|Publication number||US3888962 A|
|Publication date||Jun 10, 1975|
|Filing date||Nov 24, 1972|
|Priority date||Nov 24, 1972|
|Publication number||US 3888962 A, US 3888962A, US-A-3888962, US3888962 A, US3888962A|
|Inventors||Ostertog Robert J, Page Anthony J|
|Original Assignee||Johns Manville|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (13), Referenced by (5), Classifications (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent 1 Ostertog et al.
[4 1 June 10, 1975 INSULATING PRODUCT AND DRY PROCESS FOR ITS MANUFACTURE  Assignee: Johns-Manville Corporation,
 Filed: Nov. 24, 1972  App]. No.: 309,395
 US. Cl 264/122; 264/109  Int. Cl. 329.] 5/02  Field of Search ..264/109,l2,121,115,
264/121, 122, DIG. 49; 108/122, DIG. 2
 References Cited UNITED STATES PATENTS 2,462,255 2/1949 Charman et a1. l06/DIG. 2 2,646,381 7/1953 Duvall 264/121 2,744,045 5/1956 Collins 264/115 2,825,388 3/1958 Hale et al. 264/115 2,859,484 11/1958 French at al.... 264/122 2,940,134 6/1960 Heritage 264/109 3,042,578 7/1962 Denning 162/171 3,096,227 7/1963 Elten 264/109 3,418,403 12/1968 Garnevo 264/121 3,453,355 7/1969 Rudloff 264/121 AQUEOUS SLURRY 3,482,287 12/1969 Flewwelling 264/115 3,492,264 l/l970 Hahn 264/109 3,508,301 4/1970 Brown 264/109 Primary ExaminerJay H. Woo Attorney, Agent, or FirmRobert M. Krone; Stephen C. Shear  ABSTRACT A low-density perlite insulation board is continuously formed by depositing a uniformly-distributed mix on a traveling belt to form a continuous length of board. The mix includes less than about 80 percent by weight of water. The solids portion of the mix includes expanded perlite in amounts of 50 to 85 percent by weight of the solids portion. The dry forming process permits elimination of the fiber customarily incorporated into perlite insulating board. A binder material is included in the mix for adhering the mix ingredients together to form a structurally integral board. The mix is formed in a mixing zone containing air where the ingredients are exposed to intensive mechanical shearing forces for less than 10 seconds. The top surface of the board is shaped to obtain a planar top surface, the board is compressed, and then water is removed from the board.
10 Claims, 2 Drawing Figures INSULATING PRODUCT AND DRY PROCESS FOR ITS MANUFACTURE FIELD OF THE INVENTION This invention relates to thermal and acoustical materials and their manufacture. More particularly, this invention relates to a dry process for forming perlite board and to the insulating board produced by this method. The term dry process as used herein refers i BACKGROUND OF THE INVENTION Insulation boards or panels containing expanded perlite have enjoyed considerable commercial success because of their desirable thermal and sound insulating properties, and because the board is resistant to fire. Such boards conventionally contain 608O percent of expanded perlite, a material which contains numerous sealed bubbles which have a subatmospheric internal pressure.
Because perlite board contains a large quantity of inorganic perlite, any organic materials, such as organic binder materials, are dispersed around and upon the perlite particles. Even when relatively high percentages of organic materials are used, the board will not readily support its own combustion, probably because the perlite tends to isolate the combustible material. As a result of the nature of the perlite particles, perlite board furnishes considerable fire protection.
At the present time, perlite board is primarily produced by a filtration process which involves depositing a dilute aqueous slurry containing less than solids on a traveling wire screen which is part of a Fourdrinier machine. This prior art wet process is very similar to a papermaking process.
The wet process for forming perlite boards has produced a generally satisfactory board, but in some respects possesses disadvantages. A large capital investment is required for equipment for the wet process. The basic Fourdrinier machine is expensive, and because of the large volumes of water that are used in the wet process, large capacity tanks and pumps are necessary. Further, the wet process of making perlite board requires large expensive multi-deck dryers; for example, a SOO-foot-long, S-deck-high dryer has been used to dry perlite boards.
