Abstract:
A laminated steel having a non-continuous viscoelastic layer. The viscoelastic material is absent (voided) at certain predetermined locations of the laminated steel, particularly predetermined potential weld locations. Preferably, the outside surface of at least one of the metal sheets is marked to indicate each location of absence of the viscoelastic material. Advantageously, welding of the laminated steel at the absences of viscoelastic material will be more easily performed than if the viscoelastic material had been present at the weld site.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to laminated steel having a continuous viscoelastic layer sandwiched between two sheets of metal. More particularly, the present invention relates to a laminated steel in which the viscoelastic layer is non-continuous, particularly at predetermined potential welding locations.  
       BACKGROUND OF THE INVENTION  
       [0002]     Laminated steel has two sheets of metal (usually, but not necessarily, steel) which are adhesively joined together by a viscoelastic layer therebetween. An advantage of the viscoelastic layer is its vibration attenuating properties, wherein vibration (noise or sound) acquired and/or conducted by either or both of the metal sheets is damped by the viscoelastic layer. Laminated steel is desirable in the automotive industry for utilization in body components since the vibration damping provided by the viscoelastic layer results in quieter motor vehicles.  
         [0003]     The viscoelastic layer must have two essential qualities: (1) it must provide vibration damping by conversion of vibration into thermal energy with particularly excellent performance around a predetermined operational range of temperature; and (2) it must provide a strong and lasting adhesion to each of the metal sheets. Viscoelastic materials for such purposes are well known in the art, as represented by U.S. Pat. Nos. 3,931,448; 4,942,219; 5,061,778; 5,183,863; and 5,288,813; and include, for example, compositions made of a polyester or polyesters, polyester incorporating a plasticizer, polyester incorporating an organic peroxide, polyurethane foam, polyamide, ethylene-vinyl acetate copolymer, polyvinyl butyral or polyvinyl butyral-polyvinyl acetate incorporating a plasticizer and a tackifier, coplymer of isocyanate prepolymer and vinyl monomer, or another copolymer.  
         [0004]     In a typical manufacturing process, as described in Example 1 of U.S. Pat. No. 5,288,813, each of the metal sheets is coated (to a depth of 25 micrometers) with a viscoelastic material, then the coated surfaces are joined together under pressure (20 kg/cm 2 ) at an elevated temperature (220 degrees C.) for a selected time (30 seconds).  
         [0005]     While laminated steel performs very well in terms of structural integrity and vibration damping, it suffers from difficulty to weld because of the viscoelastic material at the weld site.  
         [0006]     Accordingly, what is needed in the art is a laminated steel wherein the viscoelastic layer is non-continuous such that at predetermined locations the viscoelastic material is absent, particularly absent at predetermined potential weld locations.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is a laminated steel wherein the viscoelastic layer thereof is non-continuous. By the term “non-continuous” is meant the viscoelastic material is absent (voided) at certain predetermined locations of the laminated steel, and wherein the predetermined locations are preferably known potential weld areas of the laminated steel. It is to be understood that although the term “laminated steel” is used herein, it is to be interpreted to mean any kind of metal sheets (steel, stainless steel, aluminum, etc.) joined together by a viscoelastic layer.  
         [0008]     According to the method of the present invention, a viscoelastic material is applied, as for example by spraying or printing, onto a surface of at least one of the metal sheets. The viscoelastic material is applied by the applicator using, for example, a computer program or a mask, whereby the viscoelastic material is applied non-continuously to the inside surface of at least one of the metal sheets, wherein local regions of the inside surface are free of the viscoelastic material (i.e., the inside surface has absences of viscoelastic material). Thereafter, the interior surfaces of the metal sheets are arranged so as to mutually face each other, then are compressibly joined to thereupon form the laminated steel.  
         [0009]     In the preferred embodiment of the laminated steel according to the present invention, the outside of at least one of the metal sheets is marked, as for example durable markings provided by printing, so as to indicate each location of absence of the viscoelastic layer.  
