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Green Sand Metalcasting Foundry News

"K" - Glossary of Foundry Additives (Green Sand Foundry Supplies) 

Posted by Hill and Griffith Company on Apr 10, 2018 12:18:02 PM

K - Foundry Additives Glossary

KAOLIN (See: BONDING CLAY-CLAYS-FIRECLAY)
Kaolin is commonly called "kaolinite" as well as "China clay" in the ceramic industry. It is a hydrous aluminum silicate. It is a clay that has the composition of (2SiO2 • Al203 • 2H20). It is used through­out the foundry industry from refractories to bonding purposes, as well as in many foundry compounds and commercial foundry mixtures.
The fireclays used in the foundry are commonly called "kaolinites" but the fireclays contain impurities such as feldspar, fine quartz sand, mica and iron oxide. A true kaolinite clay generally has a specific gravity of 2.6 to 2.63 and a Moh's hardness of 2.0 to 2.5. When wetted, kaolin can be made into shapes and will retain these shapes after they are baked or fired. Most commercial "Kaolin" grades of clay are used by the ceramic industry and the whiter burning "Kaolins" are washed and shipped from the South for use as Green Sand Foundry Supplies. 

KAOLINITE (See: CLAYS -KAOLIN)

KELP (See: SODIUM ALGINATE)

KEROSENE (See: CORE OILS-FUEL OIL-OILS-PETROLEUM)
Kerosene is known in some localities as "Coal Oil." It is a light, oily, liquid prepared from the distillation of petroleum oils. It distills­ off after the gasoline. It is a hydrocarbon having the composition (C10H22 to C16H31). Its specific gravity is between 0.75 and 0.78. It burns freely but it is not so volatile as to be explosive, therefore, it is used in the foundry to prevent molding sands from drying-out. It is, and has been, used to replace some percentage of seacoal. Many liquid partings contain kerosene. Core oils contain kerosene, as a low tem­perature and faster baking ingredient, or a similar light oil.

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KIESELGUHR (See: DIATOMACEOUS EARTH-TRIPOLI) 
Kieselguhr is a form of tripoli found in Germany and is more 
widely used as an insulator because it has a low density and a low thermal conductivity. Kieselguhr obtained from Oberhole, Germany contains about 88% silica, traces of alumina (Al203), some organic matter, and it contains about 8% to 10% combined water. It is used as an insulating product in the foundry.

KLEAN SURF IRON OXIDE (See: HEMATITE -IRON ORE OXIDE - IRON OXIDE)
Klean Surf is a carefully selected iron ore mineral having from 32% to 42% ferric oxide (Fe2O3) content. 
The combined silicates and non-metallic oxides which accompany the ferric oxide (Fe2O3 ) are responsible for the lower hot plastic defor­mation required in a satisfactory foundry mold or core sand mixture.
A certain amount of mineral oxides blended by nature with the ferric oxide (Fe2O3 ) are required to develop this hot plastic deforma­tion at elevated temperatures. These silicates and metallic oxides which accompany Klean Surf actually sinter when heated at a low temperature and also improve the hot plastic deformation. In some industries, Klean Surf is called "a self-fluxing mineralizer." This self-fluxing ability associated with Klean Surf Iron Ore Oxide allows a stickiness, or tackiness, to develop at lower temperatures which holds the sand grains together, much as a plastic cement adheres to non-plastic granular materials. This prevents "flaking," "raining" or "spall­ing" of the sand grains during pouring of the metal. It is a valuable asset to ferrous and nonferrous sand mixtures whether used in mold or core sand mixtures.

Recommended Foundry Use
Klean Surf is added to foundry mold or core sand mixtures to not only color the mixture but also to further improve its hot properties when subjected to heat.
From 0.5% to not more than 2% by weight of Klean Surf is sufficient to color and to promote the plastic deformation which pre­vents spalling and cracking of rammed core or mold mixtures. This is particularly true with steel sand mixtures. Less veining, metal pene­tration, and burn-in are noted where Klean Surf is used in such mix­tures. Some foundries use up to 6% by weight iron oxide to prevent pinhole porosity and to furnish specific sand mixture properties.

To Avoid Veining
Klean Surf furnishes cleaner casting surfaces and prevents the core or molding sand from abrupt volume changes when subjected to thermal shock. One of the most aggravating defects associated with incorrectly prepared cores is "veining." Where veining appears in deep contours, or on the surfaces of cores which are surrounded by heavy metal sections, Klean Surf additions have cured the problem. It may be necessary to add up to 3 % by weight where most severe veining occurs. Generally, less may be added to overcome this troublesome and costly defect. Where pouring may be too rapid and the mold or core is subjected to volume changes due to the heat shock generated by an uneven gating system, Klean Surf is recommended to regulate these difficulties.

