Method and apparatus for spray applying fiber-reinforced resins with high ceramic fiber loading

One aspect of the present invention is a spray gun adapted for spray-applying fiber-reinforced resins with ceramic fiber loadings of at least about 55 wt-%. Such novel spray gun has an inlet for admitting the fiber-reinforced resin; an air inlet for atomizing the fiber-reinforced resin; a catalyst inlet; and an outlet for expelling catalyzed fiber-reinforced resin from the spray gun. The spray gun also has a straight-line delivery channel in fluid communication with the resin inlet, the catalyst inlet, and the outlet. A flow actuator is provided for selectively actuating admission of the fiber-reinforced resin and the catalyst into the spray gun. The resin inlet and the catalyst inlet are disposed for admitting resin and catalyst, respectively, in line into the straight-line delivery channel. The air inlet is disposed for admitting air into the straight-line delivery channel at an acute angle with and in the direction of flow in the straight-line channel and is located after both the resin inlet and the catalyst inlet. Another aspect of the present invention is an apparatus for spray-applying fiber-reinforced resins with ceramic fiber loadings of at least about 55 wt-%. Such apparatus includes the novel spray gun, a tank for housing a fiber-reinforced resin; a pump for pumping fiber-reinforced resin from the resin tank to the spray gun resin inlet; a tank for housing catalyst for the resin; a pump for pumping catalyst from the catalyst tank to the spray gun catalyst inlet; and an atomizing air supply in communication with the spray gun air inlet.

CROSS-REFERENCE TO RELATED APPLICATIONS 
None 
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
Not applicable. 
BACKGROUND OF THE INVENTION 
The present invention relates generally to fiber-reinforced molding of 
parts and more particularly to spray equipment for spray-applying 
fiber-reinforced heat-curable resins containing high ceramic fiber 
loadings. 
In the manufacture of a wide variety of fibrous-reinforced parts (e.g., FRP 
or fiber glass reinforced parts), it would be desirable to spray apply a 
unsaturated resin (catalyzed, heat-curable, unsaturated polyester resin) 
which would contain a high loading (e.g., say, 55% to 75% by weight) of 
reinforcing fiber (e.g., ceramic fiber like wollastinite fibers of 0.0017 
to 0.0059 mm in average particle diameter with aspect ratios of from about 
5 to 17). Unfortunately, conventional spray equipment will not properly 
spray such resins with such high fiber loadings. The spray equipment, 
especially the spray guns, become plugged easily by the ceramic fibers 
which makes down time of the equipment particularly troublesome at 
commercial operations. It is troublesome enough to spray conventional 
catalyzed unsaturated resins because of premature gelation problems, 
cleaning of the equipment during down time cycles, and the like. To add a 
high loading of ceramic fiber means that the equipment would have to spray 
a resin mix having the consistency of oatmeal, and a mix that is quite 
abrasive due to the ceramic fiber content. 
One approach to solving the problem of air void surface defects in FRP 
parts, as proposed in U.S. Pat. No. 4,568,604 (expressly incorporated 
herein by reference), involves the spraying of ceramic fiber-loaded resins 
over a layer of gel coat which covers the mold. Such a process is limited 
in its ability to spray high loadings of ceramic fiber (a mixture of 
calcium silicate and mica). Still, the need for being able to spray resins 
with high ceramic fiber loadings is underscored by this patent. 
The present invention addresses the foregoing problems associated with 
spray-applying high fiber loaded, thermally-curable, catalyzed resins used 
in molding of fiber reinforced parts by use of uniquely designed spray 
equipment. 
BRIEF SUMMARY OF THE INVENTION 
One aspect of the present invention is a spray gun adapted for 
spray-applying fiber-reinforced resins with ceramic fiber loadings of at 
least about 55 wt-%. Such novel spray gun has an inlet for admitting the 
fiber-reinforced resin; an air inlet for atomizing the fiber-reinforced 
resin; a catalyst inlet; and an outlet for expelling catalyzed 
fiber-reinforced resin from the spray gun. The spray gun also has a 
straight-line delivery channel in fluid communication with the resin 
inlet, the catalyst inlet, and the outlet. A flow actuator is provided for 
selectively actuating admission of the fiber-reinforced resin and the 
catalyst into the spray gun. The resin inlet and the catalyst inlet are 
disposed for admitting resin and catalyst, respectively, in line into the 
straight-line delivery channel. The air inlet is disposed for admitting 
air into the straight-line delivery channel at an acute angle with and in 
the direction of flow in the straight-line channel and is located after 
both the resin inlet and the catalyst inlet. 
