Dispensing – Processes of dispensing
Reexamination Certificate
2000-09-01
2001-11-13
Shaver, Kevin (Department: 3754)
Dispensing
Processes of dispensing
C222S145200, C222S145500, C222S149000, C222S504000, C239S117000, C239S433000
Reexamination Certificate
active
06315161
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a method and apparatus for dispensing and applying multi-component foamable fluid plastic materials such as polyurethane foams.
DESCRIPTION OF THE PRIOR ART
Foam application systems are commercially available that apply multi-component foamable fluid plastic materials, preferably polyurethanes. The standard reactant fluids comprise a plastic material fluid component and an isocyanate fluid component bearing comparable viscosities and used in comparable ratios.
Typically, a foam application apparatus will include a cylindrical mixing chamber having separate orifi or fluid inlet openings for each reactant component and an axial passage transverse to the direction of the inlet passages for allowing the mixed or reacted fluid to exit the mixing chamber. The mixing chamber is typically mounted in a support body structure. The dimensional tolerance between the mixing chamber and valve body is made sufficiently close so that the reactant fluids cannot flow therebetween. Standard reactant fluids are generally sufficiently viscous to prevent them from flowing between the mixing chamber and valve body.
A cylindrical rod or valve needle having an external diameter nearly the same as the internal diameter of the cylindrical mixing chamber moves forwardly and rearwardly in the mixing chamber. In the forward position, the valve needles close off the fluid inlet openings to prevent any fluid from entering the mixing chamber. In the rearward position, the valve needle is retracted under hydraulic pressure to expose the inlet openings to permit their respective fluids to flow in the mixing chamber and impingement mix therein. When enough reacted fluid has been dispensed, the valve needle moves to its forward position to once again close the inlet passages and prevent reactant fluid flow into and mixing in the mixing chamber.
One apparatus of this type is disclosed in U.S. Pat. No. 4,377,256 to Commette, et al. Another is disclosed in U.S. Pat. No. 5,339,991 to Synder. One common problem that is disclosed in U.S. Pat. No. 5,339,991 is that conventional foam applications commonly seize up after a few thousand shots requiring cleaning of the valve components and mixing chamber before reuse.
Another problem has recently developed with respect to foam application guns. Recently developed chemistry using non-standard reactant fluids may also be used to make a “low MDI” plastic foam. Low MDI foam includes one reactant fluid that includes either no isocyanates or a relatively small amount of isocyanates and a second reactant fluid that includes a resin component. Some of these non-standard reactant fluids are not as viscous as the standard reactant fluids and may tend to seep and “cross-over” from one inlet opening to another between the mixing chamber and the valve needle body.
SUMMARY OF THE INVENTION AND ADVANTAGES
The invention includes a method and apparatus for dispensing and applying multi-component foamable fluid plastic materials such as polyurethane foams. The apparatus includes a mixing chamber that is defined by an axial passage in the support body structure. The mixing chamber is configured to receive reactant fluids for mixing and to allow the mixed reactant fluids to exit through an opening at an axial outer end of the axial passage. Two generally transverse fluid inlet openings are formed in a wall of the axial passage and are configured to admit reactant fluid into the mixing chamber. Two mixing chamber fluid inlets are formed in the support body structure and are configured to provide fluid communication between reactant fluid sources and the mixing chamber through the respective inlet openings. An elongated valve needle is supported in the axial passage for reciprocal longitudinal movement between forward closed and a rearward open positions. The valve needle is configured to expose the inlet openings when retracted to the rearward open position to permit the reactant fluids to flow into the mixing chamber from the respective inlet openings and impingement mix therein. The valve needle is configured to close off the inlet openings and dispense the mixed fluids from the mixing chamber through an opening at the outer end of the axial passage while being advanced to the forward closed position. The valve needle includes a first helical groove configured to purge the mixing chamber of unreacted and reacted fluids.
Unlike the prior art of record, the valve needle includes second and third helical grooves disposed generally parallel to the first helical groove in a triple-start helix configuration. As a result, when valve needle moves from the closed to the open position, only helical grooves (no circumferential grooves) move past the inlet openings in the mixing chamber. It is impossible for any two inlet openings to be connected by a fluid path until the needle is in the open position. The triple-start helical grooves also help to eliminate metal-to-metal surface area contact between the rod and the axial passage because the additional grooves reduce the amount of outer circumferential surface area that the needle presents to the axial passage. The three groove configuration also fills with hard polymer faster, more completely and more uniformly than a single or two-groove helix. This is because the configuration of each groove in the triple helix is such that each groove is presented more frequently before the inlet openings as the valve needle moves in the axial passage. Still further, the three groove configuration provides more scraping action along inner walls of the mixing chamber and across the face of the inlet openings which keeps the inlet openings free of partial obstructions.
The invention also includes a method for mixing and applying foamable resin. According to the method, the needle grooves are pre-filled with a suitable material before supporting the valve needle in the axial passage before completing the assembly of the apparatus. The grooves are pre-filled to prevent reactant fluid crossover. By sealing the grooves against leakage the pre-filling obviates the need for an end user to initially fill the grooves by taking multiple preparatory shots. This eliminates the wasted reactant fluids required to make the number of shots (approximately 80-120 shots for low MDI foam) that may otherwise be necessary to fill the grooves before the apparatus can be reliably used for its intended purpose. Without pre-filling, there is a much higher chance of cross-over occurring around the needle—especially when the gun is not used for a period of time or is left sitting still while heated and under pressure.
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patent: 5
Bezaire Leon J.
Matijega Roney J.
Snyder Robert D.
Buechner Patrick
Jesco Products Company, Inc.
Reising Ethington, Barnes, Kisselle, Learman & McCulloch, P.C.
Shaver Kevin
LandOfFree
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