Good questions. Let me respond to your questions about the toggle plate and the end bars separately -

First, you've got a fine old machine there and it's likely well worth the effort to uncover what ails the toggle plate issue. The same form of breakage on four occasions would seem to be something beyond coincidence.

A good place to start would be a thorough check of how square and parallel the main frame is, both to itself and relative to the pitman. It'd be best to measure the frame for being square to itself, then check the pitman to itself for being flat and square.

Measure the location of the toggle plate to the frame. Since it sounds like the t-plate is being loaded more on one side than the other, static measurements need to be taken of the t-plate location while the plates are not in the crusher. For example, the pitman could be square to the stationary side frame, but not necessarily to the toggling side. Anything more than .150 inches out of square or plane of the overall dimensions will need to be corrected.

We've seen a number of jaw crusher frames go out of square and become trapezoids, rather than the square cornered rectangle they started out as. Corrections to bent frames can be accomplished with hydraulic pressing and external structural reinforcing. We've seen external "girdles" used to surround the perimeter of the crusher frame.

Pick your own uniform surfaces to measure to. You could start by checking the pitman to the frame that the stationary jaw is mounted to, and then work the other way to insure that the pitman is also square to the toggle block and back of the frame. That's a good place to start, and then determine how to correct any error you find will be dependent on where any discrepancies are found.

My recollection is that this model has a single pitman tension spring, so uneven spring tensions shouldn't be an issue. Something bent is more likely. We've seen dual tension spring crushers where the spring pressures weren't maintained well enough in order and resulted in problems similar to the ones you describe. It turns out that just because a spring is set at the correct height, that doesn't mean it's applying the proper pressure. The thorough measuring of your crusher is a good place to start in determining your toggle plate problem.

Regarding the bearings on your crusher, the short reply is -- the larger the end radius, the better. Here's a little background: toggle plates started out as an "over scienced" crusher component, that ended up being the victim of the accountants' sword for several manufacturers. Universal Engineering Corp. is one of the manufacturers that really got caught up in both ends of this mess, although several other manufacturers are in the same boat.

Originally toggle plates started out with an "s" shaped profile and ball type ends. This was done to theoretically provide proper loading of the bearing surfaces of both the plate and seat. The only way to economically produce this shape was as a casting. These parts were typically made of cast iron and intended to serve as a "fuse" (so to
speak) for potential overloads on jaw crushers.

As time went on and the cost of producing patterns and castings increased, someone at the original Lippmann Engineering Works determined that a flat carbon steel plate could be developed to break in a fashion similar enough to the time tested s-plate, but at a much lower cost. Other crusher manufacturers took up with this rocker type t-plate trend and followed suit. The downside, however, was coming up with a way to attach a "ball" type end that would fit existing toggle seat configurations. That wasn't feasible, hence the development of a larger end radius plate and accompanying seat. This was called the "rocker" type t-plate and seat assembly.

Providing a large end radius on a flat plate part was pretty easy, either as a casting or as a carbon steel plate fabrication. For example, if you have a 2" inch thick plate, you machine a 5 degree by 1.000 inch taper to both sides of the end of a plate and blend the intersect point either by hand or further machining. You make a matching radius seat and you're in business.

We've found that a carbon steel plate bearing against a manganese seat burnishes and laps in the best to make plates and seats a viable working friction surface. We've even seen an old trick of soaking a burlap sack in gear oil and placing that between the seat and plate to quiet things down. Fact is, the whole principle is pretty much a stone age technology. This has been improved upon with the advent of hydraulic t-plates available from a couple different manufacturers.

There you have it: toggle plate designs really "just kind of happened". Universal Engineering got caught in the parts availability mess of whether particular crushers had rocker ends or ball ends available in the seats and plates for the last change-out. We know they've got to be compatible, so we have to offer all combinations. Again, our preferences are carbon steel rocker plates with large radius ends and compatible manganese seats -- that will burnish and lap themselves together -- for the longest possible run.

Frankly, we've not adopted or applied that process of wear surface protection. We've seen it applied successfully in some areas exposed to sliding abrasion. However, our customers have not presented to us enough instances of that kind of wear to have warranted the application of that technology.

There's two issues here that are difficult to deal with independently, much less at the same time. The degree to which these factors interact with one another will determine the most suitable wear material to provide.

First, alloy steels lose their toughness ability as temperatures fall. The -40 degree F figure is a plenty hostile environment! Alloy steels become less resistant to breakage in temperatures this low.

Second, the compressive strength value of the material being reduced is also a consideration, as well as the noted abrasiveness. If the compressive strength of the crushed material is low -- less than 20k p.s.i. -- a medium hardness (400 bh) high nickel carbon steel may possibly be in order. If the impact resistance is higher than the noted 20k p.s.i., then manganese steel may be more suitable.

Manganese has a better ability to maintain its toughness in cold temperatures than do carbon steels. However, manganese would be less resistant to abrasion wear. You could use a silica content factor of + .4 to determine degree of abrasive wear resistance as a lower limit wear ability factor.

The long and short of it -- if you're crushing a highly friable and highly abrasive material, use the carbon steel. If the material is both high in compressive strength and possesses a moderate to high silica content, use the higher carbon value premium manganese steel. The governing issue at hand is the compressive strength value of the material being reduced. If it's hard, abrasive and located somewhere that cold, it had better be of high value, as it's going to be difficult to produce. Sizing considerations and type of crushing equipment add to the considerations in selecting the least detrimental wear material choice.