US3692550A - Facing agents for molding sand - Google Patents

Abstract

ACENAPTHYLENE, WHEN INCORPORATED INTO FOUNDRY MOLDING SAND, PREVENTS BURN-ON OF THE SAND GRANULES TO THE CASTING SURFACE, AND PROVIDES A SAND HAVING GOD COLLAPSIBILITY AND GOOD RECYCLE LIFE.

Description

United States Patent Ofice Patented Sept. 19, 1972 US. Cl. 106-3825 14 Claims ABSTRACT OF THE DISCLOSURE Acenaphthylene, when incoporated into foundry molding sand, prevents burn-on of the sand granules to the casting surface, and provides a sand having good collapsibility and good recycle life.

This application is a continuation-in-part of co-pending application Ser. No. 18,715, filed Mar. 11, 1970, now abandoned.

This invention relates to the casting of metals in sand molds and more particularly to a facing agent useful in green sand molds for casting metals, particularly ferrous metals.

Molding sand compositions for the casting of metals generally comprise sand, clay as a binder and water as a plasticizer. Typically, green sand molding compositions contain 100 parts of sand, 3 to parts clay, especially montmorillonite clays such as southern or western bentonites, and 2.5 to 5 parts water. In addition to these basic components, it has long been the practice to employ various auxiliary agents to facilitate casting of metals in sand molds. These agents include binders, facing agents, expansion control agents and the like. These agents may be applied to the surface of the mold or dispersed throughout the sand, depending upon the particular function.

As used herein, the term facing agent refers to an additive to a foundry molding sand which inhibits or prevents burning in or burn-on or the fusing of quartz sand grains to the surface of the casting. Prior to this invention, facing agents generally were dispersed throughout the sand and have been residue products, usually distillation residues, of the coal and petroleum industries, such as sea coal, coal tar pitch, petroleum pitch, asphalt, creosote and various tars. The mechanism by which they act is not fully understood, but there are two main theories- (1) they produce a reducing atmosphere within the mold and form a gas film between the metal and the mold surface and (2) they perform a sooting action and coat the surface of the mold with carbon. Regardless of theory, the known facing agents do produce a very sooty flame when burned in air. This is not a particularly valuable criterion for selecting a facing agent, however, since many materials, such as benzene, naphthalene and antracene which produce sooty flames when burned in air are ineffective or only moderately effective as facing agents. We believe that this partial or total absence of facing action results, at least in part, because of insutficient carbon formation and deposition at the mold surface during casting. That is, these compounds volatilize and are driven away from the mold surface before significant soot formation can occur. Other materials which are less volatile and do form a carbon deposit at the mold face are known, but they too have their drawbacks. These materials, such as sea coal, pitch, asphalt and the like, contain high proportions of elemental or fixed carbon,

7 which upon pyrolysis during casting forms a rigid coke structure at the mold surface to a depth determined by the mold geometry, the casting conditions and the thermal gradient developed. This structure binds the sand grains together and causes poor collapsibility of the mold after casting. Furthermore, molding sands containing these materials are characterized by low recycle life. That is, the facing agent must be replenished frequently to allow reuse of the molding sand.

It is an object of this invention to provide a novel fac- 7 ing agent.

A further object of this invention is to provide a faC- ing agent which has improved efiiciency in preventing burn-on.

Still another object is to provide a facing agent which does not impair the collapsibility of the mold after castmg.

Another object of this invention is to provide a facing agent having a long recycle life.

These and other objects of this invention, which will be apparent from the ensuing specification, are achieved by employing acenaphthylene as a facing agent. Molding sands containing acenaphthylene provide a cleaner casting then is obtained with sands containing previously employed facing agents, and have improved collapsibility and recycle life.

Without wishing to be bound by theory, it is believed that the improved facing action observed with acenaphthylene is due to its ability to form a highly refractory, graphite-like coating on the sand granules at the mold face, as opposed to the more amorphous carbon coatings obtained with previously used facing agents. Moreover, microscopic examination of the sand at the mold surface after a casting cycle reveals that the agent of this invention provides a more uniform coating of the sand, both on individual grains and from grain to grain.

' the mold sand spaced from the mold cavity, Where it condenses, thus conserving it for reuse. This action can be observed by a simple test whereby a Pyrex test tube is charged with sand, then a thin layer (about /8 to inch) of a mixture of sand and facing agent and finally more sand. The bottom of the tube is heated at about 1800 F. and the top is exposed to ambient temperature, and when the layer including the facing agent is heated to about 1000 F. the tube is cooled and the contents examined. The sand in the top end of the tube will be found to contain acenaphthylene, while the sand in the bottom of the tube will be found to be coated with a graphite-like coating.

