We here at Unlimited Resources Corporation would like to take a few minutes to tell you the proper way for replacing hammers on your Tub-Grinder. As you know there are two basic types of hammers. The first type is the “swinging hammer” and these can usually be associated with the small low horsepower machines that are used by the small production owner. These are generally just a throw away type hammer and they can generally be run for a while and then turned and run for a while longer till you wear the other side of the knife down to where its not efficient to run it any longer. The second type of hammer is the “fixed hammer” and they typically are offered in several different designs and some even offer replaceable wear tips so you don’t have to change the hammer all the way out. You just replace the tip. These fixed hammer machines are generally the “big boys” or the “work horses” of the industry and are generally from 350 horse power to 1500 horse power in size.
Now most of the newer tub grinders are equipped with a tilt tub to make changing these hammers much easier than what the older models used to require. The first priority is to get the machines cutting area cleaned out completely to help make changing the hammers a much easier process. Second you must either tilt the tub or remove the cover on the older units to reveal the end of the hammer mill shredder and this is where you will find the lock that holds all the hammer-mill shafts or rods into place. Here you will loosen this plate by usually unscrewing either 3-or 4 bolts. Then this will allow for the lock to turn and this should expose the end of all the rods that go through the hammers and lock them into place. Many times these rods have a threaded hole in the end of the rod and this allows you to pull them if they are too tight to get out with normal amount of sliding effort.
You want to carefully mark down where each of the hammers is located on these rods so that you can get them loaded back into the machine in the proper place once you’ve pulled the rods out of place. Before you install the new hammers they need to each be weighed and the weight written down for each hammer. Then you need to carefully match each of these hammers up with another one of similar weight and this can easily be achieved by either welding a little on one or grinding a little on one to get the weights so that they match as close as possible. When you install these hammers back into the machine make sure that you match up the two hammers that you have grouped together so that they go directly across from each other in the machine. This way you have balanced the mill and this will make the machine operate much better and it will also prevent the destruction of bearings on the main shaft of the mill. This simple procedure will generally cut down a tremendous amount on the vibration that the mill causes as well.
We have visited many sites where they just removed the hammers and then installed new ones and never paid any attention to how the old hammers came out of the machine. They didn’t make any effort to weigh each hammer because they were all made by the same factory so they assumption was that they should all weigh the same. Well the fact is that we’ve seen the weight in these factory made hammers vary as much as several ounces and this can cause premature damage to your mill bearings and cause a tremendous amount of vibration damage to be done to the whole machine. So we can’t stress enough the importance in weighing these hammers individually and matching them up in identical weight pairs and making sure that you install them across from each other in the machine.
Also many times these rods that hold the hammers in place will need to be replaced because they’ve become worn so generally it’s a good ideal to order new rods while you’re ordering the new hammers. The hammers need to be replaced whenever the machine starts going down in production. New hammers will normally run close to the screen and this causes the shearing action to be greater and thus the machine operates more efficiently. If the hammers are worn they tend to be further away from the screen and this causes the shearing action to lessen thus making the way the machine operates less efficient.
Finally always make sure that the screen in your machine doesn’t have too much wear on it because it also can contribute greatly to the loss in the shearing action that the machine has because of this wear. So carefully inspect your screen each time you change out your hammers and they will generally need changing out about every four to fives times that you change your hammers as a rule of thumb.
If you follow these simple steps it should ensure that your hammer mill shredder part of your tub grinder operates at its greatest efficiency. Note: the improper placement of hammers in these mills has caused many mill bearings to fail prematurely. You and only you can keep this from happening to your machine!