System and method for forming a double-dome container

Abstract

To provide a system and method for forming a metal container with a double dome. [Solution] A bottom forming system for a metal container includes a dormer assembly that forms a double dome at the bottom of the metal container during the bottom forming process. The dormer assembly includes a first dormer and a second dormer that is movable relative to the first dormer. A method for forming the bottom of a metal container includes forming a first dome contour at the bottom of the metal container using the first and second dormers of the dormer assembly. The method includes forming a second dome contour at the bottom of the metal container by moving the second dormer relative to the first dormer.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 63 / 250,806, filed on September 30, 2021, which is hereby incorporated by reference in its entirety.

[0002] This application relates to systems and methods for forming shaped containers, and more particularly, to systems and methods for forming formed metal containers from metals such as aluminum or aluminum alloys.

Background Art

[0003] Many containers and various products such as food and beverage cans, fire extinguishers, gas cylinders, oil filter casings, damper casings, etc. are made from metal materials such as aluminum, aluminum alloys, stainless steel, brass, low - carbon steel, and various other suitable materials. The processing of forming a container from a metal material generally includes forming processes such as drawing and wall ironing, a series of full - body necking steps or other mechanical forming, and other processes for forming a metal blank into a container having a desired shape as required. In many cases, metal containers configured to hold contents (e.g., carbonated beverages) under pressure are provided with domes that extend upwardly from the bottom wall of the container to withstand deformation under pressure. However, there is a lower limit to the metal gauge of the wall of the container for the existing geometric shape of the dome. In other words, domes having a metal gauge below the lower limit will break and / or deform under pressure.

Summary of the Invention

[0004] The embodiments to which this patent applies are defined by the claims below, not by the summary of this invention. The summary of this invention is a high-level overview of various embodiments and introduces some of the concepts that are further described in the sections on embodiments for carrying out the invention below. The summary of this invention is not intended to identify any important or essential features of the claimed subject matter, nor is it intended to be used alone to determine the scope of the claimed subject matter. The subject matter should be understood by referring to the entire specification of this patent, any or all of the drawings, and the appropriate parts of each claim.

[0005] According to a particular embodiment, a dormer assembly for a bottom forming system includes a first dormer and a second dormer. The first dormer includes a first surface that can engage with the bottom of a metal container during the bottom forming process. The second dormer includes a second surface that can engage with the bottom of a metal container during the bottom forming process. The second dormer is movable relative to the first dormer.

[0006] According to some embodiments, a bottom forming system for forming a metal container includes a dormer assembly that forms a double dome at the bottom of the metal container during the bottom forming process. The double dome formed at the bottom of the metal container may include a first dome having a first dome contour and a second dome having a second dome contour.

[0007] According to various embodiments, a method for forming the bottom of a metal container includes forming a first dome contour on the bottom of the metal container using a first dormer and a second dormer of a dormer assembly. The method also includes forming a second dome contour on the bottom of the metal container by moving the second dormer relative to the first dormer.

[0008] The various embodiments described herein may include additional systems, methods, features, and advantages, which are not necessarily expressly disclosed herein but will be apparent to those skilled in the art upon consideration of the following detailed description and accompanying drawings. All such systems, methods, features, and advantages are intended to be contained within this disclosure and protected by the accompanying claims.

[0009] This specification refers to the attached figures below, and the use of similar reference numbers in different figures is intended to illustrate similar or analogous components. [Brief explanation of the drawing]

[0010] [Figure 1] This shows a bottom forming system with a dormer assembly according to an embodiment. [Figure 2] Figure 1 is a top view of the first dormer of the dormer assembly. [Figure 3] Figure 1 is a top view of the dormer assembly. [Figure 4] This is a side view of the dormer assembly in Figure 1, which includes the dormer assembly in the first configuration. [Figure 5] This is a side view of the dormer assembly in Figure 1, which includes the dormer assembly in the second configuration. [Figure 6] Figure 1 shows the bottom forming system during the first step of the bottom forming process according to the embodiment. [Figure 7] Figure 1 shows the bottom forming system during the second stage of the bottom forming process. [Figure 8] An example of the bottom of a metal container with a double dome according to an embodiment is shown. [Figure 9] An example of the bottom of a metal container with a double dome according to an embodiment is shown. [Modes for carrying out the invention]

[0011] The subject matter of the embodiments is described herein with specificity to satisfy legal requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying a particular order or arrangement between different steps or elements, except where the order of individual steps or the arrangement of elements is explicitly stated. Directional references such as “up,” “down,” “top,” “bottom,” “left,” “right,” “front,” and “rear” are intended to refer to orientations shown and described in one (or more) figures, in particular, to which the components and directions refer. The systems and methods described herein can be used with any metal, but they may be particularly useful with aluminum or aluminum alloys.

