US 3220801 A
Description (OCR text may contain errors)
1965 J. c. RILL, JR, ETAL 3,220,801
FROTH GENERATQR Filed May 31, 1962 3 Sheets-Sheet 1 INVENTORS' Nov. 30, 1965 J. c. RlLL, JR., ETAL 3,220,801
FROTH GENERATOR Filed May 31, 1962 3 Sheets-Sheet 2 7 M7 M1 9 INVENTORS' John 61 R12), J2:
Paul (ff/1426f??? Nov. 30, 1965 J. c. RILL, JR, ETA]. 3,22,80l
FROTH GENERATOR Filed May 31, 1962 5 Sheets-Sheet 5 Fneau SUPPLY TIM uv VENTORS John C: fli/Z, Jr. Pea} E S/zaeffer United States Patent ()flice Patented Nov. 30, 1965 3,220,801 FROTH GENERATOR John C. Rill, Jr., Dayton, and Paul F. Shaelfer, Lewisburg, Ohio, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed May 31, 1962, Ser. No. 199,095 3 Claims. (Cl. 23252) This invention pertains to chemistry and more particularly to mixing apparatus and mixing processes for making polyurethane foam-forming materials in an expanded form known as froth.
Cellular polyurethanes were first formed from a liquid mixture of components. Strong molds have been required to prevent the bulging of the walls when such liquid mixtures are poured into the molds because of the pressure which develops during the change in phase and thermal expansion of the gas in the mold, resulting in a volume increase of over 3600%. The expense and difficulties of providing such strong molds and reinforcing fixtures has been a strong deterrent to the extensive use of the polyurethane foams. Recently a new process producing polyurethane froth has been developed in which the fluorocarbon expansion agents in the polyurethane change from the liquid to the gas phase and are expanded before depositing in the place where it is to be lodged.
Although the froth is capable of expanding several times, the pressures generated are relatively small and no thick-walled molds or reinforcing fixtures are required. In many instances the froth can be deposited directly in the insulation space in the final products without the use of reinforcing fixtures for the walls thereof. However, one difficulty is to obtain low density, high uniformity and high insulating value with the froth-type foam. Another difficulty is that the froth tears readily and often has the membranes and cell walls ruptured permitting leakage of insulation gas from the cells and coagulation of the gas bubbles producing heterogeneously dispersed large cells which severely limit the attaining of low coefficient of thermal conductivity in the foam.
It is an object of this invention to provide a froth generator in which a froth of high quality and uniformity with low density and high insulating value can be produced whenever and for as long as desired.
It is another object to provide a froth generator which will deliver the froth by streamline or laminar flow.
It is another object of this invention to provide a froth generator in which substantially constant pressure is maintained in the mixing chamber at all times.
It is another object to produce a froth generator capable of producing a froth mixture that expands from the heat of final polymerization less than greater than the froth density.
These and other objects are attained using the apparatus and the process shown in the drawings in which the two polyurethane components such as the component containing the hydroxyl bearing polyol surfactant and catalyst hereinafter referred to as master batch and the isocyanate bearing component are circulated in separate systems and metered into an enclosed mixing chamber in stoichiometric ratio. A volatile liquid is also discharged separately into the mixing chamber in proportion to the delivery of the two aforementioned components. An agitator is rotated at high speed within the mixing chamber. The bearings for the agitator are maintained lubricated by lubricant under high pressure which may be provided with a cooling system. The outlet of the mixing chamber is provided with a loaded pressure relief valve for maintaining a predetermined relatively high constant uniform pressure within the mixing chamber. The outlet or diffuser of this loaded relief valve is flared at a proper angle which provides streamline or laminar flow proportioned to the Reynolds number of the components and the rate of expansion of the froth as the pressure drops from expansion chamber to atmosphere. The delivery of the components may be controlled by a timing device which, in addition, may provide for automatic flushing of the mixing chamber and the pressure relief valve following each usage of the froth.
Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.
In the drawings:
FIGURE 1 is a vertical sectional view of the froth generator embodying one form of my invention;
FIGURE 2 is an irregular sectional view taken along the lines 22 of FIGURE 1;
FIGURE 3 is a fragmentary view of the mixing head in section showing the valves positioned for flushing; and
FIGURE 4 is a diagrammatic view of the froth generating system.
