Double-Tower Sheet Metal Storage and Retrieval system

The Herochu double-tower sheet metal storage and retrieval system represents a deliberate balance between capital cost and operational throughput. Unlike twin independent towers that require separate hoists, controls, and safety zones, the Dual-Tower series operates a single hoist that services both towers sequentially. This configuration cuts equipment investment by roughly one-third while preserving most of the retrieval speed advantages of a dual-hoist layout. The system is part of Herochu’s broader automated vertical storage system family, sharing the same steel, powder coating, screw assembly, and 8-layer design.

Architecture of the Dual-Tower System

Two sheet metal storage towers stand side by side with a shared central column that carries the lifting mechanism. The front tower (closer to the operator or AGV) has its lower levels connected to a loading station and a lifting mechanism, forming a buffer storage zone for material pallets. The rear tower contains only standard shelves. In operation, the hoist picks a pallet from the rear tower, transfers it to an empty buffer slot in the front tower, and then immediately retrieves the next requested pallet from the front tower’s buffer. This overlapping movement reduces wait time compared to a single-tower system.

The dual-tower design also enables pallet exchange: a full pallet of incoming material can be loaded into the front tower’s buffer while the hoist is busy retrieving from the rear tower. The loading station incorporates a conveyor with roller or belt drive, compatible with manual forklift delivery or automated guided vehicles. The lifting mechanism in the buffer zone is a scissor lift or a vertical chain lift, depending on the weight class (3-ton or 5-ton per layer).

Key Differentiators from Two Separate Single Towers

When comparing the Herochu double-tower sheet metal storage series to two independent single-tower systems, three advantages stand out:

1. Cost efficiency – One hoist, one control cabinet, one safety system. The dual-tower costs about 65% of two separate towers.

2. Space utilization – The shared column reduces the total width by 400mm compared to two independent towers with a service aisle between them.

3. Energy consumption – One hoist motor draws peak power of 4.5 kW, whereas two separate towers would draw 9 kW during simultaneous operation.

The double-tower configuration does have a throughput limitation: when both towers are heavily requested, the single hoist becomes a bottleneck. Herochu addresses this by optimizing the buffer zone size. With three buffer slots in the front tower, the system can queue the next three most requested sheet types, reducing hoist travel to the rear tower by up to 60% in high-frequency retrieval patterns.

Sheet Separation and Double-Sheet Detection

The dual-tower system incorporates identical material handling intelligence as the single-tower RRW models. At the loading station, sheet separation mechanisms use compressed air nozzles directed at the edge of the sheet stack. For materials thinner than 1mm, a magnetic separator lifts the top sheet slightly before the air knife inserts. Double-sheet detection employs a pair of ultrasonic sensors that measure the gap between the lifted sheet and the stack. If the gap indicates two sheets, the system releases the lift and retries with higher air pressure. After three failed attempts, an alarm notifies the operator.

These functions are particularly valuable for automated wareshops where the storage system feeds a laser cutting machine directly. A double-sheet event that reaches the laser head can cause nozzle collision, lens contamination, or sheet jamming. Herochu’s detection accuracy exceeds 99.5% for steel sheets from 0.5mm to 12mm thickness.

Powder Coating and Corrosion Protection

All steel components in the dual-tower system receive a powder-coated finish that meets ASTM D7803 standards for corrosion resistance. The coating process includes:

• Abrasive blasting to Sa 2.5 cleanliness

• Zinc-rich primer application (60–80 microns)

• Polyester powder topcoat (80–100 microns)

• Thermal curing at 200°C for 20 minutes

The result is a surface that resists salt spray for over 1000 hours in accelerated testing. This level of corrosion protection is essential for sheet metal storage in uninsulated warehouses or coastal regions. The anti-rust property extends to the tray contact surfaces, preventing the transfer of rust to stored sheets. ESD protection is achieved by adding conductive carbon black to the topcoat, achieving surface resistivity below 10^6 ohms.

Screw Assembly and Reconfigurability

Like all Herochu storage systems, the double-tower model assembles using screws rather than welding. This choice supports several practical benefits:

• Simplified shipping – Components pack into standard 20-foot or 40-foot containers without welded subassemblies exceeding 3 meters.

• Easy modification – Shelf heights can be changed by moving the support brackets to different pre-drilled holes.

• Relocation – The entire system can be disassembled, moved, and reassembled in a new facility within two weeks.

The screw assembly uses grade 10.9 bolts for structural joints and self-tapping screws for cladding panels. A torque wrench is required for critical connections; Herochu provides a calibrated torque tool with each system. The assembly manual includes 3D step-by-step illustrations accessible via a QR code on each major component.

Integration with Production Equipment

The double-tower sheet metal storage and retrieval system is designed to operate standalone or as part of a fully automated wareshop. Standard interfaces include:

• Digital I/O (24V DC) for simple start/stop and status signals

• Serial RS-232 for basic command sets

• Ethernet TCP/IP with REST API for full control and monitoring

Herochu has pre-built drivers for popular laser cutting brands such as Trumpf, Bystronic, Amada, and Mazak. When a cutting job is programmed, the laser’s nesting software sends a sheet size and material code to the storage system. The dual-tower retrieves the correct sheet and delivers it to the loading station, where a transfer carriage or robot picks it and loads the laser bed. The entire process is trackable through an optional MES connector.

Case Example: High-Mix Low-Volume Fabrication

A job shop in northern Italy producing customized enclosures for medical devices installed a Herochu dual-tower system. Their material mix included 10 different aluminum alloys, 8 steel grades, and 3 stainless steel finishes, with sheet sizes varying from 1000×500mm to 4000×1500mm. Previously, they stored sheets on floor racks organized by material, requiring operators to walk up to 200 meters per retrieval. The dual-tower system, configured with 8 layers per tower and 3-ton capacity per layer, consolidated all materials into a 4-meter-wide footprint.

After six months of operation, average retrieval time dropped from 8 minutes to 1.2 minutes. The integrated double-sheet detection prevented three potential laser collisions, saving an estimated €15,000 in repair costs. The powder-coated surfaces eliminated the previous problem of white rust on aluminum sheets stored near a wet grinding area. The shop reported a 14-month payback period.

Conclusion

Herochu’s double-tower sheet metal storage and retrieval system offers an economical entry into automated vertical storage for shops that cannot justify two independent towers. With a single hoist, buffer zone loading station, sheet separation, double-sheet detection, and 5-ton per layer capacity, the Dual-Tower series delivers high density and moderate throughput. The screw assembly, powder-coated steel, and CE/ISO certifications ensure long-term reliability and compliance. For fabricators seeking automated sheet metal material storage without overspending, the Herochu dual-tower is a practical choice.