Abstract:
A device for the comminution of free-flowing feed material is provided that includes a housing enclosing a comminution chamber which contains a rotor that rotates around an axis, and has comminution tools over its circumference. A feeding device to transport the feed material to the comminution chamber in form of a gas-solid matter mixture, wherein the feeding device features a pneumatic sieve passage which uses the effect of gravity for removal of foreign particles from the feed material. In order to operate both the sieve passage and the device under optimal process parameters, the device features at least one inlet port for the supply of secondary air, wherein the at least one inlet port flows into the gas-solid matter mixture downstream of the sieve passage.

Description:
[0001]    This nonprovisional application claims priority under 35 U.S.C. §119(a) to German Patent Application No. 10 2014 112 599.1, filed on Sep. 2, 2014, all of which is herein incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a device for the comminution of free-flowing feed material through which air flows. 
         [0004]    2. Description of the Background Art 
         [0005]    Such devices are associated with the field of mechanical process engineering and serve to comminute free-flowing substances such as, for example, minerals, pharmaceutical and chemical substances, foodstuffs, materials containing cellulose, synthetics, and the like. Typical for such devices is an air stream produced by a rotor, so-called internal air, which assumes the transportation of the feed material into and out of the comminution device and also ensures the cooling of the feed material and the comminution tools. In addition, subject to its flow speed, the internal air determines the length of stay of the feed material in the comminution section and thus the degree of comminution. The precise adherence to the machine-specific internal air quantity during operation of generic devices is thus highly important for producing a high-quality, final product. 
         [0006]    To prevent damage of devices due to foreign particles in the feed material, it is further a known practice to provide a gravity sifter at the material infeed. By a significant change in material flow direction at the comminution device infeed, due to their mass inertia, foreign particles are separated from the material stream, wherein the separation limit is determined by the speed of the material stream. In order to adhere to a predetermined separation limit, it is thus necessary to supply the gravity sifter with a constant loading rate. 
         [0007]    A problem which arises here is that as a rule, the internal air quantity of a comminution device is much greater than the internal air quantity of the upstream sifter. Operating a comminution device with an optimal internal air quantity leads to material stream speeds in the sieve passage in which undesirably, also useful feed material is discharged from the material stream. 
         [0008]    In order to avoid this, a comminution machine through which gas flows is known from DE 43 16 350 C1, which corresponds to U.S. Pat. No. 5,529,250, and which is incorporated herein by reference, and which contains an upstream infeed apparatus with a sieve passage, wherein in the sieve passage a fan additionally feeds in air. 
       SUMMARY OF THE INVENTION 
       [0009]    It is the objective of the present invention to further improve comminution devices with an upstream, pneumatic sieve passage. 
         [0010]    The present invention facilitates the meeting of the conflicting requirements of optimal internal air quantity for the comminution device on the one hand, and optimal internal air quantity for the feeding device on the other without having to take into account economic losses or losses in quality. Thanks to the present invention, the feed material is processed according to optimal conditions in regards to sifting as well as to comminution. During gravity sifting, this allows for a reliable and precise removal of foreign particles from the mixture of gas and solid matter. It also allows for adherence to the optimal processing parameters necessary for the appropriate type of size reduction when comminuting the feed material, for example length of stay of the feed material in the comminution section, temperature of the feed material and the comminution tools, and the like, which ultimately facilitates the economic production of a high-quality, final product. 
         [0011]    According to an embodiment of the invention, the inlet port for the supply of secondary air directly feeds into the comminution chamber. This allows on the one hand for a simple and economic construction of inventive devices. At the same time, the opening for the secondary air that is situated well downstream of the sieve passage prevents an undesired influence of the secondary air on the processes taking place in the sieve passage, a condition that would impact the observance of the separation limit. 
         [0012]    In an embodiment of the invention, the inlet ports for the supply of secondary air feed into the second channel section of the feeding device with the advantage that the secondary air and the gas-solid matter mixture can mix well and thus create uniform conditions for the comminution process. Preferably, the secondary air is distributed evenly with the help of an annular channel across the circumference of the infeed channel ending in the comminution device so that the entire circumference of the infeed channel can be uniformly supplied. The secondary air coming from the annular channel can hereby feed directly into the comminution chamber of the comminution device, or indirectly via openings into the infeed channel which then leads to the comminution chamber. 
         [0013]    In order to on the one hand adapt to the feed material and the type of size reduction, but on the other hand also achieve optimal processing during the active comminution operation, a further, advantageous embodiment of the invention can regulate the secondary air quantity. For this, a regulating body is supplied, for example, directly at the inlet port or at the annular channel. 