Referring now to the drawings and more particularly to FIGURES l to 3, there is shown a froth generator 20 provided with a valve block 22 containing two parallel plug valves 137 and 139 each having two transverse parallel passages designated respectively 141, 143, and 147 located in the same plane perpendicular to the axis. When the valves 137 and 139 are turned to the delivery position, the passage 141 becomes substantially aligned with the polyisocyanate inlet fitting 149 and the delivery passage 151 which delivers into the mixing chamber 157. Similarly, the passage 145 becomes substantially aligned with the activator inlet fitting 153 and its passage and the delivery passage 155 which delivers into the mixing chamber 157. These valves 137 and 139 are preferably made of 7% glass fiber reinforced, polyethylene or polytetrafluoroethylene or polypropylene. As shown in FIGURE 2 the valves 137 and 139 are pressed respectively into the tapered recesses 159 and 161 by the compression-type coil springs 163 and 165 which are held in place by the threaded plugs 167 and 169. At their opposite ends the valves 139 have the cylindrical shafts 171 and 173 extending through the plasitc bearings 175 and 177 Within the valve block 22.
The outer ends of the shafts 171 and 173 are provided with square reduced end portions 179 and 181 on which are slidably mounted the pin-type clutches 183 and 185. These pin-type clutches 183 and 185 normally have their pins 187 urged into the apertures in the intermeshing gears 189 and 191 by the coil springs 1937 With the clutches 183 and 185 engaged the valves 137 and 139 will be rotated simultaneously by the toothed rack 195 which engages the teeth of the gear 189 to rotate both gears 189 and 191 and the valves 137 and 139 simultaneously. The rack 195 is operated by the double-acting air cylinder 197 which has its opposite ends connected by the delivery conduits 199 and 220 to the four-way valve 222 which is operated by the solenoids 224 and 226 10- cated at the opposite end thereof. The air is supplied from a compressor (not shown) through the supply conduit 228 to a regulating valve 230 which controls the flow of air into one branch of the air control system so as to maintain the pressure within this branch of the air system at approximately 125 pounds per square inch. This branch of the air control system includes a branch conduit 232 connecting with the central portion of the three-way valve 222 which is provided with discharge connections at the opposite ends connecting with the discharge conduits 234 and 236. The solenoids 224 and 226 are connected by the conductors 238 and 240 with a timer 42 which controls the supply of electric energy to the conductors 238 and 240 so as to hold the valves 137 and 139 open for a definite period of time and then recloses these valves. The timer 242 is connected by the switch 244 to the supply conductors 246.
At the rear of the mixing chamber 157 is a passage 248 connecting with the discharge outlet of an injector nozzle 250 of the pintle type. This injector nozzle may be of the same type used for injecting of fuel into the cylinders of a diesel engine, if desired. It is made to operate on pressures of about 300 to 350 pounds per square inch sufficient to keep the injecting expansion agent in the feed line in the liquid phase. This nozzle may be of the type shown in Marks Mechanical Engineers Handbook, Fourth Edition, Tenth Printing, April 1947, as shown in FIGURE 52b on page 1298 thereof, or it may, for example, include an injection nozzle holder No. KCA30SD2 with the nozzle DN4S2 made by the Robert Bosch, G.m.b.H. of Stuttgart, Germany. A volatile liquid, such as difluorodichloromethane, is stored in the supply tank 252 from which the volatile liquid is delivered by the variable delivery pump 254 driven by the motor 256 through the conduit 258, the solenoid valve 260 and the conduit 262 to the injector nozzle 250. The solenoid of the valve 260 is connected by the conductors 265 to the timer 242 in such a way that the valve 260 will be open whenever the air cylinder 197 is in the position to deliver the polyurethane components to the mixing chamber 157. The pump 254 is adjusted so as to supply the volatile liquid to the injector nozzle 250 at a pressure of between 300 and 350 pounds so that a widely distributed spray issues from the nozzle 250 into the mixing chamber 157.
