They barrel along at 70 mph, their huge cone-shaped containers turning slowly. The big part is at the bottom, and yet the cement flows -quickly sometimes- out of the spout at the top, and down the segmented troughs.
That’s a LOT of tonnage to shove UPWARDS and out that spout. What is the mechanism by which the cement is both churned/blended, and shoved up and out?
I must know.
Cartooniverse
IIRC, there is a ‘spiral thingy’ inside the barrel. When the barrel is reversed (have you noticed that), then the cement is carried up the ‘spiral’ and out the top. The ‘spiral thingy’ also assists the mixing.
Maybe someone can come back with a better description that ‘spiral thingy’ 'cos I can’t quite describe it right.
I belive it has (for lack of a better term) threads inside. Like a screw. So that when it is turing one way, the cement stays at the bottom, but when they want it to come out, they make it turn the other way so that the cement goes up with the threads. If you remember what was originally used to pump water up a hill (a long screw inside a cylinder), it would be like that.
A variation of Archimedes’ Screw
My Husband is a former cement truck driver and on occasion he had to clean inside of the barrels. He said that there are things inside the barrel called “fins” that are welded to the inside of the barrel that work to keep the concrete mixed while the barrel is turning, but when the barrel is set to turn in the oppisite direction the" fins" push the cement up and out of the barrel.
They have an auger inside
When I submitted my answer those other posts weren’t here yet! Honest!
Boy, I wanted the Straight Dope, I got the Straight Dope. Thanks !! I shoulda known it was a non-moving-parts design. I was waiting to find out HOW they kept any kind of “shoving mechanism” clean.
Live and learn. If only all queries yielded such quick and surefooted responses !
Hmmm? Cement truck? Please don’t anyone say that the screw thingy is “nine yards long.” :eek:
Umm. What?
You mean that is how the phrase regarding nine yards came into use.
Ahhh. Comprende.
A slight aside: As a carpenter, I have “poured” many slabs. We used to race to see who got to “work the chute”.
At the back of the cement truck are hydraulic controls with which you can control the amount of concrete poured, and direction of the chute right to left and up and down.
It was considered a gravy job to work the chute as opposed to dragging the concrete around.
Related cement truck question:
Once in a while I used to see what appeared to be the cement container (drum?) off the back of a cement truck lying in a disposal site. I was told that it was because when the trucks break down and can’t keep the cement drum turning, it hardens and this then requires having to remove and toss the thing. True or BS?
Is there a reason the cement isn’t unloaded from the bottom of the barrel?
Is there a reason the cement isn’t unloaded from the bottom of the barrel?
Because the existing solution works very well and requires no moving parts in contact with the cement, to clog up. Removing the cement from the bottom of the barrel would requiire some sort of hatch, and some sort of mechanism to govern flow out of the hatch. No advantages over the present system.
Between stints as a crane operator, I would drive trucks to support my food habit!! Below is a MUCH too detailed account of what happens with cement mixers.
First the truck is backed under a large hopper, all of the components for that particular mix is added then… The actuall mixing does indeed take place within the truck itself.(and they can carry as much as 12 yards… No the whole nine yards is another story)
after the components (sand rock and cement) are loaded the truck is taken to a staging area called a slump stand. There we will wash off any excess cement that may have spilled onto the truck and actually set the slump of the cement(slump is the viscosity)…
Then the truck is taken to the job site and placed in the correct position… The driver can operate the truck from inside or out! Then the drum is reversed from mixing to pour by turning the drum the other direction( The fins act as an agitator during mixing and transport, But when reversed act as an auger to lift and push out the concrete.)
After the pour is made then we do a washout, Mixers carry about 110 gallons of water and use it to thin out the concrete and for washout. Gotta wash off EVERYTHING! Even gotta reach in as far as possible to try to rinse the fins…If there is any left. the unused portion is taken back to the plant and dumped…
At the end of the day we then do a drum washout Where the Batch man will load our trucks with water and we then agitate as fast as the drum will turn to try to get any residue left over from the day’s work. Then we dump the water, park the truck and go get a beer with the boys!!
That shoulda put most of ya to sleep!!LOL
After further review I see that I never answered the OP at all.The thread was asking how the action is accomplished mechanically…
Well here goes, The drum itself is powered by hydraulics supplied via PTO(power take off ) from the truck engine itself…The speed of the truck motor and the rate at which the hydraulic flows, due to opening valves or controlls, varies the speed and direction of the drum…( I did a job once and expelled 12 yards of concrete in about 45 seconds flat, so they can really hum!!)
Craneop2, when you say that you set the slump on the slump stand, what do you mean by that? Presumably, that you add a particular amount of water?
By the way, I love these boards. You want a nuclear physicist, you got it. You want a cement truck driver? No problem.