Concrete Crushing: Getting Started

[jaclo]

Hopefully this forum is still somewhat active -

We are a heavy civil contractor that was recently awarded a nice demolition project. Actual estimates are a little hazy but we will probably be crushing ~8000 tons of concrete on this project, with more to follow.

We aren't going to buy new equipment. It's not in the cards. However, we have tracked down a decent Metso 1110 (Impact type) and are looking at a Metso ST3.5 screen + a conveyor that will likely run off of the hydraulic connections on the crusher. These are auction items that we have inspected ourselves, so unfortunately not a lot of dealer support here. Size goal for end product is 2" minus.

I just have a few questions I would appreciate any feedback on:

1. Assuming the crusher is in fine shape, is there a significant enough power draw on the crusher with a hydraulic stacker hooked up to it? We haven't purchased a stacker yet, and if we are better off with a self contained unit because of the "parasitic" nature of the conveyer running off the crusher, maybe we would just forget the hydraulic..?

2. The crusher has an iron magnet that runs perpendicular to the main output belt. One of my partners is thinking another magnet on the stacking conveyor is necessary. The project has no small amount of rebar (think industrial agriculture), but we do have a breaker on an excavator and a Genesis multiprocessing demolition "snip" that will allow us to pre-process the concrete and minimize the amount of rebar that makes it to the magnet to begin with. Is two magnets generally necessary or is it overkill?

3. We are going to have to outfit one of these units with a scale of some kind so we can get an accurate weight on our product. My thoughts are it is best to be on the crusher unit itself, as we certainly want paid every time we put something through that plant. Would we be better off outfitting the stacker or the crusher with the scale?

4. Are there any mfg's out there that make a screen/stacker combination machine? As much combing through machinerytrader as I've done, for some reason I have this thought that someone has to be making a tracked unit that will screen out an oversize product and take everything else out a main conveyor that is ~60', maybe I'm crazy.

5. If you've answered any questions here you have my sincere appreciation - If anyone has any input on basic do and do not that arent safety related I would appreciate hearing this input also.

Thank you for your time -

 

[bam1968]

I cannot help you with the crusher info. But about 5 years ago I tore down a hog confinement setup. IIRC there were 14 buildings. Basically no rebar with the exception of one building. I think the tonnage was close to what you are working with. I called a couple guys with portable units and it looked to me like it would be a break-even deal at the very best. I felt I got lucky when the county asked if they could have it. They loaded it and hauled it away. I maybe should have looked into buying a setup because since then I have tore out thousands of tons of concrete that either got buried or hauled away. It just looks to me that those things are pretty high maintainence to say the least. Hope you find the info you are looking for and have good luck with your project.

 

[Jonas302]

We don't crush concrete but I still have some input

My first though is why are you thinking 2 different machines instead of a closed circuit plant that has a screen built is? It could be your getting a great price on the crusher.. or maybe I misunderstood what you meant Are you going to be making more than one size otherwise you have to come up with conveyors to bring the screen oversize back to the crusher if you want all 2 inch minus

I prefer the scale on the stacker away from all the vibration and but if your going to make more than one pile that may not work

I highly recommend getting in touch with the dealer sales rep even though your not buying from them they will be glad to talk about things like the hydraulic draw of the stacker on that model its there job to make more contacts it makes them look good to the boss your going to need to build a relationship for parts,service new screens and what not Don't feel bad about taking there time trust me they are not selling new crushers every day most time is spent on the road beating the bushes

Should be a exciting new adventure

 

[DGODGR]

In my limited experience, most of the time the scales are on the stackers.
I have not seen a screen with a 60' stacker attached to it.
I don't know what size the rebar is but I think that the one magnet should be fine. You are definitely going to want to remove as much rebar as possible pre-crusher....even if only to help protect the main belt.
Why are you screening when you are only making a 2" minus product? I don't have experience with impact crushers, and not that specific one for sure, but I'm wondering if you might be able to tighten it up enough to make 2" minus in one pass.
I'm with Jonas on suggesting that you talk to the local rep for the crushers you are looking at purchasing. Hopefully there is some decent support for the brand as you will need parts, etc. (support) especially considering that you are not renting a new unit. In fact, I might recommend renting over buying for the quantities you have proposed and for the ease of using a new machine.