The acenaphthylene can be employed in pure form, if desired, but due to the high cost of pure acenaphthylene, it is preferably employed in admixture with one or more diluents or solvents. For example, crude mixtures, such as petroleum fractions, containing acenaphthylene may be employed to good effect in accordance with this invention. To be practically useful, such fractions should contain at least about weight percent, and preferably at least about weight percent acenaphthylene. The balance of these fractions ordinarily comprises aromatic compounds, primarily polynuclear aromatic compounds such as naphthalene and alkyl (usually methyl) derivatives thereof, and fluorene and alkyl derivatives thereof, although such fractions may contain small amounts of aliphatic compounds, alkyl benzenes and indanes and tetralins. Since alkylnaphthalenes, particularly polyalkylnaphthalenes, and fiuorenes provide limited facing action, their presence as diluents is desirable. Petroleum fractions containing at least about 70 weight percent, and preferably at least about 85 weight percent of alkylnaphthalenes, fiuorenes and acenaphthylene are especially preferred.

A commercially-available petroleum fraction which is preferred for use in accordance with the present invention is one sold by Getty Oil Co. as Aromatics 500, which contains about 90 Weight percent of the polynuclear aromatics acenaphthylene, fiuorenes and alkylnaphthalenes. The specification and a typical analysis of this fraction are as follows:

TABLE I Specifica- Spot Tests tions analysis Distillation:

IBP F It is desirable that the facing agent have a low sulfur content, i.e., a sulfur concentration of less than about 1%, since the presence of undue amounts of sulfur is deleterious to the mechanical properties of most ferrous and nonferrous metal castings.

The acenaphthylene may be incorporated into molding sand in any suitable fashion. For example, it may be mixed with the sand, in combination with other additives if desired, and the resulting sand mixture is used to form the mold. Alternatively, the sand mold may be formed and the acenaphthylene applied to the mold face by suitable techniques, as by brushing or spraying. It has also been found that the acenaphthylene can be applied to the pattern used in forming the mold, with sufficient transfer to the mold surface occurring to provide facing action.

When acenaphthylene is mixed with the sand, the amount in which it is employed is not narrowly critical, provided it is an amount suflicient to provide improved facing action. This amount can vary considerably depending upon the molding sand, the metal being molded and the molding techniques employed. For example, greater amounts of facing agent are required when the molding sand has greater clay content, a greater water content, and is composed of coarser sand or is composed of a less refractory sand, i.e. ,a sand which has an increased glassforming tendency. Increased amounts of facing agent are usually required when casting iron having a low carbon content, when casting at higher temperatures, or when the casting is allowed to cool longer in the mold. Greater amounts of facing agents are also generally required with larger castings, as well as with molding sands which have been recycled many times. Ordinarily, however, the effective amount of acenaphthylene will be in the range of from about 0.1 weight percent to about 5 weight percent.

When admixed with the molding sand, the acenaphthylene facing agent can be added as such or in admixture with other desirable additives for foundry molding sands. A particularly preferred mold of addition is to first admix the facing agent with an expansion control agent and then add the combination to the molding sands. Expansion' control agents are known to the art, and normally comprise cellulosic materials, such as wood flour, starches, cereals and the like. A particularly desirable expansion control agent is a modified starch as disclosed in U.S. Pat. No. 3,086,874. When employed in such mixtures, the facing agent and expansion control agent are combined in the proportions in which they are to be employed in the molding sand, ordinarily from about 0.5 to about 5 parts by weight of expansion control agent per part of facing agent, and preferably about 2 parts per part of expansion control agent per part of facing agents.

As noted above, .the facing agent of this invention also can be applied directly to the mold surface by suitable techniques, such as brushing or spraying. If it is applied as a spray, airless spray techniques should be employed to -ensure efiicicnt deposition of the agent on the mold surface and avoid overspray or loss of agent due to entrainment in the air stream which may occur with conventional air sprays. The amount applied to the surface is not narrowly critical, provided the desired facing action is obtained. Ordinarily amounts of at least about 0.5 gram per square foot of surface are required to achieve a useful effect, and amounts of from about 1 to about 5 grams per square foot will be most common. Still greater amounts can be used if desired, but generally are unnecessary. It is an advantage of the agent of this invention that excessive amounts applied to the surface are not detrimental.

