US2830342A - Shell molds and cores from precoated fluid coke - Google Patents

Description

United States PatentO 1 2,830,342 SHELL MOLDS AND (IGRES FROM PRECOATED FLUID CUKE Gustave Roland Meyers, Ann Arbor, and Everett G.

Gentry, Lincoln Park, Mich assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application June 5, 1956 Serial No. 589,374 5 Claims. (Cl. 22-193) The present invention relates to improved shell molds and cores, and to compositions for forming shell molds and cores. It more particularly pertains to an improved shell mold composition comprising fluid coke and a minor proportion of a resin binder.

This application is a continuation-in-part of S. N. 539,- 778 carbonaceous Molding Material for Foundry Operations, filed October 11, 1955 by the present inventors. In brief compass this invention proposes a shell molding composition comprising a major proportion of fluid coke, either raw, calcined or calcined and desulfurized, and a thermal setting resin binder. The resin binder is distended on the particles of fluid coke, i. e., the fluid coke is precoated with the resin binder.

The hydrocarbon oil fluid coking process has recently been introduced into petroleum refinery operations. In this fluid coking process, an oil, usually a low value heavy residual oil, is converted by pyrolysis to relatively lighter hydrocarbons and coke by contact with finely divided heat carrying solid particles maintained at a temperature in the range of 850 to 1500 F. or above. The heat carrying solids are preferably maintained as a fluid bed in a coking zone, but the process can be carried out in a trans fer line. The coke produced by the pyrolysis deposits on the fluidized solids, layer by layer, and becomes a part thereof. Although some of the cokeproduced by'the cracking may be consumed by burning to supply heat in the coking process, a substantial amount is removed as by-product. The heat carrying solids normally used are coke particles produced by the process such that the byproduct coke is of uniform composition. The by-product fluid coke produced has a high percentage of carbon with an ash and sulfur content characteristic of the oil feed stock.

The particle size of the heatcarrying solid used in the coking processis in the range of about 18 to 400 U. S. sieve number, with the median particle size normally being in the range of 45 to 70. V The by-product coke is of about the same size. This unique by-product coke is characterized by its spherical or ovoid shape, laminar structure, high density and hardness, and differs substantially from the cokes produced by the pyrolysis of hydrocarbonaceous solids and oils by other processes. The term fluid coke is intended to include the solid product of the fluid coking process, i. e., the by-product coke or raw fluid coke, besides the treated forms of the raw fluidcoke, described below. a

It is much preferred to pretreat the raw fluid coke received from the coking process, by calcination and/or desulfurization to decrease its volatile matter andsulfur content and to increase its density. The product soob: tanied by this pretreatment is hereinafter referred to as calcined fluid coke. Although ,desulfurization treatment of raw fluid-coke normally results in calcination of the coke, it is not necessarily always true. The term calcined fluid coke herein used, includes fluid coke that hasonly been desulfurized. Calcined fluid gives many superior and unexpected resultsover raw fluid coke. Calcinationof the'raw fluid coke to primarily increase its density and decrease its volatile matter content may be carried out by any conventional method." Generally, calcination of'fluid coke simply involves heat soaking at point of 10l0 F. The coking was at a temperature of 2,830,342 Patented Apr.- '15,; 1958 ICti' relatively high temperatures, e. g., 1800 F. or above,

for a suitable period of time. This is preferably done separate from the coking process, but may be ca'rriedout within the process, as by segmenting the burner used toheat the circulating fluid coke to form a special high ten-l perature zone from which the by-product coke can be withdrawn. The calcination or heat soaking may be car ried out while the fluid coke is in the form of a fixed,

with flue gases, can be recovered from the soaking'zone.

It will be apparent to those skilled in the art that raw fluid coke can be calcined by repeated use in the casting process, and the term calcination is intended to include this. Thus, a small amount, say 5%, raw fluid coke can continuously be added to the reservoir of material used to form molds and/ or cores in a foundry, and by repeated use become suitably calcined.

