Patent Description:
Metal extrusion presses are known in the art, and are used for forming extruded metal products having cross-sectional shapes that generally conform to the shape of the extrusion dies used. A typical metal extrusion press comprises a generally cylindrical container having an outer mantle and an inner tubular liner. The container serves as a temperature controlled enclosure for a billet during extrusion. An extrusion ram is positioned adjacent one end of the container. The end of the extrusion ram abuts a dummy block, which in turn abuts the billet allowing the billet to be advanced through the container. An extrusion die is positioned adjacent the opposite end of the container.

During operation, once the billet is heated to a desired extrusion temperature (typically <NUM>-<NUM>°F for aluminum), it is delivered to the extrusion press. The extrusion ram and dummy block are then advanced, so as to push the billet through the container and towards the extrusion die. Under the pressure exerted by the advancing extrusion ram and dummy block, the billet is extruded through the profile provided in the extrusion die until all or most of the billet material is pushed out of the container, resulting in the extruded product.

Dummy blocks for extrusion presses have been previously described. For example, <CIT>discloses a dummy block having a dummy block base, a connector for connecting the dummy block base to a stem of an extruder, a replaceable wear ring connected to a forward circumferential portion of the dummy block base, a device for releasably securing the wear ring to the dummy block base, and a device for expanding the ring to engage an inside wall of a container of an extrusion press during extrusion. The wear ring is a metal collar having a conical interior surface converging towards the dummy block base. The device for expanding the ring comprises a metal plunger having a plunger head with a conical surface for engaging the collar conical surface to expand the collar as the plunger head is forced into the collar during extrusion. The converging surfaces of the collar and the plunger head extend a sufficient distance to permit telescoping of the plunger head into the collar to an extent whereby the collar is expanded to engage the inside wall of the container.

<CIT>discloses a dummy block for a metal extrusion press comprising: a base having a first surface; an expandable collar seated against the base; a moveable plunger coupled to the base and accommodated by the collar, the plunger having a second surface configured to abut against the first surface of the base; and an outer connecting ring coupling the collar to the base. The connecting ring comprises at least one feature engaging the base and a plurality of fingers engaging the collar.

<CIT>discloses a dummy block for a metal extrusion press comprising: a generally cylindrical base having a forward surface and an outwardly extending circumferential flange; an expandable collar coupled to the base, the collar having an inwardly extending circumferential rib abutting the circumferential flange; a collar support coupled to the base and abutting the collar; and a moveable plunger coupled to the base and accommodated by the collar. The plunger has a rear surface configured to abut the forward surface of the base.

<CIT> discloses a dummy block having a pressing surface, which exerts force on a material to be pressed and at least one gap. The gap is radially symmetrical about a horizontal rotation axis of the dummy block and may be oval or conical. The dummy block has a dummy block core and a filling piece, which is fixed to the dummy block core by a centering bolt. A sealing ring is fitted between the filling piece and the dummy block core.

<CIT> discloses a short screw connected expansion ring type fixed dummy block which relates to aluminum extruders. A conical pad is connected with an extrusion stem through a connector; an expansion ring is located outside the connector and connected with the connector through a step at the tail part of the expansion ring; the inner conical surface of the expansion ring is matched with the outer conical surface of the conical pad; and a pressing sleeve is arranged between the expansion ring and the extrusion stem. The short screw connected expansion ring type fixed dummy block is characterized in that the connector and the conical pad are connected at the centers by a center ejector pin; the connector and the extrusion stem are connected by a short double-head screw; and a large ring plate and a small ring plate are arranged between the extrusion stem and the pressing sleeve as well as between the extrusion stem and the connector.

<CIT> discloses a fixed extrusion pad of an aluminum profile extrusion machine, and in particular a split cone pad of a fixed extrusion pad of an aluminum profile extrusion machine.

Improvements are generally desired. It is therefore an object at least to provide a novel dummy block for an extrusion press.

In one aspect, there is provided a dummy block for a metal extrusion press according to claim <NUM>.

The plunger disc and the plunger shaft may be separate components.

The plunger shaft may have a cylindrical portion and a frustoconical portion. The cylindrical portion and the frustoconical portion may define an obtuse angle therebetween.

The plunger disc may have a beveled bore formed therein. The beveled bore may be shaped to receive the plunger shaft. The beveled bore may define a frustoconical surface. The plunger shaft may have a frustoconical portion configured to abut the frustoconical surface of the beveled bore of the plunger disc.

