Texas company utilizes automatic system to load railcars.

For more than 50 years, WOHWA Waagenbau, founded in Germany in 1949, has been manufacturing blending and loadout systems for loading ships, trucks and railcars. About 30 years ago, WOHWA installed the first fully automatic loadout systems based on PC and PLC technology and using card readers.

WOHWA's strength lies in the designing, manufacturing and commissioning of complete, custom-tailored blending and loadout systems. Complete systems typically consist of sliding gates, belt feeders, gate/belt-feeder combos, belt weighers and the associated automation package including visualization and PLC software programming. All WOHWA products are manufactured in its own workshops.

Marble Falls operation

About two years ago, WOHWA founded a subsidiary in Vancouver, Canada, to provide better and direct service for customers in North America. Since then, several fully automatic blending and loadout systems have been installed in North America, including a fully automatic system for loading railcars at Capitol Aggregates in Marble Falls, Texas, near Austin. WOHWA's dealer for Texas, Crisp Industries, was the responsible main contractor, and in coordination with Capitol Aggregates they decided to use WOHWA technology and products for this application.

The plant has been designed for a yearly production capacity of 5 million tons, and most of the products are loaded into railcars. For this purpose, a fairly large concrete tunnel system was built on which the stockpiles are located. In the tunnel, chutes are equipped with either sliding gates or gate/belt feeder combos.

The flow-rate capacities of sliding gates depend on the characteristics of the product for which they are used and on plant-specific characteristics. Therefore, a definite maximum and minimum flow rate can rarely be confirmed in advance. However, based on previous experiences, it can safely be assumed that a gate opening of 32 in. x 32 in. results in a flow rate of about 3,500 long tph of ½-in. clean crushed material.

WOHWA's fully hot-dip galvanized and bolted sliding gates are equipped with drainage units for draining the water that has accumulated in the chutes above the gates to avoid spillage. This technology serves to prevent spilling of a product/water mix from the feeding units into the tunnel. The use of a robust rack-and-pinion drive in WOHWA gates warrants the reliable functioning of these feeding devices.

Above each sliding gate, an emergency shutoff gate has been installed to allow maintenance service at the gates without having to empty the stockpile first. If parts should become worn out, replacement parts can be ordered online from WOHWA or from the responsible dealer in the area. Spare parts lists and service instructions can easily be downloaded from WOHWA's web site.

In combination

Below the sand stockpiles at Marble Falls, the WOHWA gate/belt feeder combos have been installed. Again, the gate installed above the belt feeder is used to drain the water accumulating in the chutes. If a belt feeder is not in use, the gate closes automatically and thus prevents spillage of a sand/water mix into the tunnel. WOHWA belt feeders are also fully hot-dip galvanized and bolted. WOHWA belt feeders are designed to allow quick and easy replacement of the vulcanized endless belts. A reliable slip-on gear drive motor (for full-voltage starting) guarantees safe and fast reclaim of the material. Each unit has been equipped with wear-resisting material (XAR-400) to prevent early wear and tear of the feeding equipment.

At the Marble Falls plant, a complex conveyor system with an overall capacity of 2,000 long tph transfers the material to a buffer silo located at the loadout point, about one-half mile from the reclaim tunnel. The integrated WOHWA belt weigher SFB 64 makes it possible that the times for in-flight compensation are computed and corrected automatically with a high degree of precision and reliability. This special feature allows the loading of preselected total weights with a high degree of accuracy. After the loadout, there is no need to empty the buffer silo or transport unwanted material back to the stockpile. At the buffer silo, the product is reclaimed and loaded into the railcars in 100-ton batches.