REVERSED INTERSTITIAL PADDLES

Abstract

An inner drum for use in a dryer/mixer in connection with the production of an aggregate-binder mix includes a plurality of mixing paddles disposed on the outer surface of the inner drum and arranged in a plurality of rows. The mixing paddles are configured to rotate through a mixing chamber as the inner drum rotates within an outer drum of the dryer/mixer to mix aggregate and binder together. Interstitial spaces are formed between rows of mixing paddles and material leads, where aggregate material preferentially travels as the inner drum is rotated, extend along the mixing chamber. At least one interstitial mixing paddle is located on the outer surface of the inner drum and in one of the interstitial spaces at one of the material leads. The interstitial mixing paddle rotates through the mixing chamber as the inner drum rotates to also mix the aggregate and binder together.

Claims

1. An inner drum for use in a dryer/mixer in connection with the production of an aggregate-binder mix, wherein the dryer/mixer includes a fixed outer drum surrounding the inner drum such that the inner drum may rotate within the outer drum, a mixing chamber formed between an outer surface of the inner drum and an inner surface of the outer drum where virgin aggregate and a binder are mixed together to form an aggregate-binder mix, an aggregate inlet through which virgin aggregate may be passed into the mixing chamber, a binder inlet through which a binder may be passed into the mixing chamber, and a mix outlet through which the aggregate-binder mix may be passed out of the mixing chamber, the inner drum further comprising: a plurality of mixing paddles disposed on the outer surface of the inner drum and arranged in a plurality of rows, wherein the mixing paddles are configured to rotate through the mixing chamber as the inner drum rotates within the outer drum and to mix together aggregate and binder located within the mixing chamber; an interstitial space formed between each adjacent pair of rows of mixing paddles through which the aggregate and binder may pass; a plurality of material leads that extend along the mixing chamber and along which aggregate material preferentially travels as a result of a location and orientation of the plurality of mixing paddles; and at least one interstitial mixing paddle disposed on the outer surface of the inner drum and located in one of the interstitial spaces and also positioned at one of the material leads, wherein the interstitial mixing paddle is configured to rotate through the mixing chamber as the inner drum rotates within the outer drum and to mix together aggregate and binder located within the mixing chamber.

2. The inner drum of claim 1 wherein a first group of one or more of the plurality of mixing paddles induces movement of a portion of the aggregate in a forward direction F away from the aggregate inlet as the inner drum rotates.

3. The inner drum of claim 2 wherein a second group of one or more of the plurality of mixing paddles induces movement of a portion of the aggregate in a retrograde direction F′ towards the aggregate inlet as the inner drum rotates.

4. The inner drum of claim 2 wherein the interstitial mixing paddle induces movement of a portion of the aggregate in a retrograde direction F′ towards the aggregate inlet as the inner drum rotates.

5. The inner drum of claim 1 wherein each of the material lead passes through each interstitial space.

6. The inner drum of claim 1 further comprising two or more interstitial mixing paddles that are all located within one of the interstitial spaces and that are each positioned at one of the material leads.

7. The inner drum of claim 1 further comprising an interstitial mixing paddle located within a different one of two interstitial spaces, wherein each interstitial mixing paddle is positioned at one of the material leads.

8. The inner drum of claim 7 wherein the two interstitial spaces are adjacent one another.

9. The inner drum of claim 7 wherein the two interstitial spaces are not adjacent one another.

10. The inner drum of claim 7 wherein a different number of interstitial mixing paddles is located in the two interstitial spaces.

11. The inner drum of claim 7 wherein an identical number of interstitial mixing paddles is located in each of the two interstitial spaces.

12. The inner drum of claim 1 further comprising at least one interstitial mixing paddle positioned at each material lead.

13. The inner drum of claim 1 further comprising a shank for connecting the mixing paddles and interstitial mixing paddle to the inner drum such that a leading face of each of the mixing paddles and the interstitial mixing paddle is fixed at a selected orientation with respect to the shank.

14. The inner drum of claim 11 wherein the selected orientation of the leading face of the interstitial mixing paddle is offset by approximately 90° compared to the selected orientation of the leading face of the mixing paddles.

15. The inner drum of claim 1 wherein the plurality of mixing paddles are spaced continuously across the inner drum along an entire length of the mixing chamber.

16. The inner drum of claim 15 comprising a plurality of interstitial mixing paddles, wherein the interstitial mixing paddles are not spaced continuously across the inner drum.

17. A plant configured for the batch production of asphalt comprising said dryer/mixer, mixing chamber, aggregate inlet, binder inlet, mix outlet, and inner drum of claim 1, wherein the fixed outer drum and the rotating inner are each cylindrical in shape, wherein the aggregate inlet is a an aggregate chute through which virgin aggregate may be passed into the inner drum, wherein openings formed in the inner drum allow the virgin aggregate to pass from the inner drum in to the mixing chamber, and wherein the binder is asphalt.

