Stainless steel is a corrosion specification, not a hardness specification. That one distinction settles most arguments about what steel belongs in recycling equipment. Glass fines, grit, and steel wire grind steel down, no matter how shiny the steel is. A passive chromium oxide film does nothing to stop a hard particle from cutting a groove. What survives a wear zone is mass and replaceability: thicker plate, and bolt-out wear surfaces you can replace when they are gone. Reserve the stainless for washdown and chemical exposure, where it justifies its cost.
Corrosion and Abrasion Are Two Different Failure Modes
"We'll spec stainless, it holds up better in recycling." The instinct behind that is good. The buyer knows the machine will have hard service and wants to pay for something that survives. The problem is that the buyer is buying resistance to the wrong failure mode.
Corrosion is chemical. Iron gives up electrons to its environment and turns into oxide. Stainless resists that because chromium forms a thin, self-repairing passive film that keeps oxygen and moisture off the iron underneath. That film is the whole mechanism, and it is only a few nanometers thick.
Abrasion is mechanical. A particle harder than the surface it slides across plows a groove and carries metal away with it. A passive film has no effect on grit. Grit goes straight through the film and keeps cutting the plain metal underneath, every hour the plant runs.
In most recycling streams the main cause of damage is abrasion, not rust. If you specify against the wrong failure mode, you pay a premium for a machine. That machine wears out on the same schedule as the cheap one.
Where the Grades Actually Sit on Hardness
Abrasive wear depends on hardness. The controlling variable is the ratio between the hardness of the abrasive and the hardness of the surface that it wears. When the abrasive is much harder, material comes off fast. When the surface hardness approaches or passes the abrasive hardness, the wear rate drops sharply. The table below lists published hardness ranges for delivered material, not Remcon specifications:
| Material | Typical hardness | What it is actually for |
|---|---|---|
| A36 structural carbon steel | Roughly 120 to 160 HB | Structure. Frames, legs, supports, weldments. |
| 304 stainless (annealed) | ASTM A240 caps it at 201 HBW | General corrosion resistance and cleanability. |
| 316 stainless (annealed) | ASTM A240 caps it at 217 HBW | Corrosion resistance plus chloride and pitting resistance. |
| AR400 abrasion-resistant plate | Roughly 360 to 440 HB | Sacrificial wear surfaces. Not a structural material. |
| AR500 abrasion-resistant plate | Roughly 470 to 540 HB | Harder wear service, at the cost of ductility and formability. |
| Chromium carbide overlay plate | Overlay commonly 55 to 65 HRC | Severe sliding abrasion with low to moderate impact. |
The table shows two things. First, annealed 304 and 316 are only modestly harder than structural carbon steel. Their hardness is in the same range, not in a different class. Second, abrasion-resistant plate is not a little harder than stainless, but roughly twice as hard.
There is a metallurgical reason you cannot harden these stainless grades to close that gap. 304 and 316 are austenitic, and austenitic stainless cannot be hardened by heat treatment. It work-hardens at the surface when deformed. Work-hardening helps a little under impact. But you cannot heat treat a 304 chute into a wear part. The grades that do harden are the martensitic 400 series, such as 410, 420, and 440C. The martensitic grades get that hardness by giving up corrosion resistance. The loss of corrosion resistance removes the reason anyone wanted stainless.
What Is Actually Damaging Your Steel
Walk through a single-stream plant. List what is on the belt. Almost none of it is corrosive. Almost all of it is abrasive.
- Broken glass and glass fines. Glass is around 5.5 on the Mohs scale. It is destructive enough that most single-stream plants screen the fines out early, before the rest of the line is exposed to them.
- Grit, dirt, and sand. Quartz is 7 on the Mohs scale. Quartz is harder than glass and also harder than carbon steel, stainless, and AR plate alike. Grit, dirt, and sand come in on cardboard, containers, and anything that has been on a floor or in a truck.
- Steel wire and banding. Wire enters edges and seams, wraps around shafts, and gouges the surface instead of polishing it.
- Impact. Material dropping into a hopper or load zone is a different problem from sliding wear. Mass and cushioning solve this problem, rather than hardness.
None of that is a corrosion problem. A corrosion-resistant alloy does not protect against it.
