Rapid Rise in Productivity for Tennants
First published in the March 2025 issue of Quarry Management
New Finlay 684 inclined screen supplied by Molson Finlay Scotland boosts output at Lhanbryde Quarry
Scottish aggregates suppliers Tennants (Elgin) Ltd have long kept a fleet of ageing crushing and screening equipment running to produce the aggregates they require for their concrete batching plants and aggregate supplies.
Recent events within the company have seen Gavin Tennant stepping up to take the managing director’s role and with this responsibility, he has started to look at the overall running costs and production abilities from the ageing fleet. ‘Sadly, we lost my father recently, and whilst his methods were fine to supply limited volumes of aggregates for our own requirements, increasing downtime from the plants and an increasing requirement to buy in material we couldn’t produce in house made us rethink our policy of running older machinery,’ said Mr Tennant. ‘Replacing all of our older kit in one fell swoop wasn’t an option, but we have made a start in our Lhanbryde Quarry where we realized we could improve production figures quickly.’
The first port of call for Tennants was Mike MacKenzie at Molson Finlay Scotland, who specializes in the crushing and screening equipment sold by the company. ‘We have looked at all of Tennant’s operations and came up with a list of machines we could integrate into their operations to not only improve their productivity, but also increase the variety of material produced,’ commented Mr MacKenzie. ‘Lhanbryde Quarry was the quickest and easiest site to address the issues and working with Gavin and his team, we have introduced a new Finlay 684 tracked screen.’
The Finlay 684 is one of 10 inclined screens in the Irish manufacturer’s range, and whilst not the largest, the addition of this machine at Lhanbryde Quarry has seen sand and gravel production rates rocket to a point where the team have been able to reduce the plant’s weekly operating hours.
Powered by a Stage V CAT engine, the Finlay 684 is designed to provide a consistent grade of material day in day out. The material is loaded into an 8m3 hopper where a conveyor moves it steadily up to the two-deck inclined screen. The 684 features a 4.3m x 1.7m screenbox which can be hydraulically inclined from 18° to 37°, allowing material to pass through at different rates depending on the quality and quantity desired. The main conveyor is 1.0m wide and uses three anti-rollback plates to stop material falling back and blocking the flow. The sides of the conveyor are also fitted with substantial side skirts to stop material falling off.
There are two other material conveyors on the machine, one on each side of the screenbox. The fines conveyor on the left-hand side of the machine is 1.2m wide and extends to a maximum height of 4.15m above ground. This effectively delivers more than 106m3 of stockpiling capacity without the need to move any material. The medium-grade conveyor on the right-hand side of the 684 is slightly narrower, at 650mm, and allows up to 194m3 of stockpile capacity below it. Tennants opted for a 24mm woven mesh on the top deck with 6mm piano wire mesh on the lower, allowing them to produce three consistent grades of material. These are currently 10mm, 16mm, and 20mm, along with oversize off the main conveyor. The oversize river gravel is placed to one side to await crushing when there is a sufficient volume. Mid-size material is graded to a range of sizes with the fine material stockpiled or fed through the site’s veteran Finlay wash plant to further process the sand. In total, the site now produces 16 different material sizes, more than double what it did in previous years.
With Tennants currently using a 14-tonne excavator as the site’s prime mover, the Finlay 684’s increased productivity over the older machine has put the excavator under pressure to keep up. ‘Upping the size of the digger would allow us to improve production at the site and use the Finlay to its maximum ability, but that’s something we may do in the future,’ commented Gavin MacKenzie. ‘What we are thinking of doing is creating sufficient products at Lhanbryde before moving the Finlay to undertake a spell at one of our other quarries. Not only will this allow us to increase the range of materials we can supply from our hard rock sites, but it will also reduce the need to add additional kit for each quarry if we are able to share it between sites.’
The addition of the Finlay 684 has seen the company invest in its first new piece of kit for many years. The almost instant increase in productivity has made a huge difference to Tennants’ bottom line as large volumes of sand for their concrete batching plants can now be produced in house. ‘The Finlay has made a big difference to the way we operate,’ said Mr MacKenzie. ‘It has opened our eyes to the potential we now have in our own sites.’
Whilst this is the first machine supplied to Tennants by the Molson Finlay Scotland team, it has hugely impressed the company’s entire management team with its reliability and productivity. This has been echoed by the support and service Molson Finlay Scotland have given the company. ‘Mike has taken some time and effort to getting exactly what we needed to benefit the quarry,’ commented Mr MacKenzie. ‘Their back up and service is excellent and the assistance from Mike and his team to tweak the screen into the right specification and position helped us immensely.’
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