18. A method for forming an aggregate mix comprising the steps of: providing a dryer/mixer that includes: a fixed outer drum, an inner drum located within the outer drum, a mixing chamber formed between an outer surface of the inner drum and an inner surface of the outer drum, an aggregate inlet, an asphalt inlet, and a mix outlet, wherein the inner drum further includes: a plurality of mixing paddles disposed on the outer surface of the inner drum and arranged in a plurality of rows, an interstitial space formed between each adjacent pair of rows of mixing paddles, a plurality of material leads that extend along the mixing chamber and along which aggregate material preferentially travels as a result of a location and orientation of the plurality of mixing paddles, and at least one interstitial mixing paddle disposed on the outer surface of the inner drum and located in one of the interstitial spaces and also positioned at one of the material leads; passing virgin aggregate into the mixing chamber via the aggregate inlet; passing asphalt into the mixing chamber via the asphalt inlet; inducing movement of a portion of the aggregate in a forward direction F away from the aggregate inlet and along the plurality of material leads with the plurality of mixing paddles by rotating the inner drum in a direction R with respect to the outer drum such that the aggregate is mixed with the asphalt to form an aggregate mix; inducing movement of at least a portion of the aggregate with the interstitial mixing paddle by rotating the inner drum in the direction R; and passing the aggregate mix out of the mixing chamber via the mix outlet.

19. The method of claim 18 wherein the movement induced by the interstitial mixing paddle is in a retrograde direction F′ toward the aggregate inlet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numerals represent like elements throughout the several views, and wherein:

[0023] FIG. 1 is a sectional view of a conventional dryer/mixer used in an HMA system and production process;

[0024] FIG. 2 is depicts an inner drum of the dryer/mixer of FIG. 1, shown in a flat unrolled configuration to provide a layout map;

[0025] FIG. 3 is a detailed view of a boxed portion of the layout map of FIG. 2 denoted by “FIG. 3”;

[0026] FIG. 4 depicts an inner drum configured for use in a HMA system and production process according to an embodiment of the present invention;

[0027] FIG. 5 is depicts the inner drum of FIG. 4, shown in a flat unrolled configuration to provide a layout map;

[0028] FIG. 6 is a detailed view of a boxed portion of the layout map of FIG. 5 denoted by “FIG. 6”; and

[0029] FIG. 7 is a detailed view of a boxed portion of the layout map of FIG. 5 denoted by “FIG. 7”, which includes a reversed interstation paddle according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0030] Referring now to the drawings in which like reference characters designate like or corresponding characters throughout the several views, there is shown in FIG. 4 an inner drum 100 for use in a dryer/mixer, such as dryer/mixer 10 (shown in FIG. 1) in place of inner drum 12, in connection with the production of an aggregate-binder mix. It is noted here that, in the embodiments illustrated by this disclosure, the binder is asphalt and the inner drum 100 is used for the batch production of asphalt concrete in an HMA system and production process. However, the inner drum 100, including as part of a dryer/mixer, and also the methods disclosed herein may also be used in other industries as well.

[0031] As above, the dryer/mixer preferably includes a fixed outer drum designed to surround the inner drum 100 such that the inner drum may rotate within the outer drum. A mixing chamber is formed between an outer surface of the inner drum and an inner surface of the outer drum. Virgin aggregate and a binder may be mixed together to form an aggregate-binder mix within the mixing chamber. The dryer/mixer also provides an aggregate inlet, such as openings 34 and/or virgin aggregate inlet 42, through which virgin aggregate may be passed into the dryer/mixer and/or the mixing chamber. Similarly, the dryer/mixer also provides a binder inlet, such as upper inlet 40, through which a binder may be passed into the mixing chamber. Lastly, the dryer/mixer provides a mix outlet, such as asphalt mix outlet 44, through which the aggregate-binder mix may be passed out of the mixing chamber.

[0032] Now, with continued reference to FIG. 4 and with further reference to FIG. 5, a preferred inner drum 100 is shown in a flat “unrolled” configuration to provide a “layout map.” According to certain preferred embodiments of the present invention, mixing paddles 102 are attached to the outer surface 100A of the inner drum 100 and are arranged in rows (two of which are generally shown by lines 104 in FIGS. 4 and 5). Preferably, mixing paddles 102 are placed in these rows 104 and are spaced continuously across the outer surface 100A of the inner drum 100 along an entire length of the mixing chamber. An interstitial space 106 is formed between each adjacent pair of rows 104 of mixing paddles 102. These interstitial spaces 106 are sized to allow aggregate and binder to pass through them. Next, material leads extend along at least a portion of the mixing chamber (one of which is generally shown by arrow 108 in FIG. 5). As noted above, material leads 108 are essentially the pathways that aggregate material and asphalt take as they move through the mixing chamber along the length of the inner drum 100. Lastly, at least one interstitial mixing paddle 110 is attached to the outer surface 100A of the inner drum 100.

[0033] Unlike the mixing paddles 102, which are placed along the rows 104, the interstitial mixing paddle 110 is preferably located in one of the interstitial spaces 106 between the rows. Interstitial mixing paddles 110 may each be located within a different one of two or more interstitial spaces 106. These two or more interstitial spaces 106 may each be adjacent one another or may not be located adjacent one another (i.e., such that there is at least one empty interstitial space between two interstitial spaces that are populated with a interstitial mixing paddle 110). The same or different numbers of interstitial mixing paddles 110 may populate different interstitial spaces 106. For example, in certain preferred embodiments, two interstitial mixing paddles 110 are located within a single interstitial space 106, while more than two (or fewer than two) interstitial mixing paddles are located within another interstitial space.

