Abstract:
An expansible foaming reinforcing member for reinforcing a hollow structural member of an automobile, aircraft, boat, etc. is provided. The reinforcing member includes a synthetic, resin-based expansible reinforcing material secured to a carrier which maintains the reinforcing member at the desired location within the structural member until thermal expansion. The reinforcing material is formed of a thermally expansible composition which preferably has an expansion temperature similar to the temperatures achieved in specific stages of a particular manufacturing process (e.g., such as the temperature at which the paint bake or powder bake stage is carried out in the automobile manufacturing process). The reinforcing material of the inventive reinforcing member comprises a plurality of spaced-apart fins or ribs. During heat activation, heated air can travel between the ribs, thus allowing a greater surface area of the reinforcing material to be exposed to heat leading to improved expansion. The ribs can be configured to a shape corresponding to the cross-sectional shape of the cavity of the structural member, thus permitting the reinforcing member to be inserted into small, irregular shaped cavities.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This present invention relates generally to thermally expansible, foaming, structural reinforcing members used to provide localized stiffness to frames, rails, cavities, panels, and other structural members such as those found in automotive, aviation, or marine applications. More particularly, the inventive reinforcing members include a thermally expansible, foaming reinforcing material that is secured to a carrier or support which maintains the reinforcing member in the desired orientation within the cavity, frame, or rail of the structural member until the material is thermally expanded. The reinforcing material comprises a plurality of spaced-part ribs or fins which permit heated air to contact a greater surface area of the material so as to improve volumetric expansion performance thereof  
           [0003]    2. Description of the Prior Art  
           [0004]    During the design and development of automobiles, trucks, aircraft, watercraft, etc., much of the body structure includes hollow cavities, rails, or frame sections. Many times, the structural integrity of the body is improved through increasing the stiffness in localized critical areas. Increased stiffness in localized critical areas generally result in reduced vibration, noise, and/or fatigue propagation. Additional stiffness in these areas has also utilized energy management during crash, crush, or impact situations. Many attempts have been made to reinforce these cavities. One such method involves introducing self-sustaining reinforcing products into the cavity, either with or without a support or carrier structure. However, these methods generally result in the addition of excess weight to the structural member which is undesirable in most instances.  
           [0005]    Attempts have also been made to utilize reinforcing products which are lighter in weight or which do not use a support structure, but these attempts usually involve products which lack the necessary strength for properly reinforcing the structural member. Furthermore, many of the cavities to be reinforced are irregular in shape or narrow in size, thus making them difficult to sufficiently position currently available reinforcing apparatuses therein. Even if the self-sustaining reinforcing product is successfully inserted into the particular cavity, many times it does not sufficiently expand upon heating due to the fact that the center of the material not being properly heated during the activation process. That is, the size of the foam product is sufficiently thick that the core of the product is exposed to minimal heat, thus preventing the core from fully expanding. This can lead to an inadequately reinforced structural member.  
           [0006]    U.S. Pat. No. 5,344,208 Bien et al. is directed towards a one-piece plastic bracket for supporting a sealer block of heat expansible reinforcement material on the substructure of a vehicle. While the reinforcement assembly disclosed by Bien et al. may be useful for sealing some cavities, the sealer block provided would not sufficiently fill irregular in shape or narrow in size cavities which are common in many motor vehicles.  
           [0007]    U.S. Pat. No. 5,213,391 to Takagi discloses a body skeleton structure for a vehicle comprising an inner panel ( 3 ) of a front pillar ( 1 ) with which a bracket section ( 16 ) is integrally formed (see FIGS.  5 - 7 ). The bracket section ( 16 ) extends towards an inner surface of an outer panel ( 2 ) and includes flanges ( 17 ) having thermally foaming rubber sheet ( 18   a ) adhered to its outer surfaces. Rubber sheet ( 18   a ) expands upon heating in order to minimize gaps around the bracket section ( 16 ). The Takagi structure is deficient in that a bracket section ( 16 ) must be integrally formed with pillar ( 1 ). Furthermore, bracket ( 16 ) must have an overall shape which corresponds to that of the cross-sectional shape of pillar ( 1 ) and an overall size which is only slightly less than the cross-sectional size of pillar ( 1 ) in order to minimize the likelihood of gaps within the pillar. This requires substantial work on the part of the vehicle manufacturer, thus leading to increased costs.  
