In spring 2015 American Cement Company, based in Sumterville, Florida approached Kobo USA, a manufacturer of chains, sprockets, rollers, pans, shovels and attachments for help with its limestone reclaimer system. Here Kobo USA, a subsidiary of German-based Köbo Group, describes the installation of a chain system with an improved design.

GLOBAL CEMENT: CHAINS

Dominik Stracke, Kobo USA - The Chain People

New Köbo chain solution for American Cement

A survey of the limestone reclaimer at American Cement revealed that it was experiencing in-

creased wear and failure of the chains and shovels due to large size rocks in the limestone pile. These larger pieces come from the crusher and were also formed from smaller pieces due to the high hu-midity and stickiness of the limestone in Florida. When the shovels hit these 10-12cm (4-5”) rocks, shock loads caused damage to the chain system. The bushes of the chains had cracked and the shovels were breaking at the seams of the welded chain attachments.

The original design had attachment plates welded to one link plate of the chain. It had an alternating attachment plate that was welded to only one side of the chain. Due to this arrangement, the sequence

of the attachment alternated from the inner to outer link. The outer links were especially badly affected by the shock loads. The chain had an outside-mounted maintenance-free roller with ball bearings and seal-ing technology to protect the internal components.

“Due to the circumstances with the crusher and limestone moisture around 15%, because of the un-derwater mine, this chain system had to be improved,” said Carlos Soteldo, Engineer and Sales Manager at Kobo USA. “We cannot say that the chain was manu-factured incorrectly, but we saw a chance to improve the design to make it last in these difficult environ-mental conditions.”

Kobo USA analysed the existing chain and its failure modes at its in-house laboratory. It provided detailed reports to the customer. It had determined that the breaks were caused by very high peak loads, which caused the materials to bend before they cracked.

In coordination with American Cement, Kobo USA provided an improved chain design. Most of the dimensions were kept, but the bushing size was increased to create more strength for the dynamic shock loads. Furthermore, the sequence of the at-tachment was changed from every third link to every second link. This means that every shovel now has to drag less material. Also, the attachment is welded on both sides to the inner link plates. This stiffens the construction of the attachments. Weight and work-

ing load calculations were done for the new design and approved by the cus-tomer. The existing motor and gearbox could handle the new design of the chain and shovel spacing without requiring an upgrade.

“Our customers have the experience with the machines, we are the experts for the chains, sprockets and attach-ments. Therefore it is important for us to work hand in hand with our customers and develop solutions together,” says Dominik Stracke, CEO Kobo USA.

Kobo USA also provided a stiffer sup-port for the shovels. The existing design had seen breakages at the centre guide rollers. Due to the inclusion of a thicker

stiffening rib, larger rocks can no longer damage the shovels. Also, by using steel with a high tensile strength no expensive hard face welding needs to be

26 Global Cement Magazine September 2016 www.GlobalCement.com

Right - Figure 1: Shock loads, which were being caused by large chunks of limestone, were damaging parts of the previous system.

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“After the initial break-in period, the system is operating well without any problems...”

Osmarino Rogacheski, American Cement

applied. Replaceable scraper wear bars were attached to the sides of the shovels. These parts can easily be replaced by loosening two bolts.

Finally, Kobo USA provided the tooth rims for the new chain design, as the drive and return tooth rims were worn. By supplying the chain and sprockets, Kobo USA could ensure that hardness specifications of both parts were balanced to give optimal lifetime for all components.

The full system was supplied in the autumn of 2015, around six months after the initial contact. The installation was completed by American Cement without problems. Even with a slightly higher chain weight, the energy consumption and chain pull was

reduced. This is related to Kobo’s special outside mounted rollers with lifetime lubrication. These rollers help minimise friction and, in case of roller replacement, they can be changed without disas-sembling the chain. American Cement reports that its limestone output is more balanced than the previ-ous design and that the system now runs remotely without problems. This continuous flow of material has helped with downstream processes. “After the initial break-in period, the system is operating well, without any problems. We are happy with the results and with the support provided by Kobo USA,” said American Cement’s Maintenance Manager Osmarino Rogacheski.

Above left - Figure 2: Damaged brushing on the

original chain system.

Left - Figure 4: The new, optimised solution from Kobo

USA has operated for nine months without problems.

GLOBAL CEMENT: CHAINS

www.GlobalCement.com Global Cement Magazine September 2016 27

Above - Figure 3: Damaged link plate on the original

chain system.