Abstract:
A method of spray forming articles with a nozzle that sprays in a flat fan-shaped spray pattern. The process may be used to spray form articles having a skin formed from a polyurethane composition. Repeated passes of the nozzle partially overlap to apply a deposit having a relatively consistent thickness in a series of overlapping paths. A primary flat fan-shaped spray is flanked by a pair of secondary sprays that are outboard of the primary spray. The secondary sprays facilitate feathering the edges of adjacent deposits to provide a skin having a relatively consistent thickness.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to spray forming articles using a spray nozzle that directs a flat fan-shaped spray pattern.  
         [0003]     2. Background Art  
         [0004]     Spray forming articles with reactant elastomer mixtures, such as polyurethane, is a relatively new process that holds substantial promise for manufacturing high quality, durable parts. Parts that may be made with the polyurethane spray forming process include automotive interior parts as well as other parts. Some automotive interior parts that may be made using a polyurethane skin or polyurethane layer include instrument panel covers, console covers, inner door panels, glove box covers, floor mats, steering column covers, knee bolsters, and the like. Structural inserts and padding may be assembled to or inserted in the polyurethane skin to complete the interior part.  
         [0005]     Earlier attempts to manufacture polyurethane parts by a spray forming process have required expensive spray nozzle tips that are used to form a conical spray pattern. Generally, polyurethane spray forming process nozzles have an internal mixing chamber that have a plurality of angularly oriented injection ports that are used to develop turbulence within the mixing chamber. These elaborate spray nozzle tips, in addition to being expensive, require frequent maintenance and cleaning to assure proper performance. A conical spray pattern may yield a slightly cupped spray deposit in cross-section with a portion near the outer edges of the spray deposit being thicker than the central portion.  
         [0006]     Conical sprays generally result in higher quantities of over spray. Over spray can be in the range of 15% of the volume sprayed. Accumulations of over spray outside the useable area of a mold wastes material, burdens air handling systems and creates an unsightly mess inside spray booths.  
         [0007]     Prior art conical spray patterns require high pressure spray equipment that is designed to operate at 1000 to 2000 psi. Conical spray patterns at such pressures may be used to spray polyurethane at a rate of 16 to 24 grams per second. Processes requiring higher pressures generally require higher capital investments. An application rate of 16 to 24 grams per second is the norm but higher productivity could be obtained if the spray application rate could be increased without increasing pressure, velocity and turbulence of the spray.  
         [0008]     Simpler spray applicator nozzles have been tested in an effort to develop a spray applicator nozzle that produces a flat fan spray pattern. These nozzles were provided with a tip that has a slit formed by two intersecting arcs for producing the flat fan spray. Testing of this nozzle in a spray forming operation resulted in a flat fan spray that has thick edge portions that are separated from a relatively uniform central portion by thin areas. It is believed that this inconsistent spray thickness is caused by variation in the laminar flow pattern through the nozzle wherein the central laminar flow rate is greater than the peripheral laminar flow rate.  
         [0009]     To make a continuous skin, several spray passes must be applied next to each other. Increased accumulation of the spray deposit on the outer edges of each deposit made by a spray pass can result in a ribbed appearance on the back side of the spray applied layer. While the ribbed appearance is not generally visible on the mold side or exterior surface of a part, in some instances it may be detectable as an area of different thickness and possibly different hardness compared to the other parts of the skin. Skin thickness variations may cause problems relating to attachment to rigid inserts and retainers and may also adversely impact the uniformity of a foam padding layer thickness.  
         [0010]     These and other problems are addressed by applicants&#39; invention as summarized below.  
