Windmill Software Ltd
Windows Engineering Software
August 2001
Windmill Software Ltd |
August 2001 |
Monitor Archive |
------------------------Monitor------------------------- The Newsletter for PC-Based Data Acquisition and Control Issue 37 www.windmill.co.uk August 2001 --------------------ISSN 1472-0221---------------------- Welcome to the August Edition of Monitor. We hope you enjoy it, but should you wish to cancel your free subscription please visit http://www.windmill.co.uk/newsletter.html This month, everything you ever wanted to know about electroforming and computerisation. A story illustrating how an automated control system increases safety, provides comprehensive records and improves the quality of the finished product. CONTENTS ======== * Windmill News: Current monitoring device now available from our Internet catalogue * Automating Electroforming Processes -- What is electroforming? -- The electroforming process -- Computerised control - Controlling the current density - Monitoring voltage to prevent overheating - Monitoring temperature and level - Controlling dosing - Laboratory control: ventilation for cyanide and acid fumes - Equipment checking - Calculating the thickness of deposited metal on complex shapes - Displaying and logging data - Future developments: web-based distance learning * Data acquisition and control exhibitions ________________________________________________________ Windmill News: Current monitoring device now available over the Internet ________________________________________________________ Our on-line catalogue is now stocking a current measurement device for use with USB and ISA-bus units. This boxed unit sits outside the PC and accepts 8 current and 8 voltage inputs. For more details see http://www.windmillsoft.com/acatalog/A000_1.html ________________________________________________________ Automating Electroforming Processes ________________________________________________________ Contents ======== -- What is Electroforming? -- The Electroforming Process -- Computerised Control - Controlling the Current Density - Monitoring Voltage to Prevent Overheating - Monitoring Temperature and Level - Controlling Dosing - Laboratory Control: Ventilation for Cyanide Fumes - Equipment Checking - Calculating the Thickness of Deposited Metal on Complex Shapes - Displaying and Logging Data - Future Developments: Web-Based Distance Learning What is Electroforming? ======================= In electroforming a thick layer of metal is deposited either into a mould, or over a mandrel or model, which is usually later removed. This leaves a metallic object that is light, strong and an accurate replica. Electroforming is used in many industries, including in manufacturing precision components for the automotive and aerospace industries, in making fine jewellery and in exact reproduction of museum pieces. The Electroforming Process ========================== The mould or mandrel is placed in a tank of electroforming solution containing, for example, salts of nickel, silver or gold. The positive current from a power supply is connected to a pure metal plate at one end of the tank (the anode) and, at the other end of the tank, the negative current is connected to the piece of work to be electroformed (the cathode). The positive metallic ions are attracted to the negatively charged piece of work, where they are deposited. The metal in solution is replenished from the anode. Computerised Control ==================== At its simplest, electroforming equipment can comprise just a small bath, a battery and manual calculations. However, for larger installations with several tanks and where precision is required, computer control comes into its own. The successful metal deposition depends on many factors, most of which can be monitored and controlled by a computer. A computerised system can also control the laboratory or workplace environment. It's perhaps easiest to illustrate by using a real example. The University of Central England's School of Jewellery run eleven electrodeposition tanks. They control these tanks and log environmental data using a system provided by Biodata Ltd (www.microlink.co.uk), who employed the software expertise of Windmill Software. * CONTROLLING THE CURRENT DENSITY Every electroforming solution has a range of upper and lower electrical power limits, between which a good result may be obtained. This is called the Current Density. Too little power and no metal will be deposited. Too much and the grains might brush off as a powder. The current density, measured in amps per square decimetre or amps per square foot, has therefore to be accurately measured and controlled. To calculate the current density required, we need to know the surface area of the object - a large object consumes more energy and has a higher resistance than a smaller one. The computer ensures that the optimum current density is applied throughout the process. * MONITORING VOLTAGE TO PREVENT OVERHEATING The power supply's voltage drives the target current through the electroforming solution. The software monitors this voltage. Should it start to rise during the process it means that the resistance in the path of the current is increasing. This increase in resistance may be due to degradation of a contact point with the anode or cathode, which with