US3578595A

US3578595A - Zinc di-3-alkylphenoxy-2,2-dialkylpropyl dithiophosphate and automatic transmission fluid containing same

Info

Publication number: US3578595A
Application number: US845445A
Authority: US
Inventors: Raymond C Schlicht; Arthur W Godfrey
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1969-07-28
Filing date: 1969-07-28
Publication date: 1971-05-11
Anticipated expiration: 1988-05-11

Abstract

ZINC DI-3-ALKYLPHENOXY - 2,2- DIALKYLPROPYL DITHIOPHOSPHATE REPRESENTED BY THE FORMULA:

(((R1,R2-PHENYL)-O-CH2-C(-R)2-CH2-O-)2-P(=S)-S-)2-ZN

IN WHICH EACH R REPRESENTS AN ALKYL RADICLA HAVING FROM 1 TO 4 CARBON ATOMS, R1 IS AN ALKYL RADICAL HAVING FROM 6 TO 18 CARBON ATOMS, R2 IS HYDROGEN OR AN ALKYL RADICAL HAVING FROM 6 TO 18 CARBON ATOMS AND THE TOTAL NUMBER OF CARBON ATOMS IN R1 AND R2 IS FROM 6 TO 24 AND A HYDRAULIC FLUID OR AUTOMATIC TRANSMISSION FLUID CONTAINING SAME.

Description

il, 1971 c.sc|-n..|c|w M. Z INC DI--ALKYLPHENOXY-E R-DIMIRSYLPROPYL DITHIOPHOSPHATE AND UTOTIC TRANSMISSION FLUID CONTAINING SME mw im z, ma@

0 11 l 1 0 r 1| 1 l l..

o 1 l l l 1 o l l l I 1 O .2 4 .6 O .2 .4 .6

7707 jecana/s 7/'f'ne ,J'eto/vas l l I l 77h16 Simonis United States Patent ZINC DI-S-ALKYLPHENOXY-Z,Z-DIALKYLPROPYL DITHIOPHOSPHATE AND AUTOMATIC TRANS- MISSION FLUID CONTAINING SAME Raymond C. Schlicht and Arthur W. Godfrey, Fishkill, NSY., assiguors to Texaco Inc., New York, N.Y.

Filed July 2S, 1969, Ser. No. 845,445 Int. Cl. C09k 3/00 U.S. Cl. 252-75 5 Claims ABSTRACT F THE DISCLOSURE Zinc di-3-

alkylphenoxy

2,2 dialkylpropyl dthiophosphate represented by the formula:

in which each R represents an alkyl radical having from 1 to 4 carbon atoms, R1 is an alkyl radical having from 6 to 18 carbon atoms, R2 is hydrogen or an alkyl radical having from 6 to 18 carbon atoms and the total number of carbon atoms in R1 and R2 is from 6 to 24 and a hydraulic fluid or automatic transmission fluid containing same.

BACKGROUND OF THE INVENTION Field of invention Metal salts and esters of dialkyldithiophosphoric acid are known to be useful as additives in lubricating oil compositions. These compounds are particularly effective as oxidation and corrosion inhibitors in mineral oil based motor and hydraulic lubricating oils.

Description of the prior art U.S. 2,344,395 discloses the acids and metal salts of dialkyl phenoxy alkyl dithiophosphates having the forin which R represents an aliphatic radical having from 6 to 15 carbon atoms, R is hydrogen or an alkyl radical having from l to 4 carbon atoms and n is an integer from 1 to 10.

This mineral hydraulic oil composition was found to possess outstanding friction-stable life in the Powerglide .AT-13 Cycling Test in an automatic transmission iluid as shown by the fact that it passes the 250 hour minimum life in the Chevrolet Dexron specication. A feature of this hydraulic fluid containing the above zinc compound which indicated a need for a further improvement is that the iluid requires a conditioning period or break-in period before the fluid provides the desired smooth shifting characteristics.

The shift quality in automatic transmissions is so important to the automobile manufacturers that an industrywide test has been designed to measure torque pressure changes within the automatic transmission during the upshift sequence. The results are recorded graphically on charts and are referred to as torque traces. The test is described in Tailoring ATF Shift Quality In the Laboratory by N. A. Nann and F. Pincheck published as SAE Paper No. 650 at the SAE Proceedings in Chicago, 1965.