Since pure acenaphthylene is a solid, it must be dissolved in a suitable solvent for application as a spray. Neither the solvent employed nor the concentration of the solution is critical to this invention. All that is required is that the solvent dissolve the acenaphthylene and not interfere With its facing action and that the resulting solution contain sufficient acenaphthylene to provide adequate facing action at useful application rates and yet not be too viscous for application. Suitable solvents include aliphatic compounds and fractions such as kerosene and the like, aromatic compounds such as benzene, toluene and the like, and alcohols such as methanol, ethanol and the like. The concentration of the acenaphthylene in the solution can vary from about 1 weight percent to about 20 weight percent.

The following examples are illustrative. In the examples, facing action was evaluated by making step castings having a rectangular drag surface measuring four inches by twelve inches. The cope surface was provided with three steps measuring four inches by four inches, and the thicknesses of the steps were one-half inch, one inch and two inches. Unless otherwise specified, the molding sand employed contained parts AFS fineness number 70 sand, 3 parts southern bentonite (acid), 3 parts western bentonitc and varying amounts of water and facing agent. All parts and percentages are by weight, and the amounts of sand component employed is based upon 100 parts of the D grade sand.

EXAMPLE 1 Molding sands including 3.5 parts water and 2 parts of either the petroleum fraction identified in Table 1, above, or an aqueous 60% solids asphalt emulsion sold commercially as a facing agent were prepared by mulling the dry sand and bentonite clays for 2 minutes, adding water and mulling for minutes and adding facing agent and mulling for 5 to minutes. The molds were made by jolting cope and drag 50 times and then squeezing at full line pressure (90 p.s.i.). Castings were made using gray iron (50% new iron) at 2740 F., and shake-out was after 45 minutes. A step casting made with the asphalt facing agent had very poor peel, whereas the casting made using the petroleum fraction as the facing agent had very good peel, even on the drag surface, and flake graphite was observed on all surfaces.

Additional runs were performed to determine whether the poorer results obtained with the asphalt emulsion were due to the higher total water content (4.3 parts) or lower solids (asphalt) content (1.2 parts). In the first run, 2.7 parts water and 2 parts emulsion were employed (3.5 parts total water and 1.2 parts asphalt solids) and in the second 2.2 parts water and 3.4 parts emulsion (3.6 parts total water and 2 parts asphalt solids). Nd difference in casting appearance was observed in the two runs using 2 parts of emulsion. In the run using 3.4 parts emulsion (2 parts asphalt), however, an improvement was observed over both the runs using 2 parts asphalt emulsion in that good peel was observed in the cope of the light section. Nevertheless, poor peel was observed on the intermediate section and a partial peel on the heavy section and the drag and sides were poor.

EXAMPLE 2 A molding sand including 3.5 parts water and 2 parts of the petroleum fraction identified in Table I was prepared by mulling the dry components for 2 minutes, adding the water and mulling for 5 minutes, and adding the petroleum fraction and mulling for 10 minutes. The mold was prepared and step castings were made as described in Example 1. The 2-ram cores came out after 3 to 4 drops. The peel of the castings was excellent.

The sand was recovered, mulled for 2 minutes with 0.25 part each of southern bentonite (acid) was western bentonite, and then 5 minutes with 3.5 parts water, and the casting procedure was repeated. The cores shake out with 2 drops. Again excellent peel was observed, even in the drag.

Four additional cycles, during which only 0.25 part of each of the bentonite clays was added in each cycle, were carried out. Excellent peel was observed on the first two cycles, some burn-on (no worse than that observed with commercially available facing agents) was observed on the third, and burn-on was noted on the heavy section after the fourth cycle.

The recycle test was repeated, this time using a 60% solids asphalt emulsion used commercially as a facing agent. The dry sand ingredients were mulled for 2 minutes, then 5 minutes with 2.14 parts water, and then 10 minutes with 3.4 parts of the emulsion (for a total of 3.5 parts water and 2 parts asphalt solids). The cores came out with 5 drops. The casting evidenced heavy burnon in the drag, although the cope sections were good.

The sand was recovered, mulled for 2 minutes with 0.25 part each of southern bentonite (acid) and western bentonite and 5 minutes with 3.5 parts water and step castings were made. The cores came out with 6 to 7 drops. The entire surface of the drag of the casting was covered with sand, and although the cope was generally good, some sand adhered to the cope sections.

The retempering and molding procedures were repeated, and the castings were generally poor, with burnon evident in cope and drag.

