Abstract:
A roller is designed for adaptation into a blasthole drill and is specifically designed for use in conjunction with a rotary carriage to allow the carriage to move up and down a blasthole drill mast as needed. The roller is made of a substantially non-deformable material combined with a deformable material. Under light loads, the deformable material contacts and supports the load to provide enhanced operation of the roller. Under heavy loads, the deformable material advantageously deforms to a point which allows the substantially non-deformable material and deformable material to contact and cooperatively support the load.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to blasthole drills and to rollers for supporting a load and, more particularly, to rollers made of more than one material. Specifically, the present invention relates to a bi-material roller for use in a blasthole drill. 
     BACKGROUND OF THE INVENTION 
     There are many known rollers or wheels designed for supporting a load. For example, U.S. Pat. No. 1,408,388 to Reddaway et al. is directed to a tire and rim assembly wherein the tire includes a body portion formed of hard rubber and a central portion constituting a soft rubber resilient core. U.S. Pat. No. 1,687,113 to Stockdale describes a caster wheel formed with a rubber annulus and a tread or wear element in the shape of a disc which is fabricated of fibrous or fabric materials vulcanized to the rubber annulus. U.S. Pat. No. 4,321,727 to Sheiman et al. discloses a luggage roller including a central groove in the form of a V-shaped channel of elastomeric material and a central cylindrical sleeve formed of low friction material, such as polyethylene nylon, Teflon, or similar plastic. In U.S. Pat. No. 4,452,141 to Mistyurik, a roller with a porous surface and a central flange is disclosed. U.S. Pat. No. 5,803,235 to McGinnis et al. is directed to an idler roller which includes an impact shell with a backing layer on the inside of the shell, and a compression ring adapted to expand and engage the inside of the impact shell and an external surface of a main roller body. The load carrying capability of these types of rollers and other rollers varies as a result of their structural construction and intended use. 
     Blasthole drills are large machines used in mining operations to drill holes for explosives. A conventional blasthole drill comprises a frame supported by crawlers for movement over the ground. A mast which defines a drill hole axis is supported by the frame for movement between a substantially vertical position and a number of angled or non-vertical positions. A rotary head, which engages the upper end of a drill pipe for rotating the drill pipe and driving the drill pipe into the ground, moves relative to the mast along the drill hole axis. The rotary head is supported by rollers which move along appropriate surfaces or grooves in the mast. The rollers are designed to have a load carrying capacity to support, at a minimum, the weight of the rotary head and the weight of the end of the drill pipe supported by the rotary head. As can be appreciated, when the mast is positioned in a vertical or substantially vertical position, a light load is transferred to the rollers. On the other hand, when the rotary head is applying, a downward force for drinking, heavy load is transferred to the rollers. 
     It is known to make such rollers of an all-steel construction. 
     It is also known to provide rollers having a steel main body surrounded with an outer covering of plastic. 
     BRIEF SUMMARY OF THE INVENTION 
     A roller according to the present invention is adapted to support a load under any number of different applications. However, a roller according to the present invention is particularly useful in a blasthole drill. 
     Under certain load conditions, it may be advantageous for a roller to have particular load supporting and roller surface characteristics and yet, under other load conditions, it may be advantageous for the roller to have different load supporting and roller surface characteristics. The invention provides a roller which is capable of adapting its load supporting and roller surface characteristics as needed for different applications or changing load conditions. 
     Many of the known rollers or wheels, while capable of supporting loads under many different conditions, do not provide the desired versatility when it comes to subjecting the rollers or wheels to variable load conditions. In other words, such rollers or wheels do not include load supporting and roller surface characteristics which independently change on an as-needed basis depending on the load to be supported. Thus, a problem with these types of rollers or wheels is that while such rollers or wheels may satisfactorily operate when subjected to a given load, such rollers or wheels may not satisfactorily operate when subjected to a different load. 
     The known all-steel rollers for blasthole drills are capable of high load carrying capacity. However, a problem which exists for all steel rollers is that during light loading, the steel rollers may skid rather than roll, which may cause flat spots on the rollers, thereby adversely affecting the rollers capability to function properly and support the load. The load supporting and roller surface characteristics of the all-steel rollers do not adjust for changing load conditions. 