[0012] This specification describes systems and methods for forming the bottom of a metal container. In various embodiments, the systems and methods provided herein can form a metal container having a double dome. In certain embodiments, the dormer assembly includes a first dormer and a second dormer selectively movable relative to the first dormer. During a first step of the bottom forming process, the first and second dormers together can form a dome contour and engage with the bottom of the metal container to form the first dome contour. During a second step of the bottom forming process, the second dormer can move relative to the first dormer and further engage with the bottom of the metal container, thereby altering the geometric shape of the first dome contour to create a second dome contour so that the metal container contains a double dome.

[0013] The geometric shape of a double dome can withstand and improve dome inversion pressure compared to a conventional dome, and the double dome may allow the container to be formed from a metal with a lower metal gauge compared to a container with a conventional dome while withstanding dome inversion pressure. The use of a metal with a lower metal gauge can reduce the weight of the can (e.g., by reducing the amount of material), which can lead to cost reductions for can manufacturers. In certain embodiments, the systems and methods described herein can increase the depth / height of the dome compared to a conventional dome, modify the geometric shape of the dome contour compared to a conventional dome, increase work hardening and residual stress, and / or improve the dome inversion pressure of the container. Various other benefits and advantages may be realized by the systems and methods provided herein, and the above-mentioned advantages should not be considered limiting.

[0014] Figures 1 to 7 show a bottom forming system 100 for forming metal containers according to various embodiments. The bottom forming system 100 can be used to form at least partially various metal containers as needed, including but not limited to beverage containers. The bottom forming system 100 generally includes a dormer assembly 102 for forming the bottom 104 of the metal container. The bottom forming system 100 may also include a retainer 106 and a punch 108 that can assist in forming the bottom 104 during the bottom forming process.

[0015] The dormer assembly 102 includes at least a first dormer 110 and a second dormer 112. In some embodiments, as best shown in Figure 2, the first dormer 110 may optionally be a sleeve having a central opening 114. In these embodiments, the second dormer 112 may be an insert for the first dormer 110 and may be at least partially positioned within the central opening 114 when the dormer assembly 102 is assembled. Although the first dormer 110 is shown surrounding the second dormer 112, this is not necessary in other embodiments, and the dormer assembly 102 may have various other configurations of at least a first dormer and a second dormer. As a non-limiting example, in some embodiments, the dormer assembly 102 may include two dormers, each forming half of the entire dormer assembly 102 and positioned adjacent to one another. In this embodiment, the dormers may be positioned adjacent to one another but do not necessarily have to be positioned between them, and / or one does not have to be surrounded by the other. Other dormer configurations can be used with the dormer assembly 102 as desired. In some embodiments, the dormer assembly 102 may include three or more dormers, such as three dormers. In embodiments with three or more dormers, one or more dormers may be movable relative to and / or to a first dormer.

[0016] As best shown in Figures 2 to 5, the first dormer 110 includes a first surface 116, and the second dormer 112 includes a second surface 118. In the illustrated embodiments, the first surface 116 and the second surface 118 have nonlinear curvature. However, the first surface 116 and the second surface 118 may have various shapes or contours as needed to form a dome contour at the bottom of the metal container during the bottom forming process. In non-limiting examples, in other embodiments, the curvature of the first surface 116 and / or the second surface 118 may be increased or decreased compared to those shown in Figures 1 to 7. During the bottom forming process, the first surface 116 and the second surface 118 may selectively engage with the bottom 104 to form the bottom 104.