       SUMMARY OF THE INVENTION  
       [0011]     According to one aspect of the present invention, a spray applicator for spraying polyurethane that is used to spray form an article is disclosed that provides a more uniform and consistent skin. The spray applicator includes an applicator body having an internal cavity that receives at least two polyurethane forming components. The polyurethane forming components are mixed in an internal mixing chamber to form a polyurethane mixture that is dispensed through a nozzle defining an elongated slit-type of spray opening that dispenses the polyurethane mixture. A concentrating insert is assembled to the applicator body immediately upstream from the nozzle. The concentrating insert has a hollow central cylindrical opening, or pre-orifice. The insert concentrates the polyurethane mixture in the interior portion of the spray pattern and a reduced volume of the polyurethane mixture is applied at the lateral end portions of the spray pattern.  
         [0012]     According to other aspects of the invention, the nozzle may spray the polyurethane composition in a flat fan shaped pattern onto a mold surface. A single swath of polyurethane may be sprayed on the mold surface initially with additional spray applications being made in a predetermined path to create a skin layer with multiple overlapping swaths being applied in multiple passes of the nozzle relative to the mold. The lateral end portions of the spray pattern of adjacent swaths overlap to form a skin layer that has a relatively consistent thickness.  
         [0013]     Other aspects of the invention relate to the structural features of the concentrating ring or insert. The concentrating insert, or ring, may be retained by a sealing member that forms a seal between the ring and the nozzle. Alternatively, the ring may be a hard metal insert. The sealing member may be a plastic washer. A collar may be used to secure the nozzle and concentrating insert to the applicator body. The sealing member forms a seal between the concentrator insert and the nozzle and is held in place by the collar.  
         [0014]     The polyurethane composition may be a two-component aromatic polyurethane mixture of polyol and isocyanate that are internally mixed in the spray applicator. The spray applicator may have a helical static mixing element that mixes the polyol with the isocyanate prior to being sprayed by the spray nozzle.  
         [0015]     According to another aspect of the present invention, a spray applicator for spraying a reactant mixture to form an article in conjunction with a mold is provided. The spray applicator comprises a mix tube having a plurality of inlets for a plurality of components and an outlet for dispensing the reactant mixture that is formed as a mixture of the plural components. A nozzle for spraying the reactant mixture is in fluid flow communication with the outlet of the mix tube. The nozzle defines an interior cavity and has an elongated slit spray opening. A collar secures the nozzle to the mix tube. A flow restricting ring is disposed upstream of the elongated slit spray opening in the interior cavity of the nozzle. The flow restricting ring is retained by a sealing washer within the collar. The reactant mixture flows from the mix tube through the flow restricting ring and out of the nozzle in a controlled spray pattern.  
         [0016]     According to other aspects of the invention, the flow restricting ring defines an aperture that focuses the flow of reactant mixture in a central portion of the nozzle. The controlled spray pattern may be a flat fan spray pattern wherein the polyurethane mixture is concentrated in the interior portion of the spray pattern and a reduced volume of the polyurethane mixture is supplied at the lateral end portions of the spray pattern. The nozzle tip has a slit opening formed by two intersecting arcuate edges extending across a central portion of the tip. The nozzle may be oriented at an oblique angle relative to the mix tube that directs the reactant mixture spray in a selected direction.  
         [0017]     According to another aspect of the present invention, the ratio of the area of the opening in the flow restricting ring to the area of the slit spray opening is controlled to provide a relatively even spray pattern. The ratio of the area of the opening in the flow restricting ring to the area of the slit spray opening may be 1 to 0.4-0.6, or more particularly about 1 to 0.5.  
