Mixing it with the best

A British company has, once again, solved a design and production problem which could have far-reaching benefits to many sectors of the manufacturing industry. Failsafe Metering based in Kettering has developed a unique piece of metering-mixing-dispensing technology for two-part reactive chemicals, including adhesives, that virtually guarantees the correct mix and ratio before reaching the point of application or end product. Failsafe’s ‘Pulsmeter’ is an entirely new principle of liquid metering based on the fundamental property of liquid under pressure. That is, as liquid is subjected to high pressure, it becomes hydraulic, producing its maximum density per unit volume. In this hydraulic state, the new technology then uniformly divides the liquid into precise, volumetric units which can then be electronically checked for existence and accuracy. Failsafe’s system starts with the simultaneous metering of a small ‘dot’ of both liquid parts. In the case of an adhesive, this would consist of the resin and the hardener, typically metered in ratios from 1:1 up to 10:1. Each ‘dot’ is then automatically qualified in terms of its minimum volumetric size (squeezed at high pressure to minimum density or maximum weight per minimum volume) prior to being fired rapidly forward to, and combined within, a dispensing head from which the output forms a ‘shot’ or flow. Each ‘dot’ is qualified and, if correct, generates an electronic signal to a PLC. The result is a digital method of metering liquids. The metering is highly accurate and failsafe – the output is either correct or the system shuts down immediately, without any incorrect ‘mix’ reaching the point of application. Failsafe’s technical director Phil Thompson was responsible for the design of the new technology. He demonstrated to Eureka the principles of one of the firm’s adhesive dispensing working prototypes. There are two transfer pumps, one for the resin and one for the hardener which take the raw material from the storage containers, through hoses, to two ports on the metering unit. The two ports line up with two inlet ports on the inlet valve manifold. Two chambers are loaded up with resin and hardener and when the slots in these chambers are presented to (are exactly in line with) these ports, liquid transfers onto the next valve metering block. A metering shuttle device then waits for the liquid pressure to be presented to its face, then it pushes across and hits an adjustable contact stop. Thompson suggested that this stop is better than using a sensor as there can be no overrun with a dead stop. Simultaneously, the other port opens and displaces an exact volume ahead of it. The two products are pushed across one, on each side (A and B blocks) of the machine. Every time the shuttle is pushed across, it displaces a pre-determined volume of liquid into the dispense manifold. Then the inlet valve rotates through 180 degrees, presenting the liquid pressure to the opposite end of the metering shuttle/block. This then displaces the pre-determined volume of liquid into the manifold. Each time the shuttle makes contact with the stop device, a sensor probe sends an electronic signal to a PLC (supplied by Schneider Electric). A signal from each side (A and B) of the machine must reach the PLC in the correct sequence, otherwise the system recognises that an error has occurred and shuts down. According to Thompson, these signals are occurring several times a second up to more than 30 times a second depending on the application. “The bores on the metering and inlet blocks have no seals around the piston. So each one has to be machined to a very high accuracy, with the surface finish down to 5 microns, to ensure no liquid can pass through,” explained Thompson. An electric motor (supplied by Lenze) drives a gearbox and pulley arrangement which in turn drives the two shafts that drive the metering units. The working prototype demonstrated to Eureka was part of a robot cell, where the robot arm (supplied by Kawasaki and Toshiba) was integrated with Failsafe’s dispensing system. A local panel building firm, Stratos Systems, helped Failsafe develop the electronic side of the system. “The PLC, inverter and HMI [human machine interface] display were supplied by Schneider, who supported us very well indeed. They also helped us to develop the self-diagnostic software for the machine.” Failsafe’s system uses two pressure transducers, one on the A side and one on the B side, which test the pressures in the system. In a similar way, the ability of the liquid to push past the annular seals can be checked by the operator. And seals can also be checked for wear by looking for pressure delays in the system. There are operator instructions on the HMI and a timer alarm that warns the operator when to service the machine. There is also no need to disconnect hoses for