Desulfurization of raw fluid coke or of fluid coke that has been calcined can be accomplished in several ways. One preferred method is to oxidize the coke by fluidizing it with an oxygen containing gas at a temperature in the range of 600 to 1500 F. for a time suflicient to consume over 3 weight percent of the fluid coke. preferred method of desulfurization comprises this oxidation treatment followed by hydrogenation with a free hydrogen containing gas at temperatures above 1100 F. In some cases the fluid cokemay be desulfurized without preliminary heat soaking, by contact with a desulfurizing gas such as hydrogen, ammonia, sulfur dioxide, etc. When using hydrogen it is preferred to maintain the temperature above 1100 F.; when using sulfur dioxide; the temperature is preferably maintained above 1800 F.

In some uses it may be preferred, besides calcining the; coke, to further pretreat it as by treatment with a solvent or by impregnating it with a suitable material such as water glass or finely divided graphite to decrease its porosity.

Fluid coke as removed from the fluid coking process, When coking the customary residual oil feed stocks, normally will have a sulfur content of about 7 Weight percent or above. It is preferred to reduce the sulfur content if necessary, by the above treatments, to below about 7 weight percent to prepare it for use in foundry operations because higher amounts of sulfur may produce intolerable amounts of noxious fumes. Raw fluid coke can, however, itself be used in casting operations as hereinafter described. I

To illustrate the change in properties that occurs during different treatments of raw fluid coke, Table I is presented. The examples given for each type of coke are based on raw fluid coke having an original median particle size of about 235 microns, obtained by the fluid coking of a Hawkins residuum having a gravity of 43 API, a Conradson carbon of 26 wt. percent, an initial boiling point of 882 F. (atmos. pressure equivalent), and a 10% about 1000 'F.

An especially The calcined fluid coke example is based on treating raw fluid coke as a gravitating fluidbed in an elongated vertical calcining chamber, at a temperature of about 2100 F. for a time up to about hours.

The ,desulfurized fluid coke example was obtained by treating raw fluid coke as a gravitating moving bed in anexternally heated elongated verticalsilicon carbide brick-lined calcining tower. The coke was heated to a temperature up to about 2400" F. for a time of about 24 hours,.in the presence of a small amount of nitrogen stripping gas.

Generally speaking, calcination of fluid coke normally having a sulfur content of 1-12 weight percent, will reduce its volatile matter content below about 1 weight percent and sulfur content by S-%, and increase its true density above 1.7 grms./cc. Dcsulfurization usually will reduce sulfur content to below 3 weight percent. It is preferred to use fluid coke having characteristics falling in these ranges, as superior results are obtained even over raw fluid coke.

It has now been found that fluid coke precoated with a thermal setting resin binder forms superior shell molds for casting ferrous and non-ferrous metals and alloys thereof. The term shell mold as here used includes shell molds, mold liners, shell cores and similar molding forms, generally having a relatively thin wall thickness.

'It has been known in the art to precoat sand used in forming shell 'molds with a resin binder. The resin binder comprises a thermal setting material such as phen&formaldehydes, urea-formaldehydes, condensates of di-basic acids, and polyhydric alcohols, e. g., of maleic anhydride and pentaerythritol, and similar resins known to the art.

The resin binder may be coated on the fluid coke by known methods. Generally the binder. will comprise less than 15 weight percent of the mixture.

In the hot coating or mulling method, the coke is mixed with a liquid resin which may include an accelerator. The mixture is heated, as by using heatedair, to cause the resin to coat the coke particles.

In the cold coating method, he coke is coated with a resin using a volatile solvent. More particularly, a powder resin can be mulled with the coke, followed by mixing with an alcohol (e. g., ethyl) solvent and water. The solvent eventually evaporates, leaving the resin deposited on the coke.

Additives can be added to the molding composition before, during, or after coating the particles. For example, sand, mold release agents such as waxes or stearate base materials, or other additives or modifiers to improve green strength, volatility, flowability, etc., such as kerosene, iron oxide, clay, etc. can be added.

When fluid coke is used to form shell molds and cores, shorter investment times can be obtained because of the better heat conductivity of the fluid coke, compared to sand. Lighter shells are obtained. Because of the higher heat conductivity of these shells better castings are ob-v tained. The shells have better dimensional accuracy be cause of the lesser thermal expansion of the fluid coke.

