Model EHR-85

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 10.50" (266.7 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 6" diameter (150 mm) hole through it on the mounting centerline to provide access to the furnace bottom door and gas screen assembly. It is preferable to have a minimum 5" (127 mm) wide slot out the rear of the tower plate to clear water and gas lines or mount the furnace an additional 1" (25 mm) above the tower plate.

Height

When mounted, the distance from the top surface of the tower plate to the centerline of the draw hot zone is 3.9" (99 mm). The distance from the top surface of the tower plate to clear all top furnace fittings, power connections and insulation covers is 12" (305 mm).

Top Access

The top insulation cover and connections allow a 5.5" (140 mm) diameter, centered, clear access to the entry top port into the furnace. This clear access is to within 4.95" (126 mm) of the centerline of the draw hot zone. The standard gas screen/diaphragm assemble adds 1.56" (40 mm).

Bottom Access

The exit bottom port into the furnace is 3.35" (85 mm) from the centerline of the draw hot zone. The standard gas screen adds 1.56" (40 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

Top and bottom ports are closed with an easily replaced top (threaded) iris diaphragm assembly and bottom slide door assembly allowing a maximum entry/exit opening of 1.61" (41 mm). The top iris and bottom slide door assembly closes to a minimum 0.25" (6 mm) diameter for internal gas flow control, and for closure while changing preform rods with the furnace at maximum temperature.

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).

Gas Ports

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

• Top gas curtain, inlet.
• Bottom gas curtain, inlet.
• 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 vacuum pump.

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 single-piece liner is replaced by removing the top iris and gas screen assembly. The two-piece graphite liner top section is similarly replaced by removing the top iris/gas screen assembly. For removal of the bottom and/or bottom and top graphite liner the bottom slide door assembly and gas screen is removed. The heating element is replaced by additionally removing a top plate cover. The heating element is secured at the top to power electrodes using two taper clamps having four mounting screws each. By removing the top furnace head, the entire thermal insulation assembly can be lifted from the furnace as 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. End caps are provided to allow vacuum purging prior to operation. These solid caps are inserted through top iris and bottom door 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, 240V, 150A, 1 phase, 0-5V input.
• Furnace power contactor, 240V, 150A, 2 pole.
• Control power step-down transformer, 1 KVA, 240V/120V.
• 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.
• 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.

The power supply is capable of providing furnace power of 50 volts and 600 amperes. Furnace power required is nominally 14 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 d.c. analog output and has a digital setpoint for accurate and convenient programming. 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 upscale thermocouple break protection and output stage power feed-back to compensate for varying line voltage changes.

Temperature Sensor:

The normal control sensor for use with the EHR-85 and automatic temperature controller is the radiation pyrometer option. Included is a 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