Roll Forming Machine Drive Transmission Methods

The choice of transmission system significantly impacts machine performance, flexibility, maintenance, and cost. The main types are:

1. Line Shaft (or Common Shaft) Drive:

   • Mechanism: A single, long rotating shaft runs the length of the machine, powered by one main motor (often via a gearbox or reducer). Power is transferred from this main shaft to each forming stand via mechanical components.

   • Power Transmission Components:

     • Bevel Gears: Most common. A bevel gear on the main shaft meshes with a mating bevel gear on the top or bottom roll shaft of each stand. Provides a precise 90-degree power transfer.

     • Spur Gears: Less common for direct stand drive from a line shaft, but sometimes used within gearboxes or for specific power take-offs.

     • Chain & Sprockets: Used historically or on simpler/older machines. Less precise due to backlash and wear/stretch. Requires frequent tensioning.

     • Timing Belts & Pulleys: Offer quieter operation and some backlash reduction compared to chains, but still susceptible to wear and stretch over time. Used on lighter-duty machines.

   • Control: Speed is controlled solely by the main motor. The gear ratio between the main shaft and each stand’s roll shafts is fixed, determining the rotational speed of the rolls at that stand relative to the main shaft. Synchronization is inherently mechanical.

   • Advantages: Simpler overall control (one motor), potentially lower initial cost for simpler machines, inherent mechanical synchronization between stands.

   • Disadvantages: Complex mechanical assembly, significant power losses due to friction in multiple gear meshes, difficult to access stands for maintenance (shafts/gears in the way), virtually impossible to change the speed ratio between stands without physically changing gears (major downtime), limited flexibility, high inertia, noisy.

2. Individual (Stand-Alone) Drive:

   • Mechanism: Each forming stand (or sometimes pairs of stands) has its own dedicated motor and drive system. There is no connecting mechanical shaft running the length of the machine.

   • Power Transmission Components:

     • Gearboxes: Essential for each driven stand.

       • Helical Gear Reducers: Most common. Provide speed reduction and high torque transmission from the motor to the roll shafts. Mounted directly on the stand frame.

       • Planetary Gear Reducers: Used for very high torque requirements or space constraints. Highly efficient and robust.

       • Right-Angle Gearboxes: Used when the motor is mounted perpendicularly to the roll shafts (common configuration). Incorporate bevel gears.

     • Universal Joints (Cardan Shafts) or Flexible Couplings: Connect the gearbox output shaft(s) to the top and/or bottom roll shafts within the stand, accommodating slight misalignments.

     • Direct Motor Mount: Motors are often flange-mounted directly onto the input of the stand’s gearbox.

   • Control: Each motor is controlled independently by a sophisticated electronic control system (PLC + Drives). Speed and position synchronization between stands is achieved electronically (“Electronic Line Shaft” or “Virtual Master” control). Requires high-precision feedback (encoders) on each driven axis and fast communication networks (EtherCAT, PROFINET IRT, etc.).

   • Advantages: Maximum flexibility (speed ratios between stands easily changed via software), excellent synchronization possible, simpler mechanical access for roll changes and maintenance (no central shaft), higher overall efficiency (shorter power paths, less friction), lower inertia, quieter operation, ideal for complex profiles and quick changeovers. Allows features like adaptive forming and servo-driven flying cutoff.

   • Disadvantages: Higher initial cost (multiple motors, drives, complex control system), requires sophisticated programming and tuning for optimal synchronization.

3. Split Shaft Drive (Hybrid Approach):

   • Mechanism: A compromise between Line Shaft and Individual Drive. The machine is divided into several sections (e.g., breakdown section, intermediate section, finisher section). Each section has its own main motor driving a short line shaft within that section. Power is transferred from this section shaft to the stands within that section using bevel gears (most common).

   • Power Transmission Components: Combines elements of both Line Shaft (short shafts, bevel gears within a section) and Individual Drive (multiple section motors). Gearboxes connect the section motor to the section shaft.

   • Control: Speed of each section motor is controlled independently. Synchronization within a section is mechanical (via the short line shaft). Synchronization between sections is electronic.

   • Advantages: More flexible than a full line shaft (different section speeds possible), potentially lower cost than full individual drive, retains some mechanical simplicity/synchronization within sections. Easier access than a full line shaft.

   • Disadvantages: Less flexible than full individual drive (speed ratios within a section are fixed), still has mechanical complexity and power losses within each section, access can still be obstructed by section shafts.

Key Factors Influencing Drive Choice:

• Profile Complexity & Material: Complex profiles/thicker/higher-strength materials benefit from individual drive flexibility and control.

• Production Volume & Changeover Frequency: High mix/quick changeover favors individual drive. Very high volume dedicated lines might use Line/Split shaft.

• Required Precision & Speed: High precision and speed demand individual drive with advanced control.

• Budget: Line shaft generally has lower initial hardware cost (but potentially higher long-term maintenance/operational costs). Individual drive has higher upfront cost.

• Integration Needs: Integration with servo flying cutoffs or other ancillary equipment is seamless with individual drives.

• Maintenance Philosophy: Individual drives offer easier access.

Current Industry Trend:

Individual Drives with Electronic Synchronization are increasingly the standard, especially for new machines requiring flexibility, high precision, quick changeovers, and integration with advanced features. Line shaft drives are now mostly found on older machines or very simple, dedicated, low-cost applications. Split shaft remains a viable option for specific use cases balancing cost and some flexibility.