A railroad tie comprises a core comprising wood or a wood product, and a first sleeve encapsulating the core, wherein the first sleeve comprises at least one of the group consisting of plastic, plastic-composite, or non-plastic polymers. A second sleeve may additionally encapsulate the first. In a preferred embodiment, the first sleeve is comprised primarily of poly ethylene terephthalate, and the second sleeve is comprised primarily of high density poly ethylene.

BACKGROUND OF INVENTION 
     The purpose of a railroad tie is to connect the earth, or other intermediate supporting base, to plates which connect to rails. They also provide for the proper spacing (gauge) between rails. In turn the rails support locomotives, passenger, freight or service cars as they transit or park. 
       FIG. 1  shows the cross section of a treated timber tie  10  in a common cross section of seven inches (7″) tall and nine inches (9″) wide. Common lengths for cross ties are eight feet (8′), eight foot and six inches (8′-6″) and nine feet (9′). Switch ties are longer. In this drawing the pressured applied preservative  20  does not penetrate through the entire tie. There is a core  30  that may remain untreated. 
     Railroad ties are traditionally made of wood, though some are of concrete or all-plastic or plastic-composite. There are several standard sizes, one common size being seven inches tall by nine inches wide by nine feet long. Other standards include cross sections of 6″×8″, 6″×9″ and lengths of 8′-0″ and 8′-6″. 
     Ties must be strong enough to maintain support and gauge under lateral loads, static vertical loads, and dynamic vertical loads. The tie must be resistant to the dynamic load which can cause the tie plate to move and abrade the tie. The tie must be able to function despite environmental stresses of thermal expansion, ultraviolet (UV) radiation, attack from microorganisms, fungi, insects and other life forms. It is highly preferable that ties be installable using the existing base of standardized installation equipment and fasteners. Some rail systems use a “third rail” to conduct power to trains. For this and other reasons, railroad ties should not be conductors of electricity. 
     The predominant tie in service is a hardwood timber treated with creosote, coal tar, chromated copper arsenate or other preservative. Over time these preservatives leach from the tie to the surrounding earth and eventually migrate to the surrounding areas, including water tables. There are few safe methods for disposing of treated timber ties. Stacking them in landfills does little to retard leaching. Open air burning releases the toxins into the atmosphere. Closed effluent burning with contaminant capture is expensive. 
     Because concrete and reinforced concrete ties are highly inflexible they do not allow a flex-and-resume support of the rails. More concrete ties are required per mile of track which increases the cost per mile. The cost per tie is also higher. Further, the increased weight of concrete requires changes to installation equipment and procedures. 
     Both timber and concrete ties can accept water into cracks or grain separations. As water freezes it expands and can force the cracks wider, leading to a reduction in tie strength. For reinforced concrete ties this crack expansion can also expose the metallic reinforcing material to air, thereby initiating the deleterious effects of rust, further reducing tie strength. 
     More than ten million ties were installed as new or replacements during each of 2003-2006. With thousands of ties per mile, the introduction of a functionally equivalent or superior, longer lived, and lower life cycle cost tie is materially beneficial to rail operators, maintains or improves rail system safety, and is ecologically beneficial. 
     Thus, there is a need for a tie with a combination of lower manufacturing times, better spike retention, increased resistance to abrasion, lighter weight, and lower cost than existing concrete, plastic or composite ties. 
     There is a further need for processes for manufacturing a tie having the above characteristics in an efficient and environmentally sensitive manner. 
     SUMMARY OF THE INVENTION 
     A railroad tie according to embodiments of the present invention uses a wood, composite wood, wood-plastic or engineered plastic core and is encapsulated in one to many layers of plastic, or plastic-composite materials. A complete encapsulation is also referred to as a sleeve or a jacket. Only the outer-most encapsulating layer is exposed to the elements. A single plastic layer is, or multiple layers are, applied in a high pressure mold to promote adhesion between the core and adjacent plastic layer as well as between layers to increase strength. High pressure also helps the plastic or plastic-composite material to displace voids in the core with the result being a stronger and longer lasting product than natural wood could provide. 
     The core may be an old tie removed from service, but is still adequately strong. It may be trimmed to size and encapsulated. The encapsulation retards leaching of preservatives in the core. 
     Alternatively, the core may start as an unusable treated timber tie rendered into fibers. Rotten or otherwise undesirable fibers are separated from reusable fibers and disposed of. The reusable fibers may be mixed with a binder and formed into cores of the appropriate size. Again, the encapsulation retards leaching of any fiber-borne preservative to the environment. 
     The core may be an engineered wood, structured wood, wood by-product, plastic/wood beam or plastic composite. 
     The encapsulation may be an engineered plastic or plastic-composite section. 
