Larson Upgrades In-house Tensile Testing

May 14, 2005
The onetime blacksmith operation keeps its technological capability current.

Charles E. Larson & Sons Inc., a family-owned business that started as a blacksmith in Chicago in 1895, now forges steel, aluminum, copper, brass, titanium, and high-temperature alloys for the aerospace and nuclear industries, and other commercial sectors. Recently, the company updated its in-house tensile testing capability.

Larson has about 100 employees and occupies over 100,000 ft2 of space. The company recognizes that a lot has changed over 100 years and it has kept its technology current through careful investments. One of those investments was retrofitting the 60,000-lb. Tinius Olsen test frame. The machine, which was mechanically sound, pre-dated electronic controls

Tensile tests are routinely performed on the primary products produced at Larson — rings and bars — using a Tinius Olsen test frame. Though not nearly as old as Larson Forgings, the Tinius Olsen machine predates electronic controls; it was controlled manually.

Larson’s machine shop prepares samples either from test bars or sections of forged rings for test elongations. Test volume is moderate at about 6-12 test samples per day and covers the full spectrum of the materials run on any given day.

Prior to the retrofit, the Larson lab operated like most labs did, and many still do. The technician would attach an extensometer to the specimen, run the test, and record the strain data on a pen recorder. Then, he would build a load versus strain curve, manually calculate the yields, and write the results on a sheet of paper.

Looking back, Larson metallurgist Tom Raleigh says, “Test recording was time-consuming and inefficient. We had file cabinets all around here. We decided to computerize to make storage easier and speed things up a bit.”

When Raleigh joined Larson in 1999, one of his first tasks was upgrading the tensile testing operation. Based on his research, Raleigh decided to retrofit the machine with digital controls. He turned to Cal-Rite , a calibrator services firm, whose staff recommended that he retrofit the frame with the MTESTWindows testing system from Admet.

MTESTWindows is a Microsoft Windows-based system that controls electrohydraulic and electromechanical test frames, and records test results. Ideal for new and retrofit installations, it is a complete tension and compression test control and reporting system.

Raleigh contacted Cal-Rite Corp., a company that he had worked with in the past. “We were thinking about getting a new machine, but Cal-Rite suggested we could save a lot by getting a retrofit instead,” says Raleigh.

In researching the Admet retrofit, Raleigh discovered that by installing a personal computer in the lab and retrofitting the Tinius Olsen machine with servo controls, Larson could conduct precisely controlled tensile tests, and automatically collect and calculate results in electronic format.

The system includes an external interface box to control test frame load and strain values, as well as crosshead position. It exceeds American Society for Testing and Materials standards for accuracy and repeatability.

Smooth retrofit
The upgrade went smoothly. Admet and Cal-Rite engineers specified the required workstation, interfaces, and the servo controls for the frame. Observes Raleigh, “It was a major overhaul that went as planned and has been working flawlessly ever since.”

Training was conducted by Cal-Rite, and Raleigh, in turn, wrote a procedures manual based on the MTESTWindows users guide and trained the technician. Most of the original programs were set up by Cal-Rite so Raleigh and the technician were able to begin using the system immediately with very little ramp up. Admet and Cal-Rite provided phone support, as needed.

Now, the operator selects the test and MTESTWindows runs it and records the results, does the calculations, and presents the tensile information. The data is posted to the shop router, which is connected to Larson’s corporate computer system.

Added benefits
Raleigh discovered other benefits, too. He set up several programs on the MTESTWindows system. The various programs control the speed of elongation and provide different yield readings. He explains, “We test steel differently than titanium, for instance. And, some customers require different yield readings at 0.1% rather than the standard 0.2%.”

Another benefit comes from MTESTWindows’ flexibility. All jobs are stored by shop-order number but Larson also saves the data under the alloy type. That way, Raleigh and the other metallurgists can look at the history of the properties they get from specific materials.

“We may get a job that needs an unusual tensile level. We look at what kinds of properties we’ve gotten from a similar section and similar forging. We can call up the history and see what we’ve got statistically, because MTEST lists tests with means and averages, and standard deviation. We use that quite a bit,” he says.

The system has worked without a hitch. “The only time that I remember it failing was when we got hit by lightning,” comments Raleigh. “One of the boards was not protected and got ‘fried.’ The technician noticed that things weren’t right. We called Cal-Rite in and they found the problem. A new board was shipped. We lost only about a day’s worth of production.”