by Duratech Industries

Duratech tub grinders have a duel belt conveyor system to carry the ground material into a discharge pile. For most machines there is a limited amount of space under the hammermill for discharging the ground material. A dual belt conveyor system generally offers higher discharge capacity of the limited are under the hammermill than auger type discharge system.

As with any machine, proper preventive maintenance for tub grinders keeps operation costs as low as possible. Hammers, teeth, hammer shafts and screens are high wear items. Because of the difference in intensity and amount of use from application to application, it is difficult to formulate a rule of thumb for average wear or average longevity. Longevity ranges from 20 to 200 hours for hammers. The variables also includes how well the raw material is cleaned, how fine the material is ground and how the operator prepares the material. It is essential to check hammers and/or teeth every working day and replace or repair them as recommended by the manufacturer. Do not let the hammers wear out completely before either rebuilding them with hard surface welds or replacing them. If hammers are allowed to wear without maintenance, the hammermill may go out of balance and its shaking will cause excessive bearing wear and other vibration-related problems.

A tub grinder that has an elevated cab significantly improves the operator’s range of vision. The operator in the cab can use the grapple to pick up and place materials into the tub in a way that minimises bridging and the resulting decrease in productivity.

The type of hammers chosen should be determined by the type of material to be ground and the desired size and shape of the end product. Broad, block-faced, fixed and bell-shaped hammers that beat the material and force it through the screens for sizing, are effective for light green waste, grass, leaves and re-grinding of material. Using these hammers for such materials will reduce the wear on the hammers, thus optimising operating costs. Light material such as brush, pallets and Christmas trees that don’t have a lot of weight to carry themselves down into the hammermill are handled best by hammers with pointed teeth inserted into them.

These teeth create an aggressive, ripping action that helps pull the material into the hammermill and grind it efficiently. Because these pointed teeth act so aggressively they increase productivity when heavier material is ground. As the teeth wear, they become more pointed, and thus more productive. In contrast block-faced hammer perform best when they are new. Screens are available with openings in a range of sizes from 3/4 inch to 10 inches, allowing the customer to choose one that will produce the desired size for the end product. Avoid grinding material any smaller than necessary. The smaller the material is ground, the greater the wear on hammers and screens since hammers must make contact more often during more revolutions of the hammermill. At times it is cost effective to grind material twice – first with larger screen openings and then with smaller openings.

A grapple is unnecessary if a front-end wheel loader, truck loader or excavator with a variety of bucket attachments is available. This also give the operation mobility, but the loader must be large enough to reach and tip comfortably into a tub. Another consideration is the size and type of bucket attached the loader or excavator. A simple bucket with a typical flat bottom plate may be a common choice, but it is not necessarily appropriate for all types of material. Bucket loaders with solid bottom plates tend to pick up dirt and sand with the material pile and tip it into the tub. Dirt and sand spell trouble for tub grinders because they are very abrasive to the hammers and screens. When dirt and sand are dumped in with raw material, maintenance cost can increase four to five times due to wear and subsequent replacement of hammers. When grinding trees, green waste, pallets or poles, a grapple attachment on the loader helps grab the material and shake out any dirt before loading.

Maintenance can be reduced by using a loader or excavator with a fork bucket that has spaces for the dirt to fall out. When using a tub grinder with its own loader and grapple attachment, mobility may decrease but gains are made in operator visibility and loading technique. An operator in an enclosed cab of a tub grinder can see the material from the top and spot prohibited materials easier than the front-end loader operator on the ground whose vision is blocked as the bucket is pushed into the material pile.