US2503660A

US2503660A - Viscometer

Info

Publication number: US2503660A
Application number: US52984A
Authority: US
Inventors: Paul G Exiline; John R Aikins
Original assignee: Gulf Research and Development Co
Current assignee: Gulf Research and Development Co
Priority date: 1948-10-06
Filing date: 1948-10-06
Publication date: 1950-04-11
Anticipated expiration: 1967-04-11

Description

April 11, 1950' P, G. ExLlNE ET AL l 2,563,660

I vIscoMETER Filed oct. e, 1948 2 sheets-sheet 1 POWER SUPPLY INVENTORS n v PAUL G.IEXLIN (0 BY JQHNRMKLNS r4 ATTORNEY P. G. ExLlNE ET AL 2,503,660

VISCOMETER 2 Sheets-Sheet 2 H" UABHMmv En: Il' L w April 11, 195o Filed Oct. 6, 1948 Patented Apr. 11,

UNITED *y STAT as PATENT orrlcs 'vlscoME'rEa raul GgExune, Tulsa, oki-a., and John n. Allam, Pittsburgh, Pa., assignors to Gulf Research &

Development Company, Pittsburgh, Pa., a corporation of.' Delaware application october s, 194s, serial No. 52,984

I This invention relates to a device for studying `and measuring the rheological properties of` plastic-substances, and more'particularly. to a viscometer for determining the ow characteristics of such materials as greases, drilling muds,

` paints, gumabitumensand the like. v

The viscosities of most plastic materials will change when such materials are subjected to working For example, it is vwell known that putty, grease and bread dough become more pliable after they have-been kneaded, or more `specifically after they have been worked for a' period of time Many of these plastics become more rigid again if they are permitted to stand after they have been worked Thischaracteristic of change in viscosity or consistency with Vtrolled periods of working. Consequently, common viscometers do not give an accurate picture of how a plastic material such as a grease may `act in vvarious applications thereof.

The viscosity of a. grease identifies havior as well as its behavior when used inthe of such plastics,` due 'tothe above factors, is necessary before an accurate prediction of the behavior of a grease can be made in a particular application and under actual operating con-l its flow bey 7' claims. (Cm3-'56) from which'the apparent and absolute viscosities l character described which will furnish informationfrom which the amount of work done and lthe rate of doing work on the material under observation may be calculated. Another object accomplished by our invention is the provision of a viscometer which will furnish information of the material under observation may be calculated. A still further object accomplished by our invention is the provision of a viscometer which will permit continuous studies to be made on an initial sample of material under a variety of test conditions. A still further object accomplished by our invention is the' provision of a viscometer which will permit the testing of materials at high static pressures. Other objects appear hereinafter.

Our invention is exemplified by the accompanying drawings and the descriptive matter relating thereto. Referring to the drawings Fig. 1.is an elevation view partly in section illustrating the principal elements of our viscometer. Fig. 2 is a schematic diagram of a hydraulic engine and the elements relating thereto which may be used to operate the viscometer shown inA Fig. 1. Fig. 3 is the schematic diagram of an electrical timing system which may be used to ditions. Accordingly, these factors should also `be considered when making up schedules of specifications for various greases. It is apparent that common viscometers do n ot supply such information, rand further, do not permitv the making of continuous studies of a grease at various rates. and degrees of work to which the grease may be subjected.

Accordingly, the primary object accomplished by our invention is the provision of a viscometer which will furnish information concerning the flow characteristics of plastic materials after they v have'been subjected to various degrees-and-rates of work. A further object accomplished by our time the stroke of thehydraulic engine piston shown in Fig. 2l and the viscometer piston shown in Fig. 1.

