Pressure Control System
Feasibility study of a multi-channel pressure control system for the manufacturing of light weight ducting using bladder moulding.
Cost effective manufacture of cylindrical items such as light weight ducting can be achieved using split mould tools and inflatable bladders, otherwise known as bladder moulding. Typically, heat sensitive product material is lined inside the mould tool into which is placed the bladder. Before curing at the required temperature, the bladder is inflated to ensure the product material comes fully in contact with the mould tool. However, the bladder pressure must be correctly controlled during the curing cycle. Too much pressure at the wrong time means to much of the product materials thermo setting media will be lost, too little and the product will not be of uniform shape.
How is this done?
Jamtech have designed and developed a control system for applying the correct pressure during the curing process. This involves monitoring bladder pressure, the temperature of the mould tool and adjusting the pressure accordingly.
The block schematic for the proof of concept control system is shown below. Here, air under pressure is fed to solenoid valve #5. The simplistic method of control is to open valve #5, operated by the PC #1, to allow the air to flow into the accumulator #6 (i.e. simulated bladder). When the target pressure, monitored by pressure sensor #4, is reached valve #5 is closed. If the pressure requires reducing then valve #3 is opened which allows air to flow out of the accumulator and escape to atmosphere.
The PC was used to simulate temperature, a hypothetical pressure profile and at the same time demonstrate the ability to control air pressure in real time. Below is a screen shot showing historical measured air pressure (upper trace) and simulated temperature (lower trace).
What about the finished control system?
Jamtech went onto to produce a robust Schroff rack based design for a multichannel system including operator interface.
The above is a simplistic representation and method of controlling bladder pressure. In reality other factors had to be taken into consideration before producing a successful system. For example, the pressure control algorithm was developed to deal with different lengths of tubing and bladder size. The PC was replaced with a more robust Windows CE based HMI panel and the sensitive electronics were segregated from the rest of the system and placed in an IP65 enclosure.
Jamtech successfully demonstrated how they were able to use their specialised skills and knowledge to realise a solution.
See also: Custom Pneumatic Valve Assembly