A "shoe in" for printing papers: in 20 years, shoe presses have grown from an experimental technology to the press of choice for new and rebuilt paper machines.

Today, shoe presses are dominating new markets, such as printing paper machines.

Shoe presses have become extremely popular since they were first introduced 20 years ago and today there are more than 400 working worldwide. However, it was not until the mid-1990s that these revolutionary presses were first used for the manufacture of printing papers. Today, almost every new paper machine contains a shoe press while conventional presses are used only for limited applications.

LEARNING CURVE

The first printing grade shoe presses were used in rebuilds, mainly for woodfree grades. Design speeds of 4000 ft/min (1200 m/min) were typical in the beginning and were 50% higher than traditional presses. Machine suppliers had to learn how to control the temperatures and nip profiles in the rolls to maintain good belt life. Belt suppliers had to learn to improve belts, making them more and more durable.

As mills and suppliers have gained operating experience with these presses, additional improvements have gradually been introduced. Today, Norske Skog's Golbey PM 2 in France has reached speeds up to 6330 ft/min (1900 m/min), which was unheard of only a few years ago. The press used to be the paper machine's "bottleneck," but today it works on a par with other machine sections.

The shoe press is a revolutionary development related to of a number of products designed to improve pressing, including:

Ceramic center rolls: Ceramic center rolls were introduced in the late 1980s to replace granite rolls, which had been in use for more than a century. Ceramic covered rolls were the only choice for shoe presses because of high nip loads (deflection compensated rolls) and high roll cover wear. Today, ceramic covers such as Metso Paper's "Valrok" are used in almost every open draw press.

Belts with void volumes: The second big change came with the introduction of grooved belts to meet the demands of higher speeds and the need for good moisture profiles. Without the durability of grooved belts, shoe press technology would not have achieved today's results.

Closed draw press: Shoe presses have made the closed draw press possible. For example, Metso Paper installed a closed draw press on Willamette's Hawesville (Kentucky) PM 2, which started up in 1998. This machine has two shoe presses, four felts and had first year production of 2.81 short tons per inch of machine width per day (tons/in/day). Today, it is number two in the world in total productivity on woodfree grades.

TransBelt: For many years, papermakers have asked for closed draws. One step in that direction is the TransBelt from Albany International, a type of extended center roll cover that makes it possible to have a pick-up transfer with suction roll to the dryer section. Metso Paper has used the TransBelt technology with its SymBelt shoe press technology and dosed draws to create the OptiPress concept.

SHOE PRESS (R)EVOLUTION

There are many examples of successful rebuilds using shoe press technology, including:

SP Newsprint PM 2, the first high speed rebuild for newsprint

Willamette Hawesville PM 2, the first closed draw press with two nips

Stora-Enso Port Hawkesbury PM 2, the first new SC machine with shoe press

UPM-Kymmene Blandin PM 6, major production increases on an LWC line

Weyerhaeuser Columbus PM 1, machine is setting production records

Willamette Johnsonburg PM 5, the first single-nip shoe press

Weyerhaeuser Dryden PM 2, basic shoe press rebuild to PM from late 1980s

SP Newsprint's PM 2, the first rebuild of a high-speed newsprint machine in the world: PM 2 was installed by Valmet in 1989 and the rebuilt machine was started up in July 1998. Before the rebuild, the machine had leveled off at speeds of about 4500 ft/min, and efficiency had decreased to about 85%-86%. At that time the speed was high compared to other newsprint machines, but the mill wanted to make improvements.

The rebuild included a number of improvements designed to improve mill operations. The machine rebuild, including the shoe press, allowed substantial speed-up potential. However, since the technology was new and the machine was originally designed for just 4500 ft/min, it took two years to isolate and eliminate bottlenecks to higher speeds. Also, papermakers must be much more disciplined when operating the machine at higher speeds. Today, the mill has reached speeds close to 5500 ft/min, and efficiency for the first half of 2001 was more than 89%.

UPM-Kymmene, Blandin PM 6. Blandin Paper, Grand Rapids, Minnesota. The mill rebuilt its wet end a few years ago to address base sheet quality issues by installing a new dilution controlled SymFlo D headbox and a SpeedFormer gap former. Quality targets were met but there was no clear speed up or production increase because of press, dryer and off-line coater runnability issues. In a more recent rebuild, the old four-nip press was refitted with a new SymBelt shoe press nip in the 3rd press, the 4th press was replaced with dryers, and the small bottom rolls in the dryer section were replaced with larger ones. The main goals were to improve press and dryer runnability, increase press dryness and eliminate sheet defects entering the coater. The mill has since increased machine speed about 10%, and production efficiency has increased by 30%.

Willamette, Hawesville PM2: This is a new machine started up in June 1998 using the OptiPress concept with closed draw to the dryers and the SymSizer. In the machine's first year, production was reportedly the best ever recorded for uncoated freesheet--2.8 tons/in/day. Today, the mill is operating at around 4000 to 4300 ft/min, which is well above the dimensioning point of the machine.

Willamette, Johnsonburg PM 5: Willamette had seen the benefits of the shoe press and closed draws with its Hawesville PM 2 and was willing to take a second step. PM 2 has two nips with the shoe press and four felts; but Willamette decided to have only one shoe nip and two felts without any open draws on its Johnsonburg PM 5, a relatively new machine built in 1994. Design speed of the fine paper machine was originally 3500 ft/min. In the rebuild, the speed target was set at 4000 ft/min with improved sheet two-sidedness. This target was addressed by a SymFormer MB rebuild, press rebuild to OptiPress I, and some improvements to the dryer section.

Immediately after start-up, the mill identified major production and speed opportunities. The machine was much less speed sensitive than before. The former and press could run over a week without breaks. Once again, however, the dryer section limited runnability. This was addressed by using a new generation of HiRun blow boxes in the first dryer group.

Today, PM 5 has reached a production speed of 4000 ft/min and sheet smoothness is on target.

The addition of a shoe press can produce exceptional speed and efficiency improvements. However, it can also affect other aspects of the papermaking process. Mills must take the time to analyze and identify future potential bottlenecks and fix them at the same time the press is rebuilt. A thorough survey to analyze the paper machine for future production and speed targets significantly helps identify the corrective actions needed for a successful rebuild.

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Juha Kivimaa is senior product manager, paper machines for Morse Paper, Charlotte, North Carolina, USA. He can be reached by phone at [phone], or by email at [e-mail]