Another aspect of the present invention is an apparatus for spray-applying 
fiber-reinforced resins with ceramic fiber loadings of at least about 55 
wt-%. Such apparatus includes the novel spray gun, a tank for housing a 
fiber-reinforced resin; a pump for pumping fiber-reinforced resin from the 
resin tank to the spray gun resin inlet; a tank for housing catalyst for 
the resin; a pump for pumping catalyst from the catalyst tank to the spray 
gun catalyst inlet; and an atomizing air supply in communication with the 
spray gun air inlet. 
Advantages of the present invention include the ability to spray apply 
curable resins that contain from between about 55 wt-% and 75 wt-% ceramic 
fiber. Another aspect of the present invention is spray equipment that can 
be cleaned readily during down time cycles. A further advantage of the 
present invention is spray equipment that does not become easily plugged 
by the high ceramic fiber content in the resin being sprayed. A yet 
further advantage of the present invention is spray equipment that can 
deliver a bead of high ceramic fiber content resin by merely discontinuing 
the flow of atomizing air. These and other advantages will become readily 
apparent to those skilled in the art based on the disclosure herein.

DETAILED DESCRIPTION OF THE INVENTION 
A wide variety of molding processes can use the inventive spray gun and 
system to advantage. These molding processes include, inter alia, open 
molding, resin transfer molding (RTM), press molding, thermoplastic 
injection molding, blow molding, shrink fixtures, scrimp molding, and the 
like. These molding processes are used to manufacture a wide variety of 
parts including, inter alia., transportation components (e.g., van running 
boards, van tops, automobile bodies, truck caps, deck lids), architectural 
components (e.g., shower stalls, tanks, cowlings), boat hulls, pultrusion 
parts, heat shields, abrasion resistant surfaces, BMC (bulk molding 
compounds) parts, SMC (sheet molding compounds) parts, and the like. 
Ordinarily, resin impregnated fiber is placed in a mold which is heated, 
often under pressure, to form the ultimate part. On occasion, it would be 
useful to be able to spray unsaturated resin onto/into a fiber lay-up; 
however, heretofore such spray operation was limited to the spraying of 
resins containing a low loading of ceramic fiber. With the present 
invention, however, spraying curable (catalyzed) resins containing a high 
loading of ceramic fiber now is possible. 
Referring to FIG. 1, gun 10 is seen to be composed generally of handle 
assembly 12, mixing tip 14, and valve body 16. Handle assembly 12 is 
composed of handle 18, trigger 20, and trigger guard 22. Valve body 16 has 
resin inlet 24 and catalyst inlet 26 (see FIGS. 2 and 3) through which 
fiber-reinforced resin and catalyst, respectively are admitted into gun 
10. A unique design feature of gun 10 is the flow path for resin and 
catalyst. Work on the present invention revealed that the resin flow path 
for resins with high ceramic fiber loadings could not have any sharp 
bends; otherwise, the reinforcing fiber would agglomerate causing plugging 
problems. Thus, the flow path of resin through gun 10 commences with inlet 
24 which admits resin inline with a straight flow path which has been 
constructed into gun 10. This flow path commences in valve body 16 and 
continues into mixing chamber 28, and thence into mixing tip 14. Catalyst 
inlet 26 similarly is parallel to the resin inlet 24 in establishing a 
similar co-current in-line flow path. 
Atomizing air line 30 feeds atomizing air (atomizing gas generally, 
although air is predominantly used in industry) into gun 10 for mixing 
with the catalyst/resin mix already established in valve body 16. Work on 
the present invention also revealed that if atomizing air were admitted at 
a 90.degree. angle into the resin/catalyst flow path that agglomeration of 
the ceramic fiber with consequent plugging also would occur for resins 
highly loaded with ceramic fiber. Thus, the angle of entry of atomizing 
air into gun 10 via line 30 is at an acute angle with, and in the same 
direction as, the flow of resin/catalyst in gun 10. 
Finally, the resin flow path in gun 10 encounters mixing tip 14 which is a 
typical in-line spiral mixer (e.g., TAH static mixer). Finally the 
catalyzed resin is sprayed from gun 10 via nozzle which terminates mixing 
tip 14. It will observed, however, that a straight flow path has been 
established in gun 10 from entry of resin into gun 10 via inlet 24 to its 
expulsion from gun 10 via nozzle 32. While mild bends in the flow path 
probably could be tolerated, sharp bends are to be avoided in order to 
avoid plugging of the gun by the high ceramic fiber loadings contained in 
the resin fed to gun 10. Finally, air line 34 is activated by trigger 20. 
