Rotating spray head for spray urethane

A system and method for spray application of polyurethane used to spray form an article is disclosed. A spray nozzle is rotated as the polyurethane composition is sprayed onto a mold surface to apply a swath of polyurethane to the mold surface. The spray nozzle may be of an internal mixing or external mixing type that is moved relative to a mold surface in a path to create a skin layer with multiple partially overlapping swaths being applied in multiple passes. A motor and gear drive are used to rotate the nozzle tip and associated structure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to spray forming polyurethane articles using a rotating spray nozzle.

2. Background Art

Spray forming articles with polyurethane elastomer is a relatively new process that holds much 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 a shaped polyurethane layer include instrument panel covers, console covers, inner door panels, glove box covers, floor mats, steering column covers, and knee bolsters, and the like.

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. These elaborate spray nozzle tips, in addition to being expensive, require frequent maintenance and cleaning to assure proper performance. A conical spray pattern yields 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.

In a previously filed application, applicants' assignee disclosed a method for spray application of polyurethane to form an article that includes supplying a polyurethane composition to a spray nozzle that sprays the polyurethane composition in a flat fan-shaped pattern onto a mold surface. A swath of polyurethane is applied to the mold surface as the nozzle and mold surface are moved relative to each other in a predetermined path. A skin is created by partially overlapping swaths that are applied in multiple passes of the nozzle relative to the mold. The skin layer formed has a more consistent thickness due to the flat fan-shaped spray pattern in comparison to prior art methods that employ conical spray patterns.

Even with the improvements associated with applicants' prior proposed system, the fan shaped pattern can be irregular and sensitive to the orientation of the robot arm while spraying. There is a continuing need to minimize imperfections in the sprayed coating layer and speed of application. By increasing the rate of material deposition, process cycle times can be reduced. Another aspect of the urethane spray forming process to be improved is to increase control of the spray application in undercut areas of a mold and in highly contoured areas. It would also be advantageous to reduce the difficulty of programming the robot that is used to spray the polyurethane. Finally, it would be advantageous to make the system more robust and error tolerant. To the extent that the positioning of the robot arm can be made less critical, design constraints can be broadened making more parts suitable for urethane spray forming.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to a method for spray application of polyurethane for spray forming an article. The method comprises supplying a polyurethane composition to a spray nozzle and rotating the spray nozzle as the polyurethane composition is being sprayed onto a mold surface. The nozzle and mold surface are moved relative to each other in a path to create a skin layer with partially overlapping swaths being applied in multiple passes of the nozzle relative to the mold. A skin layer is formed by the method that has a substantially constant thickness.

According to other aspects of the invention as they relate to this method, the polyurethane composition may be supplied to the spray nozzle in two separate streams that are mixed after the composition is sprayed from the nozzle. Alternatively, the method may relate to the polyurethane composition being supplied to the spray nozzle in two separate streams that are mixed in the nozzle before the composition is sprayed. The rotating step may be performed intermittently as the polyurethane composition is being sprayed onto the mold surface. The nozzle, in one embodiment, is moved by a robot during the spraying step. 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 mixing element that mixes the polyol and isocyanate prior to being sprayed by the spray nozzle.

Another aspect of the invention relates to a system for forming a polyurethane layer on a surface comprises a spray gun for spraying a liquid reaction mixture comprising polyol and isocyanate in the form of a fan shaped spray pattern onto a mold surface to apply a swath of mixture to the mold surface. A motor and drive apparatus are connected to the spray gun to rotate the spray gun as it sprays the mixture. The spray gun is moved relative to the mold surface in a path to cover the mold surface whereby a layer is formed that has a relatively constant thickness.

Other aspects of the invention as they relate to the system comprise the motor being either an electric motor or an pneumatic motor. The drive apparatus may comprise a drive gear connected to the motor and a driven gear connected to the spray gun. The drive apparatus may alternatively comprise a drive gear connected to the motor and a driven gear connected to the spray gun wherein the drive gear and driven gear are interconnected by a chain. Alternatively, the drive apparatus may comprise a drive wheel connected to the motor and cylindrical surface associated with the spray gun.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring toFIG. 1, a robot10having an external mix spray gun12is illustrated. The spray gun sprays a polyurethane material in a spray pattern14onto a mold surface16.