SUMMARY OF INVENTION The novel compounds of this invention are represented lby the formula:

l l L H H L R2 2 in which each R represents an alkyl radical having from 1 to 4 carbon atoms, R1 is an alkyl radical having from 6 to 18 carbon atoms, R2 is hydrogen or an alkyl radical having from 6 to 18 carbon atoms and the total number of carbon atoms in R1 and R2 is from 6 to 24.

The preferred compounds are those in which each R is a methyl group, R1 is an alkyl radical having from 8 to 15 carbon atoms and R2 is hydrogen. A particularly preferred class of compounds are those in Which the alkyl radical attached to the aryl ring, namely R1, is characterized by having a predominantly straight chain structure, i.e. an alkyl radical in which the ratio of straight chain carbon atoms to -branched-chain carbon atoms is at least 2:1 and preferably at least 3:1. Compounds having this structure are particularly outstanding in providing an automatic transmission iluid having smooth shift characteristics over the entire useful life of the fluid. These compounds also have utility as insecticides and pesticides.

Novelty and the outstanding characteristics of the zinc compounds of the invention reside in the employment of the structural linkage:

where R has the value given above between the alkaryl group and the dithiophosphate group in the compound. Analytical studies show that this hindered-type structure resists degradation of the compound under conditions of use in an automatic transmission. Similar known compounds Without the hindered structure produce an automatic transmission fluid characterized by undesirable hard shifting or hard clutch lock-ups during the start-up or conditioning period in automatic transmission service. It is only after these compounds undergo some chemical structural change in the zinc dithiophosphate compound that they then provide a tluid having smooth shift characteristics.

The preparation of the zinc compounds of the invention depends primarily on the preparation of and proper characterization of the alcohol reactant. The subsequent reactions with phorphorous pentasulde and neutralization with zinc oxide are well known. The following examples illustrate the preparation of the zinc compounds.

Example 1.-990 grams (9.5 moles) of 2,2-dimethylpropanediol1,3 and 1237.5 grams (10.5 moles) of diethyl carbonate were added to a reactor together with 9.9 grams of sodium methoxide catalyst. The mixture was heated to 95 C., and held at this temperature for one hour. The ethyl alcohol produced was distilled olf under reflux and the temperature then raised to remove the unreacted diethyl carbonate While the reactants were held under a nitrogen atmosphere.

1285 grams of the solidified reaction produced were melted, transferred to a flask and vacuum distilled through an 8" column. The residue was recrystallized from benzene and vacuum distilled again. The recovered 5,5-dimethyl-Z-m-dioxanone had a melting point of 102.5- 104 C. as compared to a reported 1l0-11l C.

260 grams (2 moles) of 5,5-dimethyl-2-m-dioxanone and 440 grams (2 moles) of nonylphenol and 35 grams of potassium carbonate were added to a reactor, slowly heated to 136 C. and then held at this temperature for an hour. The temperature of the reaction mixture was gradually raised to 190 C. (20 C. raise in temperature/ hour) and held at 190 C. for about 116 hours. The evolution of CO2 caused a Weight loss of 86 grams. The product was dissolved in A600 grams of n-heptane and then consecutively water washed, washed with dilute HC1, sodium carbonate solution and finally Water washed.

The n-heptane and water were distilled from the reaction product and the latter vacuum distilled through an 8" column to a pot temperature of 197 C. and a head temperature of 168 C. under 1.4 mm. Hg pressure. 354 grams of the reaction product was recovered having a refraction index of 1.5012. Analysis shown below confirmed the product identity iS -dimethyl-y-(p-tert-nonylphenoxy) propanol.

l Consistent with alkylphenoxy alkyl dlthiophosphate structure.

Infrared 327 grams (1.07 moles) -dimethyl-'y-(p-tertnony1- phenoxy) propanol were added to a mixture of 58 grams (0.26 mole) of phosphorus pentasulfide, 177 grams of mineral oil and 266 m1. of n-hexane over a period of 4.25 hours while the reaction temperature was slowly raised to 103 C. The mixture was held at this temperature for 3.5 hours and then filtered. The reaction product was then added to a slurry of zinc oxide, 21 grams (0.26 mole) 87 ml. of n-hexane over a period of 2.5 hours while the mixture was held at a temperature of 33 C. or below. The mixture was then heated to 74-78 C. for about 5 hours and 4.4 ml. Water (4.7 theory) azeotroped o. The temperature was increased to 103 C. and held at this level for 5 hours after which the unreacted zinc oxide was filtered of, 6.3 grams (0.05 mole) of zinc carbonate, 100 ml. n-hexane and 2 ml. of water were added to the reaction product and the mixture further heated at 74 C. for 2 hours and at 80 C. for an additional hour. The water was azeotroped off and the product filtered and stripped to 127 C. at 1 mm. Hg pressure. The final product yield was 514 grams. Analytical tests shown below confirmed the identity of the product as zinc di-3- (p-tert-nonylphenoxy) 2,2 dimethylpropyl dithiophosphatc:

Theory: zinc, 3.00; phosphorus, 2.87; sulfur, 5.95. Pound: zinc, 2.85; phosphorus, 2.84; sulfur, 5:60.

lExample II.-768 grams (3.72 moles) of p-tert-octyly 4 -dimethyl-'y-(p-tert-octylphenoxy) propanol as indicated by the following analysis:

The above alcohol was reacted with phosphorus pentasulfide and zinc oxide as in Example I to produce zinc di-3(ptertoctylphenoxy)2,2-dimethylpropyl dithiophosphate having the following analysis:

Theory: zinc, 3.14; phophorus, 3.0; sulfur, 6.15. Found: zinc, 3.2; phosphorus, 3.1; sulfur, 5.6.

The zinc di-3-allrylphenoxy-Z,Z-diallrylpropyl dithiophosphates of the invention provide unexpected improvements in automatic transmission fluids over the known zinc di-dithiophosphates. Zinc di3alkylphenoxy2,2di alkylpropyl dithiophosphates provide outstanding frictionstable life in such a fluid and pass the Powerglide JXT-13 Cycling Test by providing a minimum of 250 hours life in this test. In addition and in contrast to the known zinc compounds, the zinc salts of this invention provide an automatic transmission fluid characterized by having surprisingly smooth shift characteristics from inception and throughout the life of the iiuid.

The automatic transmission fluid incorporating the improvements of this invention is, of course, a critically balanced formulation containing a combination of additives to provide dispersant, extreme pressure, corrosioninhibiting, viscosity and friction-modifying properties to the hydraulic iiuid. A Ikey component of this fluid is the zinc cli-3-alkylphenoxy-Z,2-dialky1propyl dithiophosphate which imparts oxidation and corrosion inhibiting properties resulting in a long friction stable life and the highly desired smooth shift characteristics.

In accordance with this aspect of the invention, a novel hydraulic transmission fluid is provided comprising a major proportion of a mineral lubricating oil and a zinc cli-3alkylphenoxy-2,2diallrylpropyl dithiophosphate defined above, which when employed in a critically formulated automatic transmission iiuid unexpectedly provides a fluid having smooth shifting characteristics from the moment of introduction in service as well as a long friction-stable life to produce a highly effective fand qualified automatic transmission fluid. The hydraulic fluid of the invention comprises at least 86 weight percent of a mineral lubricating oil, 0.1 to 5.0 weight percent of a zinc di-3-alkylphenoxy-Z,2-dialkylpropyl dithiophosphate, 0.5 to 10 weight percent of a viscosity index improver comprising a concentrate of a nitrogen-containing polymer of mixed alkyl and aminoalkyl esters of methacrylic acid having a molecular weight ranging from 25,000 to 1,250,- 000, 0.5 to 5.0 Weight percent of a detergent-dispersant comprising the reaction pro duct of polyethylene polyamine and an alkenyl succinic anhydride 0.01 to 5.0 percent of an alkanephosphonic acid and from about 0.05 to 5.0 percent of an alkylated diarylamine.

The mineral lubricating oil which constitutes at least 86 weight percent of the composition is a refined oil or a mixture of refined oils selected according to the viscosity requirements of the particular service. For automatic transmissions, where the requirements include an SUS viscosity ofthe compounded oil at 210 F. of 49 minimum up to 60, and at 0 F. of 7000 maximum; the base oil or the major component thereof is generally a distillate oil lower than the SAE 10 Grade motor oil, such as one having an SUS viscosity at F. of less than 150, and generally between 50 and 125. The distillate fraction can be a refined paraiiinic distillate or a refined naphthenic distillate or ia mixture thereof. The liash point of the distillate component of the base oil will generally be above 300 F., if the distillate fraction constitutes the entire base oil, its ash point will usually be above 375 F.