TABLE II Mix N0 1 '2 Fluid coke (through ,i-e mesh), lbs. (See col. 3,

Table I.) 115.5 Juniata bank sand (A. F. S. No. 96), lbs 1 150 Resin, lbs; 6.0 6. 0 Methyl alcohol, cc. 900 750 Water, cc 200 200 Mixing equipment-Beardsley-Piper Speedmuller. Mixing time-4O sec. dry, 3 min. wet and until dry and free-flowi.ug. Shell mold forming technique:

Equipment-Beardsley-Piper automatic shell former. Patterntemp.-400450 F. Oven equipment Burdett gas bumers (no hood). Curing temp.Approx. 10U0-1200 F. Bonding equipment-Shell Process Inc. bonding x ure. Pattern release agent-DoW-Gorning XF-496 fluid (silicone). Average investment time, seconds 13 15 Average curing time, seconds 25 30 Average shell thiclmess, inches Au 94a 1 Approx. equal volumes.

TABLE 111 Percent retained on- 1 2 3 Sieve No.

Fluid coke .Tuuiata Fluid coke reclaimed bank sand through by heat of lie" mesh iron in shell molds A. F. S. fineness No 96 73 The castings from the shells have a smoother surface finish and are less troubled by veining because the shells are formed predominantly of carbonaceous materials. One method of forming a shell mold is to drop or blow the resin coated fluid coke into or onto a heated pattern having a temperature of about 350750 F. The plastic partially thermal sets and builds up a coherent fluid cokc shell next to the pattern. The thickness of the shell is related to the pattern temperature, dwell time on the pattern, and the type mixture. It may vary in thickness from' about to one inch or more. The loose fluid coke mixture is then dropped away from the shell, and the shell, still on the pattern, is further cured by heating. The shell is then stripped from the mold. A mold release agent, or parting agent, may of course be used to facilitate the stripping of the shell. Silicone parting solutions are customarily used. The same general procedure can be used for cores. In some cases, the core may be made solid without a central cavity.

Example 1 The fluid coke used was the desulfurized coke identified in Table I. The fluid coke was coated with shell molding resin by the cold coating method for comparison to silica sand coated in the same manner. The resin used was a phenol-formaldehyde type resin, identified as Durez Resin No. 17786. Table II gives information on the compounding of the resin coated sand and fluid coke. Table III, in columns 1 and 2, gives the sieve analysis of the solids.

Calcined fluid coke and the powdered resin were charged into the muller and mixed 40 seconds dry, then the alcohol and water (mixed) were added and'mixing continued for about 3 /2 minutes, by which time the solvent had evaporated and the resin coated particles were again dry and free flowing. The material was then passed through a As-inch sieve to break up any lumps and to assure more complete evaporation of thesolvent.

Shell molds were made consecutively with these sand and fluid coke mixtures on the same pattern. The shell former used operated on the dump box principle. From these tests it was determined that the investment time and cure time were less for the resin coated calcined fluid coke molds. Because cure time is usually a limiting factor in the rate of shell mold production, an increase, in this case, of 20% in production due to the higher heat conductivity of the calcined fluid coke is a definite advantage. The resin coated calcined fluid coke molds were more easily stripped from the pattern and a much less frequent application of silicone release agent to the pattern was required. Thefluid coke shell mold could be reseat-. ed on the cold pattern, whereas the sand shell mold had shrunk sufliciently to prevent it being replaced on the pattern. The fluid coke shell molds, therefore, are more true to pattern dimensions than are sand shell molds.

Example 2 In another comparative test, resin coated fluid coke and resin coated sand'compositions were made up to prepare shell molds vfor casting generator. rotors. Table IV shows the composition and the method of making shells. The coating process was carried out in the same manner and with the same equipment asused in Example 1.. The shells were about 7 thick. Because of the lighter bulk density of the fluid coke, a slightly larger amount of resin was used in preparing the resin-coated fluid coke mixture, i. e., thebulk density of the fluid coke results in more particles per weight, which necessitates a larger resin content on a weight basis. 1

TABLE IV MixNo Fluid coke (through Me" mesh), lbs. (See col. 3,

TableI 77 Juniata bank sand (A. F. S. N o. 96), lbs 150 Resin, l 5 6 Methyl alcohol, cc 550 750 Water, on I 133 200 Mixing equipment-Beardsley-Piper Speedmuller.

