Metal Casting Zone Info Blog

Posts Tagged ‘mold’

Has anyone tried it?

Can you just cover it with carbon,preheat the mold and don’t cast anythign to big?

silver Tree, gold Casting

I’ve seen on the internet where people use a pile of sand packed tightly to impress the object they want to cast and pour the molten metal into the hole in the sand. Even with fine sand, this does not produce the smoothest surfaces and sometimes the sand becomes embedded in the casting. I knew someone who cast pewter statues and he used this green foam-rubber looking stuff to make molds. Anybody know what I’m talking about?

Steel casting is a specialized form of casting involving various types of steel. Steel castings are used when cast irons cannot deliver enough strength or shock resistance. Examples of items that are steel castings include: hydroelectric turbine wheels, forging presses, gears, railroad car frames, bodies for valves and pumps, machinery used in mining, marine equipment, and engine casings. Steel castings are categorized into two general groups: carbon steel and alloy steel.

The methods of casting steel: The Szekely method consists of employing metal molds, one of the chief points being to coat the molds with chalk and paraffin. Shaw also employs metal molds. Slavianoff’s electric casting method appears to be simply a method of melting steel by connecting it to one terminal of a strong electric circuit, the crucible in which it is to be melted, or the plate on which it is to be cast being attached to the other.

In the so-called sand core process, a sand core is cast in the ingot which is afterward worked down as usual; it was claimed that the sand did not injure the material, but this, as well as any advantage, is extremely doubtful. In Norton’s fluid rolling process, fluid steel was to be worked direct into sheets by pouring it through revolving rolls properly adjusted, with the idea of preventing blowholes, and reducing the usual amount of scale.

Bessemer’s method for making continuous sheets consisted in running molten steel between two water-cooled steel rolls, separated a suitable distance; the speed of the rolls was regulated according to the thickness of the sheet. In Whiteley’s process for the production of plates, molten steel was run into a revolving cylinder and formed a shell which was taken out, cut open by a saw, and then rolled down. Pielsticker and Mueller’s process was devised for producing bars, rods, and similar material direct from fluid steel by first passing it through dies, and then finishing the resultant material in a rolling mill or under a hammer.

Malleable or cast-iron castings are sometimes united by heating in contact to a high temperature; this is termed “bumming” together. It is sometimes necessary to make an addition to a casting to complete or to replace a portion which has been broken off. For this purpose the casting already made is placed in a mold of the proper shape and molten metal poured in.

The solid metal must be heated up to a sufficiently high temperature, and there are two methods which are usually distinguished as (a) casting on, where the solid metal is heated with a flame, and (b) burning on, where the molten metal is first caused to run into and out of the mold until the solid portion has been sufficiently heated, when the outlet hole is closed, and the mold allowed to fill up.

Wm. Chalk’s method for uniting a sleeve or boss of cast iron, etc., on a wrought- iron shaft consists in heating the shaft to a welding temperature, putting it in a suitable mold, and pouring around it the molten metal.

Falk’s method is somewhat similar, and is intended for uniting the ends of rails; an iron mold is placed around the ends, and extremely hot metal is then poured around them until they are partially fused and will unite readily. Permanent mold casting (typically for non-ferrous metals) requires a set-up time on the order of weeks to prepare a steel tool, after which production rates of 5-50 pieces/hr-mold are achieved with an upper mass limit of 9 kg per iron alloy item (cf., up to 135 kg for many nonferrous metal parts) and a lower limit of about 0.1 kg.

General steel (http://www.generalsteelcorporation.com/) cavities are coated with a refractory wash of acetylene soot before processing to allow easy removal of the work piece and promote longer tool life. Permanent molds have a limited life before wearing out. Worn molds require either refinishing or replacement. Cast parts from a permanent mold generally show 20% increase in tensile strength and 30% increase in elongation as compared to the products of sand casting. The only necessary input is the coating applied regularly.

Typically, permanent mold casting is used in forming iron, aluminum, magnesium, and copper based alloys. In the modern era, the process is highly automated with the use of robotic equipment and computers.

