Apparatus For Ejecting A Mixture Of Liquids

Abstract

Two mutually reactive liquids, such as the components of a polyurethane foam, are mixed together and ejected onto a substrate by means of apparatus that pumps the liquids separately and remotely mixes them only at the last moment. Heretofore, the liquids were separately pumped by means of parallel reciprocating proportioning pumps to which the liquids are fed under pressure; and as a result of this feed pressure the outlet pressure of the pumps varied with respect to the direction of stroke. By rearranging the pumps in tandem opposed relation, and driving them by a constant pressure motor such as a double-acting fluid motor, a counterbalancing effect is created which effectively reduces the pressure variation as the stroking action reverses.

Description

The present invention relates to apparatus for ejecting a mixture of liquids, more particularly a mixture of mutually reactive liquids such as those that form a foam on a substrate and that cure by reacting with each other, for example, the components of a polyurethane foam and elastomeric coatings.

Such mixtures of liquids are ejected from a mixing chamber under pressure onto a substrate, for example by apparatus such as is disclosed in Gusmer U.S. Pat. Nos. 2,890,836 and 3,263,928. As the liquids are highly reactive with each other, they cannot be mixed together in the apparatus until the last possible moment, or else they will react in the apparatus and clog the apparatus. Therefore, as the mixture must be ejected under pressure, it is necessary to pump the mutually reactive liquids to elevated pressure by separate pump means, the reactive liquids following generally parallel flow paths from separate sources of the respective liquids to the mixing chamber from which they are ejected onto the substrate.

The proportion of the liquids in the mixture that is ejected must be maintained constant and must be closely controlled. Accordingly, it is necessary carefully to regulate the quantity of each of the liquids that is pumped to the mixing chamber; and for this purpose, proportioning pumps of the reciprocating piston type are often used, the valves of which pumps are arranged to create pumping action when stroked in either direction, thus providing continuous flow. Because the pumps are bifunctionally used as a measuring device, it is necessary to prevent cavitation; therefore the pumps must themselves be pressure fed.

The feeding of the proportioning pumps under pressure, however, gives rise to a problem: During the refill stroke of the proportioning pump, the feed pressure to the pump will add to the outlet pressure of the pump; while during the displacement stroke of the proportioning pump, the feed pressure becomes nullified by the closing of the inlet valve. There is thus a fluctuating variation in the outlet pressure of the proportioning pump, which in magnitude, by virtue of the mechanical design of the pump, actually is multiplied to twice the feed pressure to the proportioning pump.

Accordingly, it is an object of the present invention to provide such apparatus in which the outlet pressure of the proportioning pumps tends to be much more uniform than heretofore.

Another object of the present invention is the provision of such apparatus which will be relatively simple and inexpensive to construct, easy to operate, maintain and repair, and rugged and durable in use.

Briefly, the objects of the present invention are achieved by coupling the two proportioning pumps in opposed tandem relationship and driving them by a single double-acting fluid motor. Quite unexpectedly, it has been found that the undesirable pressure fluctuation at the outlet at both proportioning pumps is thus greatly reduced and under certain circumstances virtually eliminated.

Other objects, features and advantages of the present invention will become apparent from a consideration of the following description, taken in connection with the accompanying drawing, which is a schematic view of apparatus according to the present invention.

Referring now to the drawing in greater detail, there is shown apparatus according to the present invention for ejecting a mixture of liquids, comprising an ejection head 1 in the form of a barrel 3 with an elongated cylindrical mixing chamber 5 therein that is open at its discharge end, that is, at its right hand end as seen in the drawing. A pair of opposed inlets 7 and 9 extend through the side walls of barrel 3 and open into chamber 5 substantially tangentially of chamber 5. A plunger 11 is slidably disposed in barrel 3 and is manually actuable to reciprocate between the position shown in the drawing, in which the inlet openings 7 and 9 are both exposed for the flow of materials to be mixed into chamber 5, and a rightward position as seen in the drawing in which plunger 11 closes the inlet openings 7 and 9 fully fills the chamber 5 thereby completely to eject the reactive mixture from chamber 5. The construction and operation of ejection head 1 is known in the art and need not be further described. It can for example be as disclosed in the above-mentioned Gusmer U.S. Pat. No. 3,263,928, in which case the chamber 5 is of uniform cross sectional configuration substantially throughout its length, including the discharge opening, so that foam may be ejected from ejection head 1; or ejection head 1 can have the form shown in the above Gusmer U.S. Pat. No. 2,890,836, with a discharge opening reduced in diameter as compared to the mixing chamber, for the ejection of a spray.