The collar may comprise a rear portion coupled to the base, and a forward portion configured to elastically deform outwardly. The wall thickness of the rear portion may be greater than a wall thickness of the forward portion. The forward portion may abut an outer surface of the plunger disc.

The forward surface of the base comprises a planar central portion, and a beveled portion surrounding the central portion. The plunger disc may have a rear surface that is parallel to the planar central portion of the forward surface of the base. The rear surface may be non-parallel to the beveled portion of the forward surface of the base.

In one embodiment, there is provided a metal extrusion press comprising the dummy block as described above.

Embodiments will now be described more fully with reference to the accompanying drawings in which:.

As used herein, an element or feature introduced in the singular and preceded by the word "a" or "an" should be understood as not necessarily excluding the plural of the elements or features. Further, references to "one example" or "one embodiment" are not intended to be interpreted as excluding the existence of additional examples or embodiments that also incorporate the described elements or features. Moreover, unless explicitly stated to the contrary, examples or embodiments "comprising" or "having" or "including" an element or feature or a plurality of elements or features having a particular property may include additional elements or features not having that property. Also, it will be appreciated that the terms "comprises", "has", "includes" means "including by not limited to" and the terms "comprising", "having" and "including" have equivalent meanings.

As used herein, the term "and/or" can include any and all combinations of one or more of the associated listed elements or features.

It will be understood that when an element or feature is referred to as being "on", "attached" to, "connected" to, "coupled" with, "contacting", etc. another element or feature, that element or feature can be directly on, attached to, connected to, coupled with or contacting the other element or feature or intervening elements may also be present. In contrast, when an element or feature is referred to as being, for example, "directly on", "directly attached" to, "directly connected" to, "directly coupled" with or "directly contacting" another element of feature, there are no intervening elements or features present.

It will be understood that spatially relative terms, such as "under", "below", "lower", "over", "above", "upper", "front", "back" and the like, may be used herein for ease of description to describe the relationship of an element or feature to another element or feature as illustrated in the drawings. The spatially relative terms can however, encompass different orientations in use or operation in addition to the orientation depicted in the drawings.

Turning now to the drawings, <FIG> shows a simplified illustration of an extrusion press for use in metal extrusion. The extrusion press comprises a container <NUM> having an outer mantle <NUM> that surrounds an inner tubular liner <NUM>. The container <NUM> serves as a temperature controlled enclosure for a billet <NUM> during extrusion of the billet. An extrusion ram <NUM> is positioned adjacent one end of the container <NUM>. The end of the extrusion ram <NUM> has a dummy block <NUM> coupled thereto, which is configured to abut the billet <NUM> for advancing the billet through the container <NUM>. An extrusion die <NUM> is positioned adjacent a die end <NUM> of the container <NUM>.

During operation, once the billet <NUM> is heated to a desired extrusion temperature (typically <NUM>-<NUM>°F for aluminum), it is delivered to the extrusion press. The extrusion ram <NUM> with the dummy block <NUM> coupled thereto are then advanced, so as to push the billet <NUM> through the container and towards the extrusion die <NUM>. Under the pressure exerted by the advancing extrusion ram <NUM> and dummy block <NUM>, the billet <NUM> is extruded through the profile provided in the extrusion die <NUM> until all or most of the billet material is pushed out of the container <NUM>, resulting in an extruded product <NUM>.

The dummy block <NUM> may be better seen in <FIG>. The dummy block <NUM> comprises an inner dummy block base <NUM>, an outer collar <NUM> coupled to the dummy block base <NUM> by shrink-fitting, a plunger disc <NUM> positioned forward of the dummy block base <NUM> and seated against the collar <NUM>, and a moveable, axial plunger shaft <NUM> seated against and extending through the plunger disc <NUM> and coupled to an interior of the dummy block base <NUM>. During use, when the dummy block <NUM> abuts a billet <NUM>, the plunger shaft <NUM> and plunger disc <NUM> are configured to move rearwardly, and the plunger disc <NUM> is configured to elastically deform outwardly, which in turn causes a forward portion of the collar <NUM> to elastically deform outwardly.

