Spinner hanger tunnel blast machine for cast iron cookware at Mecánicos Unidos, Colombia

Castings leave the foundry with residual sand and scale, and they need an even surface before finishing. A 12-inch skillet and a grain mill body go through the same line, hanging on racks, in high volume.
MU already knew the process: the tunnel was sized with its own production data. It wanted more capacity per cycle and a process that did not depend on the operator's hand. It also works with G40 angular steel grit, which cleans faster but wears the machine much more than steel shot.

A stop-and-go tunnel with rotating hooks:

• 14 hooks rated for up to 1,000 kg travel along a 32 m overhead conveyor and enter the cabinet in pairs.
• Inside, each hook rotates on its axis and stops at three positions in front of the blast wheels, so the blast reaches the whole part with no shadow areas.
• Parts can be up to 1.3 m in diameter and 1.7 m high.

The conveyor indexes step by step: loading and unloading take place with the conveyor stopped, which is safer for the operator. The track rises at the loading zone, so no pit was needed.

Angular grit cuts harder than shot, and it also wears everything it hits. That is why the machine is protected at every impact point:

• Double cabinet lining: a welded manganese steel base with bolted high-chrome cast iron plates on top, replaceable without cutting.
• Double-wall blast wheels: manganese steel housing and high-chrome internal liners with labyrinth joints. Blades are high-chrome and replaceable.
• Labyrinth seal between the motor coupling and each wheel housing, to keep the abrasive in.
• Bucket elevator in manganese steel plate and screw conveyors with hardened boron steel flights.

Each part family has its own recipe on the screen. When it is selected, the machine sets automatically:

• the speed of each blast wheel, with a variable frequency drive;
• the abrasive load: each abrasive valve has an electric actuator that opens or closes it according to its wheel motor's amperage; in the validation it reached the set value in about 5 seconds;
• the blast direction: each wheel's control cage moves to the position set in the recipe;
• the hook rotation speed.

Each blast wheel has a vibration sensor with an alert on the screen, and the machine has communication for remote assistance. The screen also runs the hot-spot test wheel by wheel, without taking anything apart.

In a foundry, the molding sand that comes in with the parts ends up mixed with the abrasive and wears it down. The cleaning system has three stages:

• Separator with an abrasive curtain and air wash, with sensors and an alarm on the screen.
• Magnetic separator that removes sand from the mix.
• Recirculation valve that keeps cleaning the mix while the wheels are not blasting.

The magnetic separator was tested at our plant with a half-sand, half-grit mix: after the third pass, the sand left with the abrasive was negligible.

Dust is captured by a CART 36 C cartridge dust collector with 672 m² of filter area.

Besides interlocked doors, the machine uses a «blind spot» logic. To start a cycle, the operator has to press a button placed where the whole cabinet interior is visible, which makes them walk around the machine and check that nobody is inside.

• 43 gross tons a day. That was the plant's throughput in August 2025, according to Andrés Mejía Cardona, owner and CEO of MU.
• The machine's validation record states that the blasting quality exceeded the customer's expectations.
• In its first months at MU's plant, the overhead conveyor ran without incidents.