CANMET: Canada's metals treasury.
"He was crouched over a small induction furnace, a spectre amid a fearsome shower of sparks and blinding flare, wreathed in white smoke and dodging splashing metal. Wearing his old, burn-scarred asbestos coat, he hand-cranked a wringer from an ancient washing machine, his homemade device for adding magnesium wire to molten iron."
That is one researcher's recollection of J.E. Rehder, an early (1949) investigator of ductile iron and a resourceful research metallurgist at Canada's fledgling Physical Metallurgy Research Laboratory (PMRL). Like his colleagues, he was a hands-on foundryman with a broad metals background and an insatiable interest in how metals behave.
The lab was formed in 1940 as the foundry research arm of the Canadian government's Dept. of Mines and Resources. Today, a half century later, it is still at the forefront of basic metals research, providing unprecedented transfer of metals technology directly to Canada's private industry.
Starting with three men handling about 20 projects a year, the lab's activities by 1943 exploded to more than 100 scientists and technicians researching 700 projects, mostly for Canada's war effort. Almost overnight, Canada became one of the world's most prolific metallurgical resources.
At the close of World War II, PMRL's efforts were redirected toward private sector developments in metal physics, special alloys, improved metallurgical processes and metal service performance.
The rapid growth of PMRL resulted in its classification as a separate division in 1947, with John Convey as its first director. Recognized worldwide for his contributions in the fields of metallurgy and minerals, he became the first Canadian to head the American Society for Metals.
Known initially as the Physical Metallurgy Research Laboratories (PMRL), it was renamed the Physical Metallurgy Division (PMD) in the 1970s and shortly reverted to PMRL. In 1986, in line with a new mandate, it became the Metals Technology Laboratories (MTL), an entity of the Canadian Centre for Mineral and Energy Technology (CANMET).
Lore of the Lab
The early years at PMRL were filled with anecdotes of people working against time, devising makeshift apparatuses and coping with the unknowns of a highly complex discipline. One can only marvel at the remarkable metallurgical strides that were made, but there were some harrowing intervals, too.
Take the time, for instance, during an early steel degassing experiment involving molten steel in a bottom-pour ladle sealed in a tank. Several people were located around a deck on the tank, including a visiting metallurgist. During the test, there was a muffled explosion inside the tank and the tank cover broke free. In the ensuing confusion, the visitor bolted from the deck and onlookers swore he broke the record for the indoor 40-yard dash, clearing the foundry exit in seconds.
The incident prompted the suggestion that, henceforth, running shoes might be the most appropriate safety boot for foundry visitors.
Older staffers recall a young engineer, who was studying fluid sand molding, became furious when he was not allowed on the foundry floor wearing short pants and open-toed sandals. He was livid when a photograph of him so attired was removed from one of his reports.
Early lab workers will never forget an investigation into the formation of vermicular graphite in heavy-section ductile iron to see if the presence or absence of thermal current in a solidifying mass affected the presence or absence of this undesirable graphite form.
To minimize thermal current, a device was made in which unidirectional solidification would occur by molding the side walls in exothermic material and using a water-cooled copper chill on the base. Operators were instructed that the metal stream must be moved around to avoid pouring the molten stream in any one area for too long.
Murphy's law prevailed that day. The original ladle operator was unavailable, and the new man missed the pouring instructions. When the mold was partially filled, an ominous bubble began forming in the metal. As the engineer in charge yelled "Stop," there was a loud bang and a spray of molten iron scattered onlookers.
At the same time, a clamp on one of the cooling hoses blew off and a visitor, watching through a mezzanine window, was left with a lasting impression of PMRL as the clamp crashed through the window--narrowly missing him.
In a world that had blundered into a global conflict, early work at the lab was concentrated on solving immediate foundry production problems of all kinds. Most concerned armament and war materials production, but its visionary work had a significant influence after the war.
The lab was noted for its outstanding effort in nonferrous alloys used in ammunition and for naval hardware. But no foundry problem or process was overlooked by the organization.
The sheer scope of its investigations--ranging from patternmaking, molding, furnace operations, casting and shakeout to the reuse of raw materials--spawned many changes in foundry production in the succeeding decades. A few of the lab's milestone projects are noted below.
Sand--Some of the earliest work done by PMRL involved sand research. Core oils and their effect on core properties were investigated and led to the development of a metal penetration test to evaluate different core formulations and metal penetration resistance. The degree of penetration severity was changed by varying the ferrostatic heads acting on the cores.
Using PMRL's Mobile Foundry Laboratory, researchers found that nearly every visited foundry experienced sand problems, correlating that 75% of all casting defects were sand-related. This prompted greater effort at PMRL to control sand preparation techniques and test procedures.
