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Many fire extinguishers are equipped with pressure gauges, which were once made of copper bronze. While soft soldering was once the preferred method for manufacturing pressure gauges, a material switch to stainless steel ushered in induction-curing adhesive bonding as a new assembly method.
FT Manovia, based in Buggingen, Germany, specializes in the manufacturing of pressure gauges for fire extinguishers, with an annual production of 5 million units. Founded in 1998, the company is the largest European manufacturer of fire extinguisher manometers and has a worldwide customer base. Manovia is certified according to ISO 9001:2015 and has its own production facility in Shanghai since 2005.
A key part of pressure gauge production is connecting a copper bronze Bourdon tube to a brass housing. These components were once joined via soft soldering. However, given that new fire extinguishing agents can be corrosive to the copper-bronze compounds, a more robust material was needed. Due to its inert properties, stainless steel was selected as the new tube material. However, this made soft soldering an unsuitable method for joining the tube and brass housing. Finding a new, time- and space-efficient method was thus imperative.
Purely mechanical processes such as cramping or shrink-fitting were too time-consuming and cost-intensive to work as suitable solutions. Adhesive bonding soon became the method of choice for joining these components. As corrosive materials come with high safety and media resistance requirements, Manovia opted to use a heat-curing epoxy resin.
In its production facility, Manovia could have implemented oven curing processes, in which the adhesive cures in 30-to-60-minute cycle times. This, however, would have required an oven of at least five meters in length with a heat output of 45 kW in order to meet its target production yield. Not only would that have required an immense amount of space, but also high purchase and energy costs.
In order to avoid such unprofitable and costly changes, DELO and Manovia held a process optimization workshop to determine a suitable alternative. Together, both parties discussed different opportunities, and induction curing turned out to meet all of Manovia’s requirements.
After a change to stainless steel, adhesive bonding was the only suitable joining technology.
Induction curing is an efficient solution for metallic materials such as stainless steel. During inductive heating, the metallic component is exposed, either partially or completely, to an alternating electromagnetic field created by a current-carrying Bourdon tubes. The field generates eddy currents within the material, flowing opposite the original current and heating the material. Induction therefore heats up electrically conductive components rapidly, reducing time and thus accelerating the curing process.
After further tests including a twelve-month field test, the process was enhanced to allow optimal adhesive curing in only five seconds. The inductor, which is specified to Manovia’s particular needs, requires little space compared to a curing oven and consumes just 2 kW of power.
Since the adhesive is at least as important as the curing process, the company opted for an induction-suitable structural adhesive from the DELO MONOPOX line of one-component epoxy resins. Its ultra-high chemical resistance was particularly appealing as the final bond has to withstand corrosive fire extinguishing agents. The selected structural adhesive has good flow behavior and therefore has good processing properties for production. It is also well suited for metal bonding and applications requiring both strength and reliability.
Induction-curing adhesives allow Manovia to fully automate and make cost effective their fire extinguisher pressure gauge production. Best of all, seeking an alternative paid off, as FT Manovia was subsequently awarded the Innovation Prize the German State of Baden-Württemberg.
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DELO is a leading provider of high-tech adhesives. For over 25 years, we have offered solutions for the automotive, electronics, and semiconductor industries. Our innovative technologies set industry standards. Companies like Bosch, Huawei, and Siemens rely on DELO for superior adhesive technologies
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