Work holders – Holder inserted within work aperture – Expandable mandrel
Reexamination Certificate
2000-09-30
2002-07-02
Watson, Robert C. (Department: 3723)
Work holders
Holder inserted within work aperture
Expandable mandrel
Reexamination Certificate
active
06412765
ABSTRACT:
This invention relates to a mounting and locating mechanism for box manufacturing apparatus, and more specifically to a mounting block over which a hollow, end-less tin box shell is placed before an end is secured to a peripheral edge at one end of the shell. Yet more specifically, the mechanism of the present invention is particularly suited to tin box manufacturing apparatus wherein the substantially planar ends of the boxes are secured to peripheral edges of the shells by inward deformation of said edges such that the outer surfaces of the tin box walls are substantially planar in the region of the end.
It should be mentioned that in the alternative method of attaching the planar ends, end-seaming apparatus is used, the apparatus being commonly known as a round and irregular seamer. This apparatus usually comprises a plurality of seaming heads arranged equidistantly from a central axis of a mandrel having a forming surface around which one end of the end-less tin box shell is disposed. Additionally, an end is held in substantially planar contact with a face of said mandrel and the shell and end are provided with formations which at least partially interlock prior to the seaming operation. The seaming heads are brought to bear against the mandrel in the region of the interlocking formations of shell and end to compress same thus forming a seam around what is effectively the base of the tin box thus formed. It will thus be understood that the seaming operation takes place on the external surface the shell.
The present invention is most particularly suited to a different type of tin box construction wherein the end is secured to the end-less tin box shell by deformation of one of the edges of said shell internally of the tin box such by means hereinafter described.
Moreover, the present application is most applicable to apparatus for the manufacture of tin boxes having a rectangular, square, or other regular quadrilateral shape, but it is to be pointed out that the person skilled in the art will appreciate that the mechanism hereinafter described can be equally applied to tin boxes having alternative cross-sectional shapes.
Apparatus currently in use for securing an end to an end-less tin box shell comprises a expansible mandrel which is reciprocally driven into and out of a forming tool.
In general, an indexable table is provided beneath the mandrel having at least four indexable positions and a plurality of forming tools are disposed at suitable locations thereon. The forming tools consist of a rectangular block having side walls which define a cavity of a size and shape generally corresponding to that of the tin box which is to be manufactured, and a base which consists of a thrust plate springingly mounted on the table and having a rectangular or other shape groove therein which receives the partially curled edges of both the end-less shell and the end to be secured thereto in interlocking relationship. The sequence of operations during the securing of an end to an end-less shell is as follows:
In a first indexable position of the table and end-less shell having a partially curled lower edge is deposited within the tool such that said edge is received within the groove in the thrust plate, and the side walls of said shell are bounded to the outside by the walls of the forming tool.
The table is then indexed to a second position whereat an end is deposited, within the forming tool by being placed proximate the base of the tool internally of the shell. The end is ideally provided with a peripheral flange or other suitable formation which is also received in the groove in the thrust plate, the deposit of the end being so as to ensure interlocking engagement or adjacent disposition of the partial curl provided on one edge of the shell and the said formation on the end within said groove.
The table is then indexed to a third position such that the forming tool is directly beneath the reciprocally actuated expansible mandrel. The mandrel is brought down into the cavity defined by the side walls of the shell within the forming tool until the lower face of the mandrel comes into contact with the end disposed at the base of the cavity. It should be mentioned at this point that the dimensions of the mandrel are ideally marginally less than those of the shell, but that the cross-sectional shape is broadly the same. The mandrel can thus enter the cavity without interference from the side walls of the shell.
The construction of the mandrel itself is complex but to aid understanding a sectional view through and a plan view of a mandrel of prior art configuration is shown in
FIG. 1
, and in general it consists of a lower contact face A which behind which retreat one or more wedge components B, C, D having inclined faces which retreat inwardly of the mandrel towards its centre. Depending on the extent of expansion of the various faces of the mandrel block which is required, and its particular cross-sectional shape, the angles of inclination of the various inwardly retreating faces of the wedge components can vary.
The usually vertically orientated side faces and/or corners of the mandrel can be displaced outwardly against the action of springs which bias same towards the centre of the mandrel, and each of the four side walls will consist of a separate component, having a correspondingly inclined surface which communicates with a respective inclined surface of the wedge component from which the lower contact surface is comprised. To ensure as smooth and uniform outward displacement of the side walls of the mandrel, a plurality of T-shaped guides of a suitable low-friction, high wear metal are usually secured within grooves E, F, G, H provided on the inclined faces of the wedge components, and the correspondingly inclined portions of the side walls of the mandrel are provided with suitable grooves which receive the T-shaped formations of the guides.
Hence, when the lowermost contact surface of the mandrel is brought to bear against the thrust plate trapping the end therebetween, the side faces of the mandrel move outwardly by virtue of the vertical motion of the wedge components. The degree of expansion is dependent on the dimensions of the mandrel when contracted, and the internal dimensions of the tin box to be manufactured, but in general a small tolerance will remain between the fully expanded side walls of the mandrel and the internal surface of the side walls of the shell within the forming tool. This is to allow for correct seating of the partially curled edge of the shell within the groove on the base of the forming tool.
After the mandrel is fully expanded, the end is clamped securely in place between the mandrel and the forming tool, and the shell can move slightly in the cavity of the forming tool. At this stage, further vertical motion of the mandrel within the cavity does not cause any further expansion of the mandrel, but instead the mounting plate to which the mandrel is springingly mounted is brought to bear against the uppermost edge of the shell which stands proud of the forming tool. This occurs because the compression force provided by the springs which bias the mandrel away from the mounting plate is overcome, and as a result of the vertical force applied around the uppermost edge of the shell, the curl of the lowermost edge of said shell is completed within the groove around the corresponding and interlocked formation provided on the end, and thus the end is secured to the shell. After the completion of the curl, the mandrel is removed from the tool.
The table is then indexed to a fourth position, and the completed tin box is removed from the forming tool.
It will be immediately apparent to those skilled in the art of accurate machining of engineering components that to machine the wedge components which form the lower contact surface of the mandrel, or the T-shaped guides attached thereto, and the correspondingly inclined surfaces of the side walls of the mandrel is an exceedingly difficult task, especially considering the tolerances which must be achieved to ensure
Meltog Ltd.
Watson Robert C.
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