The results of these tests are summarized in Table II.

TABLE IL-RECYCLE LIFE OF FACING AGENTS Petroleum fraction of Table I 1 Asphalt 1 Core Core removed Casting removed, Casting Cycle drops appearance drops appearance 1 3-4 Excellent- 6 Cope, good, drag, heavy burn-on. 2 2 do 6-7 Burn-on on cope and drag. 3 1 ..do 5-7 Poor, heavy burn-on. 4 1-2 do 5 1 Some burn-on 6 2-3 Burn-on on heavy sections.

1 2 parts per 100 parts sand. 2 3.5 parts 60% aspahlt emulsion (2 parts asphalt) per 100 parts sand.

As is evident from Table II, the petroleum fraction was markedly superior to the asphalt as a facing agent, both initially and as to recycle life. Thus, at equivalent solids content in the first cycle, the petroleum fraction yielded a superior casting, was completely effective through 4 cycles and was of some benefit through 6 cycles, while the asphalt was not fully effective in the first cycle, and its effect rapidly deteriorated to essentially nil in only 3 cycles.

EXAMPLE 3 The petroleum fraction identified in Table I, above, was blended with wood flour to provide a composition containing 70 parts wood flour and 30 parts petroleum fraction. Molding sand was then prepared by dry mulling the said including 2 parts of this blend for 2 minutes and then wet mulling with 3.5 parts water for 10 minutes. A step casting was produced as described in Example 1.

The experiment was repeated, except that a commercially available blend of equal parts of wood flour and asphalt was substituted for the petroleum fraction-wood flour blend.

The casting obtained with both additives were equal in appearance, despite the fact that the petroleum fraction was employed in lower amounts (0.6 part) than the asphalt (1 part).

EXAMPLE 4 Employing procedures and amounts similar to those described in Example 1, except that 1 part of acenaphthylene was employed as the facing agent, a casting was made with gray iron new, /3 remelt) at 2790 F. The casting evidenced no burn-on on the cope faces and the drag had only a light burn-on. The cope surface at the heavy section had several hollows that apepar to be caused by gas. Castings made with the same sand, but with no facing agent, exhibited heavy burn-on in the cope and drag. Castings made substituting 1 part of the petroleum fraction of Table I for the acenaphthylene were not quite as clean on the cope surfaces as that first obtained, but were equal in the drag.

EXAMPLE 5 A number of polynuclear aromatic compounds, or mixtures thereof, were subjected to proximate volatile matter tests (ASTM Test D-244 modified only by heating at 900 F. or 1000 F. for 7 minutes) and observed for formation of a sooty smoke and a graphitic residue in the crucible. Of all of the materials tested, only acenaphthylene was observed to spontaneously ignition with the formation of a sooty smoke and leave a substantial graphitic residue. The results of these tests are summarized as follows:

Two strips of sand, one admixed with 0.5 weight percent acenaphthylene, and the other admixed with 0.5 weight Ignition Ignition and sooty Carbon and sooty Carbon flame PVM 1 Deposit flame PVM Deposit Naph thalcne 2-methylnaphthalena. Dimethylnaphtalene. 'Irirnethylnaphthalen Biphenyl Phenanthrene Fluorene Acenaphthene Acenaphthylene A 500 Plus dimethylnaphthalene Plus t-rimcthylnaphthalcne Plus fiuorene 9 Yes None.

Yes. Yes. Yes. Yes. Yes.

1 PVM=Proximate Volatile after. 2 A clear brown residue was observed. 3 Mixtures of equal parts A 500 and the named compound.

From the foregoing it is apparent that only acenaphthylene or compositions containing it underwent spontaneous combustion, had a significant amount of non-volatile matter and left a graphitic residue in the cruicible. Of the materials evaluated which did not contain at least some acenaphthylene, only crude anthracene evidenced a significant non-volatile matter content (less than 99 percent), but it did not ignite. Moreover, crude anthracene is known to contain a high proportion of fixed carbon, which probably contributed to the carbon deposit, since pure anthracene left little or no residue. On the other hand, acenaphthene did spontaneously ignite with the formation of a sooty flame, but this material did not leave a carbon resdiue and was essentialy 100% volatile. Thus, of the materials tested, only acenaphthylene and mixtures containing it evidenced both the high sooting activity combined with the ability to deposit in situ a substanial carbon deposit which is essential to a superior facing agent.

