Patent Application
20050238749
The invention relates generally to a feed shoe of the type used in powder metallurgy processes, for feeding and depositing finely divided or pulverized particulate material, such as powdered metals and the like, into a die cavity for compacting. More particularly, the invention relates to a feed shoe having an adjustable gate member incorporated into a front portion of the feed shoe.
In powder metallurgy and other technologies using particulate materials, such as ceramics and carbides, products and parts are formed by pressing finely ground or atomized powders into a desired shape within a die cavity. Generally, the powders are compacted in the die cavity at room temperature and the then semi-dense compact is removed from the die and heated to bond the powders into a unified, dense mass. In powder metallurgy, the heat bonding procedure is generally known as sintering or in the case of ceramics and carbides, firing.
When these and similar procedures are employed, means are required for delivering measured amounts of powder or particulate to a die cavity on a powder press. Typically, feed shoes operate to deliver the powder or particulate material to the die cavity during the press cycle, commonly using a gravity assisted fill system, although pressure and vacuum assisted systems are also known. The process involves movement of the feed shoe containing particulate material on a shuttle which slides the feed shoe forward along the table of the die press to a position at which the bottom hole in the feed shoe is exposed, overlies, and registers with the die cavity, and deposits enough loose powder to fill the die cavity. Thereafter, the shuttle slides the feed shoe back along the table of the die press into a retracted position, which cuts off the flow of particulate material from the bottom hole of the feed shoe into the die cavity. The edge of the bottom hole of the feed shoe also levels off excess powder from the top of the filled die cavity as the feed shoe is retracted. The particulate material is then pressed into an article and the article is ejected from the die. The shuttle then slides the feed shoe forward along the table of the die press displacing the ejected article and again exposing the bottom hole of the feed shoe as it overlies and registers with the die cavity, and the process is repeated.
The design of the feed shoe is critical to the quality of the part being produced. However, conventional feed shoes typically are of a general design, configured to give average results when used to produce parts of an average geometry and size. In some application, for example the production of thermal battery pellets, the pellets can be disproportionately thin compared to the overall size, making the pellets naturally difficult to produce. One of the most notable problems is the die fill consistency. The thickness of the pellets makes it difficult to get an even die fill from front to back, thus magnifying the powder fill imbalance that is already an inherent problem with conventional die fill methods. “Powder pull-out,” which is the tendency of the leading edge of the bottom hole in the feed shoe to drag feed material from the front to the back of the die cavity, typically occurs in the front of the die cavity as the feed shoe is retracted after filling the die cavity. In addition, the conventional feed shoe design does not allow thickness adjustment on a part from side to side which occurs as a result of tooling flatness, press set up, and the like. These are major problems for parts that are very thin to begin with, leading to tapered thickness, poor strength, and an increased number of rejected parts.
The conventional feed shoes can also perform inadequately in regard to providing weight consistency between die cavities in dual die cavity platforms, thus limiting the capability to press pellets with large areas and obtain the increased production benefits of dual cavity pressing. Also, the feed tube which delivers feed material, e.g., powder, into the feed chamber is not necessarily configured for optimum, even powder distribution across the width of the feed chamber. This likewise leads to inconsistent die cavity fill; in this case, from side to side. Moreover, the conventional feed shoe design is not conducive to low press cycle times. In particular, the configuration of the conventional feed shoe requires the top ram has to have a relatively high vertical travel in order to clear the feed shoe during the die cavity fill operation, thus increasing the overall cycle time.
Accordingly, there is a need for an improved feed shoe which is configured to reduce or eliminate the problems which can be common with conventional feed shoes described hereinabove.
According to the invention, a feed shoe can be provided comprising at least one feed chamber, two shown, each having an open bottom portion and an open front portion, and a gate at the open front portion defining a front wall of the each feed chamber. Alternatively, a main gate and an optional auxiliary gate can both be provided adjacent the open front portion of the feed shoe. This optional auxiliary gate could be used to provide an additional shear plane, which is independent of the main gate so the height of the shear plane is adjustable. This feature may be conducive for improved die fill. Each main gate can have a lower edge adjacent the open bottom portion, and this lower edge can define a leading edge of the feed chamber. The gate can be vertically adjustable relative to the front portion, and, moreover, each side of the gate can be is individually vertically adjustable. In this way, the leading edge can be skewed, wherein one side is positioned at a different vertical position relative the opposite side in order to compensate for thickness variations from one side of a part to the other.