     The plastic covered rollers for blasthole drills were designed to address some of the problems associated with the all-steel rollers by providing a surface with better frictional properties for certain load conditions, particularly light load conditions. Nevertheless, a problem which exists for these types of rollers is that during heavy loading, the large loads may excessively compress the plastic coverings and cause the plastic to flow outward and over the edges or sides of the steel roller main body. Too large of a flow in the plastic can result in high stresses in the bond between the main body of the steel rollers and the plastic outer covering thereby possibly causing the bond to fail. 
     Accordingly, the present invention provides a roller that alleviates these problems and many other problems common to known rollers or wheels. More particularly, the present invention provides a bi-material roller which is capable of supporting various loads, i.e., light loads or heavy loads, and which is also designed to properly roll, rather than skid, under any given load condition. A bi-material roller according to the present invention is particularly capable of use in a blasthole drill which is notorious for subjecting load supporting rollers to various load conditions. 
     In one aspect of the present invention, there is provided a roller which is rotatable about its axis, and which is adapted to support a load. The roller includes a roller body having a first substantially non-deformable, generally cylindrical outer surface located radially outward with respect to the roller axis. The roller further includes a second deformable, generally cylindrical outer surface located radially outward with respect to the roller axis. 
     The outer surfaces are configured and arranged such that under a light load condition, the second deformable surface extends farther radially outward than the first substantially non-deformable surface. Under such a light load condition, the deformable surface of the roller is in contact with and supports the load while the substantially nondeformable surface of the roller is not in contact with and does not support the load. The surface properties of the deformable material allow the roller to roll under light loads whereas, as pointed out, an all steel roller may undesirably skid under such load conditions. 
     The outer surface of the rollers are further configured and arranged such that under a heavy load condition, the second deformable surface deforms to a point where the second surface does not extend farther radially outward than the first substantially non-deformable deformable surface. Under such a heavy load condition, both the deformable and substantially non-deformable surfaces are in contact with and cooperatively support the load. The non-deformable surface ensures that the roller is capable of supporting the heavy load while, at the same time, the roller is constructed so as to prevent the deformable surface from being overstressed or deformed beyond an acceptable range. A roller according to the present invention is unlike the prior plastic covered rollers which may perform in a less than acceptable manner if subjected to heavy loads as previously discussed. 
     In a preferred embodiment, the roller body and thus the first substantially non-deformable surface is made of steel and the second deformable surface is made of plastic. 
     In one aspect of the present invention, there is provided a deformable material which includes the second deformable surface. At least a portion of the deformable material mates against a portion of the main roller body. In another aspect of the present invention, the main roller body includes an annular groove wherein at least a portion of the deformable material is positioned. 
     According to another aspect of the present invention, there is an open, annular area defined between a portion of the deformable material and a portion of the main roller body. Thus, as the deformable material is caused to deform, at least a portion of the deformable material or second surface extends into or over the open area. However, the open area is configured between the respective surfaces such that under heavy loads, the deformable material is prevented from deforming beyond an acceptable range. 
     In a preferred embodiment, there is provided a roller having a second deformable material including a third deformable, generally cylindrical outer surface located radially outward with respect to the roller axis, wherein the first substantially non-deformable surface is located between the second and third deformable surfaces. In this embodiment, under a light load condition, the second and third surfaces extend father radially outward than the first surface so that the second and third surfaces are in contact with and support the load while the first surface is not in contact with and does not support the load. Moreover, under a heavy load condition, the second and third surfaces deform to a point where the second and third surfaces do not extend farther radially outward than the first surface so that the first, second and third surfaces are in contact with and cooperatively support the load. 
     In accordance with one aspect of the present invention, the main roller body is made of steel and the deformable material is made of plastic. In another aspect, the main roller body is provided with an additional annular groove adapted to receive at least a portion of the second deformable material. In a preferred arrangement, the main roller body is provided with another open area adapted to accommodate the expansion of the second deformable material or third deformable surface in much the same manner as the first open area is adapted to accommodate the first deformable material or second deformable surface. In a highly preferred embodiment, a roller according to the principles of the present invention is adapted for use in a blasthole drill. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a blasthole drill in which the present invention is employed. 