Another problem of the wet process which is rapidly becoming more acute, is the method of disposing of large quantities of water. The need to meet more stringent effluent standards that are being established by state and federal governments has imposed further capital and operating costs on the wet process manufacturers of perlite board. These costs result from the necessity of providing improved water disposal installations.
The strength requirements for finished perlite board have affected the speed at which the product can be manufactured in the wet process because of the interrelationship between fiber length and drainage time. The use of fibers having sufficient length to promote strength without the use of large quantities of binder, has tended to slow the dewatering of the board during the basic filtration-forming step. Thus, only relatively slow production speeds have been commercially achieved in wet processes for forming perlite board.
A technique for manufacturing a lightweight insulating product without using large quantities of water is disclosed in US. Pat. No. 3,344,217 to Mogg et al. This patent discloses blending together a lightweight insulating mix containing fibers and expanded perlite in a gaseous medium until they are uniformly blended. The gaseous medium is thought to avoid fiber agglomeration and to promote uniform mixing. Subsequently, an aqueous system is added to the dispersed fiber and perlite to uniformly wet these components.
A central feature of the technique disclosed in US. Pat. No. 3,344,2117 is the use of a gaseous medium to disperse the mix ingredients and prevent their agglomeration. An air mixing tower or other conduit including precise feeding requirement for control of the feed rates of the perlite, binder, fibers, and air would be necessary to maintain the air-to-solids ratio within the necessary range. Although the air mixing disclosed in the patent is not a high intensity mixing procedure, it is thought to be conducted using a turbulent flow of air. As described by the patentees, this turbulence during blending cannot be too high, or it will disturb previously blended material that has been deposited.
There has continued to exist a need for an improved process that can produce a high quality perlite board while using relatively inexpensive equipment, and that can operate at more rapid production rates.
OBJECTS OF THE INVENTION Accordingly, it is an important object of this invention to provide an improved dry process for manufacturing perlite board.
Another object of this invention is to provide a new and improved continuous process for manufacturing perlite board which can be run on apparatus requiring a low capital expenditure.
A further object of the invention is to provide a pro cess which is capable of continuously manufacturing perlite board at rapid production speeds.
Yet another object of this invention is to provide a process for producing perlite board that uses less process Water than the known wet process.
A still further object of the invention is to provide a perlite board having desirable overall strength and insulation characteristics, and which possesses superior interlaminar strength compared to the board produced by conventional wet, papermaking type processes.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention.
SUMMARY OF THE INVENTION The invention provides a continuous process for making a low density perlite board. Expanded perlite and a stream of aqueous slurry are fed to a mixing zone containing air. The slurry includes about 5 percent to about 15 percent of binder solids, which preferably comprises bentonite clay, asphalt emulsion, and starch. The perlite and the slurry are passed through the mixing zone while intensely agitating the ingredients of the mix for less than about 10 seconds to intimately admix the solids components of the mix and form a fluffy mass having a density (dry basis) of from 5.5 to 7.0 lb/cu.ft.
The fluffy means is continuously deposited across the width of an endless conveyor to form board stock, and the top surface of the board stock is shaped to obtain a planar top surface. Subsequently, the board stock is compressed to the desired board thickness, and water is evaporated from the compressed board.
It is preferred that the mix be deposited directly onto caul plates from the mixer, because the mix does not possess high levels of wet strength unless a rapid setting synthetic resin or tacky adhesive is included in the binder.
The invention provides an insulating board having a density below lb/ft., a modulus of rupture of at least 40 psi, and a laminar strength of over 10 psi. The board consists essentially of (a) from 65 to 75 percent by weight of expanded perlite; (b) from to 25 percent by weight of binder; and (c) from O to 10 percent of waterproofing agent.
Preferably, the binder is predominately bentonite clay, and in presently preferred formulations; bentonite and starch are used as binders in a weight ratio of about 4: l. Asphalt emulsion may be included in the binder as a waterproofing agent.
While perlite is a friable material that is easily degraded, it has been found that degradation of the perlite has not been a problem in the process of the invention in which the mixing, while intense, is of a short duration.
The new dry process possesses many advantages over wet papermaking type processes for manufacture of perlite boards. Specifically, the dry process avoids filtration, and thus permits the use of relatively large perlite particles which could not be used in the wet process due to their tendency to float to the top of the slurry. Through the use of different graded sizes of perlite particles and the attainment of a more uniform distribution of individual components of the mix throughout the width and height of the board, a more uniform board can be obtained and more uniform control of the thermal insulating properties of the final product can be achieved.
