Patent Document

FIELD OF THE INVENTION 
     The present invention relates to the art of and science of detecting plastic or other elastomeric materials which are used in conjunction with food processing, and more particularly, to materials that have metal particulates embedded therein for easy detectability during or subsequent to the food processing. 
     BACKGROUND OF THE INVENTION 
     The use of plastic materials in the food processing industry has heretofore posed unavoidable health risks, principally due to the difficulties in detecting the presence of such materials when they are accidently introduced into the food product. Likewise, other elastomeric materials such as rubber materials are frequently utilized as components in the food processing system which processes the food product. When these materials are subjected to temperature change or wear, or even due to mechanical breakdown over the passage of time, their brittleness tends to increase resulting in an easily fracturable material. For this reason, these materials commonly fail through breakage or sloughing off of small pieces, often resulting in piece fragments being introduced into the food product. 
     Conventional techniques for detecting such materials within the food stuff have included screening or filtering of the food stuff. This solution, however, is viable only when the food stuff being processed is in liquid form and where no particulates are present in the food stuff. Moreover, such screening or filtering can unnecessarily alter the characteristics of the food stuff and requires additional expense in the food processing equipment. Accordingly, there has been no easy or practical method to detect elastomeric materials which are inadvertently lodged within the food product. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improvement over the prior art with a material that may be readily used in food processing applications, such as to fabricate plastic or rubber/elastomeric piece parts used as components in a food processing system. The material according to the present invention includes a first plastic or elastomeric material constituent and a second metal constituent. The metal constituent is preferably mixed with the plastic material constituent at a relatively small percentage by weight so that it does not effect the properties of the plastic material. The metal constituent, however, is detectable with a conventional metal detecting device so that the presence of the material within a food product can be determined. 
     In another aspect of the invention, a method of detecting the presence of a material in a food processing application is provided. The method includes the steps of providing a material to be used in conjunction with the food processing application where the material comprises a first plastic or elastomeric constituent and a second metal constituent. The food product is processed in a next step. Thereafter, the food product is scanned by a metal detecting device in order to determine whether the material is present in the food product. Finally, the metal detecting device provides an appropriate alarm or other signal when the presence of the material is detected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified block diagram representation of a fabrication process for forming a piece part from a plastic material according to one embodiment of the present invention. 
     FIG. 2 is a simplified block diagram representation of a food processing line that may utilize one or more plastic piece parts fabricated as is shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Generally, the present invention relates to materials and components formed using a polymeric material, such as a plastic or rubber/elastomeric material that is utilized in a food processing application. The material of the present invention comprises a first polymeric material constituent and a second metal constituent that is detectable with a conventional metal detecting device. 
     One intended use for the material made according to the present invention is for fabricating piece parts such as plastic diaphragms used in pumps, blades or impellers in mixers or for smaller parts such as washers or O-rings in fitted connections and the like, in food processing applications, particularly those where metal detecting equipment is already in place. Inasmuch as the material is detectable by such metal detecting equipment, the invention directly addresses safety concerns caused by the introduction of these types of materials into a food product during processing. 
     FIG. 1 illustrates a simplified block diagram representation of a process  10  utilized to fabricate a piece part made of a plastic material according to the present invention. As shown therein, a raw polymeric material denoted by a block  12  is supplied to a plastic compounding machine  14  as will be readily understood by one skilled in the art. In addition, a powdered metal denoted by a block  16  is added to the machine  14  during a melt process of the polymeric material. The powdered metal is preferably added to the compounding machine  14  at a rate of approximately one (1) per cent to five (5) per cent by weight of the polymeric material. 
     The plastic compounding machine  14  mixes the raw plastic and powdered metal to provide a homogeneous mixture of plastic and powdered metal in which the powdered metal becomes embedded within the interstices of the plastic material. Additional material components, such as fiberglass, may also be added to achieve such desired properties as increased strength. This blend is then pelletized to make raw feed pellets denoted by a block  18 . One method for pelletizing the blend is by extrusion of the blend under pressure, followed by chilling and cutting as will be understood by those skilled in the art. 
     One preferred polymer that may be utilized in the formation of the plastic material is a polyoxymethylene copolymer (also known as acetal copolymer) such as the one sold under the tradename Celcon M90 CD3068, and manufactured by Hoechst Celanese Corporation. This particular copolymer has a melting point of 165 deg C. and a specific gravity of 1.4 to 1.8. Other suitable polymers may likewise be utilized. For example, the polymer may alternatively comprise a polyphenylene sulfide (also known as PPS or polyphenylene sulfide) such as the one sold under the tradename RTP 1303 TFE 15 LE Natural, manufactured by RTP Company, Winona Minn. 
     RTP 1303 TFE 15 LE Natural has a specific gravity of 1.44. 
     Similarly, while many metal materials which are detectable by conventional metal detection equipment may be used, one preferred material is a metal powder such as a stainless steel powder. For example, austenitic steel, such as 410SST or 17-4 type steel may be utilized. One specific suitable metal powder is the stainless steel powder marketed by Ametek Specialty Metals Division of Eighty-Four, Pennsylvania. This metal powder is also known as Tool Steel powder or Pre-alloyed stainless steel powder. The powder has a specific gravity in the range of 7.5 to 9.3 and is a fine gray powder. Other powders may be used which are detectable by known detection means while being of sufficiently small particle size to permit molding of the polymer. 
     The pellets  18  are thereafter supplied to an injection molding machine  18 , which operates in a known fashion, to mold finished plastic piece parts denoted by a block  20 . In this way, various plastic component pieces that are used in a food processing system may be fabricated according to the present invention. For example, the pieces fabricated in this manner may include plastic sleeve bearings, blades or the like. 
