product review - vacuum furnace engineering, - · pdf filevacuum furnace control system...

Honeywell HC900 Hybrid

Vacuum Furnace Control System

PRODUCT REVIEW

©VAC AERO International Inc., Oakville, Ontario, Canada

Making a Difference – VAC AERO Control Systems

With heat treaters under increasing pressure to maximize plant efficiency and minimize costs, the ability to monitor and control operating conditions simply, efficiently and accurately is essential in thermal processing applications. VAC AERO control systems have developed over recent years to match the finely balanced requirements of improved furnace performance, adherence to industry regulations and increased operating efficiency.

VAC AERO furnaces come equipped with the Honeywell HC 900 hybrid controller; a state-of-the-Art control system with digital control programming and advanced Operator Interface and Data Acquisition. The HC900 regulates thermal cycles and monitors all electrical and mechanical functions of the furnace ensuring consistent repeatability with reduced dependence on human operators. The system features built-in safety interlock and alarm features that protect both the furnace and the load from overheating or loss of vacuum or other unsafe operating conditions.

What is a Process Controller

“Adaptive” process control systems are utilized on today’s advanced vacuum furnaces. Depending on the process, different variables exist that must be monitored, controlled and/or changed during the cycle to achieve maximum throughput, repeatable processes and stringent quality results. Sensors monitor a selected process or equipment parameter and send the gathered data back to a controller, which then compares it to a predetermined value or setpoint. Through calculations, a controller sends a signal back to the device to make the proper adjustments to obtain a “controlled” process.

Control systems on vacuum furnaces optimize and regulate temperature and pressure to achieve the required process conditions and produce repeatable results. Programmable Logic Controllers (PLCs), sensors and computers make this all possible. In turn, data trending, real-time process monitoring and data collection for permanent retention is commonplace. By analyzing this data, new cycles, containing modified variables, can give better results in less time.

Vacuum Processing Involves sophisticated Temperature Control

VAC AERO’s vacuum heat treating and brazing furnaces are used for special process applications that involve bringing materials to high temperature with a minimum of surface reaction (oxidation). In addition, surface and internal contaminants on molten metal applications are volatized and removed. Furthermore, temperature control in a vacuum heat treating environment can be difficult because of the changing heat transfer characteristics of the furnace as it moves from conduction and convection to radiation.

VAC AERO furnaces operate batch cycles with varying products and processes that commonly require regulation of temperature, vacuum and sequence logic. The temperature and vacuum interact extensively with the logic making recipe management an important function. Based on this need for more complicated temperature cycles, a control system with setpoint ramping, as well as multiple

Typical VAC AERO Control Cabinet


setpoints, is a must. Vacuum furnace cycles usually incorporate a heating ramp and quite often a reverse or backward ramp. Ramp rates are usually displayed in “degrees per hour or minute”. The rapid heating rate of a vacuum furnace demands precise control, including setpoint program control with soak guarantee inputs. Overshoot of temperature setpoints is usually not tolerated. Setpoint program control is often applied to the temperature, vacuum level and gas pressure with extensive interaction between these programs and also with the logic control.

Typical Vacuum Heat Treating Cycle

A typical heat treating cycle starts after the product is loaded into the furnace and the door is clamped shut. Vacuum furnaces usually have a two-stage mechanical vacuum pump. Control of the “mechanical vacuum pump,” or “roughing” pump, has the minimum requirements of a selector switch, motor starter with overloads and fuses. The roughing vacuum pump lowers the pressure to about 0.05 Torr (50 microns). An optional diffusion pump can lower the pressure to below 1 x 10-3 Torr (1 micron). Some processes require an inert gas such as argon to be fed into the furnace at a low flow rate, allowing the pressure to rise to about 0.50 Torr (500 microns). This process is called partial pressure (PP) heat treatment.

The “vacuum blower” or booster, which compresses gas or atmosphere going to the mechanical pump, has a pressure switch to prevent the vacuum blower from turning on until the appropriate vacuum threshold is obtained. A typical threshold might be 30 Torr. The pressure switch can be electronic such as a Pirani gauge, or it might be a simple mechanical switch. Turning on the vacuum blower too early will overload the drive motor and causes overloads to trip or fuses to blow.

