1434
INDUSTRIAL AND ENGINEERING CHEiMISTRY
for reaching an agreement on what practical conditions can be considered as ideal or representing best practice. The heat losses, for instance, that may be considered as necessary and unavoidable in the burning of fuel under boilers are not capable of being fixed or standardized. On the other hand, it may perhaps justly be questioned whether, as now recommended by the A. S. T. M. methods, the net heating value should be derived by deduction of the full quantity of the latent heat of vaporization of water at the temperature to which the bomb is cooled after combustion. Lichty and Brown (2) derive thermodynamically an average value of 970 inst.ead of 1040 B. t. u. per pound of water condensed as being the correct average heat given up in the bomb by the water in condensing, over and above what would be given up hypothetically if it were cooled without condensation. This latter basis, they say, is the correct one on which to establish net calorific value. It remains more or less of an arbitrary matter, and it can hardly be said that any one factor is more correct or more reasonable than another for deriving an arbitrarily defined value. The intention is to have this arbitrary deduction
Vol. 23, KO.12
from the gross value represent as nearly as possible the heat derived from water in the products, and to many it will appear that this heat should be taken as the total derived in the bomb from cooling and condensing the water formed. An illustration may be taken of a lignite containing 25 per cent moisture, and hydrogen sufficient to bring the total water formed in combustion to 60 per cent; or a sugar waste or distillery slop containing 38 per cent moisture and forming a total of 75 per cent water when burned. Should a boiler or other industrial heating device using such materials be charged with the gross heating value in considering efficiency of its performance? And yet, should not the fuel be charged with the gross when there is a question of relative efficiency of the fuel's performance? Also when comparing, in general, fuel values of such materials with those of higher-grade materials, such as coal, would not the net values give a truer relative valuation? L i t e r a t u r e Cited (1) Am. Soc. Testing Materials, Standard Method D 271-30,1930Standards, II,.725. (2) Lichty and Brown, IND. END.&EM., 23, 1419 (1931).
Some Problems in LubricationIof Rocker Arms' E. W. Zublin TEXAS PACIFICCOAL & OIL CO., FORTWORTH, TEXAS
OMMERCIAL airline operators have reported repeatedly that trouble is being had with the lubrication of rocker arms and the ball ends of the push rods. Most of the airport engineers admit that the trouble is due to faulty design rather than to poor qualities of the greases employed. This, howeuer, does not remedy the situation, as they have to maintain their flying schedules with present-day equipment and provide the maximum possible safety. Owing to economic conditions, the companies have been forced to reduce the operating overhead to a minimum, and one step in this plan for greater economy has consisted of lubricating the rocker arms and pulling the push rods of the engines at increasing time intervals. Less than 3 years ago, 10-hour service between the pulling of the push rods was considered excellent. Now, in some places, a minimum of 40 hours is required. Greases must be such that the balls of the push rods do not run dry within the specified period. Squeaking caused by the movement of the balls in the rocker-arm cups indicates absence of lubricant.
C
larger air-transportation companies revealed that the different sections employ different types of greases, and that what is good for one seems to be useless for the other. Aluminumsoap greases, with their peculiar increase in consistency in the range from 100' to 250' F. (37.8' to 121.1" C.), appear especially suited to comply with the first five demands and in particular they will resist the tendency to run off except a t temperatures above 300 ' F. (148.9 C.). However, hydrolysis frequently causes them to break down, and this trouble is so serious that some mechanics will reject any grease that becomes rubbery when heated with a match on a thin metal plate. They believe that this rubbery consistency is the cause of the failure to maintain lubrication, not realizing that it is the greatest virtue possessed by aluminum-soap greases, and that the cause of the trouble lies in the breakdown of the soap. Samples of broken-down greases, when examined under the microscope, showed the characteristic floccules of aluminum hydroxide. Field Experience
Required Properties
Greases used for this type of lubrication should combine the following properties:
(lo)
They must be soft; minimum, 300 penetration a t 77' F. (25 C.). (Softness is required to avoid damage to the roller bearings when charging same.) (2) They must lubricate a t 0' F. ( -17.8' C.). (3) They must lubricate a t 350' F. (176.7' C.) (4) They must not gum or carbonize at 350' F. (176.7' C.); ' (5) They must not run off a t any temperature between 0 and 350' F. (-17.8' and 176.7" C.). (6) They must be fairly resistant to moisture; they should not hydrolyze into aluminum hydroxide and free fatty acid. (7) They must not break down under the consistent pounding effect of the push rods on the rocker arms.