Another advantage of the present invention is the increased production line speeds that are possible. Presently, the wet processing of perlite board on Fourdrinier equipment is accomplished at relatively low speeds. In contrast, significantly higher production speeds can be attained by the practice of the invention since production speed is not limited by a filtration process.
An advantage of the dry process, which directly results from the use of a reduced amount of process water, is the reduction in drying requirement that is needed. Also, there are not losses of material as in the wet process, since the materials do not go into a suspension where they can be lost in the waste water which is filtered through the board.
A still further advantage of the dry process is that it affords better thickness control of the final product than the wet process. This advantage permits depositing the fluffy mix and then shaping the top surface of the board stock at an incline to the horizontal.
Since capital costs and most operating costs, such as drying, are significantly lower in the dry process than in the wet process, the binder component can be selected from a large number of materials, including synthetic resins that impart a combination of desired properties such as strength and water resistance to the final product board, without making the price of the board uncompetitive. Some binders can be used which are not compatible with the wet process because material in water or passed through the filter with the white water. For example, any solution binder in a wet process operation would be lost with the white water that passes through the deposited solids and the forming screen.
DESCRIPTION OF THE DRAWINGS Of the drawings:
FIG. 1 is a diagrammatic side elevation of apparatus that can be utilized to practice the method of the present invention; and
FIG. 2 is an elevation of an embodiment of the insulating board of this invention installed to provide a sloped roof.
DETAILED DESCRIPTION OF THE INVENTION In accordance with the invention, a process is provided for forming low density perlite board from a substantially uniformly distributed mix by feeding l238 parts of expanded perlite per 100 and 62-88 parts per 100 of an aqueous slurry to a mixing zone containing air. The slurry contains from about 5 to about 15 percent of binder solids.
The mix contains less than about percent by weight of water as contrasted to the dilute slurries used in wet paper-making type processes which usually contain over percent water.
Preferably, at least 50 percent by weight of water should be present in the mix to perform the function of distributing water-deposited binder throughout the mix. The use of less than 50 percent by weight water in the mix would require the presence of a free-flowing, low viscosity binder.
Expanded perlite makes up a major portion of the solids component of the mix, preferably from 60 to 80 percent by weight of the solids present in the mix. As will be discussed in more detail below, the dry process of this invention permits wide flexibility in the choice of the binder materials.
The size of the perlite particles incorporated in the mix have an effect on the strength and the density of the product. Generally, the perlite particles can be from ultra fines to about one-eighth inch in diameter (4 mesh) (US. Standard Screen Size). Relatively large particles of perlite adsorb less water per unit weight than smaller particles of perlite, because the larger particles have a smaller surface area per unit of volume. Thus, when large perlite particles are used, the weight percent of solids both in the mix and at subsequent stages of the process is advantageous maintained at a higher level than the percentage of solids in a board made of ultrafine particles. Larger particles also tend to be more fragile and must be handled more gently prior to their deposition on a traveling screen, to prevent excessive shattering. Surprisingly, however, degradation of the perlite particles either does not occur to any great extent, or does not create problems in the finished board. Perhaps because fibers are not necessary in the dry process board and, if present, act more as a filler rather than as components of a structural network, it is not necessary that the perlite particles be of any particular size or size gradation.
In the dry process of this invention, it is not necessary to incorporate fibers in the mix, and there is no problem of dewatering an aqueous slurry. This dewatering step tends to slow up a wet paper-making type process and frequently dictates the selection of binders that are water insoluble and possess good dewatering properties.
Perlite board fabricated by the dry process. to be commercially attractive, must possess a certain minimum strength. Also, the perlite board just after its deposition on a traveling belt must possess sufficient green (wet) strength to withstand automated handling procedures. For these reasons, it is necessary to include an adhesive binder in the mix. usually at levels of from 15-30 percent by weight of the solids in the mix. for imparting strength to the board. Suitable binder materials include clay. bituminous emulsions, sodium and potassium silicate. aluminum phosphate. pitch, various resins. and natural and modified starches. Also. it is possible to include a small amount, from 0.1 to l percent by weight of the solids in the mix. of a synthetic resin binder such as a ureaformaldehyde resins, polyvinyl acetate resins, acrylic resins. and polyvinyl alcohol; or refined petroleum distillate products; or tacky hydrocarbon resins.
