The manganese liners require a solid base to fully bear against, due to the immense forces put upon them -- both from the crushing work, and from the movement that the work hardening process creates.

Without a substantial base for the part to bear against, the manganese itself would soon fail due to fatigue. There have been a very few crusher manufacturers that have tried to provide metal-to-metal fit cone parts. To provide fitted tapers that bear line on line in a machined state requires very good quality machine tools... too good to be viable in the machining of manganese steel. Not only does manganese work harden with crushing action, but machining the parts hardens them as well.

Manganese steel is a difficult material to machine; it's very hard on both the tools and the machines. As a result, maintaining equipment well enough to provide the kind of accuracy required for fitted machined surfaces hasn’t proven to be cost effective.

The additional time required to machine a part to this degree of accuracy raises the cost of the parts considerably, as well. Most crusher makers have found that shorter, more accurately obtainable machined surfaces on cone crushers is the most viable solution. Filling the remaining casting voids with backing material has proven most effective.

I haven't seen the fitting method that's to be used in this new Metso model. For a related subject, please see my response to a previous question regarding non-backed liners with metal-to-metal fits.

Some attempt at metal-to-metal fitting is likely being used with this new Metso model. The old Symons/Nordberg Gyra-Disc crushers were the most successful run of crushers with metal fit mounting. However, they were relatively short and had flatter 25-degree seated parts. The longer the parts become, the more difficult it is to maintain tapered fits. Maintaining the quality of seat condition in the crusher itself becomes something to consider as well.

The term “mantle” is likely an arbitrary choice of nomenclature that just stuck.

Funk and Wagnalls defines a mantle as “something that covers, enfolds or envelopes”. Perhaps years ago someone in our industry assigned a rather formal title to the "frustro-conical" shaped piece that cloaks a crusher head.

Take with a grain of salt the accepted verbiage used to define crusher parts or equipment behavior. In such an obscure industry, there’s a tendency for folks to apply overly scientific-sounding terms to their business. (I personally find the term “interparticulate communation” to be a particularly stuffed shirt description of “rock on rock” crushing!)

The seemingly insignificant detail of the appearance of the side edge profile of a jaw crusher die has as much bearing on the performance of a jaw crusher as the tooth form or wear face design of the jaw die.

There are varying degrees of fully curved, straight, or straight with curved end profiles commonly available, as well as some specialty side profiles. Various side profiles can be used to “size” the jaw crusher to the feed material available. These are vertically symmetrical jaw dies that can be reversed top to bottom to optimize wear and more fully expend the part.

Fully curved jaws would be used when the crusher is larger than needed for the size of feed being introduced. With full curve jaws, the largest feed size wouldn’t exceed the dimension between the jaw dies just above the horizontal centerline of the crushing cavity. Rock larger than that horizontal dimension will then have its first “bite” taken at a point with a greater included angle, than what exists below that horizontal centerline. Slippage can occur with the larger feed and output reduced.

Straight jaw dies are best used when the feed blend is generally coarse with pre-scalping of fines and maximum feed opening of the crusher is required for the largest sizes of the feed material. Straight dies with a curved end are applied when the feed material includes a blend of enough volume of fines, that the end or toe of a completely straight jaw would wear off rapidly.

There are many variations of all these profiles, plus some specialty side profiles. Examples are asymmetrical cullet, tapered (thin to thick), tapered with curved ends, concave, convex, and more. Variations and cross combinations of any of these side profiles can be used to optimize crusher size to feed material. We have many examples of job designed jaw dies that were made and used specifically for particular sizing situations.

Value in the use of high alloy manganese is optimized when the material being reduced has a compressive strength value of 50k p.s.i. and a silica content of .5.

The optimum value we’ve experienced with our Xtralloy material has doubled service life under these material conditions. As both the strength and silica factors deviate one way or the other from either of these standards, the value in using high alloy manganese diminishes for different reasons. For example, a 20k p.s.i. material with a .2 silica content would reduce so easily that improved wear would be difficult to detect. On the other end of the scale, a material with an 80k p.s.i. strength value and a .8 silica content would be so difficult to fracture that the manganese casting would likely fail through fatigue being fully expended.

There’s a ratio of manganese content to carbon level that provides the most fatigue resistant manganese parts. As the intersect point between the highs and lows of those strength and abrasiveness scales deviate from the established optimum 50k and .5 values, the added benefit of the high alloy material reduces from a maximum service life increase of double. This information is based on data recorded during the development of Columbia Steel’s Xtralloy premium manganese steel.