GB/T 33624-2017Rolling bearings - Test and assessment methods for cleanliness (English PDF)

7.2.1 Liquid sample preparation

7.2.1.1 Unless the cleanliness of the samples is so poor that the filtration speed of the liquid samples is lowered, multiple sets/pieces may be washed and measured together with the weighing method.

7.2.1.2 No scrubbing shall be carried out for the samples after opening package.

7.2.1.3 Soak cleaning. Use solvent to soak the samples in a container for more than 2 h; shake or rotate them one by one to make the impurity on the surface of the samples fall off to come into solvent. The use level of solvent shall ensure the samples are fully soaked in the container more than 10 mm.

7.2.1.4 Ultrasonic cleaning. Wash the samples twice by ultrasonic cleaning, 2 min for each time of cleaning. The use level of solvent for each time shall not be less than 200 mL and the height of solvent in the container shall not be lower than two times of the height of the samples. Multiple sets/pieces are allowed to be washed, but the samples are not allowed to be overlapped or staggered.

7.2.1.5 Washing of the samples with grooves or curls. Use solvent in the washing bottle to wash the surface of the samples to fully wash away impurity; collect the washings into the container.

7.2.1.6 All washings are liquid samples.

7.2.2 Preparation and weighing of filtration membrane

7.2.2.1 Use tweezers to take 2 pieces of filtration membrane of pore size 1.2 µm to place into two weighing bottles marked "Test (s)" and "Control (k)"; place them semi- openly into the thermostatic chamber for drying for 60 min at 60°C ± 5°C; put on the cap for them before placing them into the desiccator for cooling for 30 min; then use the analytical balance to weigh the two filtration membranes respectively; record them as ms1 and ms2. The filtration membranes shall be dried and weighed twice; the difference between the two weighing results shall not be greater than

0.2 mg; if the difference is greater than

0.2 mg, carry out drying and weighing once again and the final weighing results shall prevail.

7.2.2.2 Use tweezers to take out the filtration membranes from the weighing bottles; place in solvent to soak them before placing them flatwise on the microporous filter, with the control membrane (k) as the lower membrane and the test filtration membrane (s) as the upper membrane.

7.2.2.3 Press the upper funnel on the filtration membrane; use the clamping device to clamp the upper funnel, filtration membranes, microporous filter, lower funnel and up to 50 µm; greater than 50 µm up to 100 µm; greater than 100 µm.

7.3.3 Liquid sample preparation and counting filtration membrane preparation

7.3.3.1 Prepare liquid samples as specified in 7.2.1.2 ~ 7.2.1.6.

7.3.3.2 Select one filtration membrane of appropriate pore size in accordance with the minimum counting particle size; use tweezers to clamp the filtration membranes for soaking before place flatwise on the microporous filter.

7.3.3.3 Carry out liquid samples filtration and impurity collection as specified in 7.2.2.3 ~ 7.2.2.5.

7.3.3.4 Use tweezers to take down the filtration membranes from the microporous filter and place flatwise in the weighing bottle.

7.3.3.5 Place the weighing bottles semi-openly in the thermostatic chamber for drying for 60 min at 60°C ± 5°C; then put on the cap for them before placing them into the desiccator for cooling for 30 min

7.3.4 Counting procedure

7.3.4.1 If the samples need to be assessed using the weighing method and the particle counting method in combination, the use the test filtration membrane as the counting filtration membrane and the control filtration membrane without counting.

7.3.4.2 Use tweezers to take out the counting membrane from the weighing bottle; place flatwise carefully on the filtration membrane fixer tray; put on the cover before mounting to the clamping device on the stage of the microscope.

7.3.4.3 In accordance with the minimum counting particle size, select the objective lens of appropriate power; carry out lightness adjustment and shade correction for the microscope; set the diameter of effective filtration area, diameter of counting area, size of minimum counting particle, size segment of counting particles and other parameters; carry out scanning, particle size measurement and quantity statistics for the counting filtration membranes.

7.3.4.4 Output measuring results in accordance with the assessment items. The assessment items may include but not limited to the total count of particles larger than the minimum counting size, the count of particles of all size segments, the count of reflective particles of all size segments and the count of non-reflective particles, the maximum particle size and so on.