Housing Materials: When to Choose Stainless Steel 316 Over Aluminum Alloy

In the world of industrial automation, the internal components of a Limit Switch Box (Valve Position Monitor) often get the most attention. Engineers obsess over gold-plated contacts, inductive sensors, and terminal strips. However, the first line of defense for these critical components is the enclosure itself.

At Zhejiang KGSY Intelligent Technology Co., Ltd., we offer our APL, ALS, and DSK series in two primary materials: Die-Cast Aluminum Alloy and Stainless Steel 316 (CF8M).

Choosing the wrong material is a costly mistake. An aluminum box in a sulfuric acid plant will dissolve in months, while a stainless steel box in a dry warehouse is an unnecessary expense. This guide breaks down the chemical and mechanical differences between these materials to help you make the right investment for your plant.

1. The Standard: Die-Cast Aluminum Alloy

(The Cost-Effective Workhorse)

For 90% of general industrial applications, Aluminum Alloy is the material of choice. You will find this housing on our standard APL-210N, DSK-100, and ALS-400 series.

The KGSY Standard: Polyester Powder Coating

It is important to note that KGSY never sells “bare” aluminum. Raw aluminum oxidizes quickly. Our aluminum housings undergo a rigorous multi-stage finishing process:

1. Passivation: The raw casting is treated to remove impurities.
2. Powder Coating: We apply a robust Polyester Powder Coating (typically 60-80 microns thick).
3. Curing: The coating is baked to create a hard, UV-resistant shell.

When to Choose Aluminum:

• General Industry: Water treatment, HVAC, light manufacturing, and indoor pneumatic systems.
• Weight Sensitivity: Aluminum is roughly one-third the weight of stainless steel. If you are mounting the switch box onto a small, lightweight actuator (e.g., a small rack-and-pinion unit), a heavy stainless steel box might put too much stress on the mounting bracket or the valve stem.
• Budget Constraints: Aluminum is significantly easier to cast and machine, making it the most cost-effective option for large-scale projects.

2. The Fortress: Stainless Steel 316 (CF8M)

(The Ultimate Shield)

When the environment turns hostile, Aluminum—even with a good paint job—is not enough. This is where Stainless Steel 316 enters the picture. You will see this material option in our APL-210-316, ALS-600, and the explosion-proof KG800-SS series.

Why “316″ and not “304″?

KGSY specifically uses Grade 316 (CF8M) stainless steel. The key difference is the addition of Molybdenum (2-3%).

• Type 304: Good for general corrosion but fails against chlorides (salt).
• Type 316: The Molybdenum drastically increases resistance to pitting and crevice corrosion, specifically in chloride-rich environments like seawater or de-icing salts.

The Investment Casting Process

Our stainless steel housings are made using the Investment Casting (Lost Wax) process. This allows us to achieve complex shapes with high dimensional accuracy and a smoother surface finish than sand casting, ensuring a perfect seal for the O-rings.

3. The Decision Matrix: When to Upgrade?

If you are unsure which material to specify, evaluate your installation against these three critical “Threat Vectors.”

Threat Vector A: The “Salt Air” Test (Offshore & Marine)

If your facility is within 5km of the ocean, or on an offshore platform:

• The Aluminum Risk: Salt air attacks aluminum through “filiform corrosion.” Once the smallest scratch penetrates the polyester coating, the salt creeps under the paint, causing it to bubble and flake off. Eventually, the aluminum turns to white powder (aluminum oxide), and the IP67 seal fails.
• The SS316 Solution: Stainless Steel 316 is inherently resistant to salt spray. It does not rely on a paint layer for protection. Even if scratched, the metal self-passivates (heals itself) and does not corrode.
• Recommendation: Always specify SS316 for Offshore, Marine, and Desalination plants.

Threat Vector B: The “Washdown” Test (Food & Beverage)

In food processing, breweries, and pharmaceutical plants, hygiene is paramount. Equipment is blasted daily with high-pressure hot water and caustic cleaning agents (Sodium Hydroxide).

• The Aluminum Risk: Caustic cleaners are chemically aggressive towards aluminum. Furthermore, the high-pressure spray can chip the paint. Paint chips falling into a food production line is a critical contamination risk.
• The SS316 Solution: KGSY Stainless Steel boxes have no paint to chip. Their smooth, non-porous surface is easy to sanitize and withstands acidic and alkaline washdowns.
• Recommendation: Always specify SS316 for Food, Beverage, and Pharma.
• The Aluminum Risk: While polyester coating offers good resistance to many chemicals, it has limits. Solvents, strong acids, or continuous exposure to petrochemical vapors can soften the coating over time.
• The SS316 Solution: 316 Stainless is resistant to sulfuric acid (at certain concentrations), phosphoric acid, and most organic solvents.
• Recommendation: Consult the KGSY Chemical Compatibility Chart. For general refining, Aluminum is often fine. For acid lines or corrosive atmospheres, upgrade to SS316.

Threat Vector C: The “Chemical Attack” Test (Petrochemical)

4. Mechanical Strength and Durability

Beyond corrosion, physical strength plays a role.

In heavy industries (Mining, Steel Mills), valves are often subjected to falling debris or accidental impacts from maintenance tools.

• Aluminum: Durable, but can crack under heavy impact.
• Stainless Steel: Has a higher tensile strength and ductility. It is more likely to dent than crack, keeping the internal electronics safe even after a significant physical blow.

5. Cost Analysis: ROI Calculation

The elephant in the room is cost. A Stainless Steel 316 Limit Switch Box typically costs 3 to 4 times more than its Aluminum counterpart.

Is it worth it?

Scenario 1: The Indoor Factory

• Environment: Dry, temperature-controlled.
• Life Expectancy: Aluminum = 15 years. SS316 = 20+ years.
• Verdict: Stick with Aluminum. The extra cost of SS316 provides no ROI.

Scenario 2: The Coastal Refinery

• Environment: Salty, humid, outdoor.
• Life Expectancy:

○ Aluminum: 2-3 years before coating failure and seal compromise.

○ SS316: 15+ years.

• The Calculation: If you use Aluminum, you will replace the unit (plus labor costs, plus permit costs, plus potential downtime) 5 times in the lifespan of one SS316 unit.
• Verdict: SS316 is cheaper in the long run.

6. KGSY Product Availability

At Zhejiang KGSY, we believe in modularity. Most of our popular series are available in both materials, sharing the exact same internal mounting brackets and switching options.

Note: Regardless of the housing material, KGSY always provides a Stainless Steel Mounting Bracket standard with every box to prevent galvanic corrosion between the actuator and the switch box.

Conclusion

The choice between Aluminum Alloy and Stainless Steel 316 is not a question of “Good vs. Bad.” It is a question of “Right Fit.”

• Choose Aluminum for efficiency, standard indoor/outdoor applications, and cost-sensitive projects.
• Choose Stainless Steel 316 for harsh chemicals, salty environments, extreme hygiene requirements, and long-term reliability in the elements.

At KGSY, “Quality is Credibility.” Whether you need the lightweight efficiency of the APL-210 or the armored protection of the ALS-600, we engineer our housings to protect your process.

Still unsure about chemical compatibility?

Send us your site conditions, and our engineering team will recommend the perfect housing material.

• Website: www.chinakgsy.com
• Email: manager@zjkgsy.com
• Phone/WeChat: 086-13587661980