     The top side of the outermost encapsulation may be textured or pigmented to reduce glare or provide another aesthetically pleasing or functional appearance. The underside may be patterned to increase friction with ballast or other bed material, so as to retard lateral movement. The encapsulation(s) may be colored for an aesthetic or functional purpose. Other functional or decorative moldings may be added. These include, but are not limited to, owner identification, date of manufacturing, location of manufacturing facility, mold number, lot number etc. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Aspects, features, benefits and advantages of the embodiments of the present invention will be apparent with regard to the following description, appended claims and accompanying drawings where: 
         FIG. 1 , a cross section of a traditional timber tie showing irregular penetration of preservative; 
         FIG. 2 , a cross section of an embodiment of the invention showing a single layer encapsulation; 
         FIG. 3 , a cross section of an embodiment of the invention showing a double layer encapsulation; 
         FIGS. 4A-4C  illustrate pattern elements for a tie in ballast; 
         FIG. 5 , the bottom of an embodiment of the showing pattern elements in pattern A; 
         FIG. 6 , the bottom of an embodiment of the showing pattern elements in pattern B; 
         FIG. 7 , the bottom of an embodiment of the showing pattern elements in pattern C; 
         FIG. 8 , a bottom view of an embodiment of the showing pattern element suitable for a tunnel; 
         FIG. 9 , a side view of an embodiment of the invention showing pattern element suitable for a tunnel; 
         FIG. 10 , a cross sectional view of the core and the inner sleeve during manufacture in an embodiment; and 
         FIG. 11 , a cross sectional view of the core, inner sleeve, and outer sleeve according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  shows a railroad tie  40  according to an embodiment of the present invention. Railroad tie  40  has a cross section of 7″×9″ with a core  60  of cross section 6.5″×8.5″ encapsulated in a single sleeve  50  0.25″ inches thick. 
       FIG. 3  shows a railroad tie  70  according to another embodiment of the present invention. Railroad tie  70  has a common cross section of 7″×9″ with a of 6″×8″ core  100 , an inner sleeve  90 , 0.25″ in thickness, and an outer sleeve  80 , 0.25″ in thickness. Railroad tie  30 , encapsulated in two sleeves, holds several advantages over the railroad tie  40 , having only a single layer of encapsulation. First, plastic cools at a near-logarithmic rate. During the manufacturing process, a 0.25″ layer may cool sufficiently after only thirty seconds. A 0.5″ layer may, however, take two minutes to cool. Thus, using two layers may result in a lower manufacturing time, given the same desired final thickness. Second, using multiple sleeves allows different materials to be used for each sleeve. Third, using multiple sleeves allow the interface between the sleeves to be molded in an interlocking form, resulting in increased strength. However, it is to be understood that single, dual, or even greater levels of encapsulation are within the scope of this invention. 
     The cores  60  and  100  may be new treated timber ties reduced to the 6.5″×8.5″ and 6″×8″, respectively. Because the cores  60  and  100  are encapsulated by the sleeve  50  and sleeves  80  and  90 , respectively, the preservative in the cores  60  and  100  is retarded from leaching into the surrounding environment. Further, the cores  60  and  100  are protected from the elements. Alternatively, the cores  60  and  100  may be used treated timber ties that are structurally sound, but worn towards the outer edges. The outer edges are removed in sufficient quantity to result in the cores  60  and  100  shown in  FIGS. 2 and 3 , respectively. 
     The cores  60  and  100  may alternatively be constructed from used timber ties that are no longer structurally sound, but contain sound fibers and strands. 
     The sleeves  50 ,  80  and  90  may be constructed from any number of non-plastic polymers, plastics or plastic-composites. Preferably, inner sleeve  80  is constructed from a polyester, such as poly ethylene terephthalate, or PET. The PET may be additionally be mixed with a fine rubber, such as a rubber dust, and a stabilizer. Rubber dust performs two functions. First, one of the elements in rubber dust is carbon black, which assists in adding UV resistance to the sleeves. Second, the rubber dust consumes volume and is cheaper than plastic, i.e., a filler. The stabilizer may be, for instance, FUSABOND co-polymer, manufactured by DuPont. The stabilizer may improve the compatibility between the base plastic, such as PET, and any additives, fillers, or reinforcing agents, such as the rubber dust. Sleeves  50  and  90  are preferably constructed from a polyolefin such as high density poly ethylene, or HDPE. The HDPE may be mixed with a fine rubber dust and a stabilizer, as discussed above with respect to PET. As sleeves  50  and  90  are externally visible, a colorant may be added to the HDPE to attain the desired color. Additional additives, such as scents, may be added to the HDPE. Inner sleeve  80  and outer sleeve  90  are preferably greater than 75%, by weight, of PET and HDPE, respectively. 
