Testing keeps pace with PUCB binders.

Inside This Story:

* To keep up with new PUCB binders, test methods have been developed that accurately measure binder reactivity and amine consumption efficiency.

* Detailed within is the T-tool test method, which can help production facilities optimize amine consumption and corebox efficiency.

It's a dilemma facing most metalcasting facilities today and one that probably will not disappear anytime soon--a more competitive marketplace is forcing metalcasting facilities to increase productivity, improve quality and lower cost. But how does a firm go about producing more cast metal components in less time with less money?

The answer lies in each area of the metalcasting process. From melting to cleaning and finishing, each step has areas in which costs can be reduced and productivity can be increased.

In coremaking, phenolic urethane coldbox (PUCB) binders have continued to be the benchmark for both quality and productivity. Binder systems with faster cycle times, less core breakage, less machine downtime, lower binder levels and reduced amine usage--all of which can contribute to a healthier bottom line--are commonplace.

The coldbox coremaking cycle is typically fixed by the speed of movement of the equipment. With a given machine, there are usually opportunities for improvement only in the gas/ purge cycle, which may account for as much as one-third of the total cycle time. Reductions of just a few seconds can improve overall cycle times and machine productivity.

The required gas and purge times to fully cure the core and remove residual amines are a function of the type of binder, amine and gassing equipment. For a given piece of equipment, the opportunities for improved cycle time are with the PUCB binder and type of amine. While tri-ethyl amine (TEA) is the most commonly used catalyst gas, di-methyl, ethyl amine (DMEA), and di-methyl, isopropyl amine (DMIPA) can yield improvements in gassing efficiency and gas/purge cycle times.

New PUCB binder systems also have been developed that can improve reactivity, curing efficiency and cure speed. These binders, alone or in combination with the faster amines, can further reduce cycle time and improve productivity. In order to develop improved binder chemistries, new test methods were needed to more accurately measure binder reactivity and curing efficiency.

This article describes the development and use of a new core test method that can help production facilities optimize amine consumption and corebox productivity.

Traditional Test Methods

Several different test methods have traditionally been used to measure cure speed, binder reactivity and curing efficiency. One was used to measure bulk-cure using core tensile specimens or "dogbones." The gas and purge times on the core blower were reduced until only a portion of the dogbone would cure with loose, unbonded sand remaining in the box. The cured portion was then weighed and compared to the weight of a full core.

More reactive systems with higher curing efficiency would produce higher percentages of the full core weight. However, this test was highly variable and dependent on machine operations. Further, it was unable to discriminate between systems that showed significantly different performances in production operations with complex cores.

A somewhat more reliable test for curing efficiency was developed by using a separate gassing unit and closely controlled amine additions. The test involved ramming a specific amount of freshly mixed sand into a large closed cylinder with the gas inlet on one end and vents on the other for a straight-through flow pattern.

A measured amount of amine liquid was injected into the gassing unit and purged through the core. The amount of amine was set low enough that only a portion of the sand would cure and harden. The core then was removed from the cylinder, and any uncured sand was brushed away before weight measurement. The curing efficiency was measured as the percent of the total sand weight that cured and hardened.

While better than testing with dogbones, this method still was somewhat variable and dependent on technique. It also did not provide a good measure of cure speed and strength development of the binder. Comparisons of bulk-cure test results and field trial results often were inconclusive.

New Test Method

To find a more accurate way of testing, a new method was developed. A corebox had been designed and built to measure sand flowability during coreblowing. The box was in the shape of an inverted letter "T" with short vertical arms extending upward from the crossbar. The corebox was 2 in. deep with draft toward the parting line so that the core was 1 in. wide at the bottom and 1.25 in. wide at the parting line. The central vertical leg was 7 in. long, the horizontal leg was 9 in. across and the short vertical legs were 2 in. tall. The box also was equipped with numerous vents at different locations that could be opened and closed to modify the venting pattern.

It was assumed to be a somewhat difficult pattern to blow because of the two right angle turns the sand had to make to completely fill the box. A less-than-optimum venting pattern was used so that a highly flowable sand would fill the box at a given blow pressure, but a less flowable sand would not. Sand weights in the box could be measured to document the percent fill with a completely filled core weighing 2.4 lbs., depending on sand and blowing conditions. This was dubbed the T-tool test (Figs. 1-2). During testing with the T-tool, it was further discovered that the ends of the core would not always completely cure.