What Actually Lasts: Mass and Replaceability
Mass. If the material and the duty set the wear rate, the only factor left is how much metal the machine has to lose. Thickness sets how long the part lasts. So Remcon builds slider bed conveyors with a formed 3/16" plate steel frame and a 3/8" flat-bar slat bed. Against abrasion, extra thickness in ordinary plate gives more service life per dollar than a thinner corrosion-resistant alloy.
Replaceability. Wear is not a defect. Wear is what a wear part is for. The design question is not how to stop wear. The question is where you want wear to happen and how fast you can replace the worn part. On a Remcon slider bed, the flat-bar slat bed is replaceable. Belt edge seals are built into the bed, underneath the edges of the belt. The seals minimize the debris that gets under the belt and wears the belt and the pan from below. The wear item is a replaceable part rather than a piece of the structure. The same principle applies to skirting, chute liners, hopper walls, and the load zone. All of them should be parts that you can unbolt. We keep replacement parts and belt repair available for the life of the conveyor for the same reason.
Bolt Wear Surfaces On. Do Not Weld Them In.
Many otherwise good specifications fail when someone buys hard plate, welds it into the frame, and creates two problems at once.
The first is metallurgical. Abrasion-resistant plate is hardened, and welding heat tempers what it touches. If there is too much heat, the heat-affected zone loses the hardness you paid for. If there is too little heat with fast cooling, cracking can result. AR400 is typically welded with a controlled preheat and interpass temperature in the range of about 250 to 350 degrees Fahrenheit. The weld is made with smaller passes rather than one hot bead.
The second is practical. AR plate is a wear material, not a structural one. Once it is welded in, the wear part and the structure are the same part. Replacing it means cutting into the machine, grinding the frame flat, fitting new plate, and re-welding. Replacing welded-in plate carries a risk of distortion. Bolting keeps the two jobs separate. The frame stays the frame, the liner stays a consumable, and replacing the liner is a maintenance task instead of a shutdown. Non-metallic liners follow the same logic. Ultra-high molecular weight (UHMW) polyethylene is normally installed with mechanical fasteners through counter-bored holes. UHMW polyethylene does well against fine, dry, sliding abrasion. However, it has temperature limits, and it gouges where heavy lumps land on it at a steep angle.
Where Stainless Is the Right Choice
None of this makes stainless a bad material. Stainless is a specific material for a specific cause of damage. Where corrosion, not abrasion, ends the life of the part, specify stainless in these cases:
- Washdown. Equipment hosed down on a schedule, especially with alkaline, acidic, or chlorinated cleaners, is a corrosion problem first.
- Chemical exposure. Process chemistry, leachate, brine, and anything that sits wet between shifts.
- Food contact and food-adjacent lines. Cleanability and the passive surface are the purpose, and 304 is the common baseline.
- Chlorides and salt air. Chloride exposure is the reason to choose 316 over 304. 316 contains roughly 2 to 3 percent molybdenum, which 304 essentially does not. This molybdenum slows pitting and crevice attack in chloride service. Where bleach-based sanitizers are in the wash cycle, 316 or 316L is the base specification, not an upgrade.
Even here, be aware of the limits. Austenitic grades, including both 304 and 316, are susceptible to chloride stress corrosion cracking. Evaporative conditions, where a chloride solution dries onto a warm surface, can be more damaging to them than full immersion. Stainless resists corrosion, but it is not immune to corrosion.
Spec It Zone by Zone
The useful habit is to specify each surface instead of the whole machine. Ask what is damaging each surface. Then choose the material to match the answer. Most real machines use more than one material, and that is fine.
| Zone | Dominant failure mode | What should drive the spec |
|---|---|---|
| Frame, legs, supports | Load and fatigue | Structural steel sized for the load. Remcon uses formed 3/16" plate. |
| Belt bed and slats | Sliding abrasion under the belt | Thickness and easy replacement. Remcon uses 3/8" flat-bar slats. |
| Load zone and hopper walls | Impact plus abrasion | Mass and cushioning first, hardness second. Bolt-on liners. |
| Chutes, skirting, transitions | High-velocity sliding abrasion | A sacrificial bolted liner, sized so that replacement is a routine task. |
| Washdown and wet areas | Corrosion | Corrosion resistance. 304 baseline, 316 where chlorides are present. |
| Fasteners in wet zones | Corrosion and seizing | Corrosion-resistant hardware, so the liner still comes off in three years. |
Look at the last row. A wear liner that you cannot unbolt because the fasteners rusted solid is no better than a welded liner. A wet zone is one place where a stainless fastener justifies its cost on an otherwise carbon-steel machine.
