How shredder density determines your nonferrous yield

Non-ferrous recovery is largely determined before material ever reaches downstream separation systems. It begins inside the shredder.

For shredder operators focused on maximizing yield, one of the most important upstream variables is whether the shredder is being kept full and run at the right density. According to Randy Brace, president of Riverside Engineering, maintaining full-box conditions is essential for efficient liberation of non-ferrous metals and for reducing oversized material.

Full-box shredding means keeping the machine consistently loaded so it processes a steady volume of scrap rather than cycling through partially filled conditions. When that consistency is maintained, the hammermill can do the work it was designed to do: break down material more effectively, improve liberation, and produce a more uniform shred.

When the box is not full, those results begin to slip.

"If you're not full-box shredding, you're losing a lot of efficiency," said Brace during a session at the most recent ReMA Safety and Operations Forum. "Your scrap is larger, so you're not getting the non-ferrous liberation that you really would be likely to get. You get more long bars out of the shredder when the shredder's not full-box shredding."

That matters because downstream recovery equipment can only separate what has been properly liberated upstream. If copper, aluminum, and other non-ferrous metals remain attached to ferrous pieces or trapped in larger fragments, they are less likely to be recovered cleanly. In that sense, poor box loading does more than reduce shredder efficiency. It directly limits non-ferrous yield.

Why density matters

Brace points to shred density as one of the clearest indicators of whether the shredder is operating in an optimal range.

"What I hear in the industry is 85 pounds per cubic foot," he said. "I would say you're liberating the majority of your non-ferrous metals as you push 85."

That benchmark has shifted over time. About 20 years ago, said Brace, many operators were aiming for 75 to 80 pounds per cubic foot to maximize throughput. Today, higher-density targets are more common as operators balance throughput with improved non-ferrous liberation and recovery.

The reason for that shift is straightforward. Lower-density shredding may allow material to move through the system faster, but it does not necessarily create the particle size and liberation needed for effective downstream recovery. If density is too low, operators are more likely to see larger shredded scrap, more unprocessed long pieces, and lower recovery of non-ferrous metals.

At the same time, Brace cautions that more density is not always better.

"At 90, you're starting [to] maybe put more casting costs and electrical costs, wear and tear on everything," he said.

In other words, the goal is not to drive density as high as possible. It is to stay in the range where liberation improves without pushing wear, power draw, and maintenance costs beyond the point of meaningful return.

What yards lose when the box is not full

The losses associated with underfeeding are not always obvious in the moment. A yard may still be producing tonnage, and operators may feel the shredder is running normally. But the downstream consequences can show up in recovery rates, electrical cost per ton, and casting consumption.

Brace ties several of those effects directly to incomplete box loading.

"Your electrical costs and your casting costs are higher also when you're not keeping the box full of scrap processing," he said.

This happens because a shredder running below optimal fill is doing less productive work with each cycle. Material exits the shredder in larger pieces, non-ferrous components are not as fully liberated, and the system can spend more time effectively grinding or reworking material instead of breaking it efficiently. That affects more than throughput. It affects the quality of the shred and the value that can be recovered from it.

One indicator of this is an increase in long bars. When they increase, it is often a sign that material is not being processed with enough consistency inside the box. That can create downstream handling problems while also highlighting missed liberation opportunities.

Measuring what the shredder is really doing

Because the effects of underfeeding can develop gradually, Brace emphasizes the importance of measurement. Density targets only matter if yards are tracking them consistently and connecting them to production results.

"If you're not tracking things and if you're not measuring things," said Brace, "the plant is deteriorating whether you recognize it or not."

Operators need to know what density they are achieving and how that relates to recovery, throughput, wear, and power consumption.

Brace also points to feed consistency as one of the biggest hidden drivers of shredder performance. "Material blockage at the feed rolls [and] gaps in the feed, those two are two of the biggest stealers of your production time," he said.

Automated tracking can help identify those gaps more clearly. By setting amp thresholds and tracking how long the shredder falls below a defined load level, yards can measure underfeeding instead of relying on operator impression.

In some systems, this is configured to trigger alerts when thresholds are exceeded.

"If you are below that threshold amp, you get an alert that says, hey, you need to identify a gap in feed material, or you've got a problem getting the material in at the feed roll," said Brace.

That kind of monitoring helps operators move beyond broad assumptions about performance. A yard may believe it is running efficiently because the shredder is active, but amp-based monitoring and density tracking can reveal whether the machine is actually being fed consistently enough to support proper liberation.

Upstream discipline, downstream results

For yards trying to improve non-ferrous recovery, the takeaway is practical. Downstream systems cannot recover metals that were never adequately liberated in the first place. That makes full-box shredding and density control critical upstream disciplines.

The current benchmark of about 85 pounds per cubic foot reflects that balance point: dense enough to improve liberation and non-ferrous yield, but not so dense that added wear and energy cost erase the gains. In an operating environment where recovery value matters as much as throughput, keeping the shredder full may be one of the simplest ways to improve what comes out the other end.

This article originally appeared in the May/June 2026 issue of Recycling Product News.