Why Are 3 or 4 Dipper Passes Considered Optimal?

[Dayton3]

When reading about giant dump trucks, I've read many times that three passes with the dipper bucket (four at most) to load a truck is considered best and most economical.

Which explains why 240 ton trucks and 80 ton capacity loading shovels are so well matched.

But why?

It seems to me that it should cost the same for a dump truck to sit there through 10 passes of the bucket (as the Terex Titan 33-19 had to) as sitting there for 3 passes and spend more time on the haul road.

Either way the engine is running and burning diesel. If you have fewer bucket passes, the truck spends more time lugging up the haul road, so wouldn't it cancel out the decreased idling time?

Can someone explain this to me?

 

[AtlasRob]

When reading about giant dump trucks, I've read many times that three passes with the dipper bucket (four at most) to load a truck is considered best and most economical.

But why?

It seems to me that it should cost the same for a dump truck to sit there through 10 passes of the bucket (as the Terex Titan 33-19 had to) as sitting there for 3 passes and spend more time on the haul road.

Either way the engine is running and burning diesel. If you have fewer bucket passes, the truck spends more time lugging up the haul road, so wouldn't it cancel out the decreased idling time?

Can someone explain this to me?

A very good question put like that.

Its not only the massive machines that work like that, years ago we did 4 passes at Cat 769 trucks with a 245 exc.

The best way I can explain it is take a wheelbarrow and load it with a shovel.
Now load the same barrow with a spade,
Now do it with a very big spoon from the kitchen draw.
Now load it with 1 pass from a mini digger

In all seriousness its about productivity and to be productive you have to find the optimum number of passes to load the hauler and years of playing with the numbers has given the experts the figures we see now.

To take more than 4 or 5 passes when doing bulk muck shift means either the trucks are too big or more than likely that the loader is too small

I dont think I have answered your question :Banghead

HELP !

 

[Iron Horse]

It seems to me that it should cost the same for a dump truck to sit there through 10 passes of the bucket (as the Terex Titan 33-19 had to) as sitting there for 3 passes and spend more time on the haul road.

More time on the haul road = more loads per day = more proffit .

 

[Ross]

Three pass is good. Two pass would be better but then it would destroy the Box.

A 793 will use 10 times the fuel hauling than at idle.

3 pass a 930E with 110 ton a bucket is very productive indeed!

 

[Buckethead]

I believe the equipment and truck manufacturers did studies to find what machines/truck combination were most productive.

 

[Dayton3]

More time on the haul road = more loads per day = more proffit .

True, but if you are hauling the same tonnage per day because it takes 10 bucket passes to load your truck, then what difference does it make?

 

[Turbo21835]

Simple answer is production. You do not want any one machine sitting more than needed. A sitting machine is making you no money. If you have 3 trucks waiting to get loaded, they are not producing. Same goes for the machine loading. If it is sitting waiting for trucks, its not making money. One thing is for sure, you would rather have a truck waiting in line than having a machine waiting on a truck. 3-4 passes is optimal because it gives the next truck enough time to get there, back in, and get into position while you finish the first truck.

A few years back I was on a job loading topsoil. We had so much to move off site, we were giving it away. We had a Cat 350 loading. I had a guy in a pickup pull up and wanted a load of dirt. It took me almost as long to load his pickup as it would to load a quad axle. Its easier to load a big truck, because you dont have to worry about putting to much in at once. If I would have just let that bucket fly like i did loading the quad axles, the pickup frame would be bent, and half the load would be on the hood.

 

[Buckethead]

I had a guy in a pickup pull up and wanted a load of dirt. It took me almost as long to load his pickup as it would to load a quad axle. Its easier to load a big truck, because you dont have to worry about putting to much in at once. If I would have just let that bucket fly like i did loading the quad axles, the pickup frame would be bent, and half the load would be on the hood.

The TV commercials where they had a 235 loading a pickup truck used to make me laugh out loud!

 

[JDOFMEMI]

True, but if you are hauling the same tonnage per day because it takes 10 bucket passes to load your truck, then what difference does it make?

But, you will NOT be hauling the same, because more of the day is spent getting loaded, and less spent hauling the load.
Faster load time = Faster total cycle time, therefore more loads per shift.

Remember, in a hauling operation the loading tool, be it a loader, backhoe, shovel, pushcat, or whatever, is the controlling limit of production. You can only haul up to the maximum that the loading tool is capable of. If there is always a truck ready to load, you will get close to the maximum. If you have wait time, you will get less than the max time.

Therefore, a bigger loading tool will always load more, but if it is larger than about 1/3 the payload of the truck, there will be damage to the hauler box, suspension, and frame. Because of these facts, a loading tool sized to load the trucks you have in 3 passes is optimum.

If you have highway trucks with a 25 ton capacity, 8.3 ton, or about 5.5 cy is the optimum size loader
Move up to 40 ton off road trucks, and you need about a 12.5 ton, or 8cy loader.
240 ton mining truck, 80 ton shovel.

You can always load a bigger truck with a smaller tool, and you may maximize the loading end, but you are paying for way more truck than you need.
Trucks only make money hauling material, they do not make anything while parked waiting to be loaded by too small of a tool.

Hope this helps

 

[diggerop]

Another way to think about it is imagine that the haul trucks cycling are a big conveyor belt, you need to keep it full and no big gaps. Also if the bucket is too big for the trucks, say one or maybe two buckets you would start to lose loader productivity by having to wait for the next truck to back in more often, but then you can go to double side loading

 

[Dayton3]

Thanks everyone.

 

[Gavin84w]

Here is production P & H 5700 and 84A 777!!!!!!!!!!!!!!!!!!!!!!

1 pass 100 ton loading!!!!

 

[JDOFMEMI]

Gavin

If I recall, the 84A was actually a 85 ton rating, but in the picture it looks like about 15 ton of spillage over the lip of the bucket due to the low loading angle, so that would make it come out about right;-)

 

[tracksfan]

Ideally, you match the loader to the haulers for max production such as in JDOFMEMI post#9. however, in my past experience, I had to use what was available. In my landfill days it was a 1.5 cy 225 cat loading clay into 2 d25 4x4 trucks for a distance of a few hundred yards. not bad. Somedays it was loading 627 scrapers or my favorite a D40 4x4 in a hole with the 225 on one side and a 977L on the other. daily goal 10,000 cy. I was lucky to get a 1/3 of that.

 

[Iron Horse]

I can just imagine how many truck tyres they tore up driving over rocks that had rolled off that spillage heap beside the trucks .

 

[Gavin84w]

It was a short term deal untill they got 789,s. They then went to 2 pass loading!!