GB/T 7326-1987 Standard Test Method for Copper Strip Corrosion by Lubricating Greases

AI-translated method card — human verification pending. This is not an official translation of the standard. Unclear source values remain unverified; check the original standard and product certificate before use.

Card type: Test method

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

• Standard number: GB 7326-87 (the original cover is marked as GB 7826-87, the header of the body text is marked in multiple places as GB 7326-87, the standard number digits have source-text extraction doubts, requires confirmation against the source standard (source-text extraction))
• Chinese name: Standard Test Method for Copper Strip Corrosion by Lubricating Greases
• English name: Lubricating grease--Corrosireness to copper-Copper strip test (as in the original, the spelling is suspected to be source-text extraction noise, requires confirmation against the source standard (source-text extraction))
• Method number: Method A, Method B (the original text divides into two determination modes, Method A and Method B)
• Replacement relationship: not provided in the available source
• Approval/implementation: approved by China Petrochemical Corporation 1987-02-19, implemented on 1988-03-01
• Adoption relationship: Method A is equivalently adopted from ASTM D4048-1981 Standard Test Method for Copper Strip Corrosion by Lubricating Greases; Method B is equivalently adopted from Japanese Industrial Standard JIS K2220-1984 5.5 Copper Strip Corrosion Test Method (the original text writes “C method”, suspected to be source-text extraction noise for “Method B”, requires confirmation against the source standard (source-text extraction))

2. Scope of application and non-applicability

• Applicable for determining the corrosiveness of lubricating greases to copper.
• It has certain significance for predicting possible chemical corrosion on lubricated parts (such as some bearings containing copper or copper alloys); such corrosion may cause premature bearing damage. However, it has no relevance to most lubricated parts that are generally considered to operate under dynamic conditions in actual use.
• Not applicable for determining the ability of lubricating grease to inhibit copper corrosion caused by factors other than the lubricating grease itself.
• It does not determine the stability of lubricating grease in the presence of copper.

3. Method principle

Immerse a prepared copper strip completely in the lubricating grease sample, and heat it in an oven or liquid bath for a certain time. The conditions generally used are 100℃, 24h. After the test period ends, take out the copper strip, wash it, and for Method A compare the test copper strip with the copper strip corrosion standard color plate to determine the corrosion level; for Method B check whether the test copper strip has discolored.

4. Reagents and materials (purity / preparation)

• 2.2.1 Acetone: chemically pure (see A.1).
• 2.2.2 Copper strip: length 75mm, width 12.5mm, thickness 1.5～3.0mm; electrolytic copper with purity of 99.9% or above; may use Cu-2 (No. 2 copper) in GB 466—82 Copper Classification. The copper strip may be used repeatedly, but if the surface has deformed it cannot be used again.
• 2.2.3 Polishing material: 65μm (240 particle size) silicon carbide or aluminum oxide sandpaper or abrasive cloth; 105μm (150 mesh) silicon carbide or aluminum oxide abrasive grains; medicinal absorbent cotton. Note: In case of dispute, use polishing material made of silicon carbide.
• 2.2.4 Washing solvent: any volatile sulfur-free hydrocarbon solvent may be used as long as the test copper strip does not change luster after testing at 50℃. Suitable solvents include isooctane for knock testing (see A.3) or analytically pure n-heptane (see A.2). Because benzene may cause poisoning, its use should be avoided. Note: Under general conditions (except for arbitration), analytically pure petroleum ether (90~120℃) or No. NY-120 in GB 1922—80 Solvent Naphtha, which does not change the luster of the test copper strip, may also be used as washing solvent.
• 2.1.6 Copper strip corrosion standard color plate: composed of reproductions representing various typical test strip colors for degrees of corrosion and discoloration, embedded in a plastic plate.

