Static nosebar or live noserollers? What you need to know
Nosebars (also known as knife edges) are particularly critical in the food industry, where they’re used to transport goods over small transfers at the infeed and discharge end of conveyors. Noserollers, also called live roller assemblies, are also used for the same reason.
Our team is often asked for help by operators experiencing problems with conveyors using nosebars or noserollers. They often start by telling us the trouble is due to the belt, and they need a new and stronger one. Although we’re always pleased to discuss the vast range of belts we can offer, very often it’s not the belt that’s causing the difficulties, but other parts of the conveyor.
While we’re always glad to assist, I want to use this blog to look at the most common issues and share some key concepts to help you avoid problems in the first place. Let’s look at the most frequent challenges:
We changed from a live roller assembly to a static nosebar, and now the belt is slipping on the drive and stalling. Why is it happening? What can we do?
Live roller assemblies consist of one or a series of small-diameter rollers mounted on a common shaft. They need more maintenance than static nosebars because they use bearings or composite bearing materials, which are subject to wear and contamination. This is why operators often decide to swap out their live roller assembly for a stainless steel static nosebar, which requires no maintenance. Static nosebars can also offer a smaller radius (3 to 4 mm) compared to 10 mm+ on a live roller assembly.
It looks like a perfect solution – but when the nosebar is introduced, the friction between the belt and the static nosebar increases the belt running tension, and the drive roller has to be able to accommodate this. If the steel drum of the drive roller on the conveyor has no cover or lagging, the belt is likely to slip and lose drive or traction. The result is a complete loss of drive, or sporadic drive loss, which results in the belt juddering or floating from side to side on the drive roller, and becoming damaged.
Our advice in these cases is to increase the friction between the drive roller and the belt by putting a rubber or other friction cover on the roller. If this is not enough, the next solution is to increase the arc of contact between the belt and the drive roller. For example, by increasing this from 180 to 270 degrees, drive roller efficiency is significantly improved, and the result is that the conveyor in this improved state can accommodate much higher running tensions, and the problems are solved.
How to increase the arc of contact? Introduce a snubbing roller and engineer it onto the conveyor. You may have to change the diameter of the drive roller to ensure that the snub roller can function without bending or deflecting. This is because the snub roller diameter is often much smaller than the drive roller diameter, as this is required to achieve maximum belt lap over the drive roller. Remember: drive efficiency is governed by the number of degrees the belt travels around the drive roller, NOT by the size of the drive roller.
It’s clear that the “easy fix” of swapping to a static nosebar can become a significant engineering problem. In some cases, when engineers want to replace live roller assemblies at both ends of the belt, the compromise solution is to change just one end to a static nosebar. In other cases, operators decide to go back to their original live roller assembly and accept the extra maintenance.
Our conveyor lost efficiency, was slipping on the drive, and getting edge damage. We replaced the belt, but the problem persists. What’s going on?
In these cases, the first thing we look at is whether the conveyor has a static nosebar. If so, the next thing to examine is the drive roller. In the majority of cases the drive roller lagging has become work-hardened over time. Although friction covers start out with a high coefficient of friction, after 12 to 24 months (this lifetime can be even shorter if the application is very demanding with high tensions, a high number of stop start cycles, or high temperatures) they become very hard, friction reduces, efficiency falls, and the result is a spinning drive and belt slip. The solution: simply re-lag the drive roller.
Our belt is shrinking: it’s tighter at the edges and distorted in the center, with slack spots where the product doesn’t lie flat. What should we do?
In our experience, this usually arises where there is a static nosebar with a sharp back edge. Constant scraping by this edge damages the surface of the back of the belt, which permits ingress of product into the fabric and leads to tightening of the fibers, and this results in belt shrinkage. The problem starts at the edges because this is where there’s most debris from the product. The solution: replace the damaged belt and put a smooth radius on the back of the nosebar. Most engineering machine shops can do this.
We had two static nosebars, but the drive roller was slipping, so we replaced both nosebars with a live roller assembly to reduce the belt tension. Now we’re having tracking problems. What can we do?
In most cases, if done in line with the above recommendations, replacing a static nosebar at the infeed end should not prove much of a problem. But difficulties can arise with installing a live roller assembly at the outfeed, because this can reduce the efficiency of the tracking unit if it is located under the conveyor on the return belt path. The distance between the tracking unit and the live roller assembly is now too short. The solution: place the tracking unit further from the live roller assembly. Alternatively, put the live roller assembly at the outfeed, and on the top / conveying path place the tracking unit before the live roller assembly positioned “under the belt” (if this option is selected the tracking roller must be suitably lagged to increase friction with the belt underside and positioned to give as much lap/contact with the belt as possible).
Need help with conveyor design?
Experiencing difficulties with your conveyor? Feel free to contact me at any time, or download our Engineering Guide for fabric belts.
very good article and advise…Appreciate the insight. Will remember these points when dealing with my folks here in the States.