Doing this doubled production!

Jun. 24, 2015

Simple change yields more product—For Free!

Sometimes it is possible to produce more with less and not spend a dime in the process. This is the story of one of those times. One of our specialists visited a customer’s plant recently and the plant was not producing anywhere near rated capacity of the equipment.

Product was just trickling off the stackers.

Our man recommended a few, simple adjustments to the plant and production almost doubled. In this case, the customer had elected to set the primary crusher, a jaw, at a relatively high closed side setting (CSS). The idea seems to have been that a bigger opening would allow more rock to pass through. The CSS was 4.5 inches, which meant that top-sized rock going to the scalping screen and secondary crusher, a cone, was about 7.2 inches top size. (For jaw crushers we use a factor of 1.6 to estimate top size passing a jaw.)

Therefore, the secondary crusher, a cone, was expected to reduce the size of material much more than the crusher was ever designed to do and the cone was also set at a relatively wide CSS to try to pass the material, which meant that a lot of the material simply went round and round in the closed circuit that fed material back over the scalping screen and into the secondary crusher. Crushing was slow as the feeder operator had to give the plant a lot of breaks in the feed when the closed circuit would eventually fill up with material that would not reduce because of the open setting on the cone.

On the whole, it seems to be one of those counter-intuitive situations. We are all used to opening up a tap more to fill a glass of water faster. In a crushing plant, it might look like we could get more production through if we just open the crushers as much as possible, and a heavy flow of recirculating material might make it look like we are crushing a lot; but the reality is that these crushers are not set up to crush efficiently. The first few loads of the day might feed through the primary like crazy; but when the circuit eventually fills up, you are looking at a lot of “black belt” from the primary.

To increase production, our man had the operator tighten down on the crushers a bit. The immediate effect was that more material got screened out before it even got to the secondary crusher. The secondary crusher could now be used to grind down particles within the designed reduction ratio, and the material recirculating over the scalping screen got screened out to a much higher degree than earlier.

One of the tricks to balancing a plant is to get the finished stone out of the plant with as few steps as possible . In an ideal world, rock would be blasted in such a way that we only have to feed it over one screen and—Presto!—finished product pours out on the other side. However, rock is what it is and needs to be crushed and screened in several steps. That said, if you can get your crushers to run choke-fed, your manganese will wear less, relative to production, because you are crushing the rock against itself instead of just crushing the rock with manganese. The stone reduces in size in fewer steps and spends less time in the plant, which should mean more stone can go through the plant.

By the way, good blasting is generally one of the cheaper ways to crush stone. If you are trying to save money by spreading your blasting patterns, you’re only spending more money in plant wear when you try to crack a bunch of oversized boulders (just think about the money you spend on handling and breaking oversize.)

A word of caution: after reading this, please resist the temptation of setting down the CSS too much, because you will get to a point where the material can’t crush for lack of voids and the crusher starts to relieve crushing pressures in ways that lead to catastrophic failures.

We hope this has been useful to you. If you want to know more about how to adjust your crushers, please contact your local crusher manufacturer’s representative. NOTE: Adjusting CSS is only one of many tweaks to improve productivity and profitability. Your results might vary.

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