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10/02/2005
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Dean Palmer takes a look at a unique nozzle design that ensures beads of sealant on liquid gaskets are uniform and without any breaks or gaps
A revolutionary nozzle design for applying adhesives to liquid gaskets has been developed which ensures that the bead of sealant is uniform and without any gaps.
To do its job effectively, the bead of sealant must be without any breaks, as difficulties can arise if air bubbles find their way into the adhesive. If hand gun applicators are used, the user may notice these kinds of problem and rectify the gap immediately. However, if the process is automated, the gap can go undetected until the part being sealed fails on the line air test or a joint begins to leak.
Of course, manufacturers can use monitoring equipment to detect any changes in pressure at the dispensing head and alert the operator to any potential break problem, but, as any engineer will agree, it is often better to eliminate the root cause of the problem.
Steve Ginger, equipment manager at adhesives company Henkel Technologies, told Eureka: "One solution [to the air gap problem] is to use smaller diameter nozzles to 'fire' the sealant at the surface. But, this method causes a different problem - especially when nozzle diameters are less than 0.9mm. Blockages can occur, caused by the fillers placed within the sealant in order to achieve the required performance."
To solve the problem, Henkel has developed a unique, patented nozzle design. Ginger explained: "Its key feature is the size and shape of the outlet. The nozzle enables a small orifice size to be used, therefore preventing the sealant from being 'pulled' from the nozzle while, at the same time, allowing air bubbles to be dissipated. Also, the unique nozzle shape allows particles to pass through which would normally block conventional small diameter designs."
One of the first plants to use the nozzle is an automotive transmission factory. The company produces around 1,750 parts per day and the gasketing bead is applied using automated equipment, then inspected by a UV lamp. Once applied, a camera is used to check the efficiency of the bead. According to Henkel, prior to installing the new nozzle, the company's reject rate due to air gaps was greater than 5%. With the new nozzle design, the rate has now dropped to less than 1%.
The nozzle, which measures just 31.24mm in length, is designed to fit existing dispensing equipment so no modifications are necessary. Nozzles need to be replaced once a week, although units have continued to work effectively after this period with no adverse effects.
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Author
Tom Shelley
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