US 3608051 A
Description (OCR text may contain errors)
United States Patent  Inventor RalphK.Scott 8/1953 Macready.
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Attorneys- Keith S. Bergman and Buckhorn, Blore, Klarquist and Sparkman  WAX MOLD CASTING OF CONCRETE 6 Claims, 7 Drawing Figs.
ABSTRACT: A process to cast at least part of the peripheral surface of a concrete structural element against a wax mold which may also serve as a matrix to position form or surface elements to be embedded in the concrete. The initial mold is established from liquid wax, the wax allowed to set, and the s 40 6 6 I12 H B 4 4 um-D65 2 822 M 7 .2 m mm2 "n U 4 mm mm m mm "n "n 6 "m m m" .1 "a n" n n" n m mh m lm ml.
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mold removed from the cast formed after setting of the References C'ted concrete by hot water or steam which also serves to cure the UNITED STATES PATENTS 1916 Mickelson....................
concrete. The process allows simple mold formation for and removal from complex concrete structural forms, es
264/317 pecially 264/317 those having embedded surface elements and undercut sur- 264/DIG. 44 faces. Apparatus is disclosed to conveniently carry out the 264/DIG. 44 proc PATENTEDISEPN m1 SHEET 1 [IF 3 F/GURE 2 5 K H w H INVENTOR.
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WAX MOLD CASTING OF CONCRETE II. BACKGROUND OF INVENTION IIA. RELATED APPLICATIONS There are no applications related hereto filed in this or any foreign country at this time.
IIB. FIELD OF INVENTION This invention relates generally to the field of concrete casting and more particularly to a process and apparatus for easting part of the peripheral surface of a concrete structural member against a thermoplastic surface, such as of wax, to allow simple thermal placement and removal of the mold.
IIC. DESCRIPTION OF PRIOR ART The casting of concrete has traditionally been carried out with use of rigid molds or forms defining at least a sufficient part of the periphery of the cast structure to contain plastic concrete. This method of casting functions quite satisfactorily so long as the peripheral elements of the formed structure are substantially planar or constitute simple surfaces, but if the surfaces be irregular, undercut or of a complex nature, the casting against a rigid form has not proven satisfactory.
It has heretofore become known in the art to use various yieldable and granular substances to form a mold for complex surfaces such as those encountered with concrete panels having embedded masonry surfaces or undercut areas. Such mold materials heretofore known have generally made use of rubber, plaster, clay, sand or similar finely particulated material.
Thermoplastic substances seem not to have become well known as mold materials in the concrete forming arts, though in the art of metal casting, especially as in the jewelry and dental fields, it has become known to use wax or some similar thermoplastic substance as a sacrificial arbor material in the making of hollow molds or molds having undercut areasa process commonly known as lost core or lost wax casting. This process has generally used wax to form internal voids or chambers and not to form any substantial part of a peripheral surface; similarly, the wax has not been used as a matrix to hold or position molds or embedded structures.
My invention differs from this art by providing a thermoplastic substance to form a mold for complex peripheral surfaces of concrete and especially in using wax for this purpose. My process further differs from the known art in providing hot water or steam about the set concrete to remove the mold material during the concrete curing period, to aid in curing the concrete and substantially reducing the length of the curing period. My invention further differs from the prior art in providing novel apparatus for curing and removing a wax mold from a formed product and for thereafter separating and reclaiming the mold material.
III. SUMMARY OF INVENTION My invention provides a process and apparatus for casting concrete structures having at least part of their peripheral surface formed against a thermoplastic material which may be placed and removed by thermal activity and more particularly to such a process providing a wax mold that may be removed with hot water to aid in the curing of the formed concrete and to allow the subsequent salvage of the mold material.
To accomplish my process in the case of a slablike concrete structural element having stone particles embedded in one or more surfaces, I provide a large pan configured to contain the structural element to be formed and in this pan I provide side forms for the panel positioned on plural supports at spaced distance from the pan bottom. Rock to form the face of the panel is then placed within the side forms and liquid wax introduced into the bottom of the pan to a level sufficient to form the desired surface of cast concrete. The wax is then solidified to form a rigid lower mold surface and concrete introduced thereabove, about the rock to be embedded and within the side forms, to form a solid structure. When the concrete is set but still green, hot water is introduced into the pan about the concrete slab to remove the wax casting medium and aid in thermally and hydraulically curing the concrete slab.
