CN
New, Smarter Injectors from Cannon!
CONTINUING R & D EFFORTS IN THE FIELD OF PUR MIXING GENERATE NEW, CUSTOMER-ORIENTED, INNOVATIVE DEVICES. MAURIZIO CORTI, TECHNICAL DIRECTOR OF CANNON AFROS, ILLUSTRATES THE LATEST INJECTORS BORN FROM THIS ACTIVITY.
C a n n o n N e w s: S o m e developments regarding a new series of injectors for Polyurethane mixing have been recently announced to the Cannon Sales Network. Can you illustrate them to our readers? Maurizio Corti: In order to e x p l a i n t h e s e n e w developments I need to define some basic characteristics of these devices, that are a fundamental component of our technology. The PUR processors would like to use injectors that are able, when a sudden output variation occurs, to self-adjust, without an external action, their internal geometry and maintain a constant pressure, doing so in a very repetitive way at every output variation. Until now such an injector does not exist in a simple version. The simplest injector is just a hole in a thin wall; another model, a bit more evoluted, includes a manually adjustable needle that controls the flow of the liquid through that hole; a third, more efficient type of injector, includes a calibrated spring that allows to slide the needle backwards when a higher flow of component occurs and viceversa when the output decreases, maintaining a rather stable pressure throughout these variations. We have seen, in the past years, a certain tendency of clients and of formulations to forgive a minor lack of self-adaptation of the component ' s pressures when their output changes suddenly. Formulations have become more“ forgiving” and they only require a guaranteed minimum level of pressure during the mixing phase: when the pressure is higher than such a threshold, they perform well and the resulting foam is well structured and homogeneous. This fact allows us to look for solutions suitable for flow variations,
which are mechanically simpler than in the past, providing to the end user the great advantage of simplicity in operations, reduced cost of consumables and consistent good foam.
CN: How was this possible? MC: We concentrated on the design of a simple, reliable injector controlled by disc springs for a passive self-adjustment of the needle ' s position when the flow of component varies. We used for decades the L ' Orange injectors, which are very good for medium-low output values and viscosity of the components. Designed for the efficient pulverisation of Diesel fuel in passenger vehicles and trucks, these are real little jewels of precision mechanics, available everywhere at a reasonable cost. Unfortunately, they are not suitable for the very high output values demanded to the foaming equipment for the fast-reacting formulations that are increasingly popular, and when using very viscous materials. They are simply not available in the sizes and with the flow geometries demanded by the actual and future Polyurethane technology. Therefore we worked at the design of our own injectors, which we call“ Leak-Free” because they overcome a major limitation of the L ' Orange models, an internal leak of liquid which forced the use of a draining circuit to collect the leaked material. We mounted a seal on the shaft of the needle and that problem was past history. We then applied a different type of load to the needle, replacing the old springs with disc springs that provide higher elastic reaction and much greater repeatability than the former generation of injectors. We re-designed the annular section through which the liquid flows, having better control of the effect of the friction over the hysteresis of the needle.
CN: Quite an academic work applied industrially, it seems. What is the practical result for the consumer? MC: We can provide these“ Leak-Free” injectors in all the sizes currently requested by the market and the application, without any practical limitation in their internal geometry or size! We currently make a modular range of injectors with a nozzle diameter of up to 6 mm, able to pulverise very efficiently up to 4-5 kg / sec of A + B components. We worked very hard to identify NC machines able to match a perfect geometry between needle and nozzle, with perfect parallelism between the exit hole and the chamber where the needle works: this guarantees repetitive and homogeneous jets of pulverised material throughout the whole range of injectors, for an optimum mixing efficiency. We perfected two types of needle, with different tips, to achieve different performances:
· The conical design, looking like a sharpened pencil, generates a cone of pulverised liquid focused on a precise vertex. This generates a lot of kinetic energy in a single point of the mixing chamber, and is adapt for a wider laminar flow at higher output values.
· The cylindrical design, with the needle tip shaped cylindrically, produces a very open pulverised jet, with high mixing efficiency and a very good attitude to clean the injector ' s hole.
CN: To summarise, what benefits can a customer obtain from these new Cannon injectors? MC: The Cannon“ Leak-Free” injectors based on disc springs are available in a range of sizes suitable for all the modern formulations. They provide a superior repetitive mixing performance when the user replaces a worn out element of the injector( usually only the needle or the terminal part, for an economic running cost of the mixing head). The performances are constant between injectors of the same size, and no time is wasted in re-calibrating the head ' s parameters when changing injectors.
Two types of discspring injectors are available at Cannon, with different tips according to the utilised formulation.
A more linear response to pressure variations is the main characteristic of a disc-spring injector.
A disc-spring injector is controlled by a series of metal cups, rather than by a metal spring.
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