The mutually reactive liquids reach ejection head 1 along separate paths, as mentioned above. Thus, in the case of a polyurethane resin and the activator therefor, for example, as described in the above Gusmer U.S. Pat. No. 3,263,928, the activator may come from a supply container 13 maintained under a positive pressure of, say, 2 or 3 p.s.i.g., by a source of nitrogen 15 which prevents the entry of air and water vapor into container 13. Activator flows from container 13 through a check valve 17 and then through a piston pump 19 by which its pressure is elevated for the purpose described above, for example to 100 p.s.i.g. From pump 19, the activator proceeds through a check valve 21 to the primary pump chamber of the activator proportioning pump 23 in which a piston 25 is reciprocable under the impetus of a displacement piston rod 27. Piston 25 divides the double acting pump 23 into two chambers, primary chamber 29 and displacement chamber 31. From chamber 29, activator flows through conduit 33 and check valve 35 toward conduit 37 which communicates with activator inlet opening 7, and also toward conduit 39 which communicates with chamber 31 of pump 23. It is during the rightward stroke of piston 25, as seen in the drawing, that the pressure imparted to the activator by pump 19 tends to be additive and the outlet pressure of pump 23 to be relatively high; while it is during the leftward stroke of the piston 25 as seen in the drawing that the pressure imparted by pump 19 becomes nullified and the outlet pressure of pump 23 is proportionally lower. It is this periodical fluctuation of the pump outlet pressure that the present invention largely overcomes.

On the resin side, the path of the liquid is similar, from a container 39 maintained under positive pressure by nitrogen 41, through a check valve 43, to higher pressure through a pump 45, then through a check valve 47 to pump 49 including a piston 51 that divides pump 49 into chambers 53 and 55. From chamber 53, resin flows through conduit 57 through a check valve 59 and thence to resin inlet conduit 61 communicating with resin inlet opening 9, and also to conduit 63 communicating with chamber 55.

However, piston 51 is on the same piston rod 27 as piston 25 and is axially aligned therewith, the piston rod also being the piston rod of a double-acting fluid motor 65 comprising a double-acting piston 67 that divides motor 65 into chambers 69 and 71. In the illustrated embodiment, fluid motor 65 is a hydraulic motor fed from a source of hydraulic liquid in a sump 73 through a constant pressure, variable volume pump 75 and thence through an automatically periodically reversing spool valve 77 actuated by a solenoid S, to conduits 79 and 81 that are alternately feed and return conduits, the hydraulic liquid returning to sump 73 through a return conduit 83. Alternatively, motor 65 could be an air motor or an electric motor, so long as it remains a constant pressure motor.

In operation, the nature of the liquids, their flow rates and temperatures and the pressures imparted thereto by pumps 19, 29, 45 and 53, may all be conventional, for example as disclosed in the above-identified Gusmer patents, and hence need not be further mentioned. The activator and the resin proceed from their respective containers 13 and 29 through their respective pumps 19 and 45, in which they are elevated in pressure; although it will be understood that pumps 19 and 45 can be eliminated and if the nitrogen or other dry inert gas at 15 and 41 is of sufficiently high pressure. In any event, the liquid streams at elevated pressure flow along parallel paths to the respective pumps 23 and 49, the activator entering chamber 29 while the resin enters chamber 53. Piston 25 is moving to the left relative to chamber 29 at the same time that piston 51 is moving to the left relative to chamber 53, as seen in the drawing, so that the pumps 23 and 49 are acting in opposition to each other. During this particular stroke of the pumps, the valve 77 is in the position shown in the drawing, with hydraulic fluid being fed by pump 75 to chamber 71 and discharged from chamber 69. At the end of the stroke of the piston rod 77 with its associated pistons 25, 51 and 67, solenoid S reverses the position of valve 77 so that hydraulic fluid under pressure is fed to chamber 69 and exhausted from chamber 71, whereupon piston 67 and with it the rod 27 and pistons 25 and 51 is driven to the right as seen in the drawing, which reverses the stroke of both pumps 23 and 49.

As a result of the pistons 25 and 51 being thus coupled in opposed tandem relationship and actuated by the same reciprocating fluid motor, it is found that the discharge pressure in conduits 37 and 61, which in the past might have varied from, say, about 700 to about 900 p.s.i. depending upon the direction of stroke of the pumps 23 and 49, now varies very little from a means pressure of 800 p.s.i.

From a consideration of the foregoing disclosure, therefore, it will be evident that all of the initially recited objects of the present invention have been achieved.

Although the present invention has been described and illustrated in connection with a preferred embodiment, it is to be understood that modifications and variations may be resorted to without departing from the spirit of this invention, as those skilled in this art will readily understand. Such modifications and variations are considered to be within the purview and scope of the present invention as defined by the appended claims.

Claims

What is claimed is:

1. Apparatus for ejecting a mixture of liquids, comprising an ejection head, means for separately feeding two streams of liquids from separate sources of said liquids to said ejection head and for mixing said streams of liquids in said ejection head, said feed means comprising a pair of double-acting reciprocating piston pumps one individual to each of said streams, means for supplying each of said pumps with liquid under elevated pressure from a respective one of said sources, means for separately delivering said liquids from said pumps to said ejection head, and means for driving said pumps in opposed tandem relationship comprising a double-acting reciprocating constant pressure motor common to said pistons of said pumps.

2. Apparatus as claimed in claim 1, said motor being a fluid motor comprising piston means and piston rod means connected to said pistons of said pumps.

3. Apparatus as claimed in claim 2, said fluid motor being a hydraulic motor, and means for alternately supplying hydraulic liquid to and exhausting hydraulic liquid from opposite sides of said hydraulic motor.

4. Apparatus as claimed in claim 1, said motor and said pumps being in axially aligned relationship.

5. Apparatus as claimed in claim 1, said means for supplying liquids to said pumps under elevated pressure comprising positive displacement transfer pumps one individual to each said stream.