Tub Grinder / Hammer Upgrade
The tub grinder in this example, as an original machine, was fitted with one, single bolt 60mm X 60mm insert that bolted flush to a flat surfaced hammer with one 7/8” bolt.
This particular insert is fairly common in grinders – the older TG400 grinders, the Petersons and some Duratechs use them. In fact this little insert has at one time or another been used successfully on a variety machines. Most of their continued use is in smaller horizontal grinders.
Of course when this insert and its offsider (the 7/8” bolt) step up into the big league of serious horsepower and heavy timber it becomes obvious why many larger machines use double bolts or 1-1/4” single bolts.
The main problem was that a serious hit would twist the insert then the corner of the twisted insert would catch a piece of timber. The bolt (which is taking the entire load) snaps and you have a 1.5 kg missile flicking around (or through) your bowl.
Ideally we would have trialled a two bolt insert for this machine but we were restricted by the distance from mill to screens, so we lengthened the insert slightly, added a tang (to reduce the load on the bolt) and changed the bolt to 1” UNF with our very own custom lock washers and cone nuts.
Sounds easy – but we trialled inserts and hammers back and forth for nearly two years to reach near perfection.
This type of insert and hammer combination has increased productivity and wearlife, reduced hammer wear and our customer hasn’t lost an insert yet!
We have since applied this principle to other machines with similar outstanding results.