Referring to Fig. 1, the heart of the viscometer is .a capillary tube or restriction tube I, through which the material under observation is alternately passed in different directions. The ends of capillary tube i are coupled by means of couplings 2 to connecting lines 3 which are adapted to receive pressure lines connecting as close as possible with the ends of capillary tube i. These pressure lines 4 are in turn connected to pressure registering means shown as pressure gauges 5 so that the pressure differential across capillary tube I may be determined at all times. However, other pressure determining means, such as a differential pressure gauge connected across capillary tube l, may advantageously be used. The ends of connecting lines 3 opposite capillary tube i are fitted into collars 6 mounted on T- joints 1. The upper passages of T-joints i are provided with caps 8 and these caps are tapped to accommodate plugs- 9 so that the plugs may be removedand pressuring devices attached to permit studies to be made at high static pressures when desired. Collars 6 are also tapped to accommodate plugs i0 which may be removed to introduce the material to be tested into the viscometer. The lower portions of joints l are joined to cylinder housings II which are adapted to support a cylinder I2 therebetween. Cylinder I2 is provided with a reclprocable piston I3, the purpose of which is to force the material under observation through capillary tube I. It can be seen that a free passage exists from the capillary tube I to both sides of piston I3, so that as piston I3 is reciprocated the material being tested will alternately be forced back and forth through capillary tube I. Piston I3 derives its motivation from the hydraulic engine shown in Fig. 2 and is connected thereto by means of piston rod I4 and connecting rod I5. The side of piston I3 opposite piston rod I4l is provided with another rod I6, which may be an extension of piston rod I4, to equalize the volumetric displacement on both sides of piston I3 as it is reciprocated. Temperature control of the viscometer is provided by means of a constant temperature bath I1 contained in a housing I8 surrounding all the viscometer elements containing the material under observation. Heat for this thermobath is supplied through main electrical heater I9 which is controlled by a variable auto transformer 20. To facilitate a finer degree of heat control, main heater I9 is adjusted to produce slightly less than the amount of heat lost from the system, and an auxiliary heater 2 I, controlled by a temperature controller 22, is provided to supplement the heat requirements of the system. The temperature of the system may be observed by reading a conveniently placed thermometer 23 situated in a thermometer well 24 depending from the top of housing i8. An electrically operated stirrer 25 is provided to improve the temperature distribution within the thermobath I1.

As stated above, reciprocation of piston I3 is accomplished by means of the hydraulic engine shown in Fig. 2 which connects with piston I3 through connecting rod I5 and piston rod I4. This hydraulic engine is characterized by a cylinder 26 and a piston 21 therein which is reciprocated by the application of hydraulic pressure to alternate sides thereof. The. hydraulic pressure is supplied from a sump tank 28 and pump 29 and the flow of uid through the varioiis lines shown in Fig. 2 is as indicated by the direction of the arrows. From pump 29 the hydraulic fluid is forced through a relief valve 3u and to a pilot-operated four-way valve 3l which directs the fluid to alternate sides of piston 21. A flow control valve 32 is placed in the system to coact with relief valve 3B and bypass pressure uid to sump tank 28 when the pressure and flow of uid become excessive and consequently cony position of valve 3| is determined by a pilot valve 33 so that, depending upon the position of pilot valve 33, hydraulic fluid will be applied either to the right or left of piston 21. The connecting rod I5 or the piston rod upon which piston 2T is mounted is provided with an extension 34 which extends beyond the engine cylinder 26, and this extension 34 will of course reciprocate with piston 21. Extension 34 is provided With adjustable trigger means 35 which are adapted to cooperate with pilot valve 33 at the end of each stroke of piston 21 to reverse the flow of fluid through pilot valve 33. This will of course reverse the flow of uid through pilotoperated valve 3i so that at the end of each lill stroke of piston 21 the flow of fluid to the piston will automatically be reversed and the stroke of the piston will be reversed accordingly.

To determine the rate of ow of the material under observation through capillary tube I means to time the stroke of piston I3 are provided. Thus, knowing the volumetric displacement of piston I3 and the time of the stroke, it is possible to compute the rate of flow through capillary tube I. Since the strokes of pistons I3 and 21 are equal and since shaft extension 34 is operatively connected to piston 21, the velocity of extension 34 will be equivalent to the velocity of piston I3. For instance, to time the stroke of piston I3, a cam 36 is mounted on extension 34 so as to engage one of a pair of

