The present invention relates to extrusion mills, and more particularly, is related to pellet mills using extrusion techniques.
Extrusion-type pellet mills and the process of producing pellet material using such devices are well known in the art. In pellet mills, a mixture of material to be pelleted, or “feed,” is typically fed to a die having a plurality of extrusion holes. Pellets are generally formed when the feed is compressed and molded between a pressure roll and an extrusion die.
During the extrusion process, generally one or more extrusion rolls travel over the compression side of the die and force the material between the die and the rolls. This movement squeezes the material through extrusion holes in the die. As the material emerges from the discharge side of the die, the extrusions are severed to produce pellets. Other parts of the pellet mill may facilitate the continuous compression of feed between the pressure rolls and the die and the handling of the extruded pellets.
Each pellet mill is generally equipped with a die and roll assembly which often includes a plurality of pressure rolls, an extrusion die, and a mechanism for delivering feed material evenly along an inner interface surface of the extrusion die so that the feed can be compressed by the pressure rolls when they roll over the inner interface surface of the die. The inner interface surface of the die is also known as the compression surface or the extrusion surface.
The feed in the pellet mill 100 is forced through the extrusion holes 130 by multiple rolls 140. Note that while three rolls 140 are depicted in
In general, the rolls 140 do not come into direct contact with the inner interface surface of the ring die 110. Each roll 140 is separated from the ring die 110 by a pinch gap 170, as shown in
It is desirable to maximize production of pellets over a period of time. However, the need for frequent die maintenance may limit pellet production efficiency. In particular, where it is desirable for the die to be fabricated from materials that resist wear and abrasion for maximum pellet cutting efficiency, these characteristics may be compromised in favor of materials with adequate die structural support and rigidity characteristics.
High pressure on the section of the ring die 310 that is unsupported by the housing 320 or the stiffener ring 340 may result in the ring die 310 cracking or breaking. In some cases, the ring die 310 may split, causing a portion of the die attached to the stiffener ring to separate, causing significant damage to the rest of the machine. Replacing a cracked or broken die may be costly and time consuming, as the mill is disassembled and the stiffener ring 340 and die housing 320 are re-attached to the replacement ring die 310. Therefore, there is an unmet need for an extrusion ring die having improved structural rigidity characteristics, that may be serviced less frequently than previous pellet mills, and that may be serviced with minimal time and expense.
Embodiments of the present invention provide an extrusion die housing and insert. Briefly described in architecture, a first aspect of the present invention is directed to an extrusion die. The extrusion die includes a die insert with an extrusion surface, an outer interface surface, and a plurality of extrusion apertures passing between the extrusion surface and the outer interface surface. The extrusion die further includes a die housing having an inner interface surface, an exterior surface, and a plurality of extension apertures passing between the inner interface surface and the exterior surface. The die housing is configured to removably receive the die insert. The die insert outer interface surface is adjacent to the die housing inner interface surface, and the plurality of extrusion apertures align with the plurality of extension apertures.
In one embodiment under the first aspect, the extrusion die further includes a key configured to substantially hold the extrusion apertures in alignment with the extension apertures. The key may include a protruding member and a receiving member configured to receive the protruding member. The die insert may include a first material and the die housing may include a second material. The die may be a ring die such that the die insert rotates in rigid accompaniment with the die housing. Alternatively, the extrusion die may be a flat die.
A second aspect of the present invention is directed to an extrusion die including an extrusion surface, having a first material, an exterior surface, having a second material, and a plurality of extrusion holes passing between the extrusion surface and the exterior surface. In one embodiment under the second aspect, the extrusion die further includes an interface between the extrusion surface and the exterior surface.
Briefly described, a third aspect of the present invention is directed to a method for manufacturing an extrusion die, having the steps of forming a die housing having an exterior surface and an inner interface surface, and forming a die insert having an outer interface surface and an extrusion surface, the die housing configured to removably receive the die insert so that the outer interface surface is adjacent to the inner interface surface. The method may further include the steps of forming a plurality of extension apertures between the exterior surface and the inner interface surface, and forming a plurality of extrusion apertures between the outer interface surface and the extrusion surface, wherein the plurality of extension apertures align with the plurality of extrusion apertures.
Other systems, methods and features of the present invention will be or become apparent to one having ordinary skill in the art upon examining the following drawings and detailed description. It is intended that all such additional systems, methods, and features be included in this description, be within the scope of the present invention and protected by the accompanying claims.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principals of the invention.