There is probably no single grease that will answer all seven demands. An investigation into the practices of some of the I Received August 24, 1931. Presented before the Division of Petroleum Chemistry at the 82nd Meeting of the American Chemical Society, Buffalo. N. Y..August 31 to September 4, l e a l .
At an Atlantic seaboard airport, aluminum-soap greases are employed for the roller bearings of the rocker arm proper, while the ends of the push rods are dipped into a special soda-soap grease before being put into place. This combination is said to give minimum service of 40 hours and service up to 60 hours under the prevalent climatic conditions. At a midwestern airport, in the same kind of equipment, the foregoing combination was tried and was reported t o have failed after less than 20 hours. Soft petrolatum mixed with 150/160 bright stock is preferred, though only 20 hours of service are obtained. At a southern airport good service is obtained by using a straight aluminum-soap grease. Twenty hours are required. High temperature and absence of moisture are the outstanding climatic influences in this section. Hydrolysis causes the same greases to fail in other parts of the country. Reports from a southwestern airport indicate results similar to those obtained in the southern division. Service of
INDUSTRIAL AND ENGINEERING CHEMISTRY
December, 1931
20 to 40 hours was being obtained from straight aluminumsoap greases in these districts. Laboratory Testing
At these laboratories a machine for testing rocker-arm grease is used for evaluating lubricants as to their suitability for rocker-arm lubrication. It consists essentially of a n airplane rocker-arm assembly run under controlled conditions (Figure 1). Rocker arm. push rod, and valve spring from a Wasp engine are mounted on a frame made of 0.25-inch strip iron. A cam shaft driven by a 0.25 h. p. electric motor at about 1200 r. p. m. moves the push rod and rocker arm. A belt drive is being used. A small
1435
to be tested is injected into the bearing until some of it flows out through the feed hole in the cup. It is advisable to move the arm during the 6lling in order to force the grease into all corners and insure complete filling. Excess grease is wiped out of the cup, and the push rod is placed in position by pressing the valve spring. The machine is covered with the hood and the flame is lit. When the temperature is close t o the desired point, which should not require more than 30 minutes, the electric motor is started. The top of the push rod is inspected a t intervals, and the time is noted when it no longer receives lubricant from the bearing.
I"MI
gas flame at the foot of the frame directly underneath the rockerarm bearing provides the necessary heat. Gas heat is used in preference to electric heat, because the former provides a small amount of moisture from the combustion-enough t o cause hydrolysis of greases not resistant t o moisture. A tin hood I
r'-
Figure 2-Bleeder
Arrangement
Table I gives results of tests carried out on samples of rocker-arm greases, some of which were made in the laboratory and some bought on the open market. Need for Research
No relation is evident between physical and chemical properties on the one hand and life of lubricant on the other hand. Aluminum-soap greases from the same batch may vary in consistency a great deal, depending upon the rate of cooling. The faster they are cooled the harder they set up. As a general rule the harder grease will last somewhat longer than the softer one of the same chemical composition. Harder greases are more desirable than softer ones, as the latter have a tendency to separate on standing in warm weather. At present it is not known what properties make certain greases last longer than others. In the case of aluminum-soap greases, doubling of the amount of soap beyond a certain Figure 1-Rocker-Arm Assembly minimum does not improve the lasting qualities. Conwith a stack a t the top serves t o keep away draft and makr the effect of the moisture more pronounced.* Two thctmom~tprs sistency or viscosity as measured by the McMichael viscomeextending through the top of the hood measure the temperature ter has no bearing on it except for handling and charging. in the immediate neighborhood of the rocker arm Fluctuations Resistance to hydrolysis, of course, is important. in the gas pressure that might make temperature control difficult There is probably no greater uncertainty in any other field were minimized by the use of a bleeder arrangement as shown in of lubrication than in that of rocker-arm and push-rod Figure 2. Valves A and B are set once for all. The flame under the hood is changed by operating the bleeder valve, C. With this lubrication. Several theories advanced so far have had to be arrangement a uniform temperature not varying over/or -3' F. discarded, either totally or in part. For instance, it was (-19.4' C.) can be maintained for hours. thought that black oils produced better rocker-arm lubricants A rocker arm from a Wasp engine was chosen, because, on than bright stocks or neutrals, especially when used in combiaccount of structural reasons, it is particularly adapted for control tests. This type of rocker arm possesses a luhricating channel leading from the roller bearing to the inverted cup which serves as a bearing for the push rod. In Figure 3 the principles of this design are indicated. Grease is pushed slowly through this channel, lubricating the knob of the push rod and the inside of the cup. Only when the supply of grease in the roller bearing is exhausted will the feed into the cup cease.