Mixing time-30 sec. dry, 3 min. 20 sec. wet until dry and free-flowing. Shell mold forming technique:

Equipment-Hand-operated dump box. Pattern temp.450 F. Oven equipmentEnclosed gas burner radiant heat oven. Curing temp.-Approx. 1200 F. I Pattern release agent-Dow-Corning XF-496 fluid (Silicone). Bonding equipmentShell Process Inc. bonding fixture.

Gray iron, melted in an electric furnace, but having the same composition essentially as cupola iron, was poured into test molds at approximately 2600 F.

The castings made of the fluid coke shell mold were somewhat smoother and showed much less penetration around the sprue area than did the castings made in the resin coated sand shell molds. The Brinell hardness for each type of shell mold casting was the same. It ap peared, therefore, that nochilling and/or significant sulfur pick up was obtained from the calcined fluid coke shell molds.

It was noted that the heat of the metal burned out the resin in some areas of the fluid coke shell mold, which ateen were well exposed to air, so that the fluid coke dropped away in its original granular form. This was not detrimental to the. casting because the metal had solidified be; fore this happened. This behavior did not occur in the case of the sand shell mold, and is attributed to the higher heat transfer characteristics of the calcined fluid coke. A sample of this burned calcined fluid coke was recovered and used for rescreen analysis given in Table III, column a 3. .A comparison of the screen analysis indicates that there was no appreciable change in particle size due to the heat of the metal. It further indicates that some fines may have been burned out and that no appreciable ash was formed. This indicates that the calcined fluid coke can be recycled in molding operations without detrimental veifect.

Example 3 In this example, resin coated raw fluid coke was used to prepare shell cores. The fluid coke .was obtained by the coking of heavy Elk Basin vacuum bottoms having a Conradson carbon of about 30 weight percent, sulfur of about 4.1 weight percent, I. B. P. of 925950 F., and

an A; P. I. gravity of 0-2". The coking was conducted at about 960-980 F. at a conversion in the range of 34 36% coke make, based upon fresh feed.

The raw fluid coke had the following typical inspections: I Carbon, weight percent 89.1

Sulfur,weight percent 6.1 Ash, at 1,742 E, weight percent 0.11 Volatile matter, at 1,100 F., weight percent 0.44 Moisture, weight percent 0.24 Real density 1.45

This raw fluid coke was screened through a A mesh sieve prior topreparing the resin coated composition.

j This raw fluid coke was compared to sand in casting cylindrical gray iron castings weighing approximately two pounds after removal of gates.

'Table V lists the core mixtures used to produce the resin coated materials, and the method of makingthe compositions. The resin used was the resin used in the previous examples. Note that mixtures #1 and #3 have an equal resin content on a volume basis because raw fluid coke weighs approximately 65% the weight of an equal volume of sand.

TABLE v Mix N o 1 2 3 Heaton sand (A. F. S. No. 70), lbs.. 10 Rilgl fluid coke (through He mesh), 6.5 6.5.

Resin, weight percent 4.5 4.5 6.92. Denatured ethyl alcohol, weight 1.33 1.33"". 2.05.

percent. Water, weight percent* 0.275 0.275. 0.52. Mixing equipment-Simpson laboratory mixer. Mixing time1 min. dry, wet Until dry- 4 min.-. 7 min.

*As weight percent in sand or coke.

Note No. 1.Heaton Sand was screened through No. 30 U. S. mesh before mixing.

Note No. 2.Mix No. 1, after discharge from mixer, was passed once through No. 30 mesh sieve. Mix No. 2 was passed twice through No. 40 mesh sieve. Mix N o. 3 was passed twice through No. 40 mesh sieve.

In producing the shell cores, the core box was heated 450-475 F. In each case resin coated material was poured into the hot core box, and after suitable dwell time the excess material was vibrated from the inverted box. The core box with the invested shell core inside, was returned to the oven for 20-40 seconds to complete curing of the resin binder. The core box was then parted and the shell removed. The scratch hardness of the cores from mixtures #1 and #3 was approximately 100, while cores from mixture #2 had a hardness of approxi- -mately 90.

