SH/T 0048-1991 Determination of Apparent Viscosity of Lubricating Greases

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Card type: Test method

1. Method number / full name / English name / replacement relationship

• Standard number: SH/T 0048-91 (confirmed in 2004)
• Chinese name: Determination of Apparent Viscosity of Lubricating Greases
• English name: not provided in the available source
• Replacement relationship: From the date of implementation of this standard, the former Ministry of Petroleum Industry standard SY 2720-82 "Determination of Apparent Viscosity of Lubricating Greases" is void.
• First issued: 1965
• Reference adoption: Former Soviet Union national standard ГОСТ 7163-63 "Determination of Apparent Viscosity of Lubricating Greases"
• Proposed/technical committee/drafting: Proposed, technically coordinated, and drafted by the Research Institute of Petroleum Processing
• Approval/implementation: Approved by China Petrochemical Corporation 1991-06-28, implemented on 1992-07-01

2. Scope of application and non-applicability

• This standard specifies a method for determining the apparent viscosity of samples using an automatic capillary viscometer.
• This standard applies to the determination of lubricating greases.
• Not applicable: If the sample contains granular mechanical impurities, this method cannot be used for determination, so as to avoid blocking the capillary (4.1.3 note).

3. Method principle

The ability of a liquid to resist mutual movement when flowing is called viscosity or internal friction. The viscosity of a lubricating grease at a certain temperature is a variable that changes with shear rate. This kind of viscosity of lubricating grease is called apparent viscosity, or apparent viscosity, with the unit Pa·s.

The automatic capillary viscometer used in this standard is a variable-flow pressure capillary viscometer. A spring acts on a push rod so that the sample in the sample tube is subjected to pressure and flows out from the capillary. As the spring relaxes, the pressure in the tube gradually decreases. Therefore, this variable-flow pressure capillary viscometer can obtain a series of apparent viscosity values at average shear rates in one test. The range of average shear rates can be selected according to the radius of the capillary.

The pressure in the sample tube is converted from the height of the recording pen connected to the spring (see Figure 3). According to the system pressure, capillary radius, and length, the shear stress suffered by the lubricating grease in the capillary can be calculated according to formula (2). The average shear rate of the lubricating grease flowing in the capillary is calculated according to formula (3). Since the flow rate of this viscometer is variable, under a certain capillary condition it depends on the descending speed of the push rod. This descending speed is not easy to measure directly. Using a recording drum rotating at a certain linear speed, the working curve is recorded. Any point on the curve represents the viscosity characteristic at a certain instant. The tangent of the angle between the tangent at that point and the horizontal line multiplied by the linear speed of the recording drum is the descending speed of the push rod. According to this principle, the average shear rate of the lubricating grease in the capillary at each instant can be calculated according to formula (5). Then, according to formula (1), the apparent viscosity of the lubricating grease at each instant can be calculated.

4. Reagents and materials (purity / preparation)

• Recording graph paper: specification 110mm × 300mm (3.2).
• Industrial ethanol and dry ice: used for constant temperature during low-temperature tests (4.1.7).
• Mercury: used for capillary radius verification (Appendix A1).
• Purity and preparation of other reagents: not provided in the available source.

5. Instruments and equipment

• Automatic capillary viscometer, see Figure 1 (3.1.1). Main components: eccentric wheel 1, recording paper 2, recording drum 3, rubber ring 4, three-stage reducer 5, motor 6, rotating rod 7, motor switch 8, nut handwheel 9, steel pipe 10, constant-temperature jacket 11, bolt 12, support column 13, base 14, bakelite ring 15, nut 16, rubber washer 17, connector 18, capillary 19, nut 20, sample tube 21, push rod 22, nut handwheel 23, bushing 24, bakelite block 25, pencil clamp 26, steel ball 27, clutch 28, locking rod 29, spring group 30, clamp spring 31, fixing sleeve 32, small screw rod 33, steel pipe 34, center rod 35, washer 36, flat plug 37, nut 38, screw rod 39.
• Circulating constant-temperature bath or other constant-temperature equipment (3.1.2).
• Capillary specifications (Table 1): No. 1: R=0.1020cm, L=11.45cm, K₁=4.45×10⁻³; No. 3: R=0.0540cm, L=11.46cm, K₁=2.36×10⁻³; No. 5: R=0.0214cm, L=11.42cm, K₁=9.40×10⁻⁴.
• Recording drum linear speed settings (Table 1): W₁=1.65, W₂=0.094, W₃=0.0054 (unit not clearly indicated in the source text, requires confirmation against the source standard (source-text extraction)).
• Pressure test bench: hand-operated, 10.0MPa (Appendix A2).
• Vernier caliper: accurate to 0.01cm (Appendix A1).
• Weighing bottle: weighed to 0.0001g (Appendix A1).

