CASE STUDY: A SINGLE PART MAKES BIG IMPACT FOR PULP PROCESSOR

Located in Vancouver, BC, serving Western Canada’s three major industries—pulp and paper, petrochemicals, and oil and gas—along with

 other sectors on a global scale, Axton is one of the country’s largest fabricators.

Typically, the heavy equipment that serves as the backbone to these industries is demanding on the parts that comprise them. These large parts experience high wear, corrosion, and abrasion, and have a life expectancy between 10 and 30 years despite the stress and strain.

“To handle the corrosive environments in which these parts function, our overall mix of parts we fabricate are about 30% carbon steel, 50% stainless steel in 300 series, and the rest are high alloys from high chrome duplex, high nickel alloys, titanium, tantalum, and zirconium,” says Jim McDiarmid, Project Manager with Axton.

Why a Single Part Matters

The company has been working with SF&E to cast their large model ADI 600 screw used in wet pulp processing equipment. They concluded that for better corrosion and higher strength the part needed a material change.

A995-CD3MN alloy was selected to withstand the medium to high corrosion environment from the operation’s caustic chlorine bleach solution as well as the high strength offered with this alloy. This alloy is one out of the more than 250 alloys SF&E has worked with over its 75+ years of casting parts.

They also opted to cast the part as a segmented screw with a hard-facing overlay to resist wear. The customer’s goal is to increase output in the pulp mill within the same building footprint. Expansion is not an option because they cannot change the facility’s piping or push out the building’s walls.

What’s unique about this screw? It’s a large three-section part with a maximum dimension of 20 inches that goes into a 600-millimeter throat on the pulp processing line.

“This the first time a screw of this size has been designed this way as typically the part is one piece,” McDiarmid says.

Avoiding Downtime Is a Must

The screw’s segmented design offers better torque transfer, enabling a larger motor to drive the screw for an expected 15% production increase – keeping the processing plant’s pipes and walls in place. This design approach happened by accident when the plant attempted to reach that output increase and broke the screw. The two parts were welded together, the screw was reinstalled into the pulp mill, and the plant achieved its output increase.

In the plant, there are four screw assemblies. One was welded together, and another seriously deteriorated and needed replacement as soon as possible.

Maintenance and downtime are significant issues for pulp plants. The cost of part failure in large pulp plants means taking down the whole operation, which can come in at a couple of million dollars.

Because this is a one-piece part, if any repairs are required, plant maintenance must shut down the machine, pull out the shaft, send it out for rebuilding, bring it back, refit, and restart. This repair is a long rebuild process, but the screw is too expensive and large to keep a replacement on-site.

This repair process can lead to a complete plant shutdown, and to keep the employees working, the plant will build up inventory so that the section can keep on running. If they overrun their shutdown, they run out of inventory, and the plant goes to full shutdown, which is not easy to do for a pulp operation.

Importance of Quality and Communication

Axton turned to SF&E to cast these replacement screw assemblies, initially connecting with Kim Morgan, Sales Consultant with SF&E, who filled them in about working with the foundry. Axton does a lot of high-corrosion, pressure vessel, or pressure vessel-adjacent products. “The quality has to be there,” McDiarmid notes.

SF&E ran solidification modeling to be able to build the patterns and poured the castings. Along with producing the two screw sections, they did the castings for the throats so that the parts mated precisely.

For Axton, SF&E’s vast alloy experience was a significant factor. McDiarmid also found examples of castings the foundry had made with difficult-to-cast geometries. Once they master the design, the rest of the process is all about quality and consistency.

Because of the size of the casting and the rare occurrence of needing a new part, Axton and SF&E opted to use a temporary rather than a permanent pattern, which is more cost-effective. Working with a temporary pattern was a new experience for SF&E but turned out great for both parties.

According to McDiarmid, the key element to success for this project is the strong lines of communication with SF&E and Mitch McCaffery, Vice President of Sales and Marketing for SF&E. As the inevitable challenges arose, the two parties worked them out, with SF&E consistently improving the process to improve the result and regularly communicating back to Axton. The foundry gave this one-off project the same level of attention to quality that they give to higher-volume castings.

Regardless of the size of your part or the production run, contact the SF&E experts at sales@stainlessfoundry.com.