Published Feb 28, 2017

Metso’s versatile Lokotrack ST2.8 screens everything efficiently – even spawning stones for fresh water trout

Multifunctional is the best word to describe the Lokotrack® ST2.8™ mobile scalping screen. Veljekset Kokkonen, a crushing contractor based in Lieksa, Eastern Finland, has used their newest solution for few months, screening various sizes of crushed stone for sand, gravel, soil and – for a highly specialized use – spawning stones to help endangered fresh water trout to breed.

These spawning stones aim to restore the extremely threatened fresh water trout in Naarakoski rapids, on the Lieksanjoki watercourse. The beautiful territory is situated on the lower course of the famous Ruunaa fishing and nature conservation area.

The fresh water trout wanders from the lakes to the upper courses of rivers to breed. For this, they need proper sized stones. The smaller stones are needed to successfully lay their eggs and the larger stones, about the size of a human’s head, to protect the precious first moments of the trout babies.

Spawning and fry stones screened from a gravel bank

It was a snowy morning in October 2016 when Juha-Pekka Kokkonen, a third-generati contractor and the man in charge of crushing and screening at Veljekset Kokkonen, started up the Lokotrack ST2.8 screen at their Pekkilä soil extraction area in Lieksa.

Thanks to Metso’s ST2.8 screen, Juha-Pekka Kokkonen from Veljekset Kokkonen can offer the company’s customers an even broader range of services.“We screen three sizes of natural stones from the gravel bank. The sizes of the spawning stones vary between 30-60 mm, 20-100 mm and 100-250 mm. More than 1,300 cubic meters of gravel is being processed,” says Kokkonen.

“Working with the screen is fast. We use an eccentric throw of 14 mm, and the screen accepts as much feed as the excavator is capable of putting in. We use punch plates in three sections on the screen’s upper deck, and a steel mesh in one section, as well as on the lower deck,” Kokkonen adds.

“A good screen for any job”

Veljekset Kokkonen purchased their first mobile crushing equipment from Metso in the early 1980s. After that, they have completed it with a track-mounted two-stage plant. Last September, the company acquired a Lokotrack ST2.8 screen.

“Based on our first experiences, ST2.8 is a screen that gets the job done. So far, everything has worked well. A Finnish product is a safe choice, because it means that spare parts and maintenance services are locally available when needed,” Kokkonen stresses.

“Good fuel economy is an added bonus for us, enhancing the cost-effectiveness of screening. The efficient screen consumes only just over 12 liters per hour, which is not much for an hourly screening capacity of more than 200 tonnes,” he adds.

Veljekset Kokkonen’s operations are based on three pillars: construction sector transport services, contracting, and crushing and screening.

The family company operates mainly in Eastern Finland and employs around 20 people. They crush and screen roughly half a million tons of aggregates annually. As many of their clients are small companies, the equipment is transported from one place to another around 40 times a year.

Spawning stones for an important need

The fry stones, sized 20–100 mm, will soon make it safer for the landlocked salmon to reproduce in the Naarakoski rapids. Veljekset Kokkonen screens spawning stones for Kuopion Teho-Louhinta, the company in charge of submerging the stones in the Naarakoski rapids, commissioned by the Centre for Economic Development, Transport and the Environment for North Karelia. The work was carried out at the end of 2016 to provide the landlocked salmon with new and better spawning sites in the autumn of 2017.

The spawning stones meet a desperate need: natural stocks of landlocked salmon can only be found in a few headwaters in Finland. In rapids with a stone and gravel bottom, only around one percent of the fish stock develop into fry.

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