Big decisions: a crushing equipment industry veteran offers advice on setting up the ideal crushing plant for a recycling operation.
Materials to be recycled can come from many sources, including area construction and demolition contractors who haul rubble to a recycling yard or quarry; highway reconstruction sites that recycle torn-up pavement on the spot, which saves time and cuts hauling costs; urban demolition sites with limited space and great variety of materials; residential or commercial developments where site work includes material crushing, and the list goes on.
The purpose of this article is to present a thought process to help determine what equipment is best for different circumstances or question recommendations given by others that "just don't sound right."
ASKING THE RIGHT QUESTIONS
Some basic pieces of information are critical in starting the process. First is a prediction of the feed material. Where will most of the material come from? Will it be concrete (and what type of concrete), asphalt (ripped or milled), demolition or even rock? It is easy to want equipment to handle everything, and while that is the reality of many recycling operations, some idea of the basic needs will be helpful.
Recyclers must also ask themselves what products will be produced and at what rate. The production capacity may be as much as 400 tons per hour for producing base material from concrete, while the same plant may produce 150 to 200 tons per hour of aggregates from asphalt or other concrete materials. A common error is that operators expect too much tonnage out of their plants. While a plant may be sized for 250 tons per hour, the plant may only produce 150 tons per hour because of factors like slab size, steel, method of feed or load and carry distance.
An operator must also consider how much mobility is required. In a fixed recycling yard the equipment can be elevated for easier maintenance and cleanup. If there will be many small site jobs, where mobility and quick set-up is mandatory, the thinking is altogether different.
Flexibility is another factor. The more focused the plant and the equipment are, the more efficient the machine is and less capital will be required. It will be shown that a plant can be designed to handle most any material, but a cost, whether capital or maintenance, will be affected by the material received.
The last point is capital considerations. This one is easy to identify with. Is the operator just getting started? Should rental be considered? Should one be prepared to spend $500,000? $750,000? Is this an addition to a single crusher plant for production and reduction reasons?
The ancillary equipment sizes and capacities are matched to the production capacity of the recycling plant. A wheel loader or hydraulic excavator is used for feeding the plant and wheel loaders load out the delivery trucks with the processed materials. Hydraulic excavators fitted with jaw crushers or breakers also are used for reducing oversized pieces.
Selecting the correct recycling plant is not as simple as selecting the ancillary equipment. The plant must be designed to meet the contractor's requirements, i.e., what materials will be processed and the production demands. The manufacturer must have good service and parts availability. Downtime associated with lack of parts or maintenance is unacceptable. A recycler must find a local dealer who handles recycling plants and stocks parts.
What is to be processed and what needs to be produced has been determined, so what type of crusher is correct for the application?
Impact Crushers-An impact machine works with the simple theory of mass and velocity. Large pieces of recyclable material are impacted and accelerated by heavy masses of metal and are flung at other large masses of metal. The faster the material is accelerated, the greater the reduction. Keep in mind that the initial impact is at the point where the blow bar (sometimes referred to as the hammer), which will weigh anywhere from 300 to 800 pounds turning at speeds from 5,000 to 7,500 feet per minute, comes in contact with the feed material. It is here where the first reduction occurs. As much as 30 percent of the reduction happens here. The blow bar does not grab the feed like a hand grabs a rock. Instead the bar hits the material like a baseball bat hitting a fastball. The second reduction occurs when the material is accelerated into the curtains or aprons. If you can picture both of these reduction points, you can also better understand why the reduction and production decreases as the blow bars wear.
The beauty of an impact crusher is that it will handle and reduce any material that can fit in the feed opening. It will be the most capital cost effective machine that can be chosen. Many times impact crushers will be the only crusher in an installation. With a high reduction ratio and the ability to change the output by changing the crusher's parameters (speed and settings) we can produce quality output materials. There are downsides and compromises with anything. An impact crusher may have higher wear costs and maintenance costs, dependent upon the material, than other crusher options.
Jaws and Cones-Jaws and cones are both compression machines that work by squeezing the feed material between a moving piece of steel and a stationary piece of steel. The basic means for changing the output of a compression machine is to open or close the gap between these two pieces of steel. Production throughput is volumetric in compression machines. As we tighten the setting to produce a finer output, we close up the volumetric throughput capability. Generally speaking compression machines do not provide the amount of reduction that an impact machine does. It is rare that one compression machine will be used in a recycling operation.
