Slurring refers to a distortion in printed images caused by specific conditions during an offset printing press run.

This distortion makes dots or type appear shifted, either laterally or circumferentially, depending on the direction of the slur.

Each type indicates distinct issues that require targeted solutions.

Slurring in the Commercial Printing Market

Most slurring goes unnoticed by the average viewer, as it often requires specialized instruments or printed patches for detection.

However, in some cases, such as high-quality commercial printing jobs, slurring can be visible to the naked eye.

Causes of Circumferential Slurring

Blanket Torque

A loose blanket alters the press’s circumference, leading to speed discrepancies and paper slippage.

Ensure the blanket is torqued according to manufacturer specifications to avoid this issue.

Web Tension

In web presses, incorrect tension before or after the printing unit can cause slurring.

Adjust the tension at the roll stand, infeed unit, or successive nip points to match the press’s feed rate.

Register Shift

In multi-color jobs, the colors must align perfectly.

Persistent slurring may indicate an issue with the press’s automatic adjustments trying to match a moving registration target.

Roller Bearings

Worn bearings in inking or water rollers can cause sliding, leading to erratic slur patterns.

Check for this issue using a heat gun to measure bearing temperatures during operation.

Worn Gears

Severely worn press gears can result in circumferential slurring.

Though rare, it’s a possibility to consider after ruling out other causes.

Causes of Lateral Slurring

Lateral slurring occurs when distortions move across the press’s width.

Common causes include:

Paper Movement

Misaligned paper can shift during printing.

On sheetfed presses, ensure grippers are clean and functional.

In web presses, misalignment due to web movement or automatic adjustments can also cause slurring.

Paper Quality

Poor-quality paper, especially in web printing, can lead to tension issues. Uneven paper or batches with inconsistent properties can cause slurring. Switching to a better-quality batch often resolves the problem.

Register Shift

Similar to circumferential slurring, lateral shifts occur due to misaligned registration adjustments. Tweaking the automatic register system can help mitigate this.

Form Oscillation

To prevent ghosting, some plate forms oscillate laterally. Incorrect settings against the printing plate or rollers can cause slurring. Adjust these settings carefully to resolve the issue.

Detecting Slurring

Offset printers rely on specialized color bars with detection patches to identify slurring early.

These patches include:

Hourglass Shapes: Identify circumferential slurring.

Bowtie Shapes: Detect lateral slurring.

These tools enable press operators to spot and address slurring before it becomes noticeable to end users.