Abstract:
A solid waste magnetic separator having a material transport belt, a mechanism for generating a magnetic field, and a mechanism for supporting the belt so magnetic materials can be attracted to the belt and transported therewith as the belt moves through the magnetic field. The magnetic field generating mechanism comprises at least two magnetic assemblies aligned relative to each other in the direction of travel of the belt. A ferromagnetic pole shoe is disposed between the belt and the magnetic assemblies, thereby creating a relatively uniform combined magnetic field along the magnetic assemblies so that heavy magnetic materials attracted to the belt remain attracted to the belt as the belt moves through the combined magnetic field.

Description:
BACKGROUND OF THE INVENTION 
     This is a continuation of co-pending application Ser. No. 732,907, filed May 9, 1985, (now abandoned) which is a continuation of application Ser. No. 578,138, filed Feb. 8, 1984 (now abandoned), which in turn is a continuation of application Ser. No. 326,586, filed Dec. 2, 1981 (now abandoned). 
    
    
     This invention relates to magnetic separators and, more particularly, to magnetic separators for separating heavy magnetic materials from other materials in solid waste. 
     With more and more emphasis being placed on recycling, it is becoming more desirable to recover salvageable articles from otherwise discarded material. Much of the metallic material discarded as refuse can generally be recycled for one purpose or another, provided it can be efficiently separated from the remainder of the refuse. The metallic materials intended to be recaptured usually are generally also magnetic so that magnetic separation is a possibility for recapture. Heavy magnetic materials weighing several pounds (e.g. 8 pounds or more) present a special problem in that they are difficult to attract and retain magnetically attracted to a conveyor belt as the belt moves through a magnetic field generated by a plurality of magnetic assemblies. 
     The magnetic assemblies in prior magnetic separators typically are spaced or gapped and heavier materials tend to drop away from the belt at the gaps where there is non-uniformity in the magnetic field. For example, Barrett U.S. Pat. Nos. 3,809,239 and 3,935,947 disclose magnetic separators employing magnetic assemblies which are spaced and adjacent ones have opposite polarity. 
     Examples of other prior magnetic separators which do not produce a relatively uniform magnetic field of sufficient strength to upwardly attract and transport heavy magnetic materials along the length of a separator are disclosed in the following U.S. patents: 
     
         ______________________________________Patentee    U.S. Pat. No.  Issue Date______________________________________Palm        2,747,735      May 29, 1956Hoffman     463,305        Nov. 17, 1891King        765,013        July 12, 1904Holmberg    972,109        Oct. 4, 1910Dutton, et al       1,146,141      July 13, 1915Grondal     905,815        Dec. 1, 1908______________________________________ 
    
     SUMMARY OF THE INVENTION 
     A principal object of the invention is to provide a magnetic separator which has a relatively uniform magnetic field along its length of sufficient strength to enable it to attract and then continue to attract heavy magnetic materials while they are transported along the length of the separator. 
     Another object of this invention is to provide a magnetic separator capable of segregating heavy magnetic materials from light magnetic materials after they have been separated from other refuse. 
     For the achievement of the above and other objectives, this invention provides a magnetic separator having a continuous belt moving past magnetic assemblies which generate a magnetic field through which the belt moves. Magnetic materials discharged in the area of the magnetic field are attracted to the belt and carried by the belt through the magnetic field. 
     The magnetic field is generated by at least two magnetic assemblies aligned relative to each other in the direction of belt travel. Each magnetic assembly has the same magnetic polarity near the belt. A ferromagnetic pole shoe is disposed between the belt and the magnetic assemblies and extends over the magnetic field generating portions (magnet cores) of the magnetic assemblies. The pole shoe causes the strength of the overall or combined magnetic fields of the magnetic assemblies to be relatively uniform along the length of the magnetic field generating means. As a result, heavy magnetic materials remain attracted to the belt as it moves through the combined field. 
