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Crushing.pdf

Crushing

cone crusher, crushing tin ore

Crushing was the first stage in the process and aimed to reduce the size of the ore brought up from the underground.

The ore was broken into smaller pieces, small enough to grind.  

 In the 18th and 19th Century crushing could be done by hand using methods called ‘ragging’, ‘spalling’ and ‘cobbing’. The ore was hand sorted and the largest pieces broken or ‘ragged’ using sledgehammers. Next the ore was ‘spalled’ (broken finer) using a smaller hammer, and then ‘cobbed’ with a special long-headed hammer to break off waste rock from the ore fragments.   Next the walnut sized pieces of rock were ‘bucked’, crushed down to the size of sand with large flat headed bucking hammers. Men and Bal Maiden’s used to do this by hand but by the end of the 19th century mechanical crushers began to be introduced.

In the mid 1800’s mechanical rock breakers or jaw crushers were invented. These squeezed the rock between heavy steel jaws. Rock fed into the crusher was squeezed and broken between the jaw until the pieces were small enough to pass out through the narrow gap at the bottom. Jaw crushers reduced the rock to pieces 10-20 cms in size.

 

Photograph reproduced with the kind permission of the T Grevatt collection held by Cornwall Council

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