US2367648A - Preparation of dry sand molds - Google Patents

Description

Jam, i6, E945. A. s. NICHOLS PREPARATION OF DRY SAND MOLDS Filed April 2, 1943 Patented Jan. 16, 1945 PREPARATION F DRY SAND MOLDS Arthur S. Nichols, Oak Park, Ill., assignor to The Illinois Clay Products Company, Joliet, lll., a corporation of Illinois Application April 2, 1943, Serial No. 481,555

2 Claims.

This invention relates to metal founding.. and among other objects aims to improve the method of making dry sand molds, cores, and the like.

The nature of the invention may be readily un-A derstood by reference to illustrative embodiments thereof hereinafter described.

In the drawing:

Fig. 1 is a diagram, partly in section, illustrating one method of conditioning a mold; and

Fig. 2 is a diagram similar to Fig. 1 wherein different means for practicing the method are employed.

Generally sand used for making molds and cores in the founding of metals, both ferrous and non-ferrous, including iron, steel, aluminum, magnesium, etc., and various alloys of the same, is composed of sand grains combined with either a natural or an added clay bond, organic bonding agents, oils, sea-coal, etc., or a mixture thereof. In preparation for molding the sand and added ingredients are mixed or mulled together, and tempered with water or with an aqueous liquid binder.

The sand when molded is in the green condition and frequently receives the molten metal without other treatment. While green sand is permeable to air and gases, the permeability to the free passage 0f gases generated by thel pouring of the metal is low compared to a dry sand mold because the tempering moisture assists in partially filling the free pore space. Increasing permeability in a green sand mold sometimes requires costly expenditures for more concentrated bonds or specially selected sand grains to make the sand more open.

Drying substantially increases permeability. For example, one mixture having a green sand permeability of 70 has a dry sand permeability of 170. The green sand strength is likewise low, and in this condition the sand is generally too weak for handling in the form of cores which are molded separately from the mold itself and insertedtherein after the mold is formed. The green sand mold is frequently below the strength necessary to give a smooth nish, free from defects, on the surface of the casting and the cost of cleaning and iinishing such castings is high.

Drying substantially increases strength. For example, one mixture having a green compression strength of ten pounds per square inch develops on drying a compression strength of seventy-ve pounds per square inch.

Heretofore the green sand mold surface was sometimes made stronger by skin drying, with a torch, but in many types of casting production the entire mold is dried in an oven before being used in the casting operation. The cores are al- 'most invariably oven dried or baked before being inserted in the mold. This dryingprocess is expensive and, depending upon the size of the mold or core, takes considerable time. Considerable equipment is tied up and additional fuel and manpower needed.

I` have discovered a method of conditioning molds and cores in a very short time, so short indeed that special handling or diversion froml the production line is reduced or eliminated.

In the practice of my process I conduct air to the mold or core and cause it to pass through the permeable sand and thereby carry oir the moisture to produce a strong dry sand mold or core in a matter of seconds or minutes. In some cases the conditioning action of the air is not merely one of drying as where strength depends on oxidation of the bonding agent.

Preferably the air is passed from the mold or core face outwardly through the sand. This has the advantage of drying the most important part rst and if for any reason complete drying is unnecessary, that part to be nearest the molten metal will have been dried in a minimum time.

Drying may be accelerated by heating the air, or by drying the air, or by using heated dried air. Any appropriate method of drying or heating the air may be used. One inexpensive method of drying requiring little equipment is to pass the air through a hygroscopic substance such as fullers earth or southern montmorillonite, both or which are relatively inexpensive as compared to the chemical type of hydroscopic substances. The efficiency of these substances can be quickly and repeatedly restored by periodically passing highly heated air through the body of the material to carry off the absorbed moisture.