The dummy block base <NUM> comprises a generally cylindrical body, and has a circumferential flange <NUM> extending outwardly in the radial direction from a forward end thereof. The dummy block base <NUM> has a forward surface <NUM>, a portion of which is defined by the circumferential flange <NUM>, which has a circumferential outer surface <NUM>. The dummy block base <NUM> has a center bore <NUM> formed therein, which extends in the axial direction from the forward surface <NUM> to a central recess <NUM>. The center bore <NUM> and the central recess <NUM> are sized to accommodate a cylindrical post of the moveable plunger shaft <NUM>, described below. A plurality of threads <NUM> are formed on an interior surface defining the central recess <NUM>, which are configured to engage complimentary outer threads <NUM> formed on an exterior surface of a stem <NUM> of a stud <NUM> or other elongate projection. The stem <NUM> has a central recess <NUM> for accommodating a spring <NUM> that is configured to provide a biasing force urging the plunger shaft <NUM> away from the dummy block base <NUM>. The stud <NUM> or other elongate projection is mounted on a forward end of the extrusion ram <NUM>, and comprises four (<NUM>) spaced-apart lugs <NUM> that are configured to abut corresponding features (not shown) of the extrusion ram <NUM> to provide a bayonet-style connection.

The forward surface <NUM> of the dummy block base <NUM> has a planar central portion <NUM>, and a beveled portion <NUM> that surrounds the central portion <NUM> and that defines an angle θ<NUM> with the center axis <NUM> of the dummy block <NUM>. In the example shown, the angle θ<NUM> has a value of about <NUM> degrees. The central portion <NUM> defines a majority of the area of the forward surface <NUM>. As shown in <FIG>, the forward surface <NUM> is planar at radial positions r, as measured from the center axis <NUM> of the dummy block <NUM>, of rb < r < r<NUM>, where rb is the radius of the center bore <NUM>, and the forward surface <NUM> is beveled at radial positions r of r > r<NUM>. Also in the example shown, the value of r<NUM> / R, where R is the radius of the cylindrical portion <NUM> of the outer surface <NUM> of the circumferential flange <NUM>, is about <NUM>. The outer surface <NUM> of the circumferential flange <NUM> has a forward beveled portion <NUM> that defines an angle θ<NUM> with the center axis <NUM> of the dummy block <NUM>, and a rear cylindrical portion <NUM>. In the example shown, the angle θ<NUM> has a value of about <NUM> degrees. As shown in <FIG>, the outer surface <NUM> is beveled at axial positions d, as measured from the planar central portion <NUM> of the forward surface <NUM>, of d < d<NUM>, and the outer surface <NUM> is cylindrical at axial positions d of d > d<NUM>. As will be understood, the beveled portion <NUM> of the forward surface <NUM> accommodates elastic deformation of the plunger disc <NUM> during operation. Additionally, the beveled portions <NUM> and <NUM> accommodate elastic deformation, or "mushrooming", of the outer forward portion of the dummy block base <NUM> during operation.

The collar <NUM> comprises a generally annular body having a unitary construction and fabricated of a single piece of material. The collar <NUM> comprises an elastically deformable forward portion <NUM> having reduced thickness, and a rear portion <NUM> that is coupled to the dummy block base <NUM> by shrink-fitting. As a result, the forward portion <NUM> is effectively cantilevered with respect to the dummy block base <NUM>. The rear portion <NUM> has an inwardly extending, inner circumferential rib <NUM> that is shaped to abut a rear surface of the circumferential flange <NUM>, such that the dummy block base <NUM> and the collar <NUM> overlap in the axial direction and are thereby interlocked. In particular, the circumferential rib <NUM> has a forward surface abutting a rear surface of the circumferential flange <NUM>, and an inner surface abutting an outer surface of the dummy block base <NUM>.

The forward portion <NUM> of the collar <NUM> has a frustoconical inner surface <NUM> that is inclined relative to the center axis <NUM> of the dummy block <NUM>, and which defines a first angle with the center axis <NUM>.

The plunger disc <NUM> has a generally convex forward face <NUM> that is configured to abut a billet <NUM>, a frustoconical outer surface <NUM>, and a planar rear surface <NUM> that is configured to abut the forward surface <NUM> of the dummy block base <NUM> during operation. Although not easily visible in <FIG>, the assembled dummy block <NUM> is configured such that, when assembled, the planar rear surface <NUM> of the plunger disc <NUM> is spaced from the planar central portion <NUM> of the forward surface <NUM> of the dummy block base <NUM> by a narrow gap, and in this example the gap is about <NUM> inches (about <NUM>). The frustoconical outer surface <NUM> is inclined relative to the center axis <NUM> of the dummy block <NUM>, such that the frustoconical outer surface <NUM> defines a second angle with the center axis <NUM>. The plunger disc <NUM> has a central, beveled bore <NUM> formed therein for accommodating the plunger shaft <NUM>. The beveled bore <NUM> extends through the plunger disc <NUM> from the forward face <NUM> to the planar rear surface <NUM>, and defines a forward frustoconical surface <NUM> and a rear cylindrical surface <NUM>.

