The use of compact, highly mobile rubble-crushing plants has grown substantially in recent years. These plants are largely used in cramped urban and suburban locales to crush concrete and asphalt rubble and similar materials, sometimes including limestone. They generally can be set up for operation quickly and may be moved frequently, crushing relatively small quantities of materials at each site.

Choosing exactly the right plant size, type and crushing capacity for the anticipated — and perhaps unanticipated — needs is critical. Most operators are savvy enough and will do sufficient investigating to avoid choosing a wrong plant. But some plants are more right than others for each individual operator's needs. The difference between the right plant and the ideal plant may not be obvious. Yet it can make a difference in your profitability.

The key factors in selecting any road-portable crusher plant are mobility, efficiency and durability with low maintenance. But in the case of the compact, highly mobile mini-crusher, it is crucial to make sure the manufacturer has not sacrificed efficiency and durability to make the crushing plants small, light and mobile.

This is particularly true where the crusher and the screen are mounted together in closed circuit on one chassis, with the crusher on one end and the screen on the other. With these units the crushing and screening plants don't have to be transported separately, but they can pose some disadvantages.

The first two considerations are size and weight. Combination crushing and screening plants are considerably longer than a crushing plant alone. This affects maneuverability and takes away options in the setup configuration from site to site. But in addition, the manufacturer may have sacrificed quality in components and structural members to limit the overall weight on a single chassis.

State authorities can provide travel weights and restrictions. If a plant requires a hauling permit, such permits are normally easy to get.

The combination plants also may sacrifice clearances and ease of maintenance. Make sure the unit allows ample room for smooth material flow and ready access to all components — especially the crusher and engine — for maintenance and repairs. Minimizing downtime can be the most critical factor in determining profit and loss.

The crusher itself must be a primary impactor designed especially for concrete recycling. Be sure the plant does not have a secondary impactor modified for what might be perceived as light-duty primary crushing.

A mini-crusher may not be used for light duty very often, if at all. Although it is sized to handle smaller throughput volumes, the impactor still must be engineered and built for the rigors of heavy-duty work with minimum maintenance.

Thus, the mini-crusher should be a smaller version but not a cheapened version of a full-size primary impactor. It should offer the same features with no compromises in design, performance, structural integrity or components such as side liners and blow bars.

Why Size Matters

The crusher inlet size is another critical factor. A small inlet may require excessive pre-feed preparation to break incoming materials into pieces small enough to fit into the opening. This pre-feed prep with a hand-held pneumatic hammer or mobile hydraulic hammer is time- and labor-intensive, which can be very costly. So costly, that too much pre-feed prep can make it difficult or even impossible to make worthwhile profits. A good rule of thumb is to be wary of any crusher inlet less than 36 inches wide.

The impact crusher should be capable of handling sufficient tons per hour. Each operator must determine if he will process large or small amounts of rubble per job or per week. It also is important to know how many sites the unit will be at per month, week or day. For most mini-crusher applications, 150 tons per hour capacity should be sufficient. However, for not very much more cost, there are slightly larger but still highly mobile hydraulically controlled plants that may crush as much as 200 tons per hour and provide for greater control of product size.

There must be sufficient room under the crusher for metals and crushed materials to flow freely onto the discharge conveyor without clogging the chute or tearing the belt. Ferrous metals can be removed by an electromagnetic separator mounted on the discharge conveyor in line with the material flow for maximum efficiency and to prevent clogging. To further prevent clogging, the separator's belt cleats, pulleys and chutes should be made of a material that will not magnetize, such as stainless steel.

A well-engineered mini-plant should operate efficiently for many years with minimum maintenance and little downtime. Compare each manufacturer's maintenance recommendations. And make sure wear parts are easy to replace. For example, a hydraulically operated split housing on the impactor will save hours of downtime in replacing parts such as blow bars. And a hydraulic hood opening makes unclogging inlet jambs easier.

Finally, always talk to users experienced with the plant being considered. There are many good equipment manufacturers, and each brand offers worthwhile features. The challenge is to find the right equipment with features suited for a particular need.

Information provided by Grasan.