# Mounting positions & gas spring sizing continued: Closing force calculation

Written by: Camloc Motion Control | Published: 10/18 Similarly, the force required to close the lid (F2) can be calculated using the formula:

Closing Force F2 = Number of Springs x Spring Force F1 x Radius of Force / Lid Length Figure Seven: Closing Force F2

Worked Example

Calculation of the opening and closing forces can be achieved using the values below:

Opening Force (F1)

F1 = (50 x 9.81) x 0.8 / 0.25 x 2
F1 = 784.8N

Closing Force (F2)

F2 = 2 x 784.8 x 0.25 / 1.2
F2 = 327N Figure Eight: Opening and Closing Forces

Changing the Moving Mounting Point

What happens to the forces when the gas spring mounting position is altered? Assuming the above example is the ‘mid-point’ and the radius of the gas spring force is moved either side of this by 50mm:

Moving the moving mounting point 50mm towards the hinge (i.e. LS becomes 0.2m):

F1 = 981N (+197N increase)
F2 = 327N (no change)

Moving it 50mm further away from the hinge (i.e. LS becomes 0.3m)

F1 = 523.2N (-261N decrease)
F2 = 523.2 N (+196N increase) Figure Nine: Changing the Moving Mounting Point

The calculations show that the closer towards the hinge the moving mounting point gets, the higher the opening force required. Whereas, moving it further away the opening force reduces, but the closing force increases.

Changing the Centre of Gravity

If the centre of gravity moves nearer or further from the hinge, this will also affect the opening and closing forces. Figure Ten: Changing the Centre of Gravity

Moving the centre of gravity 0.2m towards the hinge (i.e. XG becomes 0.6m)

F1 = 588N (-196N decrease)
F2 = 245N (-82N decrease)

Moving it further away from the hinge (i.e. XG becomes 1.0m)

F1 = 981N (+197N increase)
F2 = 408N (+81N increase)