EXAMPLE 6 A %-inch diameter by 6-inch long test tube was charged with a mixture of grams of AFS 50-70 sand and 0.5 grams of acenaphthylene, and a second test tube was charged with a mixture of 10 grams of AFS 50-70 sand and 0.5 gram of acenaphthene. The two tubes were wired together and the bottoms were centered in the flame of a Meeker burner so they were equally heated. The tubes were heated for 10-15 minutes, during which time both sands began to darken, beginning at the bottoms of the tubes. With the acenaphthene-containing sample, darkening continued to a chocolate brown color, at which point the color began to lighten and, at the end, the sand became practically the same color as the initial sand sample.

In the case of the acenaphthylene-containing sample, on the other hand, darkening continued until the sample exhibited a shiny, black, coke-like color, and at the end. of the test period a strong covering of carbonaceous material remained on each sand gram. Analysis of the sand residues by a loss on ignition test showed that the acenaphthylene residue was about 10 times that of the acenaphthene residue. The acenaphthylene residue had a volatile content in this test of 1.44 percent and the acenaphthene residue a volatile content of only 0.11 percent.

From this test it can be seen that acenaphthene does not form a tenacious carbon deposit on heating whereas acenaphthylene does. Thus, only acenaphthylene can form a carbonaceous deposit at the mold surface and thereby afford good facing action.

EXAMPLE 7 A green sand mold was prepared by conventional procedures for casting an 8-inch by 8-inch square casting having a step-like configuration, one-half having a /2-iuch thickness and the other half having a 2-inch thickness.

percent acenaphthene, were deposited on the mold floor adjacent the mold walls. Then gray iron at 2750 F. was poured, and allowed to cool and the resulting casting was shaken out and brushed. The surface of the casting adjacent the acenaphthylene-treated sand had much less sand adhering to it than did the surface adjacent the acenaphthene-treated sand.

On examination of the mold, the acenaphthylenetreated sand was black and well coated with graphitic carbon to a depth of about one inch, whereas the acenaphthene-treated sand was a dull, light brown to gray color. Samples of these treated sands were taken to a depth of about /2-inch and subjected to a loss on ignition test. The acenaphthylene-treated sand was found to contain double the organic residue found with the acenaphthene-treated sand, thus confirming the persistence of the acenaphthylene residues at the mold surface to provide facing action.

EXAMPLE 8 A 6-cavity mold (each cavity having the shape of a 3 /2-inch square Z-Stepped block having a /s-inch thick step and a l /z-inch thick step) was formed from a molding sand composed of parts by weight 60 AFS sand, 4 parts by weight western bentonite, 4 parts by weight southern bentonite and 4.3 parts by weight water. Employing an air-less spray gun, a solution of equal parts by weight of the fraction identified in Table I and kerosene was applied to the mold cavities at a rate of A gram of solution per second. The length of the application varied for each cavity as follows: 1, 2, 4, 8, l6 and 32 seconds. Thereafter a test casting was made and the sample was examined for facing action. -It was found that a 2-second spray time -(or /2 gram per 30 square inches of surface) was required for effective facing action at the inch section, and a spray time of 8 seconds (or 2 grams per 30 square inches of surface area) was required for effective facing action at the 1 /2 inch step.

EXAMPLE 9 A 15 inch by 13 inch pattern plate was sprayed with a solution of equal parts by weight of the composition identified in Table I and Varsol, a kerosene-like material, at a rate of /2 gram per second for 2 seconds. The pattern was then used to form a mold of 100 parts by weight of sand, 6 parts by weight of western bentonite and 3 /2 parts by weight water, during which the solution was transferred from the pattern to the mold sand. A casting which was poured in gray iron using the resulting mold was found to be totally and completely free of sand adhesion, and had a smooth and shiny appearance. Examination of the sand revealed deposition of carbon 0n the sand grains to a depth of from about A to about one inch.

In addition to the facing action it was found that the agent provided good parting or release agent properties and prevented adhesion of the sand to the pattern. In addition, the mold surface was greatly improved. Apparently the agent reduces the interface friction between the sand and the pattern and thus permits better compaction of the sand granules at the mold face surface.

It has been found that transfer of the solution from the pattern to the mold face is substantially complete. Thus the solution is ordinarily applied to the surface of the pattern at or slightly above the rate necessary to pro vide facing action if applied directly to the mold face. As a general rule of thumb, however, it has been found sufficient to apply enough solution to the pattern so that it appears wet.