     FIG. 2 is a perspective view of a prior art plastic covered steel roller subjected to a heavy load. 
     FIG. 3 illustrates perspective side and front views of a bi-material roller according to the present invention. 
     FIG. 4 is a perspective view of a bi-material roller according to the present invention under a light load condition. 
     FIG. 5 is a perspective view of a bi-material roller according to the present invention under a heavy load condition. 
    
    
     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. The use of “consisting of” and variations thereof herein is meant to encompass only the items listed thereafter and the equivalents thereof. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Illustrated in FIG. 1 is a blasthole drill  10  in which the present invention is employed. It being understood that a roller according to the principles of the present invention is capable of use in other blasthole drills and in other constructions where the roller is designed to support a load, including those constructions where the supported load varies from time to time. The blasthole drill  10  comprises a frame  14  supported by crawlers  18  for movement over the ground. A mast  22  is supported by the frame  14  for movement relative thereto about a generally horizontal axis  26  and between a substantially vertical position (shown in FIG. 1) and a number of angled or non-vertical positions (not shown). The mast  22  defines a drill hole axis  30 . A rotary head  34  is movable relative to the mast  22  along the drill hole axis  30 . The rotary head  34  is selectively engageable with the upper end of a drill pipe  38  supported relative to the mast  22 . The rotary head  34  includes at least one roller attached thereto and adapted to ride in grooves (not shown) found in the mast  22 . As will be further explained, the rollers are designed to support the load of the rotary head  34 , drill pipe  38  and associated components during non-operation and during operation of the blasthole drill  10 . The frame  14 , crawlers  18 , mast  22  rotary head  34  and drill pipe  38  are of conventional construction and do not require a detailed description. Known blasthole drills are described, for example, in U.S. Pat. Nos. 5,622,232 and 5,653,297 both to Whisenhunt. 
     Referring to FIG. 2, a known plastic covered steel roller  42  as previously mentioned is shown. Illustrated is a main steel roller body  46  surrounded by a plastic outer covering  50 . Although not shown, a prior all steel roller would comprise the main steel roller body  46  without the plastic covering  50 . The plastic outer covering  50  is applied to and adheres to the main steel roller body  46  according to conventional methods known to those skilled in the art. Typically, an adhesive is used to create a bond between the plastic outer covering  50  and main roller body  46 . Cross-sectioned box  54  represents a load supplied to the roller  42  by the rotary head  34 , drill pipe  38  and other components as shown, for example, in FIG.  1 . Arrow  58  indicates that the box or load supplying member  54  causes a force to be exerted against the roller  42 , specifically, against the outer surface of the roller  42 . As shown, under a heavy load, the plastic outer covering  50  is caused to extrude out past the sides of the roller  42 . Flow is referred to as the condition when a load causes the plastic outer covering  50  to slide along the mating surface between the plastic covering  50  and main steel roller body  46 . Too large of flow in the plastic outer covering  50  as a result of high loading causes high stresses in the bond between the main steel roller body  46  and plastic outer covering  50  causing failure of the bond. Once the bond between the main steel roller body  46  and plastic outer covering  50  is broken, the overall performance of the roller  42  may be detrimentally affected leading to premature failure of the roller  42  or unsatisfactory operation of the roller  42 . It should be noted that, unlike plastic covered rollers, although all steel rollers are quite capable of handling heavy loads, all steel rollers may not roll as desired when under light loading conditions as previously set forth. 
     FIG. 3 illustrates a bi-material roller  62  according to the present invention which solves the problems of the prior blasthole drill rollers and other problems associated with other rollers. The roller  62  may be attached to the rotary head  34  shown in FIG. 1 in a suitable manner. The roller  62  is adapted to support a load and is rotatable about axis  66  which travels through a shaft  70 . Illustrative views of the roller  62  supporting different loads are shown and further described with reference to FIGS. 4 and 5 below. 