In practicing this process I provide a large thermally insulated, covered curing pan adapted to hold a smaller mold carrying pan, its supports and the mold in which product is formed. An associated plumbing system with a particular valving structure provides for fiow of hot liquid and admixed wax from the pan through a circulating pump and thence into a separating tank where the wax remains. The water then passes to a heater and thence to a storage tank from whence it may be recirculated to the pan or short circuited to the heater. A particular exit valve is provided to maintain a constant liquid level in the curing pan, remove floating wax from the liquid surface and provide a constant supply of liquid to keep the circulating pump primed.
In providing such process and apparatus it is:
A principal object of my invention to provide a method by which a complex surface of a cast concrete element is formed against a thermoplastic substance that may be established and removed by thermal activity.
A further object of my invention to provide such process that allows removal of the thermoplastic casting medium by thermal activity that aids in rapidly curing the cast concrete.
A further object of my invention to provide apparatus for use with such a process that allows simple and easy handling of product, and ready reclamation of expanded mold material from its liquid carrier.
A still further object of my invention to provide such a process and apparatus that are of new and novel design, of rugged, durable and reliable nature, of simple and economic design and operation and otherwise well adapted to the uses and purposes for which they are intended.
Other and further objects of my invention will appear from the following specification and accompanying drawings which form a part of this application. In carrying out the objects of my invention, however, it is to be understood that its essential features are susceptible of change in design, ordering and arrangement with only one preferred and practical embodiment being specified and illustrated as required.
IV. BRIEF DESCRIPTION OF DRAWINGS In the accompanying drawings, wherein like numbers of reference refer to similar parts throughout:
FIG. 1 is a partial expanded, isometric view of the curing pan, mold pan support, mold pan and top of my invention showing their configuration and relationship.
FIG. 2 is a vertical cross-sectional view through the curing pan and mold pan support of FIG. 1, taken on the line 22 thereon in the direction indicated by the arrows.
FIG. 3 is a vertical cross-sectional view through the mold pan and contained mold of FIG. 1, taken on the line 3-3 thereon in the direction indicated by the arrows.
FIG. 4 is a semidiagrammatic representation of the various plumbing elements of my invention showing the relationship therebetween.
FIG. 5 is a somewhat enlarged orthographic view of the particular overflow type drain mechanism used in my curing pan.
FIG. 6 is a semidiagrammatic representation of plural crosssectional views through my curing pan, showing the essential steps of the process of my invention.
FIG. 7 is a partial expanded isometric view, somewhat idealized, of a panel formed under the process of my invention with internal voids and the mold elements used to form such voids.
V. DESCRIPTION OF PREFERRED EMBODIMENT The apparatus of my invention is illustrated generally in FIG. 1 where it is seen to comprise curing pan 10 with associated plumbing system 11 supporting form pan support 12 which in turn supports form pan 13 carrying form structure 14 and product 15.
Curing pan is a rectilinear structure formed of paired opposed sides 16 structurally communicating between similar opposed ends 17 all supported upon bottom 18 to define a liquid containing volume. The bottom is provided with medial channel 19 sloping to communicate with lowermost pump 20. Plural crosspieces 21 extend across the upper surface of bottom 18 to protect it during placement and support of the form pan support in the curing pan. Lid 22, configured to fit immediately upwardly adjacent the upper peripheral side edges of the pan too, encloses the upper portion of the curing chamber.
Preferably the curing pan is formed of some structurally rigid material that does not readily transmit heat. I have formed this structure in experimental work from medially insulated, fiberglass surfaced panels and found them to be most satisfactory, but undoubtedly other materials with similar characteristics would function satisfactorily. Crosspieces 21 are of a more physically durable material, preferably wood or metal, to prevent damage to the pan and provide reasonable wear characteristics. The dimensioning and configuration of the curing pan is not critical but must be such as to allow containment of the form pan support, form pan and product within the curing chamber preferably without too much surplusage of unoccupied volume. This configuration, of course, will vary widely in different application but for ordinary configuration structural panels I prefer a pan approximately seven by fifteen feet with a depth of approximately 1 foot.
Form pan support 12 is a rectilinear member formed of similar opposed channel side elements 24 structurally communicating by means of opposed similar channel and elements 25, the sides at least having horizontally inwardly extending lower lips 26 supporting plural spaced cross elements 27. Preferably these structures are formed of metal with a configuration of the member such as to allow it to be appropriately contained within chamber 23 of the curing pan and to itself contain form pan 13.
