What materials are your crucibles made of?
Where are your crucibles manufactured?
If you want to learn more, please visit our website.
What type of crucibles does Molten Metal Systems recommend for ZnO production?
What type of crucibles can be used for melting in induction furnaces?
What crucibles are recommended for different applications (Al, Cu, Zn, Precious Metals, etc)?
Can I re-use the stand (pedestal, base block) after the crucible has been removed?
For which patterns can we get reinforced crucibles?
May I use Excel E in gas furnace?
May I use standard Excel stand with Excel E crucible or the opposite?
What is the primary difference between Excel brand and Omnimelt brand?
Can I use a crucible without a stand (pedestal, base block)?
What kind of packing is used to protect your crucible during transportation?
Can I use the same brand/type of crucible in gas burner furnaces as with an oil burner furnace?
Can I fill a cracked or damaged crucible with plastic (Al2O3 + P2O5) and continue my work?
What are the advantages and disadvantages of SiC vs. CG? Why would I choose one over the other?
I have heard that Molten Metal Systems is the only global crucible manufacturer that uses all three crucible forming techniques. Why is this and why does this set Molten Metal Systems apart from the competition?
What is a typical crucible life time?
How can I improve my crucible life and performance?
How I can eliminate problems with flux attack and lengthen crucible life time?
How I can prevent bottom cracking?
How I can prevent crucible early oxidation resulting in crucible cracks on top edge?
Why are there different preheating procedures for different crucibles and does it really matter?
If I don’t clean the crucible regularly, what can happen? How often do I need to clean the crucible?
How long is the pre heat for first use ? Can I use it for gas or oil fired burners?
How long is the first heat for precious metals if I use a gas fired burner or an oil fired burner?
What is the crucible installation procedure for bale out and tilting furnaces?
Do you have only one size of impeller on your degassing rotor?
What is the normal nitrogen flow for degassing rotors and degassing tubes?
Molten Metal Systems crucibles are manufactured using carefully selected materials designed to precisely match the crucible’s characteristics and operational performance to each customer’s metal melting, holding or transfer application. A foundry crucible contains 30-50% by weight of flake graphite, depending on the properties required. Naturally occurring graphite is normally used. The carbon content of graphite imparts high thermal conductivity and non-wettability and, coupled with its plate-like layered matrix structure, provides high thermal shock resistance. This is critical to foundry applications as temperatures can change by several hundred degrees in seconds. In addition, crucibles will normally contain 10-50% silicon carbide – depending on the desired properties. Unlike graphite, silicon carbide is synthetic, manufactured from silica sand. This material provides excellent resistance to elevated temperature erosion and to chemical corrosion. It also imparts thermal conductivity. Choosing the best grain size and structure is important for optimizing the overall microstructure to match the product to specific applications. There are two types of bonding systems used in crucibles. Tar/resin produces carbon bonds and the other - clay, produces ceramic bonds following heat treatment. >>Top
Molten Metal Systems crucibles are manufactured in several plants strategically located around the world. Our facilities can be found in Germany, Brazil, India and China. >>Top
There are several types of crucibles that we can recommended for this application including our ISO-pressed crucibles made from our Syncarb Z2 material, a specially designed mix of clay graphite. Our Syncarb Z2 products have the optimized shape and the high density required for this application. It is approved and used by many Zinc Oxide producer all over the world. Contact your Molten Metal Systems representative to get the right crucible for your application. >>Top
Molten Metal Systems offers many options for melting in induction furnaces. In order to offer the correct product for your application you will need to provide: a) the furnace working frequency in Hz, b) the furnace operating power in kW, c) the metal to be melted and d) the metal melting temperature. With this information we can recommend right product for the application. >>Top
