Coarse, medium, and fine crushed limestone products
For a limestone aggregate crushing line with an hourly capacity of 400 tons, a single main processing line suffices: a ZSW1100×4200 grizzly feeder, a PE900×1200 jaw crusher for primary crushing, a CI1521 impact crusher for secondary and tertiary crushing, and a 4YK2470 four-deck circular vibrating screen for closed-circuit classification. This setup yields four finished product sizes—0–5 mm, 5–10 mm, 10–20 mm, and 20–31.5 mm—in a single pass. Given the limestone's compressive strength of 80–150 MPa, low free SiO₂ content, and low abrasiveness, a cone crusher is unnecessary. The real challenge lies not in equipment selection, but in sizing the secondary crusher and screen based on total throughput rather than just finished product output; the closed-circuit return flow increases the load on the secondary crusher from 400 t/h to 556 t/h.
Schematic diagram of a production line featuring a jaw crusher, impact crusher, and screening equipment.
I. Equipment Selection
Selection is primarily based on material abrasiveness, followed by requirements for the finished product's particle shape; these two factors essentially dictate the equipment list:
| Process | Preferred Equipment | Selection Basis & Excluded Options |
|---|---|---|
| Feeding | Vibrating Grizzly Feeder (ZSW) | Grizzly bars pre-screen and bypass fines/soil into a separate pile, preventing clogging at the source. |
| Primary Crushing | Jaw Crusher (PE) | Large feed opening handles blasted rock up to 750mm; jaw plates are standard spares. Gyratory crushers are reserved for large-scale mines (>500 t/h). |
| Secondary/Fine Crushing | Impact Crusher (CI/PF) | Produces high-quality cubical shapes with low flake/elongation ratios; investment cost is 30%–40% lower than cone crushers. Hammer crushers cause excessive fines and require frequent hammer replacement. |
| Screening | Circular Vibrating Screen (YK, 4-deck) | Four decks produce four size fractions in one pass, eliminating the transfer conveyors, foundations, and electrical controls needed for two series-connected 3-deck screens. |
| Conveying | Belt Conveyor (B1000 / B800 / B650) | B1000 for main flow, B800 for recirculating material, B650 for finished product; belt width scales with throughput. |
| Environmental Protection | Pulse-Jet Bag Dust Collector (DMC Series) | Specifications selected based on the number of dust emission points; enclosing the workshop is a prerequisite for environmental compliance approval. |
| Sand Making (Optional) | Vertical Shaft Impact Crusher (VSI) | Added only if the 0–5mm fraction needs to exceed 40%; otherwise, it represents over-investment. |
In short: The feeder, jaw crusher, impact crusher, and circular vibrating screen are the "essential four"; conveyors and dust collectors are the "essential two"; the sand maker is included based on required gradation.
II. Model Determination: Three Calculations
The specific models for a 400 tph limestone aggregate crushing line are determined through calculation, not simply by looking up a table.
① Primary crushing model is determined by the maximum raw ore size:
Jaw crusher feed opening width ≥ Maximum raw ore size &pide; 0.85. For run-of-mine (ROM) ore ≤650 mm, select the PE900×1200 (feed opening 900×1200 mm, max. feed size ≤750 mm, discharge setting 95–165 mm, rated capacity 200–400 t/h, 132 kW). It must be noted that 400 t/h represents the upper limit of the PE900×1200’s rated capacity; if ROM lump size is ≥700 mm or continuous full-load operation (20 hours) is required, the model should be upgraded to the PE1200×1500 (feed size ≤1000 mm, rated capacity 400–800 t/h, 220 kW) to leverage the extra capacity margin for operational stability.
Primary crushing - Jaw Crusher
② Secondary crushing selection is based on throughput, not finished product output:
Assuming an oversize rate (material retained on the screen) of 25%–30%, the actual throughput required for the impact crusher is 400 &pide; (1 − 0.28) ≈ 556 t/h. There are only two options: a single CI1521 unit (max. feed size ≤350 mm, rated capacity 200–600 t/h, 200×2 kW) or two PF1315 units in parallel (single-unit capacity 100–280 t/h). A single PF1320 unit (160–350 t/h) is insufficient; this is a common selection error for the 400 t/h capacity class.
Secondary crushing - Impact Crusher
③ Screening selection is based on throughput:
The screen deck must also handle an input of 556 t/h. The 4YK2470 (screen deck 2400×7000 mm, four decks) is suitable for this range; its four decks correspond exactly to four product sizes, eliminating the need for two screens in series.
Screening - vibrating screen
| Process Step | Equipment | Model | Key Parameters (Limestone Calibration) | Power |
|---|---|---|---|---|
| Feeding | Grizzly Vibrating Feeder | ZSW1100×4200 | Trough 1100×4200mm; 300–500 t/h | 37 kW |
| Primary Crushing | Jaw Crusher | PE900×1200 | Feed opening 900×1200mm; Discharge opening 95–165mm; 200–400 t/h | 132 kW |
| Secondary/Fine Crushing | Impact Crusher | CI1521 | Max. feed size ≤350mm; 200–600 t/h | 200×2 kW |
| Screening | 4-Deck Circular Vibrating Screen | 4YK2470 | Screen surface 2400×7000mm; Equipped with 5/10/20/31.5mm mesh | 37 kW |
| Conveying | Belt Conveyor | B1000 / B800 / B650 | Main flow B1000, return flow B800, finished product B650 | — |
| Environmental Protection | Pulse-Jet Bag Dust Collector | DMC Series | Spec selected based on number of dust emission points | — |
Total installed power for main equipment is approx. 610 kW; calculated at 400 t/h, specific energy consumption is approx. 1.3–1.7 kWh/t (including conveying and dust collection). Motors are customized for local voltage (380/400/440V) and frequency (50/60Hz).
