Why Secondary Crushers Underperform in Brick Plants: Diagnosing the Fine-Material Cushioning Effect

The Complaint Every Brick Plant Shares

In recent years, brick manufacturers have reported a long list of production problems, but one issue stands out as both the most severe and the most universal: the hourly output of the secondary crusher is simply too low. In plant after plant, that machine has become the bottleneck of the entire raw material preparation line, dragging down every other piece of equipment around it. The question worth asking is why such a widespread and expensive problem persists in an industry that has been forming and firing clay, shale and coal gangue for generations.

The answer does not lie in the quality of the machinery. It lies in what is being fed into it.

Cause One: Unscreened Feed Delivers a Heavy Load of Fines

In the conventional two-stage flowsheet, material leaving the primary crusher passes directly into the secondary crusher without any screening step in between. As a result, the secondary machine receives a feed that already contains a large proportion of fine particles. Those fines are the hidden thief of throughput.

Inside the crushing chamber, fines fill the space around the lumps of material and around the hammers themselves. Whether the hammer is striking a lump or a lump is being thrown against the breaker plate, that cloud of fine material acts as a cushion. It absorbs and distributes impact energy, softens the blow, and measurably reduces the reduction ratio actually achieved per pass. The machine keeps consuming power at its rated rate while delivering far less size reduction than its nameplate specification promised.

Cause Two: Screen Oversize Returns to the Wrong Machine

The second major contributor is the circulating load. After screening, the coarse oversize is typically returned to the secondary crusher for another pass. But this return stream is mostly in the 2 to 20 mm range, while the secondary crusher was designed around the product curve of the primary stage. Its geometry, hammer mass and chamber volume are all optimized for breaking considerably larger lumps.

Using such a machine to reduce material below 20 mm is a straightforward waste of installed energy. Plant operators describe it vividly as cracking walnuts with an eight-pound sledgehammer. The crushing action degrades, the screening action degrades with it, and the plant ends up with the classic combination of high specific energy consumption and low tonnage.

What the Chamber Actually Sees

Three Practical Symptoms to Check on Site

• Rated motor current is drawn while output per hour stays well below specification.
• Screen undersize shows a persistent oversize fraction that keeps recirculating.
• Hammer and breaker plate wear accelerates without any corresponding gain in throughput.

The Real Diagnosis: A Flawed Flowsheet, Not a Flawed Machine

Both causes point to the same conclusion. The guilty party is the entry of fines into the secondary crushing stage, and once a plant is built on this arrangement, that entry is unavoidable. The problem is therefore structural. It is the process flowsheet itself that carries the defect, not the operator, not the maintenance team and not the crusher supplier's workmanship.

Recognizing this distinction matters, because it changes the conversation from replacing equipment to correcting a layout. Plants that treat the symptom buy a bigger crusher and reproduce the same losses at a larger scale. Plants that treat the cause re-sequence the flowsheet, keep fines out of the impact chamber, and recover capacity they already paid for.

The next step is to identify exactly where the flaw originated, and then to select between the two proven remedies: front-loading the screening duty, or adding a third crushing stage.