Abstract:
A process for making a drag shield for a lawn mower includes forming from a rigid plastic material a relatively inflexible first end member adapted for secure attachment via a connecting element to an associated lawn mower deck, and a relatively inflexible second end member with a web portion extending therebetween for connecting the first and second end members. The web is formed from a rigid plastic material having a sufficiently thin and substantially uniform cross section for maintaining flexibility. The web and first and second end members are integral and provided in a single piece of rigid plastic material. The process further includes forming first and second layers of flexible plastic material on opposing sides of the web portion.

Description:
FIELD OF THE INVENTION 
     The field of the present invention relates generally to flexible hinges, and more particularly to such hinges made of a polymer material. 
     BACKGROUND OF THE INVENTION 
     It known in the art to use polymer material or flexible plastic material for providing a flexible hinge or web connected between rigid and unflexible material. For example, in the power lawn mower industry industrial safety standards have demanded that shields known as either drag shields, safety shields or trail shields be connected across the rear portion of the mower to prevent stones and other debris from being thrown up at the operator as they walk behind power mower. As described in greater detail below, one known type of trail shield includes a web of flexible polyvinyl chloride (PVC) material connected between a rigid pivotal structure or tube like element of vinyl material, for connection to the rear deck of a walk behind power mower, with the other end of the web being secured to a relatively large diameter tubular structure or curved end structure for gliding along and following the contours of a lawn being mowed. Typically the PVC flexible web is laminated to the tubular attachment member, and the large diameter tubular curved ground follower rigid vinyl structure. Because of the dissimilarity of the materials, it has been found that a delamination problem exists during use. Due to the flexing back and forth of the web and the attached rigid members, the bonds therebetween tend to break away, ultimately causing premature failure of the safety device, in this example, a drag shield. However, this problem can occur for any applications utilizing a flexible web of one material connected between rigid members of another material. 
     SUMMARY OF THE INVENTION 
     With the problems of the prior art in mind, the present invention includes two opposing and spaced apart rigid members of a first polymer material connected together by a centrally located web therebetween of the same material, with the web being a continuous structure emanating from each one of the opposing rigid members, whereby the web is made thin enough to permitted it to be flexible. The rigid members including the web are in one embodiment of the invention fabricated from a common rigid plastic material. A flexible plastic material is laminated to the interconnecting rigid plastic web material on opposing sides thereof, for strengthening the web, and improving its impact resistance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments of the present invention are described below with reference to the drawings, in which like items are identified by the same reference designations, wherein: 
     FIG. 1 shows a side elevational view of a trail shield of the prior art; 
     FIG. 2 shows a cross-sectional side elevational view of another form of a drag shield of the prior art incorporating a flexible web of one material between two rigid members of another material; 
     FIG. 3 shows the flexing of a drag or trail shield as it is moved back and forth as attached to a walk behind power lawn mower; 
     FIG. 4 shows a cross-sectional view of one embodiment of the invention applied for use in a trail or drag shield; 
     FIG. 5 shows another embodiment of the invention for providing a flexible web between rigid members or structures having any given shape. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Various embodiments of the flexible hinge of the present invention are primarily described herein for use with walk-behind power lawn mower safety shields, typically otherwise known as drag shields or trail shields. However, the use of a flexible hinge of the present invention is not meant to be so limited. The flexible hinge of the present invention can be used for numerous applications suitable for plastic type flexible hinges, such as cabinet doors, tool box covers, storage chest covers, and so forth. However, by describing the present invention in relation to walk-behind power lawn mowers drag shields, problems in the prior art using such flexible hinges can be readily illustrated. 
