Overall Clearance Size

18" (450 mm) diameter is required to clear all furnace parts, extensions, water lines and gas fittings.

Mounting

The bottom of the furnace is fitted with four mounting posts, 0.56" hexagonal, for mounting to the tower plate. The posts are threaded 1/4" -20 x 1/2" deep on a 11.1" (282 mm) bolt circle. The mounting threads are equally spaced at 90°, beginning 45° from the front of the furnace.

The tower plate must have a minimum 7" diameter (178 mm) hole through it on the mounting centerline, slotted out the front of the plate, to provide access to the furnace bottom door and gas screen assembly.

Height

When mounted, the distance from the top surface of the tower plate to the centerline of the draw hot zone is 6.5" (165 mm). The distance from the top surface of the tower plate to clear all top furnace fittings, power connections and insulation covers is 16" (406 mm).

Bottom Access

The exit bottom port into the furnace is 4.10" (104 mm) from the centerline of the draw hot zone. The standard gas screen adds 6.25" (158 mm). With the furnace mounted on the tower plate using the posts provided, the distance down from the tower plate top surface to clear the exit gas screen assembly is 4.25" (108 mm).

Rear Access

Flexible power cables connect to electrodes at the top of the furnace. A 14" (355 mm) wide clear access out the rear of the tower is required to route the two cables from the furnace to the power supply.

Entry and Exit Ports

The top port is closed with a single sliding water-cooled door when there is no preform in the furnace. In the open position the door provides an opening of 2.5" (63 mm). The bottom port is closed with dual sliding water-cooled doors with a minimum opening of 0.25" (6 mm). Replaceable threaded iris diaphragm assemblies are available as options for both the top and bottom ports. The irises have an adjustable range of 0.2" (5 mm) to 2.5" (63 mm).

Radial Ports

Two 1 1/8" -16 threaded ports are provided to view the center of the furnace hot zone. Both ports view the heating element through a 0.31" (8 mm) diameter sighting hole. One port is located 45" to the right of the front of the furnace, the other 90° to the left (135° apart).

A window is installed in the left port which views through the heating element. The right port views the exterior of the element for accurate temperature control using an optional radiation pyrometer. This port is plugged, but will accept the standard window assembly.

Gas Ports

Ports with compression fittings for 1/4" (6 mm) outside diameter tubing are provided for gas inlets and venting. All fittings extend toward the rear of the furnace and service the following purposes:

• Top gas curtain, inlet, with quick disconnect.
• Bottom gas curtain, inlet, with quick disconnect.
• Radial purge, inlet - this port admits inert gas into the thermal insulation area for purge prior to beginning furnace heat-up.
• Radial pressure monitor - this port allows connection of a very low pressure gauge (1" water) to monitor interior pressure with respect to the exterior.

Vents

Gas inlets at top and bottom gas curtains flow to the center of the draw hot zone, exit this area radially, and flow outside the liner tubes to exit at the bottom of the furnace. An additional vent port is provided at the top to allow optional gas flow pattern from the bottom and exiting at the top.

Interior Access

All furnace maintenance can be accomplished without removing the furnace from the drawing tower, disconnecting any water cooling lines or removing any radial windows or control instrumentation.

The bottom graphite liner is replaced by removing the furnace bottom door/gas screen assembly. The top graphite liner is similarly replaced by removing the top door/gas screen assembly. The heating element is replaced by additionally removing a top cover plate. The heating element is secured at the top to power electrodes using two taper clamps which have four mounting screws each. By removing the top furnace head, the entire thermal insulation assembly can be lifted from the furnace on a one-piece assembly. Power cables can remain connected for all operations described.

Interior Components

The furnace interior is free of ceramics and other possibly contaminating materials. All components are solid, ultra-purified graphite having a typical ash content less than 20 ppm.

The furnace assembly is completely sealed with viton O-rings. Optional end caps are available to allow vacuum purging prior to operation. These solid caps replace the top and bottom iris diaphragms for vacuum operation.

Power Supply

The furnace power supply and controls are enclosed in separate cabinets. A base mounting enclosure, 24" wide x 28" deep x 45" high (610 mm x 730 mm x 1140 mm), contains the main power transformer and can be positioned on or near the drawing tower. Top exiting flexible power cables, 10’ (3 m) long, connect the furnace to the power transformer (longer cables optionally available). This enclosure also contains the following components:

• SCR (thyristor) power regulator, 240 V, 150 A, 1 phase, 0-5 V input.
• Furnace power contactor, 240 V, 150 Z, 2 pole.
• Control power step-down transformer, 1 KVA, 240 V/120 V.
• System fusing.
• Water distribution manifold and flow switches.

Facility sources of operation power and cooling water are connected into this enclosure.

Furnace controls are enclosed in a separate bench mounting cabinet which is provided with standard 19" notched rack mounting extensions. Cabinet size is 17" wide x 14" deep x 10.5" high (430 mm x 355 mm x 267 mm).

The control cabinet contains the following:

• Control power on-off switch.
• Furnace power on-off buttons.
• Operate/reset switch.
• Auto/manual switch.
• Sensor/transducer switch.
• Indicator lamps.
• Water flow warning lamp and alarm.
• Manual control and limit 10-turn potentiometer.
• Furnace power (transformer secondary) ammeter and voltmeter.
• Optional automatic temperature controller.
• Optional power transducer control.

The power supply is capable of providing furnace power of 50 volts and 600 amperes. Furnace power required is nominally 16 KVA, depending upon operating temperatures. The power supply range provided allows beginning operation at the higher currents and having voltage reserve available for operating as the heating element ages and its resistance increases. This allows continuous operation without the requirement to shut the system down to change transformer voltage taps.

Power is manually adjustable from 0-100% by means of the panel-mounted, 10-turn potentiometer. A safety interlock with warning lamp, audible alarm, and operate/reset switch monitors cooling water flow and will shut the system off in case of insufficient flow for furnace cooling.

Control cabinet and power supply enclosure are connected with 16’ (5 m) of cable.

Power Supply Options

Automatic Temperature Controller:

The standard temperature control instrument provides a proportional, isolated, 0-5 volt dc analog output and has a digital setpoint using accurate and convenient thumbwheel switches. The 3-mode instrument has adjustable, proportional band, reset, and rate to permit matching the controller to the thermal response characteristics of the furnace. Other features include a deviation indicator, upscale thermocouple break setpoint change and output stage power feedback to compensate for varying line voltage changes.

Temperature Sensor:

The normal control sensor for use with the HR-81 and automatic temperature controller is the radiation pyrometer option. Included is a millivolt amplifier assembled into the power control cabinet, viewing window for the front furnace radial port, and a mounting adapter designed to match the optical geometry of the furnace sighting tube.

Facility Requirements