5. Apparatus and equipment

• 2.1.1 Test tube: flat-bottomed transparent glass cylinder, inner diameter 30–33mm, height 115–125mm.
• 2.1.2 Test tube cover: beaker 50mL; glass plate 40mm×50mm; porcelain crucible or crucible cover; glass watch glass or open cork stopper.
• 2.1.3 Oven: air-circulating oven or liquid bath, capable of maintaining temperature at 100±1℃ or other temperatures with the same precision.
• 2.1.4 Polishing fixture: used to prevent the edges of the copper strip from being damaged during polishing and to firmly hold the copper strip; as long as the copper strip can be clamped tightly and its polished surface fixed on the fixture surface, any convenient fixture may be used (see Figure 1).
• 2.1.5 Observation test tube: flat glass test tube, which can protect the corroded copper strip for detailed inspection or storage (see Figure 2).
• 2.1.6 Copper strip corrosion standard color plate (with plastic sleeve protection).
• 2.1.6.1 Use a plastic sleeve to protect the printed color plate from light to prevent fading; use two different standard color plates to compare and check fading, one of which is a new color plate carefully stored without contact with light; observe under diffused light (or equivalent), first observe directly from above, then observe from an angle of 45°; if any sign of fading is observed, especially fading at the left end of the color plate, discard the more faded one of the two plates.
• 2.1.6.2 Another method: place a 20mm opaque sheet (masking tape) horizontally across the top of the colored portion of a newly purchased color plate, periodically remove the opaque sheet for observation; if the exposed portion shows any trace of fading, replace the standard color plate.
• 2.1.6.3 The color plate is a reproduction of a typical full-color plate, printed on an aluminum plate using a 4-color process, and protected in a plastic sleeve; instructions for use are on the back of each color plate.
• 2.1.6.4 If the surface of the plastic plate shows excessive scratches, the color plate should be replaced.

6. Recommended operating conditions

• Commonly used test conditions: 100±1℃, 24h (4.4).
• Other temperatures with the same precision may also be used (2.1.3).
• Heating equipment: air-circulating oven or liquid bath.

7. Sampling and sample preparation

• 4.1 Place about 60mL (about 50~70g, depending on the density of the grease) of lubricating grease sample at the bottom of a clean test tube, so that the height of the lubricating grease reaches about 80mm; carefully tap the test tube to pack the lubricating grease into the tube, make the top into a relatively flat surface, and wipe off excess lubricating grease on the tube wall.
• 3 Copper strip preparation:
  • 3.1 Surface preparation: use sandpaper of a particle size that meets the requirements to remove all surface defects from the six faces of the copper strip; final treatment with 65μm (240 particle size) sandpaper or abrasive cloth to remove all traces left by other grades of sandpaper used previously; immerse the copper strip in washing solvent; remove from the solvent and either directly perform final polishing or store the copper strip in solvent for later use.
  • 3.1.1 Manual operation: place a sheet of sandpaper on a flat surface, wet it with washing solvent, and rub the copper strip tightly against the sandpaper in a rotating motion; use ashless filter paper or wear polyethylene gloves to protect the copper strip from contact with fingers. A motor-driven machine may also be used, using dry sandpaper or abrasive cloth of suitable particle size to rub the copper strip surface.
  • 3.2 Final polishing: remove the copper strip from the washing solvent, protecting it with ashless filter paper during handling to prevent finger contact; moisten absorbent cotton with one drop of washing solvent, pick up some 105μm (150 mesh) silicon carbide or aluminum oxide abrasive grains from a clean glass plate, first polish both ends, then polish both sides; then wipe clean vigorously with new absorbent cotton; thereafter, wear polyethylene gloves or use stainless steel tweezers, and do not touch with bare fingers; clamp the copper strip in the fixture, then polish the main surface with abrasive grains picked up on absorbent cotton; polish along the long axis of the copper strip, and before returning for another stroke, make the stroke extend beyond the end of the copper strip; use clean absorbent cotton to vigorously wipe off all metal powder from the copper strip until no more dirt remains on fresh cotton; after the copper strip is wiped clean, immediately immerse it in the prepared sample. Note: Be careful that tweezers can scratch the copper strip and affect the result.
  • 3.2.1 To make the copper strip uniformly colored, it is important to polish all surfaces of the copper strip uniformly; if the edges are worn (the surface appears elliptical), the edges are likely to show heavier corrosion than the center; using a fixture facilitates uniform polishing.

8. Analytical procedure

• 4.2 To prevent the copper strip from contacting fingers, wear polyethylene gloves or use stainless steel tweezers (see Note in 3.2), insert the cleaned copper strip into the lubricating grease until the copper strip touches the bottom of the tube, with the copper strip completely immersed and covered with at least 5mm of lubricating grease. Note: For Method B, the sample may first be applied to the entire surface of the copper strip and then inserted into the sample.
• 4.3 Place the test tube on a rack, keep it approximately vertical, and loosely cover the test tube with a cover (see 2.1.2).
• 4.4 Place the rack together with the sample into an oven or liquid bath, adjust to maintain the specified temperature during the test period. Commonly used conditions 100±1℃, 24h.
• 4.5 After the test period ends, remove the rack and sample from the oven or liquid bath and allow them to cool to room temperature.
• 4.6 Copper strip inspection:
  • 4.6.1 Wear polyethylene gloves or use stainless steel tweezers (see Note in 3.2), remove the copper strip from the lubricating grease and immediately immerse it in washing solvent; after washing, immediately remove the copper strip, and dry it by blotting with dry quantitative filter paper rather than wiping; for Method A, compare with the copper strip corrosion standard color plate to check for surface discoloration and signs of corrosion, place the test strip and standard color plate so that the reflected light is at an angle of about 45° for observation; for Method B, check whether the copper strip has green or black changes.
  • 4.8.2 (the original numbering is as such, suspected to be source-text extraction noise for 4.6.2, requires confirmation against the source standard (source-text extraction)) When inspecting and comparing the test strip, if the test strip is placed in a flat tube (see Figure 2), the tube opening may be plugged with absorbent cotton, thereby avoiding the risk of leaving marks or soiling the test strip.