Bentonite clay constitutes a presently preferred binder material because it is relatively inexpensive. and is capable of providing desirable levels of board strength.
In preferred embodiments. the binder solids component of the mix includes starch and bentonite clay in a 1:4 weight ratio.
The product to be commercially attractive. must frequently also possess a high level of water resistance. Consequently. a sizing agent is often desirably incorporated into the mix for imparting water resistance to the board. Suitable sizing agents include bituminous emulsions, pitch, and the various synthetic organic resins. Some materials. such as asphalt can be used to impart both sizing and bonding properties to the mix. Thus. it is frequently desirable to incorporate a high melting point asphalt in the mix. if a brown or tan colored board is visually acceptable.
In forming the mix. it is necessary to substantially uniformly distribute the individual ingredients throughout the mix because a high concentration of perlite in any one portion of the board may result in undesirably low local strength properties. When bentonite clay is used as the binder, the mix should be subjected to short, high intensity mixing procedures, because the mix tends to become dense and sloppy when agitated for longer times at lower mixing rates. Another important consideration in forming the mix is the desirability of minimizing the handling of the expanded perlite to avoid excessive degradation of the perlite.
In the presently preferred embodiments of the invention, a substantially uniformly distributed mix is obtained by spraying a binder slurry onto perlite particles and then subjecting the mix ingredients to intense mechanical agitation in an air-filled mixing zone for a time period of less than seconds and preferably from about 1-5 seconds. Such a procedure produces a fluffy mass having a density (dry basis) of from 5.5 to 7.0 lb/cu. ft. in which the solids and air are uniformly dispersed throughout the mass.
In accordance with the invention. the substantially uniformly distributed mix. described above, which contains not more than 80 percent by weight of water is de posited on a traveling belt to form a linearly continuous layer of mix which can be converted to a continuous length of board. The mix can be deposited on the forming belt by gravity flow, or can be fed onto the forming belt using a variety of feeding means. Preferably, the mix is deposited by gravity flow from the mixing zone. The intense agitation of the wet mix in air permits deposition of a fluffy mix of low density, 5.5-7.0 lb/cu. ft.. (dry basis) which is convenient to level and consolidate.
In accordance with the invention, the top surface of the board is leveled to obtain a planar top surface. This leveling is accomplished while the mix has a water content of from 25 to percent by weight. Preferably. a portion of the mix is screeded off the top surface of the board during the leveling step and recycled. It is desirable that the quantity of recycled mix be minimized by controlling the amount of mix that is deposited on the traveling belt with relation to the speed of the traveling belt. Usually, the amount of mix that is deposited on the traveling belt will exceed by less than 20 percent the amount of mix necessary to form a board of the height that passes the leveling operation.
In accordance with the invention, the board after having its top surface leveled is subjected to compressive forces to drive air out of the board and to form a more dense board. This operation can be performed by passing the board beneath a traveling porous screen which exerts a compressive force on the board and yet permits air or other fluids to escape from the board.
Subsequently, energy is supplied to the board to raise the temperature of the board and thus dry the board and cure the binder material. It is presently preferred to pass the board through a hot air drying oven to accomplish these important functions. However, the application of energy to the board may be accomplished by a variety of methods including the use of a micro wave oven, R. F. oven. gas or electric infrared oven, or dielectric oven. In commercial operations, it is usually desirable to trim the board to its finished dimensions after it leaves the dryer.
For a better understanding of the process of the invention. a schematic drawing of equipment for producing the dry process of this invention is illustrated in FIG. 1.
Perlite is fed at a given rate from a storage vessel 10 onto a moving conveyor 12 which discharges the mix through an opening 14 into a mixing zone 16 containing air. As here embodied the mixing zone is defined by a walled container generally 17 described in more detail below.
