Servicing these eight core systems will optimise your autoclave’s performance while keeping you on the right side of compliance.
Modern industrial autoclaves are complex systems made up of a range of mechanical, process control and instrumentation engineering. Operationally, this is fantastic, enabling composite manufacturers to achieve new heights of efficiency and production not possible with older models. But it can also make looking after your equipment more challenging.
The engineering of these complex systems necessitates that several issues associated with them are properly addressed. Operators looking to improve performance and stay on top of servicing their industrial autoclaves will be asking themselves:
- Which parts of the autoclave need maintaining?
- How will servicing them improve performance?
- And how do you balance ease of maintenance with the need for increasingly complex technology that unlocks more efficient, cost-effective manufacturing?
For answers to each of these questions, read on.
For more information about our Autoclave Servicing and what’s involved, click now to download our product specifications sheet.
How do I service my autoclave?
While designs will vary from machine to machine, modern industrial autoclaves typically comprise eight core systems, each of which plays a vital role in autoclave heat treatment processes. What are they and why is it important that they are regularly serviced?
Main shell and door
“The main shell is a sealed container and provides the working space for the components to be processed under pressure, temperature, and vacuum”, explains Slater Jinkinson, Head of Sales at VFE. “All modern autoclaves also feature a quick lock door made up of toothed flanges and locking mechanisms.”
For large autoclaves, the door handling system can be a challenge. The doors need to be rotated by about 90° for loading the component or mould for cure, a task that needs to be carried out with extreme care to minimise the inertial loads.
“A good design should occupy the least space for movement of the door and have flexibility aligning the door with the shell”, Slater explains. “Internally welding the shell flange and the lock ring to the main shell substantially reduces the weight of the door locking system as it not only eliminates the massive locking ring but also the associated support system to keep the lock ring floating.”
Air circulating system
Forced gas circulation (in which gas is passed over heating elements to transfer heat) is a common feature in autoclaves. The system consists of a centrifugal fan (or ‘blower’) and ducting (pipes or fittings for channelling the air to different locations). The fan must be adequately sized to ensure the required velocity of gas on the load at ambient conditions.
The gas circulation unit also performs the task of accelerating the cooling process by removing the gas on the outside surface of the cooling tubes at a faster rate. Modern autoclaves have a flange-mounted blower motor, which is encased in a pressure-tight casing and connected to the rear of the autoclave.
Autoclaves are heated either electrically, by indirect gas firing (circulating externally heated or cooled thermic fluid) or by steam. Generally, electrical heating gives more precise ambient temperature control, is cleaner, and is more amenable to advanced computer controls.
“Modern autoclaves use silicon-controlled rectifier (SCR) drives, which form part of the closed-loop heating-control systems and can provide very fine control of the heaters”, Slater explains. “The electrical heating capacity is based on the charge and the resin requirements of the cure cycle.”
As well as delivering greater precision and compliance, an optimised electric heating system will help you to meet environmental targets by ensuring your autoclaves are running energy efficiently.
This system is meant for cooling the autoclave to ambient. Composite processing requires variable cooling rates. In electrically heated autoclaves, the heating rate is controlled by either switching off the heater banks or by varying the heater-input power.
If your autoclave system includes a closed-loop cooling system to save the water, this should also be examined. Typically, it consists of heating element coils inside the autoclave, control valves, a draining system, a cooling tower, cooling water pumps and a water treatment plant.
Autoclaves are highly pressurised, so from both an operational and a safety perspective, the system must be able to ensure that the required pressurisation rates are met.
“A typical pressurisation rate in modern autoclaves is approx. 2 bar/min”, Slater explains. “Nowadays, many autoclaves use nitrogen as the pressurisation medium instead of air. This is because the autoclave cure consumables are highly flammable in the air medium due to the presence of oxygen. When servicing your machines, review this to ensure you’re operating safely and that you’re using an appropriate medium for your loads.
The nitrogen gas pressurisation system consists of a primary compressor, nitrogen plant, booster compressor, storage tanks, and associated piping circuitry.
An advanced vacuum system is an essential ingredient of modern autoclaves. The system consists of vacuum pumps, vacuum reservoirs, buffer tanks, measurement lines, and vacuum lines.
“The measurement, vacuum and vent lines are part of the closed-loop vacuum control that ensures the required level of vacuum inside the bag and on the load”, says Slater. “A good autoclave design must provide for an adequate number of vacuum ports. It must also provide for maintaining different levels of vacuum in different bags at the same time.”
Read more about extending the life of your vacuum pump through regular maintenance.
The loading system of an autoclave consists of a loading platform for positioning the components/moulds to be cured. Increasingly in modern autoclaves, two-tier/three-tier loading systems are being employed, enabling more components to be loaded.
Could your loading system be optimised with an additional system to increase operational capacity and maximise output? If your autoclaves are already using multi-tier loading systems, are they designed correctly (based on the diameter of the autoclave) and functioning correctly?
To enable easy loading of components, often the autoclaves are built into a pit so that the top surface of the loading platform is flush with the floor. In this case, a loading bridge is required to close the gap between the autoclave door and pit. Include these in your inspections, examining both the physical integrity of the bridges as well as the pneumatic pressure used to move them.
Invariably, state-of-the-art autoclave systems are completely automated with computer control systems (‘Autoclave Control and Instrumentation Systems’.) These computers take on everything from executing the selected cure cycle, sequentially starting various subsystems, and downloading set values at regular time intervals to acquiring, storing, and archiving data, monitoring cure status and faults, generating alarms and performing sequential shut down and reporting. As such, they play a very important role in your operations, ensuring reliable processing or curing of composite structures.
“Where multiple autoclaves are present at a single site, the present trend is to connect these systems through SCADA (Supervisory control and data acquisition) systems, so that the overall efficiency of the group of autoclaves is enhanced and the utilisation of the autoclaves is optimised.” Slater Jinkinson, Head of Sales, VFE
The control system consists of programmable PID (proportional-integral-derivative) controllers for effecting the closed-loop control of several parameters. When carrying out a service, be sure to examine the controls for: temperature, pressure, and vacuum; recorders for the display, plot, and storage of all the analogue input signals such as part temperature at different locations, pressure, vacuum at different parts. Also review the PLC (programmable logic controller) for safety, interlocks, sequential operation, and status/alarm display.
Find out more about our Autoclave Management and Control Systems and how you will benefit.
How often should an autoclave be serviced?
There are many factors that affect how frequently you should service your autoclaves (or any process equipment, for that matter). What make/model are they? How frequently do you use them? How old are they? When was the last time they were serviced? What processes do you use them for and can you confidently say they are operating at optimum performance?
Given the complexity of these systems and the pace at which technology is advancing, the best way to ensure both ease of maintenance and fully optimised machines you can depend on is to engage the services of a certified heat treatment specialist such as VFE. With the right level of service contract in place (Premier Service VFE Support Package), our experienced engineers can be on-site within 24 hours (UK sites) or on a flight to your country (rest of the world) to service, repair and calibrate your autoclaves, inspecting all the core systems we have just explored in line with industry and customer standards.
As ease of maintenance goes, it doesn’t get simpler than trusting your autoclave servicing to our engineers’ hands and letting us take care of the rest.
For more information about our Autoclave Servicing and what’s involved, click the image below and download our product specifications sheet.