Air in line 34 activates valve body 16 for admitting resin and catalyst to 
flow into valve body 16 and through gun 10 for spraying. One 
commercially-available spray gun that has been modified in accordance with 
the precepts of the present invention is a Venus Pro Gun (Venus-Gusemer). 
Gun 10 is supplied resin, catalyst, and air from an apparatus such as is 
illustrated in FIG. 4. All of the equipment necessary for spraying resins 
containing a high content of ceramic fiber conveniently can be mounted on 
wheeled cart 36. This makes the apparatus portable in a plant so that 
molds in different locations and in different parts lines can be serviced 
by the same spray equipment. This flexibility makes the inventive 
equipment even more useful in commercial operations. 
Resin tank 38 preferably is made from stainless steel and is fitted with 
lid 40 which is attached to resin tank 38 by lid clamps 42a-f, and resin 
tank gauge assembly 44. Resin tank 38 is pressured by air (from a source 
not shown) via manifold 64 (described later) to, say, about 20 psi. Resin 
mix housed in resin tank 38 is withdrawn via 2 in line 46 through ball 
valve 48, tee valve 50, pump tee 52, and out valve 66 for feeding to gun 
10 (via a line not shown). Resin is pumped to gun 10 via pump assembly 56 
which can be set at, say about 25 psi, for delivering the resin mix to the 
gun at, say, about 575 psi. Ball valve 54 completes the piping for resin 
from tank 38. 
Cart 36 also is fitted with catalyst bottle 58 which is fed via catalyst 
pump 60 to gun 10 via a line not shown. Slave assembly 62 allows for quick 
adjustment of the catalyst level fed to gun 10 for the resin mix. Air 
manifold 64 (air lines therefrom not shown) distributes air to resin tank 
38, as well as to solvent flush tanks 68 and 70 (described below), and to 
pump assembly 56 which is an air-activated pump. 
The solvent flush system incorporated into the inventive spray apparatus 
system involves solvent from solvent flush tank 68 (similar in 
construction to resin tank 38) being fed to the valve on tee valve 50. 
When spraying of the resin mix is terminated, in order to prevent the 
resin from hardening in gun 10, solvent from tank 68 can be fed to gun 10 
via resin inlet 24 by shutting valve 66 and opening valve 50. Atomizing 
air to gun 10 via air inlet 30 can be maintained along with the flow of 
solvent to effectively clean gun 10. In this regard, resin flush tank 70 
(similar in construction to resin tank 38) is piped to pump solvent 
through tank 38 to flush it during down-time cycles of use of the 
inventive spray system. 
Cart 36 also can be fitted with a tank for a blowing agent (conventional 
nitrogen blowing agent, for example, such as Chrom-Tek Alcel blowing 
agent, Chrom-Tek, Collierville, Tenn.), slave assembly (like slave 
assembly 62), pump, and appropriate lines for incorporation of a blowing 
agent into the resinous composition sprayed by gun 10. 
Suitable resins for use with the inventive spray system are conventional 
for the molding art and include, for example, unsaturated polyester resins 
admixed with styrene and suitably formulated depending upon the part being 
produced, the type of reinforcement, and like factors well known to those 
skilled in this art. The use of peroxide and like catalysts also is well 
known in this art as appropriate solvents. The reinforcing agents also are 
known and include, for example, calcium silicate (e.g.,. wollastinite) 
admixed with mica. 
As noted above, the inventive spray system can be used to spray 
fibrous-reinforced curable resin systems in conventional spray patterns, 
such as described in U.S. Pat. No. 4,568,604, cited above. Alternatively, 
the resin system can blown by use of a blowing agent to achieve a 
volumetric expansion and to speed cure of the resin due to the presence of 
nitrogen gas. Finally, with the atomizing air spray inactivated, a bead of 
the resin matrix can be expelled from the gun for use, for example, to 
fill sharp corners, or for bonding and bedding parts in assembly. 
While the inventive spray system initially was designed for the rigors of 
spraying resins with high ceramic fiber loadings, it will be appreciated 
that it could be used to spray syntactic foams, bondo-type products, and 
like products. Thus, the ability of the inventive spray system to handle a 
wide variety of products adds to its flexibility and value in commercial 
settings. It will appreciated that the inventive spray gun and apparatus 
can be modified in accordance with the precepts of the present invention 
and still be within the scope of the present invention.