Patent Application
20050218556
1. Field of the Invention
The present invention relates to an apparatus and method for spray forming a polyurethane skin to be used in manufacturing a vehicle interior component.
2. Background Art
For many years, vehicle interior parts have been formed by providing a skin formed in the shape of the interior part that is filled with foam material and may also be assembled to a structural member. Vinyl skins are formed in rotocasting operations in which liquid vinyl is poured into a closed, heated mold that is rotated to coat the mold with the vinyl composition. The vinyl composition cures as a hollow skin conforming to the mold surface. While this process has been used to form high quality parts, considerations relating to the difficulty of recycling vinyl parts and minimizing volatile organic compositions in vehicle interiors is causing original equipment manufacturers to reduce the use of vinyl parts in vehicle interiors. Polyurethane skins are being developed to replace vinyl skins in interior components. Polyurethane materials reduce the quantity of volatile organic compositions in interior parts. Rotocasting polyurethane is not favored because thermoplastic polyurethane materials that may be used are very expensive aliphatic materials.
Prior art polyurethane spray systems rely upon pneumatic mixing heads that are subject to many disadvantages and limitations. Such mixing heads are generally designed to handle two chemical components. Pneumatic mixing heads tend to malfunction when spraying higher viscosity materials. Pneumatic mixing heads may be adversely affected by the quality and quantity of compressed air that is available. Pneumatic mixing heads do not recirculate through the mix head, but through a recirculation block mounted above the mixing head. Pneumatic mixing heads are not normally capable of maintaining polyurethane constituents at the desired temperature for spray forming polyurethane skins on a mold.
There is a need for a robust mixing head that is well adapted to dispensing high viscosity polyurethane components and mixtures.
There is also a need for a mixing head that provides a more uniform spray pattern and that does not rely on external screw adjustments to seat the injection pin in an orifice.
There is a further need for a recirculation circuit that facilitates maintaining the temperature of heated polyurethane forming constituents as the material recirculates until it is introduced into the spray tool mixing head.
There is a need for a mixing head for mixing polyol and isocyanate with a pigmented polyurethane forming component.
The above problems are addressed and needs are fulfilled by Applicants' invention as summarized below.
According to one aspect of the present invention, an apparatus for spraying polyurethane is provided. The apparatus includes a plurality of supply sources containing one of a plurality of polyurethane constituents. A plurality of recirculating fluid circuits are each in fluid flow communication with one of the supply sources. A mix head is connected to each of the fluid circuits and receives from each fluid circuit one of the polyurethane constituents. The mix head has a chamber in which the polyurethane constituents are mixed to form a polyurethane mixture. A hydraulically operated valve controls the flow of polyurethane constituents to the mix head. The valve has a first position in which the polyurethane constituents flow into a mixing chamber in the mix head, and a second position in which the polyurethane constituents are recirculated through the fluid circuit without being mixed in the mixing chamber. A spray nozzle assembly dispenses the polyurethane mixture when the valve is in the first position.
According to other aspects of the apparatus of the present invention, the polyurethane constituents may be polyol, isocyanate, and pigmented polyol that are provided by separate recirculating fluid circuits. The recirculating fluid circuits may each have a separate pump for providing one of the polyurethane constituents under pressure. A liquid solvent may be supplied to the mix head to purge the polyurethane mixture from the chamber in the mix head and the spray gun when the valve is in the second position.
According to other aspects of the apparatus of the present invention, the hydraulically operated valve may have a hydraulically actuated piston that is provided with separate channels through which each of the polyurethane constituents flow when the valve is in the second position. The hydraulically operated valve may be operated by a hydraulic fluid circuit that has a reciprocating piston that shifts the valve between the first and second positions. The reciprocating piston shifts a valve spool within an elongated chamber. The valve spool and chamber are sealed relative to each other as the valve spool moves between the first and second positions. A seal may be secured to the valve spool to assure that a seal is established between the spool and chamber.
According to other aspects of the apparatus of the present invention, the spray gun may have a tubular portion and a static helical mixing vane disposed in the tubular portion that mixes the polyurethane mixture as it is dispensed. The mixture of polyurethane may be sprayed by the spray nozzle assembly on a mold to form a polyurethane skin for a vehicle interior part.
Another aspect of the present invention relates to the method that is used to form a polyurethane skin for an interior part of the vehicle. The method comprises pumping an isocyanate composition and polyol composition to the mix head. A valve is selectively opened in a first position to allow the polyol composition and isocyanate composition to be injected under pressure into a mixing chamber defined by the mix head to create a polyurethane reactant mixture. The valve is selectively closed in a second position to allow the polyol composition and isocyanate composition to be recirculated. The valve is moved by a hydraulically actuated cylinder that moves a valve element within a valve body between the first and second positions. The polyurethane reactant mixture is dispensed through a spray nozzle assembly and shaped on a mold surface to form a polyurethane skin.
An alternative embodiment of the method may be practiced wherein a pigmented polyol composition is pumped to the mix head in addition to the isocyanate and polyol constituents as described above. The three constituents are injected in a first position into the mix head under pressure to create a pigmented polyurethane reactant mixture. The valve may be selectively closed in a second position to recirculate the three constituents. The pigmented polyurethane reactant mixture is dispensed through a spray nozzle assembly and shaped on a mold surface to form the polyurethane skin with the desired pigmentation.
Other aspects of the invention as they relate to the above methods may further comprise mixing the reactants with a static helical mixing vane disposed in a tubular portion of the spray nozzle assembly. The method may further comprise spraying a solvent into the mixing chamber when the valve is in the second position to purge the polyurethane reactant mixture from the mixing chamber and spray nozzle assembly. The valve element used in the method may further comprise a piston that is provided with separate channels for each of the reactant compositions when the valve is in the second position.
These and other aspects of the invention will be better understood in view of the attached drawings and following detailed description and preferred embodiments of the invention.
Referring to
Referring to
A mixing chamber generally indicated by reference numeral 30 comprises a cavity 32 that is closed on one end by a distal end 34 of the valve piston 24. The mixing chamber 30 has an outlet 36 on the opposite end from the distal end 34 of the valve piston 24 through which a polyurethane mixture may be sprayed as illustrated by the series of arrows in
The nozzle assembly 14 includes a tubular extension 40. A helical mixing vane 42 is provided in the tubular extension 40. Polyurethane constituents flowing through the tubular extension 40 are mixed by the helical mixing vane 42 and are provided to a nozzle tip 46. The nozzle assembly 14 is detachably secured to the mix head 12 by an annular retainer ring 48 that engages a tube receptacle 50. Tube receptacle 50 receives the tubular extension 40 and retains it in a fluid flow relationship with the mixing chamber 30.
Referring to
A polyol supply 56 is illustrated in
Referring now to
Seals 72, that may be O-ring seals, are retained in annular grooves 74 formed on the valve piston 24 outboard of opposite axial ends of the channels 26 and 28.
Referring to
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.
