Hydraulic hammer mill
There are three types of multiple hammer mills used to grind the rag cloth : the rag “breaker” ; the rag “grinder” ; the “break down to fibre” mill. The difference between the three relates to the nature of the operations to be carried out by the mill and subsequently by the various “finishes” on the hammer-heads. In the rag “breaker” hammer mill the hammer-heads are equipped with large pointed nails that reduce the rag cloth into fibrous “rag strips”; in the “rag grinder” mill the hammer-heads are equipped with “flathead” nails which transform the “fibrous” strips into their elementary state. Whereas the hammer-heads on the third type of hammer mill are devoid of nails and their function is to complete the refining (homogenisation) process or to rehydrate the refined paste and stock piles for “dry” periods (periods of insufficient water supply). Each mill, is normally equipped with three hammer-heads, the pounding alternates as follows: firstly the outside left, then the outside right and finally the central hammer. In the breaking mill, where the bulk is less homogenous, the circulation of the cloth is not only facilitated by the pounding order but also by a diverse impulse due to the different weight of the three hammer-heads and by the protuberance of the hammer-head lifter. In fact, in the parity of length of the single hammer, the square section of the first hammer has a 16.5 cm side; the central hammer has a 15 cm side; the third hammer has a 13.5 cm side. The first hammer lifter has a protuberance of 14 cm against the 10 cm of the other two hammers: the bigger hammer that pounds first is lifted higher and therefore pounds the fibrous bulk with a stronger pounding pushing the bulk sideways toward the smallest and lightest hammer succeeds in pushing the bulk towards the centre of the tub. The central hammer, pounding lastly pushes the bulk out to both sides of the tub. During the rag stripping stage in the breaking mill, the cloth undergoes a generous wash to eliminate all the maceration grime. Water is conducted through a rectangular basin placed on top of the mill and is filtered via a cloth filter, enters the mill tub, washing the cloth being processed and exits via the hindmost part of the mill tub. Once the rag cloth is transformed into rag strips, the material is then transferred to, via a copper ladle, the “grinding” mill where the flathead nails on the hammer-heads transform the rag strips to their natural fibre element (“pisto”). The “pisto” is then ready to be transformed to paper and is transferred to the final “refining” mill for the homogenisation process. This final mill also pounds the “pisto” produced during the abundance of hydraulic energy left aside as stockpile. For this reason the refined “pisto” is formed into a “pizza” shape. These are then placed on a hemp cloth (being an open weave cloth) over a wooden rectangular screen in order to permit the “pizza” shapes to drain off the excess water via light manual pressure. Once the “pizza” shape has attained the thickness equivalent to that of the screen then it is wrapped completely in hemp and taken to the screw press to be squeezed as much as possible. Then the hemp cloth is removed and the “pizza” is stockpiled for the dry season. Once the “pisto” is refined and homogenized in the desired quantity, it is transferred to the final “tub” for the production of paper sheets.