 

[63 caveman]

Are you going to sell the crushed material or store it for rebuild, on or off site? To give you much useful advice really need to know more about the total project.

I would be looking for a jaw crusher but it will not get you down to -2". At the very least check the wear plates in the impact crusher. If they have much wear getting every thing down to -2" may take several passes. Any bar over #5 is very hard on them and the smaller stuff likes to ball up around the drum. A single magnet will not get all the mesh and bar out but then again ten magnets will not get 100% of it nether.

The more I think about it getting everything down to -2" is going to be hard with just one crusher and the finished product is going to have so much fine material in it I wonder how useful it will be. If you screen the fines out you going to have about 30% in dust that is not very useful by itself.

 

[jaclo]

My first though is why are you thinking 2 different machines instead of a closed circuit plant that has a screen built is?

Well spotted. It's a combination of availability, pricing, and quality of machine we are getting. Everything we see that has the closed circuit is either out of the budget or a total piece of ****. There's probably one out there, but due to time constraints we had to make a move and this is where we ended up.

I prefer the scale on the stacker away from all the vibration and but if your going to make more than one pile that may not work

One pile

I highly recommend getting in touch with the dealer sales rep even though your not buying from them they will be glad to talk about things like the hydraulic draw of the stacker on that model its there job to make more contacts it makes them look good to the boss your going to need to build a relationship for parts,service new screens and what not Don't feel bad about taking there time trust me they are not selling new crushers every day most time is spent on the road beating the bushes

Should be a exciting new adventure

Thank you for your time

 

[jaclo]

Why are you screening when you are only making a 2" minus product? I don't have experience with impact crushers, and not that specific one for sure, but I'm wondering if you might be able to tighten it up enough to make 2" minus in one pass.

I fought for this one. I thought we could tighten things up and just keep a good set of blow bars in the crusher and we would lose the screen, but our dealer rep that we indeed did reach out to told us that we would need a screen as inevitably we would be getting chunks out of the crusher as big as a fist, which isn't going to work for our owner unfortunately.

Thank you for your time

 

[jaclo]

Are you going to sell the crushed material or store it for rebuild, on or off site? To give you much useful advice really need to know more about the total project.

Owner retains material and is stored on site.

I would be looking for a jaw crusher but it will not get you down to -2". At the very least check the wear plates in the impact crusher. If they have much wear getting every thing down to -2" may take several passes. Any bar over #5 is very hard on them and the smaller stuff likes to ball up around the drum. A single magnet will not get all the mesh and bar out but then again ten magnets will not get 100% of it nether.

I wanted the jaw for the simplicity also. Unfortunately our one spec we have from our owner is -2" and we were sold on the idea that we get a more uniform product with an impact. Everything our guy told us makes sense to me, he is a former kiewit guy and spent a lot of time in crushing operations with them so I have little reason to doubt him.

A single magnet will not get all the mesh and bar out but then again ten magnets will not get 100% of it nether.

Thanks for this.

The more I think about it getting everything down to -2" is going to be hard with just one crusher and the finished product is going to have so much fine material in it I wonder how useful it will be. If you screen the fines out you going to have about 30% in dust that is not very useful by itself.

Our neck of the woods has a lot of pea gravel available so it's not like the material is a great save the day road cover (it's a terrible one imo) - but people use it for that and in their lanes around their yards for fixing potholes etc. Seems to work great as a 6" sub base, but yeah the product really isn't great but the owners seem to see value in having it so that's what they're going to get.

Thanks for your feedback

 

[63 caveman]

I get it now. Sounds like a screen with feed back into impact is the only way to do it with one crusher.

Funny that we crush and #3 pile is the first to go and #2a is last to go. We only crush a small amount of #1b and #2b for best costumers because we just can't get rid of the dust byproduct.