US2468956A - Core oils - Google Patents

Description

May 3, 1949. M. s.- BURG CORE OILS Filed oct. 1v,l 1946 zsheets-sneez 1 May 3,1949. u. mum A l 2,468,956

B YM M ATTORNEY bake molded sand cores in ovens Patented May 1949 CORE OILS Meran s. Burg, cnice, Vacuum Oil Company,

lll.,assignor to Socony- Incorporated, New York,

N. Y., a corporation of New York Application October 17, 194.6, Serial No. '103,851

s claims. 1

This invention relates to an improved core oil showing a reduced tendency of sand cores made therewith to lose tensile strength on prolonged baking.

The preparation of foundry sand cores normally involves the mixing of a clean sand with a core oil, with or without the addition of water. The core oil is normally a liquid having a tendency to rapidly form a rm binder on baking in the presence of air at temperatures on the order of 400 F. and above. The base of the core oil is generally a drying oil such as linseed. Many other oils are suitable for the purpose among which may be cited perilla, menhaden and the highly unsaturated polymers derived by treating cracked gasoline with adsorbents such as fullers earth. 'I'he desirability of any one of these and other suitable drying oils depends upon considerations of price and particular conditionsA of use as well as personal preferences of foundry operators. For the purposes of this invention, the several drying oils may be regarded assubstantial equivalents.

,In addition to the primary drying oil ingredient, the core oils may also contain resins and thinners. Dryers o1' the type used in paints may also be added.

It is common practice in large foundries to of the continucores are subjectedl to substantially the same temperatures for substantially the same periods of time. The economics of such practice is obvious but'it results in overbaking of small cores and of thin yportions of ous type wherein all complex cores. As the core is subjected to baking temperatures, the tensile strength increases to reach a maximum after a period of time depending upon the nature of the core oil, temperature of baking and cross sectional area of the core. Thereafter the tensile strength declines on continued baking as will be shown hereinafter. For simplicity of consideration, it is well to refer to a standard tensile `strength briquette having enlarged ends connected by an elongated central portion of constant cross section, for example 1/2" x V2". This size-test specimen was used in tests hereinafter referred to and will be regarded as standard herein for purposes of discussion.

Using core oils in which the principal drying oil component is raw linseed oil and baking the test specimen at 450 F., the tensile strength reaches a maximum in about 60 minutes. Thereafter the tensile strength begins to decline and drops very rapidly for normal core oils for the having a molecular .weight of about 1500 and a iirst l5 minutes after which the curve assume a gentler slope and continues to decline as baking proceeds. It is apparent that an optimum baking time vcould be selected if the portions of the sand core were of constant thickness throughout. However, the thickness .of vthe core usually varies in different sections and optimum.

baking time for thin sections would be inadequate for proper baking of thicker sections. Likewise, in the selection of optimum baking times, varying core structures would render the use of continuous ovens impossible. It is therefore apparent that a reduction in the loss of tensile strength with prolonged baking is a matter of considerable importance in modern foundry practice.

It is accordingly a principal object of this invention to stabilize core oils by rendering the cores formed therewith less subject to deterioration in tensile strength on baking past the optimum period. This result is obtained by incorporating in the core oil a minor amount of a material which stabilizes the core oil in the .manner noted above.

-It has been found that certainpolymerized hydrocarbons will act to stabilize tensile strength of sand cores on prolonged baking.' An outstandcompound is the viscous polymer sold under the trade name ,Vistac No. 1 by the Standard Oil Company of California. This material is a polymer of isobutylene prepared by catalytic polymerization in the presence of boron triuoride viscosity of 3000 seconds lat 210 F. (Saybolt Universal viscosity) In general, the stabilizers to which this invention is directed are highly viscous linear polymers 'of alkene-lfhydrocarbons. They are prepared by interaction of the'oleflns in the presence of condensation catalysts of relatively high activity,

- such as boron iluoride, the active halides of aluminum and the related Friedel-Crafts catalysts. The polymers are substantially saturated, that is, the iodine numbers are nil or extremely small. The exact structure of the polymers -is not understood, but the very low iodine numbers are taken as an indication that polymerization is terminated by addition of the chain a saturated compound present in the olefin as an impurity. In general, the viscosities should range upward from about 1500 seconds Saybolt Universal viscosity at 210 F'. Molecular weights are substantially in excess of 1000 and vary somewhat depending upon the specific olefin and the manner of preparation of the polymer.

In addition to the polymerized iso-butylene mentioned above, polypropylenes and the polymers oi' butene-l. pentene-l and the other normal alkene-l compounds are found to be highly satisfactory and are used in the same manner as the polymers described in the examples specifically set out hereinafter. n

The term "polymer is used here in its broader sense of including compounds formed by the condensation of a mixture of oleiins of the type sometimes called co-polymers. Thus a polymer of propylene and butene-l is regarded as Within the scope of the invention defined in the claims. Similarly, products of polymerizing the product of mild cracking of paraflin wax are suitable.

'The stabilizing additive of this invention may be added to the core oil in any desired amounts but, in general, 10% appears to be about the practical maximum. Best results commensurate with the increased cost are obtained at additive concentrations of about 3% by weight based on the weight of the compounded core oil. In general, the additive should have a flash point above about 450 F.