     Drag or trail shields for walk-behind power lawn mowers are typically constructed as shown in the side elevational view of FIG.  1 . Typical dimensions for such a drag shield are also shown in the figure. The drag shield globally denoted by reference  1  includes a rigid tubular element  3  including a downward projecting elongated lip member  5  that is rectangular in shape as shown. The combination of the tubular portion  3  and lip member  5  together form a pivotal structure  7  for attachment to the rear deck of a walk-behind power lawn mower. The pivotal structure  7  is typically mounted to the deck of the mower on a rod that is threaded through the hole  8  of the tubular portion  3 , with the ends of the rod (not shown) securely mounted to opposing sides of the mower deck, as one example. As a result, the pivotal structure  7  is able to rotate about the rod or other mounting means. A web  9  of flexible material, in this example includes opposing ends  11  and  13  each including an elongated open channel  12 ,  14 , respectively. The end of the lip  5  of the pivotal structure  7  is mounted within the channel  12  in the upper end  11  of web  9 , shown through use of known bonding methods. The channel  14  in the lower end  13  of web  9  has the end of a lip  15  protruding from a ball structure  17 , in this example, bonded thereto. The ball structure  17  includes either an elongated structure  19  having a circular cross section, or some other form of a curved elongated element for following or dragging along the ground and moving over various contours of the ground as a walk-behind power mower is moved back and forth in cutting a lawn, as will be described in greater detail below. Typically the pivotal structure  7  and slide ball structure  17  consists of an extruded or molded rigid vinyl material, and the web  9  of flexible PVC polyvinyl chloride. 
     In FIG. 2, an alternative known design for a drag shield is shown in a side elevational view. The pivotal structure  21  includes an upper elongated tubular member  23  and a downwardly projected lip  25  that includes an interior rectangular portion, and terminates into a tapered and substantially pointed free end  27 , as shown. The lower-most slide ball structure, instead of having a lip  15  projecting rectangularly as with the slide ball  17  of the example of FIG. 1, includes a tangentially projecting lip portion  29  that terminates in a tapered pointed end  31 , as shown. As a result, the flexible web  33  includes an elongated V-channel  35  at its upper end, and a similar elongated V-channel  37  at its lower end, for receiving and bonding to the end lip portions  27 ,  31 , respectively, as shown. As in the previous example, the pivotal structure  21  and slide ball  28  consist of extruded or molded rigid PVC, whereas the flexible web  33  consists of molded or extruded flexible PVC. 
     For the two examples of the drag shield shown in FIGS. 1 and 2, the dissimilar plastic materials of the web  9  relative to the pivotal structure  7  and slide ball of  17  of FIG. 1, and similar corresponding elements of FIG. 2, are laminated together, typically during extrusion, to form a secure bond therebetween. However, there is always a possibility that the bonds between the dissimilar plastic materials may delaminate, causing failure of the drag shield and a potential safety hazard. The power mower industry has attempted to overcome this problem through use of quality control testing procedures for insuring that from a statistical basis drag shields meet “Government and Long Lawn Care Products Manufacturers Standards”. However, this statistical testing used does not permit every drag shield produced to be tested. This presents a potential safety hazard in that plastic hinges, as used in known drag shields, undergo extreme bending and flexing during use of an associated walk-behind power mower. As shown in FIG. 3, as a drag shield  1  is moved over a ground surface  39  during forward motion of an associated mower in the direction of the arrow shown, the web  9 ,  33  tend to bend as shown, and in the reverse motion of the power mower would tend to bend in the opposite matter, as shown. Accordingly, extreme stress is placed upon the bonded portions of the drag shields  1  during use. If the resulting stress applied to the bonded joints of dissimilar plastic material, causes the bonds to break, for example, the drag shield may fail due to the web portion tearing away from the pivotal structure. 