What really happens here that a rubber mold the size of a disc is spun around its central axis at very high speeds. The casting material is most often thermoset plastic which is in liquid form or its molten metal. This liquid material is poured into the mold through its opening which is in the center of the mold. So in order for solidification of the metal or the setting of the plastic as it’s called the filled mold is spun. This is essentially the spin casting process in short.

Usually the mold making substrate in spin casting is organic rubber or its vulcanized silicone. The rubber vulcanizes usually in the middle of the mold making process. Once the vulcanization process has been completed the venting and the gating process must be undertaken by the mold. This requires that the channels be carved in so in order to ensure the proper flow of material and air during the process of casting. The above two processes is carried out with the help of a tool such as a knife or a scalpel. The complexity of the mold is proportional to the time it takes to implement the gating and venting of the mold.

Spin casting machines

There are two types of commercial spin casting machines. Once type is known as a front loading machine and the second is a top loading machine. Now because of the bulkiness and the weight of these spin casting molds there are several advantages to using a front loading machine. The biggest of all advantages is its easy to use and a big time saver. As the diameter of the rubber mold grows so does its weight and when metal is cast it can become extremely heavy. Now because the loading and the unloading of is usually done the hand, people find it easier to manipulate the mold when it’s at waist level which is usually one in one swift fluid motion which is allowed by the front loading spin caster. When it comes to spin casting for commercial requirements this type of behavior is very important as it will maximize the number of casts per hour, hence making it more productive. Also top loading machines are cheaper and don’t have much of a restriction on mold thickness. This means that they are flexible.

What is Spin Casting good for?

Spin casting is a great method if you want to fabricate items with materials that are either thermoset plastics or low temperature metals. Spin casting has many advantages over other process such as Zinc die casting, and injecting molding in terms of costs as well as ease of use. There are cases in which spin casting is used as an alternative to plaster mold casting, sand casting and investment casting.

In times past, paper and pencil were the most important tools a casting designer had – and the development of a casting was a technique that was tedious and lengthy. A paper design was created ; the blue print was introduced to the die caster – who ganged up with a toolmaker. Together, a die-casting machine was chosen ; the method and mold layout developed and costs estimated. Quotations were made. The bidding winner gave authorization to his tool seller to order die steel and begin with mold coming up with. When finished, the mold was sent to the die caster for a first test. After building it into the machine, castings were made and checked for defects.

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It was not until this point in the process that those concerned got any concept about the quality of the casting. If the casting failed to measure up to the desired standards, changes would have to be made. Different process settings and minor die corrections might be done at the die-casting machine straight away – but if the first trial proved that the mold had to be modified, steel had to be ground away and welded back in other places, and that work needed to be done at the tool seller’s facility. The mold traveled back and forth between toolmaker and die caster until an acceptable casting quality was achieved. The time between starting the casting design and shipping good castings could take weeks, months or years depending on the complexity and size.

Additionally, mold designs could – and did – change, even after production had started, and those changes meant molds could have different designs, different ages and wearing patterns, and different casting qualities. In addition to mold changes, variations in production parameters like die casting machine pressures, pouring velocities and transitions, lubrication volumes and locations, solidification and cycle times changed across the casting process. The never-ending need to adjust and improve the casting stopped only when the casting wasn’t required anymore. Working toward a better casting quality kept a huge team active with involvements of the method engineer, the machine operator, mold maintenance and toolmaker, quality office, casting designer, casting machining, even assembly and material planning and handling group.

While there was a point when this type of ‘engineering’ was necessary, the business facts of today make it financially unfeasible to resume in this fashion – but despite that, this “engineering” can be found in companies that are wrestling their way through difficult times.

“The die casting industry’s capacity in the U.S. Shrunk … With the closing of plants that were not able to keep up with technology…” Daniel L. Twarog, President NADCA, Letter from the Publisher, LINKS, Feb 2009

Streamlining the method Today

With the addition of PCs into factories, the engineering process is continually changing and becoming more streamlined. Casting are now not drawn on paper and tooling dimensions don’t have to be transformed to mold drawings anymore. Computer assisted designs available in 3-dimensional volume models allow info to be transferred with the push of a button and be used as input directly into the steel machining kit. Changes in models can be made quickly and easily shared with all design departments.

