Friends new to warehouse rack maintenance often ask me: "Why, even though rust removal has been properly done, some racks feel smooth and silky to the touch, while others are as rough and abrasive as sandpaper?" Actually, the key lies in the surface roughness parameter known as Ra! This seemingly technical metric directly affects the coating adhesion of the racks, their lifespan—and even their safety. Today, let’s dive into those "behind-the-scenes contributors" that quietly influence the Ra value.

1. Construction methods determine the foundational framework

Let’s start with the most straightforward operational step. Just as the heat control in stir-frying affects the taste of a dish, the setting of sandblasting/shot blasting pressure during rust removal is essentially the "first critical process." Experienced factory workers know that if the compressed air pressure exceeds 0.6 MPa, the steel surface can be overly impacted, resulting in deep pitting—while pressures below 0.4 MPa may leave rust residues unremoved altogether. According to actual measurements, using a moderate pressure of 0.5 MPa combined with angular steel shot not only efficiently removes rust but also ensures the base material’s structural integrity remains intact.

When it comes to abrasive selection, there’s even more to consider. Quartz sand particles are round and ideal for fine polishing, while brown fused alumina, with its sharp edges and corners, is often used for heavy-duty rust removal. Here’s a real-life example: A logistics warehouse switched to a mixed formulation—70% brown fused alumina combined with 30% silicon carbide—which not only ensured excellent rust-removal performance but also kept the Ra value consistently within the optimal range of 4.5 to 6.5 μm. This resulted in surface smoothness that was nearly 30% higher compared to using a single abrasive material.

The rust-removal process for shelves significantly affects surface quality.

II. Equipment Performance Hides an Invisible Password

Don’t underestimate those roaring machines—they certainly don’t all have the same “temperament.” Take the commonly used open-type sandblasting machine, for instance. The optimal distance between the nozzle and the workpiece is 15–25 cm; too close, and you risk creating localized depressions, while too far, and efficiency suffers. Our on-site measurements revealed that when the nozzle is angled at 45 degrees during spraying, the metal surface exhibits the most uniform texture distribution, with the Ra value fluctuating within a range of no more than ±1 μm.

The capacity of the air compressor's storage tank is also a detail that’s often overlooked. Equipment with tanks smaller than 0.8 cubic meters frequently starts and stops, leading to unstable air pressure, which in turn results in unevenly distributed pinholes on the finished product. It’s recommended that everyone prioritize choosing equipment equipped with a pressure stabilization device—after all, consistent power output is the key to ensuring quality.

3. Material properties come with built-in genetic labels

Shelves made from different materials react dramatically differently to rust removal. After acid pickling and phosphating, cold-rolled steel sheets naturally achieve lower Ra values on their surfaces more easily than hot-rolled steel sheets. Comparative experiments have shown that, under identical processing conditions, the final Ra values of Q235 ordinary carbon steel are typically 1.2 to 1.8 μm higher than those of galvanized steel sheets. This is because the coating alters the material's microhardness, thereby influencing the grinding performance.

Let me especially highlight the impact of the degree of rusting. Light surface rust—just oxidation on the outer layer—can be easily removed with mild sanding, revealing a smooth, polished surface. However, if the rust has progressed to severe, flaky layers that are peeling off, even increasing the application of chemicals will leave behind honeycomb-like marks. Experienced technicians always begin with a salt-spray test and then adjust their treatment plan based on the specific corrosion level.

IV. Human factors are ultimately the decisive variable.

The same equipment can yield dramatically different results depending on who’s using it. The most common mistake beginners make is "rushing"—they try to speed up the process by cutting down the time spent on each pass, only to end up with numerous tiny rust spots left behind. Seasoned professionals, however, swear by the secret technique of "little and often": applying thin, light coats repeatedly over three passes actually produces a smoother finish than applying one thick coat all at once.

There’s another detail that many people overlook: the dust removal process. Imagine this—if you apply paint immediately after sandblasting without promptly cleaning up the resulting dust, it’s like trying to build a house on sand. The proper approach is to use clean, compressed air for a second round of blowing, followed by wiping with a sticky cloth. Only then can you ensure the Ra value measurement remains accurate.

Standing here and looking at the completely refreshed shelves, I can't help but recall what the veteran workshop master once said: " Rust removal isn’t about wearing things thinner through excessive scrubbing—it’s about identifying that "golden point of friction" where the paint can grip firmly. "The next time you see a newly manufactured shelf, why not reach out and feel the texture at the seams? Hidden within that subtle difference in touch is the entire production team’s unwavering commitment to quality."