How to determine if the conductivity of anti-static casters has decreased?

Practical Methods for Determining the Conductivity of Anti-static Casters
The conductivity of anti-static casters typically decreases gradually. A comprehensive assessment using professional testing tools, observation of operating phenomena, and environmental compatibility verification is necessary to avoid static electricity risks caused by performance failure. The specific methods are as follows:

1. Professional Tool Testing: Accurately Quantify the Resistance Value (Core Judgment Method)
Use an electrostatic resistance tester (such as a surface resistance tester or ground resistance tester) to directly test whether the caster's conductivity meets the standard (usually requiring a surface resistance of 10⁶-10¹¹Ω and a ground resistance of ≤100Ω). The specific steps and judgment criteria are as follows:
Surface Resistance Testing
Procedure: Place the two probes of the tester on the conductive tread (such as conductive PU or conductive rubber) and the metal wheel frame, respectively. Maintain even pressure (approximately 500g) and read the displayed resistance value.
Judgment: If the resistance value is >10¹¹Ω, it indicates that the conductive material on the tread is aging (e.g., uneven distribution of carbon powder) or is oily. Dust coverage has reduced conductivity. If the resistance value is less than 10⁶Ω (excessive conductivity), check for exposed metal parts (such as an exposed wheel core). While this does not affect static discharge, it may pose a short circuit risk.

Ground Resistance Test

How to Test: Connect one end of the tester to the metal caster frame and the other end to an anti-static grounding electrode (such as a copper grounding busbar) in the workshop. Start the test and read the ground loop resistance.

Diagnosis: If the ground resistance is greater than 100Ω, the caster frame is not in good contact with the ground path (e.g., loose screws or rusted axles). Static electricity cannot be effectively conducted to the ground, resulting in a loss of conductivity.

2. Observation of Operational Phenomena: User Experience Aids Judgment
Decreased conductivity can be indirectly reflected during caster use. Preliminary judgment can be made based on the following "non-quantitative signals":
Increased static-related phenomena
When pushing equipment, a slight electric shock sensation is felt when touching the equipment casing (static electricity is not fully discharged);
Static-sensitive components around the equipment (such as chips and circuit boards) experience unexplained damage (e.g., electrostatic breakdown);
When the caster rotates, increased static electricity absorption (e.g., large amounts of dust and fibers are attracted and difficult to clean) caused by friction between the tread and the ground indicates that static electricity is not being dissipated promptly, resulting in decreased conductivity.
Abnormal Physical Condition of the Caster
Cracks, chipping, or excessive wear (e.g., a reduction of more than one-third in tread thickness) on the conductive tread, or obvious signs of oil or chemical corrosion (e.g., tread stickiness or discoloration) on the surface can disrupt the molecular structure of the conductive material, leading to a broken conductive path;
Rust or seizure at the connection between the wheel frame and the axle, coupled with unusual noises during rotation, indicate poor contact between the metal parts and a blocked static conduction path.

3. Environmental Compatibility Verification: Determine Based on Scenario Characteristics
Different usage environments have different requirements for conductivity. Changes in caster compatibility can be used to assist in this assessment:
Dry Environment (e.g., electronics cleanroom, humidity <40%)
If a caster that previously conducted electricity normally in a dry environment suddenly displays an "equipment static electricity alarm" (e.g., an alarm on the workshop's static electricity monitor), and after correcting the grounding fault, it's likely that the caster's conductivity has decreased. Static electricity accumulates more easily in dry environments, and even a slight decrease in conductivity can trigger a noticeable abnormality.
Dusty/Oily Environment (e.g., chemical workshop, printing workshop)
If a large amount of dust or oil adheres to the caster surface, and "statically attracted dust accumulation" persists after cleaning, this indicates that the anti-static coating on the conductive tread has failed and is unable to reduce static electricity through its own conduction, resulting in decreased conductivity.
Low-Temperature Environment (e.g., cold chain workshop, temperature <0°C)
If the caster tread becomes hard and brittle, and "partial cracking" occurs during rotation, this indicates that the low temperature has caused the conductive material (e.g., conductive rubber) to age, disrupting the intermolecular conductive pathways and subsequently decreasing conductivity.

4. Regular Comparative Testing: Establish a Performance Change File
It is recommended to record caster resistance test data monthly to establish a "conductivity change file":
If the resistance value shows a "continuously increasing trend" (e.g., from 10⁸Ω to 10¹⁰Ω) over two to three consecutive tests, even if it does not exceed the upper limit, it indicates a gradual decline in conductivity and requires scheduled maintenance (such as tread cleaning and replacement of conductive grease).
If the resistance value suddenly changes during a single test (e.g., from 10⁹Ω to 10¹²Ω), the machine should be immediately shut down for inspection to check for tread damage, broken wheel frame grounding, or other faults to avoid safety risks caused by conductivity failure.
The above methods can promptly and accurately determine the conductivity status of anti-static casters, ensuring they continue to function stably and effectively in dissipating static electricity throughout their service life.