6. Recommended operating conditions

• Constant temperature: Connect connector 18 and the circulating constant-temperature bath with a rubber tube, and circulate until, under the specified conditions, the temperature is maintained constant for not less than 20min (4.1.7).
• Low-temperature test: Constant temperature can be maintained in a container with industrial ethanol and dry ice, using it instead of the constant-temperature jacket. A sample receiver should be provided below the lower end of the capillary (4.1.7).
• Recording drum speed: maximum speed (rotate the rotating rod to the right to the position 1) (4.1.9); during the test, successively adjust to medium speed (position 2) and minimum speed (position 3) (5.2).
• α angle range: To improve measurement accuracy, the α angle should be within the range 25°~65° (6.1).
• Other recommended operating conditions: not provided in the available source.

7. Sampling and sample preparation

• Place the sample on a porcelain plate, scrape the sample with a spatula into a thin layer of about 2~3mm, drive off air bubbles, then press the end of the sample tube 21 with the rim into the sample on the porcelain plate until the other end is filled. Scrape both ends flat (4.1.3).
• If the sample contains granular mechanical impurities, this method cannot be used for determination, so as to avoid blocking the capillary (4.1.3 note).
• After constant temperature at low temperature is completed, before starting the test, first turn the screw rod so that the push rod contacts the sample in the sample tube, so as to avoid a space formed in the tube due to cold shrinkage of the sample, which may cause noise when the push rod descends or affect data accuracy (4.1.7).

8. Analytical procedure

8.1 Preparation of the instrument

• 4.1.1 Remove the constant-temperature jacket 11, capillary 19, and sample tube 21.
• 4.1.2 Wipe the sample tube 21 and push rod 22 clean with a clean cloth.
• 4.1.3 Load the sample (see Section 7).
• 4.1.4 Lift the push rod 22 and compress the spring 30. To do this, turn nut 38 to let screw rod 39 down, so that clamp spring 31 clamps locking rod 29. A slight vibration occurs when clamping, then turn the handle of eccentric wheel 1 so that the fixing sleeve is lowered to cover the clamp spring; in this way, fixing sleeve 32 fixes locking rod 29 in clamp spring 31. After that, rotate nut 38 in the opposite direction to compress spring 30, and at the same time raise the push rod to the highest position.
• 4.1.5 Add a washer to the sample tube 21 filled with sample, connect it to bushing 24 with nut handwheel 23, and tighten the nut handwheel.
• 4.1.6 Connect sample tube 21 and capillary 19 with nut 20, and tighten the nut.
• 4.1.7 Put on constant-temperature jacket 11, fix it with nut handwheel 9, and press rubber washer 17 fitted on the capillary tightly with nut 16. Connect connector 18 and the circulating constant-temperature bath with a rubber tube, and circulate until, under the specified conditions, the temperature is maintained constant for not less than 20min.
• 4.1.8 Place recording paper on recording drum 3. The lower edge of the paper should be close to the upper edge of the lower rounded corner of the drum, then secure it with two rubber rings, one above and one below.
• 4.1.9 Turn the speed of the recording drum to maximum speed (rotate the rotating rod to the right to the position 1).
• 4.1.10 Turn off motor switch 8, and connect the electrical plug and power line.
• 4.1.11 Turn pencil clamp 26 so that the pencil lead contacts the recording paper.
• 4.1.12 Place a dish under the capillary to receive the sample.

8.2 Test procedure

• 5.1 Turn on the motor switch 8 to connect the motor circuit. At this time, the pencil draws a horizontal line on the recording paper corresponding to the spring compressed to the tightest position.
• 5.2 Quickly turn the handle of eccentric wheel 1 to raise fixing sleeve 32, locking rod 29 leaves clamp spring 31, and the push rod, under the action of the spring, creates pressure in the sample tube, and the sample is extruded from the sample tube through the capillary. Observe the movement of the pencil on the recording paper. When the drawn curve approaches the horizontal line, quickly turn rotating rod 7 to medium speed, to the position 2. After the speed is adjusted, the slope of the curve changes immediately. When it approaches the horizontal line again, turn the rotating rod to minimum speed, to the position 3. The speed of the recording drum is adjusted for the last time.
• 5.3 When push rod 22 reaches the lowest position or descends at minimum speed, turn off motor switch 8.
• 5.4 After the test is completed, immediately record on the recording paper the sample name, capillary number, test temperature, and mark on the curve the regions corresponding to different recording drum speeds.
• 5.5 Remove the constant-temperature jacket, capillary, and sample tube from the viscometer, wash and wipe them clean, and then prepare for the next test.

9. Qualitative and quantitative determination and calculation formulas

9.1 Calculation principle

The apparent viscosity value η of the sample is calculated according to formula (1): η = τ / D …………………………………… (1) Where: τ— shear stress suffered by the sample when passing through the capillary, Pa; D— average shear rate, s⁻¹.

