First published in the August 2020 issue of Quarry Management as High-Performance Chalk Mining
Successful performance tests conducted at a HeidelbergCement chalk quarry in France, using a Wirtgen 220 SMi 3.8 surface miner
On behalf of HeidelbergCement Group, Wirtgen have carried out successful performance tests using a 220 SMi 3.8 surface miner at a chalk quarry in Couvrot, France, where the goal was to increase production output compared with the site’s current mining method using a crawler dozer, whilst simultaneously reducing operating costs. Several tests were conducted in a bid to convince the customer that the smallest Wirtgen surface miner would be a viable and more efficient alternative. To do so, the surface miner’s cutting performance, turning time and fuel consumption were among the parameters recorded.
Until now, HeidelbergCement have used a bulldozer to fragment the chalk, after which a scraper loads the material into its hopper (bowl) and transports it to a temporary storage facility. From here the chalk is transported to an adjacent cement factory for processing.
As the chunks of chalk mined by the dozer are relatively large (up to 80cm), this extraction method causes several problems. First, it creates an uneven surface that has to be levelled by the dozer so that the scrapers can load the material – an additional and extremely time-consuming task. Secondly, the coarse material size means the scrapers require considerable energy and force to load the chalk fragments. This causes considerable traction issues for the scrapers, which results in, among other negative effects, an extremely high level of wear and tear to the machines’ tyres. As a result, two or three dozers are currently required per shift to level the excavated area and help push the scrapers.
In addition to the customer’s expected output of at least 500m3/h, the objective of the performance tests was to see if the aforementioned problems could be eliminated with the help of the surface miner.
High expectations validated
The 220 SMi 3.8 surface miner is capable of selectively mining raw materials with a uniaxial compressive strength of up to 35MPa at cutting depths of up to 350mm. Thanks to its 3.8m wide cutting drum, designed specifically for soft-rock mining, the surface miner achieves maximum productivity at low operating costs, making the compact machine particularly well suited to use in small-to-large extraction operations, as demonstrated in France.
During the performance tests in Couvrot, cutting zones with lengths of 150m and 300m and a width of around 40m were first mined using the 3.8m wide cutting drum. This drum was later replaced with a 2.2m wide drum and tested for a further day.
According to HeidelbergCement, the Couvrot region receives significant rainfall between October and April when huge puddles can make it difficult to extract the chalk and the moist material has a negative effect on further processing. These conditions were simulated at the beginning of the tests, with the 220 SMi 3.8 having to perform a variety of cutting tasks in muddy and wet terrain. Despite the adverse conditions, the machine mastered this challenge without any loss in performance. According to Wirtgen, all of their surface miner models feature adjustable longitudinal and cross slopes, which ensures that rainwater drains off and helps to keep the working surface dry.
Even when cutting on slopes with a gradient of up to 16%, the production output of the 220 SMi 3.8 remained high, achieving a peak cutting performance of 1,400m3/h. This represented an outstanding result for the customer, as most of the quarry’s extraction areas are located on steep slopes such as this.
The fact that the Wirtgen surface miner can easily handle Couvrot’s average rock hardness of 20–30MPa was clear even before the tests began. It is, after all, designed for rock with a compressive strength of up to 35MPa. But how would the machine perform under even harder rock conditions? Some areas of the quarry contain deposits of blue marl with a hardness of up to approximately 40MPa. This was another challenge for the Wirtgen machine which the 220 SMi 3.8 mastered with an advance rate of 5–10m/min.
Increased production output
In the final and probably most important test, the surface miner was used for an entire shift at the quarry. As part of a fleet with three scrapers and one dozer, the 220 SMi 3.8 cut at two cutting depths of 20cm and 30cm. Thanks to its powerful cutting drum and an engine output of 963PS (950hp), the 59-tonne miner was able to produce significantly smaller and more uniform grain sizes than the dozer, making the material easier to load into the scraper hopper than the large pieces of rock. In addition, the milled material lies flat on the surface, which means it does not need to be levelled with the dozer, saving additional time and costs. Also, the surface miner produces level surfaces that provide stable road surfaces for faster material transport with reduced tyre wear.
After completing the tests, HeidelbergCement were very satisfied with the results achieved by the 220 SMi 3.8. The surface miner far surpassed the target output rate of 500m3/h and at times was able to extract almost three times the specified amount of chalk per hour.
Also, due to its outstanding cutting performance and production of finer grain sizes and flat surfaces, the operator no longer needs to use a dozer, which increases output and reduces costs at the quarry. In addition, the flat surfaces reduce traction problems and scraper tyre wear. Moreover, as the chalk is pre-crushed by the 220 SMi 3.8 at the quarry, further costs arising from the use of crushers can be saved during further processing at the cement factory. In other words, Wirtgen’s smallest surface miner delivers what it promises: maximum performance and cost-effectiveness.
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