samples and the machine was designed by Thompson to have a ‘quick knock-down’ time of between 15 and 30 minutes, to keep downtime at a minimum. As Thompson explained: “The standby test at the start of a production run means that if you don’t get a failure at this stage, then you know the last run was good, because the Failsafe system checks for accuracy continuously.” The accuracy of the system is very high. The qualification process is based on an electronic signal, which is generated when each dot is tested. The signal is either correct or the system shuts down without any incorrect mix reaching the point of application. It is correct to two decimal places so if the operator requires a mixture of one part to 50 and the system tells him that his actual ratio is 1:49.99, the process is stopped. The software can be set up to record historical production data, a running log, total number of shots, service history on the machine, component wear and so on. The software also supports the InterBus network. Thompson said his company plans to develop modem links in the near future to enable companies to perform diagnostics on the machine from a remote location across a network. It’s a significant breakthrough, particularly when you consider the high levels of batch traceability required by many production environments today. Automotive and aerospace are two sectors whose design engineers are constantly on the lookout for ways of improving their designs without sacrificing traceability. This may include replacing traditional fasteners on their designs with new, high strength adhesives. These OEMs need to be able to trace any failures in their end product all the way back to the supplier and its production processes. So, as a supplier, possessing adhesive dispensing technology that virtually guarantees no incorrect mix or ratio finds it way into the OEM’s end product, is likely to give that company a clear competitive edge over other suppliers. And that is why Failsafe has had incredible interest already from material resin manufacturers. 3M were first to take an interest in Pulsmeter, and offered to send over one of its chemists to test Failsafe’s new technology. The lab technicians at 3M quickly came to the conclusion that they wanted to introduce Pulsmeter to Ford and other of its major automotive customers. As Thompson enthused: “3M came to see us and concluded that the results of our mixing were even better than their own lab tests.” Ford then got wind of the new technology and sent one of its senior production engineers (for Jaguar) to Failsafe’s site in Kettering. “Ford loved the technology, especially the fact that the system doesn’t allow incorrect mixes to reach the point of application, but it wanted us to develop the concept further so that operators didn’t have to stop the production line every time an incorrect mix or error was detected. Hence, we came up with the idea of Q-pac,” said Thompson. Q-pac’s function is to enable the operator or end user to collect QA samples from Pulsmeter, and keep a record of raw material resin for batch traceability. Its very simple to use. The operator uses a valve on the dispensing head, sets the machine to a pre-sequence which then diverts a pre-determined volume or flow of liquid through a Q-pac twin cartridge fitted just upstream of the nozzle or dispenser. This cartridge can then be removed and checked. The beauty of this method is that your operators can actually use it to simulate different production scenarios and test the outcomes. The sample is also identical to the normal flow of liquid in the production process. Aston Martin’s (now owned by Ford) technical adhesives specialist, Dr John Hill, then came to hear of the technology and, according to Thompson, was so impressed with Failsafe that he asked his suppliers (or systems integrators) of a new robot cell at the Aston Martin production plant in the UK to use the technology in the adhesive application process. One of these suppliers, Design Services Engineering of Nuneaton, subsequently ordered machines from Failsafe. Others suppliers, including Aston Martin’s body panel manufacturer Mayflower, have since followed suit. The idea for Pulsmeter came from Failsafe’s MD, Laurie Penn, who came up with the idea in the late 1998. “The metering, mixing and dispensing industry has never got it quite right. I wanted to develop a better method based upon typical problems that manufacturers were having with their dispensing equipment… One day, I was toying around with a revolver when it occurred to me that maybe I could machine gun dots and shots of liquid and check each one for existence and accuracy and then use this principle to meter liquids in a way that was failsafe.” Penn’s aim was to develop technology that solved the typical production problems that companies face when dispensing two-part chemical liquids in their