Simple Solutions That Work! Issue 13

CHRIS DOERSCHLAG KLEIN PALMER INC. ARTICLE TAKEAWAYS: • The difference between Dilute and Dense Phase in conveying and sand impact • Where sand degradation occurs prior to production • How to reduce sand velocities to reduce defects and operating costs 48 BETTER SAND REDUCES DEFECTS C onducting a survey among foundry management would no doubt discover a common goal of satisfying the customers’ expectations with a quality product. In other words, castings that meet specifications and will not turn into problems later during the machining or assembly process into the final products. Stated simply, castings without defects. Castings without defects are the result of meeting quality control requirements with certain procedures in place which are strictly adhered to. Studying defects prevention, we can find a number of definitions which all contribute to the desired outcome and can point us in the right direction. How do you define Defects Prevention? Let’s see who says what: - Corrective and preventive actions (Galin); or - The activities involved in identifying defects or potential defects and preventing them from being introduced into a product (Zahran); or - A program focusing on those process areas that are the greatest sources of trouble whether methods, technology, procedures or training (Humphrey); or As summarized by the world famous quality guru Dr. W. Edwards Deming: - It’s what is needed in improvement of the process, by reduction of variation or by change of level or both. Study of the sources of product, upstream, gives powerful leverage on improvement. Sources and causes of defects in the final casting vary all over the map but for the sake of simplicity today we will limit our discussion to sand because “Sand Matters!” Of course discovering a defect is only the beginning of the process with the next step being what to do about it. You can simply accept the fact that you are faced with a defect, try to repair it and continue production without consideration of cost, or you can spend time and effort to discover the root cause and work on eliminating it, which may require a more detailed analysis of the entire process, including the production equipment. Some time ago a foundry reported a caved-in roof over the pouring area as a result of about 15 tons of collected sand dropping from a leak in the sand conveying pipeline running above the roof. When maintenance checked out the situation it was found that the core room operators occasionally experienced sand shortages but did not think any more of it. Recognizing that something was different from normal operations would be the first step in working on preventing the defect but considering the options of fixing or eliminating the defect should have been the next step. The “fix” selected was to plug the leaky pipeline by welding a patch plate over the leak and no further analysis was attempted. A more desirable and effective process would have been to question why did the pipeline develop a leak? Could it be that the layout of the piping run needed improvement? Could it be that the air pressure and volume settings of the pneumatic conveying system were adjusted incorrectly? Could it be that the capacity of the system required to provide sufficient sand to the core room was increased from the original design tonnage? Short of reviewing all the applicable reasons for the defect the patched pipeline will probably hold up for a