[FIGURES 1-2 OMITTED]

The sub-optimal venting pattern that produced a non-fill condition during blowing also produced a more exaggerated non-cure condition during gassing and purging. The T-tool proved o be a better method of measuring curing efficiency than the bulk-cure test because of the more realistic gas flow and venting that resulted from the catalyst gas being allowed to prematurely exit through a vent, unlike the straight-through venting with the bulk cure test.

The T-tool pattern was modeled using process modeling software (Fig. 3), which predicted a complete fill using the optimum venting pattern with the vents in the sidearms open and all other vents closed. It also predicted a non-fill with the sub-optimal venting pattern with either all the vents open or the bottom vents open and the side vents closed. The model of the gassing cycle for the non-optimal venting patterns also showed incomplete curing of the cores.

The T-tool can be used to measure both binder reactivity and amine consumption. Reactivity testing is conducted on a lab coreblower where the gassing time and the amine concentrations can be closely controlled. Mixed sand is blown into the box to completely fill the cavity. This typically uses a venting pattern with side vents open and one or two bottom vents open.

While this is the best venting pattern for core filling and curing, it is barely satisfactory. With this venting pattern, blow pressures can be adjusted to completely fill the box, but gassing with normal gas pressures, gas time and purge time will typically leave some portion of the side arms uncured. It is this borderline condition that makes the test sensitive to changes in binder reactivity.

A more reactive binder will cure more thoroughly, and a less-reactive binder will leave more sand uncured. After gassing, the cured portion of the core is removed from the box, weighed and compared to the total weight of sand blown to give a percentage. Reactivity is compared between binder systems by evaluating the relative percentage of the cured weight.

The T-tool also can be used with the more precise gassing unit normally used on the conventional bulk-cure test. The sand is blown into the corebox, and a gassing manifold connected to the amine generator is used. A precise amount of amine is injected into the unit, and the gas is blown and purged through the corebox. The weight of the cured portion of the core is measured and compared to the total sand weight. This test method has the advantage of the most precise amine control but is slower and does not as closely reflect a typical production cycle.

Comparing Methods

During the development of the T-tool test, a new PUCB binder system, designated Binder "A," was under development for a large metalcasting facility. One of the important requirements of the binder was cure speed. As part of the initial screening tests, bulk-cure testing was conducted to compare the existing and new binder systems. These test results (Table 1) suggested better curing speed and efficiency with the new binder. As expected, the lower binder percentage showed better bulk-cure with less binder to react with the catalyst. However, when field trials were conducted, the new system did not perform as well as the existing system.

Additional tests were conducted with the new and existing binder systems using the T-tool. These results contradicted the bulk-cure tests and showed the existing system outperformed the new (Table 2). These results were in line with those of the production trials.

Based on the initial results showing good correlation between T-tool tests and field performance, the method was further refined to simplify and speed up testing. A three-quarter-size version of the tooling was made to run in standard lab core machines using the controlled gassing unit that had been used for bulk-cure testing. This core was 0.75 in. wide by 1.5 in. thick with a vertical leg of 5.25 in., a horizontal leg of 6.75 in. and vertical side arms of 1.5 in. The completely filled core weighed 1.1 lbs. compared to 2.4 lbs. with the full-size version. Figure 4 shows the modified test.

[FIGURE 4 OMITTED]

The T-tool test was then applied to the development of an improved binder system for the metalcasting facility. A new base resin was used to formulate several experimental systems that were compared to the "A" system. Table 3 shows the test results for the "A" system compared to four experimental systems. All of the systems with the new base resin showed significant improvement compared to the earlier system.

Production Trials

The T-tool tests led to the development of a new formulation with the new base resin that was tailored to the metalcasting facility's operating conditions. This system, Binder "B," was tested against the existing production binder and showed equivalent or better performance on the T-tool. Based on these and other test results, the new binder system was trialed in the facility under typical plant conditions. The cure speed of the new system resulted in an increase in the immediate or out-of-box tensiles of 20 psi.

