Why do some metal casters remain in good condition after a period of use, while others quickly develop rust spots?

For casters, while the rolling performance of the wheels is certainly important, the corrosion resistance of the metal frame, base plate, and connecting components likewise affects product reliability.

Especially in humid warehouses, coastal areas, food-processing facilities, and certain chemical production environments, metal components exposed for extended periods to moisture, salt, or corrosive agents may experience gradual degradation of their surface protective coatings.

So, what exactly does the “salt spray test” often mentioned when purchasing casters indicate? Does a longer test duration mean the casters are more durable?

Today, starting from practical applications, we will explore the technical rationale behind caster wheel salt spray testing.

01｜What is a caster salt spray test?

The salt spray test is a laboratory method used to evaluate the corrosion resistance of materials and surface protective coatings.

The basic principle is to create a salt spray environment under controlled conditions using a salt spray testing chamber, continuously exposing the test sample to observe surface corrosion.

For casters, common test subjects include:

Metal brackets: Observe the corrosion resistance of the electroplated layer or other surface protective coatings.

Install the base plate: Check whether the surface of the plate and the areas around the holes are prone to corrosion.

Bolts, nuts, and other fasteners: Assess the quality of surface protection at the joint.

Welding and structural connection areas: Inspect the local protective coating for any weak spots.

It should be noted that a salt spray test does not simply involve immersing the product in salt water; rather, it is conducted under specified conditions of temperature, salt solution concentration, spray parameters, and test duration.

The conditions of different test methods are not the same, and test results cannot be used interchangeably.

02 | Salt Spray Test: 24 hours, 48 hours, 96 hours—what’s the difference?

When purchasing casters, some suppliers provide salt spray test results with varying durations.

Many procurement professionals tend to hold a common misconception:

“Casters that pass a 96-hour salt spray test have an actual rust‑resistance life four times that of products that pass a 24-hour test.”

In fact, this understanding is not accurate.

The duration of a salt spray test does not equate to the product’s service life in a real-world environment.

There are three main reasons.

First, the laboratory environment differs from the real-world usage environment.

Salt spray testing typically employs controlled, continuous exposure conditions, whereas in actual use, alternating dry and wet environments, temperature fluctuations, mechanical wear, and contact with cleaning agents may occur.

Second, the corrosion mechanisms differ among various surface treatment processes.

Galvanizing, nickel plating, stainless steel, and other protective systems do not all exhibit the same corrosion resistance.

Third, the pass criteria for testing may vary.

Some tests focus on the occurrence of white rust, others on red rust, and still others evaluate corrosion based on the area affected or an appearance rating.

Therefore, comparing the number of test hours alone may not accurately assess the corrosion resistance of two caster models.

03｜Why do products perform differently in real-world use despite passing the same salt spray test?

Salt spray testing can provide important reference, but it cannot fully represent the caster’s overall corrosion resistance.

Factors that also affect actual performance include the following aspects.

① Substrate condition before surface treatment

If oil, oxides, or other contaminants are present on the metal surface, they may compromise the adhesion quality of the subsequent protective coating.

② Uniformity of protection for complex structures

Caster brackets typically include bent, punched, edged, and locally joined structures. The coating coverage in these areas may differ from that on flat surfaces.

③ Surface damage during the assembly process

Some metal components, even if they perform well in individual tests, may have their protective coatings damaged by friction or impact during assembly, transportation, or use.

④ Other corrosive factors in the service environment

For example, cleaning agents, acidic or alkaline environments, and prolonged water accumulation can all affect the corrosion rate of metal components.

Therefore, when evaluating the corrosion resistance of casters, one should consider not only laboratory test results but also actual operating conditions.

04 | When purchasing casters, how should you interpret a salt spray test report?

For procurement personnel, to determine whether salt spray test results are reliable, they should focus on the following information.

I. Confirm Test Criteria

For example, standards such as ISO 9227 and ASTM B117 cover salt spray testing methods, but the specific method to be used must be determined based on product requirements.

II. Confirmation of Test Samples

Is the test object a metal specimen, a standalone bracket, or a complete caster?

Test results for different samples should not be simply regarded as completely equivalent.

III. Confirm Test Conditions

This includes the type of salt spray, the duration of the test, and the relevant environmental conditions; avoid making judgments based solely on the number of hours.

IV. Confirmation of Corrosion Evaluation Criteria

It should be specified whether white rust and red rust are permissible, as well as the extent and location of corrosion and other acceptance criteria.

5. Verify that the test results are consistent with the supplied product.

In particular, when purchasing in bulk, it is essential to verify that the material, surface treatment processes, and production conditions of the actual supplied products match those of the test samples.

A comprehensive, traceable test report is often more informative than simply touting “how many hours of salt-spray testing was passed.”

05 | Which application scenarios should place greater emphasis on corrosion resistance?

Key Considerations for Selection Across Different Scenarios

It is important to note that good salt-spray resistance does not mean the material can withstand all chemically corrosive environments.

For example, even in environments containing specific acidic or alkaline media, material selection must still be based on the material’s properties and the actual contact conditions.

06 | Final Thoughts: Test Data Are the Basis; Matching Operating Conditions Is What Really Matters

The corrosion resistance of casters cannot be assessed solely by the number of hours in a salt spray test.

From material selection and surface treatment to structural design, production assembly, and the actual operating environment, every stage can affect the final performance.

For the buyer, rather than simply seeking longer test durations, it is preferable to define the actual operating environment and require the supplier to provide test justification that aligns with the procurement requirements.

Truly sound caster selection isn’t about blindly chasing the highest possible value for a single specification; it’s about aligning product performance with actual application requirements.