Patent Application
20050274821
1. Field of the Invention
The present invention relates to a heated spray apparatus for a reactant mixture used to form an article.
2. Background Art
Spray applicators are used to apply paint and other fluids. Some spray applicators are adapted to spray multi-component reactant polymeric material mixtures for various purposes. For example, polyurethane skins may be formed in a spray-forming process to form vehicle interior parts. Polyurethane skins are formed and may be then foam backed and/or assembled to inserts to form finished interior parts.
To form satisfactory parts that meet vigorous inspection requirements, there is a need to apply the reactant mixture used to form the skin with a substantially even surface finish and uniform spray pattern. The uniformity of a sprayed part or skin is also impacted by the speed of the reaction rate and contour of the mold used to form the part. Uneven spray patterns tend to create irregularities in the shape or surface finish of a product made with the spray-forming process. Slow reaction rates for reactant mixtures can lead to unacceptable surface imperfections such as runs, “finger marks” and heavy deposits of material at the ends of a spray-forming stroke. Uneven mold surfaces, such as mold surfaces having undercuts or narrow portions can also result in thin areas and excessive accumulation of material in products formed by the spray forming process.
Reactant mixtures may also be adversely impacted by moisture, especially while the reactant mixture is undergoing its intended chemical reaction. For example, in the formation of polyurethane skins, moisture can cause bubbles which may become entrapped in the finished product creating surface imperfections.
In some polyurethane spray-forming operations, component material heaters may be provided to heat the components of the reactant mixture prior to mixing. After the reactant components are mixed, they are provided to a spray applicator that does not have a heat source. Cooling of the reactant mixture can cause poor atomization and inconsistent results if the temperature varies. The reactant mixture is typically sprayed on a heated mold to accelerate the reaction.
These and other problems are addressed by applicants' invention as summarized below.
According to one aspect of the present invention, a spray applicator for spraying a polyurethane composition in a spray-forming process is provided. The spray applicator includes a spray tool and a jacket partially enclosing the tool that is provided with a heated gas. The spray tool comprises an elongated tubular member having at least one opening at a receiving end and at least one opening at a dispensing end. Polyurethane forming components are supplied to the receiving end of the tubular member and dispensed through the dispensing end. A nozzle tip is secured to the dispensing end for spraying polyurethane forming components as a polyurethane mixture. The jacket may partially enclose the elongated tubular member of the spray tool. A source of a heated gas provides heated gas to the jacket through a port. The heated gas is ported from the jacket through ports that are adjacent the nozzle tip to direct the heated gas to impinge upon the polyurethane mixture as it is sprayed.
According to other aspects of the invention, the jacket may be a tubular body having a first end that is disposed near the receiving end of the tubular member and a second end that is disposed near the dispensing end of the tubular member. A back end cap may be secured to the first end of the jacket and to the receiving end of the tubular member to form a seal with the tubular member. A front end cap may be secured to the second end of the jacket and the dispensing end of the tubular member to form a seal with the tubular member. The front end cap may have an annular nozzle that defines ports for dispensing the heated gas from the jacket. The inlet port through which heated gas is provided to the jacket may be a side port that receives heated gas from the source of heated gas through a conduit.
According to another aspect of the present invention, a heater for a spray applicator for a reactant mixture that is sprayed by the applicator through a nozzle having a nozzle tip is provided. The heater includes a jacket defining an enclosed space and an inlet through which heated gas is supplied and an outlet through which the heated gas is released after heating the reactant mixture in a cavity formed in the spray applicator. A heated gas dispensing port is provided in the jacket that directs the flow of heated gas around the nozzle tip that may modify the reactant mixture spray pattern after the reactant mixture is sprayed from the nozzle tip.
According to another aspect of the present invention, a method of spray forming an article with a reactant mixture is provided. The method includes supplying a multi-part reactant mixture to a spray applicator. Heating the reactant mixture to form a heated reactant mixture while in the spray applicator by supplying a heated gas to an enclosure that at least partially encloses the spray applicator. The heated reactant mixture is then dispensed from the spray applicator in a spray pattern. The spray pattern of the heated reactant mixture is shaped by directing the heated gas to impinge upon the heated reactant mixture as the heated gas is ported from the enclosure.
According to other aspects of the method of the present invention, the step of dispensing the heated reactant mixture may further comprise spraying the heated reactant mixture through a nozzle. The step of spraying the spray pattern may further comprise providing a plurality of ports in an annular ring disposed about the nozzle. Alternatively, or in addition to the plurality of ports, the step of shaping the spray pattern may comprise providing an annular opening between an annular ring and the nozzle. The method may be practiced using heated air, nitrogen, or carbon dioxide as the heated gas.
These and other aspects of the present invention will be better understood in view of the attached drawings and detailed description of the invention provided below.
Referring to
Referring to
The jacket 14 comprises a tubular body 38 that is provided with an annular nozzle 40. The annular nozzle 40 is also illustrated in
While gas directing ports 44 may be used to direct the heated gas to impinge upon the polyurethane mixture 18 spray it is also possible that heated gas may be discharged from the jacket 14 through a gap defined between the spray tip 36 and central bore 52 of the annular nozzle 40. It is believed that hot gases flowing through the ports 44 may function to increase the width of the fan spray especially at high pressures while air flowing between the spray tip 36 and annular nozzle 40 may tend to decrease the width of the fan pattern of the polyurethane mixture 18.
The heated gas may be hot air that functions to shape the polyurethane mixture 18 spray and also may speed the reaction of the polyurethane mixture by both heating the polyurethane mixture in the static mixing tube 30. The heated gas may also speed the polyurethane curing reaction by heating the polyurethane mixture directly after it is emitted from the display tip 36. Alternatively, nitrogen may be used to perform a similar function and may also function to shield the polyurethane mixture 18 from ambient and that may include substantial humidity. As a third alternative it may be possible to inject steam as the heated gas into the jacket. The steam may be exhausted through the ports 44 or through other ports (not shown) that may direct the steam away from the polyurethane mixture spray.
A back end cap 56 is provided with a seat 58 and body portion 60. The seat 58 is assembled against the opposite end of the tubular body 38 from the annular nozzle 40. The body portion 60 is supported and centered by means of one or more set screws 62 relative to the tubular body 38. Each set screw 62 is received within a threaded hole 64 that holds the back end cap 56 in a concentric relationship relative to the tubular body 38. An attachment ring 66 is used to secure the back end cap 56 to the opposite end of the tubular body 38 from the annular nozzle 40. The attachment ring 66 is secured to a threaded end 68 of the tubular body 38. The tubular body 38 extends through a central bore 70 through the end cap 56.
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.
