How to Choose a Block Making Machine: Six Numbers First

Most buyers open a price list first. That is the wrong end of the job. Before you ask how to choose a block making machine, write down six numbers about your own site: output per shift, available power, largest product and pallet size, floor area, cement budget, and the people you can put on the line. The machine follows your numbers, not the other way round. A model that looks cheap on paper turns expensive when the yard, the power supply or the crew cannot keep up with it.

We build block machines and we quote them every day. The fastest quotations come from buyers who send six clean numbers. In this guide we walk through the six numbers in the order that matters, then show how our model ladder from QT4-15 to QST1800 maps onto them.

1. Number one: output per shift, in the block you actually sell

Output is never one number. A machine rated at 165,000 to 220,000 standard bricks over 8 hours makes far fewer 390 x 190 x 190 mm hollow blocks. The mould decides the figure. On the same frame and the same cycle, our QST1800 runs 27,000 to 36,000 hollow blocks per shift, or 99,000 to 132,000 Dutch pavers at 200 x 100 x 60 mm. So start from your best selling product, not from a headline brick count.

Convert your daily target into blocks per cycle. A cycle of 15 to 25 seconds gives 140 to 240 cycles an hour on paper, and no line holds that for a full shift, because loading, pallet return and short stops eat into it. Compare your honest target against the shift output the maker publishes for each model, not against the ideal cycle count.

2. Number two: available power and starting current

Power is the number buyers get wrong most often. Our ladder starts at 22.9 kW on the QT4-15 and climbs to 104 kW on the QST1800. In practice a QST8-15 line needs roughly 45 kW of supply and a QST6-15 about 30 kW, because the machine never runs alone: mixer, conveyor, stacker and compressor all pull from the same panel.

An induction motor draws about 5 to 7 times its rated current for a moment at start. With a 15 to 20 second cycle, the vibration motors start and stop more than 140 times an hour. Size the transformer and the generator for that inrush, not for the average load. If the local grid is weak, ask about a soft starter or a servo drive before you sign.

3. Number three: product size, pallet and hydraulic pressure

Write down the largest block or paver you will ever sell, then add its pallet. Pallet sizes on our machines run from 850 x 560 x 20 mm on the QT4-15 up to 1,400 x 1,400 x 30 mm on the QST1800. A big pallet on a light frame is not a big machine. Check the hydraulic pressure too. The QT4-15, QT5-15 and QST6-15 work at 25 MPa, while the QST8-15 and the larger servo models use 31.5 MPa.

Higher pressure plus a stronger vibration force lets you reach test strength with less cement. Moulding at 31.5 MPa and 95 kN or 150 kN of vibration force holds density at a lower cement content than a press running at 25 MPa and 58 kN. For dense blocks on a small frame, look for at least 20 to 40 kN of vibration force and 16 to 20 MPa of pressure.

4. Numbers four and five: floor space, curing and raw materials

A block plant is a yard as much as it is a machine. Pallet handling, curing and stock need far more area than the machine itself. One of our typical QST8-15 lines stands in about 10 x 4 m of shed, yet the pallets still have to sit somewhere for days while the concrete hydrates.

Strength comes from hydration over the days after stripping, and it depends on temperature and moisture, not on the press. Work out how many pallets you need and how many square metres of covered curing space that means, before you pick a machine. Water to cement ratio sits between 0.35 and 0.45, so your water supply and your batching control matter as much as the mould.

Then price your cement. A 390 x 190 x 190 mm hollow block takes about 1.6 kg of binder at a 200 kg per m3 mix, and about 2.1 kg at 260 kg per m3. Fly ash can replace 15 to 30 percent of the cement, which is normal practice, but fly ash mixes gain strength slowly and must be wet cured. Trapped air is the quiet cost: every 1 percent of air left in the mix costs about 5 percent of compressive strength, and plants often add about 30 kg more cement per m3 to cover it.

5. Number six: people, training and shift cover

A typical QST8-15 line runs with 4 to 6 people per shift. Add a pallet-free stacking system and the stacking job drops to one operator. That is the machine side of labour. The other side is skill: somebody has to read the mix, watch the cycle and stop the line when the blocks start to tear.

Count the people you can really keep on site, a mechanic and a shift cover included. Ask what training is in the offer and how commissioning is handled. A machine with a plain PLC screen and clear fault alarms shortens the learning curve, and servo models cut manual handling further.

6. Five mistakes that get expensive later

Most of the damage is done before the machine lands, at the moment the numbers are written down or skipped.

• Sorting by price first. The cheapest frame usually carries the smallest pallet and the lowest pressure, so it cannot make the product you sell.
• Leaving no headroom in the power supply. Motors draw 5 to 7 times rated current at start, and a weak supply shows up later as burnt contactors, not as a clean trip.
• Reading pallet size and ignoring hydraulic pressure. A large pallet at 25 MPa is not the same machine as the same pallet at 31.5 MPa.
• Forgetting the curing yard. Pallets, cover and turning space are part of the plant cost, and they are often the real bottleneck.
• Treating cement as a negotiating point. Adding water to improve workability raises the cement bill and lowers strength at the same time.

7. Send all six numbers in one message

When you ask for a quotation, put the six numbers in one message: target output in your main product, available power in kW, largest product and pallet, floor area for machine and curing, cement and aggregate plan, and the number of operators per shift. Add your voltage, your destination and a sample of your raw materials. With those lines on the table, an engineer can size the machine, the mould and the power panel in one pass.

Send half of them and you get a range of prices that cannot be compared. Send all six and you get a plan you can build. That is the whole point of the six numbers: they turn a catalogue into a decision.