Service & Optimization for Offset Printing Machines

One of the most critical factors in a folding machine is the belt system. Belts ensure that printed products are transported cleanly and aligned precisely—the fundamental requirement for a continuous, trouble-free process at high production speeds. Transport must be absolutely secure, free of smudging, and without wrinkles. For maximum cost-effectiveness, it is also crucial that belts achieve a long service life and perform their function reliably over time.

Selecting the Right Belts

Depending on the machine type, mechanical load, and operating time, various transport belts and flat belts are used. Several technical factors play a decisive role in selecting the optimal belt:

Surface Properties

The surface requires sufficient grip (coefficient of friction) to convey the paper precisely and avoid slippage during acceleration. At the same time, the coating must not mark the paper or damage its surface. Ideally, the belts should not absorb printing ink and should be resistant to adhesive residues and silicone.

Antistatic Properties

At high speeds of up to 16 m/s, friction generates significant static charges on the paper. To safely dissipate these charges to the machine frame, belts must often be antistatic or conductive. This prevents paper sheets from sticking together and eliminates the risk of dangerous sparking within the machine.

Elasticity and Stability

The inner core (the tensile member) of the belt determines its mechanical stability. By using materials such as polyamide, polyester, or aramid, belts maintain their length even under the high tension of the tensioning cylinders, which is essential for folding accuracy. Simultaneously, the belt must remain flexible enough to handle small pulley diameters without high energy loss due to flexing work. Smooth operation also prevents the belts from fluttering.

Joining Methods (End Connections)

In post-press processing, two types of joints are primarily used: the bonded wedge joint and the adhesive-free finger joint. In both cases, a homogeneous thickness at the joint is critical. Any thickening causes an impact on the paper or leads to the belt "jumping" when contacting rollers, which severely disrupts precise operation.

Influence of Paper Quality

The paper being processed is a decisive factor for belt durability. The rougher the surface or the higher the recycled fiber content, the more abrasive the material acts on the belts. This leads to faster wear of the coating. For such requirements, specially optimized, abrasion-resistant belt types should be selected.

Details

Also available:

Read more: Belt Types for Folding Machine Services – Applicat...