i.e what are the symptoms? ■

The crusher RPM is, in part, selected to break the rock and then give it time to flow through the crusher bite before the next jaw closing. This timing is dependent on the viscoelasticity (strain rate breakage dependence and internal binding) of the rock assembly. Some rocks, with higher levels of moist clay like materials, momentarily delays motion as the cohesive-adhesive bonds between crusher jaw surface, and between internal rock binding breaks loose from gravity. The crusher designer may not know the specific material properties and has set the crusher RPM according to a general standard.

If you apply and Variable Frequency Drive, you can experiment. You may find a slower RPM will do it if the cohesive strength is high vs. the opposite is low.

There are complicated physics at work in the crusher depending on the jaw shape and toggle system as well. My comment could be one of many. Let us see other comments.

I have see crushers masticate the ore, with high clay content, that create a lump bigger than the bite opening. See the attached photos.

Attachments

large lump transfer (DOC)

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Dear Amit,

There are a number of potential remedies available for improving jaw crusher performance.

Increasing the stroke rate may be successful. I cannot say with the limited information provided. It will be the least expensive way, if it works.

Crusher liner shapes can also improve throughput. This would require rock breakage modeling to show such benefits. In order to apply a rock breakage model, we would need to test the breakage characteristics. We can discuss this outside the forum postings. ■

Open your grizzly bars on a feeder and bypass undersize material.

Regards

Ziggy ■

I am surprised that no one has mentioned the most important factors as limit jaw crusher capacity. One is called the reduction ratio. Another is the particle size distribution, another is the moisture content and another is the materials crushing index and all need to be considered in objectively reviewing a crushers application.. If a crusher (whether Jaw, Cone or Gyratory) receives feed material as contains excess fines packing will occur in the chamber and the moisture content in the fines component can cause the "mastication" as Nordell points out. If the fines are there without moisture critical crusher breakage can occur resulting in toggle plate failure or eccentric failure. In the case of the more modern higher speed roller bearing machines other issues manifest themselves. The other items not mentioned is the type of Jaw Crusher. Single toggle and double toggle machines accommodate and are selected on the basis of different material characteristics.

Lastly I'll highlight the importance of the crusher setting. If the setting is too tight capacity will be reduced. The correct answer lies in the full analysis of the feed material. Experimentation without the necessary foresight of why you're making changes can lead to disastrous results so take care. Contrary to Nordell's suggestion I would not increase the speed until a careful and objective assessment has been made of the material characteristics you're processing.

If you are not in a position to provide all the necessary information I would start by opening the crusher setting and see what degree of capacity increase you achieve. By doing so will also have less risk of failure. Maybe your settings are just too tight for a single pass. A common issue especially where the feed is not that competent and includes a high fines fraction. ■

the capacity of a jaw crusher is dependent upon fracture toughness and the elastic modulus. Models for the prediction of power consumption, breakage function/product size, and volumetric capacity have been developed based on these results. At the experimental level, the models were able to predict the specific comminution energy to within 1% and t10 (characteristic crushing parameter) to within 10%.

sorce from:Zoneding Machine ■

Amit: increasing the RPM is not the answer right now if ever actually.

To clearly and properly answer your technical question, you would need to share the width and length or gape of the crusher as a start point.

let us assume just for an example sake: your crusher was a 3042 jaw, meaning the gape would be 30 inches and the width would be 42".

like all process equipment, we have guidelines or rules.

ASSUME for an EXAMPLE: 3042 jaw:

1. We MUST determine the MAXIUMUM feed size to this size of crusher opening.

GAPE = 30" x .8 = 24" or the max feed size of material allowed into that crusher chamber by the rules.

What is your maxium feed size? larger or smaller?

2. Method of feed to the crusher being used? lets assume it is a vibrating grizzly feeder.

What opgs are your grizzly bars set at? lets assume 4" CSS or closed side setting.

Are they plugged with near size?

If so, then you are carrying fines into the JAW crusher that do not need to be there, HENCE we are reducing the jaw crushers CAPACITY and increasing operating costs by increased wear.

3. Do you have a ROCK Breaker on top of the jaw?

if not how do you clear the oversized rock going into the GAPE? from blocking the flow and reducing your tonnage?

4. is your FEEDER long enough? if not we cascade over the grizzly bars and/or onto them...plug them and puts fines into the jaw which should BYPASS. Decreasing TPH CAP.

5. if closing the CSS too tight, we ARE probably in fact reducing capacity and putting undo stresses on the JAW operation as this should only be a PRIMARY reduction point stage.

6. are your JAW DIES worn out? if that is the case, we are once again reducing total capacity and this CSS becomes biggers as the DIES wear down.

7. are we clearing below the JAW and/or plugging at that point, which can and will reduce total FLOW and CAPACITY.

JUST SOME FOOD for thought in this thorny question of JAW CAPACITY and RPM.

George Baker

MODERATOR

Originally Posted by Amit Segev

Dear all,

One of my jaw crushers is the bottleneck of a certain plant.

I wish to know if by increasing the RPM of the jaw cruser motor I would be able to feed it more material?

Assuming that the motor rating is enough.

Amit

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