Firing and Drying

High-Temperature Toll Processing

February 23, 2012
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CI0312-tevtech-inbody-200px.jpgHigh-temperature toll processing supports manufacturers in the ceramic industry with production assistance, R&D and Small Business Innovation Research (SBIR) projects, or product/process development. Toll processing capabilities often include thermal purification, graphitization and halogen purification, while typical materials are carbon, graphite, graphite foil, thermal insulation, or advanced ceramics that are processed at high temperatures in either vacuum or a controlled inert atmosphere.

Thermal purification and graphitization are done at elevated temperatures, usually 2000-2400°C. Temperatures can go up to 2800°C with an inert gas flow, usually argon. Lower temperatures may also be used, depending on the starting material.

Purity levels for thermal purification are around 100 ppm. Halogen purification is used when higher purity is required, such as for graphite used in semiconductor equipment, where certain metallic impurities can affect the product. This process is usually in the same temperature range, with the addition of a halogen gas used to diffuse into the base material and react with the metal impurity before being pumped out of the system. Typical purity levels are less than 5 ppm. In certain applications, graphite is purified prior to being coated with CVD silicon carbide.

Additional services can include coatings or other processes on a toll basis. The toll processor’s involvement in these cases, besides the technical aspect, is the liaison to many other processing systems. This can provide a layer of confidentiality between the ceramic manufacturer and the supplier in the network. In some cases, the toll customer and the owner of the toll equipment may compete on other products, so maintaining confidentiality is important.

For consistency, the process temperature profile, pressure and gas flow, etc., are typically recipe controlled, and the data is logged so it can be retrieved for analysis. Any material analysis such as physical properties or purity is often handled by a third-party testing lab or by the ceramic manufacturer.
 

Benefits
Using a trustworthy toll service provider can be beneficial to either enhance production or help develop a product or process. Additional production capacity might be needed to meet ceramic manufacturers’ requirements in several situations. Unexpected temporary spikes in sales or unanticipated system downtime can cause production bottlenecks. Short-term production issues can be addressed by outsourcing on a toll basis without adding capital equipment or, even worse, not meeting customer deliveries. In cases where additional capital is required due to extended growth, toll outsourcing can bridge the gap while the equipment is being manufactured and installed.

Toll processing provides a quick and efficient means of addressing capacity issues arising from cases of downtime in existing equipment, and to capitalize on opportunities of increased demand. In addition, it can provide a fast and cost-effective means of exploring additional market share and/or new markets by eliminating the cost and time associated with capital expenditures, purchasing, and installing the equipment.

Hot-zone configurations may limit a ceramic manufacturer’s ability to process certain components in-house, such as large diameters or long parts. The in-house system’s hot zone was most likely specified for a product mix that may change over time. Larger components may fit well in other toll provider systems with different-sized work zones.

Toll processing providers enable their customers to complete projects “off-line” without tying up production resources. Toll processing also provides ceramic manufacturers with the freedom to open up the process parameter envelope without tying up production resources, fouling production equipment or ruining production parts.
 

Challenges
A batch process is typically used to ensure that no cross-contamination occurs between different types of materials, and to allow for the process parameters to be tailored for each particular product. Each batch is dedicated to a particular manufacturer’s product or process. This can be a challenging approach, particularly in terms of costs when working with smaller loads. Additional considerations for both the ceramic manufacturer and the toll provider include material handling, packaging, and transportation to and from the toll facility.

The toll provider must also take care to ensure the system’s hot-zone materials and thermal insulation are not contaminated or degraded. In addition, care must be used in handling the multiple process gases, process byproducts, and effluent scrubbing. For example, process byproducts can range from nuisance dust to pyrophoric deposits. Finally, with multiple processes, flexibility is required for production planning, such as hot zone tooling, process gases, and material handling equipment. 
 

For additional information, visit www.tevtechllc.com.
 

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