Questions and Answers of Iron Oxide
What are Iron Oxides used for in the foundry?
For decades, Iron Oxides have been used in the foundry to minimize expansion and gas related defects. Iron Oxides soften when heated, to allow for sand grains to expand without cracking the core or mold surface. Iron Oxides will also release oxygen to readily combine with free nitrogen from the resin system, preventing nitrogen pinhole defects.
How do you select the correct Iron Oxide?
Historically, Iron oxide red has been used in cores, and Iron oxide black has been used in the molds. Today, Iron Oxides are selected by the defect that a foundry is experiencing. Iron oxide red is most commonly used for gas scavenging. Iron oxide red will readily give up oxygen to combine with free nitrogen that is being released from a resin system. When these elements combine, gas defects are greatly reduced or eliminated. Iron oxide black is commonly used as an anti-veining agent. Iron oxide black will soften and allow sand grains to expand, while keeping the core or mold surface in tact. This softening also helps with mold wall movement to prevent mold cracking. When the heated Iron oxide black softens, it provides space for the sand to expand, minimizing mold wall movement.
How does a foundry decide which size of Iron Oxide is the best fit?
Since Iron oxide red has the consistency of flour, it is very difficult to produce a coarse Iron oxide red. The most common size is 300 AFS. Iron oxide black can be sized from 100 AFS to 300 AFS depending on the type of Iron oxide black ore used. There are several factors used to determine which size is best suited for a foundry: concerns about increased resin consumption, surface finish, feeder limitations, and molding or core machine equipment.
What is the typical addition rate?
Iron oxide red is typically used at a rate of 1-2% based on sand weight. When used above 2%, foundries may need to increase resin percentage to maintain adequate tensile strengths. Minimizing resin percentage will assist in reducing gas related defects. Iron oxide black is typically used at 2-5% based on sand weight. If at 5%, and you are still experiencing veining defects, we recommend using an Engineered Sand Additive.
Will Iron Oxides affect reclamation systems or molding sand?
When using Iron oxide red with a thermal reclamation system, heating elements will need to be checked on a frequent basis to ensure heating tubes are working properly. Iron oxide black will have no effect on thermal or reclamation systems. In fact, naturally occurring Iron Oxides are more beneficial than synthetic or byproduct iron oxides. Natural Iron Oxides will not adversely affect molding sand, as compared to synthetic or byproduct additives used in molding systems. Natural Iron Oxides will eventually be broken down, and either be removed by foundries bag house,s or be removed by the heat during the pouring process. This is not the case for byproducts that are too heavy to be removed by the bag houses and are designed to work by melting. These additives tend to build up in the molding systems and lead to gas related defects, as well as burn on because they adhere to the casting surface.
This article comes from prince-corp edit released