Hearth Rolls

Omega Castings is the premier producer of alloy hearth rolls for the heat treat industry. We have achieved this level of quality by producing a hearth roll that provides the greatest value for the customer. We do this by manufacturing rolls in either a plug or tapered style with one-piece cast trunnions in the alloy most suited to the customer's application.

Yet, it takes more than quality construction and alloy to make a hearth roll that is the longest lasting in the industry. We take the time to ask the right questions, such as: “What is the loading, application temperature, and atmosphere the roll will have to serve?” We then engineer our rolls so that, in case of power failure (or other issues causing the furnace to halt motion), our rolls can support the load, at temperature, without bending.

Tapered Trunnion vs. Plug Trunnion

Many of our customers ask us what the difference is between a tapered and a plug trunnion style roll. To answer this question we must go back to the early days of heat treating, when most cast link belt and roller hearth furnaces built were equipped with tapered trunnion type hearth rolls.

Later, furnace companies and alloy producers began to examine the most frequent reasons that hearth rolls fail in service. Chief among these failures was the fracture of a shaft at, or near, the point where the trunnion starts to flare from the straight shaft. For a taper style trunnion, this transition usually occurs in the high temperature area of the furnace. The obvious solution to this problem was to move the diameter transition towards the wall of the furnace where it was cooler and, as a result, the plug trunnion was born.

As with many design changes, the attempt to gain even more occurred with the shaft material being changed to mild steel instead of alloy. Most steel shafts failed due to the nature of atmosphere by-products, which corroded the steel shafts in a very short period of time. For this reason, Omega only produces alloy trunnions. It is possible, however, to use a lower alloy plug trunnion with a higher alloy tube and, thus, reduce the cost of the hearth roll.

Benefits of Plug Trunnions

There are two major benefits to plug trunnions. As discussed above, the diameter transitions occur near the much cooler metal furnace wall, which results in delayed mechanical failures.

Second, plug trunnion hearth rolls are more resistant to metal dusting (AKA carbon corrosion). This is because they vent closer to the furnace wall where the atmosphere has already precipitated most of its carbon. This prevents carbon buildup inside the roller and, in most cases, eliminates this mode of failure.

Synchronized Rolls

In the late 1990's a design of cast-link furnace was placed into service. This 54” wide furnace, in the following years, would prove to be the best of this type of equipment yet produced. The unique feature of this furnace was that the rolls, along with the drive drum, were synchronized to turn at the same rate (ft/min). This uniform velocity meant that the belt floated over the rolls; thus, any stress on the pins and links was at an absolute minimum.

The result of this engineering was a furnace that was able to heat-treat 225 million pounds with very little maintenance. When the first belt was removed from service, it was due to alloy attrition, not from excessive stretching or loss of pitch. Not only was belt life dramatically increased, but also the ability to control belt tracking was increased.

Many existing furnaces can be retro-fitted with synchronized rolls for the hearth and, in most cases, return rolls can be added in place of skid tiles or rails. The increase in belt life and lower operational maintenance of these upgraded furnaces more than warrant the costs of the rework.

Accuracy is critical in a synchronization project. Hearth and return rolls should be machined so as to maintain plus-or-minus ten thousandths of an inch total variation with each other. This is necessary to minimize any out-of-synch condition because any error will be multiplied by a factor of three. Thus, if tubes are used in “as-cast” condition with tolerance of one-sixteenth then the roll circumferences through out the hearth could vary by three sixteenths. Over a great number of furnace cycles, this is enough to substantially reduce belt life.

Sound complex? It is to some degree. However, Omega will do this engineering for you at no cost when you purchase your belt and rolls from us.

Contact Us today with your heat resistant, high temperature, cast alloy furnace hearth roll needs. We have the staff to help you select the correct standard parts, or to engineer and then fully cast the high quality alloy parts for your specific application.







Omega Castings, Inc.
301 Fritz Keiper Blvd.
Battle Creek, MI 49037
Phone: 269-968-8105
Fax: 269-968-1661
Email:

 

 

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