What's Your Flask IQ?
Many metalcasting facilities use a flask or flask set every day for five to 20 years. Since flasks come in constant contact with sand and metal, they can wear over time and eventually affect mold quality.
However, many metalcasting facilities don’t have a procedure for assessing their flask serviceability or dimensional integrity and only review them in extreme situations, such as damage from a run-out, molten metal penetration or flask wall erosion from rust.
To address this concern, researchers have developed a system to analyze, qualify and implement a cost effective, proactive method for flask preventative maintenance.
What Is a Flask?
A flask is a frame for receiving and retaining molding sand. It is mechanically connected to the pattern and used to hold molding sand during filling, ramming, squeezing, and impact or impulse. It must have sufficient structural integrity to maintain proper mold dimensions during these mold filling functions. Equally important, a flask is a carrier frame, providing a secure fixture for the transportation and manipulation of its mold during pouring and solidification. As horizontal green sand tight flask molding lines have become more sophisticated, the dimensional and mechanical properties of the flasks also have become more critical.
What Inspection Program Should I Use?
Flasks have become a major capital investment for metalcasting facilities. Flasks often are used in a set rather than individually, so the assembled stack-up dimensional data is ultimately the most crucial information about them. However, attention should be paid to each individual flask in the set as well.
Most tight flask molding line manufactures today number their flasks and pallet cars for tracking and accountability. Regardless of the number of flasks on a molding line, the amount of wear on each flask is typically consistent, except in the case of severe molten metal damage.
One method of keeping track of serviceability and dimensional characteristics is an annual program of sampling flasks on the molding line. Testing about 2% of the molding flask sets on the line once per year is sufficient sampling for tracking this data. Inspection of the flasks, preferably by a coordinate measuring machine, can be limited to the dimensions that are critical and functional.
Manual inspection also is acceptable, if the procedural steps are consistent for each inspection. A written procedure with photos is recommended for ensuring accuracy of manual inspections. If a 2% sample represents four sets of flasks, one set should be checked every four months. At minimum, one set should be checked per year regardless of the total quantity of flasks on the molding line.
How Do I Inspect My Flask?
Ideally, the metalcasting facility has a copy of the original as-manufactured final dimensional inspection reports for its flasks (and the pallet cars, as well) to use as a benchmark for inspections. If not, equipment still can be evaluated for serviceability without any starting point data.
The goal for collecting data is to determine the amount of wear per cycle, annualized, on the critical surfaces and points of the flasks and hardware. Exclusive of material defects in the flasks, this data can be an indication of the longevity of the flasks before repair or replacement is required.
The following procedure is a good starting point.
- Make sure your flasks are permanently numbered (i.e. C-001, D-001) and record all data by flask reference number (Fig. 1).
- Start and maintain a program to measure a sampling of your flask’s critical dimensions.
- Let casting and mold quality dictate what is necessary to record. Flasks are components of a system. Know the points of your flask handling in the molding system that can affect mold quality, such as pins and bushings that can cause mold misalignment. Generically, the following processes can affect the mold and casting quality: pattern engagement, pattern strip-off/disengagement, strike-off, roll-over, drag set-on to pallet car (when applicable), drag positioning for core-setting, sprue drilling (when applicable), mold closing, mold clamping (when applicable), cope flask weight set-on (when applicable) and flask cleaning station.
- Gather only data critical for making a good mold and casting, such as surfaces used in pattern set-on and surfaces used in mold closing. This data will be different for each metalcasting facility.
- Check flask components on a regular basis. Gaging and recording data for pins, bushings, bumpers, hooks and other parts is a critical part of controlling casting scrap attributed to worn flasks. Component life correlates directly to flask life and serviceability. Worn flasks consume hardware, (e.g. pins and bushings), at a higher rate than flasks maintained within dimensional specification.
How Can I Extend My Flask’s Lifetime?
The following are general guidelines that can extend the service life of your flasks and provide indications of their dimensional stability and future serviceability.
Step 1. Evaluate casting quality and molding productivity
- Is casting quality affected by the condition of your flasks? Ultimately, this is the only determining factor for the level of care and attention the flasks need.
- Is the productivity of the molding line affected by the flasks? Do you experience lost time from jam-ups, flasks not locating or flasks out of position in the molding line?
- Do you check and maintain the flask hardware, pins, bushings, clamps, hooks and bumpers? When dealing with flasks, the sum of the parts is greater than the whole. It is good practice to change pins and bushings frequently, before they become worn and defective.
Step 2. Act on the Step 1 Evaluation
- Know the functions of your flasks that affect mold and casting quality. The functions could be pattern engagement, pattern strip-off/disengagement, strike-off, roll-over, drag set-on to pallet car (when applicable), drag positioning for core-setting, sprue drilling (when applicable), mold closing, mold clamping (when applicable), cope flask weight set-on (when applicable) and flask cleaning station.
- Know what points on your flasks are critical contact points. Today’s automatic molding lines rely on accurate flask positioning and travel from station to station regardless of the actual flask size or condition.
- Set up and maintain procedures for checking the condition of the flask and its hardware. Duplicate the conditions of the molding line as much as possible to account for possible dimensional stack-up error.
- Be consistent. Document and include procedures for flask assessment, corrective action, flask inspection, flask repairs, and specific measurement and replacement procedures for flask hardware.
~Jeff Eagens, Empire Systems Inc., Avon Lake, Ohio, AFS Green Sand Committee, 4m