Incorrect measurements pose problems for manufacturers and customers alike – and unfortunately this is an ongoing problem. Here are some of the things to bear in mind when measuring a conveyor belt or power transmission belt – including why exact measurements are essential when ordering a new belt.
Geometric length is a must – but inward length isn’t
Before placing an order for a new belt, it’s vital to take correct measurements. The manufacturer will make the belt according to the information you supply, and cannot be held responsible if the belt doesn’t fit on your conveyor due to incorrect measurements.
For light conveyor belts and transmission belts, the most important measurement is the geometric length. In effect, this is the neutral layer, which is the layer between the top and inner surfaces and the running side. In fact, it’s not so much a proper layer, as that part of the belt that’s neither tensioned nor compressed when the unstretched belt is bent.
You don’t need to provide the manufacturer with the inward measurements of your belt, as unlike the geometric length, these are not used when making your new belt.
If the measurements of your belt are calculated by a CAD system from a blueprint, you still have to check that the results are accurate. The geometric length can be measured when the not-yet-joined belt is spread out but not stretched.
- Measure a short endless belt by marking a starting point on the belt, rolling it across a plain table, and using a tape measure on the table beside the belt.
- A long unstretched belt can be measured in sections. Simply add up the measurements to get the full length of the belt. Use a thin pencil lead when marking the starting position and the sections of the belt.
Important: don’t use an old or used belt when taking measurements for a new one, as structural elongation will have made the old belt longer than it was on delivery.
Calibrated steel tape measures offer maximum accuracy
When measuring your conveyor belt or power transmission belt application with a tape measure, be sure to use one that is completely stable and of the highest quality. Ordinary tape measures may prove too imprecise, which can lead to incorrect results and margins. Calibrated steel tape measures tend to be the most exact, and these are the measuring tools used by Habasit.
Regarding dimensional tolerances, there is an ISO standard for conveyor belts. Unfortunately, this has proved much too broad and general, so Habasit has developed a system more in line with our products. You can contact your local Habasit office if you want to know more about the dimensional tolerances of our belts.
Calculating the length of your conveyor belt or power transmission belt
If you’re taking measurements on your conveyor to get an estimate of the length of your conveyor belt, remember to let the tape measure run along the exact course of the intended belt, over the rolls or pulleys. If you have a typical transmission set up, with two pulleys, and know both the diameters and the center distance, it’s possible to calculate the length of your conveyor belt that way. These are the parameters used by Habasit’s Selecalc dimensioning system. Visit Selecalc and register with your company email address.
It’s also important to take your tensioning stations into account, so that your conveyor belt or transmission belt can be properly fitted once delivered. Ideally, you need some belt sag when the tensioning station is positioned where the center distances are at their shortest. That said, you must be able to tension the belt according to the calculated initial tension (including a safety margin). Most conveyor belts with a polyester fabric should be tensioned initially to become at least 0.3% longer when stretched out. For conveyor belts with a polyamide fabric, the initial tension should be at least 0.5% longer. With power transmission belts, you need to enter the correct application dimensions and distances in Selecalc in order to get the correct belt length.
The risks and hazards of incorrectly measured belts
The most obvious problems arise when a conveyor belt or power transmission belt is longer, shorter, wider or narrower than intended: it may not be able to perform properly, and can potentially damage the equipment. The belt may slip when it is too long and not tensioned enough, or create very high shaft loads if it is too short. The shorter the belt and the fixed center distance, the more important it is to have the correct length and a narrow tolerance: +/- 5 mm accuracy on a 1000 mm long belt corresponds to +/- 0.5 % in tension, which may result in the application malfunctioning.
A conveyor belt needs some transversal tracking space, since a belt that is too wide may not be able to operate properly. Its edges can get frayed and it may end up damaged.
To get the correct measurements, please visit the Habasit website, download the engineering guides (“Engineering Guide Fabric Conveyor Belts”, “Engineering Guide Power Transmission Belts”) and follow the guidelines:
Temperature and humidity also affect the performance of your belts
The materials used in all synthetic belts, while durable and robust, are affected by factors such as the ambient temperature and humidity. You need to inform Habasit about any abnormal conditions before ordering belts. No matter how excellent the belt is, you know more about the conditions under which it will be used than we do. So this has to be discussed with our engineers before you determine the dimensions of the belt.
Do you have any questions about our conveyor belts or power transmission belts? Please contact us. You can also find plenty of other articles about our products and solutions here on the Habasit Expert Blog.