This action provides measures by means of which various lubricants can be evaluated. The time required until the knob of the push rod runs dry after the bearing has been charged full and until gum or even carbon deposit on the knob, are these measures. The procedure of the test is as follows: The rocker arm and push rod are thoroughly washed with benzene and dried. The machine is assembled and the grease
*
lnjerting additional steam did not prove successful. owing to t h e difficulty of accurately measuring and directing the small quantities of steam required.
Figure 3-Rocker
Arm
nation with aluminum soaps. Laboratory service tests pointed in' this direction. But sample 12 (Table I) was produced, being made with a bright stock and proving far superior to other lubricants of a similar type and even to those made with black oils. According to patents of Faragher (1) and Henry (Z), aluminum-dioleate greases are said to be more resistant to breakdown than trioleate. Tests carried out on both types showed this to be true in some cases but not in others. There is no doubt that different types of engines behave differently. However, in the cases mentioned in the foregoing, most teRta were carried out in the same type of engines and the rocker-
1436
INDUSTRIAL AND ENGINEERING CHEMISTRY Table I-Results
SAMPLE
TYPEMINERALOIL
SOAP
Type
Amount
%
Ala A1 A1 AI AI
10 10 10 10 10
600 S. R.,e 200 vis. a t 210 600 S R 200 vis a t 210 600 S'R" 200 vis: at 210 600 S' R" 200 vis. a t 210 600 S: R:: 200 vis. at 210
6
A1 A1 A1 AI A1 Soda
10 10 10 10 10 10 7 18
300 vis. a t 2109. R. 300 vis. at 210 S. R. 300 vis. oxidized stock 200 vis. bright stock 200 vis. bright stock 200 vis. brjght stock 200 vis. bnght stock 200 vis. S. R.
14 Soda 15' Soda
10 15
150/160 bright stock 160/160 bright stock
7 S
AI
9
Ai
io 11 12 13
of Teats on Samples of Rocker-Arm Greases PENEMCTRATIMEIN ROCKERARM
MOISTVRE
MICHAELTION MELTING UNTIL DRYAT: V1S.b AT 77 POINT 200' F. 250' F. 300" F;
(83.3" (121.1" (148.9
%
1 2 3 4 5
Vol. 23, No. 12
...
None Trace None None None
.60. . . ... 97 ..,.. ... 145
None
84 75 235 197 198 129 48
0.2 None None None None None
... ... ... .. .... ... ... ...
75
... ... ...
... ... ... ... ... ...
' P.
C.)
(O
C.)
.... .... .... .... .... .... .... ... ... ... ...
208s 156'(68.9)
253 180 82 2) 231 258 ($24.4)
... ... ... ... ... ...
.... .... .... .... .... ....
Hours 51
..* .
.. .. .. 12
.. 22
14
..
31
..
.. a .
....
C.)
C.)
Rours Rours 40 26 17 28 .11. 27 4 . . 22 8
.. ..
..
14 1s 12
.. 27
..
.... ..
RESULTSOF FIELD BXPT.AND REMARKS
lOI/i
11 . 7 6 15 50
45 8 21 12 9 10 17 16
Satisfactory in dry climate Broke down in 15 t o 20 hours Satisfactory in dry climate Same results as in (1) and (3) Chem. composition similar to (1)but contains some dioleate Same comDosition a8 ( 8 ) , but moist Fair in drv climate Not muc6good in any climate Results irregular Results irregular Fair in dry climate Good for push rods;d better than (14) and (15) Good for push rodsd Good for Dush rods in hot en- ' ginesd'
N a a n d AI 15 200 vis. S.R. 134 N a a n d AI 15 200 vis. S.R. 74 1 . Soft etrolatum 87 33 39 *. Used a t St. Louis airport 19 Hart?petrolatum 50 50 45 .. 20 Hard petrolatum 67 33 156 *. 21 Hard petrolatum 87 33 164 0 All aluminum soap reages prepared a t the Texas Pacific Coal & Oil Co. were made by stimng the soap into the coal oil, heating to 290' or 300" F (143.3' or 148.8' C.), whik stirring and drawing off immediately. b McMichael viscometer a t 100' F. (37.S0C.); spindle, 1 cm. diameter, 3 cm. immersion. C Wooden cone weight 12.09 grams. d Not recornminded for rocker arm proper because of danger of damage owing to stiffness of grease. Steam-refined stock of 600' F. (316' C.)Flash (Cleveland open cup).
