Cross strips in wide-belt sanding – identify and correct causes

Cross striations – also known as ratter marks – are fine, regular lines that run across the workpiece in a direction perpendicular to the feed direction. On the raw part, they are often barely visible and are only discovered when it is painted, oiled or stained. Then the part is a waste product, and the error is costly.

The trick: Cross-stripes have many possible causes – from the sanding belt to the contact roller to the transport belt. The good news: With two or three simple tests, you can pinpoint the cause in just a few minutes, before you have to start replacing parts. That’s exactly what this guide is for.

A first clue lies in the spacing of the strips: uniform, sharply defined distances usually indicate an underlying cause (band or roller), irregular distances indicate vibration or too low band tension.

The first step: Is it the tape or the machine?

You should answer this question first – it will save you hours. Three simple tests are enough:

1. Insert a new disc. If the strips disappear, it was due to the tape (usually the adhesive or welding seam). If they remain, the cause lies in the machine. This one test already separates half of all cases.
2. Thread test with a marker. Thickly color the tape seam with a wax or grease pen and let the workpiece pass through it. If the cross strips appear in the color of the seam, the seam is the culprit – it is too thick or the wrong type of seam for your application.
3. Change the feed speed. Let the same part pass through once faster, once slower. If the strips move apart or together, they come from the surrounding conveyor belt. If the distance remains the same, they come from a machine part – usually the contact roller.

With several grinding units: Let the heads run one after the other individually until you know which one is causing the problem. Only then is it worth taking a close look at this particular unit.

The most common causes – and what helps against them

Sliver tape and tape seam. By far the most common cause. A seam that is too thick, poorly glued, or unsuitable for the application will tear at every turn. Fix it: Use brand tape with a clean seam, the appropriate type of seam for your material, hang the tape up when not in use and store it dry.

Band voltage. Insufficient voltage causes the tape to flutter – the strips then become irregular. Adjust the voltage to the manufacturer's specifications for the respective tape type.

Contact roller. A damaged, one-sided worn-out or inaccurate roller produces uniform strips that are independent of the feed speed. Even hardened or incorrectly selected rubber (hardness, grooves) leaves marks. Remedy: Inspect the roller, re-rubberize or replace it if worn – with the hardness suitable for your sanding pattern.

Pressure bars and pressure plates. The pressure bar is intended to smooth out fine seam and roller marks. If the slats or the pressure slat band are worn or uneven, this no longer works – especially with a sanding belt that is already slightly worn out, the strips then break again. Solution: Check and replace the slats or the graphite band.

Pressing lips and grinding shoes. Slipping or unevenly applied pressure pads or shoes distribute the pressure unevenly across the width – this often shows as streaks on just one side. Remedy: Check the lips and pads, and replace them if they wear out.

Transport belt. A worn, dirty or uneven conveyor belt transfers its irregularities to the workpiece. Clean the belt and the rollers underneath and check for wear.

Oscillation. If the band oscillation is erratic or is incorrectly adjusted, cross-tracks also result. Control the oscillation movement and adjustment.

Excessive pressure, too fast of a feed speed. Excess material removal in one pass and too high grinding pressure cause streaks. Reduce the amount of material removed per pass, adjust feed speed and pressure to match material and grain size.

When wear parts are the solution

If the diagnosis indicates a worn component, the rest is easy – provided that you get the right part quickly. STEIZL is the place to go for that. At Heesemann machines, we are at the forefront of parts supply; we manufacture many wear parts ourselves, and much of it is available from stock:

• Pressure plate belts – for every machine manufacturer
• Abrasive shoes and steel plates – also for Bütfering and Costa; often a pattern or sketch is sufficient for that.
• Contact rollers and re-rubberization in the hardness suitable for your grinding pattern
• Pressing lips, continuous and segmented
• Abrasive belts and abrasives of all kinds

We can also supply additional manufacturer-specific parts upon request – or we can help you find the right source.

One call, one contact, response within 24 hours. As an independent, directly reachable source of supply, we ensure that your machine will quickly start running again cleanly.

Do you want to first narrow down the problem yourself? Our new self-help platform for fault diagnosis guides you step by step to the likely cause. If you don't get further, we are just a message away.

Outlook: Many older Heesemann machines still run flawlessly mechanically – only their control has been discontinued and is no longer available. For exactly these cases, we are currently preparing a manufacturer-independent control rebuild: a modern control that will allow your proven machine to continue running instead of being replaced. If you have an old machine with control problems, please contact us – we would be happy to add you to the interested party list.