         [0010]     Accordingly, it is an object of the present invention to provide a laminated steel having a non-continuous viscoelastic layer, wherein predetermined locations of the viscoelastic layer are absent, particularly locations whereat welds may be effected.  
         [0011]     This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a perspective view of a laminated steel with a non-continuous viscoelastic layer according to the present invention.  
         [0013]      FIG. 2  is a cross-sectional view, seen along line  2 - 2  of  FIG. 1 .  
         [0014]      FIG. 3  is a partly exploded view of the laminated steel shown at  FIG. 1 .  
         [0015]      FIG. 4  is a sectional view of the laminated steel as in  FIG. 2 , now shown in operation welded to a structural component.  
         [0016]      FIG. 5  is a schematic view of an apparatus to provide a laminated steel having a non-continuous viscoelastic layer according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Referring now to the Drawing,  FIGS. 1 through 3  depict an example of a laminated steel  10  according to the present invention. The laminated steel  10  includes a first metal sheet  12  having inside and outside surfaces  12   a,    12   b,  a second metal sheet  14  having inside and outside surfaces  14   a,    14   b  (the metal sheets being composed of any metal, most preferably steel) and a non-continuous viscoelastic layer  16  therebetween, wherein the viscoelastic layer adhesively joins the inside surface of each of the first and second metal sheets thereto. The viscoelastic layer  16  is non-continuous in the sense that the viscoelastic material  16   m  thereof is absent  16   a  at certain predetermined locations of the laminated steel  10 . Most preferably, the predetermined locations have a one-to-one positional correspondence with known potential weld areas  18  of the laminated steel  10  (discussed hereinbelow with respect to  FIG. 4 ).  
         [0018]     The viscoelastic material  16   m  of the viscoelastic layer  16  is of a type known in the art, as for a non-limiting example: compositions made of a polyester or polyesters, polyester incorporating a plasticizer, polyester incorporating an organic peroxide, polyurethane foam, polyamide, ethylene-vinyl acetate copolymer, polyvinyl butyral or polyvinyl butyral-polyvinyl acetate incorporating a plasticizer and a tackifier, coplymer of isocyanate prepolymer and vinyl monomer, another copolymer, or any other material known in the art for use in a laminated steel, as for example disclosed in U.S. Pat. No. 5,288,813, issued Feb. 22, 1994, the disclosure of which is hereby incorporated herein by reference.  
         [0019]     It is most preferred for one, or both, of the outside surfaces  12   b,    14   b  of the first and second metal sheets  12 ,  14  to have markings  20  so as to delineate the location of each of the absences  16   a  of the viscoelastic material  16   m.  In this regard, it is preferred for each of the markings  20  to delineate the position, size and shape of its respective absence  16   a  of viscoelastic material  16   m  by superposing the absence. The markings  20  can take any suitable form, as for example a solid marking or an outline marking, and may be provided by any suitable modality, such as for example printing of an ink onto one or both of the outside surfaces  12   b,    14   b.    
         [0020]     In operation of the laminated steel  10  according to the present invention as shown at  FIG. 4 , welds  24  are made of the laminated steel  10  to a secondary structural member  26 , wherein each of the welds has a weld location  18  which corresponds positionally to an absence  16   a  of the viscoelastic material  16   m.  Accordingly, the welds  24  are performed easily because the weld sites are free of the viscoelsatic material.  
         [0021]     Turning attention now to  FIG. 5 , an example of a method for making the laminated steel  10  according to the present invention will be discussed, wherein a laminating apparatus  30  is utilized.  