Disposal costs for sand prompted efforts to improve sand recovery systems. This led to an important waste sand recovery system, developed by the lab and now being prototyped. It promises a foundry cost payback of one year.
Nonferrous alloys--Because Canada is a major producer of aluminum, the lab has done substantial work with aluminum-base alloys. In the early days, work consisted entirely of providing advice on the manufacture of military hardware and the investigation of service failures, particularly aircraft components.
Considerable investigation focused on centrifugal casting, powder metallurgy and aluminum-lithium, aluminum-magnesium alloys as well as magnesium alloy development, defect analysis and casting quality.
Copper-base alloys, however, have always been a major thrust of the lab. Aside from the lab's important wartime contributions, much investigation and troubleshooting work were undertaken at PMRL in support of the return to peacetime production for Canadian industry. The lab's work encompassed weldability, shock and corrosion resistance and the development of high-strength alloys.
There was a brief interruption during the Korean War, when the lab led a far-reaching investigation on the effect of impurities and variations in zinc content on the work hardening and annealing properties of 70Cu/30Zn cartridge brasses. This was followed by its definitive work in the 1960s to discover non-nuclear uses for depleted uranium as a deoxidizer for copper and its alloys. In the oil crisis of the 1970s, the lab led in efforts to recycle scarce metals to minimize the deleterious effects of impurities on the structure and properties of widely used bronzes.
PMRL was at the forefront in work to suppress oxygen pickup in molten copper by covering risers with inert or reducing materials. It discovered a means to detect oxygen in a copper melt by observing the formation of carbon monoxide bubbles. This resulted in the production of high-performance, high-thermal conductivity copper castings for tuyeres, cooler plates, etc. The research established a melting practice for Nb-and Cr-modified Cu-Ni alloys, determining composition limits and mechanical properties in as-cast and cast-and-welded conditions.
Investment casting--The lab has undertaken efforts to speed mold formation in the investment casting process. Current practice requires each coat to fully dry prior to the next coat, a procedure that can last two days. Using the principles of electrophoresis, later modified by the use of nonmiscible slurries, the lab developed a patented process that builds a sufficiently thick coat in a matter of minutes without drying between cycles.
A further development was a modified wax that permits wax removal by microwaves rather than by the slower, more costly furnace dewaxing.
Steel--Steel casting research has been a major focus of PMRL. One of the earliest references was the development of a delayed quench heat treatment. It improved wear characteristics of tank treads from 500-5000 hours without revising heat treatment.
Different exothermic and insulating compounds as riser insulation were evaluated that led to the use of more economical rice and oak hulls. The properties of high-strength, low-alloy cast steels also were improved using radioactive tracers to study solidification of steels and the resulting degrees of segregation.
A project investigating work hardening of austenitic manganese steels indicated that a magnetic constituent, thought to be epsilon carbide, was produced on the slip planes in this alloy when cold worked.
Extensive experiments on steel desulfurization in arc furnaces and ladles used a mixture of lime, aluminum, magnesium and other materials. They were injected into the furnace through a refractory-covered lance beneath the molten metal surface, generally using argon as the carrier gas. This technique of powder injection is now widely used in the industry to achieve extra low sulfur levels in premium quality steel castings.
PMRL and the University of British Columbia researched ways to improve steel properties via an electroslag casting (ESC) process. Basically, ESC is an electroslag refining process with a modified mold to permit the production of simple shapes. The process uses a slag high in fluorspar and lime to produce low sulfur steel where the sulfur is often measured in ppm.
PMRL constructed an electroslag casting machine for castings up to 500 lb. The properties found in the middle of a 10-in. section were the same as those in a l-in. forged and rolled plate of the same composition. The reason for this is that the steel is cast and solidified rapidly in the ESC process which limits shrinkage and segregation.
A result of this work is the use of cast, water-cooled, pure aluminum molds. The water cooling channels were made of cores using a nontoxic binder. Because of the low temperature at which the binder decomposes, core removal from the contoured channels was achieved by compressed air blast.
Steel was cast into an aluminum mold cooled by line-pressure water and similar molds were made for permanent mold casting. This technique was used later to produce nickel-aluminide, an ordered alloy with excellent high-temperature properties.
ESC allowed a controlled grain size, permitting cold working of the alloy to form a relatively thin sheet unattainable by other processing techniques. The work was done in cooperation with the U.S. Dept. of Energy.
The lab also was involved in research into vacuum degassing of cast steels. In this process, a bottom-pour ladle of molten steel is sealed on top of a vacuum tank. The nozzle is above an aluminum rupture disc on the lid of the vacuum tank, and a receiving ladle is within the tank.
