The most common bottlenecks in crushed rock plants: How to fix them

As an operator in quarries and technical support for quarries, Olav Gilje has seen the same bottlenecks recur, and again.

The work is largely about planning to avoid bottlenecks. Here’s a summary of what I’ve learned and how you can solve it.

The 5 most common bottlenecks in quarries:

1. Motor and gear on conveyor drive drum

Everything in the world can be misdimensioned. More than one aspiring Petter Smart farmer who signed up for the Norwegian Championship in tractor pulling has experienced this.

Black smoke billows out of an oversized engine as the farmer sizzles with frustration, curses a little, gives up and takes a trilting smoke as comfort. A beautiful sight at the Norwegian Tractor Pulling Championships, an expensive sight in a quarry.

The same applies to carriers:
If you put on a 15-kilowatt engine while the gearbox wasn’t meant for more than 7.5 kilowatts, it’s only a matter of time before the gearbox breaks.

It may go very well for a while, but the day a rock wedges somewhere, that winter morning the tape is frozen, the engine will continue to run at its 15 kilowatts. Then it’s the gearbox, or something else, that breaks. The weakest point must yield.

Here is the solution:

The gearbox needs to be dimensioned relative to the engine, but then you may need to change the diameter of the shaft of the drum. There are many factors at play.

When calculating the kilowatt requirement for a new conveyor, you need to look at the tonnage, lifting height, length and width of the conveyor.

In addition, there should be a safety factor of about 25 percent. This one is for unexpected weight loads and shouldn’t be used to “just run a little more tonnage” because you have some leeway.

If you increase the tonnage without the safety factor being taken into account in the calculations, the assumptions for the dimensioning will break, then you risk plant stoppages.

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2. Crusher and aiming machine are not proportionate to each other

Occasionally, replacements are carried out. A common situation is that the crusher in an older plant needs to be replaced. Then, of course, you want to invest in a crusher with good capacity.

What often happens is that the aiming machine after the crusher is unable to handle the increased load.

Then you end up having to run the crusher half full, which is unfavorable for the crushing process. A half-full crusher produces material that is flaky and not very cubic and you get lower quality of final product.

Here is the solution:

Balance the plant by increasing capacity in the sieve. Much can be done by testing different types of sieve mats. There are hundreds of different types of sieve mats. They are made with different mixtures of steel, polyurethane and rubber that give different elasticity.

Different sieves have different hole sizes, density of the holes and shape of the holes (straight or cone). All of this plays into the capacity of the sieve.

Many people use the same sieve cloths as they always did, but it can be worthwhile to test different tablecloths.

Different sieves in combination with each other can increase capacity a lot. Here, a modular sieving cover may be optimal.

Read also:
The huge difference of the right sieve cloth

If changing the aiming cloths does not work, you can consider changing the aiming machine. This will be a cost/benefit calculation. If you increase the capacity of the entire plant, it may be worth the investment.

3. Uneven distribution of tick mass

It is crucial that the materials are spread evenly as early as possible. It begins with the blasting of the rock. Both the drilling pattern and the bit are crucial for a correct start. This must be optimized for each individual withdrawal.

If the blasting job is not done correctly, problems arise in the bearing piles. There, all the fine material will remain as a cone in the middle, while the coarse material seeps out on the sides. This happens often and then the drivers who load have to compensate.

In addition, they need to look at the weather in terms of precipitation and stickiness in fines. What can be loaded in stay-at-home weather should perhaps be avoided in torrential rain.

Here is the solution:

Those loading must mix the loading and make sure that the mass is well mixed. Often it does not happen. This is because drivers often lack the right knowledge that the way they load is important for the further process.

I have experienced that many drivers do not understand how important their job actually is.

Olav Gilje, technical support at Nordic Bulk

For loading to be good, the driver needs to know enough about the factors that play into the crushing process. He or she must have an understanding of the totality of the facility. That their job is not only to load and tip stones also done with it.

The solution is often good information and proper training. A professional day or course for drivers can be beneficial. Both drivers and the rest of the personnel should understand how important loading is.

4. Rollers being knocked to pieces

As a rule, the rollers last for a long time where the masses lie still on the tape, problems arise where the masses are loaded from one tape to another. Mass falling has great powers. It is important to remove the fall, so the mass slides out nicely onto the tape.

Here is the solution:

You take care of the rollers in loading by ensuring proper design of the downspout. It can be solved by embedding a shelf in the downspout, allowing it to absorb the impact of falling mass.

This is especially important in transitions and where heavy masses are transported. In some places, shock rollers, shock mats or specially designed rods must be used to cushion shocks (Impact bar).

5. Too narrow openings

If you have a funnel that conducts the mass, it can accumulate when more rock than intended, or larger than expected rocks slip through the crusher.

In any case, a bottleneck will occur, in some cases if a clogged downspout suddenly drops, it will overflow into the long term and conveyor belt.

Here is the solution:

Open the size of the hole exiting the downspout. If it is not possible to open, you may be able to change the angle of the funnel, or adjust the pace of production on individual masses.