Marble Scale

Why is weighing blocks at a quarry so demanding?

A marble block is perhaps the toughest load a scale will ever meet. It is heavy, irregular in shape and lowered onto the platform by loader, forklift or crane. As it is set down, a block often touches the deck with one corner first, then tips to settle on its full face. Those few seconds are the hardest loading the scale faces on any given day.

The environment is not easy either. A quarry brings dust, water and slurry from block cutting, large temperature swings during the day and constant heavy-plant traffic. The ground under the scale is usually not a factory floor but a foundation prepared on the quarry site. That is why, on a marble scale, both the platform frame and the load cells are chosen on different logic from a floor scale working on a level warehouse floor.

Construction: single-chassis steel platform and 30-tonne compression cells

The MK platform is a single-chassis steel frame of heavy section. It is specified as resistant to overload and impact; the aim is that when a block lands hard on one corner, the platform suffers no permanent deformation and passes the force to the cells undistorted.

Under the platform are four steel compression load cells, each with a capacity of 30 tonnes. A compression cell takes the load directly along its axis from above; this layout is widely chosen where large loads arrive with impact. Keeping cell capacity above the scale capacity leaves a safety margin against the sudden force peak at impact. For example, the four cells together are rated at 120 tonnes; when the scale’s weighing capacity is set well below that, the force reaching a single cell as a block strikes one corner also stays within the margin.

In the example configuration in the technical document, the platform measures 200 × 300 cm with a height of 50 cm. Since the MK series can be built to the required size and capacity, however, the platform is dimensioned to the quarry’s standard block size and the fork or bucket width of the machine used.

Weighing instead of estimating: working out block weight

Many quarries still calculate block weight from dimensions. For example, a block measuring 2.0 × 1.5 × 1.2 m has a volume of 3.6 m³; taking a density of about 2.7 t/m³, it comes to roughly 9.7 tonnes. That calculation is reasonable for a neatly cut prism, but real blocks have broken corners, sloping faces and cracks or voids inside. Density also varies with the type of stone.

A few centimetres of error in the measurements and a small deviation in density can add up to hundreds of kilograms per block. Where blocks are sold by weight or haulage is paid by the tonne, that difference means lost revenue or a dispute. When the block is weighed on the scale, measurement replaces calculation and each block’s weight is documented on a ticket.

Accumulation and dispatch records

The indicator’s accumulation feature stores successive weighings in memory. When each block to be loaded onto a truck is weighed separately, the indicator gives both the single block weight and the running total for that shipment. The total load the vehicle will carry is therefore known before the truck is even loaded, and any risk of overloading is spotted in advance.

Each weighing can be printed as a ticket or label over the RS 232 output and records passed to a computer. Weight information stuck on the block or painted onto it makes the block easier to trace from quarry to factory. The indicator comes with an LED or LCD display; because it can work from its internal battery as well as from 220 V, it can also be used on sites with limited power supply.