Tungsten Carbide Overlay Used
A side-by-side test of different hardfacing overlays. On the left of the tooth is Durmat NIFD, and on the right is a complex carbide premium hardfacing in wide use on wear parts. This dragline tooth was in service for three weeks digging mineral sands.
In May 1988, Dredging International began dredging at Leam Chabang, Thailand, where the Thai government was creating a port. The material to be dredged was abrasive, sticky clay with a high concentration of titanium dioxide (TiO2.) Using their 850mm (33-inch) cutterhead dredge Amazone, D.I. began the project consuming between 500 and 700 teeth per day, depending on where they were working.
Many different types of hardfacing materials were tested on the teeth, including all iron-based chromium and complex carbide types. A significant step towards the increase of cutter tooth life was made by using a tungsten carbide hardfacing product manufactured by Durum of Krefeld, Germany. The first results, with a minimum product applied, increased the life by a factor of four.
After some trials and modifications, welders applied between 1.2 and two kg of tungsten carbide per tooth, and reduced consumption of teeth to 100 hard-faced teeth per day. One tooth lasted for about 300 cubic meters of soil, using Magolux M20 and ESCO 38D teeth.
To illustrate the savings, the cost of four teeth at $55 each was $220, and the cost of one tooth with the overlay was $155, for an initial financial savings of $65. But the most impressive savings were realized with the reduction of downtime. Production continued at a higher rate because the teeth were changed less often, with a resulting drop in labor and maintenance costs.
Because of the outstanding results on the teeth, wear protection was also applied on tooth adapters, cutter arms (by welding strip plates, onto lips and inside the suction mouth,) and onto pump impeller lips.
In the late 1990’s, the Thai government let a contract for an expansion at Leam Chabang. The Italian dredging contractor Dragomar used their 16, 650hp cutterhead dredge Cyrus on the project from 1998 to 2000. Before dredging began in March 1998, Durum trained company personnel in hardfacing cutter teeth with the tungsten carbide product, creating a stockpile of hardfaced teeth that were ready when dredging began. Because a new type of tooth and cutterhead were in use, modifications in the hardfacing were made later, but by planning ahead, the customer saved money and downtime.
Durmat Inc., of Houston, Texas (known to customers as Durum USA) distributes Durum brand tungsten carbide welding tubes and wires with several beneficial features for repairing dredging wear parts.
The material can be overlaid onto itself, so a part that has been previously repaired using Durum materials can be repeatedly welded in the areas of highest wear, said Jean-Marc Tetevuide, sales manager for Durmat. Some welding and hardfacing products, because of their metallurgical structure, cannot be overlaid onto themselves, he said.
This high quality material has a higher price tag than chrome carbide overlays, but according to Tetevuide, customers make up the cost in less downtime for repairs.
Among the products Durmat supplies are iron-based materials, nickel-based materials, powders for oxyacetylene welding and spraying, PTA welding powders, and tungsten carbide powders. The company’s patented alloy NIFD, a nickel-based material, is used in “worst-case, high abrasion environments, such as dredging silica sand and shell,” said Tetevuide.
Peter Knauf, founder and president of Durum, will aid dredging companies in making a field test of the hardfacing material.
“We recommend starting with our patented Tubular Electrode DURMAT-NISE to judge the difference between hard-faced and non-hardfaced teeth,” he said. “We will teach one welder how to apply the material properly and the customer can report results to us by sending photos of worn teeth by email. If necessary, Durum will give further recommendations and proposals for material and design modifications,” he said.
For the dredging, mining and aggregate industries, the products are applied to all wear surfaces, including cutterheads, cutter teeth, bucket wheels, bucket teeth, impellers, bucket lips, drag line teeth, stabilizers, crusher rolls, crusher cones, hammers, wear plates, wear screens, centrifuges, rockbits and conveyor screws.
Companies dredging mineral sands in Western Australia, South Africa and Florida are using Durum’s tungsten carbide materials to hardface wear parts on cutterheads and bucket wheels.
Paul Green of WEAReduction, in Lake City, Florida, uses Durum products in his business, repairing dredge wear parts. Green started the company in 1996. After selling welding supplies for a number of years, he saw a need for proper application of the products he carried.
“If the alloys are not applied correctly, the customer doesn’t get the full benefit of the hardfacing,” said Green. He concentrates on augers, teeth, bucket lips and cutterheads, working with two employees to repair parts. His major customers are within a four-hour drive of his shop and he visits these companies to pick up and deliver the parts. He also arranges shipping for companies out of his immediate area.
“We will do field tests of several alloys to find out what is best for them,” said Green. “If a customer has a wear problem, we will work with them to solve the problem,” he said.
Durum products are manufactured in Germany by Durum Verschleiss-Schutz GmbH in Krefeld, a suburb of Dusseldorf. Peter Knauf started the company 25 years ago after he developed and patented a nickel-based alloy, and has since added several dozen products to his line.
He has sales offices in 20 countries, including Durmat, Inc., the United States affiliate in Houston. Durmat, Inc. sells throughout the United States, Canada, Mexico, and in other Latin American countries.