     One advantage of using a blend of powdered metal mixed with the raw plastic is that there is no perceptible effect on the injection molding process or on the structural integrity of the resulting plastic piece part. One reason for this is the relatively small particulate size of the powdered metal, for example, on the order of 45 micromm (corresponding to 325 mesh). In addition, the percentage by weight of metal added is relatively small. 
     Another reason that there is no perceptable effect on the resultant material is the relative densities of the materials. For example, when the powdered metal material, such as an austenitic steel having a density on the order of 0.3 lbs/cu in., is mixed with a plastic having a density of 0.05 lbs/cu in. in a ratio of 5 percent steel by weight and 95 percent plastic by weight, the metal material comprises only approximately 0.8 percent by volume of the resulting mixture. 
     It has been found that powdered metal that is mixed with the plastic material at a rate of about one (1) percent (by weight) may be readily detected with the use of a conventional metal detector, such as a type Metalcheck, manufactured by Yamamoto Lock. In the case of smaller piece components or for improved detectability, the percentage of metal (by weight) may be increased. For example, a mixture of powdered metal with a plastic material in the range of 2.5 percent to 5 percent (by weight) may also be used without altering the properties of the plastic material. Other ratios of metal with plastic are contemplated by the present invention although it is preferred that the metal powder component be in the range of about 1 percent by weight to about 5 percent by weight of the total composition. 
     While the presently contemplated best mode for practicing the invention includes the use of a powdered metal, other forms may be used as well. For example, metal shavings or other particulates detectable by metal detection or X-ray equipment may be deposited into the plastic material so long as the metal pieces do not substantially interfere with the formation of the final end product. 
     The present invention may also be used to fabricate other polymeric components such as rubber/elastomer components. These components may likewise be made by mixing metal powder in the above-noted concentration by weight during the processing of the rubber/elastomer. In this way, piece parts such as O-ring gaskets, diaphragms in pumps and like may also include metallic particles embedded therein that are detectable by conventional metal detection equipment. Thus, for example, an elastomeric material such as butadiene-acrylonitride rubber (also known as nitride rubber, BUNA N or NBR). One such rubber is marketed under the tradename T538 Albert Trostel Packings, Ltd. of Lake Geneva, Wis. T538 has a specific gravity of 1.28. Materials such as natural rubber, viatran, nitran and neoprene may likewise be utilized. 
     FIG. 2 is a generic block diagram representation of a food processing line  30 , including a processing machine  32  having one or more components fabricated from a polymer in the manner described above in conjunction with FIG.  1 . As shown therein, a food stuff is supplied to the machine  32  for processing. During this step, one or more of plastic and/or rubber/elastomer components contact the food stuff, and in some instances, the components or fragments thereof break off and are lodged within the food stuff. The food stuff is thereafter passed through metal detection equipment  34 . The metal detection equipment provides an appropriate signal such as an alarm signal upon the detection of the metal constituent within the component fragment. In this way, any plastic and or rubber/elastomer material embedded within the food stuff is detected so that corrective action may be taken. 
     One example in which corrective action may be taken is where the detection equipment is coupled with a divert valve (not shown) and accompanying divert stream. In this instance, the metal detection equipment provides an appropriate command signal to actuate the divert valve in order to divert the food product for a selected time interval to remove the plastic component or fragment thereof. Alternatively, the food product may pass the metal detection equipment after final packaging of the product. Typically, any container from which metal is detected is discarded. 
     Although metal detection equipment may be utilized to detect when the metallized material is present, other detection equipment such as X-ray equipment may be utilized to detect the metallized material, particularly due to the density difference between the metallized material and a food product such as ice cream or citrus juice. 
     In another preferred embodiment of the present invention, a powdered metal is mixed with a polymer material to provide a resulting thin film material that may be used as a plastic wrap in a food processing application. The resulting thin film material includes a plastic constituent, such as polyethylene, and a metal constituent preferably in the form of powdered metal. While other metal forms may be utilized in the context of this invention, one advantage of using a powdered metal is that there is no perceptible effect on the extruding process of the thin film. Likewise, powdered austenitic steel, such as 410SST or 17-4 type steel, or other suitable powdered metals may be utilized. 
     EXAMPLE 1 
     One example of a food processing system piece part made according to the present invention is a plastic scraper blade. To form the plastic pellets for this component, the following were mixed in a plastic compounding machine: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Component 
                 Weight % 
               
               
                   
                   
               
             
             
               
                   
                 Stainless Steel Powder 
                 5 
               
               
                   
                 PPS (plastic) 
                 73.2 
               
               
                   
                 Fiberglass 
                 19 
               
               
                   
                 Teflon 
                 2.8 
               
               
                   
                   
               
             
          
         
       
     
     Following the blending of the above plastic composition, the composition was pellitized. The pellets were then fed to a screw-type HPM injection molding machine to form the piece part component. The piece part component was then subjected to an abrading force to introduce a few small pieces into a liquid to simulate use in a liquid stream food processing installation. The liquid was then scanned using the Metalchek metal detector and the abraded plastic pieces were detected by the metal detector. 
     Accordingly, a plastic material with a metallic substance embedded therein for ready detectability in a food processing system that meets the aforestated objectives has been described. It will be apparent to those skilled in the art that a number of modifications can be made to the invention disclosed, particularly by those having the benefit of the foregoing teachings, without departing from the spirit of these principles. Accordingly, it is intended that the invention be limited only by the scope of the appended claims.

Technology Category: 1