Troubleshooting Tip: Holes and Busted Edges

Holes and busted edges are probably the leading cause of breaks on a paper machine. The good news is the cause is usually easy to find. Most machines have hole detectors and busted edge detectors, so the problems are automatically diagnosed. Machines that don't have these detectors must rely on dry end operators to detect the defects. Busted edges are generally easy to spot since the edges are exposed and are easily examined while on the reel. Holes on the other hand are hidden inside the reel and must be detected when the reel is being unwound at the winder. More often the holes are detected when the winder has a break which can be quite messy.

So once the issue is found, how do you find the cause of the problem? For busted edges the usual suspect is the trim squirt. The trim squirts are high pressure nozzles that are used to trim the edges off the sheet as it goes to the press section. The nozzles can get partially plugged reducing the focus of the nozzle. The nozzles can also be misaligned. Due to the position of the nozzles some buildup can form on the nozzles or nozzle apparatus. Other causes of busted edges are light edges, slice bleeds, and edge deckles. Check the weight profile to see if the edges are light and adjust accordingly. Slice bleeds can be adjusted to bring the edges up and edge deckles can be reset.

Holes can be caused by a number of things. They can be caused by material falling into the sheet, such as part of a tail that wasn't cleaned up during the previous break or a leaking shower that drips onto the sheet. The can also be caused by flaws in machine clothing or flaws in rolls on the machine. Issues with pressure screens can also cause holes. To determine the cause of the hole first examine the hole. If the hole is tear drop shaped it is likely caused by material falling into the sheet. Also see if there is some foreign material embedded in the sheet. If the hole is irregular in shape and does not appear to be caused by falling material see if there is a pattern. Does the hole occur only in one position, is there a consistent distance between holes? These are the questions that should be asked. If there is a consistency in distance, measure the distance and determine if the hole is from a roll defect or machine clothing defect. The culprit should be easily found from there unless there are multiple rolls or clothing runs that have the same circumference. If there is no pattern to the holes and it has been determined that there is no debris falling into the sheet, then further investigation is required. Stock samples should be taken at various points in the approach system to see if there are any upsets. The headbox should also be checked to see if there is anything inside that could be causing the holes.

Holes and busted edges are bad, but the causes are generally easy to find. If the cause can't be found immediately patches can be placed on holes until the next outage. However, if the problem must be solved be sure to have a checklist of areas that must be checked. Also coordinate with the maintenance crews to determine what work can be done during the downtime to shorten or delay the next scheduled downtime.