if i wanted to build a jaw crusher...

[Renze]

You are partially right: the bigger the machine gets, the less need for a jackhammer to reduce the debris untill they fit into the breakers mouth.. However, when the breaker is built to efficiently use twice the power, it weighs 4 times as much, it seems.

Some folks are renting electric 7.5 Kw driven machines that take a brick at a time. It can be pulled behind a heavy car, a van or a 4wd, weighing about 2500 kg. Taking a brick at a time isnt really something. I think if have one for rent with a 400x600mm opening, to be powered by 50 to 70 PTO hp, i think there are lots of farmers that want to turn their rubble into gravel to pave some path around the farm.
Also, i could use it myself to clean up several hog barns.

 

[Renze]

Found a home made on YouTube: Only drawback is that it requires manual chiseling to make rubble fit into the chute

YouTube - home made jaw crusher

 

[Renze]

I did a 30 minute sketch up of a 600x400mm jaw breaker in OneSpace designer home edition. I use the pro edition at work, so i dont even make the step from Autocad 2004 at my previous job, to a new Acad 2008 anymore)

I used 30 degree jaw angle, 40mm steel sheets, pin/hole connection for the reinforcement ribs, to spread the welding heat and strain, to both sides of the sideplates, i use 40mm backplates as main support structure, then a replaceable 15mm plate bolted on top of them with 30mm manganese steel round stock welded onto them every 60 mm.

questions and comments are welcome. Please remember, its just a very rough sketch for now...

 

[js5020]

Very nice job on the drawing! I have never seen one of these up close and am really interested in what the drive line would look like? How small would the crushed material be?

 

[Renze]

Jaw breakers use an eccentric shaft to make the jaw move an inch and a half, at around 400 rpm. That makes 1500 engine rpm with a 540 rpm PTO. So i dont know if it will be direct drive with just a torsion damper to get maximum fuel efficiency, or with a 1:1.25 reduction so the tractor engine can run at 1900 to 2000 rpm to get more power.

As an engineer i can do all calculations, but I dont know how much force it takes to crush a rock. Because i have no data to calculate with, the outcome will be literally a "calculated guess". So i'll just see how professional machines are built, and then overbuild it a little.

I think i need at least a 3 inch eccenter shaft. I have someone who works at a local machine shop, that has done machine and lathe work for me before on his free saturday.
Bearings, i dont think ball bearings will take the shockloads. So i'll use either toroidal roller bearings SKF - Demo
or plain steel on steel slide bearings. These require frequent lubrication, but take shockloads very well, a lot better than steel on bronze sliding bearings that require less greasing. SKF - Image


The crush size would depend on the width of the gap between both crusher jaws, which should be adjustable, either by shims behind the lower toggle plate, or by pushing a wedge behind it with bolts. I cant see how threaded rods could keep the jaws together, but when using threads to hold a wedge in place, there is the reduction of the wedge angle, as well as the friction, to hold the stuff in place.

I am not going to use expensive and heavy trapezium threaded shafts to adjust the gap.. I'll probably set it once and forget about it.

I have added a PDF of my work for tonight: the bearing plates of the moving jaw still look like sh*t, and i have changed the jaw angle from 30ｰ to 22 degrees, like pictured in a youtube video. This will reduce the jaw opening to 600x300mm, but most concrete foundations arent heavier than 250mm so it'll eat any demolition rubble i can throw at it.


I was hoping that my sketches would get some more comments of people that use crushers professional, about the jaw angle and jaw ribs... ?? Am i thinking into the right direction ? The reason that i want to build one, is that there is no such thing available in a wide radius around my place, so i cant take a look at one and have to guess dimensions from YouTube videos..

 

[Renze]

just threw in some SKF bearings, eccentercams and a shaft...
It makes a 30mm (1" 1/8) stroke on a 75mm (3") shaft.

Will need research before i can do any actual strength calculations on shaft, bearings and jaws...

 

[js5020]

I have looked at several on youtube,, most look like they have a flywheel, now these are small and old, some are shown running off a steam tractor and a belt,, do you think something like that is necessary, or will sheer hp be able to do the work?

