Calculate average nip pressure from roll load, face length and measured nip width, or the load for a target pressure, with line load and residence time.

Length along the roll axis that carries this load.

In the direction of travel; use full footprint width, not half-width.

Residence time
Blank omits residence time. Assumes the web travels through the measured nip without slip.

Nip Load (Line Load) Formula

The following example problem outlines the steps and information needed to calculate the nip load (more precisely, the nip line load: force per unit roll length).

NL = P ร— NW ร— t

Variables:

  • NL is the nip line load (force per unit roll length), e.g., N/mm (equivalently kN/m)
  • P is the average/adjusted nip pressure, e.g., N/mmยฒ (or Pa, bar, psi)
  • NW is the nip width ratio (dimensionless), defined for this example as (nip/contact width) รท (material thickness)
  • t is the material thickness (a length), e.g., mm, cm, m, in

To calculate the nip line load, multiply the average/adjusted nip pressure by the nip width, where nip width = (nip width ratio) ร— (material thickness).

How to Calculate Nip Load?

The following steps outline how to calculate the nip load (line load).

  1. Determine the nip width ratio (NW).
  2. Measure the material thickness (t) and determine/estimate the average/adjusted nip pressure (P).
  3. Use the formula NL = P ยท NW ยท t.
  4. To check this line load above, first calculate measured contact width C = NW ร— t. Choose the measured-contact model, enter C and the actual loaded roll-face length W, then solve for total load using P. The reported line load F/W can be compared with NL.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

nip width ratio (NW) = 2

material thickness (t) = 0.5 mm

average/adjusted nip pressure (P) = 1 N/mmยฒ

NL = P ยท NW ยท t = 1 ยท 2 ยท 0.5 = 1 N/mm

Here C = 2 ร— 0.5 mm = 1 mm. For an example loaded face length W = 1,000 mm, an average pressure of 1 N/mmยฒ (1 MPa) gives F = NL ร— W = 1,000 N. The measured-contact model above then reports the same line load of 1 N/mm.