The present invention generally relates to dispensing system for making, mixing and dispensing reactive chemical foam compositions for a number of end use applications. More particularly, it relates to a new and improved hand held gun and solventless dispensing system for consistently and repeatedly mixing and dispensing substantially uniform thermal insulation grade polyurethane foams characterized by extended, substantially leak-free service life.
Reactive chemical foam compositions, such as curable polyurethane foams, are presently well known and used in a number of different applications. The curable foam compositions typically comprise a two-part composition and, in the case of polyurethane foams, one part of the composition includes a polyol component and the other part includes an isocyanate component. Chemical foaming agents, curing agents, catalysts or accelerators, as well as other modifying additives, may be incorporated in one or both of the component parts. These two-parts of the foaming composition are separately stored in different containers until use.
For use, the two parts of the composition are rapidly mixed together. A rapid cross linking reaction and foam expansion commences which ultimately yields a low density, but relatively high load bearing urethane rigid foam. Expanding chemical foams are useful in such applications as thermal insulation, in floatation, in coatings and, more recently, the foams have been used in the specialty packaging industry. In the thermal insulation field, the dispensed cured foam must reflect certain desired thermal insulation values and other physical properties. The precise insulation value (K factor) imparted by the foam is directly dependent on the exact chemical composition of the dispensed foam. The mixing of the polyol and isocyanate components must occur at a proper flow ratio and mix under rapid and sufficient impingement mixing conditions for a final acceptable product to be obtained. In the past, particularly in the precise field of building thermally insulated containers for refrigeration units or shipping containers, foam components were dispensed using static mixing equipment. The static mixers relied upon dangerous organic solvents such as methylene chloride to rinse and flush the dispensers in use. Nowadays the environmental hazards of using these solvent materials renders static mixers no longer suitable for commercial thermal insulation contexts.
More recently, the urethane components including the resin or polyol component and the isocyanate component are stored under pressure in containers which are attached to solventless hand held impingement mixing and discharge guns by means of various hoses and couplings. The guns include a trigger operated dispenser valve designed to permit the two-parts of the composition to flow through the hoses and into a mixing chamber wherein the products are rapidly mixed to form a reactive and expanding chemical foam composition which exits through a foam discharge nozzle or opening. In prior art guns, the component delivery systems extending from the pressurized storage tanks into the dispenser module of the gun are typically multi-part systems and the potential for leakage at every joint therealong exists in the high pressure impingement mixing environment.
In these dispensing guns, the components are mixed by direct or indirect impingement with each other under conditions of high pressure to ensure thorough mixing. The design of the discharge valves and nozzles has become a matter of concern in the art. The component parts of the foam composition are highly chemically reactive and begin to form cured polymeric products within a matter of seconds. Premature leaking and mixing of the components within the dispensing nozzles is a serious and major concern because leakage results in undesirable curing in the nozzle causing blockage and damage to the nozzles in use. As a result, the nozzles have to be frequently replaced at considerable expense. Providing adequate seals within the nozzle assemblies in the high pressure environment has been another major problem to those in the art.
Prior art foam dispensing guns are known, for example, from U.S. Pat. No. 4,469,251, U.S. Pat. No. 4,568,003 U.S. Pat. No. 4,993,596 and from copending application Ser. No. 777,802, filed Oct. 17, 1991, now U.S. Pat. No. 5,180,082. In accordance with these prior dispensing gun arrangements, a detachable dispensing module includes a mixing chamber defined in a central bore within a polymeric insert. Typically, the polymeric insert is formed of a TEFLON.RTM. material because the reactive foam composition and its components are not adherent to the TEFLON.RTM. surfaces along the interior of the bore.
More particularly, the TEFLON.RTM. insert has a central bore extending longitudinally therethrough. A plurality of openings extend through a sidewall of the insert in communication with the bore for supplying the organic resin and the isocyanate components into the mixing chamber. A valving rod is provided in a slidable interference fit within the bore to control the flow of organic polyol resin component and isocyanate component from the side openings into the mixing chamber and discharge of the foam therefrom. Although the inserts exhibit non-adherent surface characteristics, TEFLON.RTM. materials are notorious for suffering from hysteresis or cold flow dimensional instability. Cold flow of the TEFLON.RTM. material causes a distortion or a change in the critical dimensions of the central bore and the side openings of the insert. Over time this often results in a loss of the interference fit between the valving rod and the insert. More particularly, with each activation of the valving rod, a minor film of foam product and components coats the rod. As the coating builds up on the rod, the effective diameter of the rod increases. The foam build up on the rod increases the stresses on the insert in use, leading to cold flow deformation, loss of tolerances and a loss of sealing between the rod, the core aperture and the side openings in the dispenser module. This results in cross-over contamination and blockage failures in the gun. As a result, the ability of the valving rod to effectively seal the openings to thereby prevent leakage of the reactive components into the mixing chamber is lost. Cross-overs, blockage and leakage ultimately cause obstruction within the mixing chamber which renders the dispensing module generally inoperable.
In an effort to overcome the tendency of the valving inserts to undergo cold flow deformation with a consequent loss in sealing and usefulness, conventional dispenser cartridges or modules have been provided with means for applying a constant axial and radial compressive load against polymeric insert member. Applying constant radial and axial loads on the insert tends to reduce some of the cold flow induced failures of the prior art nozzles. Applying a constant radial and axial load increases frictional forces developed between the valve insert and the valving rod which tends to increase the residual stresses on the insert responsible for cold forming. Presently, the frequency of failure is still undesirably high in view of the expense associated with replacement and repair of the mixing chamber/dispensing modules. For example, a typical commercial impingement mixing hand held foam gun may generally only be subjected to approximately 2,000 to 3,000 dispensing activation cycles before module failure is experienced. More importantly, the prior art impingement mixing guns and dispenser systems are not presently capable of consistently providing the repeatable controlled flow of component materials required to consistently meet the narrowly drawn thermal insulation rating performance criteria for modern thermal insulation uses.
Accordingly, to overcome the disadvantages of the prior art dispensing guns, it is an object of the present invention to provide a new and improved foam dispensing gun including a dispenser module characterized by prolonged or extended use lives of more than 20,000 activation/dispense cycles.
It is another object of the present invention to provide a new and improved solventless, flush-free dispenser system for thermal insulation grade foam dispensing applications.
It is a further object of the present invention to provide a new and improved hand held dispenser gun including flow controlling means to provide precise chemical metering in conjunction with matched pressure-balancing dispensing modules having carefully specified dimensions for thorough mixing to afford reliable dispensing of substantially uniform thermal insulation grade foam products.
It is another object of the present invention to provide a new and improved dispenser gun for foam compositions including new and improved unitary socket members to reduce possibility for leakage in use.
It is still a further object of the present invention to provide a new and improved foam dispensing gun including a unique cartridge mixing chamber to assure product consistency at various selected pounds per minute throughput values.
It is a further object of the present invention to provide a double acting, double power air-cylinder actuator system for moving the valving rod between its open and closed positions.
It is still another object of the present invention to provide a new and improved dispenser module for a foam dispensing gun adapted to receive a forward foam discharge guide including means for introducing a blast of air under pressure into the discharge guide behind a slug of dispensed foam to urge substantially all of the dispensed foam out of the discharge guide, to thereby purge the guide for the next shot of dispensed foam.