Ihab Saad – Tractors and dozers

Music. Hello and welcome to another class in construction

equipment. And today we're going to be talking about tractors and

dozers. We're going to learn about what their properties are, what

are they primarily used for, and then we're going to learn about

how to calculate the production rate for these different pieces of

equipment. So first of all, what are tractors and dozers? A tractor

is a self propelled machine used to pull a load or attachment or

push a load with a front mounted blade. So it's a machine that has

a blade in front of it used primarily to push a load, and it

can either be track mounted like crawler tractors or on wheels,

each one of them has its specific uses. Tractors with front mounted

blades are referred to as dozers, like in bull bulldozers, for

example.

They are quite versatile machines. So what are they used for? They

can be used to perform many earth moving tasks, primarily earth

moving tests, including backfilling trenches after

excavation is done through the excavators that we learned about

in the previous lecture, we can backfill by pushing the soil back

in that trench through the dozer clearing and grabbing it can also

be used to clear the site. If we have some rocks or some trees or

debris, it can push the debris aside to clear the site, creating

stockpiles. If we want to stockpile the soil that has been

excavated in one area for a while until it's ready for backfilling

again, then the dozers can be used for that excavating, although

that's not the primary use for double dozers, but as we learned

last time, if they are available, they can be used for that purpose,

pushing loading scrapers, as we're going to learn in future lectures.

When we talk about scrapers, there are cells that some self

propelled, scrapers that have their own engines, and there are

some scrapers that need to be pushed, even sometimes when they

are self propelled with a very big bucket. Then in this case, they

need to be pushed to be able to start moving, ripping compacted

soils or soft soft truck. We're going to see that one of the

attachment that can be added to dozers are rippers that can loosen

the soil or break soft truck, shaping slopes through some of the

motion and tilting of the blades, as we're going to see again in

this lecture, you can shape slopes and finally, spreading material.

If you want to elevate the level of the site by adding topsoil, you

can spread that material using a dozer as well.

Now, the decision to use

tracks or wheels for the dozers depend on the use and the

availability. So crawler tractors must be transported to sites,

whereas wheel tractors can be give driven from one side to another.

Of course, you cannot drive the crawler tractors on public

highways. They're going to rip the asphalt or the concrete, so they

have to be transported on the flatbed.

The crawler tractors are operated at slow speeds, six to seven miles

per hour, and they possess low ground pressure and they have high

traction. So they're not designed to be operating at high speeds,

whereas the weed tractors are operated at high speeds, up to 30

miles per hour, but they exert more ground pressure and lower

traction. Imagine if you're using that heavy equipment on a muddy

soil. Then in this case, maybe a crawler tractor is going to be

better, because it's going to distribute the weight of the

tractor on the tracks, which is going to be a line load, whereas

in case of a wheel tractor, is going to be a point load,

concentrated load under the tires of that tractor.

Tractors are not cost effective if distance to move material is

greater than 100 yards. So if that's the condition of death, if

that's the case, we're going to look at some other piece of

equipment to do that, task,

site, working conditions and scope of work determines specific size

and type of tractors to use. This is some part of your job as a

project manager, either to improve the job conditions or the site

conditions, or to look for another piece of equipment to perform the

job. Larger tractors are more productive than smaller ones, but

cost more per hour to own, lease and operate. So we always gonna

have the trade off between higher production and higher cost, or

lower production and lower cost. So there's a trade off between the

cost and the production. In this case,

we're gonna now start talking about the different attachments,

different kinds of blades that can be attached to the dozers. And

here, for example, we can see a full grown person about six foot

tall, standing in front of a blade. As you can see, that blade

is almost about 20 foot wide and about seven feet tall. And this is

quite normal on, especially in mines and quarries and so on,

pushing heavy loads in front of it.

It.

Another type is special clearing blades, which are primarily used

for land creating land clearing. So it's gonna scrape the top soil

and remove any debris or any obstacles and then push it in

front of it.

As we mentioned at the beginning of this lecture, dozers can also

be used to push scrapers. So here we have a scraper with a big

bucket, and then we're going to push it through a dozer to assist

it in its motion.

And another example, here we have the Ripper as an attachment that's

going to be used to rip the soil, whether it's tough, hard clay or

soft truck.

And now we were going to learn about the different types of

motion for the blade. If this is the bulldozer, and in front of it,

there's the blade, the blade can move this way, which is called

pilting, which is a vertical movement of the break of the blade

in that vertical level or plane. It's useful in cutting ditches,

breaking up soils in tough crust, and permits concentration of the

tractor, driving power on the limited length of the blade, so

you can tilt the blade and a small part of it's going to be in

contact with the soil, and then with the heavy power of that dozer

is going to be pushing on that tiny portion of the soil, so it's

going to create a very high level of power at that small point of

contact

another so this is the first motion. Is called tilting. The

second type of motion is called pitching. Again, here's the dozer

and here's the blade in front of it. The pitching is rotating the

blade in that direction. That pivotal movement allows the

operator to value the to vary the angle of attack of the blade

cutting edge with the ground and the pivotal movement of the blade

top towards,

towards or away from the tractor. It increases or decreases the

blade penetration by varying that angle. So that's the second kind

of motion, which is called pitching.

The fact the third one is the angling. Whereas, again, here's

the dozer, here's the blade, it's going to rotate in this way. So if

you want to push the soil aside, and the dozer is moving forward,

you tilt, you angle the blade this way. So it's going to be pushing

the soil sideways to create a clear path in front of the dozer.

So the blade is not perpendicular to the direction of travel. It

causes push material to roll off the trailing end of the blades.

Now, some of the blades can perform all three motions. Some of

them cannot. They're going to be limited to maybe tilting only, or

tilting and pitching, or pitching and angling, or, as I said, all

three of them.

So looking at the types of blades, we have four major types of

blades, the straight blade, something like this, which is

primarily used for excavation work, normally heavy duty, and it

can be tilted. It can be tilted.

It's good for penetration of hard materials, and may be equipped to

pitch as well.

The second one is the angled blade. It can be operated straight

or angled up to 25 degrees left or right of normal.

The blade can be tilted, so it can be angled and it can be tilted,

but not pitched. It's designed for side casting material.

The third one is universal blade. As you can see, it has wings on

the sides

that are canted to forward about 25 degrees, and it's efficient for

moving big loads over long distances, and it's used for

working stockpiles. The fourth one is the cushion blade, and that's

quite flat, as you can see, and it's going to be used for pushing

scrapers. So that's going to be the point of contact between the

front of the dozer and the back of the scraper.

Now to measure the production rate of the scraper, we're going to use

the generic equation, which consists of two parts, two main

parts. The first part is the cycle time. What's How long is each

cycle, and the second one is the number of cycles per hour. How

many cycles can we perform per hour? And that's going to be

measured in loose cubic yards per hour, contrary to the other

equipment that we have used so far, where we used to measure in

bang cubic yards per hour, the soil is, in this case, has already

been loosened. That's why it's going to be measured in loose

cubic yards per hour. And this is going to be dependent on the size

and configuration of the blade based on the four types that we

just discussed, the size of the tractor, the engine, power of the

tractor, and how heavy can that load be to push in front of it.

This is the material needs to be moved. So again, depending on how

far do we need to push the material, type and condition of

material to be moved. Is it? Is it loose? Is it in big chunks?

Going to put the heavy load in the trunk of your car, which creates a

heavy load on the drivers, which are the rotating tires the rear

wheel of the car, and that's going to enable the car to move. So

things like that, we're going to learn about them in our next

lecture. And this is basically the end of this lecture. I'll see you

in the next lecture.

You.