           [0008]    U.S. Pat. No. 5,755,486 to Wycech is directed towards a w-shaped reinforcement member that carries a thermally expansible resin-based material (see FIGS.  1 - 4 ). The w-shaped reinforcement member is placed in the channel of a hollow structural member over a transverse pin which fits through the slot of the w-shaped member and maintains it in position until such time as the material is heat-expanded. The Wycech reinforcement member is lacking in that it does not properly reinforce narrow or irregular-shaped cavities, thus limiting its applications in motor vehicles.  
           [0009]    Finally, other types of prior art reinforcing products are tacky in nature, and thus cannot readily be positioned at the exact required location in the selected cavity. Such products also generally present unique packaging problems to the manufacturer, and require special handling during installation.  
         SUMMARY OF THE INVENTION  
         [0010]    The instant invention overcomes these problems by providing a thermally expansible, foaming, reinforcing member for reinforcing a hollow structural member (such as one in an automobile rail) at a pre-determined location within the cavity.  
           [0011]    In more detail, the reinforcing member includes a portion formed of a thermally expansible, foaming, reinforcing material. The reinforcing material is preferably a synthetic, resin-based material which expands when subjected to temperatures achieved at specific points in a manufacturing process (e.g., such as during the paint or powder bake stages of automobile manufacturing processes). This expansion is achieved either by internally created thermal energy or by the external application of heat to activate the material. As used herein, the term “thermally expansible” means both internally created thermal energy and the external application of heat to expand and foam the reinforcing material. The expansion temperature of the material should be at least about 300° F.  
           [0012]    The expansible material of the inventive reinforcing member comprises at least two spaced-apart ribs (and preferably three or more ribs). The thickness of the ribs and the distance between these ribs should be such that, upon heat activation, the ribs will expand outward in all directions, contacting and “melding” with any adjacent ribs to form a substantially uniformly dense, expanded reinforcing material. Thus, the distance between the ribs can be varied, but preferably ranges from about 0.5-1.5 cm. In applications where the ribs are wider at their lower portions, the shortest distance between a pair of ribs should be at least about 0.1 cm, and preferably at least about 0.5 cm, while the longest distance between a pair of ribs can be varied but is preferably less than about 1.5 cm. These distances are important in order to allow sufficient heated air to contact all of the rib surfaces while maintaining the ribs sufficiently close to allow the expanded ribs to contact one another and form a uniform, expanded block of the material. Finally, the ribs are preferably integral with a base portion formed of the same thermally expansible material.  
           [0013]    In a preferred embodiment, the inventive reinforcing member further comprises a carrier to which the expansible material is secured. The carrier is useful for maintaining the expansible material in the desired location and orientation within the cavity until thermal expansion is effected. The carrier should be formed of a material having a melting point higher than the expansion or foaming temperature of the expansible material (e.g., metal or nylon). Furthermore, the melting point of the carrier should be higher than any processing temperatures to which the intended structural member will be subjected.  
           [0014]    The carrier can be sized and shaped as necessary to support the reinforcing member, while the expansible material is generally sized and shaped to correspond to the cross-sectional shape of the cavity in which the reinforcing member will be utilized. Furthermore, the size and shape of the carrier can be designed so as to assist in directing the flow of the thermally expanding material into small and/or irregular shaped crevices while simultaneously restricting the flow of the material to other locations in the cavity.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a perspective view of a molded, ribbed structural reinforcing member according to the invention;  
         [0016]    [0016]FIG. 2 is a top view of the reinforcing member of FIG. 1, with the reinforcing member rotated counterclockwise until the carrier is in a horizontal orientation;  
         [0017]    [0017]FIG. 3 is a left end view of the reinforcing member as viewed in FIG. 2;  
         [0018]    [0018]FIG. 4 is a front view of the reinforcing member as viewed in FIG. 2;  
         [0019]    [0019]FIG. 5 is a plan view depicting the reinforcing member of FIGS.  1 - 4  in a structural member after thermal expansion of the reinforcing material;  
         [0020]    [0020]FIG. 6 is a vertical cross-sectional view taken along line  6 - 6  of the reinforcing member and structural member combination depicted in FIG. 5;  
         [0021]    [0021]FIG. 7 is a vertical cross-sectional view taken along line  7 - 7  of the reinforcing member and structural member combination depicted in FIG. 5;  
         [0022]    [0022]FIG. 8 is a perspective view of an alternate embodiment of the inventive reinforcing member wherein bend tabs are utilized to retain the thermally expansible foaming material on the carrier;  
         [0023]    [0023]FIG. 9 is a plan view depicting the reinforcing member of FIG. 8 in a structural member after thermal expansion of the reinforcing material; and  
         [0024]    [0024]FIG. 10 is a vertical cross-sectional view taken along line  10 - 10  of the reinforcing member and structural member combination depicted in FIG. 9. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    FIGS.  1 - 4  illustrate a preferred ribbed reinforcing member according to the invention. Referring to FIG. 1, the reinforcing member  10  includes a thermally expansible foaming material  12  and a carrier  14 . Expansible, reinforcing material  12  is formed of a plurality of angularly oriented fins or ribs  16   a - g  having respective upper ends  18   a - g  and respective lower ends  20   a - g . Ribs  16   a - g  are each preferably integrally connected with a base  21  having a forward margin  23  so that each pair of ribs  16   a - g  forms a valley  22   a - f  therebetween, with each of the valleys  22   a - f  being formed in part by a bottom surface  24   a - f  which is a surface shared by the base  21 . Ribs  16   a ,  16   c , and  16   d  further include threaded openings  26 , shown in phantom.  