III. Production Line Overview: Closed-loop circulation determines particle shape and screen deck load.
The process flow is: Raw ore bin → ZSW1100×4200 feeder (grizzly bars for pre-screening; fines and soil are bypassed into a separate pile) → PE900×1200 primary crusher (reducing material to ≤200mm) → B1000 conveyor to CI1521 (secondary/tertiary crushing) → B1000 conveyor to 4YK2470 screen → Oversized material returned to the CI1521 via B800 conveyor, forming a closed loop.
Why use a return loop instead of simply enlarging the screen mesh for single-pass processing?
The price difference for limestone aggregates lies not in volume, but in particle shape. Jaw crushing involves single-stage compression, resulting in a high proportion of flaky and elongated particles; by returning oversized material to the secondary stage for an additional impact-crushing pass, the content of flaky/elongated particles drops significantly, and over-pulverization remains controllable. This factor is critical for ready-mix concrete plants regarding 5–10mm and 10–20mm gradations, and it determines whether the finished product can enter premium markets, such as asphalt surface courses.
The trade-off is the load on the screen deck: with the addition of returned material, the actual load on the screen and secondary crusher is 20%–35% higher than in an open-circuit setup—which is precisely why the secondary crusher and screen are sized based on total throughput.
Four screen decks separate the material into four grades simultaneously, which are then discharged into separate piles via four B650 conveyors:
| Product Grade | Typical Application |
|---|---|
| 0–5mm | Manufactured sand feedstock, plastering mortar |
| 5–10mm | Concrete fine aggregate, asphalt surface course |
| 10–20mm | Concrete primary aggregate |
| 20–31.5mm | Mass concrete, roadbed cushion layer |
The product discharge conveyors are intentionally kept short, allowing material passing through the screen to drop directly into piles; this minimizes dust generation points and reduces product segregation. Should this line be converted to a mobile setup? Choose a stationary plant if the quarry site is fixed, the service life exceeds three years, and minimizing cost-per-ton is the priority. Opt for a combination of a mobile jaw crushing station and a mobile impact crushing/screening station if quarry sites are dispersed, project timelines are tight, and frequent relocation is required.
On-site view of a four-unit mobile crushing station.
IV. FAQ
Q1: Is the 400 tph figure the nominal capacity or the actual operating capacity?
A1: The figure in the table is a nominal value, calibrated based on medium-hardness limestone (bulk density approx. 1.6 t/m³). Actual output fluctuates depending on raw ore gradation, moisture content, and the desired product mix; a 10%–15% margin should be allowed relative to the nominal value. Acceptance testing should be based on the measured continuous hourly output, not the nameplate figure.
Q2: Why are neither cone crushers nor hammer crushers recommended for limestone aggregate lines?
A2: Limestone has a low abrasiveness index; impact crusher blow bar wear is manageable, and the product shape is superior, with an investment cost 30%–40% lower than that of cone crushers. The advantages of cone crushers only apply to highly abrasive, hard rocks like granite and basalt. Although hammer crushers can achieve size reduction in a single stage, they cause excessive fines generation (surplus 0–5mm material) and require frequent hammer replacement, resulting in higher long-term costs per ton.
Q3: Why are the secondary impact crusher and screening machine sized for 556 t/h instead of 400 t/h?
A3: Due to the closed-circuit material return. With an oversize rate (material retained on the screen) estimated at 25%–30%, the secondary crusher and screen must handle the "400 t/h finished product + returned material," calculated as 400 &pide; (1 − 0.28) ≈ 556 t/h. If sized for only 400 t/h, both units would operate under long-term overload, leading to fluctuations in product quality, elevated screen bearing temperatures, and drastically reduced service life for liners and screen meshes.
Q4: How should the configuration be adjusted for raw ore with high clay content or for operations during the rainy season?
A4: At the feeding stage, use the grizzly bar section of the ZSW1100×4200 feeder to bypass fines and soil into a separate pile, preventing material clogging in the secondary crushing stage; switch to anti-clogging polyurethane screen meshes. If there are strict requirements for the silt content of the final product, a wheel-bucket sand washer and a fine sand recovery unit should be installed downstream of the product conveyor, with the overflow water settled and recycled. If silt content remains consistently high, a desliming stage should be added at the front end rather than relying on downstream remediation.
Q5: If we want to expand this line to 600 tph in the future, what provisions should be made now?
A5: You only need to make three specific provisions; there is no need to spend extra money right now:
① Design the jaw crusher foundation to accommodate a PE1200×1500 model to avoid having to break up and redo the foundation later;
② Reserve a foundation site and electrical control circuit for a second CI-series impact crusher;
③ Leave space and conveyor connection points in the screening building for the future installation of a second circular vibrating screen. Do not select a conveyor belt width that is at the absolute limit; use a B1000 size to allow for potential speed increases.
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