The improved reactivity and amine consumption resulted in a decrease in cycle time of 10% for some cores, but little or no improvement on others. A review of the venting patterns of the different core boxes suggested that those with efficient venting showed improved cycle time while those with poorer venting showed little improvement.

In some cases the amine was reduced by 50% with good cores produced within the existing cycle. This can lower material usage and cost. It also has the added benefit of reducing potential amine emissions to the atmosphere and the associated environmental concerns.

Practical Applications

While the T-tool testing was used as a means to measure binder cure speed under laboratory conditions and to help in the development of new binder formulations, the same ideas and concepts can be used to optimize amine consumption and corebox productivity in production facilities.

The T-tool test measured the percent cure using standard amine dosing levels, gas times and purge times with the binder formulation as the only variable. If the binder formulation is held constant, the other control parameters can be varied to optimize coremaking operations.

In a production environment, the gas time is the primary control for the amount of catalyst delivered to the corebox. To optimize the gas time, start with the normal production setting and incrementally reduce the gas time until soft, uncured spots begin to appear on the core, and then increase the time again until the soft spots disappear and the core is fully cured. This is the minimum gas time and catalyst level under ideal conditions.

Next, begin reducing the purge time until soft spots again appear or excessive odor is detected in the core. This will be the minimum purge time. Typically, the gas and purge times are then increased from the minimum by 10-20% to provide some "safety margin."

Once the minimum gas and purge times have been established and recorded for a particular corebox, trials can be conducted with different binders or catalysts. If it is known, for instance, that the minimum gas time is 3 sec. and the minimum purge time is 15 sec. with TEA as the catalyst, trials can be conducted to determine the minimum gas and purge time using DMEA or DMIPA catalysts.

The potential amine usage and cycle time improvements then can be compared to the standard to determine if there is a potential saving with the different catalysts. The same type of testing also can be conducted to compare new or different binder formulations.

Seeing the Benefits

PUCB binders have improved and evolved since they were first introduced more than 30 years ago to meet increasing production requirements. While the basic chemistry is mature, changes in the base resin, solvent and additive packages have led to improved performance over a wide range of production conditions. These improvements have been driven in part by better test methods that more accurately reflect production conditions.

The T-tool test has been shown to provide data on binder cure speed and amine efficiency that has led to improved binder formulations. These, in turn, have resulted in significant productivity improvements and cost savings.

Table 1. Bulk-Cure Test Results with New & Existing PUCB Binders

Bulk Cure Testing  Binder "A"  Binder "A"  Existing Binder
                     1% BOS     0.9% BOS       1% BOS

Trial 1              84.7%       92.1%          63.0%
Trial 2              84.2%       93.8%          65.9%
Average              84.5%       93.0%          64.5%

Table 2. T-Tool Test Results with New & Existing PUCB Binders

T-Tool Testing           Binder "A"  Binder "A"  Existing Binder
                           1% BOS     0.9% BOS       1% BOS

Avg. Core Weight (lbs.)     1.68        1.81           1.8
Percent Cure               69.4%       74.8%          74.5%

Table 3. T-Tool Tests Comparing Experimental Systems

T-Tool Tests         Binder "A"  Exp. 1  Exp. 2  Exp. 3  Exp. 4

Core Weights (lbs.)     0.78      1.01    1.03    0.97     --
                        0.58      0.95    0.97    1.03    0.95
                        0.71      1.03    0.85    0.95    1.02
                        0.64      0.84    0.83     --      --
Avg. Weight (lbs.)      0.68      0.96    0.92    0.98    0.93
Percent Cure           63.2%     89.0%   85.5%   91.2%   86.3%

For More Information

"Evaluating Coldbox Binders: A Practical Approach," S.G. Baker, MODERN CASTING, May 2001, p. 37-39.

R. Showman, K. Schumacher and R. King (Studebaker), Ashland Casting Solutions, Dublin, Ohio

Ralph Showman is a senior staff metallurgist for Ashland Casting Solutions, Dublin, Ohio, and the chair of the AFS 4E committee. Karl Schumacher is a chemical/ab technician and Rebecca King (Studebaker) is a senior lab technician at Ashland.