Normal Force
Mechanical resistance models define the proportional relationship between the normal force and the dry sliding resistance of two surfaces. In textile finishing, coulomb friction governs the behavior of raw fibers against metal guides before the application of liquid lubricants. This relationship determines the force required to draw yarn through processing machinery.
Surface Contact
Dry contact surfaces generate resistance that is independent of the contact area and sliding velocity under standard loads. Synthetic fibers like polyester and nylon exhibit high initial resistance when they are dry. When yarn passes over solid ceramic or metal guides, this resistance generates tension that must be carefully managed to prevent fiber breakage.
Friction coefficients must be measured under controlled laboratory conditions to verify consistency.
Tension Calculation
Winding tension is calculated using equations that rely on the dry friction coefficient of the yarn. High friction raises the temperature at the contact points, which can melt or weaken synthetic polymers. Adjusting the contact angle or guide material helps maintain the yarn tension within safe limits during winding.
Finish Limitation
Frictional behavior changes when mills apply liquid finishes to the yarn. The transition to hydrodynamic or boundary lubrication renders the dry friction model inaccurate because viscous forces begin to dominate. Operators must monitor the finish application rate to prevent this shift from causing tension spikes.