         [0018]     These and other aspects of the invention will be readily apparent in view of the attached drawings and following detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a diagrammatic perspective view of a spray forming process utilizing a nozzle having a concentrating insert in accordance with the present invention that provides a flat fan spray pattern;  
         [0020]      FIG. 2  is a cross-sectional view taken along the line  2 - 2  in  FIG. 1 ;  
         [0021]      FIG. 3  is a cross-sectional view of the spray deposited by the process illustrated in  FIG. 1  in a series of passes;  
         [0022]      FIG. 4  is a cross-sectional view of a spray applicator nozzle having a flow restricting ring, or concentrator insert;  
         [0023]      FIG. 5  is an exploded perspective view of a spray applicator nozzle having a flow restricting ring;  
         [0024]      FIG. 6  is a diagrammatic cross-sectional view of a spray applicator nozzle that does not have a flow restricting ring and the resultant spray and application pattern;  
         [0025]      FIG. 7  is a diagrammatic cross-sectional view of a spray applicator nozzle having a flow restricting ring and the resultant spray and application pattern; and  
         [0026]      FIG. 8  is an end view of the nozzle shown in  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Referring to  FIG. 1 , a spray applicator nozzle  10  is shown as its sprays a reactant mixture  12  of a polyurethane composition. The reactant mixture  12  is sprayed on a mold  16  to form a skin  18  composed of the polyurethane reactant mixture  12 . The mold  16 , as shown in  FIG. 1 , is a flat plate but it should be understood that the mold could include a contoured surface including, for example, convex and concave areas corresponding to the shape of a vehicle interior part.  
         [0028]     Referring to  FIGS. 1 and 2 , a central spray  20  forms a principal portion  22  of the skin  18  with a relatively consistent thickness. Spray edges  24  form tapered edge portions  26  on opposite sides of the principal portion  22 . The tapered edge portions  26  are intended to be layered with tapered edge portions of adjacent spray swaths and thereby provide a skin  18  of relatively constant thickness in conjunction with adjacent spray swaths, as shown in  FIG. 3 . A skin having a smooth exterior surface without distinct ridges or ribs should be understood to be one having a relatively constant thickness.  
         [0029]     Referring back to  FIG. 1 , a flow restriction ring  30 , or concentrator, is disposed in the spray applicator nozzle  10  upstream in the flow of the polyurethane mixture relative to a slit  32  formed in a nozzle tip  34  of the spray applicator nozzle  10 . A mixing chamber  36  is provided upstream from the flow restriction ring  30  and may include a static mixing element (not shown in  FIG. 1 ). An interior cavity  38  is provided in the nozzle tip  34  between the flow restriction ring  30  and the slit  32  in the nozzle tip  34 .  
         [0030]     Referring to  FIG. 4 , an applicator tool  40  is shown that includes a static mixer  42  that is used to mix polyurethane forming components comprising polyol and isocyanate prior to supplying the reactant mixture to the flow restriction ring  30  and then to the nozzle tip  34 . The flow restriction ring  30  is held in place by a retainer  46  comprising a washer-like structure that is engaged by a collar  48  of the spray nozzle  10 . The collar  48  has a threaded outer diameter  50  and is received in a threaded end opening  54  of the spray nozzle  10 .  
         [0031]     The flow restriction ring  30  in the illustrated embodiment includes a disk-shaped portion  56  that defines a cylindrical opening  58 . A cylindrical ring  60  is also provided on the flow restriction ring  30 . The cylindrical ring  60  may be received in a passageway  62  through which reactant mixture is supplied from the mixing chamber  36  to the spray nozzle  10 .  
         [0032]     The retainer  46  includes a central opening  64  that is coaxial with the cylindrical opening  58  in the flow restriction ring  30 . A counterbore opening  66  is provided in the retainer  46  that receives at least a portion of the flow restriction ring  30 .  
         [0033]     The collar  48  includes a shoulder  70  that retains the nozzle tip  34  and the spray nozzle  10 . The collar  48  establishes a seal by applying pressure to the nozzle tip  34 , retainer  46 , and flow restriction ring  30 . The collar  48  is tightened by the threaded connection between the threaded outer diameter  50  and threaded opening  54  in the spray nozzle  10 .  
