Designfax weekly eMagazine

Subscribe Today!

Archives

View Archives

Partners

Manufacturing Center
Product Spotlight

Modern Applications News
Metalworking Ideas For
Today's Job Shops

Tooling and Production
Strategies for large
metalworking plants

In a bid to ditch chrome plating, Army tests improved coatings for howitzer spindles

By Dan Lafontaine, RDECOM, U.S. Army

Efforts by U.S. Army engineers at Aberdeen Proving Ground, MD, to implement an improved coating for howitzer breech spindles aim to provide several benefits: easing the logistical burden on Soldiers, reducing hazardous waste, and saving millions of dollars.

Rust, wear, and corrosion problems force the Army to condemn breech spindles before their full service lives. A team at the U.S. Army Research, Development, and Engineering Command, or RDECOM, is leading a project to identify, validate, test, and evaluate a solution.

A 155-mm M777 medium towed howitzer at the U.S. Army Aberdeen Test Center, Aberdeen Proving Ground, MD, March 6, 2014. [Photo Credit: Conrad Johnson, RDECOM]

 

 

Project officer Maira Senick and technical lead Dr. Christopher Mulligan, both with RDECOM's Armament Research, Development, and Engineering Center, in partnership with Product Manager Towed Artillery Systems, are aiming for a production-ready coating within six months to a year.

"We're improving the performance of the howitzer, reducing the logistical burden on the Soldier, and saving the government more than $2 million per year," said Mulligan, a materials engineer. "A lot of times when you're trying to improve performance or eliminate hazardous materials, you end up with a more expensive process. Here, we're a saving a significant amount of money over the life cycle of the weapon with minimal to no increase in production cost."

Easing logistical burden, saving millions
Mulligan explained that the spindle is the howitzer component that seals the chamber and holds the pressure to prevent gas from leaking from the breech.

Chromium has been used to coat spindles for decades, but the Army has found this method often leads to a shortened service life when subjected to the rigors of Soldiers using the weapons in training or combat.

An M776 howitzer corroded chrome-plated standard obturator spindle sits next to newly plated production at the U.S. Army Aberdeen Test Center, Aberdeen Proving Ground, MD, March 6, 2014. [Photo Credit: Conrad Johnson, RDECOM]

 

 

"Any time you have corrosion, wear, or chipping, it could result in loss of the seal and affect chamber pressure and accuracy. It needs to function properly. Wear and corrosion cause malfunctions," Mulligan said.

To find and evaluate possible replacement technologies, the team developed a list of 10 primary metrics necessary for a new coating and application process. These included resistance to corrosion, mechanical wear, and high temperatures.

The group evaluated 12 material formulations in small samples and then down-selected to three based on performance and cost. The candidates currently being tested are: High-Power Impulse Magnetron Sputtering from Sheffield Hallam University in the United Kingdom, Accelerated Plasma Arc from Phygen Coatings, and Electroless Nickel Plating.

Mulligan said they are all vastly outperforming the chrome plating in terms of corrosion and wear.

To ensure the coatings can withstand the rigors of Soldier use, the ARDEC team then turned to the Aberdeen Test Center at Aberdeen Proving Ground for live-fire testing on a howitzer range.

After the first round of firing, the spindle undergoes 30 days of weathering in a caustic and acidic propellant byproduct, known as swab water, to simulate potential conditions in combat, followed by another round of firing and then a final weathering cycle.

"[Soldiers] use swab water to clean after firing, and sometimes proper maintenance is not done," Mulligan said. "We need to make sure it can withstand the firing environment and still maintain its corrosion resistance. After these are all fired and go through the second 30-day weathering cycle, we're going to put them back through accelerated corrosion testing for a five-day cycle in an environmental chamber, including salt fog as the final step."

An M777 open breech assembly shows the obturator spindle at the U.S. Army Aberdeen Test Center, Aberdeen Proving Ground, MD, March 6, 2014. [Photo Credit: Conrad Johnson, RDECOM]

 

 

Mulligan explained that following one aggressive cycle in the chamber, the chromium coating exhibits severe corrosion.

Senick said the team is constantly searching for new coating technologies and has identified a fourth option from Canada. Funding has recently been secured, and testing will begin within a few months.

"Even though we have engaged on a path forward with these promising alternatives, we continue to monitor trends and advances on the corrosion-mitigation coating field," Senick said. "We have identified a newly developed promising chemical vapor deposition type coating known as Carbonyl."

After all testing is complete, a final decision on the best process is expected within 90 days.

As the improved coatings extend the life of spindles, the logistical demands on Soldiers will decrease because fewer spare parts will need to be transported and stored. The Army would then buy fewer spindles because the requirement for replacements is reduced.

Reducing environmental hazard
Another important aspect of the project is the environmental benefit, Mulligan said. While the current spindle chrome-electroplating process is federally permitted and under close engineering controls, it generates a waste stream of hexavalent chrome, which is highly carcinogenic.

The goal is to establish a dry process that allows for a completely clean environmental method, he said.

"There are high costs associated with controlling that hazardous waste, plus the human risk. If we can eliminate the use of chrome electroplating, then we can eliminate the hazardous waste stream associated with it," Mulligan said.

The project aims to comply with a Department of Defense directive issued in April 2009 that mandates the minimization of hexavalent chromium in defense-related industrial base manufacturing, Senick said.

Senick also said that the cost of environmentally friendly processes can often be prohibitive. However, the team was able to overcome this obstacle for the spindle coatings.

"We knew that for an alternative to be even considered, it not only had to be technically qualified but economically suitable," she said. "The coatings under consideration meet this requirement."

Support from foreign comparative testing program
In order to fund the evaluation of foreign processes and materials, the group submitted a proposal through the Foreign Comparative Testing Program. FCT's mission since 1980 has been to find and evaluate "here and now" solutions to meet operational needs.

The Office of the Secretary of Defense's Comparative Technology Office evaluates the proposals and selects candidates for funding. The RDECOM Global Technology Integration Team manages the program for the Army.

Jason Craley, FCT project officer at RDECOM headquarters, said the project has been a success because it accomplishes two objectives concurrently: cost savings paired with longer equipment life.

FCT also allows Army researchers the flexibility to explore different options without having a pre-determined solution before starting the program, he said. The addition of the Carbonyl coating to the testing plan is a prime example of this flexibility.

"This effort was ahead of its time in emphasizing life-cycle cost reduction when I first worked with Benet Labs to submit the initial FCT proposal, in 2011," Craley said. "Since then, there has been an increased emphasis at the Office of the Secretary of Defense (OSD) level on affordability through extended service life due to constrained resources. Affordability is one of three OSD focus areas for the current FCT proposal cycle. The other two are interoperability with U.S. allies and new capabilities to counter emerging threats.

"The howitzer breech spindle FCT project is a forerunner to the type of effort that will be an OSD-level priority over the next few years in an era of shrinking budgets."

Published April 2014

Rate this article