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
In general, embodiments of an extrusion die housing with a removable and replaceable die insert are presented. The die insert is received by the die housing, such that the extrusion surface of the die insert is generally supported by the die housing. Material inside the die is compressed by rolls located generally on the interior of the die, so that compressed material is forced through extrusion holes in the die insert, thereafter passing through extension holes in the die housing, where the extension holes axially align with the extrusion holes.
Ring Die Embodiment
A first embodiment of an extrusion die 500 with a housing and insert is shown, in an exploded view, in
The die housing 520 has an exterior surface 560, and an inner interface surface 562. A plurality of extension holes 535 or apertures pass from the inner interface surface 562 through to the exterior surface 560. A die insert 510 has an outer interface surface 564 and an extrusion surface 566 on the interior of the die insert 510. A plurality of extrusion holes 530 or apertures pass from the extrusion surface 566 through to the outer interface surface 564. The die housing 520 is formed to receive the die insert 510. When the die insert 510 is inserted into the die housing 520, the insert outer interface surface 564 is adjacent to the die housing inner interface surface 562, so that the extrusion holes 530 axially align with the extension holes 535, for example, to within a given tolerance. Pellets may be formed by forcing material from within the die insert 510 interior through the extrusion holes 530 in the extrusion surface 566, whereafter the pellets pass through the extension holes 535 to the die housing exterior 560. Pellets may be cut or broken off outside the die housing exterior surface 560.
The die insert 510 and the die housing 520 may be formed with a taper with respect to the insert outer interface surface 564 and the housing inner interface surface 562 to allow for easier installation of the die insert 510 into the die housing 520 and an interference fit. This taper may be set, for example, so that as the die insert 510 is inserted further into the die housing 520, the fit becomes tighter. The die extrusion holes 530 may be made similar to prior art dies, for example, with a counter bored relief. The die housing 520 extension holes 535 may be slightly larger in diameter than the extrusion holes 530 in the die insert 510 to minimize restrictions of the material extruding from the interior of the extrusion die 500. Extrusion holes 530 and extension holes 535 are discussed in further detail below.
The die housing 520 may contain a back 570 adjacent to an inner edge 575 of the die insert 510 when assembled. The back 570 may assist in maintaining an axial alignment between the extrusion holes 530 and the extension holes 535. In alternative embodiments, the back 570 may include a slot (not shown) to receive the insert 510, and the slot (not shown) may, for example, be keyed or grooved or threaded to hold the insert 510 in rigid rotational alignment with the housing 520. The back 570 may be attached to a main shaft (not shown), and the main shaft may be held in a bearing (not shown) and used to rotate the die housing 520.
The assembled extrusion die 500 is shown in
In contrast, under the first embodiment shown in
In order for the extruded material to pass through both the extrusion holes 530 in the die insert 510 and the die housing 520 extension holes 535, the extrusion holes 530 and the extension holes 535 need to remain generally axially aligned.
It should be noted that while
It may be desirable for the keying mechanism between the die housing 520 and the die insert 510 to be situated apart from the extrusion holes 530 and extension holes 535.
It should be noted that other variations of keying between the die insert 510 and the die housing 520 are within the scope of this disclosure. For example, there is no objection to keys protruding outward from the die insert 510 and corresponding key holes within the die housing 520. Similarly, there is no objection to the keys being separate from the die insert 510 and die housing 520, for example, removable pins or bolts used to hold the die insert 510 in alignment with the die housing 520.
Under normal operation, the die insert 510 may be operated until the die insert 510 needs to be replaced, due to, for example, wear and/or abrasion. In some circumstances, a first die insert 510 may be replaced in favor of a second die insert 510 with characteristics more favorable to a specific extrusion material. For example, the second die insert 510 may have different extrusion hole 530 sizes or tapers than the first die insert 510. The die insert 510 may be removed from the die housing 520, and thereafter replaced by a new die insert 510. Replacement of a die insert 510 may be generally less time and labor intensive than replacement of a prior art ring die.
The material used to form the die insert 510 may be optimized for qualities needed for forming pellets against extrusion rolls, for example, hardness and low wear and/or abrasion characteristics. An example of a preferable material having superior wear characteristics for the die insert 510 includes a high chrome stainless steel alloy. The material used to form the die housing 520, in contrast, may be optimized for structural strength and stability, for example, rigidity and stiffness. An example of a preferable material for the die housing 520 includes a carbon alloy steel, such as 4140 steel. It is preferable that the material for the die housing 520 and the die insert 510 have generally proportional thermal expansion rates, for example, to maintain alignment between the die housing 520 and die insert 510 over a range of operating temperatures.
