Closed-Circuit Crushing: How Screen Returns Affect Plant Capacity

A crushing plant can receive a moderate quantity of fresh stone while its crusher handles a much larger internal flow. The difference is often material returned from the screen. Oversize particles travel around the circuit again, sharing equipment capacity with the new feed.

Closed-circuit crushing uses this return path to control product size. It also means that an individual machine's nominal throughput cannot be treated as finished aggregate plant capacity. Project buyers need to understand where tonnes enter, circulate and leave before comparing equipment proposals or deciding that a larger crusher will solve a bottleneck.

Separate fresh feed from internal throughput

Fresh feed is material newly entering the selected circuit boundary. Circulating load is the material returning for another pass. For a simple closed circuit without intermediate losses, the crusher receives both streams. The mass balance should state the boundary so that everyone uses the same terms.

An illustrative circuit receiving one hundred tonnes per hour of fresh feed and fifty tonnes per hour of return material sends one hundred fifty tonnes per hour through the crusher. Here, return divided by fresh feed gives a fifty percent circulating load. These figures explain the arithmetic; they do not predict any Dongmeng machine's output.

The discharge conveyor and screen also need to handle the internal flow. A purchase enquiry that specifies only one hundred tonnes per hour of finished production omits this duty. Conversely, a proposal advertising one hundred fifty tonnes per hour at the crusher may still produce a smaller quantity of saleable output.

Understand why particles return

The screen separates material according to the selected apertures and operating conditions. Particles above the intended cut return for further reduction. Some material that could pass may also remain with the oversize if separation is imperfect. Distinguishing these causes helps identify the correct improvement.

A tighter product requirement can increase the material requiring another pass. Changes in crusher setting and wear condition can alter the size distribution entering the screen. Changes in moisture or fines can affect separation. The circuit response depends on these interactions rather than on one isolated catalogue value.

Metso's crushing and screening guidance treats crushers, screens and wear parts as interacting process components. For an aggregate project, this supports reviewing the complete flow sheet. It does not establish a universal circulating load target or a guaranteed improvement from a specific adjustment.

Treat screening as part of the capacity calculation

A YK vibrating screen proposal should identify deck configuration, aperture arrangement and the duty assigned to each deck. Overall catalogue capacity ranges cannot establish performance at every cut size. The same machine can face different demands when the feed distribution or product split changes.

Describe the fractions the project needs to sell and where each fraction leaves the screen. Include the quantity of near-size material around the critical aperture. A screen may be busy separating material close to its cut even when its total incoming mass looks acceptable.

The proposal should also identify media type and the assumptions behind screening performance. Ask the process designer to show the estimated product and return streams. This makes the screen a defined part of the circuit rather than an accessory selected after the crusher purchase.

Follow the return route through every component

Returned oversize needs suitable conveyors, transfer points and feed arrangements. The route may look minor on a simplified diagram, but it carries production material continuously. Its design should account for expected flow, material size and changes during start-up or an interruption.

A return conveyor that restricts flow can create accumulation even if the crusher and screen are adequately sized. Transfers also need to avoid uncontrolled spillage or unsuitable material distribution. Review the equipment layout and access with the plant designer rather than treating conveyor length as the only installation variable.

Show where fresh and returning material combine. Their sizes can differ, so the combined crusher feed should be evaluated as a mixture. A stable total belt rate does not necessarily mean that the feed size distribution remains stable throughout operation.

Diagnose a bottleneck with paired observations

Before changing the circuit, collect observations that relate to the same operating period. Record fresh feed, crusher operating condition, screen feed, return quantity and finished product grading. Comparing Monday's return flow with Thursday's fresh feed can produce a misleading explanation.

If circulating load rises, examine whether the crusher is making more oversize or the screen is returning material that should pass. Representative samples from the crusher discharge and return belt can help the process team distinguish these possibilities. Sampling must follow the site's approved safe procedure.

A simple example is increased return after wet material reaches the plant. Buying a larger crusher immediately would skip the screening question. The appropriate investigation reviews material condition and screen operation first, then evaluates equipment changes against measured evidence.

Product quality remains the acceptance target

Reducing return flow is not automatically an improvement. A larger aperture may reduce recirculation while allowing unwanted oversize into the product. The plant must meet its agreed grading and shape requirements, so internal flow changes should be assessed alongside the finished material.

Likewise, tighter settings can affect throughput, wear and product distribution. The project specification should identify the permitted operating range and the method used to verify output. An attractive tonnes-per-hour figure has limited purchasing value if the corresponding product falls outside the buyer's requirement.

Agree how acceptance will address material variability. Record feed condition, operating settings and sampling method during a trial. This connects the result to a defined application and avoids presenting one favourable operating period as a promise for every quarry feed.

Compare proposals with a visible mass balance

A useful closed-circuit proposal provides a flow sheet with fresh feed, internal crusher throughput, each screen product and return flow clearly distinguished. It identifies the sizing assumptions for conveyors and transfer points as well as the major machines.

Review the proposal around the required saleable products. Ask which component limits output when the material or grading changes. A complete balance makes those trade-offs visible, allowing procurement and engineering teams to compare the same duty. That is a firmer basis for plant selection than adding individual catalogue capacities together.