     Although not shown in  FIGS. 2 and 3 , the end surfaces of railroad ties  40  and  70  are also covered by the sleeves  50 , and  80  and  90 , respectively. The end surfaces may be unadorned, or they may be impressed with information, such as the identity of the manufacturer. 
     The side surfaces of railroad ties  40  and  70  are preferably smooth to reduce friction during material handing. 
     The upper surface railroad ties  40  and  70  may be patterned in either a decorative or functional pattern. Such functional patterns include, but are not limited to, those patterns resulting in increased friction or glare reduction. 
     The bottom surface of the railroad ties  40  and  70  is preferably patterned depending on the surface upon which the railroad ties  40  and  70  are intended to be placed. For instance, the railroad ties  40  and  70  may be placed in ballast, requiring one type of patterning, or on a smooth surface such as those found in smooth floored tunnels, requiring different patterning. 
     For ties that are to be placed on ballast, the tread patterns should capture the ballast material (e.g., gravel rock) to increase friction. In  FIGS. 4A-4C  and  FIGS. 5-7 , the lines indicate ridges that protrude from the surrounding surface. The ridges need not be squared, but may instead be chamfered with a draft angle.  FIGS. 4A ,  4 B and  4 C each show an embodiment of a tread pattern section.  FIG. 4A  is a right pointing chevron section  110 , and shows two parallel chevrons each of which is bounded by three triangles. In this embodiment, the chevron section contains all 90-45-45 degree triangles, though one of ordinary skill would understand that the angles may be modified while still staying within the scope of the present invention. The chevrons are 90-degrees at the apex and 135-degrees at the sides. In this embodiment, the end result is a two square pattern. The left pointing chevron  120 , shown in  FIG. 4B , is a mirror image of the right pointing  110  chevron.  FIG. 4C  shows another section  130  composed of eight triangles (8T) where the triangles are at angles other than 90-degrees or 45-degrees. The mix of differing angles increases the probability of a rock capture and increased friction. The three patterns illustrated in  FIGS. 4A ,  4 B and  4 C may be combined in many ways to achieve a bottom surface with higher friction in ballast than a smooth bottom surface. 
       FIGS. 5 ,  6  and  7  show various combinations of the sections shown in  FIGS. 4A ,  4 B and  4 C.  FIG. 5  shows a combination  140  comprising one 8T section  130  placed between left pointing  120  and right pointing  110  chevron patterns.  FIG. 6  shows a combination  150  comprising one 8T section  130  placed between alternating left pointing  120  and right pointing  110  chevron patterns.  FIG. 7  shows a combination  160  one 8T section  130  placed before and after each pair of left pointing  120  and right pointing  110  chevron patterns. The combinations  140 ,  150  and  160  may be repeated over the length of the bottom surface of the tie. 
     The bearing surfaces of ties according to an embodiment of the present invention having a patterned bottom surface may range in width from near-zero for a knife edge to two inches (2″) wide. The molding draft angle of the raised tread to the relieved section may range between 0.01-degrees (near vertical) to 89.99-degrees (near flat). 
     Not all ties are placed in ballast. To improve performance in tunnels, or other smooth bottomed surfaces,  FIG. 8  shows a bottom surface  180  of a tie section  170  showing one inch (1″) diameter channels  174  at five inch (5″) intervals. These channels are over the length of the tie.  FIG. 9  shows a side surface or the tie section  170  showing the same spacing and channels  174  along the bottom surface  180 . Although the 5″ spacing and 1″ diameter are shown here, other combinations of spacing, diameter, and shape are possible. The channels allow for drainage. 
     Hereinafter, a preferred method of manufacturing the tie shown in  FIG. 3  will be described. As shown in  FIG. 3 , the completed tie  70  according to an embodiment of the present invention comprises three elements, the core  100 , inner sleeve  90  and outer sleeve  80 . To construct the core  100 , a whole railroad tie in a 7″×9″×8′-6″ size is first obtained. The whole railroad tie is then cut to the desired length, and then cut in half longitudinally to make two cores  100 , nominally 4.5″ tall and 7″ wide. One core  100  is set aside for later use. For the inner sleeve  90 , PET regrind is first obtained. Regrind refers to plastic feed stock that has been sorted, ground, cleaned, and otherwise processed to be ready to be used immediately. The PET regrind is then preferably mixed with a fine virgin rubber dust. A stabilizer is also preferably added to the PET regrind. The PET, rubber dust and stabilizer are placed in a blender and blended. The PET mixture is then transferred to an injection molding machine. For the outer sleeve  80 , HDPE regrind is first obtained. The HDPE regrind is then preferably mixed with a fine rubber dust, either de-vulcanized, recycled rubber or virgin rubber. A stabilizer is also preferably added to the HDPE regrind. The HDPE, rubber dust and stabilizer are placed in a blender and blended. The HDPE mixture is then transferred to an injection molding machine. 