         [0026]    Referring to FIGS.  2 - 4 , each of ribs  16   a - g  is free-standing (i.e., the ribs do not include any type of carrier or retaining means on their respective surfaces) and includes a generally flush, forward surface  28   a - g , a generally flush, rearward surface  30   a - g , and a generally horizontal, upper surface  32   a - g . Surfaces  30   c - g  and  28   a - e  are essentially parallel to forward margin  23  of base  21  while surfaces  30   a,b  and  28   f,g  are essentially perpendicular to forward margin  23  of base  21 . Each of ribs  16   a - g  include respective leftward outer surfaces  34   a - g  and rightward outer surfaces  36   a - g . Referring to FIGS. 1, 2, and  4 , it can be seen that each of ribs  16   a - g  is wider at its respective lower end  20   a - g . As a result, each of valleys  22   a - f  become narrower towards their respective bottom surfaces  24   a - f.    
         [0027]    Each of the above-described components of reinforcing material  12  is preferably integrally connected to one another and formed of the same thermally expansible composition  38 . The composition  38  used in the present invention is a dry, initially non-tacky material that develops adhesion upon expansion so that it adheres to the surrounding structural members when activated. Activation may be by heating, such as occurs in automobile assembly plants. When subjected to a temperature of at least about 300° F., the thermally expansible foaming material should have a percent expansion of at least about 40%, preferably at least about 125%, and more preferably from about 150-300%, to provide sufficient structural reinforcement and compressive strength. As used herein, the percent expansion is defined as:  
         [0028]    100×{[(the specific gravity of the material  12  before heating)−(the specific gravity of the material  12  after heating)]/(the specific gravity of the material  12  after heating)}.  
         [0029]    One preferred composition  38  for use as reinforcing material  12  is commercialized under the name SikaReinforcer (Sika Corporation, Madison Heights, Mich.). In more detail, the most preferred composition  38  comprises: from about 20-30% by weight of a styrene-butadiene-styrene (SBS) block co-polymer (e.g., Fina Clear 530®); from about 5-20% by weight of a polystyrene (e.g., Fina Crystal 500® and Fina Crystal 535®); from about 30-45% by weight of a bisphenol A-based liquid epoxy resin (e.g. Araldite 6010® and Epon 71®); from about 0.5-5% by weight of a pigment such as carbon black; up to about 5% by weight butadiene acrylonitrile rubber (Nipol 1411); from about 1-10% by weight hydrated amorphous silica (HiSil 233); from about 10-20% by weight glass microspheres (Scotchlite S60); from about 0.1-5% by weight of a blowing agent such as azodicarbonamide (e.g., Celogen AZ 765®, Celogen AZ 754A®, and Celogen AZ 130®); from about 0.1-5% by weight of a catalyst such as N,N, dimethyl phenyl urea (U405); from about 0.1-5% by weight of a curing agent such as dicyandiamide (DDA10); and up to about 5% by weight of a “kicker” such as zinc oxide to lower the blowing temperature, with all percents by weight being based upon the total weight of the composition taken as 100% by weight.  
         [0030]    A particularly preferred composition  38  for use as material  38  comprises about 12.94% by weight polystyrene, about 23.22% by weight SBS block copolymer, about 0.57% by weight carbon black, about 1.90% by weight butadiene acrylonitrile rubber, about 4.28% by weight hydrated amorphous silica, about 38.07% by weight bisphenol A-based liquid epoxy resin, about 14.75% by weight glass microspheres, about 0.46% by weight zinc oxide, about 2.85% by weight dicyandiamide, about 0.38% by weight N,N dimethyl phenyl urea, and about 0.57% by weight azodicarbonamide. In certain applications where increased compressive strength and reduced foaming and expansion is desired, the foregoing may be adjusted such that the polystyrene is reduced to about 12.63% by weight, the SBS block copolymer is reduced to about 22.59% by weight, and the butadiene acrylonitrile rubber is increased to about 2.85% by weight.  
