Assembly

• Inspection of printing blanket gauge, format and rails. Visual inspection of printing blanket surface and back. The same applies to U-sheets and foils. This avoids the need for short-term lift dismantling and changes.
• Measurement of the printing blanket lift outside the machine. This reduces surprises.
• Blanket should be wider than U-sheet/foil. This reduces the ingress of washing agent and ink between cylinder and underlay(s) and between underlay(s) and printing blanket.
• Make sure that dirt particles do not get into/under the printing blanket lift. This means careful cleaning of the cylinder surface, tensioning channel, tensioning tool and assembly environment before lifting the printing blanket.
• The format edge formation may be reduced using a format sheet assembly.

• For blankets with formatting, always assemble the straight printing blanket edge to the A or B side. Formatting reduces the formation of gaps in adjacent printing blankets and the resulting paper folds.
• Overlapping printing blanket assembly with adjacent printing blankets: After tension has been applied to the printing blanket for the first time, the overlap must be positioned edge-to-edge using a "bone folder". The tension between the printing blankets also reduces the formation of gaps.
• When using screws in printing blanket tensioning rails, the screws in the centre of the tensioning rail should be tightened first. The least bending of the rail in the centre of the tensioning rail.
• Apply tension to the blanket up to the torque value specified by the machine manufacturer – see below.
• Do not forget to "roll in" after assembling the printing blanket. "Rolling in" reduces the need for retensioning and doubling.
• In printing blanket tensioning systems with simultaneous tensioning at both ends of the blanket, the blanket should be "rolled in" in both directions of rotation. This procedure reduces retensioning and doubling.
• Measuring printing blanket lift after "rolling in" and retensioning allows you to reduce surprises.
• Data on the printing blanket assembly with date, printing blanket type, U-sheet/foil gauge, lift height, assembly force, reason for dismantling should be carefully recorded.
  Inspect and record printing blanket lift heights at regular intervals.
  Such measurement data should be recorded and evaluated on a regular basis. It can be very useful when evaluating a printing blanket.

For rotatable wheels, shafts and screws, the torque – given in Nm – is the product of the magnitude of the applied force and the perpendicular from the axis of rotation to the direction of the force.

Depending on the printing blanket tensioning system, tension of 1.5 to 130 Nm is applied to printing blankets. In the process, a printing blanket is elongated (stretched) between approx. 1% and 2%.

Low torque values, e.g. 1.5 Nm, are appropriate in the case of clamping screws on tensioning rails. High torque values, e.g. 125 Nm, apply to tensioning spindles in large-format offset machines.

The torque specified by the machine manufacturer should always be observed using a torque spanner. Torque spanners that are not adjustable and only allow the prescribed torque value have proven their worth.

Calibrate the torque spanner on a regular basis and keep the tensioning elements clean and in good condition.

The purpose of applying tension to the printing blanket using torque spanners is to ensure reproducible printing blanket tension levels in all printing units and by all operating forces.

Source © 2010 ContiTech AG, ALL RIGHTS RESERVED