The advantages of the invention are clearly shown by comparison of typical core oils described in the following examples. The results of baking cores formed with some of these oils are clearly shown by Figures 1 and 2 of the drawings annexed hereto which represent graphically the change in tensile strength withA baking time of core oils containing the additive of this invention as compared with core oils from which the additive is lacking.

l Example 1 A typical core oil of the type known as light because of its color was prepared by blending 40% of raw linseed, 30% of tall oil and 30% of kerosene. A second core oil was prepared according to the invention by substituting 5% by weight of Vistac No. 1 for an equal amount of the kerosene in the basic composition. Standard test specimens were prepared from a mixture of 7 parts by weight of sand, 2 parts by weight of Water and 1 part by weight of one of the above core oils. Afterv thorough mixing by tumbling, this composition was molded into test specimens which were then placed in an oven with the thermostat set at 450 F. Test specispecimen prepared from the oil containing no stabilizer. The numerical values showing percentage loss in strength are based on the maximum strength attained by the composition under consideration and it will be noted that these numerical values do not reiiect the entire picture since the maximum value for the straight oil is considerably below that of the stabilized oil.

Example 2 A dark oil was also prepared in a manner similar to that reported in Example il 'Ihe basic composition contained 40% raw linseed, 10% tall oil, 15% kerosene and 35% of a highly unsaturated hydrocarbon polymer purchased from Pure Oil Company under the name Petropon No. 1158 (iodine number approximately 200). The stabilized core oil was prepared by substituting 3% Vistac No. 1 for part of the kerosene. The results of forming test specimens and baking as in Example 1 are reported in the following table and shown graphically in Figure 2.

mens formed from each of the oils were removed at the end of 45, 60, 75 and 90 minutes and broken on a tensile strength testing machine. The results are tabulated below.

Core Oil Baking Time Containing tmlgi uwstaw ore P. s i. P. s. i. 45 195 197 251 210 75 212 155 181 145 These results are even more sharply pointed out in .Figure 1 which is based on the above table. Particular attention is called to the sharp drop in tensile strength of thecurve representing the Baking Time qflg Straight Oil P. s i. P. s i 45 197 172 60. '265 260 215 207 225 197 Example 3 A core oil having a basic formula of 40% by weight linseed oil, 30% by weight tall oil and 30% kerosene was tested for improvement by addition of a polypropylene prepared by polymerization of the propene in the presence of aluminum bromide. The polypropylene used had a molecular weight of about 1700 and the S. U. V. viscosity at 210 F. was 1600 seconds. These cores were prepared usingthe basic formula and basic formula plus 3% by weight of the polypropylene. Tensile strengths of the test cores are tabulated below:

Containing Baking Time Polypropy- Straight Oil iene Example 4 A further test was made, substantially identical with that reported in Example 3 except that the propylene employed had a molecular weight of 2900 and a viscosity of 3500 seconds. The results are tabulated as before:

. Containing Baking Time Polypropy- Straight Oil iene Example 5 In a further test similar to the two preceding examples, there was used a polypropylene having a molecular weight of 4000 and a viscosity of `5500 seconds. The results in tabular form fol- I claim: 1. A core oil comprising a predominant quantity of a drying oil and about 3% of a viscous, substantially saturated hydrocarbon polymer of isobutylene having a ilash point above about 450 F.

2. A core oil comprising a predominant quantity of a drying oil and a minor amount, not more than about 120%, of a viscous, substantially saturated hydrocarbon polymer o isobutyiene having a flash point above about 450 F.

3. A method for forming sand cores which comprises mixing sand with a core oil comprising a predominant quantity of a drying 011 and a minor amount, not more than about of a viscous, substantially saturated hydrocarbon polymer of alkene-l hydrocarbo said polymer having a flash point above about 450 F., molding the -srultant mrxtur' e and baking the molded mixe 4. A 'method for forming sand cores which comprises mixing sand with a core oil comprising a predominant quantity of a drying oil and about 3% of a viscous, substantially saturated hydrocarbon polymer of alkene-l hydrocarbon, said flash point above about 450 F., molding the resultant mixture and baking the molded mixture,

5, A core oil comprising a predominant quantity of a. drying oil and about 3% of a viscous, substantially saturated hydrocarbon polymer of propylene having a ash point above about 450 6. A core oil comprising a predominant quantity of a drying oil and a minor amount, not more than about 10%, of a viscous, substantially saturated hydrocarbon polymer of propylene having a ash point above about 450 F.

7. A core oil comprising about of linseed oil, about 30% of tall oil, about 25% of hydrocarbon thinner, and about 5% of a viscous. substantially` saturated hydrocarbon polymer of isobutylene having a. flash point above about 450 F., a molecular weight of about 1500 and a viscosity (Saybolt Universal viscosity, at 210 F.) of about 3000 seconds.

8. A core oil comprising about 40% of linseed o il, about 30% of tall oil, about 27% of hydrocarbon thinner, and about 3% of a viscous, substantially saturated hydrocarbon polymer of propylene having a flash point above about 450 F., a molecular weight between about 1700 and about 4000, and a viscosity (Saybolt Universal viscosity, at 210 F.) between about 1600 and about 5500 seconds.

MARTIN S. BURG.

` REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,778,329 Mason Oct. 14, 1930 2,047,297 Stahl July 14, 1936 2,051,840 Gerhart Aug. 25, 1936 27,062,346 Zimmer Dec. 1, 1936 2,142,039 i Abrams Dec. 27, 1938 Remy Feb. 24, 1942

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