One method of introducing the air into the sand is to pass the air through the pattern While it is still against the mold or core face. For this purpose the pattern is provided with passages and perforations or slit-like openings which distribute the air eiiciently over the face of the mold or core. Where the thickness of the sand is not excessive or the permeability too low, drying may be eiected so quickly as not substantially to retard reuse of the pattern If the mold is removed from the patternbefore drying, the air may be introduced by applying-a tightly fitting hood or cover over the ask-con.. taining the sand,todeliver the air to the Vface of.. the mold, from Where it permeatesandpasses through the sand, escaping with the collected moisture through the outside of the mold.

If it be impracticable for any reason to introduce the conditioning air at the mold face, it may be introduced at a side or sides of the mold and pass through the mold to escape on the opposite side or sides or where ever escape be possible. The pattern may or may not be removed depending on the naturepf .they mold and character of the pattern. ',Ih'mfnethodgwould apply to many types of cores wherein the body to be conditioned is surrounded by the core box or pattern.

The action of the air in changing the sand from the green to the dry condition in instances where an oil type lander is used, as in most cores, and some molds, is not merely one of moisture removal, but involves an oxidation or setting of the binder. Where development of strength depends on something'more than mere drying, and as by oxidation of oils, the air should preferably bel heated. Y

' The drawingr illustrates two YVmethods of conditioning al sand mold.y In'Figi '1? a distributing hood orm'niiold 10' isv applied -to a flask after the-pattern has`:been removed.A "Air delivered by the blowerffi ifis properly conditioned by drying or. ashore shown, by passing it through a heater l2; "andi then it`is"deliveredlbyconduit il. The air kfirst Astrikes the molding face I4 of sand, drying' :it'filrstfand'thenpasses through the body of the" sand? conditioning it` by drying it and/or oxidizing anyY organic' binder therein and then emerges through* alrero'te'face of the mold. In the presentfcase the support I5` on which the iiaslk'rests perforated as at I6 to facilitate the escapeof the air. -f 5 .InFig `2 4conditioning of the moldis eected before the pattern has been withdrawn. As there shown the pattern fis provided with a series of perforations orductsii'l adapted to convey air through the pattern 'and deliverA it to the molding race Vlrof the mold fromwhichit passes through the sand; conditioning the 'sand as inthe method illustrated iniFig. 1',- escapingthroughthe opposite face i9 of vthe mold.' In the. present instance the ducts il through the pattern `are relativelylarge and'contain terminal vents 20 having a plurality of smaller-holes soas to distribute the air moreuniformiy. .if 1 y A vmanifold 22 similarto thatfemployed in the case of Fig. 1 and which may either be a part of the pattern or separate therefrom distributes the conditioned air from the conduit 2l to the respective ducts l1 in the pattern. The air is conditioned and delivered by a fan Il and conditioner I2 as in the case of the method illustrated in Fig. 1. After conditioning of the mold the pattern is then withdrawn.

The illustrative method completely revolutionizes foundry practice where sand molds are involved. It permits the use of the stronger and more permeable dry sand mold where it has heretofore been economically and physically unsuitable. It reduces the time of the molding operation where dry sand molds are necessary, and it simplifies core making. It completely eliminates drying and baking ovens and the separate handling of the molds or cores into and out of these structures. It frees tremendous amounts of flask and conveying equipment formerly tied up in the drying operation, and liberates the great area of floor space formerly required for the accumulation of molds and drying ovens.

Obviously the invention is not limited to the details of the illustrative embodiments of the invention herein described since these may be variously modied. Moreover it is not indispensable that all features of the invention be used conjointly since various features may be used to advantage in diil'erent combinations and sub-combinations.

Having described my invention, I claim:

1. The method of preparing dry sand molds which is characterized by introducing drying air through openings in the pattern while in the mold to distribute the air over the mold face and causing currents of air to pass through the sand in the mold from the mold face outwardly until the currents of air have carried away enough moisture to develop dry sand strength in the mold. then removing the pattern from the mold.

2. The method of preparing dry sand molds which is characterized by passing air currents through the sand in the mold from the mold face outwardly while the pattern remains in the mold,

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