[0034] Unlike the mixing paddles 102, the interstitial mixing paddles 110 are preferably not spaced continuously across the outer surface 100A of the inner drum 100. On the other hand, like the mixing paddles 102, each interstitial mixing paddle 110 is preferably positioned at one of the material leads 108. Placing the paddles 102, 110 at the material leads 108 helps to ensure that the material moving along the material leads comes into contact with the paddles. For this reason, in preferred embodiments, each material lead 108 passes through each interstitial space 106 at least once along the length of the mixing chamber. Furthermore, in preferred embodiments, at least one mixing paddle 110 and/or interstitial mixing paddled 110 is positioned at each material lead 108.

[0035] With continued reference to FIG. 4 and with further reference to FIGS. 6 and 7, the paddles 102, 110 each preferably include a leading face 112 for contacting (e.g., pushing) aggregate material during the mixing process, which is described in more detail below, and also a shank 114 for connecting the paddles to the outer surface 100A of the inner drum 100. Preferably, once the paddles 102, 110 are attached to the inner drum 100, each is fixedly held in a selected orientation (i.e., angle) with respect to the shank 114 and the inner drum 100. In this description, the orientation of the paddles 102, 110 is defined based on the orientation of the leading face 112. For example, the paddles 102, 110 are oriented at an angle θ equal to 0° when oriented vertically and the leading face 112 is pointed away from aggregate inlet 116 (shown in FIG. 4). The paddles 102, 110 are oriented at an angle θ equal to 90° when oriented horizontally (i.e., parallel with axis A) and the leading face 112 is pointed upwards away from the mixing chamber. In this particular embodiment, each of the mixing paddles 102 is oriented at an angle θ of approximately 45°. The orientation of the interstitial mixing paddle 112 is offset from the orientation of the mixing paddles 102 by approximately 90° and is, therefore, oriented at an angle θ of approximately 135°.

[0036] When the inner drum 100 is used to produce an aggregate mix, virgin aggregate and asphalt are first passed into the mixing chamber via the aggregate inlet and asphalt inlet, respectively. Next, the inner drum 100 is rotated about axis A (FIG. 4) in direction R. This rotation of the inner drum 100 causes the mixing paddles 102 and the interstitial mixing paddle 110 to each rotate through the mixing chamber of the dryer/mixer. The leading face 112 of each of the paddles 102, 110 tends to move and direct the aggregate (and asphalt) material within the mixing chamber. The motion of the mixing paddles 102 induces movement of a portion of the aggregate in a forward direction F away from aggregate inlet 116 as the inner drum 100 rotates. Similarly, like mixing paddles 102, the motion of the interstitial mixing paddle 110 induces movement of a portion of the aggregate as the inner drum 100 rotates. In each case, this movement of the aggregate facilitates the mixing of aggregate with the asphalt.

[0037] In general, aggregate material prefers or would tend to travel along the material leads 108 (in the direction indicated by the arrow) as a result of the location and orientation of the mixing paddles 102. Thus, as shown in FIG. 6, the aggregate material tends to travel from one mixing paddle 102 to the next mixing paddle in the forward direction F as the inner drum 100 is rotated. In some cases, the interstitial paddle 112 also causes the aggregate material to tend to travel from in the forward direction F. However, the direction that the aggregate material ultimately travels depends on the orientation (i.e., the angle θ) of the paddles 102, 110. As shown in FIG. 7, if one of the paddles 102, 110 is oriented at an angle θ that is greater than 90°, such that the right-hand side of the paddle is higher than the left-hand side (as viewed in FIG. 7), the paddle is likely to induce movement of the aggregate in a retrograde direction F′ toward the aggregate inlet 4 instead of away from it. This is manifested by a flow of the aggregate material along reversed path 108′ that is different from (and preferably opposite to) the material lead 108. An advantage of movement of aggregate in the retrograde direction F′ is that such motion would increase the residence time and provide more time for mixing of aggregate and asphalt to occur.

[0038] Thus, in certain embodiments, it may be possible for mixing paddles 102 to direct aggregate material in two different direction. In those cases, for example, a first group of mixing paddles 102 may be arranged and oriented to induce movement of a portion of the aggregate in the forward direction F away from the aggregate inlet as the inner drum rotates in direction R. At the same time, a second group mixing paddles 102 induces movement of a portion of the aggregate in a retrograde direction F′ towards the aggregate inlet as the inner drum rotates. Additionally or alternatively, the interstitial mixing paddle 110 may be configured to induce movement of a portion of the aggregate in either the forward direction F or in the retrograde direction F′ as the inner drum rotates, depending on the angle θ of the interstitial mixing paddles.

[0039] Although this description contains many specifics, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments thereof, as well as the best mode contemplated by the inventor of carrying out the invention. The invention, as described herein, is susceptible to various modifications and adaptations as would be appreciated by those having ordinary skill in the art to which the invention relates.