[0017] In various embodiments, the second dormer 112 is selectively movable relative to the first dormer 110. In certain embodiments, the second dormer 112 is axially movable relative to the first dormer 110, while in other embodiments, the second dormer 112 may include additional movement relative to the first dormer 110. In embodiments where the second dormer 112 can be positioned within the central opening 114 of the first dormer 110, the second dormer 112 may be movable within the central opening 114. Various mechanisms, devices, or features, including but not limited to various mechanical systems, pneumatic systems, hydraulic systems, magnetic systems, combinations thereof, and / or other devices or systems as needed, can be utilized to enable the second dormer 112 to be movable relative to the first dormer.

[0018] Referring to FIGS. 4 and 5, in certain embodiments, the dome assembly 102 includes at least a first configuration and a second configuration of a first dome 110 and a second dome 112. By moving the second dome 112 relative to the first dome 110, the dome assembly 102 can be adjusted to be in the first configuration or the second configuration. In some embodiments, in the first configuration, the second dome 112 is in a first position relative to the first dome 110, and in the second configuration, the second dome 112 can be in a second position relative to the first dome 110 offset from the first position. In various embodiments, as will be described in detail below, the second dome 112 may be in the first position during a first stage of the bottom forming process and in the second position during a second stage of the bottom forming process.

[0019] FIG. 4 shows the dome assembly 102 in a first configuration where the second dome 112 is in a first position relative to the first dome 110. As shown in FIG. 4, in the first position, the second surface 118 can be continuous or flush with the first surface 116 such that the first surface 116 and the second surface 118 together form a first dome contour.

[0020] FIG. 5 shows the dome assembly 102 in a second configuration where the second dome 112 is in a second position relative to the first dome 110. As shown in FIG. 5, in the second position, the second dome 112 is moved relative to the first dome 110 such that the second surface 118 is no longer continuous or flush with the first surface 116. In particular, the side surface 120 of the second dome 112 may optionally extend over the first surface 116. The second surface 118 offset from the first surface 116 forms a second dome contour. In FIG. 5, the offset position of the second dome 112 relative to the first dome 110 is exaggerated for clarity of the figure, but during the bottom forming process, it is not necessary to move or offset the second dome 112 as much as shown in FIG. 5.

[0021] As described above, in addition to the dome assembly 102, the bottom forming system 100 may optionally include a retainer 106 and a punch 108. In certain embodiments, the retainer 106 includes a receiving region 122, and the dome assembly 102 may be positionable and movable within the receiving region 122 during the bottom forming process. The punch 108 and the retainer 106 may be used to further shape the bottom 104 of the metal container during the bottom forming process. However, the specific punch 108 and retainer 106 shown are not to be considered limiting, and in other embodiments, punches and / or retainers having other shapes, contours, features, etc. may be used as needed. In further embodiments, the bottom forming system 100 may include fewer or additional features as needed.

[0022] Hereinafter, the bottom forming process using the bottom forming system 100 will be described in detail. Referring to FIG. 1, prior to forming the bottom, the bottom 104 of the metal container can be supported relative to the dome assembly 102, optionally using a retainer 106 and / or a punch 108. In some embodiments, the punch 108 can move the bottom 104 to engage the retainer 106 before forming the dome assembly 102.

[0023] Referring to FIG. 6, during the first stage of the bottom forming process, the dome assembly 102 can engage the bottom 104 while the dome assembly is in a first configuration. In certain embodiments, the dome assembly 102 engages the bottom 104 by moving the dome assembly 102, moving the bottom 104 (e.g., using the punch 108), or a combination thereof. As shown in FIG. 图6, the dome assembly 102 in the first configuration forms a first dome having a first dome contour on the bottom 104. Optionally, during the first stage of the bottom forming process, the punch 108 can further advance towards the retainer 106 to further shape the bottom 104.

[0024] Referring to Figure 7, during the second step of the bottom forming process, the second dormer 112 moves relative to the first dormer 110 so that the dormer assembly 102 has a second configuration. The movement of the second dormer 112 relative to the first dormer 110 lifts the bottom 104 and reshapes it to include the second dome, so that the bottom 104 becomes a double dome (i.e., including the first dome 126 formed during the first step and the second dome 128 formed during the second step). Optionally, as shown in Figure 7, the second dormer 112 moving to the second position reshapes the bottom 104 so that at least a portion of the bottom 104 does not come into contact with the first surface 116 or the second surface 118, and a gap 124 may be formed at least partially between the dormer assembly 102 and the portion of the bottom 104. In certain embodiments, the movement of the second dormer 112 relative to the bottom 104 to lift the bottom 104 increases the maximum dome height / depth, alters the geometric shape of the dome contour on the bottom 104, and increases work hardening and residual stress of the bottom 104. In certain embodiments, the movement of the second dormer 112 in the second stage of the bottom forming process can improve the dome inversion pressure, which may allow the use of lower gauge metal for the bottom 104 compared to conventional bottom forming processes.