Eliminate Cuts and Washes
Certain steel foundries have stated that where 2% to 4% by weight of Klean Surf has been added to certain molding mixtures, Klean Surf acts as a filler, thus preventing cuts and washes of the mold due to brittle sands. Many companies have actually reduced silica flour and zircon flour additions by substituting less expensive Klean Surf oxide. In this case, Klean Surf acts as the fines, which furnish the mechanical properties of the silica flour fines.
Contrary to general belief, this low eutectic mineral ore when properly classified, graded, and ground specifically for foundry use, furnishes more desirable properties than other foundry grade or type of oxide sold for commercial use.

Protection Against Pinholing
From 1 % to 6% Klean Surf oxide helps to prevent pinholing. One of the specific reasons given is that the oxides of the metal such as Wiistite (FeO) is changed to (Fe3O4) when the Klean Surf (Fe2O8) is present in the core or molding sands. 

Steel Sand Mixtures
Steel foundries have found that with certain high purity silica sands it is best to add from 0.5% to as much as 2% by weight of Klean Surf to promote early fusion and prevent spalling of the sand mixtures which occur with increased volume changes when the mix­tures are heated at higher temperatures. Klean Surf blends well with bentonite bonded sand mixtures. Its action is quite worthwhile where cuts and washes of the mold occur at certain gated areas where too much metal enters the mold from one in-gate. Where metal impinges against a mold-wall surface, the addition of Klean Surf is highly recommended so that a quick fused refractory bond is formed by the Klean Surf when the metal first impinges against the mold-metal interface.

Commercial Grades-Sieve Analyses
(1) Finer Grade-approximately 90% passes a U.S. Standard Sieve No. 200.
(2) Granular Grade-65.0% is retained between the U.S. Stand­ard Sieve Nos. 40 and 140. Less than 10.0% passes the U.S. Standard Sieve No. 200.

Specific Gravity
Klean Surf when calculated with no more than 0.5% natural moisture is usually between 3.0 to 3.6. It varies as the mineralizer composition varies.

Color
Klean Surf varies from dark red to light brown, or purple-red. 

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Mechanical Properties
Klean Surf furnishes molding and core sand mixtures slightly higher green compression strengths. A small addition of Klean Surf may add as much as 1.5 psi additional green compression strength, depending on the base sand used and on the amount of temper water added to the mold or core sand mixtures.

Coatings
In certain mold or core coatings, as much as 5% by weight Klean Surf may be used to give them a color and a harder surface when applied. Also, it stabilizes the coating during the pouring operation with less fear of spalling. In this case, Klean Surf offers some proper­ties similar to a clay addition, even though it is not considered clay-like in nature and doesn't absorb as much of the liquid binders. A lite-off spray containing 12 parts by volume of isopropyl alcohol, 1 part of Colloidrez 7104 phenolic resin, and 5 parts of Klean Surf does as effective a job as a mold coating.

Additions to Naturally Bonded Sands
As an addition to naturally bonded sands, it improves stability under heat and lengthens the life of the naturally bonded sands. All naturally bonded sand mixtures are improved somewhat by Klean Surf additions. Proof of its usefulness and value is more reliable than opinions,
and Klean Surf is highly recommended to the interested foundrymen.

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-P.C.E. Value -
The P.C.E. test (Figure 127) shows the controlled fusion of Klean Surf which permits plastic deformation in mold or core sand mixtures when heat is applied. The Klean Surf sand mixture has started melt­ing, but the "B" and "C" commercial iron oxide samples haven't started to fuse even at 2345°F. (1285°C.).

Theory of Use
Klean Surf is a basic ferric oxide, but one that has other minerals present.
Klean Surf must not be confused as being another "iron oxide," or a "ferric oxide," else its true value may be lost.
Klean Surf prevents and cures metal penetration and excessive casting burn-on. The reasons and technology are simple.
A careful study should accompany each investigation where var­ious iron oxides are being added to sand mixtures or being evaluated by the foundry. Basic opinions or preconceived ideas do not hold up in the face of facts. Klean Surf is an excellent sand additive in both ferrous and non-ferrous foundries.
In the casting of ferrous metals, ferrous oxide (FeO) or "Wlistite" is constantly formed. This is not the same as ferric oxide (Fe2O3). Wlistite (FeO) has a melting point of less than 2500° F. (1371 °C.). Wlistite is one of the most corrosive metallic oxides developed in the mold cavity when ferrous metals are cast. This troublesome Wlistite, a ferrous oxide (FeO), constantly forms as molds are being poured. As the mold gases oxidize, the gases will, in turn, continue to oxidize the iron. Furthermore, water in green sand molds constantly reacts to form more Wlistite. This highly basic oxide reacts violently with silica (SiO2) sand, which is strongly acid.
Even when mold gases, or slightly reducing gases are formed, the formation of Wlistite continues. As FeO is formed when iron reacts with water, so is a constant quantity of hydrogen gas. The hydrogen gas gives the slightly reducing gas in the mold. The following chemical reaction occurs as rapidly as the speed of an electric computer, as hot iron reacts with water.