Molten Metal Systems provides solutions for most melting requirements. The specific crucible for a particular application depends upon several factors including furnace type, metal to be melted, and other applications variables. In order to correctly identify the best crucible for your application please contact one of our sales people in your region. >>Top
Molten Metal Systems strongly recommends that a new stand be used whenever replacing the crucible. >>Top
The most common type of crucible that can be reinforced is the roller formed type. The process for manufacturing reinforced wall crucibles is less costly for roller formed crucibles. >>Top
Excel E can be used in gas furnaces when melting or holding Aluminum but only when a light (or no) flux is used. Excel E can also be used in a gas furnace for Zinc Oxide production. >>Top
Using a standard Excel stand (pedestal, base block) with an Excel E crucible is not recommended. >>Top
The mixture of raw materials that are used to produce the products are different for the two products. >>Top
A crucible can be used without a stand (pedestal, base block) in an induction furnace. A stand (pedestal, base block) must be used in all other types of furnaces. >>Top
Molten Metal Systems uses a variety of packing materials to ensure its products are protected in the best possible way for their transportation to customers. Smaller crucibles are packed in cardboard box with packing material insulation to provide added protection. Larger crucibles are packed using wood pallets and strapping to ensure they do not move during shipping. >>Top
Typically you can use the same type/brand of crucible in a gas burner furnace as you can in an oil burner furnace. >>Top
Molten Metal Systems does not recommend that any cracked or damaged crucible be repaired. Morgan MMS highly recommends that damaged or cracked crucibles be taken out of service immediately for safety reasons. >>Top
The advantages of a given product over another depends primarily on the working temperatures and heating cycles of the application. SiC products versus rib formed clay graphite will typically have better thermal conductivity. SiC versus isotatic pressed clay graphite will have better thermal shock resistance. >>Top
Molten Metal Systems has a long history in the crucible industry. Over the years it has experimented and perfected manufacturing techniques that are critical to the production of high quality and top performing crucibles. The three forming techniques that Molten Metal Systems has perfected are roller forming, rib forming and ISO static pressing. Each of these methods are used to provide our customers with the quality products manufactured by us. >>Top
Performance Issues
Each application is different. Crucible life depends on a number of variables including furnace type, metal melted, flux usage, operator practices, etc. To get the optimal life out of your crucible, use a Molten Metal Systems crucible recommended by your local sales person. >>Top
There are several key activities that will help to ensure you optimize your crucible life and performance. While the product quality built into a crucible by its manufacturer is one key to long service life, another key is held by metal casters themselves. That key is providing the best possible crucible care on the job. Choosing the right crucible, handling your crucible with care and proper installation will make an important contribution to crucible service life. In addition, proper preheating of the crucible before first use and caring for your crucible during normal operations will help to make the crucible last as it was designed*.
By working closely with your Molten Metal Systems representative to select the right crucible for your melting, holding or metal transfer operation you will be eliminating potential applications issues. Upon receipt of your crucible, be sure to inspect it carefully and handle it with care when moving it to storage or to your furnace. Install it properly according the Molten Metal Systems installation procedures. Preheat it according to the Molten Metal Systems guidelines. Operate it within its design parameters. Protect it from physical and thermal damage. And replace it immediately when it is damaged or worn. Follow these rules and your crucibles will provide excellent service life, operational efficiencies and significant economies.