Form pan 13 is a rectilinear member similar in shape to form pan support 12 and is adapted to be carried between the side elements thereof. The pan comprises similar opposed sides 28 structurally joined by opposed ends 29, all supported upon bottom 30. Preferably this pan is of a substantially liquid-tight construction to aid placement of liquid wax casting material. Its configuration necessarily limits the dimension of form structure 14 carried therein and consequently the size and configuration of a product formed therewith. This pan is preferably constructed of metal to provide appropriate rigidity and structural characteristics.
Form structure 14 is not critical to my invention and may be of any of the general types heretofore used in the concrete forming arts so long as it appropriately supports the concrete structure to be formed during its plastic state, in conjunction with the form pan and thermoplastic mold surfaces associated therewith. The particular form structure illustrated is for use in formation of rectilinear slablike structural panels having embedded masonry in one surface. This type of form comprises similar opposed sides 31 releasably joining similar opposed ends 32, all supported at a spaced distance above the bottom of form pan 13 by plural depending spacers 33. The spacers are not necessary but generally convenient to allow placement and removal of thermoplastic casting medium between the ultimately formed product and pan bottom. Many other types of ready made and adjustable forms commonly used in the concrete forming arts may be adapted for use with my process.
Plumbing system 11 as seen in FIGS. 1, 4 and 5, provides drain 34 communicating with the lower portion of sump in curing pan 10 and thencely passing by sump line 35 through shutoff valve 36 to stand pipe 37. Pump line 38 exits from the bottom of stand pipe 37 to thence pass through shutoff valve 39, strainer 40 and shutoff valve 41 to pump 42. Sump short circuit line 43 communicates from drain 34 through shutoff valve 44 to line 38, between strainer 40 and shutoff valve 39. Pump 42 communicates by output 45 to tee 46 from whence it splits into separator line 47 passing through shutoff valve 48 and check valve 49 to separator chamber 50 and reservoir short circuit line 51, passing through shutoff valve 52 into reservoir 53. Separator 50 communicates through water output line 54, in parallel with heater 55, through shutoff valve 56 between the heater input and output to tee 57, from whence it splits into pan hot water line 58 communicating through shutoff valve 59 to the curing pan and reservoir 53. Reservoir output line 62 communicates through shutoff valve 63 to the curing pan and short circuits through return line 64, carrying shutoff valve 65, to pump line 38. Wax line 66 communicates from separator 50 through shutoff valve 67 to the form pan.
The separator preferably is physically positioned above the curing pan and the reservoir positioned above the separator to allow appropriate gravity flow of fluids into the curing pan. This requirement could be changed, of course, by appropriate use of additional pumps.
The overflow structure illustrated in FIG. 5 maintains constant water level in the curing pan 10 above drain 34 and simultaneously maintains a prime for pump 42. This structure provides vertical pipe 68 slidably fitting within drain 34 and extending upwardly therefrom. Tee 69 communicates horizontally from the upper part of this pipe through shutoff valve 70 to input pipe 71. Short nipple 72 extends upwardly from tee 69 to threadedly engaged input pipe 73 for adjustable vertical motion relative to the tee. Flotation collar 76 is provided about the upper part of input pipe 73 to maintain the input pipe orifice at a level to receive liquid substantially from the liquid surface to aid in removing wax. With this construction, valve 70 may be opened slightly to allow sufficient water to pass into pump line 38 at all times to maintain a prime in pump 42 and at the same time input pipe 73 may be vertically adjusted to the desired level to allow overflow at that level to maintain the level.
In this regard it is to be noted that the flotation collar will maintain the input at the liquid level whatever it be, but the input may not move below a predetermined level as the downward progress of pipe 68 will be stopped when it contacts the upper surface of drain 34.
The process of my invention may now be better understood in light of the description of the apparatus used to carry it out. The specific embodiment illustrated shows the forming of a concrete panel having masonry elements embedded to form a part of the finished surface. To form such a product with the apparatus described I proceed thusly:
Step I. Assemble the apparatus as previously described with curing pan 10 carrying form pan support 12 in turn supporting form pan 13, all appropriately arranged to communicate with the plumbing system as illustrated and described.
Form structure 14 is then established within form pan 13 to be supported at a spaced distance above the pan bottom by spacers 33 and to enclose the side periphery of finished panel 15 so that plastic concrete may be supported within the form element.
