Printing Knowledge Share: Printing Unit — The Heart and Soul of Offset Presses
Hello! Welcome to Printm.cn's knowledge sharing. Today, we will delve into the core component of offset presses—the printing unit. Understanding the working principles and structure of the printing unit is key to evaluating equipment condition and improving print quality.
1. What is a Printing Unit?
The printing unit is the core module of an offset press that performs the actual printing function. Multi-color offset presses typically consist of multiple identical printing units connected in series, with each unit responsible for applying a specific color of ink (following the CMYK or spot color system). The precision of a single unit directly determines the stability of the entire machine and the quality of its output.
2. The "Five Key Components" of a Printing Unit
A standard offset printing unit primarily consists of the following five key parts working in coordination:
Cylinder Assembly — The Skeleton of the Unit
Plate Cylinder: Carries the exposed and developed printing plate.
Blanket Cylinder: Transfers the ink image from the plate cylinder to the substrate via its rubber blanket. This is why offset printing is called "indirect printing," as it protects the plate and adapts to various substrates.
Impression Cylinder: Provides back pressure and works with the blanket cylinder to clearly imprint the image onto paper or other materials.
Relationship: The diameters of the three cylinders must maintain an exact proportional ratio (usually 1:1:1) to ensure smooth transfer and dot reproduction.
Inking System — The "Blood" Circulation System of the Unit
Function: Transfers ink evenly and quantitatively from the ink fountain to the plate.
Process: Ink Fountain → Ink Fountain Roller → Oscillating Roller → Distributor Roller → Damping Roller → Form Roller → Plate.
Key Point: The axial movement of the oscillating roller is crucial for evenly distributing ink. The number and pressure adjustment of the form rollers directly affect the uniformity of ink on the plate.
Dampening System — The "Balance Master" of the Unit
Function: Forms a uniform water film in non-image areas to prevent ink adhesion using the "oil-water repulsion" principle.
Composition: Mainly consists of the water fountain, water fountain roller, oscillating water roller, distributor water roller, and form water roller.
Core Challenge: Achieving
ink-water balance. Too much water causes ink emulsification and paper deformation; too little water leads to scumming (dirty printing).
Paper Feeding and Transfer System — The "Traffic Hub" of the Unit
Function: Precisely feeds, positions, and transfers the substrate (e.g., paper) after impression.
Key Components: Transfer Grippers and Cylinder Grippers. They must operate accurately and transfer smoothly, as any slight deviation can cause misregistration.
Control System — The Brain and Nerves of the Unit
Function: Modern high-end offset presses (e.g., Heidelberg, Manroland) are equipped with sophisticated CNC systems in their printing units.
Control Content: Remote adjustment of ink key settings, cylinder pressure, ink-water balance, etc. Systems like CPC/CP Tronic (Heidelberg) or OPC (Manroland) enable data-driven, repeatable, and precise control.
3. How to Evaluate the Printing Unit When Purchasing Second-hand Equipment?
As professional second-hand equipment advisors, we recommend focusing on the following during inspection:
Cylinder Condition: Check for scratches, dents, or rust on the cylinder surface. Observe the wear on the cylinder bearers, which is a key indicator of machine usage intensity and maintenance.
Bearings and Gears: Listen for abnormal noises during operation and check for gearbox oil leaks. Excessive clearance in cylinder bearings directly affects registration accuracy.
Inking and Dampening Roller Performance: Check for aging, pressure marks, or deformation of rubber rollers, and ensure the pressure adjustment mechanisms are responsive.
Gripper Structure: Check for even wear and consistent force of the grippers, which is critical for precise paper transfer and avoiding ghosting.
Control System Functionality: Test all control buttons, motors, and displays for proper operation, and ensure remote adjustment functions are responsive and accurate.
Conclusion
The printing unit is the culmination of offset printing technology, and its precision, stability, and controllability directly determine the final product quality. Whether considering new machines or high-quality second-hand equipment like those offered on our platform, a deep understanding of the printing unit will help you make wiser investment decisions.