*Refer to the Molten Metal Systems installation and heating procedures when first installing and initially using your crucible. Refer to the article on our website entitled “Key Steps To Maximizing Your Crucible’s Service Life” to find tips and guidelines for getting the most performance out of your crucible. >>Top
Use only limited amounts of flux at the specified temperatures and for limited time. First, make sure that the metal has been completely melted. Next add flux and mix it thoroughly with the metal. Make sure to clean all the ash and oxides from the crucible during the melt and after it has been emptied. Be sure to clean the crucible in the hot stage often. Molten Metal Systems recommends the use of Excel Tricoat PD for optimal crucible life if the fluxes are borax or NaCl (used normally in copper/copper alloys and precious metal). If using Sr and Na fluxes in aluminium alloys, Molten Metal Systems recommends our Syncarb or Alustar crucibles. >>Top
Use the correct stand (pedestal, base block) size as recommended by your Molten Metal Systems representative. The stand should be made from the same material as the crucible material. Preheat the crucible carefully according to Molten Metal Systems recommendations. Do not use any parting refractory material to separate the crucible from the stand. >>Top
You must ensure that the furnace burner is adjusted correctly. The furnace chamber must be closed to prevent air access in to melting chamber. The top edge of the crucible should be covered with a furnace ring that is of the correct size. >>Top
Crucibles are made of different materials with different properties. So they may require different preheating procedures. Discuss with your local representative if you have questions. >>Top
Normally the crucible should be cleaned after each melt or at least once per shift in holding applications, or any time that dross starts to become stuck on the crucible’s inside surface. If dross is not cleaned from the crucible, then it is likely that during the next heating the dross (with a much higher thermal expansion than the crucible material ) will cause a crack in the crucible wall. >>Top
To get the correct instructions for preheating please consult your local representative or view our Installation and Heating procedures on this website. >>Top
To get the correct instructions for preheating please consult your local representative or view our Installation and Heating procedures on this website. >>Top
All furnaces have different designs and therefore should be dealt with individually. Please consult your local representative or view our installation and heating procedures on this website. >>Top
Foundry Products
No, we can supply a range of diameters to suit customer’s applications. Our standard degassing rotor has a 6 vane impeller which is 150mm diameter with a 90mm dia shaft with a variety of couplings to suit customers degassing machines. We can also supply a larger 6 vane impeller in diameters ranging from 180 to 200mm. >>Top
Thank you for your interest in Zircoa crucibles. The information contained in this Engineering Guide has been compiled over a period of many years, and is based on the experiences of Zircoa’s professional team as well as input from many users of our crucible products. The information herein is provided as a courtesy to our customers, and is intended to offer guidance to both novice and experienced founders alike.
Nevertheless, this document is still only a guide. It should not be considered a fixed set of operating instructions. Rather, Zircoa considers it a dynamic document, continuously changing to reflect the latest industry trends and user feedback. Except where safety is a concern, our customers are encouraged to evaluate new ideas and concepts. However, we do ask that results of these evaluations, whether positive or negative, be to allow us to continue to improve our products.
The organization of this guide follows a chronological process from crucible selection through analysis of crucible failure modes. Novice users may find it helpful to read through the entire document in the order presented. Experienced users, on the other hand, may be better served by using the guide as an occasional reference or a refresher for specific topics of interest.
Finally, this guide is by no means intended to be the end-all of information and assistance that Zircoa provides to our customers. Our sales and technical staff members are always available to offer support, whether by , or personal visits. Please feel free to contact us to discuss your needs.
Zircoa specializes in the manufacture of high temperature Zirconia and Zircon crucibles for the investment casting and precious metal industries. This section describes our four basic compositions, and offers some selection guidelines. We also offer if you are unsure which composition is right for your needs.
Stabilized Zirconia Crucibles
The following three compositions have been specifically developed for use in non-interrupted vacuum melting operations (please see the Data Sheets, on the left and hyperlinked below, available from our Website in PDF form, for more detailed information on these compositions):
Composition is a magnesia-stabilized zirconium oxide with high density and high strength. It is recommended as the “best choice” of crucible materials for melting the entire range of commercial alloys. It exhibits superior resistance to both thermal shock and erosion. Low thermal expansion and non-wettability make this one of our most popular crucibles.
Composition is a calcia-stabilized zirconium oxide. This composition contains fused grog, and can be used in high temperature (>º C) applications. It provides superior resistance to erosion, exhibits good thermal shock resistance, and is recommended where high purity is required because of corrosive alloys or high temperatures.
Zircon Crucibles
Composition is used primarily for melting platinum-group alloys, and is designed for “dirty refining” applications (especially when glassy or siliceous slags are present). Composition has high strength, is very resistant to cracking, and performs well at very high temperatures. Please see the Data Sheet for more detailed information on this composition.
Note: Zircoa offers a variety of crucible backup materials. Please contact your Zircoa representative for recommendations relating to your particular application. Data Sheets are availableavaiable from our Website in PDF form.
310 Traditional Grouted-Coil Installation (refer to Figure 1)
3.1.1. Be sure that the melt coil is sized appropriately for the selected crucible.
3.1.2. Clean and inspect the coil for damage. Repair areas where grout is loose, thin or missing.
3.1.3. Check the refractory dish (base) of the coil assembly, making sure that it is not cracked or damaged in any way. The dish must be strong enough to support the crucible and its charge at temperature.