It is not necessary that the form elements be supported at a spaced distance above the bottom of form pan 13, but this generally is desirable to allow a ready circulation of hot liquid between the panel and the pan bottom to place and aid in removing the thermoplastic casting material. If the forms be not spaced from the pan bottom they may be quite conveniently maintained in position upon the form pan by establishing wax between the adjacent surfaces of form and pan to maintain an adhesive bond. The forms may be releasably joined to form a self-supporting unit or may be appropriately supported by parts of the form pan or structures thereabout. The nature of the particular form is not critical so long as it be sufficient to maintain the plastic concrete in appropriate shape in conjunction with thermoplastic casting medium, until the concrete is set.
Step 2. Facing material for the panel, in this instance particulated rock, is placed within the peripheral limits of form structure 14 resting upon the upper surface of form pan 13. The material may be placed in any desired array and may generally comprise any of the surfacing materials used in the structural arts. The incidental mechanics of the panel, however, must be considered to provide some type of surfacing material that may be bonded within the backing concrete, preferably by reason of undercut angular protrusion therein, and these protrusions within the concrete must be appropriately related to panel thickness to provide the desired resultant strength. After placement of the facing material, reinforcing matter of the common types used in structural concrete may be positioned thereabove, if desired, for enclosure in the panel to be formed.
Step 3. Form pan 13 is flooded with heated liquid wax from separator 50 by opening shutoff valve 67 and allowing the liquid wax to flow through line 66 into the form pan preferably without too much turbulence. The wax will flow about the facing material and is allowed to enter until the desired level of finished surface of concrete in the panel is attained.
If the wax solidifies too quickly it may create an irregular surface or dams may be formed completely preventing access of liquid wax to some mold areas thusly forming an imperfect mold. This is especially a problem if the facing material or ambient atmosphere be relatively cold. To alleviate the problem the form pan or facing material or both may be preheated to a temperature near the melting point of the particular wax. To accomplish this preheating function most conveniently, hot water may be circulated in the curing pan and about the form pan and its contained facing material until their temperature be sufficiently raised. lf much preheating is to be done it may be convenient to construct an additional preheating pan (not shown) slightly larger in dimension than the form pan to fit outside the form pan so that hot water may be circulated in the preheating pan to conserve the required amount of hot water and make the heating more rapid.
I prefer to use a petroleum wax of the paraffin type for my mold bed; one such wax successfully used is Chevron candle wax number 135 produced by the Standard Oil Company of California and having a melting point between 130 to 132 fahrenheit. Obviously, other waxes and thermoplastic substances of similar nature might be used for the purposes of my invention, but paraffin has been found most desirable because of its shrinkage on solidification; its melting at a convenient thermal level substantially lower than the boiling point of water but yet substantially higher than nonnal room temperatures; its relatively low cost, at present market some odd cents per pound; and its low density and insolubility to any appreciable extend in water, which allows a ready gravity separation of the admixed liquids. Other products having some or all of these characteristics might be adapted to use with my invention, however, if not so well.
In establishing the mold bed it is to be noted that the wax will encase the ultimately outwardly projecting surface of the panel to be formed and thusly will allow formation of concrete about the masonry product somewhat behind the supporting mold pan bottom, depending upon the wax level, so as to provide a finished product with the appearance of a struck-mortar joint-that is, one having the concrete recessed a distance from the surface. Since the wax forms a quite smooth surface this surface character will be created in the concrete formed thereagainst.
It is further to be noted that from the method of placement of the masonry aggregate, a substantially planar finished surface of the aggregate will be automatically formed since it is supported upon the form pan by gravity prior to placement of wax and by reason of the placement of wax in the liquid state, no disturbance of product will be occasioned thereby. The depth of wax molding the lower surface of the cast concrete panel is somewhat greater than the spaced distance between the lower portion of form structure 14 and pan bottom 30 so that after the wax solidifies the form structure will enclose a five-sided container defining a cavity sufficient to support a plastic substance such as concrete prior to setting.
Step 4 The wax is cooled to set to a solid state or freeze. Normally this setting is accomplished by heat loss to the atmosphere without special facilities, especially in the case of relatively thin layers of petroleum waxes. The ambient atmosphere is normally in the seventy degree range, or not much thereabove, and petroleum waxes may be selected with the melting point in the neighborhood of to l40fahrenhei t, so the setting is normally fairly rapidly accomplished by side dissipation of heat to the ambient atmosphere. It is, of course, possible to introduce auxiliary coolant in or about the form pan. If auxiliary coolant be desired it is preferable not to directly introduce a liquid coolant upon the liquid wax mass, as this tends to disturb the wax surface.