 

[Renze]

I sure need a heavy flywheel, the force is applied in only 1/4 of the revolution of the crusher shaft (my guess) so it will run very jerky, bust PTO driveshafts and cause excessive wear on the tractor as well, because then it will use the rotating mass of the rest of the driveline, from the pistons all the way to the PTO shaft, causing undue stress in the rest of the power source.
The flywheel needs to be heavy enough to store the unused energy in 3/4 of the crusher shaft rotation, and release it in (a part of) the crushing stroke.

The thing with flywheels is, the heavier you make the flywheel the smoother the engine rpm will be, and give less load on the engine and PTO. However if the flywheel is too heavy, the energy released on the jaws during a blockage, is so tremendous that it will damage the crusher.

The heaviest excavator mounted concrete demolition cutters have a max force of 150 ton. Off course a solid concrete slab which these babies can cut to pieces, is much tougher than a cut-loose piece of concrete of the same thickness, but a jaw crusher applies the force over multiple jaw ribs.
Nonetheless, i think i'm safe when i use that 150 ton force as a benchmark for designing the strength of the crusher parts, including the shear bolts in the toggle plate.

Nobody could supply me with some first-hand practical tips, so i'll calculate for 150 ton.
On the crusher shaft is a multi directional (-100% to +100%) shockload, theoretical prescription is a minimum of 3 for this type of load, so i will use a safety margin of 5 to be sure that weakenings like for example, the keyways milled into the shaft, wont bite me in the @rse.
On the housing comes a single direction (0 to 100%) shockloads, to which the books prescribe a safety margin of 1.5
I used to design trailer frames with a safety margin of 2, which were often overloaded. So i expect the crusher will withstand the peak loads that occur every once in a while, just as the trailer frames are overloaded AND hit a pothole every once in a while at the same design safety factor.

I have calculated a bit on the backplate with ribs, trying to remember the rules that apply to odd shaped structures, CoG, moment of inertia, etcetera.
I have to get into it, but i can tell i need to beef up the backplate ribs from 100mm to at least 150mm and maybe more.
I am calculating with St.52.3 (S355 or Fe590), a fairly cheap mild steel with a 1.5 times higher yield strength than standard construction steel.

If the side plates of the crusher start to wear, i will weld hatches of abrasive resistant welding rods on them. Its a lot cheaper than cutting those 350 kg plates out of Hardox, Manganese or Borium... I also expect that mild steel will be better resistant against fatigue around the welds.

 

[638]

Renze,

About 40 years ago I worked on a small crusher at the company I was with at the time. It ran two excentric shafts, one at the top and one at the bottom of the movable plate. They were chain driven together and timing of the two shafts was critical for proper operation. If I remember correctley, the top shaft had a total throw of about 2" and the bottom shaft about 1/2" or less.

 

[Renze]

638, thanks for the reply, you gave me information i was looking for. I will use 2 inch stroke (50mm) instead of the 30mm stroke.

The lower eccenter with a half inch stroke, modern crushers use a toggle plate that causes the lower end of the jaw to "chew" as well, have a look at this video:
YouTube - Jaw Crusher

I have seen smaller crushers that have a toggle plate in 2 halfs, bolted together in the middle at a 10 degree angle (like a boomerang)
When the force is too much, the 10 degree angle will guide the compressive force aside, which causes the bolts to rip apart.

A double eccenter shaft is more expensive to manufacture ( i am cost aware, even though this might be an expensive hobby anyways) and i'd rather have a 1 euro bolt to break, than a chain link, which is much more expensive and time consuming to replace.

I think i'll change the shaft/eccenter design, instead of torching and lathing an eccenter which is attached to the shaft with a keyway, its better to use a bigger diameter shaft and have an eccentric end lathed to it. This way there is no weakening keyway in the shaft, and no worries about keys that get smashed because of continuous pounding.

In a job i had a couple of years ago, i have opened Wacker vibrating plate compactors because i heard a cling sound when the engine was idling. I found the eccenter weights (that cause the vibration) to be loose on the shaft because the key and keyway were all busted... ITs hard to keep a key in place in this type of load situations.