The mixing chamber 157 is provided with a projecting pin-type agitator for thoroughly mixing the components of the polyurethane with the volatile liquid until the liquid completely penetrates the two components. The agitator 264 is fastened to the lower end of the agitator shaft 266 driven at its upper end above the valve body 22 by an electric motor 268. The shaft 266 is surrounded by a hardened ring 270 sealed within a recess in the valve body 22 by an O-ring seal. Also, sealed to the valve body 22 is a bearing housing 272 provided with a lower needle bearing 274 and an upper ball bearing 276. The bearing housing 272 is also provided with a recess receiving the hardened ring 278 sealed with an O-ring seal to the housing 272. Between the rings 270 and 278 the bearing housing 272 is provided with a shaft seal chamber 280 containing an upper running seal 282 bearing against the lower face of the ring 278 and a lower running seal 284 bearing against the upper face of the ring 270. Between these rings 282 and 284 is a compression-type coil spring 286 supplying the force to hold the rings 282 and 284 against the adjacent faces of the rings 278 and 27 0. The rings 288 and 290 of elastomeric material are provided for sealing the running seal rings 282 and 284 to the shaft 266. The shaft seals 282 and 284 are lubricated by a lubricating system including a pump 292 which discharges the chemically inert lubricant into the shaft seal chamber 280. The lubricant is recirculated through the outlet 294 and the cooling conduit 296 back to the inlet of the pump 292. A relatively high pressure such as about 200 pounds per square inch is maintained in the seal chamber 280 for preventing any of the components of the mixture from flowing upwardly out of the mixing chamber 157 around the shaft 266. This lubricant pressure also assures good lubrication for the running shaft seals 282 and 284.
The prepolymer or isocyanate bearing component is delivered from the supply tank 321 through a conduit 323 to the variable delivery pump 325 driven by the electric motor 327. The pump 325 is adjusted to deliver the prepolymer or isocyanate bearing component through the conduit 329 to the inlet 149 at a rate calculated to give the desired ratio of this component to the other components supplied to the mixing chamber 157. When the plug valves are in the recirculating position shown in FIGURE 3, the resin is returned through the outlet 331 and the return conduit 333 to the tank 321. The tank 321 includes a mixer or agitator 335 driven by the electric motor 337. It also includes a jacket 339 preferably of insulating material and air space which may contain an electric heater 341 controlled by the thermostatic switch 343 responsive to the temperature of the thermostat bulb 345 located within the insulated enclosure 339. The conduits 329 and 333 are surrounded by the electric heaters 347 and 349 which are either manually or thermostatically controlled in response to the temperature of the valve block 22.
The activator component is supplied from the supply tank 351 through the outlet conduit 353, the variable delivery pump 355 driven by the motor 357 and the feed conduit 359 to the activator inlet 153. When the valves are turned to the recirculating position shown in FIG- URE 3, the activator component passes from the inlet 153 through the passage 147 in the valve 139 to the recirculating outlet 361 which connects through the return conduit 363 with the tank 351. The contents of the tank 351 are agitated by the agitator 36S driven by the electric motor 367. The tank 351 is enclosed within an insulating jacket 369. The space between the jacket 369 and the tank 351 may be heated by an electric heater 371 under the control of the thermostat 373 having a thermostat bulb 375 within the jacket 369.
The conduit 359 may be surrounded by the electric heater 377 while the return conduit 363 may be surrounded by the electric heater 379. Each of these heaters may either be manually controlled or controlled according to the temperature of the valve block 22. If it is desired to operate the tanks 321 and 351 at temperatures below room temperature at any time, they may be surrounded by the refrigerant evaporators 381 and 383 which have their outlet connected through the evaporator regulating valves 385 and 387 and the suction conduit 389 to the inlet of the compressor 391 which is driven by an electric motor 393. The compressor 391 delivers the compressed refrigerant to the condenser 395 from which the liquid refrigerant is delivered through the supply conduit 397 under the control of the regulating valves 399 and 420 to the thermostatic expansion valves 422 and 424 having their thermostat bulbs in contact with the outlet of the evaporators 381 and 383. These expansion valves 422 and 424 deliver the liquid refrigerant under reduced pressure to the evaporators 381 and 383 where the liquid refrigerant evaporates to cool the tanks 321 and 351.