The second angle defined by the conical outer surface <NUM> and the center axis <NUM> of the dummy block <NUM> is slightly greater than the first angle defined by the frustoconical inner surface <NUM> and the center axis <NUM>, to ensure that the plunger <NUM> and the collar <NUM> do not become jammed during use. In the embodiment shown, the difference between the second angle and the first angle is about <NUM> degrees. As will be understood, if the angle of inclination of the conical outer surface <NUM> were the same as, or less than, the angle of inclination of the frustoconical inner surface <NUM>, these surfaces would jam as the plunger moves rearward into the collar <NUM> such that when the dummy block is removed from the container, the spring <NUM> would not have sufficient force to return the plunger <NUM> to its initial position.

The planar rear surface <NUM> of the plunger disc <NUM> has a radius r<NUM>, as measured from the center axis <NUM>. Although the forward face <NUM> is generally convex, the curvature is slight and as a result the thickness of the plunger disc <NUM> is nearly uniform across its diameter. The plunger disc <NUM> has a thickness, t, at the radius r<NUM>. In the example shown, the plunger disc <NUM> has an aspect ratio, A = (t / <NUM>·r<NUM>), of about <NUM>. As will be understood, the relatively low value of aspect ratio A, as compared to plungers of conventional dummy blocks, allows the plunger disc <NUM> to flex easily and to remain in the elastic regime during operation.

The plunger shaft <NUM> comprises a forward, generally frustoconical portion <NUM> defining a convex forward face <NUM> and a frustoconical surface <NUM>, and a cylindrical post <NUM> extending rearwardly from the frustoconical portion <NUM> and defining a cylindrical surface <NUM>. The cylindrical post <NUM> is sized to extend through the center bore <NUM> and into the central recess <NUM> of the dummy block base <NUM>. A connector <NUM> is fastened to a distal end of the post <NUM> within the central recess <NUM> for coupling the moveable plunger <NUM> to the dummy block base <NUM>, and for providing a surface against which the spring <NUM> abuts.

At the transition in shape between the frustoconical portion <NUM> and the cylindrical post <NUM>, the frustoconical surface <NUM> and the cylindrical surface <NUM> define an obtuse angle α, where <NUM> < α < <NUM> degrees. In the example shown, the angle α has a value of about <NUM> degrees. As will be understood, the obtuseness of the angle α allows stress concentrations existing between the plunger shaft <NUM> and the plunger disc <NUM>, and stress concentrations existing within the plunger shaft <NUM> between the frustoconical portion <NUM> and the cylindrical post <NUM>, to be greatly reduced. In a complementary manner, the forward frustoconical surface <NUM> and the rear cylindrical surface <NUM> of the beveled bore <NUM> formed in the plunger disc <NUM> define an angle β therebetween, where β = (<NUM> - α), which in the example shown has a value of about <NUM> degrees.

During use, the extrusion ram <NUM> with the assembled dummy block <NUM> and stud <NUM> mounted thereon is advanced through a container <NUM> to force a billet <NUM> through the extrusion die <NUM>. A forward force is applied by the extrusion ram <NUM> to the billet <NUM> via the dummy block <NUM>. In return, an opposing force is applied by the billet <NUM> to the dummy block <NUM>, which causes the plunger disc <NUM> and the plunger shaft <NUM> to move rearwardly toward the dummy block base <NUM>. During this rearward motion, the plunger disc <NUM> abuts against the dummy block base <NUM> and undergoes elastic deformation in the outward direction, which in turn applies pressure against the frustoconical inner surface <NUM> of the collar <NUM>, causing the forward portion <NUM> collar <NUM> to elastically expand and deform outwardly. With the energy of impact with the billet absorbed by the elastic deformation, the force applied by the extrusion ram <NUM> can be transferred directly through the core of the dummy block <NUM> to the billet. At the end of the stroke, the extrusion ram <NUM> with the dummy block <NUM> mounted thereon is returned to its starting position in the container <NUM> to receive the next billet. With the opposing force previously applied by the billet <NUM> now removed, the spring <NUM> pushes the plunger shaft <NUM> forward to its initial position, and the elasticity of the plunger disc <NUM> returns the plunger disc <NUM> to its original shape, which in turn causes the forward portion <NUM> of the collar <NUM> to elastically return to its original shape.