The shell cores were set in green sand molds and were poured with gray iron melted in a production vcupola. On shaking out these castings, it was noted that the raw fluid coke shell cores, bonded with 4.5 weight percent resin, collapsed quickly and the castings were free of adhering core material.

Castings produced from each shell core were crosssectioned for examination of the cored areas. The surface finish of the cored area of the casting produced with the shell cores from mixture #2 was somewhat smoother than the casting produced with the sand shell cores, both being free of any veinings.

These examples show the superiority of the fluid coke shell molds made by precoating fluid coke with a resin. The fluid coke shell molds are more true to pattern dimensions than similar sand shell molds, and impart smoother surface finish to the castings.

Having described this invention, what is sought to be protected by Letters Patent is succinctly set forth in the following claims. I

' What is claimed is:

1. A shell molding composition consisting essentially of a major proportion of fluid coke and a thermal setting resin binder, said resin binder being distended on the particles of fluid coke, said fluid coke having been produced by contacting a heavy petroleum oil coking charge stock at a cokingtemperature with a body of fluidized coke particles in a reaction zone wherein the oil is converted to product vapors and carbonaceous solids are continuously deposited on the coke particles, removing product vapors from the coking zone, heating a portion of the coke from the coking zone in a heating zone to increase the temperature of said fluidized particles, re-

turning a portion of the heated coke. particlestfrom the heating zone to the coking zone and withdrawing coke product particles.

2. The composition of claim 1 wherein said binder comprises greater than and less than 15% of said composition.

3. The composition of claim 1 wherein said binder is distended on said fluid coke by dry-mulling the binder with the flui'd coke, adding a solvent, continuing the mulling,

and then drying.

4. The composition of claim 1 wherein said fluid coke consists of calcined fluid coke having a volatile matter to product vapors and carbonaceous solids are continuously deposited on the coke particles, removing product vapors from the coking zone, heating a portion of the,

coke from the coking zone in a heating zone to increase the temperature of said fiuidizedparticles, returning a portion of the heated coke particles from the heating zone to the coking zone and withdrawing coke product particles, placingsaid mixture on a heated pattern, forming thereby a thin hardened layer of saidqcomposition in the form of said pattern, and recovering from said pattern a shell mold.

References Cited in the file of this patent UNITED STATES PATENTS 1,467,112 Lucier Sept. 4, 1,871,315 Gann Aug. 9, 1932 1,886,252 Gann et al. Nov. 1. 1932 2,304,751 Hake et a1 Dec. 8, 1942 2,657,974 Cook Nov. 3, 1953 FOREIGN PATENTS 674,421 Great Britain June 25, 1952 511,794 Canada Apr. 12, 1955

Claims (1)

1. 5. A METHOD OF MAKING A SHELL MOLD, WHICH COMPRISES FORMING A LOOSE MIXTURE OF A MAJOR PROPORTION OF FLUID COKE AND A THERMAL SETTING RESIN BINDER DISTENDING ON SUCH FLUID COKE, SAID FLUID COKE HAVING BEEN PRODUCED BY CONTACTING A HEAVY PETROLEUM OIL COKING CHARGE STOCK AT A COKING TEMPERATURE WITH A BODY OF FLUIDIZED COKE PARTICLES IN A REACTION ZONE WHEREIN THE OIL IS CONVERTED TO PRODUCT VAPORS AND CARBONACEOUS SOLIDS ARE CONTINUOUSLY DEPOSITED ON THE COKE PARTICLES, REMOVING PRODUCT VAPORS FROM THE COKING ZONE, HEATING A PORTION OF THE COKE FROM THE COKING ZONE IN A HEATING ZONE TO INCREASE THE TEMPERATURE OF SAID FLUIDIZED PARTICLES, RETURNING A PORTION OF THE HEATED COKE PARTICLES FROM THE HEATING ZONE TO THE COKING ZONE AND WITHDRAWING COKE PRODUCT PARTICLES, PLACING SAID MIXTURE ON A HEATED PATTERN, FORMING THEREBY A THIN HARDENED LAYER OF SAID COMPOSITION IN THE FORM OF SAID PATTERN, AND RECOVERING FROM SAID PATTERN A SHELL MOLD.