Agitating – Having specified feed means – Impinging jets
Reexamination Certificate
1998-04-10
2003-01-07
Cooley, Charles E. (Department: 1723)
Agitating
Having specified feed means
Impinging jets
C366S304000, C422S133000
Reexamination Certificate
active
06502978
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process and apparatus for producing a polyurethane mixture for use in manufacturing structural panels or molded pieces such as, for example, door panels for automobiles or other vehicles and the like.
2. Description of the Related Art
Inert filler material, such as reinforcing fiber, is often used in the production of structural panels or, more generally, molded pieces of reinforced polyurethane material. Inert filler material improves both the rigidity and the mechanical properties of molded pieces of reinforced polyurethane material and structural panels.
For the purposes of the present invention, the term “filler” is understood to mean any solid, inert and fluidizable material, including also any material which can be transported by an air or gas flow. Such filler material can be used for filling and reinforcing purposes and can be suitably pretreated waste material. The filler material may therefore be in the form of powder, granulates, fibers of various lengths, continuous fibers, or any other suitable material which may be fluidized by an air flow, such as natural or synthetic fibers, a finely ground synthetic material, or recycled foams, finely chopped wood, milled cork, sawdust or the like.
For the purposes of the present invention, the term “long fibers” is understood to mean fibers whose length is equivalent to or greater than 3-5 mm, up to several centimeters or more, not excluding the use of continuous fibers.
When fillers are used in molded products, there is often a problem in obtaining an adequate mixture of the chemical reactants with the filler material, especially where the filler material is long or fragile. GB-A-1,245,216 and U.S. Pat. No. 4,397,407 both discuss methods of embedding a fluidizable filler material into formable mixtures of reactive chemical components.
In GB-A-1,245,216 filler material of reinforcing fibers is fed directly into a mixing chamber. The reactive chemical components are injected into the mixing chamber at right angles to the reinforcing fibers as they flow through the mixing chamber.
This process is unsatisfactory particularly where the filler material comprises long or very long fibers, fed in large amounts. The air flow transporting the filler, and the filler material itself, prevent close contact and homogeneous mixing of the reactive chemical components with the filler. Consequently, the resulting molded product contains defects which makes it commercially unacceptable.
U.S. Pat. No. 4,397,407, in contrast, describes a process where a foamable mixture of reactive chemical components is first prepared in a separate high-pressure mixing chamber and then fed by a long duct into an annular chamber where the reactive chemical mixture is blended with a filler, such as a granular material or short reinforcing fibers. The feeding duct leads to one side of the annular chamber, opposite to a discharge duct, and is formed by a movable tubular element which is connected to the mixing chamber by an additional channel.
This procedure also leads to inadequate mixing of the fillers with the reactants. In fact, when the reactive liquid mixture comes into contact with the flow of fibers or filler material, the reactive liquid mixture has lost most of its turbulence and kinetic energy inside the long feeding duct. By the time the reactants and the filler are combined, they have both assumed a substantially parallel flow.
The mixing procedure described above is also unsatisfactory where the filler is composed of a delicate material, such as glass fibers, which require simple, linear paths without pronounced curves and deviations.
U.S. Pat. No. 4,332,335, the complete disclosure of which is incorporated herein by reference, describes a head for mixing and ejecting reactive liquid components. The device described therein features a small mixing chamber separate from the discharge duct in which mixing takes places under high turbulence condition so as to prevent problems arising from imperfect mixing of the reactive liquid components. In the use of this mixing head the flow of the mixture is directly injected into a closed cavity of a mold or poured into an open mold by reciprocating the mixing head.
GB-A-1,579,543 and WO-A-96/35562 describe other apparatus where a tubular flow of liquid polyurethane material passes through an annular duct and comes into contact outside of that duct with reinforcing fibers axially flowing through a feeding channel concentrically arranged to the annular duct.
In particular, WO-A-96/35562 (“WO'562”) describes a device for the production of molded pieces of formable synthetic material containing long reinforcing fibers and suggests that a high-pressure mixing head can be used for the production of polyurethane materials. In WO'562 the polyurethane mixing chamber is connected to an annular discharge duct via an intermediate duct, so that the reactive polyurethane mixture is separately prepared and fed into the discharge duct in the form of a tubular flow. The tubular flow of reactive polyurethane mixture then comes into contact with the fiber reinforcing material.
According to the examples of
FIGS. 1 and 2
of WO'562, filler reinforcing fibers are fed into the discharge duct through a separate pipe member which coaxially extends along and beyond a cleaning member reciprocating inside the annular duct to discharge the mixture.
The use of a movable separate cleaning member to feed the reinforcing fibers may severely limit the performance of this type of apparatus, since the tubular cleaning member comprises inner and outer surfaces adhering to the cylindrical surfaces of the annular discharge duct. These surfaces are completely wetted by the polyurethane mixture during each supply step. The film of the mixture remaining between the interfaces thus tends to cause the cleaning member to adhere strongly to the double surface of the annular duct thereby completely blocking movement of that cleaning member. To avoid this blocking problem, a large hydraulic cylinder must be used for the cleaning member. This hydraulic cylinder must be able to exert a strong enough force to release the cleaning member during its rearward movement. The necessity of using a hydraulic cylinder with these capabilities increases the weight of the entire mixing apparatus and makes reciprocation of the mixing apparatus over the cavity of a mold more difficult.
Furthermore, given the fact that the adhesion forces between the contacting surfaces of the discharge duct and the cleaning member, with a length equal to or slightly more than five times its diameter, exceed the tensile stress of steel, it must be concluded that the dimensions of the resistant cross-sections of the cleaning member must be largely increased in order to prevent the tubular cleaning member and the fiber feeding pipe member from breaking or becoming damaged.
Finally, the use in WO'562 of an intermediate connecting duct between the mixing chamber and the annular duct discharging the polyurethane mixture dampens the flow of the polyurethane mixture thereby causing the reinforcing fibers to not be effectively mixed and homogeneously wetted with the reactant mixture.
Furthermore, the intermediate connecting duct will require its own cleaning member and corresponding hydraulic operating cylinder.
All these factors lead to complications in designing mixing apparatus and considerably increase the weight and dimensions of the apparatus itself.
Although WO'562 suggests that the design of the apparatus could be simplified by connecting the mixing chamber directly to a discharge duct, into which the pipe member for feeding the reinforcing fibers extends, this design would still suffer from the drawbacks discussed above.
WO'562, therefore, fails to disclose a suitable, lightweight apparatus design which would allow for improved wetting of fillers and operating conditions. The general teaching of WO'562 is limited to providing a separate, centrally located pipe for feedin
Bonansea Alberto
Fiorentini Carlo
Afros S.p.A.
Cooley Charles E.
Shook Hardy & Bacon LLP
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