contacts

31 and 38 at the start and nish of each stroke of the system. These contacts are integrally connected with an electric timing system so that the time of each stroke may simply be read from a clock or recorder. An example of such a timing system is shown in Fig. 3 wherein a clock 39 is provided to register the time of each stroke. This clock is operatedby a motor 40 which is constantly running, having been connected across a source of power. An electrically operated magnetic clutch 4I is provided to produce operative engagement of motor 40 with the clock mechanism whenever clutch 4I becomes energized, or more specically, when both of

contacts

31 and 38 are closed. Thus, in the positions of the elements as shown in Fig. 3, as cam 36 moves to the left, contact 38 will become closed and clock 39 will begin to operate. However, upon reaching the end of its travel, cam 36 will open contact 31 causing the de-energization of clutch 4i so that the operation of clock 39 will be stopped. Upon the reverse stroke cam 36 will close contact 31, starting the clock, and nally will open contact 38, stopping the clock at the end of the piston stroke. A condenser 42 may be connected across the contacts to suppress arcing.

The operation of the viscometer simply consists in introducing the material to be tested into the system and starting pump 29 to operate the hydraulic engine and reciprocate piston I3. Temperature controls may be varied as desired and the speed of recprocation of piston I3 may also be varied at will by minor adjustments in the hydraulic system. The remaining test procedure then consists in reading from pressure gauges 5 the pressure differential across capillary tube I and observing the time of each piston stroke.

It is then possible to compute from known information and that information which is observed during testing operations the apparent and absolute viscosities of the material within the viscometer. Polseuille is credited with the mathematical development which led to an equation which would permit measuring Viscosity of a. Newtonian liquid by means of capillary tubes. One form of this equation is as follows:

u=1rPr4= Pr/2L Shearing stress wherein asoaeoo r=Radius of capillary tube. L=Length of capillary tube. P=Pressure differential across the capillary tube. Q=Flow rate. B1=Shearing stress at they capillary walls.

I'he equation for shearing stress at the capillary walls is as follows:

lrPy

wherein r, P and L are as designated hereinabove. Using the value of R obtained from Equation 2 and the value of S1 obtained from Equation 3, the absolute viscosity may be obtained merely by dividing the shearing stress by the rate of shear in accordance with Newtons fundamental den'- nition of viscosity:

The above viscosity information can be obtained at any time since continuous studies of a sample are made possible by the use of our viscometer. The material under test can be worked any amount before viscosity results are recorded. The material under test may then be worked even more and another group of viscosity results may be recorded. At the end of any working schedule, viscosity data may be recorded, a rest period permitted, and another set of viscosity data may be obtained. These working schedules may include various rates at which the work had been done and both the rate of doing work and thevamount of work done may be determined and expressed in fundamental units. These results are obtained from the flowpressure data as shown in the following equations:

wherein P= Pressure diierential across the capillary tube.

-g-Flow rate through the capillary tube.

The flow rate may be obtained simply by dividing the volumetric displacement of piston I3, which is-.xed and easily obtainable, by the time'required for each stroke. Total work done merely requires a multiplication of the work rate by the time involved:

Total work= W=(%7X t (6) n' the work rate changes, an 11: usually wm due #francaises wherein ing feature.

a j to. the thixotropic nature of thematerial under observation, the total work may be obtained by making a diagram of work rate yplotteqzi .as a.

function of .time and thenintegrating the area under the curve. f

Itis apparent that many modiilcations of `our inventionmay be made yand many equivalents of the elements shown herein may be substituted without departing from the spirit of the invention. For example, this invention is not to be limited to the particular type oi' engine disclosed herein for reciprocating piston i3, as many other engines known to the art would be suitable. Furthermore, the means employed for the timing of l the stroke of piston I3 is included herein merely to illustrate a method which may; advantageously be used-and should not be considered as a limit- Other means for determining iiow rate may be used without departing from lour invention. For instance, a flow gauge may be installed in the system directly in the path of the material being passed through the capillary tube. In addition, theform of temperature control which has been illustrated may be variously.'

modified and changed, the important thing being that adequate temperature control is constantly v maintained during operation of thek viscometer.

