Auger Mixing Angle

Auger Mixing Angle

Postby LeeMR on Thu Oct 15, 2009 8:30 pm

I know others must have encountered this issue. With our augers having to be at a 25-30 degree mixing angle, you are quite frequently limited to the distance that you can "chute" your mix to the desired location. Or, you have to get over a fence, into a wheelbarrow on a raised loading dock, get to the back of a long slab, pour into a pump, etc. You can only reduce water by so much, to get proper hydration, and thus you can only increase your mixer auger angle by so much. A customer wants you to "wet up" the mix a little, and before you know it, you have mix running out the top of your hopper. So you reduce your auger angle, and your customer looks at you like you have two heads, because he wants to send that mix a further distance. It is kind of lame that we can't operate at higher angles.

It seems there must be a better way to increase our auger angles. I came across a company called "International Mobile Mixers". They claim with their closed flighting, that they can obtain a 45 degree auger angle, with up to an 8 inch slump. Sounds good to me! If this is true, why can't these other companies do the same? Has anyone experimented with different augers, to get more angle?

I know that practicing the "KISS" method is the best. But somehow I feel that the manufacturers have dropped the ball on this issue. We are using what I see as aging technology on auger systems. There has to be a way to tighten up the tolerances between the auger and the auger boot/tube, to enable us to have higher mix angles, with wetter mixes. Not to mention the secondary benefit of keeping the concrete mixing in the auger boot longer.

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: Auger Mixing Angle

Postby smnstn on Tue Oct 20, 2009 3:08 pm

Lee -- this is a very sore point in the industry. It is the final stage of any proprietary equipment design that can be engineered. After that, the mix is out in the atmosphere and on its way to the ground. A chute is a chute, but there are some special latch and hook designs that have nothing to do with the mixing.

The ability to get mud up the tube and out a distance or to achieve an elevation is reliant on many things -- the clearance of the auger in its boot, the wear on the protective blades, the characteristics of the mix needed, the pattern of the internal flighting, the rpm of the mixer and the speed with which the materials are delivered into the auger throat are a few. First of all, you should not be able to comfortably insert your fingers between the flighting and the boot. The wear will be different near the bottom than the top. You may have to change the first third of the wear blades on your flighting three times for every one time of those near the top. Rubber booting will stretch. There is material available that will not stretch, but it is expensive. Sometimes it's possible to trim the boot along its steel retainer strip and drill new holes, remounting it as much as an inch closer to the blades. But stretch has to be really significant to get into that. Make sure your screw (auger) is turning at the correct rpm. Check your manual for that speed. If you are frequently trying to get mud up and out, call your manufacturer's service department and see if you can increase mixer rpm. I like to see a minimum of 300 rpm, but not all machines are designed to operate at that speed.

Now comes the proprietary engineering part -- the configuration of the mixer flighting on the shaft can determine the ability to pump mud high and far. Several manufacturers have an alternative design that will facilitate high discharge. International Mixers as well as Cemen Tech are two of these companies. I have utilized both of these on projects myself with mixed results. If the mixing chamber with the shear paddles is too high on the shaft, your concrete will not be sufficiently re-consolidated for discharge and you will experience stone and sand "striping". This does not impact customers favorably, but the concept works because the first two-thirds of the mixer is nothing but solid flighting. I think you need a minimum of three complete solid flights above the final mix paddles to consolidate your mix adequately. Some high discharge mixers turn as fast as 400 rpm. This may be OK if you have a large bore mixer that will hold enough material to enlist gravity as a helpmate in the mixing process. If not, you will be separating and spraying your component materials all over the place. But big bore, high rpm mixers require a lot of power; so usually this is a specially designed unit from the PTO right on back to the mixer motor. Finally, some mixers are well-designed with a "flinger" just in front of the bottom bearing. This is a device that resembles a single mixer paddle on the bottom of the shaft, and is pitched so that it propels material falling into the mixer throat forward and up the auger.

Of course you can keep the mixer turning and "jog" material into it for special pours that require height. But be aware that this generates heat and wear. A really hot summer day can kill your hydraulic motor and/or valves. The fluid should be synthetic anyway for mobile mixer applications because some days you will get it hot enough to blister the paint on the hydraulic tank.

The short answer to your actual question is "Yes", the high discharge mixers do work, but be careful what you ask for. I can help you in this area if you do not get satisfaction from the manufacturers. You might check with the original manufacturer of your particular unit and see if an updated component auger or complete mixer is available for that model.

Simon
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