A metered amount of an aqueous slurry including water, binder solids, and optionally a waterproofing or sizing agent is sprayed onto the perlite at the top of the mixing zone through a plurality of nozzles 15. In the mixing zone, intense mechanical shearing forces are exerted on the mix by spike rollers 18 that are arranged in pairs and rotated so that the rollers of each pair rotate towards each other. The spike rollers 18 can be driven at various speeds depending on the size of the spike rollers and the density of the mix that is desired on the traveling belt. For example, when the spike rollers have an overall diameter of 6 to 12 inches. the rotation of the spike rollers is desirably at the rate of about 1000 to 1500 rpm. to produce a fluffy mass.
The bottom wall of walled container 17 is formed by a traveling belt 20 formed of a fluid impervious material. Container 17 provides a substantially closed container surrounding the spike rollers 18. Opening 14 which is provided in container 17 for the introduction of the mix is preferably narrow as illustrated in FIG. 1 to limit the rate of entrance of air into the container and to prevent the escape of dust from the container.
Stationary fingers 22 are mounted on end walls 25 of container 17 to insure that material passing downwardly between end walls 25 and the spike rolls 18 is subjected to shearing forces. The lateral clearance between the spikes of a pair of rollers 18, and the clearance between the spikes of a roller 18 and an adjacent finger 22 is preferably two to four times the diameter of the largest perlite particle.
If an integral bottom wall is provided for container 17, the bottom wall is positioned below forming belt 20 so that the belt 20 is exposed to receive the airdispersed mix. The side walls of container 17 are preferably spaced apart a distance which is approximately the desired width of the board.
Forming belt 20 is preferably a moving endless belt conveyor of a liquid-impermeable material such as rubber, rubberized canvas or the like. The upper run of belt 20 moves to the right in the arrangement shown in FIG. 1.
Forming belt 20 passes the deposited mix under a picker roll 27 which levels off the top of the deposited mix and removes the excess material which can be recycled. Because the air-deposited mix has a significantly greater thickness at the time of passing the leveling operation, which is performed by picker roll 27, as compared to the thickness of the product, any inaccuracy in the leveling operation is minimized during the subsequent compressing steps.
An air permeable or impermeable member, such as endless screen 30 or a belt, exerts compressive forces on the layer of mix to consolidate the material. Rollers 32 and 34 drive screen 30 at the same linear speed as belt 20. Preferably, screen 30 exerts compressive forces of from 20 to 40 psi on the layer of mix.
The low density insulating board product of this invention in general comprises the same ingredients which were present in the solid component of the above-described mix, and from to 3 percent water. Because there is no filtration step in which water can dissolve materials from the mix, there is substantially no loss of solid components of the mix and the finished board possesses the same ingredients and approximately the same weight ratios of ingredients as the solids portion of the mix.
Visually, the dry process board of this invention is quite similar to perlite boards produced by a wet, papermaking type process. However, the board of the present invention tends to possess better interlaminar strength than wet process board.
For a clearer understanding of the invention, a specific example is set forth below. The example is illustrative, and should not be understood as limiting the scope and underlying principles of the invention in any way. All percentages listed in the specification and claims are weight percentages unless otherwise noted.
EXAMPLE Roof insulation boards are formed from a dry mix of plastic consistency and containing about 75 percent water and 25 percent solids. The solids portion comprises 70 percent expanded perlite, 20 percent bentonite clay, percent asphalt emulsion (Flintsize 205 60 has overall strength and thermal insulation properties The mix is subjected to intense shearing forces within mixing zone 16 and then is deposited on a traveling belt. The layer of mix is leveled by passage beneath a picker roll and the leveled layer of mix is subsequently compressed to remove air from the layer of mix by passage beneath a traveling wire screen. The layer of mix is subsequently compressed under a solid roller and then passed through a drying oven where the board is dried to a moisture content of about 0-3 percent.
Subsequently, the board is cut and trimmed. The dry process board thus produced at a lower density level that are comparable to perlite board produced by a typical commercially utilized, wet, papermaking type process, and exhibits superior interlaminar strength, as shown by Table I below.
43 to 54 (desired) Laminar Strength (psi) 15 4.0 (minimum) 8.0 (desired) Water Absorption 0.75 1.5 (maximum) (7r by volume) Thickness required for 1.09 L08 0.36 conductance value (inches) Flame Spread Rating 10 25 In addition to the desirable strength and insulation properties the board of the Example possesses significantly greater flame resistance than standard wet process board.