As mentioned above, by individually optimizing the structural characteristics of the housing 520 and wear characteristics of the insert 510, the overall mass of the extrusion die may be reduced relative to the extrusion surface area, when compared to prior art extrusion dies. It should be noted that while the relative thickness of the die housing 520 and die insert 510 may be generally equal in some embodiments, there is no objection to embodiments having other proportions, for example, a relatively thick die housing 520 with a relatively thin die insert 510, or a relatively thin die housing 520 with a relatively thick die insert 510.
The thickness of the die housing 520, corresponding to the length of the extrusion holes 535, may be determined based upon, for example, the density of extrusion holes 530 and extension holes 535 in relation to extrusion surface area of the die insert 510. For example, if there is a high density of extrusion holes 530, there is a correspondingly high density of extension holes 535. A higher density of holes 530, 535 may result in the need for a thicker die housing 520 to provide sufficient structural support to the die insert 510. Similarly, a lower density of holes 530, 535, may allow for a thinner die housing 520.
Two Piece Housing
Under the fourth embodiment, a die insert 1110 may be at least partially retained against the die hub 1120 by the die housing ring 1125. Under the fourth embodiment, the die housing ring 1125 may be removed to replace the die insert 1110. Material is forced through extrusion holes 1130 in the die insert 1110, passing through extension holes 1135 in the die housing ring 1125.
Extrusion Holes
A detail of the extrusion holes 530 and extension holes 535 is shown in
In general, the extrusion holes 530 are substantially circular in cross sectional shape, and have a first diameter for a first segment of the extrusion hole 530. The first segment begins substantially at the extrusion surface 566, and ends at a first step 1230. The first segment maintains the first diameter throughout the length of the first segment. The length of the first segment may be determined to facilitate plug-free formation of pellets, as familiar to persons having ordinary skill in the art. At the end of the first segment, the extrusion hole 530 widens to a second diameter for a second segment at the first step 1230. The second diameter is larger than the first diameter. The diameter of the second segment may remain constant as the second diameter, or may taper from the second diameter to a third diameter at an interface 1220 between the die insert 510 and the die housing 520.
Each extension hole 535 in the die housing 520 may generally have a fourth diameter at the interface 1220, where the fourth diameter is generally larger than the third diameter. The larger fourth diameter of the extension holes 535 in relation to the smaller third diameter of extrusion holes 530 may serve to avoid the plugging of extruded material, and may also serve to provide some tolerance in axial alignment between the extrusion holes 530 and extension holes 535. This tolerance is to allow extruded material to pass from the extrusion holes 530 to the extension holes 535 even if the die insert 510 is slightly misaligned with the die housing 520. The extension holes 535 may have a fifth diameter at the die housing exterior surface 560, where the fifth diameter is equal to or larger than the fourth diameter. The extension holes 535 may gradually widen through a series of steps 1232, 1234, 1236, as shown, or through a taper. There may be an ingress taper 1210 around the rim where the extrusion hole 530 meets the extrusion surface 566.
Flat Die Embodiment
As noted above, while the first, second, third, and fourth embodiments of a die housing and die insert are based on a ring die, there is no objection to embodiments of a die housing and die insert with other die configurations. For example, a fifth embodiment of an extrusion die 1300 is a flat die shown in
Turning to
As with the ring die embodiments, the fifth embodiment may have tapered or stepped extrusion holes 1330 and extension holes 1335, wherein the diameter of the extrusion holes 1330 is smaller than the diameter of the extension holes 1335 to avoid plugging and to provide generous tolerances for axial alignment between extrusion holes 1330 and extension holes 1335. Similarly, the thickness of the die housing 1320 may be different from the thickness of the die insert 1310.
In summary, embodiments of an extrusion die housing with a removable and replaceable die insert have been presented. The die insert is received by the die housing, such that the extrusion surface of the die insert is entirely supported by the die housing. Material from inside the die is compressed by rolls located generally on the interior of the die, so that compressed material is forced through extrusion holes in the die insert, thereafter passing through extension holes in the die housing, where the extension holes axially align with the extrusion holes.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. For example, while the die insert has been generally described as being removable and replaceable, there is no objection to an embodiment where the die insert binds to the die housing in a non-removable fashion. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.