Already have a trommel screen?
When a ballistic separator makes sense.

Two machines. Two different sorting questions.

A trommel asks: what can pass through these openings?

A trommel moves material through a rotating perforated drum. Items able to pass through the openings leave as an undersize fraction; retained material travels onward. A drum with different screening sections can produce several size groups—not just two outputs. Its task is size classification: it controls the size range presented to the next process.

Passing or remaining on a screen does not, by itself, identify a material as paper, plastic or metal. A piece of film and a container may both remain in the selected size fraction. Their subsequent behaviour can still be very different.

A ballistic separator asks: how does this material move?

An inclined deck of moving paddles encourages flat, flexible items and rolling, rigid items to follow different paths. These are commonly called the 2D and 3D fractions. Perforated paddles can also remove a screen-underflow fraction. Shape, surface characteristics and the condition of the material affect how it responds. The deck does not identify a polymer, metal grade or paper grade; it creates physical streams for the next process to handle.

The labels describe behaviour, not a chemical analysis. The 2D stream may contain both film and paper; the 3D stream may contain several plastics, cans and other objects. Further sorting is normally needed when the objective is a specific saleable material.

When the combination earns its place.

The strongest reason to use both is a clear requirement at the next process. Consider a size-classified packaging stream that still contains loose film, paper and rigid containers. If the plant needs separate routes for flexible packaging and containers, a behavioural split may be useful before more selective recovery.

1. The retained fraction needs two different routes

Separating the flat fraction from the rolling fraction creates an opportunity to configure each route around its own material. One may need film and paper sorting; the other may need container and metal recovery. That opportunity has value only if the conveyors, downstream equipment and output destinations can use the split.

2. Downstream sorting needs better-prepared feed

Lightweight material can require different handling from rigid containers. On a high-speed belt, loose film can lift, overlap or move unpredictably, while bottles and cans tend to roll or remain more stable. A separate 2D route allows the receiving belt, air control and any later sorting equipment to be arranged for light material. Adding a separator without checking the receiving belt and its capacity may simply move the bottleneck.

3. There is a specific duty for each screening stage

A first size cut and a later behavioural split can be complementary. But the fines-removal duties need scrutiny. If the trommel has already removed the relevant undersize material effectively, an identical downstream cut may add little. Residual fines, newly released particles or a deliberately different aperture may justify a further cut; this needs to be demonstrated on the actual feed.

A possible route through the two stages.

The diagram below shows one concept for a prepared mixed-recyclables stream. It sends a selected trommel fraction to ballistic separation. The other trommel outputs follow their own routes. It deliberately does not assign an aperture or throughput: those decisions belong to the feedstock assessment.

The condition of the feed matters as much as the sequence

Bagged, attached or entangled items cannot be assumed to behave like the individual materials inside them. A wet paper-and-film clump is a different test material from loose dry film. Before selecting the sequence, establish whether the feed needs opening, removal of unsuitable objects or other preparation. Do not assume that every line needs shredding, or that shredding will always improve the split.

Machine design also matters. Deck inclination, paddle perforation and surface, feed distribution, width and length can all affect how material moves through a separator. Select these details from the sorting duty and the actual feed, rather than from a generic capacity figure. A configuration that suits loose dry packaging cannot be assumed suitable for wet, attached or heavy mixed material.

When another separator may not help.

An additional machine creates capital cost, transfer points and maintenance work. It should solve a demonstrated process problem. Hold off on specifying a ballistic separator when:

• The objective is only size grading. If the existing screen produces the size groups required by the next operation, adding behavioural separation may have no useful duty.
• The feed is already sufficiently separated by behaviour. A mostly uniform stream may offer too little benefit from another 2D/3D split.
• The real constraint is elsewhere. Feed surges, a blocked transfer or an undersized receiving conveyor should be investigated before adding separation capacity.
• There is no viable destination for the new streams. Creating additional fractions does not make them saleable or suitable for disposal without further assessment.
• The proposed machine is not suitable for the feed. Large dense objects, abrasive material, persistent tangles or wet agglomerates require an explicit suitability review.

A different pre-treatment method, a change to feeding, or another separation technology may be more appropriate. The comparison should start with the required output, then work backwards through the process.

Verify the split—and the whole-line result.

A short video of a machine running is a useful introduction. A retrofit decision needs a more complete record. Use the following questions to structure a trial and a layout review.

1. Is the test feed representative?

   Record where it came from, its size range, moisture condition, composition and preparation. Include normal variation instead of testing only the easiest material.

2. What load actually reaches the separator?

   Measure the selected trommel stream, including peaks. State whether the flow is in m³/h or t/h and record bulk density where converting between them. Do not size the second machine from the total plant intake alone.

3. What is in every output?

   Collect timed samples from all relevant streams. Measure both the share of target material recovered and its concentration in the target output. Include valuable material lost to the other fractions.

4. Can the plant accommodate the change?

   Check transfer heights, conveyor loading, support structure, power, access, dust management and the installation window. Reserve space for safe inspection and maintenance.

5. Does the improvement survive a full operating assessment?

   Compare the baseline and proposed route using matched feed conditions. Include saleable output, reject treatment, energy, cleaning, wear parts and downtime—not just the separator’s nominal capacity.

Maintenance deserves its own line in the assessment. Review access to the deck, paddles, drive, lubrication points and discharge areas. Confirm which wear parts are included, how they are replaced, what lifting or isolation procedures are required, and which spares should be held on site. Do not treat a general “low-maintenance” claim as a substitute for a documented maintenance scope.