         [0031]    The composition  38  can be formed by mixing the SBS block co-polymer with a small portion (about {fraction (1/40)}th of the total amount) of the bisphenol A-based liquid epoxy resin in a heated mixer until the temperature of the mixer reaches from about 240-260° F. (the temperature of the mixture within the mixer is at least about 175° F.), and the mixture is substantially homogeneous, at which time the polystyrene is added to the mixer and mixing is continued. After the polystyrene is substantially mixed with the SBS block co-polymer/epoxy resin mixture, the remainder of the bisphenol A-based epoxy resin is slowly added to the mixer, stopping and starting the mixer as necessary, with the ingredients being thoroughly mixed to obtain a substantially homogeneous mixture. The desired amount of this mixture is placed in a heated mixer (set at a temperature of about 250° F.) and mixing is commenced. While mixing, the carbon black and rubber are added to the mixer and mixing is stopped once a homogeneous mixture is obtained within the mixer. Either the silica or glass microspheres is added to the mixer, and mixing is resumed and continued until the mixture is homogeneous. This step is repeated, adding the other of the silica or glass microspheres.  
         [0032]    The temperature of the mixer is then set to a temperature below 160° F., the blowing agent(s), catalyst(s), kicker, and curing agent(s) are added, and mixing is resumed and continued only until the mixture is homogeneous. The resulting mixture is then preferably extruded into strands (at an extruder temperature of 170-180° F. and screw rotation speeds of about 400 rpm) and cut into pellets. The resulting pellets are injection molded at a temperature of about 180-200° F. using injection molding equipment designed to form the desired shape of the reinforcing material  12  to be attached to the carrier  14 .  
         [0033]    Referring to FIG. 1, the carrier  14  comprises a flat plate  40  and upper and lower vertical plates  42 ,  44 , respectively. In the embodiment shown, plates  42 ,  44  are essentially perpendicular to plate  40 . Plate  40  and plate  44  are joined at bend  46 , with plates  42 , 44  being essentially parallel to one another. Reinforcing material  12  is secured to carrier  14  by way of push-pins  48  which are inserted through holes  47  in plate  40  and into openings  26 . Referring to FIG. 3, the overall width of reinforcing material  12  is slightly greater than the width of plate  40 , creating an “overhang” area  49 .  
         [0034]    The carrier  14  is formed of a material having a melting point that is higher than both the activation (i.e., foaming) temperature of the composition  38  of which reinforcing material  12  is formed and the temperature to which any structural member containing the reinforcing member  10  would be exposed. In the embodiment illustrated, carrier  14  is formed of steel.  
         [0035]    The size and shape of the carrier  14  is not critical, so long as carrier  14  is capable of fitting within the cavity of the particular structural member in which it is to be utilized. Furthermore, the flow of the reinforcing material  12  should be sufficiently directed by the carrier  14  during expansion so that the expanded material contacts and adheres to the cavity walls and substantially fills any crevices.  
         [0036]    In application, the reinforcing member  10  is preferably provided to a manufacturer preassembled (i.e., with the non-expanded material  12  attached to carrier  14 ) for insertion into the cavity of the desired structural member, such as during construction of an automobile. FIGS.  5 - 7  illustrate the positioning of reinforcing member  10  in an automobile structural member. In the embodiment illustrated, a box-shaped structural member  50  is formed of steel and comprises four sidewalls  52   a - d  which cooperate with an endwall  54  to form a box-shaped cavity  56 .  
         [0037]    Reinforcing member  10  is inserted into structural member  50  in such a manner that the overall configuration of reinforcing material  12  corresponds to the rectangular cross-section of cavity  56 . That is, reinforcing member  10  is inserted into cavity  56  so that the flat upper surfaces  32   a - g  of ribs  16   a - g  are substantially in contact with the surface of wall  52   b , while the rearward surfaces  30   c - g  are in contact with endwall  54 . Finally, surfaces  30   a,b  are positioned adjacent wall  52   c . Lower vertical plate  44  is positioned adjacent wall  52   a  upon insertion of reinforcing member  10  into cavity  56 . Plate  44  is then fastened to wall  52   a  via welds or rivets  58 , thus stabilizing reinforcing member  10  within the cavity  56  until such time as the structural member  50  is exposed to an elevated temperature sufficient to activate the reinforcing material  12 , causing it to foam. In applications where structural member  50  is a component of a vehicle, any of a number of process or manufacturing steps may be carried out on the vehicle body prior to thermal expansion without affecting the ability of the reinforcing material  12  to expand when exposed to the actual activating temperature.  
