Carbonite Furnace HST, Furnace VST User Manual
Installation, Operation &
Maintenance Instructions
1200°C Split Tube furnaces
types HST & VST
This manual is for the guidance of operators of the above Carbolite products and
should be read before the furnace is connected to the electricity supply.
1.0
Please read the controller manuals before operating the furnace.
CONTENTS
Section page
1.0 Introduction 1
2.0 Installation 3
3.0 Operation 5
4.0 Maintenance 7
5.0 Repairs & Replacements 8
6.0 Fault Analysis 11
7.0 Circuit Diagrams 12
8.0 Fuses & Power Settings 15
9.0 Specifications 16
Manuals are supplied separately for the furnace controller
(and overtemperature controller when fitted).
MF13 – 3.31
HST, VST
INTRODUCTION
1.1 VST & HST models
The VST range comprises split tube furnaces designed for use vertically, with several mounting
options: the furnace may be provided with no stand; or with a wall bracket; or it may be fitted to
one of two stand designs – near and far.
The HST range uses the same insulated split case as the VST, fitted inside an outer case designed
for horizontal use – though this may be fitted to an L-stand which allows for both horizontal and
vertical use.
All models have a separate control box connected by electrical conduits or leads.
Voltage and Power Control
1.2
All models in this range, from March 2001, are supplied with heating elements designed for use
over the voltage range 200V-240V or 3-phase equivalents. The Carbolite control system
incorporates a “power limit” which effectively limits the voltage to 208V. It is most important that
any alternative system provided by the customer should be able to limit the power accordingly.
See sections 3.6 and 8.2.
Switches and Lights
1.3
1.4 Warning Symbols
Supply Light: when the furnace is connected to the electrical supply the
light in the adjacent switch glows
Heat Switch: the switch disconnects power to the heating elements; unless
this switch is off there is a danger of electric shock when inserting objects
into the furnace
Heat Light: the adjacent light glows or flashes to indicate that power is
being supplied to the elements
DANGER of electrical shock– read any warning printed by this symbol.
DANGER – hot surface. Read any warning printed by this symbol.
WARNING: all surfaces of a furnace may be hot.
2.0
DANGER – read any warning printed by this symbol.
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HST, VST
INSTALLATION
2.1 Unpacking & Handling
When unpacking or moving the furnace always lift it by its case or main body. Never lift it by its
insulation or by a fitted work tube. If possible use two people to carry the furnace and remote
control box. Remove any packing material from inside the furnace before use.
If an optional or special stand is separately supplied, assemble the furnace on to it. These models
may be supplied for customer mounting and may require customer preparation of mounting
components before installation.
Siting
2.2
Place the furnace in a well ventilated room, away from other sources of heat, and on a surface
which is resistant to accidental spillage of hot materials. Do not mount the furnace on an
inflammable surface.
Ensure that there is free space around the furnace. Do not obstruct any of the vents in the control
box: they are needed to keep the controls cool.
Ensure that the control box is placed in such a way that it can be quickly switched off or
disconnected from the electrical supply - see below.
Setting Up
2.3
If the furnace is supplied with a work tube or any accessories fit these into position.
For optimum temperature uniformity, insulating plugs should be placed in the tube ends as shown
in fig.1. With a long inner work tube, the stem of the plug assembly should line up with the end of
the tube as in fig.2. Alignment of radiation shields is similar to that of plugs. With these models,
split end plugs are supplied; unless ordered for a specific tube size, these require shaping to fit the
tube or work piece: use a round file.
If stainless steel seals with gas inlets are supplied they are to be fitted as shown in fig.3; the stem
of any insulating plug should touch the seal. Stainless steel seals for vertical use: a hook and eye
arrangement holds the upper insulating plug assembly; alternatively a gland nut.
Horizontal models: if heavy fittings are to be clamped to the end of an extended work tube they
can increase the bending stress at the centre of the tube. Support such fittings in such a way that
expansion of the tube is allowed.
If a metal work tube is being used in the furnace, ensure that it is earthed for operator safety.
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HST, VST
2.4 Electrical Connections
Connection by a qualified electrician is recommended.
The furnaces covered by this manual normally require a single phase A.C. supply, which may be
Live to Neutral non-reversible, Live to Neutral reversible or Live to Live. Some models may be
ordered for 3-phase use (and if so, are “universal” – see section 2.5).
Check the furnace rating label before connection. The supply voltage should agree with the
voltage on the label, and the supply capacity should be sufficient for the amperage on the label.
If the actual supply is not the same as the voltage on the label, then the controller power limit may
need to be adjusted: set the Heater Switch to off, connect the furnace and see section 3.6.
The supply should be fused at the next size equal to or higher than the amperage on the label. A
table of the most common fuse ratings is also given in section 8.1 of this manual. Where a supply
cable is present there are internal supply fuses: customer fusing is preferred but not essential.
Furnace with supply cable: either wire directly to an isolator or fit with a line plug.
Furnace without supply cable: a permanent connection to a fused and isolated supply should be
made to the internal terminals after temporary removal of the furnace back panel.
Connection by line plug: the plug should be within reach of the operator, and should be quickly
removable.
Connection to isolating switch: this should operate on both conductors (single phase) or on all live
conductors (three phase), and should be within reach of the operator.
The supply MUST incorporate an earth (ground).
CONNECTION DETAILS
Supply Terminal label Cable colour
1-phase
N Blue To neutral to the other power conductor
PE Green/Yellow To earth (ground) to earth (ground)
supply Terminal label Cable colour
2- or 3-phase
L2 Black to phase 2
L3 Black to phase 3 except 2-phase
N Light Blue to neutral except delta
PE Green/Yellow to earth (ground)
L Brown To live to either power conductor
L1 Black to phase 1
Live-Neutral Reversible or Live-Live
supply type
Do not connect a furnace ordered for three phase use to a single phase supply or to the wrong type
of three phase supply – except as indicated in sections 2.5 and 7.7.
