For as long as castings have been produced in green sand molds, there has been the need to minimize variation.  As productivity increased over the years, sometimes it came at the expense of the green sand mold. Hot sand, worn equipment and other contaminants entering the sand system have a negative effect on mold consistency. 

One solution to improve casting quality through improved molding sand are additives such as OPTIMULL from Refcotec Inc. These additives have shown positive results of battling short mixing/mulling, large dilutions of core sand and new sand and worn equipment.   

OPTIMULL is a proprietary blend of organic and inorganic materials specifically designed to help reduce overall green sand variation, improve mold quality and reduce casting scrap. This material effectively reduces the surface tension of the temper/flush water added at the muller. It also improves the interaction between the bentonite platelets and with the water by reducing the inter-particle forces that hold the clay platelets aggressively together. Additionally, it softens the water and increases the clay solubility. 

This results in:
•    Reduced high degree of edge-to-face orientation occurring in bentonite, resulting in more clay surface available for hydration.
•    Less “latent” or “dormant” clay.
•    The water now has better opportunity to wet out the clays. Essentially, the water acts “wetter.”
•    Since the water is more effective, less is required.
•    Since it wets out the bentonite better, less bentonite is necessary.
•    Mixing/mulling is easier.
•    Core sand and new sand can wet out better now. There is more opportunity for the bentonite to attach to these sand grains.
•    Bentonites mull in easier.
•    Short mulling is less of an issue since the mulling has been enhanced.
•    Mold edges do not dry out as much, resulting in less friability.

Benton Foundry

Benton Foundry is a state-of-the-art, fully-automated facility that pours approximately 175 tons of gray and ductile iron per day of which 60% plus is cored, with expansion plans to pour 225 tons per day. Cored assemblies with up to six cores have been a skill set addition over the last ten years. This has increased sales but added a return core sand dilution issue. The whole sand system is turned over in less than seven weeks with core sand additions.

Benton Foundry is no stranger to green sand additives. For 35 years the addition of a liquid green sand additive at the muller had been a regular practice. This practice has reduced bentonite consumption by 13% or more. When their vendor announced that they would no longer be manufacturing the product Benton Foundry was using, a search for a suitable replacement had begun. Benton Foundry trialed other green sand additives in the Fall of 2018, and after extensive data collection and casting analyses, Benton Foundry decided on the OPTIMULL product. 

Rather than just attempt to replace their previous material, an extensive trialing period was initiated. 

While trialing the green sand additives, Benton Foundry found that not only did the OPTIMULL continue to allow them to run clays at 13–16% lower levels by using a green sand additive, but it allowed them to further reduce the clay levels by an additional 6–8% beyond this. The foundry also reported that cracked molds were reduced by 11%, Benton Foundry also estimated that the material provided them with an additional 13 to 14% in cost savings. What was most impressive is the clay usage decreased during a period of time where the core sand influx and the pounds of core resin actually increased as well, to over 110 tons per week. Stated another way, 2,500–3,000 pounds of resin added per week, while maintaining consistent properties. Instead of having to add more clay for the additional core sand influx, the clay addition continued to decrease. 

Weil-McLain

Weil-McLain, a division of The Marley-Wylain Company, is a leading North American designer and manufacturer of hydronic comfort heating systems for residential, commercial and institutional buildings since 1881. 

Weil-McLain wanted to trial the OPTIMULL green sand additive due to the concerns and issues that they were having centered around misruns and other defects they felt may be related to poor mulling or poor activation of their bentonites in their preblend. Of particular concern were the numerous misrun defects in the thin-walled castings that they associated with gas that would prohibit the metal flow in the narrow cavities of the molds. In the past, moisture reduction was tried, but this would sacrifice the friability of the prepared sand, resulting in increased inclusion type defects. With the green sand additive, Weil-McLain was able to significantly improve the misrun defects. The moisture in the molds was reduced by 9%, without negatively affecting the friability of these same molds. Clay usage was reduced by 12-14.5%. Scrap attributed to gas defects was reduced by 66%. Not only was Weil-McLain able to fix its misrun issues with the decreased water, which had generated the gas prohibiting good metal flow, the permeability on the molds increased by over 2.5% allowing for better gas ventilation and in turn improved metal flow.

Both of these foundries continue to use the OPTIMULL today, and they are willing to share their experinces with any foundry that may have an interest in this green sand additive.