9. Qualitative and quantitative determination and calculation formulas

• 5.1 Method A: express the corrosiveness of the sample according to a certain level on the copper strip corrosion standard color plate that matches the appearance of the test strip.
  • 5.1.1 When the change in the test strip indicates that it is between two adjacent corrosion levels on the standard color plate, judge the sample according to the corrosion level with heavier discoloration. If the test strip shows a darker dark orange than 1b in the standard color plate, the strip still belongs to level 1b; but if any sign of red is observed, the strip is considered to belong to level 2.
  • 5.1.2 If the brass-colored base strip of 3a is completely covered by a magenta color, the purple-red 2a strip may be mistaken for a 3a strip. To distinguish them, immerse the test strip in acetone (see A.1); the 2a strip will appear like the 1b strip, while the 3a strip will not change color.
  • 5.1.3 To distinguish the 2c strip from the 3b strip, place the test strip in a 20mm×150mm test tube, and heat on a hot plate at 315–370℃ for 4–6min; insert a high-temperature distillation thermometer into another test tube and lay it horizontally on the hot plate, and observe its temperature to adjust the hot plate temperature. If it is a 2c strip, it will show the color of the 2d strip and the surface colors of successive levels; if it is a 3b strip, it will show the color of the 4a strip.
  • 5.1.4 If the test strip is contaminated by fingerprints or if stains are produced by contact with small water droplets or air during heat treatment, redo the test.
  • 5.1.5 If a higher corrosion level appears along the edges and corners of the flat surface of the test strip than on most of the test strip surface, the test must also be redone; this situation is mostly caused by wear of the test strip edges during polishing.
• 5.2 Method B: check whether the copper strip has green or black changes after the test.
• 6 Judgment of results: if the two results of repeated determination are different, the test should be redone; if the two results of the repeated test are still different, judge the sample according to the test strip with severe discoloration.
• Classification of copper strip corrosion standard color plate (original table):
  • Level 1: a light orange, almost the same as newly polished copper strip; b dark orange.
  • 2 grade: a purplish red; b light purple; c multicolored with light purplish blue or silvery white or both separately covering the purplish red; d silvery white; e brass color or golden yellow.
  • 3 grade: a magenta covering brass color; b multicolored (peacock green) shown by red and green, but without gray.
  • 4 grade: a transparent black, dark gray, or brown with slight peacock green; b graphite black or lusterless black; c glossy black or jet black shiny black.
  • Note ①: The copper strip corrosion standard color plate is a reproduction of the color plates represented by these descriptions in the table.
  • Note ②: The table includes freshly polished copper strips, only as an indication of the outer surface of the test piece before the test; even with a completely non-corrosive sample after the test, such an appearance cannot be reproduced.
• Calculation formula: not provided in the available source.

10. Precision

• The original Chapter 6 only specifies: if the two results of repeated determinations are not the same, the test should be redone; when the two results of the retest are still not the same, the sample is judged according to the test piece with severe discoloration.
• Another passage in the source extraction is severely garbled and unreadable; the content is suspected to be precision or result expression, cannot be recognized, requires confirmation against the source standard (source-text extraction).
• Specific precision values (such as repeatability, reproducibility): not provided in the available source.

11. Report

• 7 Report: Method A reports the corrosiveness of the sample according to one of the grades listed in the table, and reports the test time and temperature. Method B reports the corrosiveness of the sample according to whether there is green or black change on the copper strip, and reports the test time and temperature.

12. Normative references

• GB 466—82 “Classification of Copper”
• GB 1922—80 “Solvent Naphtha”
• ASTM D4048-1981 “Test Method for Copper Strip Corrosion of Lubricating Grease” (Method A equivalently adopted)
• JIS K2220-1984 5.5 “Test Method for Copper Strip Corrosion” (Method B equivalently adopted)
• Appendix A (Supplementary Document) Notes: A.1 acetone; A.2 n-heptane; A.3 isooctane (the extracted chemical name is garbled; requires confirmation against the source standard (source-text extraction)).

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