning of the dome plug may not be adequately compressed, resulting in a decreased spring force as the preset compression of the spring is generally fixed by the manufacturer. As this occurs, again the dome plug will fail to adequately form can bottoms of specified thickness during high cyclic operation.
Accordingly, there remains a need for a bottom forming apparatus which can adequately operate at a high cyclic rate for a sustained period of time without substantial deleterious impact on components responsible for resilient positioning of the clamp ring and the dome plug, minimize the time required to access and repair components comprising the bottom former assembly, provide an affordable and inexpensive alternative to replacing components responsible for resilient positioning of the dome plug while retaining the preset compression of the spring, and attain greater capability of allowing the ram to overextend without substantial impact or damage to the components comprising the bottom former and, in general, to other bodymaker components.
BRIEF SUMMARY OF THE INVENTION
In order to overcome the numerous drawbacks apparent in the prior art, an improved device for forming can bottoms of specified thickness has been devised.
It is thus an object of the present invention to provide a bottom former capable of greater control of forces acting on the clamp ring through incorporation of an expanded gas chamber to allow for gas expansion and less pressure buildup on operating components generally responsible for resilient positioning of the clamp ring.
It is another object of the present invention to provide a bottom former that is readily adaptable to fit existing bodymaking equipment without undue difficulty or substantial modification of components generally comprising the bottom former.
It is another object of the present invention to provi
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