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Water is the strongest offender in molding sand mixtures in devel­oping more of this corrosive ferrous oxide. To calculate, 3% temper water in a green sand mixture is actually 3 pounds of water in 100 lbs. of the sand mixture. The three pounds of water present are capable of producing 12 lbs. of Wiistite (FeO). However, as the FeO is formed, so is 63 cubic feet of hydrogen gas developed in the mold. This is the reason some mold cavities show a slightly reducing atmosphere, even though the very corrosive and damaging metallic oxide (FeO), Wlistite is being created. 
If moisture increases, so does the manufacture of Wlistite (FeO) in the mold increase. Thus, very damaging metal penetration and burn-on occur on the hot castings in the mold. Severe corrosive attacks on the molding sand continue as the casting is held in the mold before shake-out.
The harder the molds are made, the more this corrosive, ferrous oxide (FeO) is accumulated in the mold, as less permeability is avail­able. The Wlistite attack occurs on both the molds and the castings. The less the venting, the more severe the ferrous oxide (FeO) attack on mold and casting.

Gas Theory
When iron or steel is first poured into a mold; to further com­plicate the above chemical and corrosive action, the larger amount of carbon monoxide (CO) produced further adds to the problem. This reaction is further generated by the oxygen in the mold which com­bines with the carbon in the metal and in the mold. As this carbon monoxide (CO) increases, the very penetrating and corrosive iron penta-carbonyl [Fe(CO)5] is formed at less than 600 ° F. (316° C.) temperatures. The [Fe(CO)5] is formed first before the formation of the Wlistite (FeO) by the iron-water reaction.
In many cases, the presence of a reducing agent may not have any deterrent influence on the reaction of the water with the metal in forming Wiistite (FeO), but may actually hasten it. The iron penta­carbonyl developed, starts the degree of metal penetration and burn-on on the casting. The corrosive reaction of the FeO against the silica sand grains continues, as the pressure and percentage of iron penta­carbonyl increases.

Liquid Theory
Most sand and ceramic technologists have calculated that when Wlistite (FeO) attacks silica sand, it forms a solution of approximately 20% silica with the ferrous oxide (FeO) which is fayalite (Fe2 SiO4). The melting point of fayalite is less than 2190° F. ( 1199° C.).
Deep metal penetration between sand grains always occurs when fayalite is formed. As the FeO (Wlistite) is manufactured in the mold cavity, silica is consumed and more fayalite (Fe2 SiO4) is formed. As more iron penta-carbonyl is formed, the mold-metal reactions occur in lightning-like fashion. Silica (Si02) is consumed by the FeO like sugar dropping into water. The more surface of the silica sand grains which is exposed, the more the silica is consumed by the ferrous oxide (FeO). The deeper that fayalite (Fe2 SiO4) penetrates into the sand voids, the larger the voids and openings become. These voids are then filled with the following and continuous hot liquid metal, lubricated by the thinner, metallic slags, fayalite, and metallic oxides.
Iron (Fe) is precipitated as the temperature drops in the mold, when fayalite forms and completes its reaction. Fayalite needs a re­ducing atmosphere to form and live. The precipitated iron (Fe) between the sand grains also has a very binding effect between the mold and the casting. The ever present, fayalite and slag, helps to cement the metal to the sand mold or core.

Solution
A solution to this unusual metal penetration problem is the use of Klean Surf iron oxide (FeP3). The Fe2O3 unites with the Wiistite (FeO) as it is formed, thus magnetite (Fe3O4) is created. The cor­rosive and damaging fayalite (Fe2SiO4) is not formed because of the flooding of the mold with excess oxygen from the oxide. Neither is the iron penta-carbonyl formed at the lower temperatures because the Klean Surf when heated releases oxygen. Metal penetration and burn­on is much less, or nil, on the castings. Because so little of this phe­nomenon is presently understood by the foundryman, he is generally fearful of adding the higher 3% , 4% or 5% amounts of Klean Surf. Carbons can be eliminated as Klean Surf additions are carried higher. Cleaner surfaces on the castings are formed with higher iron oxide percentages in particularly hard, high pressure formed molds having less or no vents. 

KYANITE (See: CYANITE)
Kyanite or cyanite has the chemical formula, (Al2O3 • SiO2). Decomposition begins at about 1325°C. (2415°F.) with the formation of mullite and a silicate glass. (See: pages 531-532 for its use.)

Review of "Glossary of Foundry Additives" by Clyde A. Sanders, American Colloid Company


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