The mixing chamber 157 is enclosed in a mixer housing 426 provided with an outlet connection 428 of ample size to provide for streamline or laminar flow of the reactants from the chamber 157. This outlet connection 428 is connected to an annular pressure relief value 430 of such design and capacity as to provide for streamline or laminar flow of the reactant mixture. This pressure relief valve is provided with an inlet chamber 432 Within a cap member having at the bottom a passage blocking wall and radial passages 434 above said wall extending outwardly from the chamber 432 into the space 438 enclosed by the sleeve 436 of elastomeric material which is sealed at both ends. This space 438 surrounds the inlet portion of the pressure relief valve 430 as well as the outlet portion 440 containing the discharge passage 442. Between the closed or plugged end of the inlet fitting or cap member containing the chamber 432 and the open end of the outlet fitting 440 is a gap 439 through which the mixture flows after emerging from the passages 434 and flowing downwardly around the closed end of the inlet fitting. An air chamber housing 444 surrounds the sleeve 436 and is connected by the fitting 446 and the conduit 448 with the three-way solenoid operated valve 450. This valve 450 is supplied through the conduit 452 from the manually adjustable pressure regulating valve 453. The operating soleniod of this valve 450 is connected by the conductors 456 to the timer 242 so that during the delivery period it connects with the branched supply conduit 452 and during the recirculating period it is connected to the exhaust conduit 454. The valve 453 is adjusted to deliver air at a pressure of between 70 and 100 pounds per square inch in accordance with the total flow rate and the volatile liquid concentration to obtain the best product.
To illustrate typical operation, the application of 70 to 100 pounds of air pressure surrounding the sleeve 436 contracts the sleeve into the spaces 438 and 439 and by cooperation of the sleeve 436 with the adjacent outer surface of the bottom wall of the inlet chamber 432 maintains a pressure within the mixing chamber 157 at about 90 to 125 pounds per square inch. The maintenance of a substantially uniform high pressure within the mixing chamber 157 assures high quality cell lattice uniformity consistent with low density of the cellular polyurethane. The volatile liquid is uniformly distributed throughout the mixture. The outlet fitting 440 is provided with a flared discharge nozzle or diffuser 458 which diverges at a rate to provide streamline or laminar flow proportional to the Reynolds number of the components and the rate of expansion of the froth as the pressure drops from the expansion chamber to atmosphere. For example, for a flow rate of 200 feet per minute, the nozzle preferably has a diameter of 1% inches at the top and 1% inches at the bottom. The included angle of the flare is about The flared portion has a length of about 2%; inches. It expands the mixture from 100 pounds per square inch gage and a density of 72 pounds per cubic foot down to atmospheric pressure and a density of about 2.5 pounds per cubic foot. The lower rim is chamfered externally at an angle of about 30 to the axis as indicated by the reference character 460 so as to provide a sharp edge at the bottom of the flared section to prevent any material from curling upwardly or otherwise adhering at this point. The mixture issues from the flared outlet 458 with a consistency resembling aerated shaving cream. After it is deposited in the insulation space or other place wherein it is to be located, the exothermic reaction of the ingredients raises its temperature so that it expands about thereby reducing its density to between 1.7 and 1.8 pounds per cubic foot. This material, when the reaction is completed and the material is cured, provides a strong product which will retain its high insulating value for many years.
As one specific example, the tank 321 may be charged with 100 parts prepolymer F. The prepolymer F is composed of 75 parts of polyisocyanate ingredient A and parts of polyether C. The isocyanate ingredient A is composed of 80 parts 2,4 diisocyanate and 20 parts of 2,6 diisocyanate. The polyether C contains 1 mol of sorbitol and 10 mols of propylene oxide. It has an OH number of 495, an acid number of .30 and a viscosity (cps.) at 83 F. of 7500. The water by weight is less than .05%. The tank 351 is supplied with a mixture of parts of polyether C to 29.5 parts of activator mixture 1. The activator mixture I, expressed in parts by weight, includes 26 parts of N,N,N',N'-tetrakis (Z-hydroxypropyl) ethylene diamine, 3 parts triethylene diamine,
6 and .5 part emulsifier made up of propylene glycol and 10% polyethylene glycol. The tank 321 is kept at a temperature of between about 80 and 82" F. while the tank 351 is kept at a temperature between about 98 and 102 F. The ingredients in the proportion of parts prepolymer F from the tank 321, 59.5 parts activator I from the tank 351 and 20 parts difluorodichloromethane from the tank 252 are mixed in the mixing chamber 157 to form the froth. The froth leaves the nozzle at a temperature of between about 80 and 85 F.