         [0034]     Referring to  FIG. 5 , the structure of the spray applicator nozzle  10  is shown in greater detail. The spray nozzle  10  is received by the applicator tool  40 . The collar  48  engages the nozzle tip  34  with a shoulder  70  bearing upon the nozzle tip  34 . Nozzle tip  34  includes a slit  32  formed in the nozzle tip  34 . The nozzle tip  34  engages the retainer  46  and defines an interior cavity  38  in conjunction with the retainer  46 . The retainer  46  defines a central opening  64  and a counterbore opening  66  in which the flow restriction ring  30  is at least partially received. Flow restriction ring  30  includes a disk-shaped portion  56  that defines a cylindrical opening  58 . A cylindrical ring  60  is provided on the flow restriction ring that is coaxial with the opening  58  and aligns the flow restriction ring with the passageway  62  in the applicator tool through which the reactant mixture  12  is supplied to the nozzle  10 .  
         [0035]     Referring to  FIG. 6 , a prior art fan spray nozzle  80  is diagrammatically illustrated. The fan spray nozzle  80  is provided with a reactant mixture, the flow of which is represented by laminar flow vector arrows  82 . The rate of laminar flow through the fan spray nozzle  80  is greatest in the central portion of the nozzle  80  with the rate of flow being reduced progressively as it approaches the peripheral edges of the nozzle  80 . Laminar flow characteristics through the fan spray nozzle  80  are believed to contribute to the formation of heavy fingers of spray  84  that are separated by areas of thin spray  86  from the primary application spray  88 . The heavy fingers of spray  84  result in heavy edge deposits  90  that are separated by thinner deposits  92  from the primary deposit  94  of the skin  18 . The heavy edges in the flat spray pattern make it necessary to overlap adjacent spray swaths to a greater extent than if a smooth edge tapered spray pattern is provided. Increasing the degree of overlap between adjacent passes necessitates application of a larger amount of material to cover or smooth inconsistencies in the spray pattern.  
         [0036]     Referring to  FIG. 7 , a spray applicator nozzle  10  including a flow restriction ring  30  is diagrammatically illustrated with its associated spray pattern and spray deposit. The flow restriction ring  30  is comprised of the disk-shaped portion  56  that defines the cylindrical opening  58  through which the reactant mixture  12  is directed into an interior cavity  38  defined by the nozzle  10 . A focused internal flow arrow  96  illustrates the relatively linear and uniform laminar flow pattern produced by the flow restriction ring  30 . It is also understood that a limited amount of turbulence may exist within the interior cavity  38  of the nozzle  10  that is diagrammatically represented by the curved lines  98  inside the interior cavity  38 . As the reactant mixture  12  flows through the cylindrical opening  58 , it is focused in the central portion of the slit  32  formed in the nozzle  10 . The spray produced includes a central spray  20  and tapered spray edges  24 . The skin  18  produced has a central portion  22  of relatively consistent thickness and two tapered edge portions  26  on the outer edges of the principal portion  22 . The tapered edge portions  26  may be partially reticulated with holes, or gaps, being filled in by an adjacent spray forming pass.  
         [0037]     Referring to  FIG. 8 , an end view of the nozzle is provided to illustrate the relationship of the slit  32  in the nozzle tip  34  relative to the cylindrical opening  58  formed in the disk-shaped portion  56  of the flow restriction ring  30 . The slit  32  is preferably formed by intersecting arcuate edges.  
         [0038]     The relationship of slit  32  to the cylindrical opening  58  may be analyzed in terms of an equivalent orifice diameter (EOD). The relationship of the EOD of the cylindrical opening to the EOD of the slit and may vary depending upon the flow rate of the reactant mixture. For example, at flow rates of 15 grams per second, an area ratio of 0.52 produced an acceptable skin having a principal portion  22  with a constant thickness and tapered edge portions  26 . It is believed that an area ratio of 1:0.4 to 0.6 may also produce acceptable skins at a flow rate of approximately 15 grams per second.  
         [0039]     The flow rate may be expressed as: 
 
Q=AV 
 
         [0040]     wherein: 
        Q=the flow rate     A=the area     V=velocity        
 
         [0044]     The area of the cylindrical opening  58  in the flow restriction ring  30  is approximately twice the size of the area of the slit  32  formed in the nozzle tip  34 . The diameter of the cylindrical opening  58 , as tested, is between 0.12-0.36 inches.  
         [0045]     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.