In summary, the present invention avoids a filtration step which has been necessary in prior commercial wet process perlite processes, and permits the use of perlite particles which could not be used in wet, papermakingtype processes. Increased production speeds are possible in accordance with the invention. Also, there are no losses of material and there is better thickness control of the finished product in the new dry process, as compared to the wet process.
FIG. 2 illustrates the manner in which perlite board manufactured in accordance with the process of the invention and formed to provide an inclined top surface can be used to build up an incline on a dead level roof deck. A plurality of sloped boards 40 from the top surface of the insulation layer. Sloped boards 40 are placed on boards 42 of uniform thickness. In this manner, the top surface of the insulation layer can be provided with a constant pitch that will provide for good drainage of water even though the insulation layer is built up from a level roof deck. Ordinarily perlite board is cut to 4-foot lengths, and in the dry process of this invention the width of the deposited mix is maintained at about 4 feet. In FIG. 2, therefore, the horizontal dimension of boards 40 and 42 therefore would customarily be 4 feet.
What we claim is:
l. A continuous dry process for making a low density perlite board comprising:
a. feeding 12 to 38 parts per 100 of expanded perlite, and a stream of 62. to 88 parts per 100 of aqueous slurry to a mixing zone containing air, said slurry including about to percent of binder solids and said perlite being the major solids component in the combination of perlite and slurry and in the ultimately formed board;
b. passing the perlite and the slurry through the mixing zone while exposing the mix to intense mechanical shearing forces for less than about 10 seconds to intimately admix the solids components of the mix and form a fluffy mass having a density on a dry basis of from 5.5 to 7.0 lb/cu. ft.;
0. continuously depositing said fluffy mass across the width of a traveling endless conveyor to form board stock;
d. shaping the top surface of said board stock to obtain a planar top surface;
e. compressing said board stock to the desired board thickness; and
f. evaporating water from the compressed board.
2. The process of claim 1 in which the fluffy mass contains from to 50 percent by weight of solids.
3. The process of claim 2 in which the fluffy mass contains on a solids basis about 70 percent perlite, about 5% waterproofing agent, and about percent binder.
4. The process of claim 1 in which the aqueous slurry is sprayed on the perlite at the top of the mixing zone.
loose density of from 3 5. The process of claim 1 in which a portion of the mix is screeded off thetop surface of the board during the leveling step and is recycled, and the quantity of recycle is minimized by controlling the amount of mix deposited on the traveling belt, in relation to the speed of the traveling belt, to exceed by less than 20 percent the amount of mix necessary to form a board of the height that passes the screeding operation.
6. The process of claim 1 in which the fluffy mass is deposited on caul plates which are carried by the conveyor.
7. The process of claim 1 in which about percent of perlite, and sufficient slurry to provide about 20 percent bentonite clay, about 5 percent starch, and about 5 percent of a waterproofing agent per unit of time are fed to the mixing zone.
8. The process of claim 1 in which the stream, of aqueous slurry is sprayed under pressure onto a stream of perlite particles at the top of the mixing zone, and the mix ingredients pass downwardly through the mixing zone and onto the endless conveyor due to gravity.
9. The process of claim 1 wherein said solids components of said mix by dry weight consist essentially of (a) from 65 to percent of expanded perlite, (b) from 15 to 25 percent of binder, and (c) from O to 10 percent waterproofing agent.
10. The process of claim 1 wherein said perlite has a to 5 lb./cu. ft.
UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,888,962
DATED June IO, I975 INVENT 1 Robert J. Ostertog, et al It is certified that error appears in the above-identified patent'and that said Letters Patent are hereby corrected as shown below:
Column 2, line 15 Patent No. should read "3,344,217"
Column 2, l ine l8 "requirement" should read "equipment" Column 3, line l "means" should read "mass" Column 3, line 53 "not" should read "no" Column 4, l 1'ne 53 "advantageous" should read "advantageously" Column 7, line l "rollers" should read "rolls" Signed and Scaled this seventh Day of 0'ct0ber1975 [SEAL] Arrest:
c. MARSHALL DANN- (ommissiuner oflatenls and Trademarks RUTH C. MASON Arresting Officer
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