Additional interlocks exist that do not allow the heating system to be enabled until the furnace has pumped down to a low vacuum Operator Interface Main Overview Screen

Typical Vacuum Pumping System


setting, usually on the order of 0.05 Torr (50 microns). Should the furnace be equipped with a diffusion pump, the heating system and temperature control is further held off until the furnace reaches sub-micron levels. These values are usually programmed into the vacuum-measuring instrument on simpler control schemes, or they could be part of a recipe on more exotic control system systems.

The pressure increases as the temperature rises and contaminants volatize. Control of the vacuum is maintained at about 0.50 Torr (500 microns) in partial pressure processes or below 10-4 Torr in high vacuum processes. If the vacuum deviates from the specific setpoint by more than a specific value, the temperature program is held until the condition is corrected. The temperature program goes through a series of ramps and soaks. After a high temperature soak, the quench process activates and the temperature is allowed to drop. An increased flow of inert gas and circulation of cooling water in the furnace walls and heat exchanger cools the work. The cooling lowers furnace pressure, requiring additional pressure control. During the cooling, the pressure is typically controlled between 0.85 Barr to 10 Barr depending on process type. A light or horn is usually activated as an indication to the operator that the cycle is complete. The operator then brings the furnace back to atmospheric pressure manually and unloads the product.

Honeywell HC900 Hybrid Control - Modular, Advanced Loop and Logic Controller

The advantage of the Honeywell HC900 hybrid controller is that the logic and process control is performed in the same box. This approach saves money on inputs and outputs that otherwise are required to pass information from the PLC to the ramp/soak programmer and vice versa.

The “hybrid process control system” is a combination PID process controller with many PID loops available through software and integral ramp/soak programmer. Instead of a dedicated loop controller with ramping capability, the system is programmable to have one or more PID loops available with any of them coupled to RAMP/SOAK programmer modules.

The hybrid controller also has PLC logic capability, so this type of controller replaces the ramp/soak programmer and also the conventional PLC. Most systems have a color Human Machine Interface (HMI) to allow the operator to take control of the entire furnace operation. Most PLCs are programmed in ladder style logic. However, the HC900 hybrid controller is programmed through the use of function blocks.

Multiple Processes / Multiple Racks


Utility Monitoring and Interlocks

Due to the very high operating temperatures possible with vacuum equipment, extreme care must be given to assuring utilities are available at all times and, in the event of loss of utilities, that the furnace is automatically put into a safe condition. Checks and precautions center around verifying, for example, water pressure and water flow to all water-cooled components. Without water flow to the heating system transformer, the casing, power feed-through, diffusion pump and other water-cooled members, severe damage could occur to the furnace as well as unsafe operating conditions. The alarm circuits are usually provided by hardwired relays, alarm contacts and interlocks.

Display on an HMI is often provided to alert operators as to the problem, but alarm action and intervention is always hardwired. Alarm circuits are usually provided by a separate source of electrical power as standard practice. Gas supplies for quenching, usually nitrogen or argon, are also tested by the use of pressure switches and must be “ON” before a typical vacuum furnace cycle can start. Recommended practice is also for a furnace operator to visually verify the above situations are met as a further precaution. Under loss of power, the evacuation valve is always closed to prevent air from back-streaming through the vacuum pumps and into the furnace. Many customers maintain water flow with a natural gas or gasoline-powered backup water pump. Some systems go to “city water” during power failures also. Once the safety requirements are satisfied, which includes all utilities being present, water is flowing to all water-cooled components, no alarms are active and the furnace has been evacuated to the preset levels, the heating system is then allowed to turn on.

Control Needs for a Diffusion Pump

Most VAC AERO furnaces are equipped with one or more diffusion pumps to allow the vacuum levels to be further reduced by a factor of 1,000 or more. While a typical vacuum furnace can operate at 0.05 Torr (50 microns) while heating, diffusion pumps can further reduce vacuum pressure to 1 x 10-6 Torr (0.001 micron) or even lower with larger pumps. Diffusion pumps have no real moving parts. However, they have an electric heater that heats the diffusion pump oil to approximately 175°C (350°F) or higher. The electric heaters typically free run and have a mechanical high-temperature switch to turn off the

Utilities Alarms

Two Pumping Systems


heaters should water flow be inadequate. The diffusion pump has a large inlet valve, often called a right angle valve, which is the same diameter as the diffusion pump. A downstream valve, called the fore line valve, is provided for connection of the outlet of the diffusion pump to the mechanical vacuum pump and vacuum blower. Control of the right angle valve and the fore line valve are controlled by the PLC when the diffusion pump is to be activated. Prior to be being able to use the diffusion pump, the diffusion pump heaters must be on for at least 30-60 minutes to allow the pump oil to become vaporized. A vacuum sensor is also used downstream of the diffusion to assure the gases from the diffusion pump are being sufficiently taken away. Should the downstream sensor exceed a preset level, the right angle valve will immediately close until the vacuum level returns to a safe level.