The leading edge of the gate can further have a profile which is a function of the type of feed material to be deposited into the feed chamber. More particularly, for example, the profile can be serrated, rounded, angled, or flat.
The gates, or main gate where an auxiliary gate is used, can further be provided with a specially configured inner surface facing the feed chamber. This inner surface can defines a front wall of each feed chamber and can thus alter the shape of the feed chamber. The inner surface can be flat, curved, or V-shaped, and can further have a lower portion thereof, near the open bottom of the feed chamber, provided with a certain profile which increases in thickness upwardly from the open bottom portion. Specifically, for example, the profile can be a stepped configuration wherein the thickness of the gate increases in steps from a lower edge thereof upwardly. The steps result in the feed material in the feed chamber being sheared in separate planes when the feed shoe is retracted after depositing feed material in the die cavity.
Alternatively to configuring the inner surface of the gate in different shapes, a separate main gate can be provided having an outer surface adjacent a separate gate member, and an inner surface which is specially configured in a flat, curved or V-shape, as described above. The inner surface of such a main gate can similarly be provided with the stepped profile which shears the feed material in separate planes.
Further in accordance with the invention, the feed shoe can further comprise an attachment portion for retaining one end of a material feed delivery member, or feed tube, in communication with the feed chamber. A separate feed tube can be provided to supply each separate feed chamber. The attachment portion can be adjustably attached to the feed shoe such that the end of each feed tube can be adjusted relative to each feed chamber to facilitate delivery of the material into the feed chamber. The attachment member can be adjustable front to back, side to side, and angularly. The attachment member can also be designed having a low profile such that the die press need not retract vertically as much as with a conventional feed shoe, which reduces press cycle time and speeds up the production process.
Other details, objects, and advantages of the invention will become apparent from the following detailed description and the accompanying drawings figures of certain embodiments thereof.
A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:
Referring now to
Generally, the bottom of the feed shoe 10 rests slidably? on a platen in which a die cavity is formed, and the feed shoe 10 is attached to a member called a shuttle via pins 20, 21 projecting from each side of the feed shoe 10 (only the feed shoe 10 is shown). The shuttle is operated to move the feed shoe 10 on the platen between a starting position and a second position at which the bottom hole 16 in the feed shoe 10 coincides with the die cavity. When the bottom hole 16 coincides with the die cavity, i.e., overlies in alignment therewith, the material in the feed chamber will be deposited, for example via gravity, into the die cavity. To ensure that the die cavity is completely filled with material, the feed chamber 14 is generally sized to hold more feed material than can be received in the die cavity. Therefore, such that some feed material remains in the feed chamber 14 over and above the opening of the die cavity. After the feed material is deposited into the die cavity, the shuttle is operated to retract the feed shoe 10 back to the starting position. As the feed shoe 10 retracts, the leading edge of the bottom hole 16 will level off the excess material which cannot be received in the die cavity. A press is then operated to compact the feed material in the die cavity, the compacted part is subsequently ejected from the die cavity, and the process can be repeated for as many parts as are to be made during a given production run.
The view in
When the optional auxiliary gates 44, 46 are present, the lower edges thereof will define the leading edge of each feed chamber 32, 34.
According to the invention, the main gates 36, 38 can be attached to the front of the feed shoe 30 in a manner that permits the main gates 36, 38 to be vertically adjusted relative to the front portion. In particular, the main gates 36, 38 can be adjusted upwards away from the surface of the platen, and in doing so can permit some feed material to pass under the lower edges 40, 42 of the main gates 36, 38 when the feed shoe 30 is retracted, thus reducing feed material, e.g., powder, “pull-out.” Moreover, each side of each main gate 36, 38 can be individually vertically adjustable such that the lower edges 40, 42 of each can be skewed, i.e., one side of each of the main gates 36, 38 can be positioned higher off the platen than the other side. This adjustment feature can be provided to compensate, if needed, for part thickness variation, which can be cause by an uneven platen, die cavity, or underside of the feed shoe 30 or shuttle.