“Universal Wiring” (year 2000 onwards)
2.5
When (and only when) ordered for 3-phase use these furnaces are supplied in a form in which they
can be easily rewired between 1-phase and 3-phase supplies. This applies to 3-phase+N and 3-
phase delta in the ranges 380/220V–415/240V and 200-240V, but does not apply to 3-phase star
without neutral (e.g 380V or 440V).
To alter the configuration, remove the control box back panel and alter the connections between
the supply terminal block and the EMC filters, using the appropriate diagram from section 7.7.
Models ordered for single phase only are not affected and cannot be converted to 3-phase.
If in doubt, please consult Carbolite.
3.0
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HST, VST
OPERATION
The instructions for operating the temperature controller are given in a separate manual.
If the furnace is fitted with a time switch, see also the supplementary manual MS03.
If cascade control is fitted, see the supplementary manual MS07.
3.1
Operating Cycle
The furnace is fitted with a combined Supply light and Instrument switch. The light is on
whenever the furnace is connected to the supply. The switch cuts off power to the control circuit.
There is also a Heater switch which can be used to disconnect power to the elements.
Connect the furnace to the electrical supply. The Supply light should glow .
Operate the instrument switch to activate the temperature controller; the O position is off, the
I position on. The controller becomes illuminated and goes through a short test cycle.
Set the temperature controller to the desired setpoint or program - see the controller manual.
Overtemperature option only. If the overtemperature controller has not yet been set as required,
set it and activate it according to the instructions in the appropriate manual.
Switch on the Heater switch, located on the instrument panel. Unless a time switch is fitted and is
off, the furnace starts to heat up. The Heat light(s) glow steadily at first and then flash as the
furnace approaches the desired temperature or a program setpoint.
Overtemperature option only. If the overtemperature trip operates then an indicator in the over-
temperature controller flashes, and the heating elements are isolated. Find and correct the cause
before resetting the overtemperature controller according the instructions supplied.
To switch off power to the heating elements, use the Heater Switch. To switch the furnace off, use
both the Heater switch and the Instrument switch. If the furnace is to be left off, isolate it from the
electrical supply.
General Operating Advice
3.2
Heating element life is shortened by use at temperatures close to maximum. Do not leave the
furnace at high temperature when not required. The maximum temperature is shown on the
furnace rating label and on the back page of this manual.
Operator Safety
3.3
The ceramic materials used in furnace manufacture become electrically conductive to some extent
at high temperatures. In these models there are partially exposed heating coils in the chamber and
there is danger of contact even with the furnace closed. DO NOT use any conductive tools within
the work tube without isolating it. If a metal work tube is used,
Switch off the Heater switch whenever loading or unloading the furnace. The elements are
isolated when the Heater switch is OFF. This switch cuts both sides of the circuit directly or via a
contactor (a contactor is used in models where the rated current exceeds 16 Amps).
it must be earthed (grounded).
Tube Life
3.4
A ceramic work tube may be cracked if workpieces are
inserted too quickly or at temperatures below 900°C (when the
tube is more brittle). Large pieces should also be heated slowly
to ensure that large temperature differences do not arise.
Poor thermal contact should be encouraged between the
workpiece and the tube; crucibles or boats should be of low
thermal mass and should have feet to reduce the contact with
the tube (fig. 4).
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HST, VST
Do not set too high a heating rate. Large diameter tubes are more susceptible to thermal shock
than smaller. Tubes which extend beyond the heated part of the furnace are more at risk. A general
rule for maximum heating rate is 400/internal diameter (°C/min); for 75mm i/d tubes this comes to
5°C per minute. The controller can be set to limit the heating rate.
Pressure
3.5
Work tubes are not able to accept high internal pressure. When gas seals or similar fittings are in
use, the gas pressure should be restricted to a maximum of 0.2 bar (3 psi). A pressure of about half
of that should normally be sufficient to achieve the desired flow rate. The customer must ensure
that the exhaust path from the tube is not blocked, so that excess pressure does not occur.
Power Adjustment
3.6
The furnace control system incorporates electronic power limiting. The power limit parameter
OP.Hi is accessible to the operator, and can be used to adjust the furnace to the actual supply
voltage.
The models covered by this manual (March 2001 onwards) are designed for use over the range of
voltages 200V-250V (or, if ordered, 100V-125V), and the power limit parameter is set
accordingly. These models may be relocated to a different voltage within the range: the power
limit should be reset to match the voltage. See section 8.2.
To alter the power limit
Set the Heater Switch to Off to prevent heating while adjusting the power limit.
Press Page until
displayed. Press Down T or Up S once to display the value of
oP (output list) is displayed. Press Scroll 4 until OP.Hi (Output High) is
OP.Hi (it is good practice to write
down the original value). To alter the parameter to the desired value use Down T or Up S.
A power setting of zero prevents the furnace from heating: useful for demonstrating the controls
without taking power.
Do not increase the power limit simply “to get more power”. The elements could burn out, or a
fuse could blow.
Running at Low Temperatures
3.7
The power limit may be adjusted to a low level to achieve better control when running the furnace
at a low temperature. No hard and fast rules can be given, but, as an example, to run at
temperatures only up to 600°C try a power limit of 50%. Control stability may fall off again if a
setting below about 40% is used.
Before changing the power limit, record its factory setting for possible future use.
4.0
6 MF13
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