For any crushing and screening operation, the most important factor in ensuring success is to select the equipment that results in the lowest cost per tonne on the ground. That could well mean buying the more expensive option due to its increased reliability, increased production, and larger feed size ability. Jason MacDonald, Product Manager – Crushing and Screening has summarised what to think about when selecting your crusher.
Benjamin Franklin: “The bitterness of poor quality remains long after the sweetness of low price is forgotten”.
As margins continue to get tighter and compliance costs increase, it becomes increasingly important to understand your real costs of operation including repayments, fuel usage, wear costs, wages, mobilization and demobilization costs (you’re not earning while your equipment is on the back of the truck), the impact of weather events, how many hours per week you can achieve and how many weeks per year you can work. These factors make it critical to know what profit margin is required to make your operation profitable. Don’t base your figures on 60 hours per week and 52 weeks per year and a 10% profit margin – you will be disappointed.
There are also many maintenance issues depending on your location – a northern hemisphere cold climate requires different options with cold climate oils, oil heaters, block heaters, anti-freeze, etc. in winter when compared to a southern hemisphere 50 degree Celsius summer that requires hot climate oils and much larger cooling packs to deal with the heat.
The cheapest crushing in hard rock is done in the ground using explosives for production blasts with a tight pattern and less than 5% oversized–secondary breaking of oversized afterward is very expensive with a more open blast pattern and >10% oversize. An extra 30 or 40 cents per tonne will seem incredibly cheap when faced with 100’s of machine-hours to hammer oversize and the reduced production through the crushing plant.
Will your crusher chassis last less than 10,000 hours or will it last over 30,000 hours? Repairing cracks in a crusher chassis due to fatigue is not a quick fix.
In a multistage operation the opportunity cost of unscheduled maintenance can be enormous with a dozer, excavator, wheel loader all parked up, maybe trucks, lost sales and employee wages while no production occurs.
SOS oil samples and scheduled maintenance to OEM recommendations are cheaper than breakdown maintenance.
Make sure it is always operated on level ground – a 1- or 2-degrees downhill slope is acceptable – not uphill or sideways. Operating the equipment on a cross or uphill slope will result in reduced production and increased wear costs.
The 3 major crusher types found in most quarries, mines, recycling centers, and contractors’ fleets are the jaw crusher, cone crusher, and the impact crusher. Selecting the correct equipment increases productivity and decreases downtime events ( the biggest killer of profits ) and for a contractor means that they can finish the contract earlier and move to the next one – increasing the amount of money that can be earnt into a smaller time period resulting in more profit.
Bigger is not always better when you must account for transport costs and operational costs, it’s no good having a crusher capable of doing 400 tonnes per hour if the feeding and stockpiling equipment can’t keep up, it could result in more wear due to not being able to “choke” the crusher. It will also increase costs with higher fuel burn and increased payment costs. A multi-stage crushing circuit needs to be balanced so that the downstream parts of the plant can cope with the feed from the primary crusher and doesn’t result in a blockage or recirculating loads building until there is a stoppage. I haven’t found anybody yet who really loves using a shovel, but some are pretty good at it.
In selecting the correct or best fit for the application some of the important points that need consideration are:
- Feed Size and Feed Grading
- Abrasion and Hardness of the material
- Clay and Moisture contents
- Reduction Ratio required
Generally, if you want to maximize production and avoid blockages you should only feed material that is less than 80% of the inlet opening or “Gape”.
There is a trade-off between different crusher types as the table above shows. An Impactor can take large feed size and due to its reduction ration can achieve up to 20:1 reduction when used in a closed circuit. The one impact crusher can achieve the same result as a jaw and a cone with less capital outlay and can achieve better beneficiation of softer material (improves the quality of the finished product by eliminating softer material). The flip side of this is that if the material properties include high abrasion or very hard rock, the wear costs and production achieved will be prohibitive to make a decent profit or possibly result in a large loss. Quartz and Granite can be extremely abrasive, Basalt can be very hard, while Limestone and Dolomite are usually softer and very low abrasion.
The quality of wear parts is also critical – cheap blow bars in an impactor can result in 10’s of thousands of dollars of damage if they break while crushing due to poor casting or cheaper metals.
Higher manganese content doesn’t always result in longer wear life in very abrasive rock – the manganese will be stripped out of the parent metal before it has a chance to work harden.
It is important to get the right advice to suit your application and have a solution tailored to your needs – not something pushed on you because it is cheap, old stock or it’s what the dealer has in their yard.
Expectations of product shape, size, tonnages, abrasion, rock hardness, contamination, clay, and moisture contents all need to be discussed to ensure that there is no bitterness as a result of a large purchase.