quite high current passing through can lead to overheating. The software alerts operators and can automatically shut down the tank if necessary. * MONITORING TEMPERATURE AND LEVEL The tank takes time to reach its operating temperature. The computer therefore starts heating the tanks before the start of the working day, so that it is ready when people arrive. The software monitors the tank for high or low temperatures, which indicate a failure of the heating controller. It also monitors the level of liquid in the tank - automatically turning the heating off if the liquid level falls. * CONTROLLING DOSING Dosing pumps are used to replace chemicals that are consumed in the electrodeposition process. The gold alloy tank in the School of Jewellery, for example, has 3 dosing pumps - each independently controlled. Chemicals are consumed on a current/time basis. The computer monitors the current through the tank and automatically doses the tank at regular ampere-minute intervals. However, the system also allows people to manually request a dose be applied, recording this event. There is also a push-button on the tank panel to disable automatic dosing. This interfaces with the computer through a digital input. The computer checks this digital input before proceeding with dosing - raising an alarm if the dosing is thus disabled. The software requires operators to acknowledge the alarm to confirm that dosing is suspended. * LABORATORY CONTROL: VENTILATION FOR CYANIDE FUMES Because of the use of cyanide and acid based electroforming solutions, the workplace has to have adequate ventilation. In the School of Jewellery, the acid and cyanide lines are provided with fans to extract the air above each tank. These fans have a scheduled on- off cycle, typically on for 5 minutes in every 20. They can also be switched on and off manually when required. The computer monitors pressure switches in the ventilation ducts to ensure that the fans are operating correctly. Any failure and it sounds an emergency alarm. * EQUIPMENT CHECKING At the beginning of an electroforming process, the computer checks all the necessary equipment is in place. For example - it makes sure that the correct tank filter is connected. Should the filter be missing, or of the wrong type, the computer alerts operators, switches off the power to the filter and refuses to start the electroforming process. The computer controls each tank's equipment, such as filters, agitators and aerators, through digital outputs. Should any of the equipment fail during the process, the computer sounds an alarm and if necessary shuts down the process for that tank. SubscribingTo receive Monitor every month please fill in your e-mail address below. We will not pass your address to any third parties, nor send you any unsolicited e-mail. | |
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Copyright Windmill Software Ltd 2001 PO Box 58, North District Office, Manchester, M8 8QR, UK. E-mail: monitor@windmill.co.uk, Tel:+44 161 833 2782 http://www.windmill.co.uk/  Free measurement news feed...Designed by Studholme.net |
A corner of the University's
new Electroforming Laboratory
*
CALCULATING THE THICKNESS OF DEPOSITED METAL ON COMPLEX
SHAPES
It can be difficult to calculate the surface area of
some complex shapes. This is important as the thickness
of metal deposited is proportional to the current
passing through a unit of surface area multiplied by
time. However, if we have a test piece of work with a
known surface area, the computer can measure the
percentage of current going through the test piece. It
can then calculate the amount of metal deposited on the
test piece and therefore calculate the thickness of the
plating material. This, providing the test piece is not
located in a preferentially good position in the tank,
will be less than or equal to the thickness of metal
deposited on the work itself.
*
DISPLAYING AND LOGGING DATA
Each tank has its own display page with buttons for
Running and Pausing. Alarm messages are displayed and
tanks are shown in different colours for different alarm
states. More detailed display pages are available, for
example for heater and filter information. History
graphs are also displayed. All data, including alarms
and manual events, are logged to disk.
*
FUTURE DEVELOPMENTS: WEB-BASED DISTANCE LEARNING
Future developments for the School of Jewellery's system
include a distance learning facility. Students will be
able to view activity within the laboratory through a
web browser and see the status of the various
electrodeposition tanks. Using the web system, the
lecturer will be able to remotely interact with the
student.
*
This article has highlighted some of the advantages and
uses of a computerised system. It increases safety -
shutting down tanks should conditions not be right, not
starting processes if the necessary equipment is not in
place, sounding emergency alarms if cyanide extractor
fans are not working correctly, and so on. It provides
comprehensive records of the processes, logging all data
to disk including information about tasks performed
manually, any alarm conditions that occurred and the
steps taken to remedy the situation. It also improves
quality by ensuring optimum conditions.
For more information on a computerised electrodeposition
system contact Windmill Software at