The feed shoe 30 can further comprise a feed tube attachment member 50, which can include a pair of hollow tubular portions 52, 53, each having one end 54, 55 connectable to feed tubes and an opposite end 56, 57 communicating with the feed chambers 32, 34. As shown, the attachment member 50 is connected to the feed shoe 30 in a manner which enables each end 56, 57 of the hollow tubular portions 52, 53 to be adjustable side to side, front to back, and angularly with respect to each feed chamber 32, 34. For example, curved slot and pin arrangements 51 can permit the angular adjustment capability, longitudinal slot and pin arrangements 58 can provide the front to back movement, and angled spacer blocks 59 can enable the side to side positioning as well as angular adjustment in that plane. However, it is to be understood that alternative configurations of providing these types of adjustability could be devised by those of ordinary skill in the art in view the embodiments described herein.
Referring now to
According to the invention, the auxiliary gates 44, 46 are optional, and the lower edges 40, 42 of the main gates 36, 38 are the lower, leading edges of the feed shoe 30. Thus, the same types of profiles described above for provision on the lower edges of the auxiliary gates 44, 46 can also be provided on the lower edges 40, 42 of the main gates 36, 38. For example, the rounded profile of the lower edge 62 of auxiliary gate 60 would be provided on the lower edges 40, 42 of the main gates 36, 38, on the edge facing toward the feed chambers 32, 34. As explained above.
Whether provided on the main gates 36, 38 or on the auxiliary gates 44, 46, the edge profiles can be optimized depending upon, e.g., can be a function of, the particular feed material being used. Different profiles can be used to address the aforementioned feed material “pull out” which can occur when the feed shoe 30 is retracted over the die cavity. Initially, the profile may need to be determined experimentally to see which works best with different types of powders. Through testing, certain profiles have been found to function better with different feed materials. For example, the rounded profile, which can be, for example, a ⅛″ radius (half radius), can tend to perform best with hard powders, such as cathode and anode. On the other hand, the straight, flat profile can tend to perform best with soft powders, such as electrolyte. The particle size distribution can have an effect on powder pull-out, and therefore die fill consistency. The largest permissible particles in the size distribution of the powder approaches the thickness of the pellet, leading to the possibility that these large particles stick up too high in the die and can be “grabbed” by the leading edge of the main gate (or auxiliary gate when used) during feed shoe retraction. As these particles are pulled back, they may act as a plow and may thus remove excessive amounts of powder. In view of this, the serrated lower edge could be used on the auxiliary gates, being attached in the front of the main gates. The gaps in the serrated edge could permit the larger particles to pass through, reducing the plow effect and associated powder pull-out. In test using a serrated lower edge, no significant improvement in pellet quality was exhibited for cathode and electrolyte powder, but the serrated edge could still potentially be beneficial with other types of powders.
In
The main gate 80 also has a lower most edge adjacent the open bottom of the feed chamber 32, 34, but where auxiliary gates 44, 46 are used, the lower most edge of the main gate 80 can terminate at a downward most extent which is less than the downward most extent of the lower edge of each auxiliary gate 44, 46. Thus, as described previously, the lower edges of the auxiliary gates 44, 46 will define the leading edge of each feed chamber 32, 34 when the auxiliary gates 44, 46 are used along with the main gates.
As shown best in
As would be known to those of ordinary skill in the art, the vertically adjustable feature of the main gates 36, 38 can be provided in various ways, for example, using fine thread jackscrews to provide precise vertical height adjustment, and employing springs to hold pressure against jackscrews to secure the gate in position after adjustment. Also, to even more securely maintain the main gates 36, 38 in a desired position, locking setscrews could be employed.
As mentioned above, the inner surface of the main gates can be used to change the shape of the feed chambers 32, 34, which can be accomplished according to the invention by forming the main gates 36, 38 with differently configured inner surfaces, as shown in
The main gate 100 having the V-shaped inner surface 102 exhibited the best performance for the cathode power compared to the main gates 80 and 90 having the flat 82 and curved 92 inner surfaces, but only by a small margin. However, the main gate 100 with the V-shaped inner surface 102 exhibited a more significant improvement when electrolytic powder was used as the feed material.