The substance used as form material when solid must be reasonably rigid and have no great plastic flow upon stress caused by plastic concrete thereabove. Petroleum wax fulfills these requirements as before specified but undoubtedly other substances such as thermosetting plastics would accomplish the same ends, if not so well.
Step 5. Plastic concrete is introduced within the cavity enclosed by the form structure to form the concrete slab. Most commercially used concrete mixtures are adaptable for use with my invention, so long as they have sufficient flow and cohesion to fill the voids existing about the periphery of the form and form a solid mass therebetween. For most structural elements it is preferable to have a high strength concrete, preferably an eight sack mix formed with relatively small gravel particles and no more water than necessary to allow proper placement. Such a mix used in experimental work by me, sets in approximately a 13-hour period and cures thereafter to a compressive strength of approximately 4.300 pounds per square inch.
It is desirable that a concrete that sets rapidly to a relatively high strength can be used with my process as it appears that the ultimate strength of the product is more closely related to preset time than to accelerated curing time thereafter, and since the set and curing times limit production, it is desirable that both times be as short as possible.
The placement of concrete within the form should be accompanied by appropriate mechanical agitation to remove voids from the concrete and cause it to bond into a homogeneous solid intimately communicating with the wax form material therebelow and the facing material carried thereby. To accomplish this I prefer to use mechanical vibration supplied by an ordinary concrete vibrator. After proper establishment of concrete within the form the backside of the panel (that now facing upwardly) may be finished at the appropriate degree of set according to the finishing methods presently available in the concrete forming arts. The concrete is then allowed to remain in formed position until a set of some reasonable strength (say one to 300 pounds per square inch) has developed therein and the concrete mass is sufiiciently rigid to be self-supporting.
It is to be noted that at this stage of my process, either prior to pouring concrete or thereafter, the form pan may be removed from the curing pan to allow use of the curing pan with other form pans.
Step 6. The set concrete slab is returned to the curing pan, if necessary, the there subjected to heat introduced, in this instance, by means of a liquid carrier, in this instance water, for a period of time sufficient to remove the wax forming material and to reasonably cure the concrete structure.
So long as water is maintained in the plumbing system it may be circulated from separator 50 through line 54, into heater 55 and thence through line 60 into reservoir 53 from whence the overflow may recirculate through line 51 and back through separator 50. By this means water in reservoir 53 may be kept at a predetermined temperature by regulating the thermal input of the heater. Line 51 is primarily for the rapid draining of the curing pan as it cuts the friction losses otherwise involved in boosting liquid from the curing pan to the reservoir. Water in the reservoir when desired for use in the curing pan may flow through line 62 into the curing pan but preferably a direct flow through the heater is established through line 58, both by regulation of the appropriate valves.
By one method or the other hot water is introduced into the curing pan, preferably maintained at a reservoir temperature of approximately 165 degrees fahrenheit, an outlet temperature of 150 to 155 degrees fahrenheit, and a curing pan tem' perature of approximately 145 degrees fahrenheit. The drain structure may be regulated to maintain the water level in the curing pan above the top surface of product therein, so that the product is completely immersed in hot circulating water, or this may be accomplished by direct circulation from drain 34 to pump 42, thence through the separator 50 and heater 55 and back through line 58 to the curing pan. Circulation is maintained until the wax form material is substantially removed and the product has cured to the desired strength. Generally with concrete mixtures as indicated, I prefer to cure the product between 4 and 12 hours, about 80 percent of the ultimate strength, however, being developed substantially within the 4-hour period.
It is to be noted in the illustrated embodiment that as water is introduced into the curing pan it will circulate therein and cause the wax mold material to melt to a liquid state, since the water temperature is above the melting point of the wax material. The admixed liquid wax and water will then pass through drain 34, into line 38 and thence through pump 42 to separator 50. The separator is large enough that there is little turbulence to maintain admixture and since the liquid wax is insoluable in and less dense than the hot water, it will tend to rise to the top of the separator tank where is will be maintained in the liquid form until needed. Hot water will remain therebelow and pass on through the heating cycle to the hot water reservoir 53 or to the curing pan to be reused as needed. Substantial recovery of wax mold material is obtained by this method of separation, generally averaging above 95 percent.
The hot water bath generally removes substantially all of the wax mold material from concrete masonry surfaces. If there be a residue, however, this may be desirable as a finish for the product, but if not, such residue may be removed after final curing by means of an additional steam cleaning in the traditionally familiar fashion; such a residue may also be removed by water washing of the hot product immediately after removal from the curing pan.