Referring toFIG. 2, a spray gun12of the external mix type, is attached to a rotating support structure20indicated by the circular arrow adjacent the supporting structure20. Constituents of the polyurethane mixture are combined in a mixing area22illustrated as a circular area inFIG. 2. It should be understood that the mixing area may take various shapes and configurations as a result of the high velocity flow of the atomized particles. The polyurethane is sprayed over an in-mold coating24to form a polyurethane skin26in multiple passes to provide a polyurethane skin having uniform thickness. A recess28is an example of an area of a mold that is difficult to apply a spray coating with prior art spraying systems. The rotating spray gun facilitates forming polyurethane skins in areas that are difficult to access such as the recess28. The rotating spray gun12provides a generally circular spray pattern that is more evenly distributed as a result of the rotation of the spray gun.

Referring toFIGS. 3,4and5, a spray gun12of the external mix type having an external spray tip nozzle30is shown in greater detail. The external spray tip nozzle30has a central spray port32and two inwardly directed spray ports34. The spray tip nozzle30is secured by a retainer cap36to a circular head portion38. An inner double seal ring40functions as a support and a seal between the spray tip nozzle30and head38. An outer ring seal42forms a seal between the spray tip nozzle30and head portion38. A wand46is enclosed by a rotatable sleeve48. A first fluid flow channel50is formed in the center of the wand46. A second fluid flow channel52is defined around the periphery of the central tube54that defines the first fluid flow channel50.

Bearing rings56are provided between the wand46and sleeve48to provide a bearing surface as the wand46rotates within the sleeve48. The grooves58that receive the rings56could be formed in either the wand46or sleeve48.

A motor60is provided for rotating the spray gun12. The motor60may be either pneumatic or electric. The motor60is operative to rotate drive gear62causing driven gear64that is associated with or secured to body66that may be formed as part of the sleeve48.

A housing cap68and housing base70are secured to opposite ends of the body66. An annular gap72is provided between the housing base70and body66. A circular rib guide74is disposed in the annular gap72. The body66and housing base70rotate relative to the circular rib guide74and wand46when the motor60rotates the drive gear62and driven gear64.

A circular rib anchor78is retained by a gun body cap80in a space82defined between the gun body cap80and a gun body84. A seal ring86is provided at the end of the wand46to seal between the end of the wand46and the gun body84. An annular inlet88is defined by the gun body84through which polyol is supplied to the second fluid flow channel52. A seal ring90is provided between the gun body84and central tube54. A center inlet92is provided to direct isocyanate into the first fluid flow channel50is that defined in the center of the central tube54. A hose94is connected by a quick connect96to the gun body84. A source of polyol98and a source of isocyanate100are connected to the spray gun12by the hose94so that separate streams of isocyanate and polyol may be directed to the spray gun12.

Referring toFIGS. 6 and 7, an internal mix rotating spray gun110comprising an alterative embodiment in the present invention is illustrated in detail. The internal mix rotating spray gun110has a fan spray nozzle tip112that is secured to the end of a mixing wand114. A seal ring116seals between the nozzle tip112and mixing wand114. A helical mixing element118is provided in a central bore120formed within the mixing wand114. An annular base122of the mixing wand114is adapted to be connected to a body portion124. Face seal rings126are provided in annular face grooves128to establish a seal between the annular base122and body portion124. Shaft seal rings130are provided in radial grooves132to seal the interior of the body portion124. A motor134is provided with a drive gear136that operatively engages a driven gear138that is associated with and connected to the body portion124so that the body portion124is rotated when the motor134is actuated. An end cap140secures the mixing wand114and annular base122to the body portion124. A base cap142secures an annular rib144on a stationary shaft146. The motor134rotates the body portion124and wand114relative to the stationary shaft146.

A spray gun assembly cap148having a threaded inner diameter150is used to secure the spray gun110to a gun body (not shown) that may be a two component spray gun of conventional design. A polyurethane inlet152is provided in the center of the stationary shaft146. Polyol and isocyanate are supplied through the polyurethane inlet152. A seal ring154is received in a radial groove156to form a seal between the stationary shaft146and the two component spray gun.

FIG. 7illustrates the structure of the mixing wand114and helical mixing element118. The helical mixing element118is received within the bore120formed in the center of the mixing wand114.