[0025] Figures 8 and 9 show two non-limiting examples of the bottom of a metal vessel formed by the dormer assembly described herein. The bottoms shown in Figures 8 and 9 are provided as examples, and other bottoms may have a variety of other contours as needed, depending on the dormer assembly used.

[0026] Figure 8 shows a non-limiting example of a bottom 804 of a metal vessel formed by a dormer assembly, which may be similar to dormer assembly 102 and includes a first dormer and a second dormer. The bottom 804 includes an end 838 having a first dome 826 and a second dome 828. As shown, the first dome 826 has a first dome depth 830, and the second dome 828 has a second dome depth 832. In the illustrated embodiment, the first dome depth 830 is 0.1638 inches, and the second dome depth 832 is 0.430 inches. In certain embodiments, the second dome depth 832 is the maximum dome depth of the double dome. In the illustrated embodiment, the second dome 828 also includes a diameter 834 and a radius of curvature 836. In the illustrated embodiment, the diameter 834 is 1.550 inches, and the radius of curvature 836 is 0.050 inches. In other embodiments, the first dome depth 830, the second dome depth 832, the diameter 834, and the radius of curvature 836 may be other values ​​depending on the dormer assembly, as needed.

[0027] Figure 9 shows a non-limiting example of a bottom 904 of a metal vessel formed by a dormer assembly including a first dormer and a second dormer, which may be similar to the dormer assembly 102. The bottom 904 includes an end 938 having a first dome 926 and a second dome 928. As shown, in this example, the first dome 926 has a first dome depth 930 and the second dome 928 has a second dome depth 932. In the illustrated embodiment, the first dome depth 930 is 0.245 inches and the second dome depth 932 is 0.443 inches. In certain embodiments, the second dome depth 932 is the maximum dome depth of the double dome. In the illustrated embodiment, the second dome 928 also includes a diameter 934 and a radius of curvature 936. In the illustrated embodiment, the diameter 934 is 1.300 inches and the radius of curvature 936 is 0.050 inches. In other embodiments, the first dome depth 930, the second dome depth 932, the diameter 934, and the radius of curvature 936 may be other values ​​depending on the dormer assembly, as needed.

[0028] A collection of exemplary embodiments is provided below, including at least some expressly listed as “exemplary” to provide further explanation of various exemplary embodiments of the concepts described herein. These examples are not intended to be mutually exclusive, exhaustive, or limiting, and this disclosure is not limited to these examples but rather encompasses all feasible modifications and variations within the scope of the issued claims and their equivalents.

[0029] Example 1. A dormer assembly for a bottom forming system, comprising: a first dormer having a first surface configured to engage with the bottom of a metal container during a bottom forming process; and a second dormer having a second surface configured to engage with the bottom of the metal container during the bottom forming process, the second dormer being movable relative to the first dormer.

[0030] Example 2. A dormer assembly according to any of the preceding or succeeding examples or a combination of examples, wherein the second dormer is movable within the first dormer.

[0031] Example 3. A dormer assembly according to any of the preceding or succeeding examples or a combination thereof, wherein the first dormer is a sleeve and the second dormer is a movable insert within the sleeve.

[0032] Example 4. A dormer assembly according to any of the preceding or succeeding examples or a combination of examples, wherein the second dormer is movable axially relative to the first dormer.

[0033] Example 5. A dormer assembly according to any of the preceding or succeeding examples or a combination of examples, wherein the dormer assembly can be arranged in a first configuration and a second configuration, in which the first configuration the first surface is continuous with the second surface and together forms a first dome contour, and in the second configuration the second surface is offset from the first surface and the second surface forms a second dome contour.

