Firing and Drying

Toll Firing Success

April 1, 2011
KEYWORDS kilns / toll firing
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A toll firing service provider's (TFSP) success is measured by its ability to provide timely and consistent service to its customers. Toll firing services mean different things to different customers, depending on their needs. However, services could include defining kiln schedules, determining availability, choosing temperatures or soak times, testing fired material, or simply responding positively to customer inquiries.

Regardless of the services needed, several important factors should be considered when selecting a toll firing provider.

Loaded kiln cars.

Material Expectations

At the start of the selection process, familiarize yourself with the material you need to have fired. In these beginning stages, the TFSP is primarily going to be interested in the material itself, so it is a good idea to know if any potential dangers will be present before, during or after the firing. To that end, it is a good practice to supply a Material Safety Data Sheet (MSDS) with your quote request so the TFSP can review potential environmental, carcinogenic or handling concerns before proceeding.

It is also important to relay your expectations of success to your TFSP, who needs to know what you are trying to achieve with the material through the firing. Some of the common gauges of success include a specific surface area, bulk density, weight or color.

In addition, you will want to have an idea of what you consider an acceptable yield. Initial sample testing can usually determine whether or not the expected yield can be achieved. All of this information will be helpful to the TFSP because it lets them compare results to their previous experiences and gives them a preliminary idea of the kiln requirements.

This loaded kiln car is ready to be pushed into a tunnel kiln.

Firing Capabilities

Once the material expectations are understood, the focus can be placed on the actual firing. Each toll firing service provider has different capabilities regarding the available kiln type(s), atmosphere, kiln capacity and firing cycles. However, each of these individual factors is important.

Kilns

Since different kilns have different capabilities, making the correct match is vital to the end result. A good TFSP should have a variety of kilns available to enhance customers' options. Typical kiln varieties might include periodic (or batch) kilns, continuous roller hearth kilns, tunnel kilns, elevator kilns, rotary kilns or pit kilns.

The TFSP should be able to provide technical information, including atmosphere, maximum temperature, minimum temperature, ramp rate capabilities and hot zone details, for each of its kilns. Outlining your temperature and soak time expectations to the potential TFSP is typically the easiest way for them to make a match.

Atmosphere

A firing project sometimes calls for a specific firing atmosphere, such as hydrogen or nitrogen. Each TFSP has distinctive capabilities for these types of requests. For example, some kilns run strictly on natural gas, which means that it is not possible to add any type of atmosphere to the firing. Depending on their resources, different facilities, kilns and TFSPs may have those options available.

Capacity

Interestingly, the required capacity changes for every individual project. Some R&D-type projects might include two pieces of 2 x 1 x 1-in. bar, while a separate project may require 40 tons of material to be pushed through a kiln each month.

Kiln capacity can be dictated by several factors, including kiln type, dimensions, firing cycle and soak times. An additional consideration should be given to the size of the sagger or other ceramic vehicle used to transport the material through the fire.

Firing Cycle

Perhaps one of the biggest misconceptions that potential customers often have involves the firing cycle. Every kiln is different, which means that every new firing has the potential for issues to arise. Many customers ask for a recommendation about a soak time or ramp rate on a particular provider's kilns, but the answer depends entirely on the material that needs to be fired. While the TFSP's expertise is not with the material itself, they should certainly be willing to assist in answering any technical questions related to kiln operation.

The fastest way to ensure success is to use a thorough sample testing program. With such a wide range of materials, it is important to work closely with your TFSP during this stage. Adjustments to soak times, ramp rates and temperature during testing will ultimately yield the end product you desire.

Other Considerations

One of toll firing's key components is the ceramic sagger or kiln furniture that holds the material during the firing. Some TFSPs manufacture their own saggers; these are usually included in the price of the firing. In other cases, customers might want to provide their own saggers or use a material formula that the TFSP does not have.

Either way, an effective TFSP should be willing to work with customers to reach a solution. If the customer is not going to provide their own saggers, some consideration should be given to the content of the saggers to ensure that they will not contaminate the product. Generally speaking, the TFSP should be able to work with you on your ceramic needs.

You may want to consider the cost of shipping the material to and from your customer. Selecting a TFSP located near your facility may save a significant amount of time, as well as money on shipping costs. You can also discuss warehousing options with your TFSP. Warehousing can be advantageous if you have large quantities (perhaps a truckload) that need to be shipped together to save shipping costs.

Ask prospective TFSPs about their capabilities for packaging. Some common forms of deliverable materials include sacks, supersacks, barrels or drums. It is important to know that your TFSP has the capabilities to process each of these.

You should also discuss how the material is to be shipped back. For instance, if the material is sent in a drum, will a second, empty drum be included to return the material? While these may not seem like major logistical issues, it is best to know all of the potential "hidden" costs.

It is also a good practice to ask the TFSP what has been fired previously in the kiln. After prolonged or consistent use, the lining of a kiln can become sponge-like and retain particles of previous material, especially if the material is very fine and susceptible to being airborne. If a material is held in the kiln lining and the kiln blower adds air circulation, your product could easily become contaminated.

Another factor to contemplate, albeit to a much lesser degree, is the cleanliness around the vicinity of that particular kiln. While it may be a difficult variable to control, a good TFSP should strive for a very clean facility in and around its kilns. There have been documented instances in which a material was contaminated because adjacent kilns had a loose powder, unnoticed by anyone, that was blowing around the facility. Some TFSPs will be able to put up shields or dividers; however, as mentioned previously, this can sometimes be a difficult factor to control.

Finally, some parts require post-firing services, tests or additional processes. Most TFSPs are generally able to screen, sift or break down the material to a specific grain size. Keep in mind that these services usually incur additional costs, which should be weighed against performing the process in-house.

Successful Production

Choosing the best TFSP for your company should not be an overwhelming task. Find an experienced company with which you are comfortable-one that makes economic sense and offers the capabilities you need.

Remember that the best way to determine whether or not a process will be successful is through a significant sample testing program. Once testing success is achieved, you are better assured of success in production.

For more information, contact Ipsen at P.O. Box 420, Pecatonica, IL 61063; call (815) 239-2385; fax (815) 239-2387; or visit the website at www.ipsenceramics.com.

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