Normally to conserve heat during the curing operation, lid 22 will be placed in position on top of curing pan 10, but again this is not essential and the lid may be left off if desired.
Step 7. After the product has cured as aforesaid to the desired strength and the wax mold material has been removed therefrom, the water in the curing pan is removed through the plumbing system to reservoir 53. The side forms are then stripped from the finished panel and it is removed from the forming pan for future use or storage as particular circumstances may require. The apparatus is then inoperative condition, ready to be recycled in the same fashion as aforesaid to create a second structure.
In test operations with the physical conditions specified and a concrete slab some 4-inches thick and four by eight feet in linear extend, an approximately 8-hour cycle has been established to allow formation of three structures within a 24- hour day. In this regard it is to be noted from the nature of the apparatus specified that plural form pans, and form pan supports if necessary, might be used with a single curing pan to allow a more rapid sequencing of operation so that one curing pan may be involved with the curing operation substantially all of the time.
It is to be noted, as illustrated in FIG. 7, that appropriately shaped pieces of thermoplastic casting element may be used as expendable arbors in forming holes or protrusions within the concrete structure. A side block 74 may be attached to the inside of form structure 14 to form holes in the panel sides, especially adapted to aid in fastening adjacent panels together and to aid in their manipulation prior to structural embodiment. Similarly an internal arbor 75 may be used to form central holes or channels if such should be desired in a structural product. These wax forming elements 74, 75 might be quite conveniently attached for support upon the forms by thermally softening the attachment surface and maintaining it in appropriate position upon the adjacent form surface until an adhesive bond be formed by a liquid or plastic layer or wax between the solid arbor and the supporting surface. Obviously, such elements could also be positioned by auxiliary mechanical supports such as heretofore known in the concrete forming arts.
With the use of such arbors to form voids, it is to be noted that when the product is cured the arbor material will be melted and removed as other similar material supporting the undersurface of the formed panel.
It is further to be noted that although the use of hot water is disclosed to remove thermoplastic mold material and cure product, other thermally active media such as steam, other hot gasses, and various other hot liquids would serve the purposes of my invention.
The foregoing description of my invention is necessarily of a detailed nature so that specific embodiments of it might be set forth as required, but it is to be understood that various modifications of detail, rearrangement and multiplication of parts may be resorted to without departing from its spirit, essence or scope.
Having thusly described my invention, what I desire to protect by Letters Patent, and
What I claim is:
1. A process of forming a concrete member having solid elements partly imbedded in a surface of said member, which comprises:
supporting a layer of said elements on a horizontally extending support at the lower portion of a mold for concrete with each of said elements partly submerged in a layer of molten thermoplastic material;
cooling said material to solidify said material and form a wall for said mold; thereafter introducing into said mold and into said intimate contact with the exposed surfaces of said elements and said solidified material a layer of a concrete mix;
maintaining said concrete mix in contact with said elements and said solidified material until said concrete sets to form said concrete member;
heating said solidified material and said concrete member with a liquid, which is immiscible with and has a greater density than said thermoplastic material and which is heated above the melting point of said thermoplastic material to melt said material and wherein said heated liquid is circulated to remove the melted thermoplastic material from said concrete member.
2. The process of claim 1 in which the solid elements and the mold are heated to a temperature near the melting temperature of the thermoplastic material and the molten ther moplastic material is thereafter added to the mold.
3. The process of claim 2 in which the thermoplastic material is a petroleum wax.
4. The process of claim 1 in which the melted thermoplastic material is separated from the heated liquid by difference in density.
5. The process of claim 1 in which the thermoplastic material is a petroleum wax and said liquid is water.
6. The process of claim 5 in which said heating includes sub merging said mold containing said concrete member and solidified wax in a circulating stream of heated water to melt said solidified wax and remove melted wax from said concrete member and to accelerate the further setting of said concrete.
23 3;" UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,608,051 Dated September 21. 1971 Inventofls) RALPH TT It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
r Co1umn 4, line 10, after "reservoir" (first occurrence) insert --hot water line 60 communicating to air vent 61 and thence reservoir--. Column 5, line 49,"extend" should read --extent-- Column 7, line 52, "inoperative" should read in operative--. Column 1, line 57, "extend" should read --extent--.
Signed and sealed this 21st day of March 1972.
EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents