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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