Case Study: High Temperature Fans

Overview:

Daniels Fans was approached for assistance by a European steel company that specializes in high quality strip steel for band saws and similar products. The issues facing the steel company were:

• The heat treated steel was failing quality control tests due to uneven heat treatment of the steel.
• The company was unable to meet sale demand with its 12 bell type pit furnaces due to long cycle times.

Daniels Fans was able to assess the situation and provide a solution, which has delivered marked results.

Problem:

Uneven heat treatment is typically the result of inadequate or nonuniform air flow over the products. The inadequate or nonuniform air flow leads to longer cycle times to ensure every section of each part is brought to the necessary heat treat temperature.

There are several issues that impact the performance of pit furnaces, as well as other types of furnaces. Cycle time, which determines the quantity of product that can be treated in a given period, is related to heat transfer efficiency. Faulty heat processing can increase the percentage of rejected product. In most cases, pit furnace downtime is due to fan breakdown.

Solution:

The Daniels team proposed improving pit furnace performance with an upgraded fan, featuring an innovative, high-performance diffuser. This fan solution optimized the impeller/diffuser design for efficient heat transfer throughout the load, avoiding hot or cold spots. The fan was designed to maximize air flow and withstand a furnace operating temperature of 1650 °F.

The client initially installed the new fan in one furnace to evaluate the improvements gained from the upgrade.

Result:

The new fan installation resulted in the elimination of quality control test failures, significant reduction in heat treatment cycle time as well as lower energy and operating costs.

Based on the results achieved, the steel company retrofitted their other furnaces with the new design, for a total of 12 units. Following the pit furnace upgrade, the company was able meet normal sales demand using only nine furnaces. The remaining three furnaces are now available for peaks and standby capacity.

The performance and reliability of the fan units has been time-tested, with only three spare impellors being supplied in the 15 years since the original installation.