The shear stress τ in formula (1) can be calculated according to formula (2): τ = P·R / (2L) = K₁·P ……………………… (2) Where: P— pressure in the sample tube, Pa; R— capillary radius; L— capillary length; for a given capillary, K₁ is a constant that can be calculated in advance. The pressure P can be found from the corresponding recording pen height in Table 1.

The average shear rate D of the sample at a certain instant can be calculated according to formula (3): D = 4Q / (πR³) ……………………………… (3) Where: Q— is the flow rate of the specimen at a certain instant, cm³/s; R— is the capillary radius, cm.

The flow rate Q in formula (3) can be calculated according to formula (4): Q = πR₁²·W·tgα …………………………… (4) Where: R₁ — radius of the push rod, cm; W— is the linear velocity of the recording drum, cm/s; α— is the angle between the tangent to the point representing a certain instant on the working curve and the horizontal line, (°).

Substituting formula (4) into formula (3) gives: D = 4R₁²/(R³)·W·tgα = K₂·tgα …………… (5) For different capillaries and different recording drum linear velocities, the corresponding K₂ values can be calculated in advance.

Substituting formula (2) and formula (5) into formula (1) gives: η = K₁·P / (K₂·tgα)

In general, only the similar viscosity at a specified temperature and specified average shear rate is often required. To improve the measurement accuracy, the angle α should be within the range of 25°~65°. According to the average shear rate required by the test, select a capillary of suitable diameter and a recording drum speed. In this way, use a protractor to draw a tangent to the working curve at the pre-calculated angle α. From the recorder pen height at the tangent point, use Table 1 and formula (2) to calculate the shear stress, which is the instantaneous shear stress value when the average shear rate reaches the test requirement. Using formula (1), the similar viscosity at the specified temperature and specified average shear rate can be obtained.

9.2 Example Illustration

Determine the similar viscosity of a certain grease at 25℃, and obtain the working curve (Figure 2). The capillary used has a radius of 0.0540cm and a length of 11.460cm. The similar viscosity value of this grease at an average shear rate of D=100s⁻¹ is required:

• Sample name: xx grease
• Capillary number: No. 3
• Test temperature: 25℃
• Test date: x year x month x day
• Operator: xxx
• η=29.2Pa·s

6.2.1 is found in Table 1. According to the capillary used, when D=100s⁻¹, it is found that at the third speed setting, 71.1° is more suitable. Draw a tangent to the working curve at an angle of 71.1° to the horizontal line, find the tangent point, and from the two working curves read the heights of this tangent point as: h₁=45.0mm, h₂=45.5mm (read from bottom to top).

6.2.2 From Figure 3, find the corresponding P values when h₁=45.0mm, h₂=45.5mm, which are respectively: P₁=123×10⁵Pa, P₂=125×10⁵Pa.

6.2.3 Because τ=K₁P (Pa), from Table 1 it can be seen that for the capillary used, K₁=2.36×10⁻³, so the τ values are respectively: τ₁=2.36×10⁻³×123×10⁵=2.90×10³Pa, τ₂=2.36×10⁻³×125×10⁵=2.95×10³Pa (can be found in the pre-calculated Table 2).

6.2.4 According to formula η=τ/D, respectively obtain: η₁ = 2.90×10³/100 = 29.0 Pa·s η₂ = 2.95×10³/100 = 29.5 Pa·s Therefore the average value is: η=29.2Pa·s

6.2.5 Using a similar method, the η value at any shear rate can be obtained. More than four points can be found, and a graph of the relationship between η and D can be drawn. From the graph, the similar viscosity value at any value of D can be found.

9.3 Table 1 Automatic Capillary Viscometer Relationship between D and α

Note: Some values in Table 1 are doubtful due to the presence of source-text extraction noise and require confirmation against the source standard (source-text extraction).

9.4 Table 2 Relationship between pressure in the specimen tube and recorder pen height and shear stress values for capillary No. 1, No. 3, No. 5 τ=K₁P

Note: This table is based on formula (2) τ=R/(2L)·P=K₁P. For a given capillary, the value of coefficient K₁=R/(2L) is a constant and can be calculated in advance. In the formula, the pressure P value can be found from the graph 3 of the relationship between the pressure in the sample tube and the recorder pen height. For different capillaries, the corresponding τ value can be obtained. Some values in Table 2 are doubtful due to the presence of source-text extraction noise and require confirmation against the source standard (source-text extraction).

10. Precision

The difference between two repeated determination results shall not exceed 10% of their arithmetic mean (Section 7).

11. Report

Take the arithmetic mean of two repeated determination results as the determination result (Section 8).

12. Normative References

• Former Ministry of Petroleum Industry standard SY 2720-82 "Determination of Apparent Viscosity of Lubricating Greases" (withdrawn)
• Former Soviet Union national standard GOST 7163-63 "Determination of Apparent Viscosity of Lubricating Greases" (adopted by reference)
• Other normative references: not provided in the available source

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Reference Q&A