After reaching a desired vacuum, the molten metal is allowed to flow onto the aluminum disc, melting it. A vacuum is drawn on the metal stream that causes it to break up into discrete particles. Gases dissolved in the metal are sucked out and the falling metal collected in the receiving ladle and poured. Degassed, high-strength AISI 4340 steel can be produced with enhanced low-temperature impact properties due to the ability to restrict the silicon content to low levels. The process also allows production of extra low carbon stainless steel by a technique using iron oxide additions to ladle prior to the ladle spray degassing.
Problems with dissolved nitrogen in stainless steel castings when returns are remelted may give rise to gas defects in the form of nitrogen porosity or brittleness caused by susceptibility to rock-candy (intergranular) fracture. A 0.1% zirconium addition (a strong nitride former) following aluminum deoxidation prevents such defects in castings and doesn't affect other mechanical properties.
PMRL engineers developed the first working oxygen probe using a zirconia tip together with a reference material of known oxygen content. In the initial tests, air was used as the reference material. At high temperatures, the zirconia becomes electrically conductive, varying with the amount of oxygen in the medium exposed to the zirconia. By measuring the electrical potential between the tip and the reference material, the oxygen content of the medium can be estimated closely. Consequently, the oxygen content in a heat of steel can be determined as easily as taking the temperature.
The probe is now widely used throughout the steelmaking industry as well as in numerous other applications where the oxygen content is important.
Ductile iron--Producing graphite directly as a spheroid in cast iron was discovered in 1948. The technique required a low-sulfur cast iron (below about 0.015%S) and the introduction of a sufficient quantity of magnesium or cerium into the molten metal. Because of its low boiling point (1107C), when Mg is added to molten iron at a temperature around 1450C, the reaction is quite violent. Most commonly, Mg is alloyed with ferrosilicon or nickel to reduce the violence and improve recovery. A computer-controlled wire inoculation system has since been developed.
Another aspect of ductile iron production examined at MTL was the application of X-ray fluoroscopy to the inmold process. In this process, the MgFeSi alloy is contained in a pocket within the gating system with the runner located above the pocket. The mold is poured with Mg-free iron and the MgFeSi dissolves into the metal stream to produce ductile iron.
It was claimed initially that the MgFeSi dissolved very quietly and without vapor bubbles. The fluoroscopy test allowed the production of a film, showing bubbles in the metal stream and clearly demonstrating that large amounts of magnesium vapor are released. The film attracted wide interest and has been the basis of design modifications to inmold systems.
Canmetcoat--A troublesome problem with mining tar sand was the excessive wear on steel bucket wheel excavator teeth. The teeth wore quickly--measured in days--and the downtime needed to replace them was expensive. In the 1960s, the foundry section produced castings on which the surface was alloyed with another element directly in the mold.
A major problem was the formation of gases from the binders used to hold the metal powder that formed the alloy layer in the mold. Tests found that the powder could be held by vacuum in a specially designed core. The vacuum also helped to remove the gases always present in metal powders. It also forced the metal matrix around the metal powder to produce a substantial alloy layer on the solidified casting.
The life expectancy of these teeth was about twice that of conventional teeth, but the process didn't lend itself to high production. Subsequent work concentrated on a promising technique in which a layer of bonded abrasion-resistant powder is applied to the surface of a sand core. A vacuum is applied to the sand core just prior to pouring and left on for a short time following the pour. Teeth made by this process are being field tested.
It is not possible to assess the economic benefits the work of MTL's Foundry Section has had on the North American foundry industry. It certainly has been significant, however.
Canada can be proud of the work performed over the last 50 years. International recognition has been given to members in the form of awards, gold medals, scientific recognition and best paper awards. Among these are the following:
1955--J.E. Rehder, AFS Peter L. Simpson Gold Medal
1963--J.W. Meier, AFS John A. Penton Gold Medal
1973--S.L. Gertsman, AFS Thomas W. Pangborn Gold Medal
1982--J.0. Edwards, AFS William H. McFadden Gold Medal
1966--J.W. Meier and A. Couture, AFS Howard Taylor Award
1969--J.W. Meier, AFS Charles Edgar Hoyt Memorial Lecture
1989--M. Sahoo, AFS Award of Scientific Merit
Additionally, MTL's work has been published in periodicals, abstracts and magazines devoted to foundry research. The Ottawa laboratories are the target of many post-graduate fellows and metallurgists from around the world.
Canadian foundries face increasing global competition and their best hope is to produce castings of superior quality at reasonable prices. This can only be accomplished through better technology and improved production practices. This is the goal of the Foundry Section for the next 50 years.
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|Title Annotation:||Canadian Centre for Mineral and Energy Technology|
|Date:||Jan 1, 1993|
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