[0034] Example 6. A dormer assembly according to any of the preceding or subsequent examples or a combination of examples, wherein the first dormer and the second dormer are configured to together form a first dome on the bottom of a metal container during a first step of the bottom forming process, and the second dormer is configured to form a second dome on the bottom of the metal container during a second step of the bottom forming process.

[0035] Example 7. A bottom forming system for forming a metal container, comprising a dormer assembly configured to form a double dome at the bottom of the metal container during a bottom forming process, the dormer assembly comprising a first dome having a first dome contour and a second dome having a second dome contour.

[0036] Example 8. A bottom forming system according to any of the preceding or subsequent examples or combination of examples, wherein the dormer assembly comprises a first dormer and a second dormer, the second dormer being selectively movable relative to the first dormer.

[0037] Example 9. A bottom forming system according to any of the preceding or subsequent examples or combination of examples, wherein the dormer assembly comprises a first configuration and a second configuration, in the first configuration, the second dormer is in a first position relative to the first dormer such that the first dormer and the second dormer together form the first dome, and in the second configuration, the second dormer is in a second position relative to the first dormer such that the second dormer forms the second dome.

[0038] Example 10. A bottom forming system according to any of the preceding or succeeding examples or a combination of examples, wherein the first dormer is a sleeve and the second dormer is a movable insert within the sleeve.

[0039] Example 11. A bottom forming system according to any of the preceding or succeeding examples or a combination of examples, wherein the second dormer is movable axially relative to the first dormer.

[0040] Example 12. A bottom forming system according to any of the preceding or succeeding examples or combination of examples, wherein the first dormer comprises a first surface, the second dormer comprises a second surface, and the second dormer is movable relative to the first dormer such that at a first position of the second dormer relative to the first dormer, the first surface is continuous with the second surface, and at a second position of the second dormer relative to the first dormer, the second surface is offset from the first surface.

[0041] Example 13. A bottom forming system according to any of the preceding or succeeding examples or combination of examples, further comprising a punch and a retainer having a receiving region for a metal container, wherein the dormer assembly is movable within the receiving region.

[0042] Example 14. A method for forming the bottom of a metal container, comprising: forming a first dome contour on the bottom of the metal container using a first dormer and a second dormer of a dormer assembly; and forming a second dome contour on the bottom of the metal container by moving the second dormer relative to the first dormer.

[0043] Example 15. A preceding or succeeding example or combination of examples of the method, wherein forming the second dome contour includes moving the second domer axially relative to the first domer.

[0044] Example 16. The method by which either the preceding or succeeding example or a combination of the examples is described, wherein forming the first dome contour includes moving the first dormer and the second dormer together in an axial direction in a first direction to engage with the bottom of the metal container, and forming the second dome contour includes moving the second dormer relative to the first dormer in a first direction.

[0045] Example 17. A method by which either the preceding or succeeding example or a combination of the examples is performed, wherein forming the first dome contour further involves using a punch to form the first dome contour on the bottom of the metal container.

[0046] Example 18. A method by any preceding or succeeding example or combination of examples, wherein the first dormer is a sleeve, the second dormer is an insert within the sleeve, and forming the second dome contour involves moving the second dormer while the second dormer is at least partially within the sleeve.

[0047] Example 19. The preceding or succeeding example or combination of examples of the method, wherein forming the first dome contour includes engaging the first surface of the first dormer and the second surface of the second dormer with the bottom of the metal container.

[0048] Example 20. A method by which either the preceding or succeeding example or a combination of examples is described, comprising moving the second dormer relative to the first dormer such that forming the second dome contour does not cause at least a portion of the bottom of the metal container to come into contact with the first or second surface.

[0049] Example 21. A metal container having a bottom formed by the method of either the preceding or succeeding example or a combination of the examples.

[0050] Example 22. A metal container according to any of the preceding or following examples or combination thereof, wherein the metal container comprises aluminum or an aluminum alloy.

[0051] Example 23. A metal container according to any of the preceding or following examples, or a combination of the examples, including a metal gauge with a reduced bottom.

[0052] The embodiments described above are merely possible examples of embodiments and are provided solely for the purpose of a clear understanding of the principles of this disclosure. Many variations and modifications may be made to the embodiments(s) described above without substantially departing from the spirit and principles of this disclosure. All such modifications and variations are intended to be incorporated herein within the scope of this disclosure, and all possible claims for individual embodiments or combinations of elements or steps are intended to be supported by this disclosure. Furthermore, certain terms are used herein and in the following claims, but they are used in a general and descriptive sense only and are not intended to limit the embodiments described or the following claims.