production process – especially those that require batch traceability. Adhesives, polyurethanes, silicones, acrylics, polyesters and polysulphides all fall into this category. In fact, any company that uses a liquid whose function is to bond, seal, encapsulate, coat, thermally insulate, dome, mould, impregnate or prototype a component, should be interested in Penn’s new technology. Penn’s credentials are impressive. He has been at the forefront of two-component application since 1965 – a time when manufacturers weighed out each chemical constituent by hand. Since then, he has designed a series of groundbreaking systems. In 1971, he invented and patented the relatively simple, yet versatile ‘Posiload’ metering pump for use within his newly-developed ‘Twinflow’ metering, mixing and dispensing machines. In 1975, he then pioneered the high pressure metering, static mixing and injection of high ratio polyester for Resin Transfer Moulding for production of the Matra car. And, from 1978 to 1984, he developed the first, patented, two-part ‘Supermix’ coaxial cartridge technology which was licensed to the UK, US and Australia. In the late 80s, Penn turned his attention to bridging the gap between cartridges and the larger dispensing machines by pioneering the concept of the hand-held DX meter-mix-dispense machine. This gave customers the opportunity to bulk buy their two-part chemicals, but then be able to apply it with a relatively low cost technology. This eventually led to him founding Failsafe Metering in 1999, and in 2000, the company won a DTI Smart Award for funding innovation. Thompson explained that most manufacturers are faced with constant uncertainty over the reliability and integrity of their metering, mixing and dispensing technology. “Whether a product or component is bonded with an adhesive manually, or whether it is bonded automatically by a machine, the reality today is that these processes are far from ideal and are not completely failsafe.” He went on to say that, in his experience, some two-component users check their meter-mix-dispense machine ratio only once a day. “On average, a Failsafe meter-mix-dispense machine automatically checks, assures and records each part of the mixed ratio as correct at a rate of 100 times per minute. “Other two-component users check the dispensed volume of a mixed shot or bead per product once a day. On average, a Failsafe machine automatically checks and records this as correct more than 100 times per minute,” he added. The third scenario, said Thompson, is in robotics. “Many robotic applications of single and two-part resin systems are unsupervised. Independent of supervision, Failsafe machines check for, record and only allow correct performance.” And the fact is that many quality control departments cannot guarantee that the samples they take from their dispensing machine truly represent the quality of the rest of the batch used in the production system. The process, said Thompson, is sometimes a case of ‘trial and error’, can be subject to drift and can result in, at best, scrapped product, or to product disasters in the field. He suggested that body panels coming loose from motor vehicles is an example of extreme failure in a vehicle assembly plant or a tail lift of an aircraft wing failing in mid-flight. Thompson claimed that the versatility of Pulsmeter makes it ideal for both automated and semi-manual operations because it provides management with options for both real time monitoring and/or permanent electronic recording of every event during the metering, mixing and dispensing process. According to Thompson, the cost of Failsafe’s complete system, including transfer pumps, PLC, inverter drive, gearbox and motor, HMI and software is in the range £10k to £25k. But a scaled down version, with simplified HMI and software, is currently under development. The potential applications are enormous. Thompson reckoned that electronics has huge potential as it uses potting technology for its components. He also mentioned wind generation turbine blades, lubrication and injection of grease into engine bearings, boat building, extrusion of windows, agricultural vehicles and textile bonding as other possible applications. As Dr Bayer, who developed the world’s first reactive, two-part epoxy resin, once said: “I challenge somebody to develop the equipment to dispense this material!” It appears Failsafe has answered his call. Fail Safe Metering Design Pointers * Failsafe’s new meter-mix-dispense technology is designed for two-part chemicals, including adhesives, and ensures only the correct mix ratio reaches the point of application * The system has a very high accuracy level, down to two decimal places for mix ratios, and is self-diagnostic * 3M has shown a keen interest in the technology and Ford has asked its system integrators to use the technology on its Aston Martin range