The PLC is used to enable the heaters, both valves and, most importantly, “valve timing,” which is critical to prevent any form of back-streaming from occurring. The diffusion pump also requires a small holding pump, which is another vacuum pump downstream of the diffusion pump. The holding pump is also controlled by the PLC, a motor starter, overload and fuses.

Partial Pressure Control and Vacuum Sensors

Most of the time, a vacuum furnace will operate attempting to remove all air (atmosphere) and contaminants from a hot zone, and the pumps are running full out. There are times, however, when too hard of a vacuum can vaporize materials being processed. A typical application is high-speed M series steel, which is routinely processed at 1175°C (2150°F) or higher. This series of steel has chromium, among other alloys, that if exposed to high vacuum levels would deplete the chromium content through vaporization.

Motors and Valves

Trend Cycle with Partial Pressure


To alleviate this condition, “partial pressure” control is activated where argon or nitrogen gas is bled into the furnace while the vacuum pump is trying to take it away. A typical partial pressure setting for M series steel would be 0.75 Torr (750 microns). The partial pressure circuit is usually activated above a threshold temperature, 1010°C (1850°F) for example. At temperatures below 1010°C (1850°F), the vacuum system runs at full out and vacuum levels could be easily under 0.05 Torr (50 microns). Above 1010°C (1850°F), the partial pressure circuit is activated (usually by the PLC from a Recipe request) and a solenoid valve allows nitrogen or argon gas to flow into the vessel. Once the partial pressure setpoint is reached, 0.75 Torr (750 microns) in this example, the solenoid is closed. A dead band prevents the solenoid from cycling too quickly.

Another variation of partial pressure control allows a high-flow sweep gas to pass through the furnace. In this situation, furnace pressure may be much higher, easily in the 2-10 Torr range. This higher pressure is usually just a result of the higher gas flow going into the furnace. This high flow of gas is designed to move contaminants in the furnace quickly away through washing or sweeping. The vacuum pump typically runs full out in this situation, and the inlet gas flow rate is controlled via a fixed orifice or mass flow controller.

Vacuum furnaces require at least one vacuum sensor, and some furnaces can easily have three or four. Generally, the vacuum furnace uses a small sensor to measure the actual vacuum level, and a vacuum instrument digitally displays the vacuum level and also generates a recorder or controller output voltage. The vacuum instrument also provides switch contacts or trips. Traditional output voltage ranges are 0-10 VDC or 4 – 20 ma. “Trip contacts” are important and are used as thresholds to turn on the heating systems, activate valves or turn on the vacuum booster.

VAC AERO’s Furnace Control System is Versatile & Operator-Friendly

Control of temperature is executed with a powerful algorithm set that satisfies the most demanding application requirements. Multiple tuning constants may be used to tailor the control response to the dynamic characteristics of the furnace.

Approach limits allow maximum heating rates without overshoot, reducing cycle time and optimizing efficiency. The HC900 integrates the setpoint programmer, loop and logic functions within a single device. The Setpoint Program capability of the HC900 is used to control the temperature profiles with up to 1000 different profiles, appropriate for a wide range of products, can be created and stored for use when these products are processed.

For example the figure to the right shows a typical heat-treat cycle profile that uses the load guarantee soak function (as event 7) to control critical soak temperature. The cycle profile also contains other events used to control diverse functions required by a heat-treatment cycle (high and low vacuum level, partial pressure, quench, etc.).

Heat Power Adjustment Screen


A single configurable database integrates both the loop (proportional, modulating) functions and the logic (discrete, boolean) functions required by the process. User-friendly operator displays provide the operator with dynamic information about the status of each run as it progresses. Alarms are announced in color on dedicated displays and can be acknowledged directly from the Operator Interface.

The data acquisition and control capability of the HC900 permits ongoing process analysis to define and implement the control strategies while maintaining high production with safety and at low cost.