The great value of computerization lies in the chance to develop, design and build at virtually the same time. These parallel working conditions decrease the development time and speeds ‘time-to-market’ to a level that wasn’t even dreamt of years ago. Computerization in the engineering and manufacturing process have also permitted for more precise machining equipment in the tool shops, customized die steels and heat treatment processes that allow changes based factors such as : length of production run and material in direct contact to the melt or for better heat transfer and heat flow.

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I’ve seen on the internet where people use a pile of sand packed tightly to impress the object they want to cast and pour the molten metal into the hole in the sand. Even with fine sand, this does not produce the smoothest surfaces and sometimes the sand becomes embedded in the casting. I knew someone who cast pewter statues and he used this green foam-rubber looking stuff to make molds. Anybody know what I’m talking about?

Casting is one of the earliest known forms of metal working. In its most simple form, it involves heating metal until it is molten and then pouring it into a mold. As the metal cools it takes the shape of the mold. Early castings were crude in finish with a large amount of surface anomalies that required a great deal of machine work to get the required quality of surface texture. Modern casting techniques produce awfully fine tolerations and the casting requires little finishing work.

The artist who creates metal art castings should be both a foundry man and an artist. Bronze is one of the earliest alloys known to occupy and is formed up of tin and copper. Being malleable, it becomes a liquid of low viscosity when liquified and thus has the power to fill even tiny crevices in a mold, permitting for the production of castings with fine detail. Though bronze castings are the most typical, nearly any metal can be cast. The artist wishes to grasp what kind of mold to use with what metal. And he must know the way to melt metal.

The casting process starts with the creation of the mold. The most typical type is known as the Lost Wax Casting technique. Being straightforward to create and with the facility to create molds with fine detail, it’s the artists’ favorite. First the artist creates a wax sculpture. This sculpture is then used to form a mold. Molds can be made of a selection of materials from sand to latex, depending on the quantity of detail needed. Latex is employed when highly fine detailing is concerned since it forms a skin like coating on the sculpture and picks up even the minutest detail. The sculpture is then removed from the mold.

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Molten wax is then poured in the mold till the necessary thickness is achieved and the wax copy is then removed and any defects on the surface removed. A shell is then built round the copy using a mixture of sand and liquid silica. The shell is heated until the wax softens and runs out thru a drain hole left in the shell.

The final mold is then ready and the molten metal is poured into it. After it has cooled and taken the shape of the mold, the shell is removed and the completed casting is available.

The artist then removes and imperfections which will remain on the casting after which it is either painted of coated to give it the desired finish.

Metal art castings may be of any size, from the tiniest piece of gold jewelry to a huge cast statue to big to even fit inside. The good thing about this kind of metal art is the fine detail that can be produced. Modern metal softening techniques make sure that the molten metal that enters the mold is without imperfections and strong enough to safely hold a diamond ( in the case of jewelry ) or withstand the rigors of nature ( in the case of garden sculptures ).

Additionally, once the mold is created, many copies of the art work may be produced.

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I have a wax figure i would like to cast into metal bColloidald to coat it with some sort of ceramic material except clay to fire melt the wax out leaving a perfect mold for a metal pour. Is this Colloidal silica liquid and I add sand to it or is it the other way around. Or do I need to use something completely different.

I want to use something that is faster than ” lost wax casting ” and I was wondering if I could machine a reusable 2 piece mold to pour molten silver in . Let it harden, separate the mold and pop out the unfinished product . I know there might be a proplem with the mold warping , but if I use a mold, lets say each half being a inch or so think . Also what type of releasing agent if any would I use prier to each use of the mold . I was told that talcum powder would be a good releasing agent , but that sounds a little odd ? What i had in mind was pouring about 2 ounces of silver at a time into a mold with the out side diameter of 2″x5″x7″ .