Jaw and Cone Crusher Myths & Total Operating Costs

Impact Crushers Process Soft- to Medium Hard Rocks Without a Primary Crusher

A common misperception is that impact crushers struggle with hard rock and in primary crushing applications. This is far from the truth. This article clarifies what applications can be done by mobile impact crushers instead of traditional jaw and cone crusher setups.

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Abrasiveness, feed size, and material hardness are the 3 main determinants if you can use an impact crusher over a jaw and cone crusher train.

• Abrasiveness describes the property of the rock that causes wear by friction. Silica content in your rock is a driver for material abrasivness.
• Feed size describes the largest input piece dimension diameter.
• Material hardness has a significant affect on crusher performance it doesn't exclude an impact crusher from processing hard rock. The harder to rock gets the smaller the feed size needs to be to avoid damages. Besides material hardness the break resistance is also important. In other words, material can be hard but still break easily.

 

Everybody talks about wear but nobody about the reduction ratio

Inexperienced salesmen put forward impact crusher wear costs which are higher than for compression based jaw and cone crushers. The statement without context is true but omits one essential fact: an impact crusher works harder to downsize material. In other words, an impact crusher can reduce the material significantly more than a jaw and cone crusher. The ratio of input size vs the output size describes the so-called reduction ratio.

Common reduction ratios and feed size example:

Reduction ratio example: jaw, cone, impactor   Maximum reduction ratio Feed material Output size Jaw crusher 6:1 24" 4" Impact crusher 24:1 24" 1" Cone crusher 5:1 4" 0.8"

 

10 reasons to replace your jaw and cone crusher setup with a mobile impact crusher

 

If your application permits to use an impact crusher over a jaw and cone crusher setup there are numerous reasons that support the use of an impact crusher.

1. Less fuel burn: Only one machine burns fuel. For example, if you can save 8 gal / h in fuel over 1,500 hours a year at an average fuel cost of $4.50 per gallon this equates
   a saving potential of $54,000 in fuel.
2. Less maintenance costs: Less fluids and fewer grease points, conveyor belts, and filters to maintain.
3. Faster start-up and shut-down procedure: Simple and efficient procedure. Less risk to get the start-up procedure wrong. Less downtime during a blockage. For example, if your mobile impact crusher produces 300 tons per hour and saves you 30 min every day you can produce an additional 150 tons per day. Assuming you produce 150 days a year this adds up to an additional 22,500 tons of material.
4. Lower parts inventory: Instead of stocking parts for a jaw and cone crusher you can reduce your parts inventory to what is needed to operate a single impact crusher.
5. Lower moving costs: Cutting your equipment transport costs in half improves your bottom line.
6. Easier setup: Setting up a jaw and cone crusher and an additional screening plant is time consuming and need to be tuned in before you can start crushing. Jack-knifing a screening plant for a closed-circuit operation adds an additional challenge.
7. Improved material quality: Produce quality cuboid material. More chips and fine production.
8. Increased versatility: a mobile impact crusher allows you to venture into different application such as on-site concrete recycling or producing roadbase with just a closed-circuit mobile impact crusher instead of a crusher and a separate screening plant.
9. Lower training effort: Trust your guys around the machine because they need to handle only one type of machine.
10. Lower risk for downtime: If one machine is down your entire crew is down. Using a single impact crusher reduces the number of moving parts in your processing operation that can go wrong, so that you reduce the risk for downtime and increase profits.

Rather than manufacturer's names; we are going to focus on types of crushers; these being Jaw Crushers, Impact Crushers, Cone Crushers, and Shredders. To determine which of these crushing technologies is best for your application, we must first know the material that needs crushed and to what particle size.

Hard Rock:

Many rock quarries crush hard rock. In these applications we highly recommend a jaw crusher as the primary crusher, which reduces the rock down to 3-4', and then a cone crusher as the secondary crusher to further reduce down to the desired size. Often times the secondary crusher is not used and the primary crusher conveys into a screening plant which separates the material into 3 products.

Not all jaw crushers are designed to handle hard rock though. In fact, most of the smaller jaw crushers on the market are only designed to crush concrete, block, and brick and not hard rock. 

In many cases you may hear of a customer adding shims to a jaw crusher, allowing the jaws to become closer (for example 2'), to make a finer product. This can be easily done; however, you run the risk of damaging your crusher. A secondary result is that production will be cut in half and your jaw plates will experience quicker wear.

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Concrete / Concrete Block / Brick:

For this material we normally recommend a jaw crusher, impact crusher or a recycling shredder; however, other variables come into play to determine which is best. Is dust an issue? Am I wanting a finer or coarser material? Is there a great deal of rebar in the material? 

My favorite (newer) technology is the shredder for concrete, block, and brick. This shredder can also crush asphalt in 100 degree weather which is a huge perk. It also allows for less prep work (by accepting larger material) and is superior when dealing with contaminants like rebar. Out of all of the options on the market, the shredder produces the least amount of dust and is the easiest to run.  

My second favorite technology for this application is the jaw crusher. It experiences slightly less wear than a shredder but considerably less than an impact crusher. The jaw produces a little more dust than the shredder but much less than an impact crusher. Jaw crushers are not recommended for asphalt unless it is below freezing temperatures. 

My least favorite type of crusher is the impact crusher. It is true that impact crushers have higher production and the most reduction compared to the two previously mentioned technologies; however, it is at a cost. Impact crushers create a great deal of dust and wear parts must be replaced on a regular basis. In short, you must have access to a mechanic given that blow bars need to be replaced frequently. It's worth noting that this article is written from the perspective of the smaller operator who does not have full time mechanics. If I had full time mechanics and my material was basically clean then I would suggest the impact crusher despite its faults since it will yield the most production, the most reduction, and can also handle asphalt in high temperatures.

Asphalt:

The most popular type for crushing asphalt is the impact crusher. The wear on the machine is significant, but it yields the most production. I personally like the Shredder for this application as the cost per ton is considerably less and, compared to an impact crusher of similar cost, and the shredder will accept larger pieces meaning less prep time. There are many shredder manufacturers on the market, but only one that we recommend for recycling concrete, block, brick, and asphalt; the CAMS Shredder, as it is specifically designed for such material. The CAMS Shredder can also shred extremely dirty or even muddy concrete with no issues. If you have any questions or interest in a machine, feel free to call us at GrinderCrusherScreen to answer your crushing equipment questions.

If you'd like to learn more about various Crushers, please see our other articles like: "What is a Jaw Crusher", "What is an Impact Crusher", and "Are Reduction Ratios different between Crushers?"

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