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Choosing the Right Tub Grinder

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Choosing the Right Tub Grinder

This is a brief introduction to tub grinders and some of the factors you should be considering when planning to purchase a new or used tub grinder.

Tub grinders have been around for roughly 30 years and are aptly named for the large round tub or infeed.  Tub grinders rely on gravity and tub rotation to feed material into the hammermill at the bottom of the tub which performs the grinding function. 

There have been some noteworthy improvements over the years, but the design has remained largely the same.  A Tub Grinder is basically a power unit with a driveline, a torque limiter and a hammermill.  Some designs employ a belt drive instead of a torque limiter, but the purpose is similar.  There are a variety of makes and models of tub grinders available in wide ranges of sizes and capabilities.

When selecting a tub grinder, the first three questions you will need to address are:

  1. What kinds of material are you planning to grind and how will you feed it
  2. What production rate do you require
  3. What will the finished product be (usually described by the maximum acceptable length)

Once you have answers for these questions you are ready to begin finding the right tub grinder for your application.  Choosing the right tub grinder boils down to choosing a machine with the right combination of price, condition, and features to achieve your objectives.

The primary features and options to consider include:

  1. Tub and Hammermill Size – Tub and Hammermill size are important for several reasons.  One, it is simply much easier to feed a larger tub, and two, you get much more production out of a larger tub and hammermill.  Regarding tub size, I’m talking specifically about the size of the tub base rather than the top of the tub (which includes the flange).   Although the diameter of the top of the tub will determine how easy the machine is to feed, it is the bottom of the tub that will allow material to get to the hammermill and actually determine production as a larger tub base allows more material access to the hammermill and reduces bridging problems.
  2. Horsepower – If you need more production, or to grind large material (like stumps) you are going to need more horsepower to keep the mill turning.  Industrial tub grinders start at around 400 horsepower up to as much as 1200.  All else equal, great horsepower generally equates to higher production, however actual production rates will vary greatly based on several factors such as: size and hardness of the material processed, moisture content of the material, size of the screens in your grinder, and the rate at which you are able to feed the machine.
  3. Grapple – Do you have a means to load the machine, or are you going to reply on a mounted grapple.  Grapples are convenient when doing contract work or grinding in different sites where hauling an extra loader or excavator is inconvenient or expensive.  For operation in a recycling facility most operators use wheel bucket loaders as they are typically more efficient at feeding the grinder than the grapple.

b2ap3_thumbnail_6-IMG_20130703_141145_562.jpgMost of the manufacturers use similar engines, drivelines and torque limiters so no need to get too far into those details across the various brands.  Once you have addressed the first set of questions, there are still a lot of other factors that might be important to you in your operation including but not limited to:

  1. Fixed Hammers or Swing Hammers – this used to be a significant consideration, but most tubs these days have fixed hammers.  Swing hammers are excellent for extending the life of your grinder and made a great finished product for playground mulch or animal bedding, but they do not handle larger material well (say anything over 18”).  Generally it’s best to keep material under roughly 12” when running swing hammers.  Of course the size and horsepower of the grinder will play an important part in the capabilities of the grinder.
  2. Dry or Fluid clutch – Grinders used a manually engaged dry clutch for nearly 25 years.  In the early to mid 2000’s most manufacturers began offering hydraulic clutches on the machines.  Couple things to know; the dry clutches are vulnerable to damage from operator error but are easier and cheaper to repair.  They also give the operator a little more manual control over the driveline.  Hydraulic clutches take most of the user error out of the equation and typically last longer, but cost two or three times as much to replace and add an electronic component to operating the clutch in most cases.
  3. Reversible Fans – A reversible fan on the engine enables the grinder to reverse the flow of air through the radiator.  This allows you to blow out all of the dirt that has been sucked up into the radiator.  If you are operating in an extremely dusty environment a reversible fan can extend the life of your engine.  If you don’t have a reversible fan than we recommend you do your best to keep the radiator upwind from the tub while operating and to clean out the radiator manually periodically throughout the day.
  4. Magnetic Head Pulley or Cross Belt Magnet for removing ferrous metals.  This shouldn’t be a deal breaker as you can add a magnetized head pulley onto most grinders, just plan to spend somewhere around $3 and $5 thousand for the magnet and metal chute.
  5. Carb Restrictions – Although not a major consideration for most states, anyone operating in California should be well aware of carb laws which restrict the use of older non-permitted engines in the state.
  6. Tilt Tub – Nearly all current tub grinders come equipped with a tub tilt feature which allows you to dump or tilt the tub up 90 degrees.  This is handy for emptying the tub, or more importantly, accessing the hammerill and driveline for repairs and maintenance.  When considering older machines (early 90’s models and older) some grinders may not be equipped with this feature.
  7. Remote Control – Remote controls are useful when operating a tub grinder.  Mostly for the emergency stop feature and ability to stop turning the tub and feeding the grinder before approaching for shut down.  Typical remote functions on a tub grinder include
    1. Emergency Stop
    2. Tub Forward / Reverse
    3. Conveyor On/Off
    4. Increase / Decrease Engine RPM
    5. Engage Clutch (less common)
    6. Availability of Parts and Service – Most grinder parts are off-the-shelf, and there are a variety of vendors that supply wear parts.  If you are willing to look for parts and service the machine yourself than you will may be able to get a great deal on a less common or discontinued brand.  If you require dealer service and support, than you will likely need to pay a little extra for it.

These are several of the features and options that you will need to consider before purchasing the right tub grinder.  If you have any questions or would like assistance in finding the right machine, please fill out the contact us form or give us a call.  We look forward to working with you.

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