As will be appreciated, the thin profile of the plunger disc <NUM>, and specifically the low values of thickness t and aspect ratio A, advantageously allow the plunger disc <NUM> to be flexible and to more easily deform elastically during operation, as compared to plungers of conventional dummy blocks. Additionally, the low values of thickness t and aspect ratio A enable the plunger disc <NUM> to more easily remain in the elastic deformation regime and not enter the plastic deformation regime, as compared to plungers of conventional dummy blocks.

As will be appreciated, constructing the plunger disc <NUM> and the plunger shaft <NUM> as separate components allows the plunger disc <NUM> to be readily replaced, such as due to wear or damage, while allowing the plunger shaft <NUM> to be reused. This advantageously lowers the cost of repair and maintenance of the dummy block <NUM>, as compared to conventional single-piece plungers of conventional dummy blocks.

Additionally, and as will be appreciated, constructing the plunger disc <NUM> and the plunger shaft <NUM> as separate components allows an obtuse angle to be incorporated into the shapes of these components, which advantageously allows stress concentrations between the plunger shaft <NUM> and the plunger disc <NUM> to be greatly reduced, as compared to conventional single-piece plungers of conventional dummy blocks. Further, the obtuse angle between the frustoconical portion <NUM> and the cylindrical post <NUM> advantageously allows stress concentrations within the plunger shaft <NUM> itself to be greatly reduced, as compared with other possible shapes of plunger shaft.

As will be appreciated, the configuration of the dummy block <NUM>, and in particular the coupling of the dummy block base <NUM> and the collar <NUM>, eliminates the need for lengthy bayonet connector lugs extending from the base that would otherwise be needed to for a conventional bayonet-style connection. As a result, the diameter of the dummy block base <NUM>, and in turn the contact area between the dummy block base <NUM> and the plunger disc <NUM> (sometimes referred to as "pad area"), are greater than those of conventional dummy blocks. Additionally, and as will be appreciated, the circumferential flange <NUM> advantageously contributes to the increased pad area. The increased pad area advantageously allows a greater force applied by the extrusion ram <NUM> to be transferred through the core of the dummy block <NUM> to the billet <NUM>, as compared to conventional dummy blocks having bayonet-style connections. This configuration advantageously enables the dummy block <NUM> to be operated at higher extrusion pressures than conventional dummy blocks.

The dummy block may be differently configured. For example, although in the example described above, the plunger disc <NUM> has an aspect ratio, A = (t / <NUM>·r<NUM>), of about <NUM>, the dummy block may alternatively be configured such that the plunger disc preferably has an aspect ratio of an <NUM> < A < <NUM>. In other examples, other suitable values of aspect ratio, A may be used, provided the aspect ratio allows the plunger disc <NUM> to flex easily and to remain in the elastic regime during operation.

Although in the embodiment described above, the collar is coupled to the dummy block base by shrink-fitting, in other embodiments, the collar may alternatively be coupled to the dummy block base in other ways, such as by one or more fasteners, for example.

Claim 1:
A dummy block (<NUM>) for a metal extrusion press comprising:
a generally cylindrical base (<NUM>) having a forward surface (<NUM>) and an outwardly extending circumferential flange (<NUM>);
an expandable collar (<NUM>) coupled to the base (<NUM>), the collar (<NUM>) having an inwardly extending circumferential rib (<NUM>) abutting the circumferential flange (<NUM>);
a plunger disc (<NUM>) seated against the forward surface (<NUM>) of the base (<NUM>) and accommodated by the collar (<NUM>); and
a plunger shaft (<NUM>) extending through the plunger disc (<NUM>) and coupled to the base (<NUM>),
wherein the circumferential flange (<NUM>) of the base (<NUM>) has an outer surface (<NUM>) having a rear cylindrical portion (<NUM>) and a forward beveled portion (<NUM>), and
wherein the forward surface (<NUM>) of the base (<NUM>) comprises a planar central portion (<NUM>), and a beveled portion (<NUM>) surrounding the central portion (<NUM>).