Operations Focus: Think Twice

There are many ways in which crushing and screening equipment can be configured to produce more than one product on the same production line. Whether a screen or a primary crushing plant's grizzly section is being used to further separate material, it is possible to make multiple products at one job site.

Gerry Mangrich of Universal Engineering Corp., Cedar Rapids, Iowa, says that while making more than one product often is possible, the decision to produce multiple products at a job needs to be driven by the demand and potential profit for those products.

"The most economic recycle operation will make a single stock pile of base material," says Mangrich.

He adds, "You need to make sure there is enough of a financial gain involved to justify the costs you are going to incur not only in the investment but also in your maintenance expense to create that product."

Universal Engineering serves the quarrying and recycling industries. Contractors new to crushing often want to buy used equipment from the quarrying industry. Mangrich says that while most quarrying equipment is designed to make multiple products, that may not be the most practical choice if the most desired salable product is base material. Quarry equipment may also prove inadequate to handle the rigors of reinforced concrete with rebar and wire mesh.

"There are areas of the country, such as in Florida where Redi-Mix operations are starting to look at recycled concrete in lieu of virgin aggregate in the mix of new concrete. That is where you really get involved in multiple products and controlled gradations," says Mangrich.

A typical two-product scenario might involve splitting out some of the fines in order to make a coarser stone along with a base material. Adding a screen will allow operators to make a preferred product, but both products should be salable.

"Virtually everything a recycle contractor puts into his hopper becomes a valuable product," Mangrich says. "One of those products will be the cash cow, or the predominant revenue generator."

Even if operators are only using a primary plant with no screen, there is an option to pull out the fines through the grizzly section of the crusher and creating a separate product. One example of this, according to Mangrich is pulling the organics (soil and plant matter, etc.) out through the grizzly with the use of a flop gate and cross conveyor. The organics become a backfill product and the clean, crushed product becomes a more valuable material. It is also possible for an operator to reduce the amount of fines in the primary product by utilizing the grizzly section. Depending on the desired product, an operator can then make use of the crusher's flop gate to blend some or all of that material back into the crusher run.

If an operator is using a screen to make more than one product, Paul Smith of KPI-JCI Astec Mobile Screens, Yankton, S.D., says operators should look at the material specification versus the output gradation from the crusher. This can help determine if any splits need to be made to make a spec material.

Additionally, operators should make sure the screens are large enough to handle the loads of the crusher "or else you'll bottleneck the system and increase your costs," says Smith.

Once the crushing plant is running, operators typically make sure the products are meeting specification with a "belt cut" and sieve analysis.

"There are also some new devices that employ belt sweeps and scales to weigh material to determine percentage of product sizes, as well as optic sensors that can measure material and provide real-time gradations," Smith adds.

According to Smith, some signs that a screen may need to be adjusted or the equipment might not be right for the application include carry-over of sized product that should have passed through a deck opening, plugging or blinding of the deck, or material that is out of spec.

Many job sites that are recycling on-site have to contend with tight space, which makes the configuration of a stockpile important. Mangrich recommends using a radial conveyor instead of creating the typical cone-shaped stockpile. The radial conveyor has wheels that swivel and allow for a radial configuration or a wall of material to pile up.

"Radial conveyors offer a convenient way to handle excess inventory rather than moving the plant or working the stockpile," Mangrich says. "Ideally, stockpiles should never get too high if the material is being used on the job site or sold as soon as it is produced. However, this is not an ideal economy."

Producing more than one product may require more equipment such as additional screening decks, conveyors and chutes, but the effort and investment can add value to a project.

To determine if further processing is worthwhile depends on the added production costs, what demand the additional product has in the market place and what production rate needs to be achieved to complete the job on time. The right combination of circumstances can allow contractors to reap the benefits of creating more than one product to sell or use.

The author is associate editor of Construction & Demolition Recycling and can be contacted at ksmith@gie.net.