A preferred base oil comprises approximately 70 to 95 percent of a rened distillate oil and 5 to 30 percent of a rened residual fraction which imparts desired high flash point and lubricity'to the base oil. A preferred residual fraction comprises a paratlln base residuum which has been propane deasphalted and subjected to centrifuge dewaxing and which has an SUS at 210 F. below about 250. A particularly effective base oil mixture comprises 65 percent of a furfural refined, acid-treated, clay-contacted, solvent dewaxed, parailin base distillate having an SUS at 100 F. of 100; a viscosity index about 100, a flash above 380 F. and a pour below about +10 F., 22% o f an acid-treated naphthenic base distillate having an SUS at 100 F. of 60, a flash above 300 F. and a pour below 40 F., and 13% of a paralin base residuum which has been propane-deasphalted, centrifuge-dewaxed, and claycontacted and which has an SUS viscosity at 210 of about 160, a flash above 530 F. and a pour of -{-5 F.

The zinc di- 3 alkylphenoxy 2,2-dialkylpropyl dithiophosphate defined above, which is a critical component of the automatic transmission iluid, is employed in a concentration ranging from about 0.10 to 5.0 weight percent based on the hydraulic iluid composition with the preferred concentration being from 0.50 to 2.5 weight percent.

The viscosity index improvement of the transmission fluid of the invention is effected with a nitrogen-containing methacrylate ester polymer having the formula:

wherein R is an alkyl group, a dialkyl aminoalkyl group or a mixture of such groups containing from 1 to 20 carbon atoms and n is a member providing a molecular Weight of the polymer in the range from 25,000 to 1,250,- 000 and preferably from 35,000 to 200,000. Various methacrylate ester polymers of this type are known which possess pour depressant and viscosity index improving properties. A very effective material of this type is a copolymer of the lower C4-C14 alkyl methacrylate esters. A commercial methacrylate copolymer of this type which is primarily a 'viscosity index irnprover corresponds to the formula in which R represents about 32 percent lauryl, 28 percent butyl, 26 percent stearyl and 14 percent hexyl groups and having a molecular weight above 50,000. The methacrylate ester copolymer is employed in the base oil in a proportion ranging from about 0.5 to percent by Weight preferably from 1.0 to 5.0 weight percent based upon the hydraulic oil composition in order to impart the desired viscosity, viscosity index and pour point. It is understood that other methacrylate ester polymers of the foregoing type can be employed.

A dispersant is essential in the automatic transmission fluid. An effective dispersant comprises a composition resulting from mixing a substituted succinic compound, selected from the class consisting of substituted succinic acids having the formula:

R--CHCOOH CHZGOOH and substituted succinic anhydrides having the formula:

R-CHCO in which R is a large substantially aliphatic hydrocarbon radical having from about 50 to 200 carbon atoms with lat least about one-half an equivalent amount of a polyethylene polyamine and heating the resultant mixture to ellect acylation and remove the water formed thereby. Suitable amine are diethylene triamine, triethylene tetramine and tetraethylene pentamine. The reaction involves amidation of a dicarboxylic acid or anhydride thereof with a polymer to produce an acyclic diamine, a cyclic diamide, a polymeric amide or a combination of these types of products. It will be noted that the amide groups may further react to form imide groups in the process.

At least one-half of a chemical equivalent amount of the polyethylene polyamine per equivalent of substituted succinic anhydride or acid must be used in the process to produce a satisfactory product with respect to dispersant properties. Generally, it is preferred to use the reactants in equivalent amounts. Equivalency of the polyethylene polyamine reactant is on the nitrogen content, i.e. one having four nitrogens per molecule has four equivalents per mole. This reaction involves the splitting out of Water and its removal as it is formed. The reaction product is eective in amounts ranging from about 0.5 to 5.0 weight percent. Methods for preparing the polyethylene polyamine reaction products are well known and have been described in U.S. 3,131,150 and 3,172,892.

The alkane phosphonic acid additive of the invention is represented by the formula:

in which R is a straight chain aliphatic radical or a predominantly straight chain aliphatic radical having from about 11 to 40 carbon atoms. By a predominantly straight chain aliphatic radical is meant one in which at least percent and preferably percent of the carbon atoms are in a single straight chain. The phosphonic acid function may reside on either a terminal or internal carbon atom of the chain or on a side chain appending to the main alkyl chain. A preferred class of the alkane phosphonic acids are those in which the alkyl radical is a straight chain radical having from 12 to 18 carbon atoms and a more particularly preferred class because of this durability, are the acids in which the alkyl radical has from 12 to 14 carbon atoms. Generally, the alkanephosphonic acid is employed in the transmission lluid in an amount ranging from about 0.01 to 5.0 percent by weight with the preferred concentration of the alkanephosphonic acid being from 0.05 to 0.5 weight percent.

