Simple Solutions That Work! Issue 13

32 your supplier is key to getting the right coating for the job. KEY #2: COATING PREPARATION We must understand a fundamental truth that a coating is only as good as the core or mold surface upon which it is applied. The goal is still to get the right amount of properly prepared coating on the core or mold every time. Coatings contain multiple components and are slurries, not solutions. They typically are shipped as a heavy slurry to avoid settling and shipping a large carrier component. These factors make mixing until homogenized very critical to the process. Suppliers have formulized steps to help in this area, but the foundry must still do their part to insure a well-mixed, homogeneous product is being used in production. • Utilize the right size mixer to get good mixing without shearing. • Assure movement without dead spots while avoiding air entrapment or vortex. • Choose the proper blade and proper rotation to move the coating around and across dip tanks. • Coating tank design is also critical. Stainless steel construction, round or rounded corners, baffles, 2:1 to 3:1 tank to blade diameter, and mixer off set and placement are key. • Document the coating preparation process. Whatever type of mixing and tank design your foundry has decided on utilizing, make sure the coating is well mixed before placing into service and then properly mixed while being used. This is a major source of coating variation in the foundries of today. KEY #3: QUALITY CONTROL. Once the coating is mixed and diluted to the operating parameters, it must be controlled. There are several test methods available to the foundry and new technology is being developed around those methods every day. We are seeing more automation and real time testing that take out some of the operator variation but the fundamental tests are the same. You should incorporate at least 3 of the following into your control plan. Foundries are multivariable so our test methods have to be multivariable if we want to get a true picture of what is changing. Checking multiple properties of the coating is key. 1. Baume - Figure 1 2. Flow Cup - Figure 2 3. Brookfield Viscosity 4. Density (weight per gallon) 5. % Solids 6. Wet or Dry Mil Deposit Thickness KEY #4: PROPER APPLICATION Technique. Remember the goal is to get the right amount of properly prepared coating on the core or mold every time. Whether you are dipping, spraying, brushing or flow coating, it is important to minimize variation in technique. Concentrate on several key parameters for each method. All of the following process parameters Figure 1: Baume Figure 2: Flow Cup Figure 3: Brookfield Viscosity Figure 4: Density (weight per gallon) Figure 5: % Solids Figure 6: Wet Mil Thickness