The apparatus includes provision for automatically flushing the mixing chamber 157, the agitator 264, the outlet 428 and the passages 432, 434, 438 and 442 after each delivery. For this purpose a suitable solvent such as trichloroethylene or methylene chloride is delivered through the pipe 462 to the solenoid valve 464 which is electrically connected by the conductors 466 to the timer 242 to open the valve 464 for a brief period such as five seconds following the termination of each delivery. This valve 464 supplies the solvent through a pipe 468 through the inlet connection 470 in the valve body 22. When the valves are in the position shown in FIGURE 3, this solvent is delivered through the passage 472 which delivers the flushing liquid through the passage and the branch passage 474 into the passage 157 which leads into the mixing chamber 157. This flushing liquid flushes out the components out of the mixing chamber and the passages connecting therewith so that they will not congeal. After the five second solvent flushing, the timer 242 closes the valve 464 and through the conductors 480 opens for ten seconds the air solenoid valve 482 to allow air from the branch conduit 484 to flow into the conduit 468 which supplies the air to the flush inlet connection 470, the passages 472, 145, 174, to the mixing chamber 157, the pressure relief valve 430 and the discharge nozzle 458. This removes the solvent from the apparatus. The mixture flushed out is delivered to a waste drum.
While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.
What is claimed is as follows:
1. A froth generator including an enclosure enclosing a mixing chamber provided with an outlet, means for delivering components to the mixing chamber, said mixing chamber being provided with a cap-shaped outlet member having laterally extending outlet passages, an outlet nozzle spaced from said cap member having an endless entrance rim adjacent said cap member spaced at a substantially uniform distance away from the cap member throughout its adjacent surface, a flexible sleeve surrounding the outlets in said cap member and the space between said rim and said cap member, means for sealing the ends of the sleeve to the cap member and the nozzle, means providing a sealed enclosure surrounding said sleeve, and means for applying a fluid under pressure to said sealed enclosure.
2. A polyurethane froth generator including an enclosure enclosing a mixing chamber, means for delivering predetermined proportioned quantities of polyurethane forming components to the mixing chamber including a volatile liquid gas generating ingredient, mixing means in said mixing chamber for mixing said components, valve means for controlling the discharge of said components into said mixing chamber, said mixing chamber being provided with an outlet passage having in it a coaxially aligned circular passage blocking means, an outlet nozzle spaced from said passage blocking means having a circular entrance adjacent to and spaced at a substantially uniform distance away from and coaxially aligned with said passage blocking means throughout its adjacent surface, a flexible sleeve surrounding and concentric with said passage blocking means and having one end sealed to the full peripheral extent of said nozzle, means for sealing the other end of said sleeve to said mixing chamber enclosure peripherally around said outlet passage, and means for substantially uniformly concentrically contracting said flexible sleeve around said passage blocking means to control the flow of fluid from said mixing chamber substantially uniformly around said passage blocking means to said nozzle.
3. A generator as specified in claim 2 having means providing a sealed enclosure surrounding and sealed to end portions of the flexible sleeve, and means for applying a fluid under pressure to said sealed enclosure for contracting the sleeve, said outlet nozzle having a flared discharge passage which diverges at a rate to provide laminar flow of the fluid.
References Cited by the Examiner UNITED STATES PATENTS Hoffman 27762 Arf 27762 Hoppe et al.
Corby et al.
Geldern et al. 23252 Cole 23-252 MORRIS O. WOLK, Primary Examiner.
JAMES H. TAYMAN, JR., Examiner.