BOILERS, PUMPS & VALVES FEATURE DRY VACUUM TECHNOLOGY IN HEAT TREATMENT PROCESSES
Vacuum technology is an indispensable part of metal heat treatment. Vakuum- Härterei Petter (VHP) conducted an evaluation in which an oil lubricated rotary vane vacuum pump was replaced by a Busch COBRA NX screw vacuum pump. The vacuum pump was installed as the forepump of a 3-stage system to supply a heat treatment oven with the objective of finding an efficient alternative to the vacuum generators previously used. After a year of testing VHP is completely convinced by dry screw vacuum technology and in future will invest only in ovens equipped with COBRA NX screw vacuum pumps. VHP specialises in high quality heat treatment under vacuum and has nine vacuum ovens. The materials handled are mainly high alloy steels but non-ferrous metals are also heat treated. The core activities are hardening, annealing, brazing, soldering and tempering. VHP’s customers include companies in the food, medical, forming and transmission technology sectors. Custom heat treatment for individual customers is offered and a variety of processes and parameters are available to generate the desired surface properties with reproducible and documented results. The fundamental role of vacuum in
VHP has traditionally used oil lubricated rotary vane vacuum pumps to supply all the ovens. A year ago one of these was replaced by a COBRA NX screw vacuum pump designed specifically for heat treatment applications. No operating fluids are present in the compression chamber, making contact between the pumped medium and oil or other operating fluids impossible. This is achieved by two screw profiles which contra-rotate in the compression chamber without making contact with each other or the housing. This simple construction makes the COBRA NX a robust and economical forepump for the vacuum supply system.
heat treatment processes is to prevent unwanted reactions between the material components and ambient oxygen as these may have an adverse effect on the surface properties of the metal. The pressure reduction allows the process to be controlled more precisely. The pressure, temperature and duration of the process can be set to suit specific materials and controlled according to material characteristics such as the vapour pressure curve. Quenching of the metal after heating is usually carried out with nitrogen but sometimes argon.
COBRA NX screw vacuum pump as the forepump of a three-stage vacuum system
The COBRA NX operated for a year in a three-shift system and no servicing work was carried out within this period. Power consumption remained the same as the old vacuum pump but the substantially increased pumping speed allowed heat treatment processes to be carried out more rapidly. Both VHP directors agreed that the COBRA NX is the ideal forepump for their future requirements and when ordering new ovens will insist on models equipped with them.
Busch T: 01952 677432
www.busch.co.uk
/ FACTORYEQUIPMENT
FACTORY EQUIPMENT | SEPTEMBER 2015 13
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