Best idea is to ask your Metso representative.  They should be able to support their equipment better than some random strangers on an Internet web forum.

Sathia, the image you show looks choked to me. There really is not much going on in terms of forces at the very top of the crusher cavity. Maybe they expect you to keep the bottom 2/3 full and use the top 1/3 as a buffer zone.

Choke feeding does increase crusher efficiency and capacity is increased as the effect of rock crushing rock prolongs jaw plate life. However full Choke feeding does require more horsepower and produces more fines. Therefore be on guard for crusher chamber packing. Is your motor underpowered?

The feed should be over the stationary jaw with the discharge end of the feeder at a height and distance from the feed opening that will enable elongated rock to tip into the crushing chamber instead of bridging across the moving jaw. Ideally, when economics allow, a pneumatic rock breaker can be mounted close to the crusher opening to effectively deal with bridging in the crusher chamber.

Choke-feed implies a completely filled crushing chamber (or as full as the design will permit), with a sufficient head of material above the receiving opening to keep the crusher full continuously. This contrasts with regulated-feed, which implies that the flow of material to the crusher is throttled to a point somewhat below the capacity of the machine, so that the crusher is never completely filled.

However, as Alex says, have you asked Metso? Let us know what their reply is please.

For improve C140 jaw crusher performance processing granite stone, which is a high hardness rock (WI>16 kwh/t) I recommend:

• To follow Metso recommendation about 2/3 full camera using level control loop
• To limit the maximum feed size to the crusher improving blasting pattern in the mine to get P80 around 250 mm
• To install a protective grate 600 mm slot (parallel bar separated 600 mm).  Metso recommends 850 mm as maximum feed size for medium hardness ore, but in this case the feed size must be limited because the ore hardness in order to improve throughput and mechanical equipment protection
• Verify performance of tph and power draw setting these conditions in the Bruno simulator

I think to summarize this discussion, Metso recommend 2/3 full simply in recognition that not much crushing is done in the upper 1/3 of the chamber.  More so on a double toggle machine, but still relevant on the single-toggle machine is that the horizontal movement of the swing jaw on both an absolute basis (inches or mm) and a relative basis (% of gap between opposing liners) is greater at the bottom of the chamber and this is where most of the crushing is done.  There really is no benefit in filling the top 1/3, as it doesn't give you any higher throughput, and as has been alluded to, it just means more rock to dig out if the crusher stalls.

The other factor to keep in mind is that a jaw crusher's primary purpose is to reduce the top size of the feed material in preparation for the downstream processes, not to generate a lot of fines, so while there is particle on particle crushing, it is not to the same extent as one would see in a cone crusher.  So from my perspective, the concept of "choke feeding" is not so applicable to the jaw crusher as David commented.

The issue about contacting a Metso rep is that it's harder and harder to find one who is a specialist in crushing, many of them have either died of old age, retired, or gone to work for the competition.  The remaining ones are generalists, and know a bit about the complete line of Metso products, but are not specialized in any particular equipment.  This is not a cheap shot at Metso, the same is true for the other major vendors.  Apologies in advance to any Metso lovers out there - :-).

I hope this helps.

Andrew

Good day.

Dear Members,

Thank you very much for all your kind information. Please found below for METSO comment.

"The cavity level as mentioned in the referred topic is 2/3 which is good enough; this is more relevant to the operation who do not feed. That is the minimum or an average level we expect everyone to feed.

Choke feeding is achieved with the combination of good feed gradation(best recommended fragmentation) and the cavity level. To obtain best product output gradation to cater to desired feeding material for the downstream crushing so that secondary crusher gets it uninterrupted, no bridging, and no over sizes for smooth running.

With improper Primary blasted feed to C Jaw means even to get 2/3 level with 1, 2 or 3 boulders are sufficient. But what is preferred is more graded material to be fed in order to attain good inter-particle crushing to generate relatively finer feed preparation to feed to the secondary unit.

Feeding above 2/3 level is OK as long as the feed material is within the cavity and not with over sizes. When operate at higher level unnoticed and relatively larger top sizes likely to get entangled or get feed opening blocked that would lead to down time.

So it is necessary to understand ROM and O&M point of view to obtain the best result as well as O&M challenges for smooth optimum performance."

Generally the feed level is maintained at 2/3 level so that there is enough space to receive the elongated boulders from the ROM without bridging. The C-140 is sufficiently powered to handle a coarse feed as long as the boulder is able to enter the crushing cavity. All or most rock on rock crushing takes place in the bottom half of the crushing cavity. Therefore there is no significant advantage in feeding the crusher to the top level, rather there is the probability of bridging if an elongated boulder does not slide in properly. This will lead to down time affecting productivity.