Shredding Equipment Focus--Second Time Around

PLANT LIFE. Used shredders should be rebuilt, of course, but special care should be taken to replace bearings and oil seals. Many times oil seals on older machines are made of metal or similar materials and should be replaced with modern lip seals.

Also, temperature sensors (thermocouples) and vibration sensors are added via drilled holes in the pillow block housings and provide early signs of trouble. The sensors allow the machine to be shut down and the problem fixed before any major damage is done to the shredder.

Repairs to the housings on a used machine are to be expected, but this can quickly eat up the savings a second-hand machine can provide if significant work must be done. Housings should be checked for bowing or movement of the steel. One common problem is movement of the bearing pedestals, causing the new bearings to not sit square and level.

MOTORING. Shredder drives take many forms, from AC or DC electric motors to diesel or natural gas engines. The use of surplus diesel or natural gas engines to drive shredders continues to grow steadily.

Engines can save a significant amount of money, because they can be found many times for pennies on the dollar, while electric motors can be quite expensive. Engines, however, require more complex power transmission systems to drive the shredder. Many times this is a belt drive with a tensioner and clutch to allow starting of the engine. This drive can easily cost more than adding an electric motor to drive the system, but careful selection of the motor can avoid this problem.

Engine use requires a clutch and jackshaft or a clutch and cardan (drive shaft) arrangement. Many older style locomotive engines that run at slow speeds (800 RPM) cost much more to use because the slow speed dictates a large drive shaft and clutch. The use of a higher speed (1,800 RPM) diesel engine, by contrast, will cost much less.

All engines should have bearings checked and the compression tested. Mounting the engine on rails will allow the engine to be moved in order to properly tension the belts. The use of multiple engines will require a load-sharing arrangement among them; a number of very good engine controllers are on the market that can do this electronically.

SOLID FOOTING. Foundations can be designed for larger shredders (future upgrades), but it is important to verify that the original concrete foundation will have enough mass to support a larger shredder.

The concrete needs to be able to absorb momentary shredder imbalances. Also, this extra mass must be spread out over the available subsurface soil to avoid overloading.

Soil testing is critical for shredder foundations, and this testing should be performed before any foundations or slabs are poured. Many times, surprising soil conditions are found below the ground, and almost all soil conditions (including swampy and marshy) will allow for the placement of a shredder with the necessary mitigations, which many times are not as expensive as anticipated.

IN CONTROL. Electrical controls, such as the thermocouple for main bearing temperature and vibration sensors, are standard on virtually all new equipment available today.

These electric controls are easy to add to an older system and should be considered necessary when rebuilding a used shredder. These are tied into the starter for the motor so that the motor will be shut off when a problem occurs. These items can detect problems before damage occurs or limit the damage as much as possible.

Newer electrical controls allow computer control of all equipment. This can reduce the high cost of maintenance and retrofits because system modifications require only minor programming changes instead of running new control wires.

Additionally, real-time video images of your operation can be put on the World Wide Web and accessed through any computer, thus allowing you to see your operation while away from the office. Likewise, data, such as bearing temperature, vibration levels, tons of material run per shift, electrical usage and power factor, etc., can be sent electronically.

Retrofitting your old control center to record data electronically eliminates the need to record data by hand. This also means that the data is available immediately.

START AND FINISH. Whether using new or used equipment, scrap processors should be certain to leave plenty of room downstream of the shredder for future expansion.

In the recent past, downstreams have gone from magnetic separation and air-cleaning to large and complicated systems that can sort many different types of nonferrous metals from each other. This trend can be expected to continue and will result in downstreams that take up more floor space.

It is hard to improve on the simplicity of the grouser-pad style infeed conveyor, but most new infeed systems include hydraulic controls. Retrofitting a used conveyor with a new hydraulic system can add a great deal of operating flexibility because of the ability of a hydraulic system to be more controllable and better able to operate under difficult conditions.

Manufacturers of shredding equipment would rather supply an entire system of new equipment—as opposed to utilizing used equipment—for some very good reasons. Many times, the cost of utilizing second-hand equipment can exceed the cost of new equipment. Also, performance parameters for older machines may not correspond to those of new machines, so adjustments to the system have to be made to compensate.

Used equipment often times can be purchased and used more efficiently than buying new equipment, but costs can exceed the price of new equipment if you are not careful. With some prior planning, scrap processors can find that used equipment can be profitable.