3.1.4. Check the new crucible for possible defects: excessive internal pits, holes, cracks, etc.
3.1.5. Be sure to record the crucible lot number.
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3.1.6. Place enough crucible backup material (Zircoa composition recommended) in the bottom of the coil to bring the crucible lip to the desired height (a minimum of ¾” is recommended). Firmly tamp to provide a compacted, level base for the crucible.
3.1.7. Place the crucible into the container and apply a downward pressure while twisting the crucible to seat it firmly in the bottom of the container. Make sure that the space between the coil and crucible is uniform.
3.1.8. Continue adding backup material while ramming it in place with a blunt pointed tool. You may find it convenient to use a small air operated ramming tool, or a hand held vibrator, to help pack the backup material in tightly. When using a ramming tool, be careful not to strike the side of the crucible. When using the hand held vibrator, apply the vibrator to the lip of the crucible as the backup material is poured in. Either method will assist in compacting the backup material.
3.1.9. When ramming is completed (backup material ~1/2” from the top of the coil), pack the remaining space with high temperature wool or rope, or finish with a traditional cap.
3.1.10. If applicable, replace the top seal plate and fasten securely.
3.1.11. Using a vacuum or compressed air, clean out the inside of the crucible and the entire coil assembly.
3.1.12. If the crucible installation was done outside of the furnace, store the entire coil-crucible assembly in a warm, dry place until ready for use.
Note: A properly rammed crucible, supported in compression at temperature, will stay in place through the roughest treatment, and will not leak through to the backup material if minor cracking occurs. Process trials will determine the best technique for each furnace operation.
Figure 1. Representation of Traditional Grouted-Coil Installation
3.2. “Two Crucible” Installation (refer to Figure 2)
The “two crucible” or “crucible within a crucible” system utilizes a secondary crucible to contain both the melting crucible and the crucible backup material. This concept allows for “pre-installation” of the crucible, at a convenient time and location, therefore eliminating valuable furnace downtime.
3.2.1. Be sure that the melt coil and the backup crucible are sized appropriately for the selected melting crucible.
3.2.2. Check the new melting crucible for possible defects: excessive internal pits, holes, cracks, etc.
3.2.3. Check the new backup crucible for cracks or other defects that might weaken it.
3.2.4. Be sure to record the crucible lot number.
3.2.5. Place enough crucible backup material (Zircoa composition recommended) in the bottom of the backup crucible coil to bring the crucible lip to the desired height (a minimum of ¾” is recommended). Firmly tamp to provide a compacted, level base for the melting crucible.
3.2.6. Place the melting crucible into the backup crucible and apply a downward pressure while twisting the crucible to seat it firmly. Make sure that the space between the melting crucible and the backup crucible is uniform.
3.2.7. Continue adding backup material while ramming it in place with a blunt pointed tool. You may find it convenient to use a small air operated ramming tool, or a hand held vibrator, to help pack the backup material in tightly. When using a ramming tool, be careful not to strike the side of either crucible. When using the hand held vibrator, apply the vibrator to the lip of the melting crucible as the backup material is poured in. Either method will assist in compacting the backup material.
3.2.8. When ramming is completed (backup material ~1/2” from the top of the coil), pack the remaining space with high temperature wool or rope. Materials that will harden upon drying or use are not recommended.
3.2.9. Using a vacuum or compressed air, clean out the inside of the melting crucible and the “cap” area between the two crucibles.
3.2.10. Store the entire two-crucible assembly in a warm, dry place until ready for use.
3.2.11. Clean and inspect the coil for damage. If grouted, repair areas where grout is loose, thin or missing.
3.2.12. Check the refractory dish (base) of the coil assembly, making sure that it is not cracked or damaged in any way. The dish must be strong enough to support the entire two-crucible assembly and its charge at temperature.