         [0022]     The laminating apparatus  30  includes a frame  32 . Disposed on the frame  32  is a roller set  34  including first and second rollers  34   a,    34   b  which are pressed towards each other via a press  36 . A first metal sheet  12 ′ is delivered from a first metal sheet roll  12   r  under guidance of a guide roller  40 . A second metal sheet  14 ′ is delivered from a second metal sheet roll  14   r.  The viscoelastic material  16   m′  is selectively applied to the inside surface  14   a′  of the second metal sheet  14 ′ via an applicator  42  connected with a bulk source  44  of the viscoelastic material. The applicator  42 , which may be any suitable applicator, as for example a printing or spray head, is preferably controlled by an electronic controller  46  so that the absences of viscoelastic material (see  16   a  in  FIGS. 1 through 3 ) are automatically provided; however, alternatively, a mask  48  may be employed to mechanically provide the absences of the viscoelastic material. A conventional heating apparatus  38  serves to melt or soften the non-continuous viscoelastic material  16   m′  carried on the second metal sheet  14 ′.  
         [0023]     Also attached to the frame  32  is a conventional block laminator  50 , which includes an upper plate assembly  52  physically and thermally coupled to an upper heat exchanger  54  and a lower plate assembly  56  physically and thermally coupled to a lower heat exchanger  58 , wherein the upper and lower heat exchangers are used for cooling. The upper heat exchanger  54  is connected to a plurality of actuators  60  for applying selective pressure to the forming laminated steel  14 ′ as is slides between the upper and lower plate assemblies  52 ,  56 . Details of a suitable block laminator are disclosed in U.S. Pat. No. 5,851,342, the disclosure of which is hereby incorporated herein by reference.  
         [0024]     A pair of print heads  62 ,  64  are provided on either side of the forming laminated steel  10 ′, whereby one print head  62  prints on the outside surface  12   b′  of the first metal sheet  12 ′ and the other print head  64  prints on the exterior surface  14   b′  of the second metal sheet. The print heads  62 ,  64  print markings (see  20  in  FIGS. 1 through 3 ) indicative of the locations of the absences of viscoelastic material (see  16   a  in  FIGS. 2 and 3 ), as discussed hereinabove. Preferably the printing by the print heads  62 ,  64  is controlled by the aforesaid electronic controller  46 , otherwise a mask (not shown) may be utilized to control the printing of the markings.  
         [0025]     In operation, the metal sheets  12 ′,  14 ′ are drawn into the laminating apparatus  30  in unison, and the applicator  42  selectively applies the viscoelastic material  16   m′  onto the inside surface  14   a′  of the second sheet  14 ′(it is to be understood that this is merely an exemplification, as the applicator could apply the viscoelastic material to the inside surface  12   a′  alternatively or additionally). The viscoelastic material is applied in a non-continuous manner so that absences (or voids) of the viscoelastic material (see  16   a  in  FIGS. 2 and 3 ) are provided. The absences of viscoelastic material are initially sized to take into account melting and/or squeezing in the laminator apparatus  30  so that the final sizes of the absences are appropriate to provide viscoelastic absent welds at the predetermined weld areas, as discussed hereinabove.  
         [0026]     The heater  38  melts or softens the viscoelastic material, then the inside surfaces of the first and second metal sheets are squeezed together by the roller set  34 , thereby ensuring good adhesion of the viscoelastic material to the metal sheets. Additionally at this stage of operation, the viscoelastic material has a proper thickness and the non-continuous distribution of the viscoelastic material has properly sized absences.  
         [0027]     Next, the forming laminated steel  10 ′ is delivered to the block laminator  50  while the viscoelastic layer  16 ′ is still hot, wherein the metal sheets are respectively in contact with the upper and lower plate assemblies. The block laminator applies selective pressure to the forming laminated steel  10 ′ and at the same time cools the hot viscoelastic material  16 ′, whereupon the viscoelastic material permanently bonds to the first and second metal sheets.  
         [0028]     Next, the print heads  62 ,  64  print markings (see  20  in  FIGS. 1 through 3 ) onto the outside surfaces  12   b′,    14   b′  of the first and second metal sheets to delineate the locations of the absences of the viscoelastic material.  
         [0029]     Lastly, the fully formed laminated steel  10 ″ is either rolled or cut into size and shaped (if necessary) as needed to provide a laminated steel  10  (see  FIG. 1 ) for production. During production, welding (as shown at  FIG. 4 ) is easily performed at any of the absences of viscoelastic material.  
         [0030]     To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.