The alkylated diarylamine employed in the lubricating oil of the invention corresponds to the formula:

in which Ar represents an aryl radical, R represents an aliphatic radical having from 1 to 30 carbon atoms and x is an integer from 1 to 2. The principal aryl radical represented by Ar are phenyl and naphthyl. The preferred aliphatic radicals are those having from about 8 to 16 carbon atoms. Effective alkylated diarylamines include N-(p-n-tetradecylphenyl)1naphthylamine, N-(p-tert-octyl-phenyl)-1-naphthylamine, N (p dodecylphenyl) 1- naphthylamine, di-(p-tert-octylphenyl) amine and di-(pn-dodecylphenyl) amine. The alkylated diarylamine is employed in a concentration ranging from about 0.05 to 5.0 weight percent with the preferred concentration ranging from 0.20 to 2.0 percent.

Anti-foam agents are conventionally employed in hydraulic fluids because the iluids are rapidly circulated in operation and air can be entrapped. For this purpose, a silicone fluid of high viscosity, such as a dimethyl silicone polymer having a kinematic viscosity of 25 C. of about 1,000 to 1,000,000 centistokes and above is preferably employed. A very satisfactory anti-foam agent Afor this purpose is prepared by diluting 10 grams of la dimethyl silicone polymer (1000 centistokes at 25 C.) with kerosene to provide a solution of cubic centimeters. From 0.005 to 0.025 percent by weight of this concentrate is generally employed in the hydraulic fluid to provide from 50 to 200 parts per million of the silicone polymer based on the hydraulic fluid composition.

The following example illustrates automatic transmission uids of the invention in comparison to similar fluids.

Example IIL-The base oil employed in the fluids below comprised 68 percent of a furfural-rened, acidtreated, clay-contacted, solvent-dewaxed, paraffin base distillate having an SUS at 100 F. of 100; a viscosity index about 100, a ash above 385 F. and a pour below +10 F.,22 percent of an acid-treated naphthenic base distillate having an SUS at 100 F. of 60, a ilash above 300 F. and a pour below 40 F. and 10 percent of a paraldn base residuum which has been propane-deasphalted, solvent-dewaxed and clay-contacted and which had an SUS viscosity at 210 F. of 160, a ilash of about 540 F. and a pour below F. This base oil mixture had a ash above 375 F., a pour below 0 F. and a viscosity index of about 93.

The composition of the test iluids are set forth in Table I below:

TAB LE I Transmission fluid composition, wt. percent 1 A B C Base oil 90. l5 90. 15 90. 15 Methacrylate copolymer 2 4. 00 4.00 4. 0o Tetraethylene pentamine alkenyl succinic anhydride reaction product 3 3. 90 E. 90 3. 90 Zinc di-3-nonylphenoxy-2,2dimethy1propyl dithiophosphate of Example I. 1. 25 Zinc di-3-t-octylphenoxy-2,2dimethylpropyl dithiophosphate of Example II 1. 25 Zinc dinonylphenoxyethyldithiophosphate 4 1. 25 n-Tetradecanephosphonic acid 0.10 0. 0. 10 2,2-diethyl4,4'di-tertoctyldiphenylarnine 5 0. 60 0. 60 0. 60

1Atllinids contained 150 ppm. of dimethyl silicone solution.

2Approx. 35 wt. percent oil solution of copolymers of butyl, lauryl, stearyl and dimethyl aminoethyl methaorylates in approximately 21:53:22z4 weight ratio.

3 Approx. 50 wt. percent oil solution of the reaction product of alltenyl suocinic anhydride in which the allrenyl radical is from polybutene of about 1,100 molecular weight and tetraethylcne pentamine in an amine to anhydride mole ratio ranging from 0.7-1.0.

4 Zinc salt from the reaction of uonylphenol-ethylene oxide and P255 followed by reaction with zinc carbonate. Employed in a 68 percent by wt. oil solution.