The positive side to the compression machines is that they are better suited for concrete, especially concrete with steel. The compression machines tend to be the higher capital cost machines, but can deliver the lowest operating and wear costs. Another positive characteristic is that compression machines tend to hold their value longer than machines of other styles.
One large caution with compression machines: Because of their nature, the jaw or especially the cone does not like asphalt feed. The squeezing of asphalt will work in the cold winter months, but summer will create "pancakes" and not reduction in compression machines. This is one of the compromises faced in selecting the right tool. It also helps to point out why it is important to prioritize the material that will be processed. So while the cone may be poor in asphalt and the impact a better choice in asphalt, the cone can be a better choice in concrete and materials where wear cost is a concern.
ON THE MOVE
Once equipment is selected, layout and configuration can be addressed. How mobile does an operator need to be? What about tracks versus wheels?
Whenever possible, raise the plant in the air to help with cleanup and safety. Many portable operations sacrifice ease of cleaning and maintenance for travel height. Raise the plant either with the hydraulic jacks equipped with the plant or through other means. This will allow for cleanup with the skid steer rather than requiring humans and shovels. While all shoveling cannot be avoided, taking a few extra moments to plan for cleanup and access can make for a more productive and efficient operation.
In many yards, mobile plants are being used rather than stationary. Mobile plants are more readily available, can be set up faster, can be moved at a later date (either onsite or to a new site), will have greater resale value, and may not require the same permitting process as fixed plants.
Now, tracks or wheels? Track plants have long been the norm in Europe and other parts of the world where space requirements are small and excavators are the preferred choice of plant feed. For some 10 years track plants have gained in popularity within the United States, more popular in urban areas but still spotty in rural areas.
For in-city demolition jobs, track plants can be an ideal choice. They are small, compact and can run within hours of arriving onsite. Track plants generally have the same crushers as their wheel mounted cousins, but feeders, hoppers and on-board screens are likely smaller with tracks than wheels. Wheeled plants are designed for loader feed with bigger feeders and hoppers and are generally thought to have higher capacity potential than tracks. The cost of the track mounted impact plant versus the wheel-mounted version is basically the same. So back to the questions answered up above. What are the priorities for this equipment? Material, space and production levels will lead to what is the best choice.
These are big decisions to make. Equipment acquisition is not something one does every day. It can affect what potential the company has in the future. It is also a high entry cost business. Most people start small and trade up or add on as market savvy and knowledge increases.
No two operations are ever the same. The variables--including the human factor--are many. In addition, no matter how intensive the investigation and thought process used to choose the equipment, the operator will always learn more every day. Learn from your people. Learn from others, including vendors and competitors. Be open to new thoughts and ideas. Start with the thought process so that you attempt to make a fact-based, priority-driven decision. You will thank yourself.
RELATED ARTICLE: Wired in.
The Flex-Mat 3 Self-Cleaning Screen Media from Montreal-based Major Wire Industries Ltd. has been designed to increase screening efficiency and improve throughput in aggregate and mining applications, as well as asphalt and concrete recycling operations.
For Recycled Asphalt Paving (RAP), the stain less steel Flex-Mat 3 is designed to eliminate blinding, particularly in warm weather when recycled asphalt material can turn hot and sticky, according to a news release from the manufacturer. Flex-Mat 3 can be used on top, middle and bottom screen decks.
Flex-Mat 3 is also designed to eliminate blinding that occurs when processing dry and dusty material, making it a good match for recycling concrete.
Flex-Mat 3 is a non-woven, self-cleaning screen media that employs single wires running from hook to hook and bonded in place with lime green polyurethane strips aligned to each crown bar. The individual wires vibrate independently, helping to eliminate blinding, pegging and closing on screen boxes of all types and sizes.
It is available in sizes ranging from 40 mesh to 4 inches.
More information about the product is available at www.majorwire.cc.
Mark Krause is a long-time crushing equipment advisor who currently is an aggregate specialist for Airing Equipment in Iowa. He can be reached at (319) 213-0370 or firstname.lastname@example.org.
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|Title Annotation:||OPERATIONS FOCUS|
|Publication:||Construction & Demolition Recycling|
|Date:||Sep 1, 2006|
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