     The roller  62  includes a main roller body  78  which includes a first substantially non-deformable, generally cylindrical outer surface  74  located radially outward with respect to the axis  66 . Preferably, the roller body  78  and thus the surface  74  are made of steel. In the illustrated construction, the main roller body  78  includes a pair of annular grooves  82  and  86  (see FIGS. 4 and 5) spaced apart in the direction of the axis  66 . The bottoms of the grooves  82  and  86  are located radially inward as compared to the surface  74  with respect to axis  66 . A pair of steps or shelves  90  and  94  which are parallel to axis  66  extend between the inwardly cut grooves  82  and  86 , respectively, and raised outer surface  74 . The steps or shelves  90  and  94  are located farther radially outward than the bottoms of grooves  82  and  86  but not as far radially outward as the outer surface  74  (see FIGS.  4  and  5 ). 
     The roller  62  also includes a pair of deformable, annular parts or members  98  and  102  seated in the grooves  82  and  86 , respectively, of the main roller body  78 . Preferably, the deformable parts  98  and  102  are made of a deformable plastic material suitable for use according to the principles of the present invention. The deformable materials  98  and  102  may be applied to and caused to adhere to the main roller body  78  according to any number of suitable methods. The deformable parts  98  and  102  respectively include generally cylindrical outer surfaces  106  and  110  which are located radially outward with respect to the axis  66 . As best shown in FIG. 3, the outer surfaces  106  and  110  extend farther radially outward than the outer surface  74 , the purpose of which will be further explained below. As shown, the deformable parts  98  and  102  extend above the grooves  82  and  86  and beyond the steps or shelves  90  and  94  thereby defining open areas  114  and  118  respectively located on either side of the first raised outer surface  74 . The function of the open areas  114  and  118  will be discussed in more detail below. 
     FIG. 4 illustrates a roller  62  according to the present invention under a light load condition. Cross-sectioned box  122  represents the load supplied by the rotary head  34 , drill pipe  38  and other components as shown in FIG.  1 . However, box  122  can represent any load supplying member. Arrow  126  indicates that box or load supplying member  122  causes a force to be exerted upon the roller  62 . As shown, under a light load condition, the deformable materials  98  and  102  may be slightly compressed. However, under a light load condition, the deformable outer surfaces  106  and  110  remain extended farther radially outward than the substantially non-deformable outer surface  74 . Under such a light load condition, the properties of the outer surfaces  106  and  110  ensure that the roller  62  properly rolls along a surface such as a groove found in the mast  22  of blasthole drill  10  as such is shown in FIG.  1 . As can be observed, the deformable surfaces  106  and  110  contact and support the load  122  while the non-deformable surface  74  does not contact and does not support the load  122 . Thus, unlike prior art steel rollers which may skid under light load conditions, the bi-material roller constructed according to the principles of the present invention rolls as desired. 
     FIG. 5 illustrates the roller  62  according to the present invention under a heavy load condition. Box  130  is similar to box  122  of FIG. 4 except that it supplies a greater load, as shown by arrow  134 , to the roller  62  as compared to box  122 . As explained, such a situation may occur when a mast  22  of a blasthole drill  10  is located in a non-vertical position. As shown, under a heavy load condition, the deformable materials  98  and  102  are compressed a greater amount as compared to the compression shown in FIG.  4 . As illustrated, the deformable materials  98  and  102  deform to a point such that the outer surfaces  106  and  110  do not extend farther radially outward than the first surface  74  with respect to axis  66 . Thus, the outer surfaces  106  and  110  as well as outer surface  74  contact and support the load  130 . As the deformable materials  98  and  102  are compressed, at least portions of the deformable materials  98  and  102  expand into the respective open areas  114  and  118 . Unlike the prior plastic covered rollers which may be adversely affected under heavy loads causing the plastic to deform beyond an acceptable amount, the open areas  114  and  118  are adapted to ensure that the deformable parts  98  and  102  of the roller  62  are not caused to flow beyond an acceptable limit. 
     Variations and modifications of the foregoing are within the scope of the present invention. For example, the rollers may include a single deformable part or multiple deformable parts. Also, one configuration of a roller according to the present invention could include a deformable part positioned between a pair of non-deformable outer surfaces of a non-deformable roller body. Moreover, the open areas may be defined in any number of different ways so long as the deformable material has a place to go when deformed and, so long as the deformable material is prevented from being overstressed under heavy loads. Further, a roller according to the present invention may be adapted for use in many other applications other than a blasthole drill according to the principles of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art. 
     Various features of the invention are set forth in the following claims.