I. What Is an Electric Crockmeter?

The Electric Crockmeter is one of the core pieces of equipment for colorfastness testing in the textile industry. It is primarily used to evaluate the degree of color transfer from dyed fabrics under dry and wet friction conditions. This instrument simulates the friction between fabrics and other objects that occurs during everyday wear and, through standardized testing methods, provides objective data for product quality control.

It is suitable for various types of dyed, printed, and coated fabrics and is widely used in quality testing across industries such as apparel, home textiles, and footwear materials.

II. Testing Principle

The Electric Crockmeter operates by securing a standard white cotton cloth (crocking cloth) to the friction head and performing reciprocating friction on the surface of the test specimen at a specified pressure (typically 9 N) and stroke length (typically 104 ± 3 mm). After friction is completed, the rub fastness grade of the tested fabric is determined by evaluating the degree of color transfer on the friction cloth.

The tester is motor-driven, and both the number of friction cycles and the speed can be preset; compared to manual rub fastness testers, it provides more stable test results and better repeatability.

III. Preparations Before Testing

1. Sample Preparation

Take a sample of the fabric to be tested, with dimensions of at least 50 mm × 200 mm, ensuring that the test area is flat, free of wrinkles, and free of defects. If the sample is a printed fabric, test and record the results for both the background color and the pattern separately.

2. Preparation of the Abrasion Cloth

Use a white cotton abrasion cloth measuring 50 mm × 50 mm that complies with the requirements of GB/T 3920 or AATCC 8. Prior to testing, the abrasion cloth must be conditioned for at least 4 hours under standard atmospheric conditions (temperature 20 ± 2 °C, relative humidity 65 ± 4%).

3. Preparation for Wet Abrasion (if conducting a wet abrasion test)

Immerse the conditioned friction cloth in distilled water until its water absorption reaches 95%–100% (i.e., the wet mass is approximately twice the dry mass). After removal, squeeze out excess water using a wringing device or by hand to ensure the moisture content meets standard requirements; the cloth must not drip water.

4. Instrument Inspection

- Confirm that the power supply is properly connected and the instrument is properly grounded

- Check that the surface of the friction head is flat and undamaged

- Confirm that the friction stroke and number of friction cycles are set correctly

- Check that the clamping device is secure

IV. Detailed Operating Procedures

Step 1: Install the Test Specimen

Securely fasten the prepared fabric to be tested on the instrument’s specimen table, with the fabric facing upward. Press it down with the clamping plate to ensure the test area is taut and does not shift.

Step 2: Install the Abrasive Cloth

Take a dry (or wet) standard abrasive cloth and secure it to the friction head. Ensure that the warp and weft directions of the abrasive cloth match those of the test specimen, and that the cloth surface is flat and free of tension.

Step 3: Set Test Parameters

Set the following parameters according to the test standard:

- Friction stroke: 104 mm (standard setting)

- Reciprocating frequency: Typically 1 cycle per minute

- Number of friction cycles: 10 cycles for dry friction, 10 cycles for wet friction (specific values subject to the test standard)

Step 4: Start the Test

Press the start button; the instrument will automatically complete the set number of friction cycles. Do not touch moving parts during the test, and observe whether the operation is smooth.

Step 5: Remove the Friction Cloth

After the test is complete, carefully remove the friction cloth, avoiding contact with the friction area. After the wet friction test, the friction cloth must be air-dried at room temperature or dried according to the method specified in the standard.

Step 6: Evaluate Results

Compare the friction cloth with the GB/T 251 or AATCC color-transfer gray scale to determine the color-transfer grade. Record the colorfastness grades for both dry and wet friction separately. The grading scale ranges from Grade 1 to Grade 15, with Grade 5 being the best and Grade 1 the worst.

V. Frequently Asked Questions

Q: Why do the ratings for dry and wet rubbing usually differ?

A: During wet rubbing, dyes are more likely to transfer from the fabric to the rubbing cloth; therefore, the wet rubbing colorfastness rating is typically lower than the dry rubbing rating. This is normal, but both must meet the requirements of the relevant product standards.

Q: What should I do if the test results fluctuate significantly?

A: First, check whether the test specimens have been adequately conditioned, whether the rubbing cloth meets standards, and whether the moisture content is consistent. Second, check whether the pressure of the instrument’s rubbing head is uniform and calibrate it if necessary.

Q: The wet rub fastness ratings for dark-colored fabrics are consistently low. How can this be improved?

A: This is usually related to dye selection and the fixation process. It is recommended to start with the dyeing and finishing process by optimizing dye selection, improving the fixation rate, and enhancing the post-treatment washing, rather than relying solely on testing methods.

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