12/12/2003 - "It Can't Be Done" but BTI Did It

The Nexfor Norbord OSB plant opened in Alabama in the year 2000 and promptly bought a very large floor scale from Birmingham-Toledo, Inc.  Norbord manufactures not only 4' x 8' OSB, but also larger boards, even up to 24' in length.  Of course, they didn't buy a 24' floor scale, so they were not able to weigh all of the products which they produced.  The quality department uses the floor scale to weigh many of the bundles of boards, but sampling, while statistically very close, can never truly tell the whole story. Inbound and outbound truck scales provided total weights of shipments, but the quality department wondered if a solution was possible to somehow capture the weight of each and every board produced.

Birmingham-Toledo was asked to propose several possibilities within the plant where weighing could be used to improve Norbord's quality.  The plant's large conveyor system was a logical first choice.  Upon leaving the press, each board is sent down a conveyor system which was manufactured by an OEM.  The OEM apparently had little or no experience in the weighing industry.  They had attempted to incorporate weighing by simply placing low cost weigh modules under each of four conveyor legs, wiring them to a junction box, and then to the Norbord PLC. 

Not only had they chosen a poor product which did not have the capability to achieve the accuracy Norbord desired, but they had also provided Norbord with a poor installation.  There were no adjustment shims installed with any of the weigh modules.  Failing to adjust a weigh module system to compensate for an uneven floor or machine eliminates much of the accuracy and repeatability. 

More importantly, there was no timing device to control the flow of boards.  Often there are two to three boards almost end-to-end on the conveyor weighbridge, while at other times there are no boards on the weighbridge at all.  A photo eye with a stopping device would have been a simple solution, but the OEM apparently did not know that weighing devices require a few seconds to capture a weight.  A lower rung manufacturer requires several seconds to capture a weight.  Overall, it was simply a poor design and application.

After leaving this area of the conveyor system, boards are bundled automatically and sent to one of five exit conveyors, dependent upon size and quality.  They are then transported by a short rail section to a final large exit conveyor which is able to hold any size bundle of boards from 8' to 24' in length.  Immediately after this final exit conveyor are two lines which send the bundles through one of two painting and banding areas.

When Norbord began to look for weighing solutions, the OEM suggested that each of the five smaller exit conveyors be placed on weigh modules to create five new scales.   This appeared wasteful to Birmingham-Toledo, with the final large exit conveyor only 100 feet away.  Even with the "down-and-dirty" cost of the weigh modules used by the OEM, cost made the option of five new scales impractical.  Concerning the final exit conveyor, the OEM had stated that, "It can't be done."  They felt that the final exit conveyor was too large and had too much dead weight to be able to weigh the bundles accurately.    

At a weight of 7000 pounds, the 10' x 24' conveyor is rather substantial.  Another problem was the conveyor drive motor.   It was mounted to the floor and would have to be made a part of the weighbridge in order to achieve a true and accurate scale.  The motor weighed over 500 pounds itself and would require even more weight to be added in the form of a steel supporting structure. 

Birmingham-Toledo, confident that these problems could be solved with the superior Mettler-Toledo product, proposed a system including eight 2,500-pound capacity Flexmount weigh modules and a JagXTREME controller with Allen-Bradley RIO interface.  A dual scale card was also included.  This gives Norbord the option to integrate the existing low cost weigh modules into a better quality controller in an attempt to achieve their desired accuracy.

System installation began with construction of a steel supporting structure and relocation of the drive motor.  The following picture may give you an idea of the size of the 10' x 24' conveyor section.  Notice the Birmingham-Toledo technicians as a size reference.

Below you will see part of the mammoth conveyor section as Birmingham-Toledo certified weighing technician Jerry Ash cuts away one of the legs in preparation for inserting a Mettler-Toledo Flexmount weigh module.

Next you will see the motor supporting structure.  The motor has been removed, and the new structure has been fabricated on site, welded in place, and primed for painting.  Notice the remaining conveyors in the distance which lead to the painting and banding area.  Notice as well the finished product painted bright yellow with green lettering.

Next you will see the same area after painting and re-installation of the drive motor.  Notice the Flexmount weigh modules under each supporting leg.

The next picture shows a closer view of the Mettler-Toledo Flexmount weigh module, as well as an MT stainless steel junction box (with cover open) on the next conveyor arm.

One of the problems encountered by BTI certified scale technician Jerry Ash, who headed up this part of the project, was with the motor's drive chain.  Norbord's engineer had provided BTI with a drawing for relocation of the motor.  The drawing had an error in height of the new location.  When Jerry Ash realized this error, it was decided that he would correct the problem through fabrication of a "notch" in one of the support beams.  This allowed for any loosening and slackening of the drive chain during its operation.

After fabrication, the Mettler-Toledo Flex mounts and JagXTREME were installed.  Norbord decided to have BTI install the JagXTREME directly inside one of the Norbord PLC cabinets.

Norbord now has the capability to view the weight of each and every bundle of boards as it leaves their production line and before it is painted and strapped.  The information is available to a quality department lab technician by eye sight or through the company PLC.

For the other half of the project, Birmingham-Toledo suggested utilizing the belt conveyor located at the opposite end of the plant.  This is in the open-air section of the facility, approximately one-half mile away.  Account representative Robert Proctor claimed to have walked over five miles on the first day of the shutdown, going from one crew to the other.  Since Toledo no longer manufactures a belt scale, Birmingham-Toledo chose a Thayer scale for this application due to QC Mike Ellington of Norbord having had experience with the brand, as well as to Thayer's great reputation.  Below you will see the Thayer weigh bridge before installation of new green idlers (rollers).

The Thayer scale will weigh incoming material, allowing Ellington and his lab technicians to analyze the process even more.  The information will also be output directly into their Allen-Bradley PLC.  Birmingham-Toledo certified weighing technician Dean Bolton, who headed up this section of the project, worked many long, hard hours in installation of the scale.  Both projects were accomplished during Norbord's December shutdown, so time was short and tension was high.  Both Bolton and Ash did exemplary work, especially considering the deadline, the cold weather, and the long work hours. 

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