     A mold is formed in the desired shape of the final product. If two layers of sleeves are desired, two molds may be necessary. Alternatively, molds are available that may reconfigure themselves, allowing both layers to be formed in a single mold. The core  100  may be suspended in the mold in various ways, such as by a rod. The hole in the sleeves resulting therefrom may be filled in at a later time. 
     The 4.5″×7″ core  100  is placed in the mold. Then, the PET injection molding machine supplies the PET mixture into the mold to form the inner sleeve  90 . After the inner sleeve  90  is formed, the HDPE injection molding machine supplies the HDPE mixture in the mold to form the outer sleeve  80 . Alternatively, if a single mold is used for both layers, PET is first injected, then allowed to cool. Then, the mold may be reconfigured, and the HDPE may be injected into the mold. 
     In a preferred embodiment and referring to  FIG. 10 , the inner sleeve  290  is molded so as to have a solid base layer in contact with the core  270 , with fingers protruding therefrom. These fingers give inner sleeve  290  a ridged surface.  FIG. 11  shows a cross-section of a portion of a completed tie. It shows inner sleeve  290 , including fingers, as well as the outer sleeve  280  having opposite, interlocking fingers, and a solid layer. In a preferred embodiment, the sides and top of the tie comprise an inner sleeve  290  having a 0.25″ thick solid layer and 0.5″ fingers, as well as an outer sleeve  280  having 0.5″ fingers and a 0.25″ solid layer, resulting a total thickness of 1.0″ because the fingers interlock. Given a 7″ wide core  270 , this results in the desired final width of 9″. The bottom of the tie is preferably formed in a similar fashion, only differing in that the outer sleeve  280  additionally includes 0.5″ of high friction ridges. By forming the first and second sleeves in the above fashion, the sleeves may be formed and cooled quicker than if, for instance, each of the two sleeves were a 0.5″ solid layer. This is because two sleeves, each having a 0.25″ solid layer with 0.5″ interlocking fingers, will cool quicker than two sleeves, each a 0.5″ solid layer, even though both result in a total encapsulation of 1.0″. 
     In an alternate embodiment, rather than obtaining PET and HDPE regrind, PET and HDPE recyclate may instead be obtained. Recyclate refers to plastic feed stock that has been sorted by type but requires further processing to remove contaminants, such as labels and traces of previous contents, and grinding before being ready for use. Before being introduced to the respective mixers and if the PET or HDPE recyclate is obtained in baled form, the PET or HDPE bales are placed in a debaler, wherein the bales of PET or HDPE recylate are broken apart into a more manageable stream of recyclate. PET or HDPE recyclate from the debaler is then forwarded to a shredder, wherein the large pieces of PET or HDPE recylate are reduced into smaller shreds of plastic. The shreds of PET or HDPE are then forwarded to a separator, which separates the PET or HDPE from non-plastic elements such as labels. The non-plastic elements may be removed to a closed effluent furnace where they can be burned as fuel to generate some electricity. The separated shreds of PET or HDPE may used identically to the PET or HDPE regrind above. 
     In another embodiment, old and scrap ties may be recycled to obtain new cores  100 . First, remaining metal, such as plates and spikes, are removed from the old and/or scrap ties. The ties are then rendered into fibers and strands which are sorted. Rotten, overly short, or otherwise undesirable fibers may be disposed of by sending them to a closed effluent furnace to be burned to generate electricity. The remaining fibers may then be mixed with a binder such as, for instance, an iso-cyanate resin, heated and pressed to form a large sheet or billet. The large sheet or billet may then be processed to create ready-to-use cores of a desired size, which may be used identically to the 4.5″×7″ cores  100  in the process described above. The core  100  produced by the this method is greater than 80% wood fibers, by weight. 
     In another embodiment, scrap tires may be recycled to obtain rubber dust. Scrap tires may first be subject to a gross shred which turns the tires into crumbs. At this stage, the tire crumbs still contain metal fibers, such as remnants of steel belting and valves, and the rubber in the tire crumbs is vulcanized. Tire crumbs may be used as fuel in a closed effluent furnace. Alternatively, the tire crumbs may be finely shredded to de-vulcanize the rubber. The resulting finely shredded rubber dust may be used instead of the virgin rubber dust in the process described above. The shredding process also separates the metal from the shredded rubber dust. The metal may then be sold to a recycler. 
     While we have shown illustrative embodiments of the invention, it will be apparent to those skilled in the art that the invention may be embodied still otherwise without departing from the spirit and scope of the claimed invention. For instance, although the exemplary embodiments disclosed above have been generally limited to the traditional rectangular-shaped tie, non-rectangular embodiments also lie within the scope of the present invention.