Choosing the Right Furnace, part 1: Heating Method

On a practical basis, in heat treatment operations where a large variety of products is being processed, it is rarely possible to select a furnace that is ideal for each specific product. Selection is often narrowed to that equipment which offers the best performance for high-production.

However, in this entry we would like to discuss the fundamentals of heat transfer to help customers select the furnace which is the most economical, but also practical for a given job. Any heat treat furnace must be built strong enough to 1) support the load of the work, 2) have sufficient heating capacity to produce the desired weight per unit time, and 3) at the desired temperature, produce compliant parts.

Classification of Furnaces

  • Temperature range is a logical means of classifi­cation in many shops because a furnace designed for operating over a temperature range from slightly above room to about 1100°F (595°C) is different from equipment designed for operation in the higher temperature ranges, the reason being that materials of construction are selected for their suitability to a given temperature range.
  • Method of operation also is a common means of classifying heat treating furnaces. There are two general groups, batch furnaces and continuous furnaces.
  • Heating Medium. One common, although very broad, means of classification is the heating medium used. This may be a gaseous medium (which may include vacuum), or a liquid bath such as molten metal or salt. Source of energy, whether gas or electricity, is another means of classifying furnaces.

The following infographic shows the different methods of heat transfer in heat treatment operations and provides a quick guide on the sources of energy available

Victor Zacarias

Heat treat management expertise: CQI-9, AMS2750

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How often is the System Accuracy Test required?

In pyrometry, a System Accuracy Test is an on-site comparison of the furnace temperature vs a separate test thermocouple/instrument to assure the accuracy of the control and recording systems.

It is very important to track the results from these tests since the information changes over time. When conducted properly, this simple test helps the heat treaters to take preventive actions and maintain a reliable temperature system.

The following infographic shows a brief guide for SATs performed on equipment where parts are heat treated according to the aerospace specification AMS2750

Victor Zacarias

Heat treat management expertise: CQI-9, AMS2750

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