Why Do Some Casters’ Surfaces “Bulge”?

Why do some casters’ surfaces “bulge”?

During routine inspections of casters, wear, cracks, and chips are relatively easy to detect. However, there is another subtle anomaly: localized bulging on the wheel surface, appearing as if it has “swollen into a lump.”.

Initially, there might only be slight unevenness, but the wheel can still rotate. As it continues to be used, the bulging area may become increasingly noticeable, accompanied by phenomena such as cracks and localized damage.

This type of issue deserves special attention, as it may not be ordinary surface wear but rather related to the internal condition of the wheel material.

When a castor shows localized bulging, instead of continuing to observe whether it “can still rotate,” it’s better to first determine: what exactly is happening inside the wheel surface?

1. What is the difference between a wheel surface bulge and normal wear?
Normal wear typically occurs in the contact area between the wheel surface and the ground, manifesting as gradual material consumption and slow changes in the wheel surface shape.

A bulge, on the contrary, refers to a localized outward protrusion.

When turning the wheel by hand, you can observe this position periodically passing over the ground. If the protrusion is relatively pronounced, the equipment may even produce a rhythmic sense of undulation during operation.

Therefore, once a localized “heightening” of the wheel surface is detected, it should not be treated as ordinary wear and tear.

It more resembles an anomalous signal requiring further investigation.

2. Where do the bubbles and voids inside the material come from?
Taking partially rubberized industrial wheels as an example, the wheel surface requires processes such as material preparation, molding, and subsequent treatments during manufacturing.

If the related process control is not ideal, there may be bubbles, voids, or localized structural inhomogeneities within the material.

When these issues are hidden inside the wheel surface, they may not be directly visible on the product’s exterior.

After the casters are put into use, the wheel surface continuously undergoes loading and rolling, with internal weak areas subjected to repeated stress, leading to potential gradual manifestation of anomalies on the exterior.

This is why some casters appear completely normal when first installed but develop localized swelling after being used for a period of time.

3. “Swelling” may also be related to the bonding region
For wheels composed of different materials, it is also necessary to identify where the anomaly occurs.

If the bulge is near the bonding area between the wheel surface and the hub, further inspection of the bonding condition between the two materials should be conducted.

Because once the local bonding state becomes abnormal, the wheel surface may experience abnormal deformation during load-bearing and rolling processes.

Therefore, when inspecting a dent, you cannot focus solely on the highest point.

Let’s take a closer look around the bulge

Are there any fine cracks?

Are there any abnormal gaps at the edge of the wheel surface?

Is there a significant difference in the state when pressing different positions?

These phenomena all contribute to further narrowing down the scope of the issue.

4. Why can’t the bulge be simply ‘flattened and continued to be used’?
On site maintenance sometimes presents a processing approach:

Since it’s just a little protruding, can’t we just fix the protruding position and make the wheel round again?

This approach is not recommended as a routine handling method.

Because bulging is only an external manifestation.

If the problem comes from internal voids, local structural abnormalities, or changes in the bonding area of the material, removing the surface protrusions may not eliminate the internal causes, but may further damage the original wheel surface structure.

So when encountering obvious bulges, a more reasonable approach is to evaluate the overall condition of the casters, replace them if necessary, and conduct disassembly and analysis on the abnormal wheels.

5. How to check if there is only one bulging wheel in the same batch?
If all other casters on the same device are normal and only one shows obvious bulging, you can first record its installation position and damage form.

Then check if there are any special working conditions at that location.

If there is no significant difference in usage environment and stress state, it is worth further investigating the reasons from the material and manufacturing status of the caster itself.

If similar phenomena occur in similar locations for the same batch of products, it is even more important to retain the samples and compare the bulging position, internal state, and usage conditions before the occurrence of abnormalities.

Failure analysis may only leave the word ‘broken’ without any on-site information.

6. Can internal issues be detected in advance during acceptance?
Merely relying on the naked eye cannot detect all internal defects.

However, in bulk procurement or important equipment applications, risks can still be reduced through methods such as appearance consistency inspection, sample trial assembly, and observation of actual operating conditions.

Especially for sample testing, we should not only focus on whether the push is smooth or not.

After running for a period of time, the wheel surface can be re observed for any abnormal protrusions, cracks, local deformations, or other changes.

The truly valuable trial is to see what happens to the product after it has undergone actual working conditions.

7. After discovering the bulge, please leave three pieces of information
Take photos of the drum position and the entire wheel;

Secondly, record where the casters are installed and how the equipment is used;

Thirdly, if replacement is necessary, try to keep the abnormal wheel and do not discard it immediately.

Because many internal issues can only be identified by disassembling, cutting open, or further examining the truly abnormal areas.

Having complete on-site information will provide more basis for subsequent judgments.

Write it at the end
The difference between bulging on the surface of the casters and normal wear is that:

The problems you see may be on the surface, but the real starting point is hidden inside the material.

Therefore, when there is a sudden local protrusion on the wheel surface, don’t just think about grinding it flat, and don’t continue to ignore it just because it can still rotate.

Record first, then inspect, and identify the cause in order to determine whether this is an occasional phenomenon or a material or process issue that deserves further attention.

The quality judgment of casters is not only based on how beautiful they are when they first leave the factory, but also on whether their structure remains stable after experiencing real loads and long-term operation.

For more information, please feel free to contact GLOBE Team!