         [0014]    Further openings can be provided for air intake in the rear panel of the comminution device. The secondary air can be supplemented via these openings so that the amount of secondary air that is to enter the area of the feeding device can be smaller. At the same time, additional air in the rear panel region allows for a more uniform cooling of the comminution device. 
         [0015]    The invention shows that very good results can be achieved when the secondary air quantity is 10% to 50% of the internal air quantity, though preferably 15% to 35%, most preferably 25%. 
         [0016]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
           [0018]      FIG. 1  is a vertical section through a first embodiment of a device according to the invention; 
           [0019]      FIG. 2  is a cross section through the device shown in  FIG. 1  along the line  11 - 11  shown there; 
           [0020]      FIG. 3  is a vertical section through a second embodiment of a device according to the invention; and 
           [0021]      FIG. 4  is a vertical section through a third embodiment of a device according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIGS. 1 and 2  show a comminution device  1  according to the invention in the form of a turbo mill. The comminution device  1  has in essence a cylindrical housing  2  which is tightly connected with the base via a stand  3 . The housing  2  encloses a first chamber  5  in which the comminution takes place, and a second chamber  6  that serves to produce air flow and discharge feed material. The two chambers  5  and  6  are consecutively arranged with respect to the housing axis  4  and connected with each other via an opening  7  that is concentric to the axis  4 . At the front side, the housing  2  is closed by a front panel  8  and back panel  9 . The back panel  9  has a concentric opening in the region of the axis  4  in which a horizontal shaft bearing  10  is situated for the rotatable inclusion of a rotor  11 . The rotor  11  is comprised of a shaft  12  that is coaxial to the axis and which end situated outside the housing  2  carries a pulley with numerous grooves  13  for power coupling with a driving mechanism. The end of the shaft  12  resting in the housing  2  extends through both chambers  5  and  6 , wherein the shaft section situated in the first chamber  5  carries an impeller  14 . The impeller  14  is mainly composed of a hub  15  to which a baffle disk  16  and radial bars  17  connect radially outwards. Comminution tools in the form of impeller wear plates  18  are attached to the ends of the bars  17  which form the rotor circumference. The active edges of all wear plates  18  are situated on a common circle track which is opposed by a baffle rail  19  formed by the inner circumference of the first chamber  5 , subject to a radial working gap. 
         [0023]    The rotor  11  further encloses a fan wheel  20  which is also attached torque-proof by a hub  21  on the shaft  12  and extends diagonally outward with a cone-shaped plate  22  into the second chamber  6 . In the outer circumferential area of the cone plate  22 , air blades  23  that are directed radially outwards are arranged at uniform circumference intervals which generate the internal air of the comminution device  1  during operation of the rotor  11 . The removal of sufficiently comminuted material takes place via a product discharge  24  which tangentially flows out from the second chamber  6 . 
         [0024]    To supply the comminution device  1  with feed material, the front panel  8  features a central opening  25  situated axially opposite the shaft  12 , to which a feeding device  30  with an integrated gravity sifter attaches. The feeding device  30  has an infeed channel  31  with a first channel section  32  formed as a falling chute and a second channel section  32  attaching thereto at an angle, which flows into the first chamber  5  of the comminution device  1 . In the region of the first channel section  32 , flow conducting bodies  26  are arranged at the inner surface which help determine the flow direction. The infeed channel  31  undergoes a change in direction of approximately 180° in the region of transition from the first channel section  32  to the second channel section  33 , which is linked to a reversal in direction of the material stream. In the outer circumference of the area of redirection, the infeed channel  31  has an opening  34 . This area thus forms a sieve passage  35  in which due to their weight and the associated mass inertia, heavier particles in the feed material do not follow the direction of the other material stream. Instead, due to active gravities they are discharged from the feed material through the opening  34 . 
         [0025]    The longitudinal portion of the second channel section  33  situated directly in front of the feed opening  25  is encircled by an annular channel  36  which is fed with secondary air  40  via a pipe socket  37  radially merging into it. To control the quantity of air, the flow area of the pipe socket  37  can be adjusted via a damper  38 . The side of the annular channel  36  facing the comminution device  1  is open so that secondary air in the annular channel  36  uniformly spreading over the circumference of the second channel section  33  enters axially into the first chamber  5  of the comminution device  1  and mixes there with the gas-solid matter mixture from the infeed channel  31 . 
         [0026]    During operation of a device  1  according to the invention, the gas-solid matter mixture  27  is fed via the first channel section  32  of the sieve passage  35  with an optimum speed and optimum mixing ratio for gravity sifting. Foreign particles in the feed material are discharged through the opening  34  in the area of the sieve passage  35  by the redirection of the material stream. The feed material ultimately reaches the first chamber  5  of the comminution device  1  via the second channel section  33  of the infeed channel  31 . 