     In another embodiment of this invention, a second magnetic field generating means is provided downstream from the first field generating means in the direction of travel of the belt. The second magnetic field generating means has an opposite polarity from the first field generating means and the pole shoe extends over the magnetic field generating portion of the second magnetic field generating means. The resulting overall or combined magnetic field is relatively uniform over the first magnetic field generating means and then diminishes before where the belt passes over the second magnetic field generating means. 
     If a means for switching the polarity of the second field generating means is added to this embodiment, and the second field generating means assumes the same polarity as the first means, all magnetic materials will be carried along the belt and released near the end of the pole shoe. When the polarity of the second generating means is opposite the first, however, the lesser strength of the magnetic field before the second magnetic field generating means causes heavier magnetic materials to fall away from the belt while lighter magnetic materials are reattracted to the belt. In this manner, heavy magnetic materials are segregated from lighter magnetic materials. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a combination supply conveyor and refuse separator partially in section. 
     FIG. 2 is a view taken generally along line 2--2 in FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With particular reference to the drawings, a refuse separator 10 is illustrated in combination with a supply conveyor 11, receptacles 12, 13, and 14 and splitter baffles 15 and 20. The function of the receptacles and splitter baffles is to physically segregate separated heavy magnetic 18, light magnetic 16 and non-magnetic material 22, therefore, no particular form of either is necessary. As will be discussed hereinafter, however, the location of the splitters is a factor to be considered in operation. 
     The refuse separator 10 is intended to receive refuse from the supply conveyor 11 and carry the magnetic portion of the refuse over the splitter baffle 15 while the non-magnetic material 22 falls, by reason of gravity, into the receptacle 12. To this end, the separator 10 includes a belt 24 which travels in a counterclockwise manner around a head pulley 26, an end pulley 28 and an idler roller 30 and has upper and lower generally horizontal extensions 32 and 34. The head pulley 26 is driven in a counterclockwise direction by a suitable drive mechanism (not shown) and the belt 24 is driven by the head pulley 26. 
     A magnetic arrangement is located within the area defined by the belt 24, i.e., above and near the lower portion or run of the belt 24. In this embodiment, the magnetic field generating means 36 consists of three magnetic assemblies, a first or upstream magnetic assembly 38, a second magnetic assembly 40 downstream of the first magnet 38 along the direction of travel of the belt, and a third magnetic assembly 48 immediately downstream of the second magnetic assembly 40 along the direction of travel of the belt. The first magnetic assembly 38 is in the form of an electromagnet having a central core 42 surrounded by an electrical coil 44. This is a conventional electromagnet construction and when the coil 44 is energized the end of core adjacent the belt 24 will assume a magnetic polarity, e.g. north. The first magnetic assembly 38 usually has a greater magnetic field than the other magnetic assemblies in order to initially attract the magnetic materials to the belt. 
     The second magnetic assembly 40 is also in the form of an electromagnet including a core 46 adjacent the belt 24 which assumes the same magnetic polarity as the first magnetic assembly. The third magnetic assembly 48 has the same magnetic polarity as the first and second magnetic assemblies. 
     It should be appreciated further that the entire magnetic field generating means 36 could be made of electromagnets or permanent magnets as desired, or a combination of permanent and electro. Electromagnets do afford a possible safety advantage when work must be done in the area of the separator in that they can be turned off and cleared of all material. 
     A pole shoe means 50, made of a ferromagnetic material such as iron, is disposed between the belt 24 and the magnetic assemblies and extends over the magnetic field generating portions, i.e., cores, 42, 46 and 52, of all three magnetic assemblies. The pole shoe 50 causes the magnetic fields generated by each of the magnetic assemblies to blend so the overall or combined magnetic field along the length of the field generating means 36 is relatively uniform, as illustrated by line 54 in FIG. 1 which is a graphical representation of the strength of the combined magnetic field. The combined magnetic field 54 causes magnetic materials attracted to the belt 24, including heavy magnetic materials 18, to remain attracted to the belt as it moves along the length of the field generating means 36. 
