User's Manual for the Laminate Curl Calculator

Application

To find out the effects of the differential tensions going into a laminating nip - depending on the thickness and modulus of the two webs, labelled 1 and 2. The curl induced by temperature and humidity effects is shown in the Temperature Humidity Curl Calculator. An overview of curl and its minimisation when laminating are given in The Web Handling Handbook by Roisum, Walker and Jones in Chapter 12.

Strain

A web will stretch under tension. In the LLC the tension is expressed in N or lbs. If you use N/m divide N by metres or for pli divide by in. The % Strain (the scientific name for degree of stretching) gets larger for:

• Higher tension (for a given width)
• Smaller width (for a given tension)
• Thinner web
• Lower modulus

Curl

If the two %Strain are not the same then the laminate will tend to curl once it is out of the nip. The curl can be calculated in terms of its radius. The calculation is surprisingly complex and sometimes it takes a while to figure out why changing one of the inputs (such as modulus) produces the calculated result. This is because the curl depends not only on the differential stretch but also on the ability of the laminate as a whole to be bent - which depends on the combined modulus and thickness of the two webs.

A positive value of curl means that it curls with Laminate1 inside and a negative value means that it curls with Laminate2 on the inside.

A smaller radius means a tighter curl which may mean trouble further into production - when the roll is cut into sheets or even when the roll is in storage as that stretch likes to even itself out. Note that in these calculations, any curl with a radius >9999mm is shown as "0", meaning there is no curl.

The ideal is to get zero curl by ensuring that the two stretches are identical, which in practice means reducing the relative tension for the web with the lowest combination of ModulusxThickness.

More complex cases

There is a very powerful curl calculator within TopWeb from RheoLogic which allows multiple laminates and which takes into account thermal and hygroscopic curl plus the additional curl imparted via distortion of the rubber roller.

How To Use

Choose the units of measure as either Metric or US. As you enter the key values you get instant feedback on the key outputs in the blue boxes. Some users prefer to use Text entry (it's more precise). Others tend to prefer Slider entry (especially on smaller devices). Feel free to choose whichever is the most useful for any occasion.

While you can choose either Metric or US units, you cannot specify which type of units within those systems are used. The most common usage is fixed. For example, thickness will given in µm (0.000,001 meters) and mils (0.001 inches). Pay special attention to make sure that your input/output values are in the units specified or convert to/from as needed.