How it worked
The iron was made from a mixture added into the furnace stack of 3 main ingredients - crushed iron ore, charcoal as the fuel and a flux to help the process along. The iron ore came from the company’s mines near Dalton-in-Furness. The charcoal was made in local woodlands, although increasingly brought from further afield as supplies ran thin. The flux was either limestone, quarried locally, or lithomarge, a type of kaolin, shipped from Ireland. Although most charcoal furnaces changed over to using coke as their fuel in the 1800s or before, Backbarrow did not make the switch until 1926/7.
The iron-making ingredients were stored until needed in large stone barns on the hillside above the furnace. This was very convenient for deliveries by rail after the Lakeside branch of the Furness Railway was opened in 1869.
Once the furnace was lit, the fire was kept going by a blast of air from bellows powered by a water wheel. As the temperature inside increased, a chemical reaction took place, and molten iron dropped to the base of the stack. The materials inside the furnace were kept topped up for as long as the ‘campaign’ continued – for weeks or years. Molten iron was released from the hearth at the base of the furnace and flowed to the casting floor. Slag – waste from the process – was dumped around the site, so that the ground level now is higher than it was when the furnace was built.
Especially in the early years, some items were cast directly from the furnace, but production was mainly of blocks of iron (pigs) which were sold to foundries elsewhere as their raw material. In the early years this included forges such as the one at Cark nearby, and to places like Liverpool and Bristol by sea. By the 20th century sales were worldwide, to major firms such as Ford, Fiat and Singer Sewing Machines.
The furnace and its hearth were rebuilt several times during its working life. New technologies were introduced so that production increased from a few hundred tons a year in the 1700s to 2000 tons a week by the 1960s. The waterwheel was replaced by a steam engine and then by turbines. Ovens were constructed to produce hot air rather than cold for the blast.
Water for the pitch-back wheel was taken off the River Leven at a weir just upstream of the works. This also supplied the turbines, the first of which was installed in 1866, to generate power for the site. Once the furnace went over to hot blast, water was also needed to cool the jets that supplied the blast to the hearth, and some for the boilers that made steam to power the blowing engine that created the blast.
On the hillside above was built a holding tank, supplied by water from a spring. This was used to power a lift that carried a man and his full barrow to the top of the stack.
In the early 20th century, as well as the changeover to using coke, two cupola furnaces were erected either side of the main stack. These were a simpler form of blast furnace, blown by cold compressed air, and they generated a big increase in the quantity of iron produced by the company.