Implementation

The HC900 is a panel-mounted controller, connected to a computer based operator interface. All field signals terminate at the controller. The controller has universal analog inputs, analog outputs and a wide variety of digital input and output types. This controller will provide all the vacuum furnace control functions.

Configuration.

The Hybrid Control Designer tool in the following page provides advanced configuration techniques allowing a variety of strategies to be easily implemented. The run-mode configuration monitoring and editing capability allows these strategies to be tested and refined as process knowledge is gained.

HC900 Rack Mounted in a Panel

Live Cycle Profile Monitoring Screen


HC Designer: Interface to the HC900 Logic Program

Control Cabinet for a Horizontal Furnace


Specifications

Typical VAC AERO hardware/software configuration

Honeywell’s Experion HS SCADA Software

Televac MC300/MM200 Vacuum Gauge Controller

Honeywell UDC 3200 Over Temperature Controller

Industrial 15" LCD Touschscreen

Computer interface

Honeywell HC-900 Hybrid Controller Platform Features

Data Acquisition

Graphic Configuration

Integrated Operator Interface

Logic Control

Process Control

Recipe Handling

Sequence Control

A New Level of Process Control

VAC AERO Vacuum Furnaces come equipped with the Honeywell HC900 System

Honeywell’s process control technology is helping VAC AERO to improve system functionality and performance in its furnaces, while also helping our customers improve overall levels of control and reduce operating costs.

The Honeywell HC900 Hybrid controller is an advanced process and logic controller with data acquisition comprised of proven hardware components, suitably hardened for an "industrial shop" environment of a wide range of vacuum processing operations. The HC900 controls and regulates machine functions, furnace temperature, thermal cycles and runs the Set Point Programmer. The HC900 integrates with Honeywell’s Experion HS software to provide Supervisory Control and Data Acquisition (SCADA) using a large color touch-screen LCD for operator interface.

Controls Cabinet


Honeywell’s HC-900 Hybrid Control System provides accurate digital data collection and archiving capabilities accessible through a remote or networked system that can be analyzed from virtually anywhere by operators and process engineers at any time and in real time. It is optimised to anticipate all normal operating and alarm conditions allowing optimal control and monitoring for higher productivity, reduced costs and increased quality.

VAC AERO control systems have been operating reliably through thousands of service hours and numerous systems are operating in the field. All control system innovations are fully tested and perfected in our own heat treating facilities before being offered to our customers. VAC AERO control systems can also be fully customized to suit any unique customer requirements.

VAC AERO’s process controller is based on the Honeywell HC900 hybrid controller together with Experion HS SCADA software.

Key Benefits of the HC900 Hybrid Controller:

Compatibility with plant wide SCADA and network integration.

Process cycle validation.

Extensive alarm and event management and reporting.

Temperature control using advanced algorithms, auto tuning, and multiple zone digital trimming.

Operator sign-on/sign-off security to limit operator control of individual functions.

Enhanced maintenance and troubleshooting management.

Experion HS System Overview

Experion HS provides a powerful, versatile software platform for supervisory control and data acquisition (SCADA) supporting a wide range of process applications. One of the most important features of the Experion HS solution is that communications between the server and clients has been optimized for use over poor quality, low bandwidth links. In addition, communication between the server and controllers is also optimized to reduce the required bandwidth.


Experion HS integrates with a wide range of Honeywell and third-party devices, thereby leveraging existing control investments and enabling complete integration of process information. Process information is accessible by operators, process engineers and plant level computer systems, allowing control and monitoring for higher productivity, reductions in costs, higher product consistency, and less waste.

Experion HS makes use of proven technologies that include:

Microsoft Windows XP/Vista/7 Professional Client/Server architecture for process visualization, alarming, history collection, and reporting functions;

Standard displays including process groups, loop detail, trending, alarm, event and setpoint programmer screens to get your application running quickly

Graphic display builders for developing custom HMI displays

Communication interfaces to Honeywell products such as HC900 controllers plus third party interfaces

Open architecture supporting OPC Server and OPC Client, Excel Data Exchange, and ODBC

Salient Features of the Honeywell HC900 Process Controller & Experion HS Platform

The HC900 Hybrid Controller combined with Experion HS interface meets all of the requirements for safe and productive process operation with maximum operator convenience, including:

Program control of sequencing and variables vs. time

Proportional (PID) modulating loop control

Logic functions for equipment and process status

Alarm detection, annunciation and logging

Data acquisition and data logging

Recipe configuration, local storage and download capability

Easily programmable by operators in engineering units

Multiple processes / multiple racks


Sixteen (16) programmable events for integration with sequence control functions

Alarms and events may be programmed to send an e-mail message

Modbus/TCP protocol allows interfacing to HMI, data acquisition and OPC server software

Open Ethernet connectivity via Modbus/TCP protocol that provides plant wide process access and data acquisition

Ethernet port supports direct PC connection or external Modem connection for configuration upload, download and maintenance

Isolated, universal analog inputs allow mix of analog input types on same card, saving I/O cost

Auto tuning and fuzzy overshoot protection for quick start-up and proper control operation

Storage of up to 1,000 recipes for fast, error-free product selection

Up to 1000 programs, of 2 to 50 segments in length, can be stored on the Experion HS server.

Storage of up to 1,000 time/temperature profiles. Each profile may be part of a recipe.

Any HC900 can support up to eight (8) peer controllers for exchange of analog or digital data over Ethernet

Additional Features:

Bar-coded data functionality may be used to enter batch information.

Extensive equipment diagnostic and monitoring to maximize process availability

Extensive set of advanced algorithms for maximum process performance

Large screen, factory floor, Operator Interface provides user-friendly displays along with local trending and data archiving capabilities

Operator sign-on/sign-off security provides up to 255 control levels to limit operator control of individual items of plant and equipment.

Supports direct PC connection or external Modem connection for configuration upload, download, debug and maintenance.

Profile Definition Screen

HC900 Controller Status Screen


Utility Monitoring & Interlocks

Due to the very high operating temperatures possible with vacuum equipment, extreme care must be given to assuring utilities are available at all times and, in the event of loss of utilities, that the furnace is automatically put into a safe condition. Standard alarm functions include:

Alarms and events may be programmed to send an e-mail message or call a pager.

Alarm / Event Log reports all alarms and events in a specified time period.

Alarm Duration Log reports the time of occurrence and elapsed time before return-to-normal for specific alarms in a specified time period

Alarm Pager (optional). Setpoint alarms may be sent to an alarm paging or messaging system.

Standard system displays make it easy for operators to learn and use the system. An extensive range of standard displays is available including:

Menu/navigation displays

Alarm summary

Event summary

Trends

Operating groups

System status displays

Configuration displays

Loop Tuning displays

Diagnostic and maintenance displays

Summary displays

Recipe and set point programmer interface displays

Data Collection and Storage

The supervisory system provides many built-in reporting functions. Standard report functions include:

Integrated Excel reporting provides the ability to launch a report built using Microsoft Excel.

Batch reports collect history for points and events that occurred during a process production run. Static batch data may also be added to the report such as batch number, customer name, lot size, etc.

Batch Reports collect batch data and load detail information, history for a set of points (up to 50) and events that occurred relative to a process production run.

History Archiving

Pumps Maintenance - Timers


Reports may be generated periodically or on an event-driven or demand basis. Report output may be directed to screen, printer, file or directly to another computer for analysis or viewing electronically.

History collection is available over a wide range of frequencies in both average and snapshot/production formats. A large amount of history can be retained online, with automatic archiving allowing retention of, and access to, unlimited quantities of historical data.

Flexible trend configuration allows trends to be configured. Real-time and historical data are presented together on the same trend.

The data storage feature can be used to log process information during the cycle to an internal hard drive disk or to a plant network storage device for a permanent record.

Monitoring & Displays

The complete thermal processing operation can be monitored and controlled from the easy to use, standard and/or customized displays. These screens will make it easy for operators to learn and use the system. Our controls engineers will assist you in designing the right displays for your application.

The Latest Control Technology for Your Vacuum Furnace

The HC900 Hybrid Controller offers a complete solution that can handle the entire furnace control process, featuring system control and monitoring functions that can be customized to meet your specific application requirement. Additional functionality can be integrated simply and quickly into the system, including data logging, collection and archiving, timers and other automation and control functionality as required. The HC900 can be set up to provide remote control and monitoring with data accessible through a remote or networked system available at any time and in real time.

HC900 control technology enhances the performance of VAC AERO furnaces significantly, with improved process visibility and multiple functions combined into a single solution cost effectively. This allows our customers to benefit from reduced set-up times and faster, more efficient day to day processes, ultimately resulting in considerably increased productivity, efficiency and profitability.

Excel Batch Report History Graph

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