Achieving Isothermal Extrusion

Superior Performance of the Granco Clark Triple-Patented Taper Quench

Isothermal extrusion—maintaining a constant metal temperature during the extrusion process—is necessary for the production of uniform, high-quality profiles. Three methods for regulating extrusion temperature are currently in use: press slowdown, differential heating and taper quenching. Because isothermal extrusion requires very precise temperature control, not all of these methods are equally effective, nor do they all offer the same level of productivity, efficiency and product quality.

Press Slowdown

Isothermal extrusion can be accomplished mechanically by adjusting the speed at which the billet is extruded through the press, slowing it down in order to maintain a constant temperature. Press slowdown can be automated with the use of inexpensive software. Although press slowdown can result in a slight increase in production, this process is detrimental to product quality. The front to rear profile variations actually increase due to the changing die face pressure.

Differential Heating

This process is used to create a pre-extrusion temperature gradient within the billet to compensate for the heat generated during extrusion. Shock Heating, Induction and Flame Impingement are the methods most often used. The taper created by differential heating is non-linear, however, and does not create the precise temperature gradient necessary for isothermal extrusion. Differential heating is also impractical for heating short billets (less than 24" long) because the temperature gradient decays nearly as fast as it is created. In addition, the cost of acquiring and operating the necessary induction equipment can be substantial.

Taper Quenching

Taper quenching employs a narrow ring of water to selectively remove heat from the billet, creating a precise temperature gradient that anticipates the heat generated during extrusion. This process was invented by Granco Clark, originators of the triple-patented Taper Quench.

How It Works

After a billet is uniformly heated, it moves through the Taper Quench, where the "water impingement ring" –– a band of water jets surrounding the path of the billet –– limits cooling to a small section of the billet at any given time. Computer controls monitor the rate at which the billet passes through the quench ring, regulating the degree and extent of cooling by dictating how long any particular part of the billet is exposed to the ring. By selectively and rapidly extracting heat along the length of the billet, taper quenching creates the true linear taper necessary for isothermal extrusion.

Efficiency

The Granco Clark Taper Quench can apply a temperature gradient of 50° to 250° F anywhere along the length of the billet. It typically takes less than ten seconds to achieve a gradient of 200° F, for a total cycle time of less than 25 seconds. The linear taper is created with speed and precision, promoting high efficiency and uncompromising quality. The Taper Quench also allows for the extrusion of longer billets, which further increases productivity and recovery.

Automation

The Granco Clark Taper Quench can be installed independently. A typical installation connects to the press controls with three wires. It can also be connected to the Granco Clark Supervisory Control System for automated download of the temperature model for each profile.

A standard feature of the Taper Quench is an intelligent control package that tunes the billet taper without operator intervention. This patented program works in conjunction with a constant-speed controller to provide isothermal extrusion.

Value

The Granco Clark Taper Quench has the lowest acquisition cost, and when combined with a gas-fired billet heater, the lowest operating cost of any option that provides the required temperature gradients for isothermal extrusion.

Taper quenching is the only way to truly achieve isothermal extrusion while optimizing efficiency, productivity, quality and value. The Granco Clark Taper Quench can give you the competitive edge.

For additional engineering and performance specifications, contact us at (616) 794-2600 or via e-mail at gcinfo@grancoclark.com.