Direct Drive vs Belt Drive vs Belt and Gearbox Drive for Heavy Plate 4K No.4 Polishing Machines

When a buyer sees a motor connected directly to a working roll, the design can appear compact and advanced. A belt-and-gearbox arrangement may look more complicated and may even be mistaken for a lower-cost solution. For hot-rolled thick-plate polishing, however, appearance does not determine performance. The important questions are how the drive handles torque, impact, uneven plate surfaces and continuous heavy-duty operation.

LEBON has used and evaluated three working-roll drive arrangements: direct drive, belt drive, and belt drive with a dedicated heavy-duty gearbox. For our hot-rolled thick-plate 4K polishing machines, we standardized the third arrangement after practical production experience showed that it was better suited to fluctuating grinding loads.

What 4K Polishing Means in This Application

In this article, 4K refers to a grinding and polishing process used to improve the surface of hot-rolled stainless steel plates. It is not related to screen resolution. Hot-rolled thick plates may have scale, surface waviness and thickness variation, so the working roll does not see a perfectly stable load. When a high point on the plate enters the grinding zone, the drive system must absorb a rapid increase in resistance without repeated shutdowns or damage to the motor and inverter.

The Three Working Roll Drive Systems

Direct Drive

In a direct-drive arrangement, the motor is coupled directly to the working roll. The structure is compact, the transmission path is short and mechanical transmission losses can be low. It can be suitable when the grinding load is light and stable and the motor is correctly sized for the application.

The limitation appears when the load changes sharply. Impact from an uneven thick plate is transmitted directly to the motor and coupling. In the configurations tested by LEBON for heavy-plate production, this increased the risk of motor overload, inverter trips and production interruption. Meeting the peak-load requirement may also require a larger motor, which can increase installed power and energy use.

Figure 1  Direct-drive arrangement with the motor coupled to the working-roll system.

Belt Drive

A belt drive separates the motor from the working roll and can absorb part of the shock load. Belts are also familiar maintenance items and are relatively easy to inspect and replace. This arrangement gives more cushioning than a rigid direct connection.

A conventional belt drive does not, by itself, provide the torque multiplication needed for demanding thick-plate grinding. Under a heavy or unstable load, belt slip and speed fluctuation can occur. For this reason, LEBON no longer uses a belt-only arrangement as the standard working-roll drive for continuous heavy-duty 4K polishing of hot-rolled thick plates.

Figure 2  Belt-only drive arrangement.

Belt Drive with a Dedicated Gearbox

In the selected LEBON design, the motor transmits power through multiple belts to a dedicated heavy-duty gearbox. The gearbox reduces speed and increases the torque delivered to the working roll, while the belt stage provides useful shock absorption. This is not a planetary gearbox selected for high positioning precision; it is a purpose-built reduction system for heavy grinding loads.

Based on LEBON internal operating comparisons with our earlier configurations, this arrangement approximately doubled available working-roll torque and reduced power consumption by about one third under the evaluated production conditions. Actual results depend on plate grade, thickness, flatness, abrasive sequence, grinding pressure and line settings. The design also reduced overload events and helped extend the working life of the motor and inverter.

Figure 3  LEBON belt drive with a dedicated gearbox for hot-rolled thick-plate 4K polishing.

Technical Comparison

Why Direct Drive Is Not Automatically More Advanced

A direct connection is not inherently good or bad. Its suitability depends on the load profile, motor sizing, coupling design and protection strategy. Likewise, the presence of belts does not automatically indicate cost cutting. In a heavy-duty polishing machine, a more appropriate engineering question is: how does the drive behave when the plate is uneven and the grinding resistance suddenly rises?

For LEBON, the answer came from production rather than appearance. We first used direct drive and belt-only systems, observed their behavior as processing volume increased, and then developed a dedicated reduction arrangement. The current design reflects the requirements of hot-rolled thick plates: higher low-speed torque, better tolerance of impact loading, fewer overload interruptions and stable operation over long shifts.

How to Select a Working Roll Drive

Before selecting or comparing a polishing machine, buyers should provide the actual production range and evaluate the following points:

· Plate material, thickness, width, length and typical flatness;

· Incoming surface condition and the amount of material to be removed;

· Target finish and abrasive sequence;

· Required throughput and continuous operating hours;

· Peak grinding pressure and expected load variation;

· Motor, inverter and overload-protection strategy;

· Maintenance access, belt inspection and gearbox service requirements.

Frequently Asked Questions

Is direct drive more efficient than a belt drive

A direct drive can reduce mechanical transmission losses, but total production efficiency also depends on whether the system can maintain stable grinding under peak loads. Repeated overload trips, reduced grinding pressure or an oversized motor can offset the benefit of a shorter transmission path.

Does a belt drive mean the machine is lower quality

No. Belt transmission can provide shock absorption and serviceability. Its suitability depends on belt sizing, pulley arrangement, tension control and whether additional torque multiplication is required.

Why add a gearbox for hot rolled thick plates

A reduction gearbox converts motor speed into higher working-roll torque. This helps the machine handle changing grinding resistance caused by plate waviness and heavy stock removal.

Why does LEBON use an AC motor with a VFD

LEBON uses AC variable-frequency motors because they provide adjustable speed, reliable operation in industrial polishing environments and practical maintenance. DC motors generally demand more maintenance and stricter operating conditions for this application.

Can one drive design suit every polishing machine

No. Thin cold-rolled sheets, coils and hot-rolled thick plates create different load conditions. The drive system should be selected around the actual material range, surface condition, output target and duty cycle.

Conclusion

The best drive system is not the one that looks most familiar or copies a well-known machine. It is the one that performs reliably under the real production load. For hot-rolled thick-plate 4K polishing, LEBON uses a belt drive with a dedicated heavy-duty gearbox because our practical operating experience showed better torque delivery, load tolerance and long-term stability than the earlier configurations we tested.

To discuss a 4K polishing solution for your plate thickness, width, surface condition and output requirement, contact LEBON MACHINERY or submit your production specifications through our website.