Valves in action -
Back pressure regulator UV 5.5
Recirculation to a urea tank in the production of wood fiberboards
Wood fiberboards and other wood-based materials are created by shredding round wood, the structural elements of which are re-joined under pressure. Further processing methods create various products with very special properties.
For production, debarked tree trunks are chopped into chips, screened and broken down into high-quality fibers between the grinding disks of a refiner. Immediately after the fibers have been discharged from the refiner, adhesive and additives can be sprayed on in the so-called blow line, in which the fibers reach the velocity of sound. The glued fibers are distributed onto a conveyor belt. This produces a fiber mat, whose air content is removed by pressing, with the glue curing in the press under the impact of the pressure and high temperatures. The mat is pressed to the specified thickness and then cooled down. After that, the finished board can be decorated by sanding and coating and made to measure.
The fiberboard produced in this way has a homogeneous structure so that it can be processed like solid wood. Medium-density fiberboard (MDF) is mainly employed for furniture and flooring and interior finishing. High-density fiberboard (HDF) is often used as backing boards for laminate flooring.
TASK // Maintaining pressure in the urea circuit
A leading manufacturer of thin, highly refined MDF and HDF wood fiberboards produces an average of 300,000 m2 of raw boards per day at his plant in Poland. Urea-formaldehyde resins, which cure quickly and have good dry bond strength, are used to glue the fibers. At the manufacturer's plant, a pipe leads from the urea circuit to the consumer. When the urea consumer is switched on, a control valve opens and doses the required amount. A pump in the urea circuit provides the minimum required dosing pressure and runs continuously.
SOLUTION // Back pressure regulator UV 5.5
The self-acting UV 5.5 regulates the upstream pressure to the set point of 5 - 6.5 barg without pneumatic or electric control parts. The body and medium-wetted internal parts are made of 316L stainless steel and are highly resistant to the fluid, an aqueous 25 to 40% urea solution with a pH value of 9 to 10. The temperature of the medium varies from 5° to 40°C, the flow rate is 1.05 m³/h. The remaining quantity of urea not required by the consumer is fed back to the urea tank via the UV 5.5 back pressure regulator. This provided the wood fiberboard manufacturer with a valve that was optimally tailored to his plant parameters.