In addition to the shape of the inner surfaces 82, 92, 102, as well as the specially profiled lower edges, described hereinabove, each of the differently shaped inner surfaces 82, 92, 102 of the main gates 80, 90, 100 can be provided with a specially designed profile on at least a lower portion 88, 98, 108 of the inner surfaces 82, 92, 102 thereof, i.e., the portion 88, 98, 108 of the inner surfaces 82, 92, 102 near the open bottom of the feed chambers 32, 34. For example, the lower portion 88, 98, 108 can have a profile, or cross section, which has an increasingly thicker cross section upwards from the open bottom of the feed chambers 32, 34. As shown in each of
As shown in
A feed shoe 30 according to the invention, as described above, can also overcome problems associated with conventional feed shoes particularly related to non-uniform die fill. Non-uniform die cavity filling can result in non-uniform part density, which may affect the part quality, properties and production yield. Non-uniform die cavity fill can be the result of, for example, powder pull-out, uneven leveling of the die cavity, and the lack of independent weight control between the multiple die cavities housed in a common die platen. Non-uniform die cavity fill can also be caused by inconsistencies between individual die cavities, which can be attributed to variations in tooling heights/flatness, as well as powder flow. Therefore, the production advantage of multiple die cavity pressing may not be fully exploited without independent weight control over the feed material deposited in each feed chamber.
As described previously, these disadvantages are overcome by the feed shoe according to the invention using a gate member which is height adjustable, such as to allow powder to flow from this opening, which can reduce powder pull out as the feed shoe retracts over the die cavity. The gate member can further also be skewed to compensate for part thickness variation, enabling improved side-to-side fill consistency. In addition, the inner surface of the gate, or the inner surface of a separate insert, can be configured to change the shape of the feed chamber, and in particular can have a stepped configuration to alter the powder shearing planes. Shearing separate planes of powder over the die reduces the weight of the powder and the affect it has on the powder in the die cavity as the feed shoe levels the powder.
When pressing multiple die cavities, a feed shoe according to the invention can have multiple feed chambers and a gate associated with each feed chamber. The separate gates can facilitate individual die cavity fill changes to meet part weight requirements while pressing multiple parts within the same cycle. The adjustable gate provides a controlled leakage, i.e., permits powder to roll under the leading edge of the gate during feed shoe retraction, which not only reduces the effects of powder pull-out, but also facilitates independent weight control of feed material deposited in each die cavity. This makes it possible to satisfactorily press two pellets at one time, thus doubling the production rate. By adjusting the gate so there's controlled leakage or a powder film left over the die as the shoe retracts, the die fill volume and part weight are effectively increased. For example, if the left side is producing parts that are at nominal weight and the right side is producing parts that are light or out of specification, the right side gate can be adjusted to increase the powder weight in that die only. Now both dies are producing parts that are in tolerance. If the press had independent die control with respect to the lower punches then the individual weight adjustments could be accomplished. However this press feature would require separate feed shoes since they would need to move independent of one another or so they could move with the separate dies. Typical presses have one die platen that houses each die. Therefore, adjusting the die fill for one die will change the others unless the lower punch is adjustable. However, the lower punch adjustment feature has load and space limitations. [Explain how adjustable gate—allowing controlled leakage—enables independent weight control of each die cavity.]
The provision of multiple, isolated feed chambers, and a separate hollow feed tube attachment portions for each feed chamber better facilitates powder flow. In addition, the angular, side to side and front to back adjustability of the attachment member can also contribute to reducing problems associated with powder distribution within the feed chambers of conventional feed shoes. The feed shoe can be made from, for example, 304 stainless steel to provide increased durability over time while maintaining a corrosion resistance. The gate can be constructed from, for example, a durable tool steel, and can also be coated with TiCN for increased wear resistance.
Although certain embodiments of the invention have been described in detail hereinabove, it will be appreciated by those skilled in the art that various modifications to those details could be developed in light of the overall teaching of the disclosure. Accordingly, the particular embodiments disclosed herein are intended to be illustrative only and not limiting to the scope of the invention, which should be awarded the full breadth of the following claims and any and all embodiments thereof.