One of the most important advantages of our invention is that it provides a viscometer which is capable of making viscosity determinations of a thixotropic material after it has been worked for a period of time. Another advantage is that both the amount of work done and the rate of doing work may be varied so that a more accurate indication of what the material under test may do under actualoperating conditions can be obtained. This is partly due to the fact that scribed herein are intended to be merely illusfl trative of our invention and in no manner should they be considered as limitations thereof or as limiting the scope of the appended claims hereinafter made. v

What we claim is:

1. A device for determining the ilow characteristics of a plastic material, comprising a capillary tube, a cylinder to receive the material to be tested, said cylinder connecting with the ends of said capillary tube, a reciprocable piston in said cylinder for alternately passing the material under observation in different directions through said capillary tube, means to reciprocate said piston,fpressure determining means connecting with the ends of said capillary tube, means for,

determining the rate of flow through said capillary tube, and means for maintaining said capillary tube and the material under observation at a substantially constant temperature.

2. A device for determining the flow characteristics of a plastic material, comprising a capillary tube, a cylinder to receive the material to be tested, said cylinder connecting with the ends of said capillary tube, a reciprocable piston in said cylinder for alternately passing the material under observation'in different directions through said capillary tube, means to reciprocate said pisasoacco ton, pressure determining means connecting with the ends of said capillary tube, means for timing the stroke of saidpiston, and means for maintaining said capillary tube and the material under observation at a substantially constant temperature.

3. A device for determining the flow characteristics of a viscous material, comprising a capillary tube, a cylinder to receive the material to be tested, said cylinder connecting with the ends of said capillary tube, a reciprocable piston in said cylinder for alternately passing the material under observation back and forth through said capillary tube, an engine to reciprocate said piston, pressure determining means connecting with the ends of said capillary tube, means for timing the-stroke of said piston to determine the rate of now of material through said capillary tube, and means .for maintaining said capillary tube and the material under observation at a substantially constant temperature.

4. A device for determining the iiow characteristics of a viscous material, comprising a capillary tube, a cylinder to receive the material to be tested, said cylinder connecting with the ends of said capillary tube, a reciprocable piston in said cylinder for alternately passing the material under observation back and forth through said capillary tube, an engine to reciprocate said piston, pressure responsive means connecting with the ends of said capillary tube to determine the pressure diilerential thereacross, vmeans for timing the stroke of said piston to determine the rate of ilow of material through said capillary tube, and means for maintaining said capillary tube and the material under observation at a subvbaci: and forth through said capillary tube, a reciprocating engine operatively connecting with said piston to provide motivation therefor, pressureresponsive means connecting with the ends of said capillary tube and exhibiting means associated therewith for determining the pressure differential across said capillary tube, means for timing the stroke of said piston to determine the rate oi now oi material through said capillary tube, and a constant temperature bath for maintaining said capillary tube and the material under observation at a substantially constant temperature.

6. A device im determining the iiow characteristics of a viscous material, comprising a capillary tube. a cylinder to receive the material t0 be tested, means connecting the ends of said cylinder with the ends of said capillary tube. a reciprocable piston in said cylinder ior alternately passing the material under observation back and forth through said capillary tube. a variable speed reciprocating hydraulic engine operatively connecting with said piston to provide motivation therefor, pressure responsive means connecting with the ends of said capillary tube and exhibiting means associated therewith'l for determining the pressure diiierential across said capillary tube, a pair of electrical contacts operable by said reciprocating engine and timing means controlled by said contacts for timing the stroke of said piston to determine the rate o! ow ofA material through said capillary tube, and a constant temperature bath for maintaining said capillary tube and the material under observation at a substantially constant temperature.

7. In a grease viscometer characterized by a capillary tube and pressure responsive means to determine the pressure diiierential thereacross as grease is passed through said capillary tube, the improvement which comprises a cylinder to receive the grease to be tested, means connecting the ends of said cylinder with the ends of said capillary tube respectively, and a reciprocable piston in said cylinder to alternately force the grease under test back and forth through said REFERENCES CITED The following references are of record in the le of this :patent:

FOREIGN PATENTS Country Date f Great Britain June 17, 1920 Number