16 17 18
...
arm machine was run always under substantially the same conditions. It is fairly certain that the knock-rating of the gasoline employed has a great deal to do with the lasting qualities of the rocker-arm greases, as knocking gasoline causes higher cylinder temperatures, If non-detonating gasoline is used, temperatures not in excess of 350" F. (176.7' C.) around the rooker-arm boxes are to be expected. Reports of certain tests carried out a t various airports claim higher temperature, however. Unfortunately it has not been possible to ascertain the knock-rating of the fuels used in these tests. Existing Specifications
DifEculties of a nature similar to those described here were experienced by the Air Corps of the United States Army. As will be remembered, the Army in insuing specification Y-3558 for rocker-arm lubricants did not specify any consistency, and the only requirement is that the grease shall be a homogeneous mixture of minerdoiland pure odorless aluminum soap containing no filler. The United States Navy in specification E l 0 0 designates aluminum-soap greases containing at least
..
..
..
.. ..
.
15 per cent of aluminum stearate or palmitate, and having an A. S. T. M. penetration of 300 to 360. It is found here that this specification can include greases from the poorest to almost the best. On the other hand, the very best aluminumsoap grease found here so far contained only 10 per cent soap. The present situation calls for a thorough study and the development of new tests. Pressure viscosities a t temperatures of from 0" to 350" F. (-17.8" to 176.7' C.) are necessary. Tests for the adhesive and cohesive qualitiee, resistance to hydrolysis, and breakdown upon continuow pounding should be found and developed. Possibly the Knopf adherometer (3) may give some information. The service test employed in these laboratories gives a good indication, but owing to the fact that the tests can be run under a single atmospheric condition only, it9 application is not wide enough. Literature Cited (1) Faraghu, W.F., et al., U. S. Patent 1,550,608(Aug. 18, 1925). (2) Henry, R. W.,e t al., U. S. Patent 1,891,882(Nov. 13, 1828). (3) Knopf, C. L., Am. Petroleum Inst. "Methods of Testing Automobile Gear Lubricants," December, 1928.
Hydrolysis of Starch by Carbonic Acid' Milton A. Dewey' and Norman W. Krase DEPARTMENT OF CHEMISTRY,UNIVERSITY OF ILLINOIS,URBANA, ILL.
HIS l a b o r a t o r y has
The hydrolysis of starch to reducing sugars can be to a s o l u t i o n c o n t a i n i n g p r e v i o u s l y repo&d effected by carbon dioxide solutions in water at eleabout 10 per cent by weight preliminary work on vated pressures and temperatures. The rates of hyof acetic acid. m e the p r o p e r t i e s of aqueous drolysis at 156", 18609 and 216" C. and at 1000 pounds only a m o d e r a t e concentra(70.3 kg.1 carbon dioxide Pressure are linear functions tion of a c i d , t h e a u t h o r s solutions of carbon dioxide of time. It is still uncertain whether or not this rewere, n e v e r t h e l e s s , enunder pressures of carbon dic o u r a g e d to make further o x i d e U P t o a b o u t 2500 action is monomo~ecu~ar. studies of the propertiea of pounds per square inch (175.8 kg. per sq. cm.). This work ( 1 ) indicated that car- carbonic acid under pressure by other methods. Jenkinson bonic acid could displace acetic acid from aqueous solutions (3) began work on the hydrolysis of starch by carbonic of calcium acetate until the resulting acidity corresponded acid and his results indicated the feasibility of obtaining glucose sirups by this treatment. Kleiderer and En& (4), 1 Received August 28, 1931. using Jenkinson's apparatus, studied the hydrolysis of inulin * Present ad&-, Midcontinent Petroleum Corp., Tulsa, Okla.
T