3.2.13. Insert the entire two-crucible assembly into the coil, and secure with clamps or brackets as necessary.
Note: The backup crucible must have sufficient strength under operating conditions to support the expanding zirconia melting crucible without cracking. Although specific backup crucible selection should be based on the needs and testing results of each user, Zircoa composition (please see Data Sheet available from our Website in PDF form) is recommended as a starting point.
Figure 2. Representation of “Two Crucible” Installation
WARNING!
Note: Zircoa’s crucibles are designed to contain molten materials under a fully supported condition. At no time should Zircoa’s crucibles be used in a free standing or unsupported condition.
It is important to both Zircoa and our customers that comprehensive records be kept regarding the function and performance of our crucibles. Understanding what factors cause variation in a range of applications and circumstances allows Zircoa to continuously improve its products, and pass these improvements along to our customers.
Therefore, we ask our customers to record, at minimum, the following data for each of our crucibles:
5.1. General Guidelines
It has been our experience that shop-operating practices substantially influence the performance of our crucibles. A fixed set of operating parameters, which will maximize both crucible life and the quality of castings produced, should be implemented. Both objectives can be accomplished by emphasizing the following and optimizing wherever possible:
5.2. Thermal Expansion Considerations
Figures 3 below shows thermal expansion curves from 0- degrees Celsius for composition . Due to the nature of zirconium oxide, and its inherent phase changes during heating and cooling, it is important that these curves be considered when using our crucibles.
The blue line on each curve (corresponding to the left y-axis) represents dimensional change, as a percentage, of the material over the temperature range. The red line on each curve (corresponding to the right y-axis) represents the recommended maximum heating rate, in degrees Celsius per minute, of the crucible. It can be seen that a slower heat-up is recommended in the temperature range of about -° C, where the dimensional changes are most extreme,
In general, to avoid problems associated with thermal expansion upon heating, and dimensional hysteresis upon subsequent cooling, Zircoa recommends the following:
In addition, Zircoa strongly advises against practices that involve cooling the crucible to room temperature before the end of its useful life with the intent of reheating at some later point in time. As the curves show, the dimensional changes of the crucible during cooling are different than those experienced during heating, which makes it more likely that thermal expansion problems will occur during subsequent re-heating cycles. If an extended period of time between melts is unavoidable, it is recommended that a method of maintaining temperature during this period be used.
Figure 3. Thermal expansion curve for Composition .
6.1. Sharing Information with Zircoa
Despite the best efforts and intentions on the part of both Zircoa and our customers, occasionally problems do occur. When a problem arises, it is in the best interest of both parties to attain a swift resolution. To do so, a thorough evaluation and a high level of cooperation are required.
Therefore, we ask the following of our customers:
6.2. The “Zircoa Crucible Questionnaire”
Zircoa has developed a comprehensive troubleshooting questionnaire for our customers’ use. By completing this questionnaire and sharing the results with Zircoa, we are in a much better position to quickly identify the cause of, and provide corrective action for, any crucible performance problems.
Please follow this link to begin the troubleshooting processcontact your Zircoa representative to obtain a copy of this questionnaire.
6.3. Different Types of Failures / Possible Causes
6.3.5. Erosion
Erosion is a complex phenomenon, influenced by a variety of factors. Several of the more common forms are discussed below:
6.3.5.1. Thermal-mechanical erosion does not involve any interaction between the crucible material and the molten alloy. In this type of erosion, crucible particles dislodge from the crucible body. This is generally caused by either thermal shock or physical abuse, and can usually be prevented by adhering to good, basic foundry practices.
6.3.5.2. Wetting erosion occurs with particular molten alloy-crucible combinations with a high interface tension. Although wetting itself cannot be significantly reduced, its effects on the quality of cast products can be minimized by the judicious use of wash melts and proper campaign sequencing.
6.3.5.3. Chemical erosion is due to reduction-oxidation reactions occurring between reactive elements in certain alloys and the zirconium oxide crucible. Although impossible to eliminate, the reaction can be reduced by limiting both the amount of superheat and the residence time of the molten alloy in the crucible.
Please Note: We intend this to be a reliable guide, but we do not guarantee the applicability, completeness, or accuracy of the information. Users should make their own tests to determine suitability for their application.
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