     The pole shoe 50 can have a paddle-like shape as shown in FIG. 2. That is, the pole shoe 50 includes a wider section 49 in the vicinity of the first magnetic assembly 38 and a narrower section 51 otherwise. The shoe 50 is generally as wide as the cores of the various magentic assemblies, and has a thickness sufficient to permit the blending of the magnetic fields. Thus, as shown in FIGS. 1 and 2, the pole shoe 50 has an upstream end located adjacent and terminating beneath the end of the first or upstream magnetic assembly field generating portion or core 42 and having a shape generally conforming to the shape of the end of the first magnetic assembly field generating portion or core 42, and, downstream from the first magnetic assembly 38, the pole shoe 50 has a width generally conforming to the widths of the downstream field generating portions or cores 46 and 52. In the preferred embodiment, as shown in FIG. 2, the shape of the end of the first magnetic assembly field generating portion or core 42 is circular and the upstream end of the pole shoe 50 is circular. 
     In operation, the supply conveyor 11 carries refuse into the magnetic field 54 of the separator so magnetic material contained in the refuse is attracted to the belt 24 in the area of the first magnetic assembly 38. The non-magnetic material 22, such as paper, falls by gravity into a receptacle 12, and the magnetic material travels with the belt 24 beyond the splitter baffle 15. 
     Under circumstances where it is desirable to segregate the heavy magnetic materials 18, such as blocks of steel, from lighter magnetic materials 16, such as cans, the separator 10 further includes a second magnetic field generating means 56 downstream from the first field generating means 36 in the direction of the path of travel of the belt. The second field generating means 56 is a fourth or downstream magnetic assembly 57 including a core 58 and having a construction similar to the magnetic assemblies 38, 40, and 48, except that its polarity is opposite to the polarity of the three magnetic assemblies making up the first magnetic field generating means 36. 
     The pole shoe 50 extends over the core 58 of the fourth magnetic assembly 57 and has a downstream end terminating beneath the downstream magnetic assembly 57. By extending the pole shoe 50 into the magnetic field of this second field generating means 56 having the opposite polarity, e.g. south, the strength of the magnetic field along the length of the separator diminishes in the area of the second field generating means 56. By the time magnetic materials carried by the belt 24 reach the end of the first generating means 38, the resulting magnetic field is significantly diminished. In operation, heavy magnetic materials 18 carried by the belt 24 are released as the magnetic field starts to diminish near the second magnetic field generating means 56, and fall by gravity into the receptacle 13. Lighter magnetic materials 16 are released further along the path of the separator toward the end of the pole shoe 50 and fall by gravity into the receptacle 14. The splitter baffle 20 is located between the points where the heavy and lighter materials are released to facilitate their segregation. 
     Under certain circumstances, it may be desirable to allow either all magnetics to be carried the entire length of the pole shoe, or to have the heavier magnetics drop off first and then have the lighter magnetics drop off further along the length of the separator. This may be accomplished by having the invention include a switching means 60 for reversing the polarity of the second field generating means. When the polarity of the second field generating means assumes the polarity of the first field generating means, the separator will carry all magnetics the entire length of the pole shoe, provided the appropriate magnetic field strengths are used to assure a relatively uniform magnetic field along the length of the pole shoe. This uniform magnetic field is illustrated by line 62 in FIG. 1. 
     The idler roller 30, head pulley 26 and end pulley 28, together with both magnetic field generating means 36 and 56 and the pole shoe 50, are all supported from a common frame structure. A complete showing of the structural framework of the refuse separator is not necessary to understand this invention. The entire separator assembly can also be mounted for horizontal movement to permit adjustment of its position relative to the end of the supply conveyor 11, for example, like in the manner described in Barrett U.S. Pat. No. 3,809,239 which is incorporated herein by reference. 
     It is to be understood that the invention is not confined to the particular construction and arrangement of parts herein illustrated and described but embraces all such modified forms thereof as come within the scope of the following claims.