     To overcome the problems in the prior art, the present inventor recognized that the stress placed upon bonded joints between dissimilar plastic materials must be overcome or substantially reduced, to enhance the reliability of such products using flexible hinges as drag shields. After much experimentation in a long-term development project, a new flexible hinge was developed that substantially overcomes the problems of delamination and/or bond breakage in the prior art. With reference to FIG. 4, as configured for use in an improved drag shield  41 , one embodiment of the invention includes in a web portion  43  having a three layer configuration of laminated materials. The centermost web layer  45  consists of the same material as the upper pivotal structure member  47 , and lower slide ball member  49 , all of which in the preferred embodiment are extruded or molded together in a single piece. The pivotal structure  47  includes an elongated tubular member  51 , with a regularly directed and downwardly projecting substantially rectangular limp portion  53 , having downwardly projecting converging end portions  55  and  57  terminating with the relatively thin extension thereof forming the web portion  45 . Similarly, the slide ball structure  49  includes an elongated portion  59  having a circular cross section, with a radially directed and upper wardly projecting lip portion  53  that is substantially rectangular in cross section, with its uppermost portion having ends  63 ,  65  converging to the lowermost portion of the central web  45 . In the preferred embodiment of the invention, the pivotal structure  47 , and slide ball structure  49  consists of a rigid olefin material, such as Montell 7823®(trademark of Montell, Inc.) or equivalent. This material is a high impact copolymer polypropylene made utilizing metallocene catalyst technology, that compared to other materials has superior mechanical and thermal properties. Although this plastic material is a rigid material, the present inventor determined that by making the thickness of the web  45  of this material about 0.02 inch, the web could be made to be flexible in this area. 
     To strengthen and reinforce the web area, a layer of flexible olefin material is formed in a first layer  67  on one side of the central web  45 , and a similar layer  69  on the opposite side of the material of the central web  45 . In the preferred embodiment, the flexible olefin is provide by either DOW/DUPONT 8480®(manufactured by a Dow Corning Company, and Dupont Corporation) or EXXON EXACT 0201®(manufactured by Exxon Corporation), or the equivalent. This material is a metallocene polyethylene, more particularly a saturated ethylene octane copolymer. Compared to other plastic materials, this material provides superior long term stability, improved weatherability, and high impact resistance. 
     Also in a preferred embodiment, the outer flexible plastic webbed layers  67  and  69  are laminated directly to the rigid plastic material of the central web  45  in an extrusion process. Further in the preferred embodiment, the thickness each one of the outer layers  67  and  69  is about 0.030 inch, making the total thickness of the central web to be about 0.08 inch, in this example. The flexible plastic layers  67  and  69  serve not only to strengthen the central web layer  45  against breakage or cracking, but also insure that the inventive drag shield meets various impact test requirements, such as CPSC No.1205.4, ANSI\OPEI B 71.1, and EN 836, and other specifications introduced by various manufacturers for guaranteeing the safety performance of drag shields. Tests completed of the inventive design in FIG. 4 have proved that the delamination problem of the prior art has been substantially eliminated, due in large part to the avoidance of any discontinuities or breaks in the material, such as by joints, between the centralmost web portion  45 , and the rigid end structures, in this example being the pivotal structure  47  and slide ball structure  49 , respectively. However, although the olefin materials indicated previously are at the present time considered the preferred materials for use with the flexible hinge structure of the present invention, such materials are not meant to be limiting. It is believed that improvements can be made to the inventive flexible web through the careful selection of the thicknesses of the central web portion  45 , and outer web portion layer  67  and  69 , in addition to modifying the plastic materials used for these portions for improving impact resistance and flexibility for meeting different requirements and uses for the inventive flexible web. 
     As has been indicated previously, the flexible web of the present invention is not limited to use with walk-behind power lawn mower drag shields or trail shields, but has multiple uses in any applications where a plastic hinge is used. For example, as shown in FIG. 5, a generalized application of the inventive flexible hinge  80  is shown connected between two rigid plastic end members  82  and  84 . As with the application for use in the drag shield, the inventive flexible hinge  80  includes a thin central web layer  86  consisting of the same rigid plastic materials as end portions  82  and  84 , and being formed as a single piece therewith thereby avoiding any discontinuities or breaks therebetween. Flexible plastic layers  88  and  90  are bonded on opposing sides of the rigid plastic central web portion  86 . The central rigid plastic material of web portion  86  is made thin enough to be flexible. 
     In static pull tests using 100 pounds static weight over 50% of the profile the present inventive flexible hinges using the identified preferred olefin materials in the drag shields had no breaks or separation of the web from the rigid members. In comparison, drag shields of rigid PVC and flexible PVC failed at over 50 pounds static weight over 50% of their profile. 
     Although, various embodiments of the invention have been shown and described, they are not meant to be limiting. Those of skill in the art may recognize certain modifications to these emboiments, which modifications are meant to be covered by the appended claims.