High speed paper drying

A paper drying process for controlling the amount of shrinkage permitted in a paper web in the drying section to preserve stretchability and improve curl resistance, comprising:

• partially drying said web on a first group of drying cylinders, said web supported on a first supporting fabric and held on to said fabric by pressure differential means exerting forces normal to the major surfaces of said web as the web travels on its suporting fabric from dryer cylinder to cylinder and about said cylinders;
• continuing drying said web on a second group of drying cylinders, said web supported on a second supporting fabric and held onto said fabric by pressure differential means as detailed in the above step,
• said second group of drying cylinders operating at a rotational peripheral velocity less than that of said first group of drying cylinders, said speed being selected to attain desired shrinkage and stiffness;
• and
• transferring said web from said first fabric of said first group of drying cylinders to said second fabric of said second group of drying cylinders by employing pressure differential means acting on said web normal to its major surfaces to effect transfer without subjecting said web to peeling or velocity stresses.

A paper machine for controlling the amount of shrinkage permitted in a paper web in a dryer section to balance stretchability and stiffness, comprising:

• a first group of dryer cylinders for partially drying said web wrapped by a first dryer fabric for receiving said web and transporting the web in supporting contact about said first group of dryer cylinders, said first fabric subject to pressure differential means for holding said web onto its supporting fabric by employing forces normal to the major web surfaces sufficient to overcome velocity-related stresses on all portions of the web;
• a second group of dryer cylinders for continuing the drying of said web, operating at a lower peripheral speed than said first group of dryer cylinders, said second group having a second dryer fabric means and pressure differential holding means similar in function and operation to said first group;
• and
• a transfer means for transferring said web from said first fabric of said first group of drying cylinders to said second fabric of said second group of drying cylinders, said transfer means comprising pressure differential means for acting on said web normal to its major surfaces to effect transfer without subjecting said web to peeling or velocity stresses.

A process for optimizing paper machine dryer section performance, including reducing power requirements, for a paper machine wherein a paper web is transported on a supporting means from a last press nip through at least a first portion of a series of heated drying cylinders and said web is held to said supporting means by employing, in part, vacuum box means for exerting pressure differential forces normal to the major web surfaces sufficient to overcome velocity-related stresses on all portions of the web during said transporting, said optimizing steps, comprising:

• measuring the wet web strength of said paper web at intervals along the machine at the local web temperature and dryness at each interval;
• calculating velocity stress for a desired machine speed at said intervals along the machine at the web dryness found at each interval;
• comparing the velocity stress value at each interval along the machine with the corresponding measured wet web strength;
• and
• shutting down all vacuum boxes in the paper machine beyond that point in the drying process where velocity stress is less than the measured strength, wherein the paper web is thus strong enough through increased dryness, to be self-supporting and independent of machine velocity stresses.