Grinding rods do not require cascading as do ball charges, thus enabling rod mills to be operated at lower peripheral speeds than ball mills.Less void spaces exist in a rod charge tan in a ball charge. Therefore, these is more grinding contact between metal an ore per surface are of media in a rod mill. Lower steel consumption per ton of product occurs in a rod mill than in a ball mill due to better contact between steel and ore. The action within the rod mill causes the energy of rods to be directed to the largest sized pieces of ore. Often in a ball mill the balls grind on one another or against ore already ground fine enough.
As we know, ball mill is similiar with rod mill, and they are all important and widely used for grinding line.Ball mills and rod mills are both excellent mining machines for grinding ores into fine powders and particles. However there are some advantages to using rod mills rather than ball mills for larger mining projects including greater efficiency, better grinding performance and lower energy costs. Though ball mills are used more often rod mills can be the better option for specific mining ores and larger site projects. Rod milling in the size range utilized is more efficient than ball milling in that the desired product is obtained at a lower cost per ton. This is due to several reasons:
Rods are more suited than balls to breaking larger pieces of ore due to their much higher weight. (Energy is equal to hall the product of the mass times the velocity squared). Larger media are capable of transmitting moiré energy per collision.
Another key factor in choosing a rod machine over a ball type press is void space. You ideally want as little open space as possible so you have more grinding contact between the rods and the ore. Ball mills need more open space so the balls inside can cascade and grind but this space lessens the contact between metal and ore per surface area. Again, depending on the site project media rods won”t necessarily always be the better option but if you are concerned about void space in your grinding process a rod machine may be the right choice.
In a rod mill it is important that the rods stay essentially parallel to one another. If rods become misaligned, grinding action is lost and more importantly, rod entanglements will occur. For this reason, rod mills are designed with their length roughly 1.3 to 2.0 or more times their diameter. Rod mill size depends on the feed and product size, capacity, type of grinding circuit and the power required to achieve the grind. The limitation on rod mill length is in the ability to make rods that will remain straight enough not to tangle. The current practical limit on rod length is about 20 feet. The diameter of a rod must increase as the length increases if the rods are not to sag appreciably under their own weight.
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