Essential Quality Considerations for Buying a Heat Treatment Furnace
Purchasing a heat treatment furnace is a significant investment for any heat treater, whether captive or commercial. Ensuring that the furnace meets all applicable quality requirements is crucial, as it is not only your responsibility but also can lead to delays and additional costs. This article outlines key quality concerns to consider when purchasing a heat treatment furnace.
Determining the Purpose and Process
The intended use of the furnace—whether for nitriding, through-hardening, carburizing, or another process—will direct the purchase towards a specific furnace design and manufacturer. For example, carburizing requires an integral quench furnace with an endothermic generator, while solution and aging of INCO 718 parts require a vacuum furnace with controlled cooling. When in-house expertise is lacking, consulting a metallurgical expert or furnace manufacturer can help in selecting the appropriate furnace for the intended process.
Should You Buy a New or Used Furnace?
The decision to buy a new or used furnace depends largely on available capital and usage frequency. If you have the capital, it’s often easiest to purchase a new furnace as it should be running to specifications right out of the box.
Of course, used furnaces are a great way for a business to save some money. The important thing is that you must consider the repairs and upgrades that may be necessary to ensure it works for your requirements. Sometimes the costs to repair an old furnace can approach or even exceed the price of a new furnace, making a new purchase more viable.
Establishing Quality Requirements
Quality requirements are paramount, whether the furnace is new or used. The first requirement typically involves establishing temperature uniformity characteristics, which are often specified by your customer.
For example, let’s say you have three customers with the following requirements for their parts:
- Customer 1: Temperature 2,500°F; CL-5 (±25°F)
- Customer 2: Temperature 1,500°F; CL-2 (±10°F)
- Customer 3: Temperature 1,900°F; CL-2 (±10°F)
First, you must identify the class of the furnace you will need, which is based on the temperature uniformity tolerance required for the parts. In the information above, we can see that we need at least a class 2 furnace (CL-2 (±10°F)). Next, you need to identify the temperature range required. The lowest temperature required in the above example is 1,500°F, while the highest is 2,500°F.
In the end, you need a class 2 furnace with a temperature range of 1,500°F-2,500°F.
Flowing Down Quality Requirements
Once quality requirements are established, they must be clearly communicated to the furnace manufacturer or seller. Manufacturers and refurbishers usually understand their equipment's capabilities and can commit to these requirements. However, distributors may have limited knowledge and may not guarantee that the furnace meets all quality standards. It’s crucial to request the seller to perform a temperature uniformity survey before shipment to ensure the furnace meets specified requirements. Remember, this survey does not replace the initial TUS, SAT, and instrument calibrations required by AMS 2750, which must be performed by the heat treater.
Purchasing a furnace is a complex process that requires thorough planning and clear communication of quality requirements. By establishing these requirements early and ensuring they are flowed down to the manufacturer or seller, heat treaters can simplify the purchasing process and ensure the furnace meets all necessary standards.
