Spanish to English Tech/Engineering

Por su parte, la continua de anillos ofrecía respuestas atractivas a la carestía del carbón y a la disponibilidad limitada de agua. Idéntica solución imponía la necesidad de ahorrar mano de obra cualificada y cara, generalmente masculina pero a veces también femenina. La instalación de continuas obedecía a la necesidad de reducir los costes de mano de obra, independientemente de su composición por sexo . Esto quire decir que las selfactinas fueron sustituidas por continuas en las fábricas en que la selfactina era el baluarte del trabajo cualificado masculino , pero también en las fábricas que emplaban mujeres en las selfactinas.

My draft:The ring frame, however, was an attractive solution to the shortage of coal and the limited availablility of water. It was also the solution to the need to save on skilled, expensive labour, generally male but sometimes female. Ring frames obeyed the need to reduce the cost of labour, independently of the gender composition of the workforce . What this meant was that the self-acting mules were replaced by ring frames in factories where the former was the bastion/stronghold of skilled male labour but also where women were employed.

Apart from confirming if I got the significance right, what about the translation for baluarte. To my mind stronghold or bastion (or bulwark) is not entirely correct here to refer to the machine/male labour relationship (this machine required skilled, hence generally male, and thus expensive labour, the other alternative would require less skilled = feamle labour).