Questions to Ask Before Anyone Writes Stainless on the Drawing
- What is actually damaging this surface? Name the material, not the industry.
- Is there standing water, washdown, or process chemistry here, or is it only dusty?
- Which surfaces are expected to wear out, and how do we get them off the machine?
- Is the wear item bolted or welded? If welded, what does replacing it cost in downtime?
- Would another 1/16" of ordinary plate solve this at a lower cost than a different alloy?
Ask these questions in the same discussion as belt selection and drive sizing. Our guides on how to read a conveyor belt spec and what to ask before you buy a conveyor cover the rest of that checklist.
Spec Every Surface for What Is Damaging It
Remcon has built heavy-duty recycling equipment since 1977, and the principle has not changed. Glass, grit, and wire are going to take metal off your equipment. The only question is whether they take it off a part you can unbolt in an afternoon or off the frame itself.
Tell us what is on the belt, where the water and the chemicals are, and which surfaces you replace too often. We build to order and quote per job. So the specification follows the application, not a catalog page, for bins and hoppers and sorting conveyors as well as for a belt conveyor. If a thicker piece of ordinary plate will do the job, we will say so.
Stainless vs. Abrasion FAQ
Is stainless steel more abrasion resistant than mild steel?
Barely. Stainless resists corrosion, not abrasion. Under ASTM A240, annealed 304 is capped at 201 Brinell and 316 is capped at 217 Brinell. Structural carbon steel such as A36 is typically about 120 to 160 Brinell. The two stainless grades are in the same hardness range as structural carbon steel, not in a different class. Abrasion-resistant plate like AR400 is roughly 360 to 440 Brinell, about twice as hard as either stainless grade.
What is AR400 steel and how does it compare to stainless?
AR400 is abrasion-resistant plate that is graded by hardness, not by chemistry. Its hardness is typically about 360 to 440 Brinell. AR500 is harder, roughly 470 to 540 Brinell, with less ductility. Both are much harder than 304 or 316 stainless. However, they offer no meaningful corrosion resistance, and they are wear materials, not structural ones. AR plate is widely used in industry for sacrificial liners and wear surfaces.
When should you use stainless steel in recycling equipment?
If corrosion is the failure mode, use stainless. These cases include regular washdown, chemical or process exposure, food contact, standing water, and salt or chloride environments. 304 is the common baseline. If chlorides, brine, or bleach-based sanitizers are present, choose 316, because it contains roughly 2 to 3 percent molybdenum. This molybdenum slows pitting and crevice corrosion. Do not specify stainless to resist abrasion.
Why bolt wear liners on instead of welding them in?
Two reasons. First, welding heat tempers abrasion-resistant plate, so the heat-affected zone can lose the hardness you paid for. Also, AR400 typically needs a controlled preheat and interpass temperature of around 250 to 350 degrees Fahrenheit to weld properly. Second, a welded liner becomes part of the frame, so replacing it means cutting into the frame. A bolted liner is a consumable that you replace without touching the structure.
Can stainless steel be hardened to resist wear?
Not the grades most people mean. 304 and 316 are austenitic and cannot be hardened by heat treatment. Austenitic stainless work-hardens at the surface when deformed. Work-hardening helps slightly under impact. But you cannot heat treat a stainless chute into a wear part. The martensitic 400-series grades such as 410, 420, and 440C do harden by heat treatment. However, they give up the corrosion resistance that made stainless attractive.
What steel does Remcon use in its conveyor frames and beds?
Remcon slider bed conveyors use a formed 3/16" plate steel frame with a bed of replaceable 3/8" flat-bar steel slats. Belt widths range from 12" to 72". The frame is specified for structure. The slats are specified as a replaceable wear item. So the part that wears out is the part that you can replace. We build every conveyor to order and quote it per job.