Forming section beam changeout case study and mechanical audit

A mill in the southern US requested assistance from Valmet with the change out of two fourdrinier cross tie beams. Valmet held an initial meeting with the mill and contractor to review the job and procedures. During a visit to the machine, equipment condition told us that initial removal procedure needed to be reconsidered. It was decided to fasten the two cross ties together on the back side of the machine. The front side was already fastened together with the front mounting bracket.

Fourdrinier beam change out

Work began by cutting the fourdrinier saveall next to the saveall trough. When making this first cut, we had to follow with a welder to tack weld the top hat back to the top skin of the saveall pan. This was needed because we were cutting out the original weld from the top hat to the top skin of this pan and we didn't want them to separate. After this first cut, we made a second cut cross machine. We also removed a section of saveall to allow access to the top of the second cross tie beam. Two lift lugs were welded to the front side and one to the back side, allowing the contractor to use come-alongs to lower the cross ties to a cart sitting on the floor of the fourdrinier pit.

Other issues discovered

As in many cases with older formers, once we were hip-deep in the project we discovered other issues. In this case, the saveall pan on the fourdrinier was severely deteriorated. In the process of tack welding the top hat back to the top skin section of the saveall pan, the top hat would crumble. The original pans and cladded cross ties were made of 304L SS. These were rusting and deteriorating from within. Discussion with the mill resulted in a temporary correction; making C channels from 14ga. to cover the deteriorated area of the top hat. This would help to contain any foreign matter that would come out of the saveall and find its way to the fourdrinier wire. We also noted the top of the saveall trough to be in the same condition. We made a 14ga. angle sheet metal piece and covered this area as well.

New beams installed

After welding lift lugs to the cross ties to allow lifting them back into the machine with come-alongs, we were able to install the two new beams into the machine. Once they were secured into place, all bolts were installed. We finished up by tack welding the second cross tie angle support back to the saveall trough, covering the access hole in the saveall pan and bending the cover piece slightly for a good, accessible fit. The cover was welded into place and all welds were polished to prevent further rusting. A new angle sheet metal shield was then installed on the first cross tie because the original piece could not be salvaged.

Recommendation

Valmet personnel recommended that the mill look at future replacement of the saveall pans on the fourdriner as they were corroding, basically crumbling apart. It was just a matter of time before they would drop pieces onto the fourdrinier wire causing a costly premature replacement.

Forming section mechanical audit

Maintaining good forming section frame condition is important to provide for safe, reliable and high-quality operation of the paper machine. A key input for good maintenance is a thorough mechanical audit, which provides the condition of all the key components of the forming section.

Aging Fourdriniers with corroded framework and out dated designs contribute to inefficiency, poor sheet quality, safety concerns and wire and sheet breaks. Additionally, many older formers are running at speeds well above their original design on grades that are more critical than originally intended.

There are several reasons to conduct a mechanical audit of the forming section:

• Safety - A damaged frame structure or roll connections may present a serious risk.
• Reliability - Rusted connections may cause unplanned shutdowns or additional damage due to a roll falling on the wire.
• Quality - Structural integrity of the frames is important for the good operation of the forming section.
• Improvements - Preliminary check of structures provides a good base for planning improvements.

The audit includes a visual analysis consisting of:

• Frame condition - Plate thickness measurement when required, Audition of cantilevering beams
• Frame fastening to base plate
• Roll fastenings
• Cleanliness of the machine
• Guide, stretcher and doctor wear and general condition

If the wire has been removed during the shutdown, additionally:

• Dewatering elements condition
• Roll surfaces

Benefits

Benefits of the forming section audit include:

• Reduces risk of damage in the frame structure
• Reduces need for unplanned shutdowns
• Ensures high-quality operation
• Provides a foundation for future improvements

Forming section improvement package

A former improvement package from Valmet includes replacement of the couch cantilever beam, removable blocks and other framework elements, upgrades to roll removal systems, savealls and crossbeams, breast roll lowering equipment, table elements, mist collectors, and the incorporation of modern designs for guides, stretchers and wire changing equipment. These and other new former improvement products will boost machine runnability and efficiency to help your operation meet the demands of today's challenging marketplace.

Most formers supplied prior to 1980 were made from low-grade stainless steel instead of the 316 or 317 low carbon stainless steels commonly used today. These high-grade stainless steels offer premium corrosion resistance.

Foming section improvements

In addition to the use of better materials, Valmet’s current saveall design uses primarily single wall construction. This design calls for the use of thicker plates, which eliminates the need for internal supports and welds required with double wall construction.

Valmet uses certified weld procedures, qualified welders and environmentally safe, non-acid passivation methods to ensure the longest lasting contamination free parts are delivered and installed on your machine.

With the cost of fabrics and downtime spiraling higher and safety regulations tightening, these relatively simple improvements are becoming an attractive and cost effective way for papermakers to extend the life of older vintage formers.

If your forming section is a bottleneck to obtaining better quality and operating results, contact your Valmet representative to request a former section audit. Find out what Valmet can do for you.