Calender Speed Changes Result in Undesirable Gum Wall Thickness Changes

When the calender is running there are forces generated that try to separate the rolls. These separating forces are proportional to calender speed, although the relationship is not linear. The hardness of the rubber stock and bank temperature determines the magnitude of separating forces. The thickness of the gum wall being calendered also affects the separating force, with thinner gum walls generating larger separating forces.

These separating forces are large, as much as 160,000 to 300,000 lbs., at each actuator. The calender frame literally stretches from these forces. When the forces vary, the amount of stretch varies, resulting in the roll gap varying and this causes the gum wall gauge to vary.

From the previous post, it is obvious that speed changes should be avoided to the extent practical. A speed reduction from 50 ypm (yards per minute) to 10 ypm can result in a gauge decrease of 2 mils (.002”). Likewise a speed increase of 40 ypm from 10 or 20 ypm to 50 or 60 ypm can result in a gauge increase of 2 mils. Different calendars have different degrees of frame stiffness so the magnitude of the gauge change for a given speed change will vary accordingly.

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