         [0038]    As the structural member  50  is baked, and the expansion (i.e., activation) temperature of the reinforcing material  12  is reached, the reinforcing material  12  begins to expand in all directions. That is, the reinforcing material  12  expands towards the cavity walls  52   a - d  and  54  forming expanded material  60 . To a limited degree, reinforcing material  12  expands beyond upper vertical plate  42  at location  62  (see FIG. 7). Furthermore, reinforcing material  12  expands somewhat beyond flat plate  40 , however, flat plate  40  serves to restrict the material from flowing in a direction away from wall  52   d  thus directing the expanding material against the cavity walls  52   a - c  and  54  and into the corners of the cavity  56  (see FIGS.  6 - 7 ). Advantageously, this results in a dense and uniform distribution of expanded material  60  within this rather tight area of the structural member  50 .  
         [0039]    An alternate embodiment of the inventive reinforcing member is shown in FIGS.  8 - 10 , with like numbers corresponding to those numbered parts discussed previously with respect to FIGS.  1 - 7 . In this embodiment, thermally reinforcing material  12  is secured to carrier  14  via bend tabs  64   a,b . Each of bend tabs  64   a,b  is formed by removing a strip of metal from flat plate  40  to create openings  66   a,b . These metal strips are then passed through openings (not shown) in base  21  of reinforcing material  12  between ribs  16   a,b  and  16   d,e . The metal strips are bent away from the respective plate openings  66   a,b , and against surfaces  24   a,d , to form an “L” configuration having respective upper legs  68   a,b  and respective lower legs  70   a,b . Reinforcing material  12  is thus secured to carrier  14  where it will be maintained until thermal expansion thereof. FIGS.  9 - 10  illustrate reinforcing material  12  after thermal expansion to form material  60 . As illustrated, the ribs  16   a - g  expand outwardly in all directions thus covering tabs  64   a,b . Furthermore, base  21  expands somewhat through openings  66   a,b  as shown in FIG. 9.  
         [0040]    It will be appreciated that the ribbed design of reinforcing material  12  in both embodiments allows for improved expansion of the reinforcing material  12 . That is, the valleys  22   a - f  serve as a pathway through which the heated air can travel during thermal activation. This allows the heated air to contact a large number of surfaces (i.e., leftward and rightward outer surfaces  34   a - g  and  36   a - g  as well as surfaces  28   a - g , 30   a - g , and  32   a - g ) of the reinforcing material  12  so that substantially all of the material  38  (from the surfaces to the inner core) is caused to foam, and thus expand. This is different than prior art thermally expansible, foaming, pre-formed parts which generally have core sections which receive little exposure to the heat, thus resulting in cores which are not fully foamed.  
         [0041]    The expanded material  60  has a compressive strength (using a sample having a diameter of 2 inches and a length of 4 inches and a compression rate of 0.5 inches/minute) of at least about 1200 psi, preferably at least about 1400 psi, and more preferably at least about 1600 psi. Prior to expansion, the material  12  has a specific gravity (with reference to water) of at least about 0.90, while the specific gravity (with reference to water) of the expanded material  60  is less than about 0.47, preferably less than about 0.37, and more preferably less than about 0.32. The expanded material  60  has a ratio of compressive strength:specific gravity after bake of at least about 2500:1, preferably at least about 3000:1, and more preferably at least about 3600:1.  
         [0042]    Although the present invention has been described with reference to the preferred embodiments illustrated in the accompanying figures, it is noted that substitutions may be made and equivalents employed without departing from the scope of the invention. For example, although the preferred embodiment is illustrated in connection with a structural member of a motor vehicle, the inventive reinforcing members may be employed in other structural members as well (e.g., in a boat, in an airplane, etc.). Furthermore, while SikaReinforcer is cited as one preferred material of which reinforcing material  12  can be formed, any material meeting the above-described strength and expansion properties is suitable.  
         [0043]    Finally, although five fin-shaped ribs  16   a - g  are depicted in the attached figures, it will be appreciated that the number of ribs can be modified as necessary, depending upon the length of expanded material desired in the particular structural member as well as the thickness of each rib. The shape of the ribs  16   a - g  can also be altered as necessary, depending upon the cross-sectional shape of the cavity into which the reinforcing member  10  is to be inserted. Furthermore, while push-pins  48  are depicted for securing reinforcing material  12  to carrier  14 , other fasteners can be used as well such as adhesives or other fastening means.