5 Contained a minor amount of 2,2-diethyl-fl-tert-octyldiphenylamine.

In the above example, automatic transmission Fluids A and B are representative of the present invention while Fluid C represents a prior art uid. All of these fluids pass the Powerglide AT-13 Cycling Test of the Chevrolet Dexron specification.

The shifting quality of Fluids A and C was determined by monitoring the torque pressure changes in an automatic transmission during the upshift sequence in the ATF Shift Quality Test described in the SAE paper. The results of this test are shown on the accompanying drawing. FIGS. 1 and 2 are the torque traces for Fluid A. FIG. 1 records the shift characteristics after 1/2 hour in the test run and FIG. 2 gives the same information after 44 hours in the test.

FIGS. 3 to 5 show the shift characteristics for Fluid C at 1% hour, 24 hours and 4l hours in the test.

The critical upshift period is that part of the curve between a and b for each ligure. This portion of the curve illustrates the pressure changes occurring on the clutch plates over approximately 1/2 second of time during transmission upshift.

A study of FIGS. 1 and 2, which are the torque traces for Fluid A, shows that during the critical upshift period the clutch plate pressure and the quality of shifting illustratcd by the torque traces between a and b was smooth over the entire test period.

A study of FIGS. 3 to 5 shows a marked change in the shift characteristics of Fluid C in the test period. FIG. 5 indicates smooth shift characteristics. FIG. 3, in contrast, shows a sharp increase in clutch plate pressure represented by the sharp peak and abrupt reversal in the torque trace curve. This is indicative of harsh, undesirabe shift quality during the break-in period for this fluid. After 24 hours, FIG. 4, the shift quality of this fluid has improved some- 8 what and, after 41 hours, the shift quality has reached the point of desired smoothness.

The difference in quality of performance between Fluids A and C is attributed solely to the structure of the zinc compound, the zinc compound used in Fluid A, namely Example I, being chemically stable in automatic transmission service to provide smooth shift qualities for its entire service life while the zinc compounds in Fluid C undergoes some chemical change during the break-in period during which time smooth shift qualities are not realized.

Obviously, many modifications and variations of this invention may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as set forth in the claims.

We claim:

1. A hydraulic fluid comprising at least 86 weight percent of a mineral lubricating oil and from 0.1 to 5.0 percent of a zinc di3C6 18 alkylphenoxy2,2dialkylpropyl dithiophosphate having the formula:

in which each R represents an alkyl radical having from l to 4 carbon atoms, R1 is an alkyl radical having from 6 to 18 carbon atoms and R2 is hydrogen or an alkyl radical having from 6 to 18 carbon atoms, the total carbon atoms in R1 and R2 being from 6 to 24.

2. A hydraulic fluid according to claim 1 in which said zinc dithiophosphate is zinc di-3-nonylphenoxy2,2di methylpropyl dithiophosphate.

3. A hydraulic fluid according to claim 1 in which said zinc dithiophosphate is zinc di-3t-octylphenoxy2,2di methylpropyl dithiophosphate.

4. A hydraulic uid according to claim 1 in which the ratio of the number of straight chain carbon atoms to branched-chain carbon atoms in R1 and R2 is greater than 2: 1.

5. A hydraulic fluid according to claim 1 in which said mineral lubricating oil consists of about 68 percent of a furfural rened, acid-treated, clay-contacted, solvent-dewaxed, paraffin base distillate having an SUS at F. of 100, a viscosity index about 100, a ilash above 380 F. and a pourbelow about -1-l0 F., 22 percent of an acid-treated naphthenic base distillate having an SUS at 100 F. of 60, a ash above 300 F., and a pour below 40 F. and 10 percent of a paraliin base residuum which has been propane-deasphalted, centrifuged-de- Waxed, and clay-contacted and which has an SUS viscosity at 210 F. of about 160, a ash above 530 F. and a pour of +5 F.

References Cited UNITED STATES PATENTS 2,344,395 3/1944 Cook et al 252-32.7E 3,131,150 4/1964 Stuart et al. 252-51.5A 3,175,976 3/196'5 Foehr 252-75 3,259,579 7/1966 Rogers et al. 252-75X 3,293,181 12/1966 Stuart 252-332.715.

FOREIGN PATENTS 534,385 12/1956 Canada 252-498 LEON D. ROSDOL, Primary Examiner D. SILVERSTEIN, Assistant Examiner U.S. Cl. X.R. 252-32]