If desired the solution can include other ingredients, such as diluents and the like. In those instances in which the pattern has large vertical surfaces, it is desirable to incorporate a thixotroping agent, such as amorphous silica, into the solution.

What is claimed is:

1. In a method for forming a green sand mold for casting metals comprising forming a green sand mixture of sand, clay and water into said mold, the improvement of incorporating acenaphthylene into said green sand mixture at least at the surface of said mold in an amount sufiicient to provide effective facing action during subsequent casting.

2. A method according to claim 1 wherein said acenaphthylene is admixed with said sand, clay and water before forming said mold.

3. A method according to claim 2 wherein the amount of acenaphthylene is from about 0.1 to about 5 weight percent, based upon the weight of sand.

4. A method according to claim 2 wherein said acenaphthylene is in the form of a petroleum fraction containing at least about 70 weight percent of polynuclear aromatic compounds of the class consisting of naphthalene and methyl derivatives thereof, fiuorene and methyl derivatives thereof, and acenaphthylene, there being at least about weight percent of acenaphthylene in said fraction.

5. A method according to claim 1 wherein said acenaphthylene is applied to the mold surface after formation.

6. A method according to claim 5 wherein the amount of acenaphthylene is from about 0.1 to about 5 weight percent, based upon the weight of sand.

7. A method according to claim 5 wherein said acenaphthylene is in the form of a petroleum fraction containing at least about 70 weight percent of polynuclear aromatic compounds of the class consisting of naphthalene and 10 methyl derivatives thereof, fluorene and methyl derivatives thereof, and acenaphthylene, there being at least about 20 weight percent of acenaphthylene in said fraction.

8. A method according to claim 5 wherein said ace naphthylene is sprayed onto said surface in solution in as solvent therefor.

9. A method according to claim 5 wherein said acenaphthylene is applied to the surface of the pattern employed in forming said mold, whereby acenaphthylene is transferred from said pattern to said mold face during formation of said mold.

10. In a molding sand composition comprising sand, clay as a binder and water as a plasticizer, the improve ment of acenaphthylene in an amount sufficient to provide effective facing action to a mold made from said composition.

11. A composition according to claim 10 wherein said facing agent is present in an amount of from about 0.1 to about 5 weight percent, based upon the sand.

12. A composition according to claim 10 wherein said acenaphthylene is in a petroleum fraction containing at least about weight percent polynuclear aromatic compounds of the class consisting of naphthalene and methyl derivatives thereof, fiuorene and methyl derivatives thereof and acenaphthylene, there being at least about 20 weigth percent acenaphthylene in said fraction.

13. A composition useful as an additive to molding sand including from about 1 to about 5 parts by weight of a cellulosic expansion control agent and about 1 part by weight of acenaphthylene.

14. A composition according to claim 13 wherein said acenaphthylene is in the form of a petroleum fraction containing at least about 70 weight percent by polynuclear aromatic compounds of the class consisting of naphthalene and methyl derivatives thereof, fluorene and methyl derivatives thereof, and acenaphthylene, there being at least about 20 weight percent of acenaphthylene in said fraction.

References Cited UNITED STATES PATENTS 2,476,933 7/1949 Wallace 106-3825 2,668,774 2/1954 Heyl 10638.25 3,241,984 3/1966 King et al. 10638.8

LORENZO B. HAYES, Primary Examiner US. Cl. X.R.

UNITED STATES PATENT oTTTcE QERTIFICATE 0F I ECTEQN Patent No. q 6o 550 Dated September 19. 1972 Inventor(s) R. E Melcher et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 5, line #9, "was" should be --and-.

Col. 6, line ll, "said" should be --sand--.

Col. 6, line 60, "apepar" should be --appear--.

Col. 6, 1ine75, "ignition" should be --ignite--.

Col. 7 in the Table, under "A 500" in the left hand column inse t the following line Naphthalene 3, Yes, 98.16, Yes--; in line 2-Methylnaphthalene, under heading PVM (first occurrence) "99.88" should read --99.98--; in line Phenanthrene, under heading PVM (first occurrence) "99.98"

should read --99.90--; in line Biphenyl, under column Carbon Deposit insert --none--.

Col. 7, line 36, "resdiue" should read --residue--.

Col. 10, line 33, "by" should read ---of---.

Signed and sealed this 20th day of March 1973.

(SEAL) Attest:

EDWARD NLFLETCHERJR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents -'ORM PO-1050 (10-69) USCOMM-DC 6O376-P69 LLS. GOVERNMENT PRINTING OFFICE: I969 0-366-334