         [0027]    The internal air necessary for optimum comminution of the feed material is drawn in by the fan wheel  20  of the comminution device  1 , wherein the amount of air necessary is much greater than what is provided by the gas-solid matter mixture  27 . In order to nevertheless supply the comminution device  1  with enough air without diminishing the efficiency of the gravity sifter, the air volume difference is introduced as secondary air  40  into the first chamber  5  of the comminution device  1  via the pipe socket  37  and the annular channel  36 . In this way, it is possible to operate both the gravity sifter in the area of the feeding device  30  and the comminution device  1  in adherence to optimal process parameters. 
         [0028]    The comminution device  1  illustrated in  FIG. 3  for a large part relates to the one described in  FIGS. 1 and 2  so in order to avoid repetition, reference is made to those using the same reference signs. In contrast to the embodiment described above, the secondary air  40  in the comminution device  1  in  FIG. 3  is not directly fed from the annular channel  36 ′ into the comminution device  1 , but instead indirectly via the second channel section  33 ′ of the feeding device  30 . For this purpose, the annular channel  36 ′ is closed on all sides, wherein the second channel section  33 ′ features several openings  39  in uniform circumference intervals in the region encircled by the annular channel  36 ′, for example 2, 3 or 4 openings  39 . The secondary air  40  thereby flows radially from the annular channel  36 ′ through the openings  39  in the second channel section  33 ′ of the infeed channel  31  and there already interfuses with the gas-solid matter mixture  27 . 
         [0029]      FIG. 4  shows an embodiment of the invention in which the comminution device  1  is exemplified by a whirlwind mill. The whirlwind mill has a cylindrical housing  42  which encloses a comminution chamber  43 . At the circumference, the housing  42  is surrounded by a housing cover  44  which is open towards the bottom for the formation of a product discharge  45 . The housing  42  serves to hold a rotor  46  which is rotatable inside a shaft bearing  47 , centrally inserted in the back panel  45 . The shaft  48  of the rotor  46  thereby carries a multi-groove plate with its end situated outside the housing  42  via which the rotor  46  is powered. At the end opposite the shaft  48 , there are an impeller  49  formed by a hub cone  50  coaxially situated on the shaft  48 , a support disk  51  and a washer  52  plano-parallel thereto, which all receive axially aligned impeller wear plates  53  at their outer circumference. 
         [0030]    A central baffle rail  54 , connected in axial direction on each side to a sieve rail  55 , sits opposite the impeller wear plates  53  spaced by a comminution gap. The sieve rails  55  are hereby set off in radial direction from the housing cover  44 , thereby forming an annular channel  56  via which the sufficiently fined material is removed and fed to the product discharge  45 . 
         [0031]    In the front panel  44 , an opening  57  concentric to the rotational axis is arranged which is connected to the feeding device  30 . The feeding device  30  largely corresponds to the ones described in  FIGS. 1 to 3  so that for the same characteristics, the aforesaid is valid. The feeding device  30  thus includes an infeed channel  31  with a first channel section  32  and a second channel section  33  which are separated from one another by a sieve passage  35 . The second channel section  33  thereby attaches to the opening  57  in the front panel  44  of the invented device  1 . 
         [0032]    For the infeed of secondary air  40 , an opening  58  is provided directly in front of opening  57  in the second channel section  33  of the infeed channel  31 . Outside of the second channel section  33 , the opening  58  is surrounded by an air duct  59  which is formed by the front panel  44  and the second channel section of the feeding device  30  situated opposite thereto, as well as two plano-parallel side plates  59  which connect the front panel  44  with the feeding device  30  and are at a distance to each other. A swivel-mounted damper  50  with which the amount of secondary air  40  can be regulated is embedded in the air duct  59 . 
         [0033]    During operation at the impeller  49 , the whirlwind mill generates an air stream (internal air) with the impeller wear plates  53  and the air blades  23  which constitutes the propulsion for the material stream through the mill. The whirlwind mill thereby draws in the feed material  27  through the feeding device  30 , where in the sieve passage  35  area, unsuitable feed material is removed. The sifted feed material then travels through the opening  57  via a disk-shaped channel between the support disk  51  and the washer  52  to the impeller wear plates  53  and the baffle rail  54 . From there, after sufficient comminution, it reaches the lateral sieve rails  55  and from there is channeled out of the whirlwind mill via the annular channels  56  and the product discharge  45 . 
         [0034]    Since the intrinsic internal air amount of the whirlwind mill is significantly greater than what is necessary for the area surrounding the gravity sifter, secondary air  40  is fed into the whirlwind mill via the air duct  59  and the opening  58 . Additionally, air can be fed into the comminution chamber  5  through the openings  61  at the back panel  45  of the whirlwind mill in order to supply the whirlwind mill with sufficient internal air. 
         [0035]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.