Claims

1. A dormer assembly for a bottom forming system, A first dormer having a first surface configured to engage with the bottom of a metal container during the bottom forming process, A second dormer having a second surface configured to engage with the bottom of the metal container during the bottom forming process, the second dormer being movable relative to the first dormer, The dormer assembly comprising the above.

2. The dormer assembly according to claim 1, wherein the second dormer is movable within the first dormer.

3. The dormer assembly according to claim 1, wherein the first dormer is a sleeve, and the second dormer is a movable insert within the sleeve.

4. The dormer assembly according to claim 1, wherein the second dormer is axially movable relative to the first dormer.

5. The dormer assembly can be arranged in the first configuration and the second configuration. In the first configuration, the first surface is continuous with the second surface, and together they form the first dome contour. The dormer assembly according to claim 1, wherein in the second configuration, the second surface is offset from the first surface and the second surface forms a second dome contour.

6. The first dormer and the second dormer are configured to together form a first dome at the bottom of the metal container during the first step of the bottom forming process. The dormer assembly according to claim 1, wherein the second dormer is configured to form a second dome on the bottom of the metal container during a second step of the bottom forming process.

7. A bottom forming system for forming a metal container, comprising a dormer assembly configured to form a double dome at the bottom of the metal container during a bottom forming process, the dormer assembly comprising a first dome having a first dome contour and a second dome having a second dome contour.

8. The dormer assembly comprises a first dormer and a second dormer. The bottom forming system according to claim 7, wherein the second dormer is selectively movable relative to the first dormer.

9. The dormer assembly comprises a first configuration and a second configuration, In the first configuration, the second dormer is positioned in a first position relative to the first dormer such that the first dormer and the second dormer together form the first dome. The bottom forming system according to claim 8, wherein in the second configuration, the second dormer is in a second position relative to the first dormer such that the second dormer is configured to form the second dome.

10. The first dormer is a sleeve, The bottom forming system according to claim 8, wherein the second dormer is a movable insert within the sleeve.

11. The bottom forming system according to claim 8, wherein the second dormer is movable in the axial direction relative to the first dormer.

12. The first dormer comprises a first surface, and the second dormer comprises a second surface, The bottom forming system according to claim 8, wherein the second dormer is movable relative to the first dormer such that, at a first position of the second dormer relative to the first dormer, the first surface is continuous with the second surface, and at a second position of the second dormer relative to the first dormer, the second surface is offset from the first surface.

13. A punch and A retainer having a receiving area for a metal container, further comprising The dormer assembly is movable within the receiving region. The bottom forming system according to claim 7.

14. A method for forming the bottom of a metal container, The first dome contour is formed on the bottom of the metal container using the first and second dormers of the dormer assembly, A second dome contour is formed on the bottom of the metal container by moving the second dormer relative to the first dormer, The method, including the method described above.

15. The method according to claim 14, wherein forming the second dome contour includes moving the second domer axially relative to the first domer.

16. Forming the first dome contour includes moving the first dormer and the second dormer together axially in a first direction to engage with the bottom of the metal container, The method according to claim 14, wherein forming the second dome contour includes moving the second domer in the first direction relative to the first domer.

17. The method according to claim 14, wherein forming the first dome contour comprises using a punch to further form the first dome contour on the bottom of the metal container.

18. The first dormer is a sleeve, and the second dormer is an insert within the sleeve. The method according to claim 14, wherein forming the second dome contour involves moving the second dormer while the second dormer is at least partially within the sleeve.

19. The method according to claim 14, wherein forming the first dome contour includes engaging the first surface of the first dormer and the second surface of the second dormer with the bottom of the metal container.

20. The method according to claim 19, comprising moving the second dormer relative to the first dormer such that forming the second dome contour does not cause at least a portion of the bottom of the metal container to come into contact with the first or second surface.

21. A metal container having a bottom formed by the method described in claim 14.

22. The metal container according to claim 21, wherein the metal container comprises aluminum or an aluminum alloy.

23. The metal container according to claim 21, comprising a metal gauge with a reduced bottom portion.

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