Material Bin Bridging

Material Bin Bridging

Postby LeeMR on Mon Oct 12, 2009 9:45 pm

I know I'm not the only one who has experienced material bridging in bins, whether it be wet materials, or cold weather, or simply road vibration compacting the materials. I've made it a habit to occasionally empty my bins totally (usually every 1 to 2 weeks, depending on material conditions), and reload with fresh material, fluffed up with the loader before loading. I know I have averted a bridging problem on more than one occasion, because upon opening my gates fully to unload, I've had bridged material beginning to build behind the gates.

I've been trying to come up with an idea how to deal with bridging, in the event it happens in the middle of a pour. I've tossed around several ideas. Attaching a vibrating "fork" which would sit inside the bin, just before the gate, or other such ideas. I don't know where in the bins other mixers have bridging issues, but in a Zim mixer, the bins tend to unload from the front to the back. Unless I'm in need of a full load, I will load the bins heavy in the front, and leave the back as low as possible. I've found this works well for two reasons. One, not being loading fully in the rear, exerts less pressure on the material behind the gate, and it seems to help with the bridging. Two, if I do have a bridging issue, it is easier to dig down to the gate to alleviate the bridged material.

Here is the experiment I intend to try. I'm going to mount a piece of 6" SDR 35 sewer pipe vertically, inside the back of each bin, just behind the gates.The pipe will extend from the top of the bin, down to a point just above the gate. I'll mount them with some type of u-bolt to the end plate of each bin, and then put a cap on top of the pipe. This will keep the pipe empty of material while loading. In the event of a bridging issue behind the gate, all I have to do is pop of the cover from the pipe, and insert a rod (possibly made of re-rod, with a small L on the end. This will allow me to probe through the pipe, and get at the material behind the gate, and break away any bridged material.

I know it seems simplistic, but isn't the KISS method what's usually the best? I'd like to know anyone's thoughts, or other ideas that anyone had come up with to deal with bridging. Other than the obvious of course, which is to keep the materials dry, and under cover. Ideal is great, but not always obtainable.

Thanks,

Lee G.
Lee Gentile

MIX-RITE CONCRETE
http://www.mix-rite.com
888-MIX-RITE (649-7483)
228 Dedham Street
Norfolk, MA 02056
lee@mix-rite.com
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Re: Material Bin Bridging

Postby CONEXPCJ on Thu Oct 15, 2009 12:10 am

Lee, you came to the right place. The intent and purpose of this site has no better example! Material bridging at one time or another has no doubt affected every one of us. The easiest solution we have found is to mount a manually activated vibrator in the vicinity of the sand gate on the back side of your bins. Your equipment manufacturer can assist you in figuring out the most advantageous location for it and the intensity (size) required. Their experiences with the size of the truck and intensity required will eliminate your need for r&d and assure success.
Concrete Express, Inc.
Salem, CT
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Re: Material Bin Bridging

Postby smnstn on Tue Oct 20, 2009 3:24 pm

Hopefully your vibrators operate cyclically (pulse) while you are operating. If not, fix them so that they do. You need this feature to ensure consistent flow of materials. Another thing you can do is pull the piston out of the vibrator(s) to see if it's worn out or working at all. Clean it up just like on a hot rod engine, and make sure your vibrator lines are accepting a mist of 10 W oil or machine tool oil. Then check to see what pressure they are operating at. Most piston vibrators operate best at 70 psi. This is too low a pressure on most machines, because when the air pressure drops that low some air actuated components will cease to function. A happy medium must be found, but if you cannot regulate the vibrators below truck pressure of 125 psi, see if the air lines have ball valve shutoff on them, and that these vibrators are the only thing on that circuit, then if the valves are fully open with the handle in line with the feed line, and off when it's at 90 degrees to it, turn all vibrator valve handles to 45 degrees and see if you get more effective vibration. Never continuously run vibrators designed to promote flow. They must pulse.

Roll your pile when you load. I'm sensing a pattern here with your slump variation and bridging problems. Without being able to examine your sand, these are the two things I suggest. Providing a rod pocket for bridging may present some flow problems. Can't comment accurately here. You can try closing the gates down to the drag chains for travel, then remember to open them to spec to pour.

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