When a caster develops a crack in its bracket, the most common on-site assessment is often: “Could it be that the equipment is too heavy, causing the caster to crack under the load?”

However, in actual use, some casters that have developed cracks have not experienced any obvious overload and have even been in normal service for an extended period. Nevertheless, the cracks gradually emerge at bend points, near bolt holes, or in structural transition zones, and then progressively propagate.

In this case, another failure mechanism needs to be considered— Fatigue failure.

It’s not the same as simply crushing the caster in one go.

I. What is fatigue failure in casters?

You can think of it as simply bending a metal strip back and forth.

A single slight bend may not cause noticeable damage, but if the material is repeatedly bent at the same location, cracks may eventually develop.

The same holds true for casters.

During equipment movement, the support structure is continuously subjected to loads arising from payload, steering, start–stop operations, and ground irregularities. While each individual load may not be sufficient to induce significant deformation, repeated cyclic loading can gradually lead to fatigue damage in certain localized areas.

Therefore:

The absence of obvious overloading does not necessarily mean that structural cracks will not occur.

II. Why do cracks often initiate at “localized locations”?

Metal structures do not experience the same stress at every location.

Bending zones, the edges of holes, locations where cross-sections change abruptly, and certain joint areas may all give rise to relatively concentrated stress states.

Under cyclic loading, microcracks tend to initiate preferentially at these locations.

At first, the cracks may be extremely fine and difficult to detect with the naked eye.

As the equipment continues to operate, cracks gradually propagate until they eventually develop into clearly visible structural damage.

This is also why some casters appear to have “suddenly cracked”—in reality, the crack may have been developing for some time.

III. What is the difference between fatigue cracks and irreversible deformation?

If the equipment is subjected to a severe impact or an obvious overload, the support structure may undergo significant permanent deformation, such as fork spread, base plate warping, or overall distortion.

Fatigue failure, on the other hand, may be entirely different.

The bracket’s overall appearance remains normal, but minor cracks have already appeared in localized areas.

Therefore, when inspecting casters, simply checking whether they are bent is not sufficient.

For equipment used frequently, it is also necessary to inspect the bracket for any abnormal cracks at the bending points, around the holes, and in the primary connection areas.

IV. Which operating conditions warrant greater attention to fatigue issues?

The first category is High-frequency turnover equipment 。

Even if the individual load is not extreme, if the equipment is moved frequently each day, the casters will endure an ever-increasing number of cycles.

The second category is Equipment with relatively concentrated route impacts 。

For example, repeated long-term passage over fixed joints, grooves, or uneven surfaces can generate similar dynamic effects each time.

The third category is Equipment that frequently changes direction 。

As the caster continuously changes direction, the direction of the forces acting on the bracket also keeps varying.

The fourth category comprises mobile devices that operate continuously in vibratory environments.

The common characteristic of these operating conditions is not that they are “particularly severe” once, but rather… The same effect is repeatedly produced.

5. If one caster wheel is found to be cracked, is replacing just that one sufficient?

You could be a bit more cautious.

If the casters on the same piece of equipment have similar service lives and have been subjected to comparable operating conditions over an extended period, then when one caster develops fatigue cracks, the others should also be inspected concurrently.

In particular, if fine lines, rust streaks, or unusual marks appear at the same structural location, do not simply wipe them away and continue using the item.

At the same time, the equipment’s operating route should also be inspected.

If casters are consistently subjected to impact at a fixed location, simply replacing them with new ones—without addressing the floor surface or the operating conditions—will not eliminate the recurring problem.

VI. Why “replacing it with a thicker bracket” may not be the complete answer?

Upon detecting a crack, the most straightforward approach is to increase the thickness of the bracket.

Increasing structural strength through appropriate design can indeed improve certain operating conditions, but fatigue issues cannot be assessed solely in terms of thickness.

Material condition, bending geometry, local transitions, manufacturing quality, equipment load, and actual operating conditions can all influence the outcome.

If the root cause stems from a long-term, severe stressor, simply upgrading a single component does not constitute a complete failure analysis.

A more effective approach is to first identify the crack. Where do you start, and why does it always begin there?

7. During routine inspections, you can focus on these areas.

For industrial carts that are used frequently, you can take the opportunity to inspect them during maintenance:

Are there any fine cracks at the bending locations of the bracket?

Are there any abnormal marks near the mounting holes or structural openings?

Are there any cracks or localized deformations in the fork and the primary attachment areas?

Do several casters on the same piece of equipment exhibit similar conditions?

If an anomaly is detected, it is best to promptly halt operations that could exacerbate the damage and conduct a more thorough investigation into the root cause.

Written at the end

The structural failure of a caster does not necessarily result from a single instance of “excessive load.”

Often, what truly warrants vigilance are those effects that may not seem serious but recur daily.

A single impact may not cause damage, and even after a hundred impacts, no issues might be apparent; however, with repeated exposure over the long term, the material’s properties can gradually change.

Therefore, when a caster bracket develops cracks, rather than simply asking:

“Was this one overloaded?”

Why not ask one more question:

“How many times has this location been subjected to repeated stress in the past?”

From the perspective of shifting from “single‑use load capacity” to “long‑term cyclic loading,” it becomes easier to understand why casters develop structural cracks after a period of use.

Have you ever encountered a situation where, despite no obvious bending in the caster bracket, you suddenly discover tiny cracks? Where do these cracks typically appear—around the bend, near the mounting holes, or elsewhere? Feel free to share your experiences in the comments.