Insulation producers constantly seek ways to improve product quality. This can lead to an optimised - and hence lower cost - production process, higher sales prices and an enhanced reputation in the market. This article looks at how the use of ‘M-Rays’ can achieve these aims by improving producers’ control of insulation thickness and density.
What is an M-Ray? Put simply, it is a term coined by Hammer-IMS to act as shorthand for millimetre-length waves. These are a sub-section of the microwave portion of the electromagnetic spectrum. The region, as the name suggests, includes wavelengths of 1-10mm at frequencies of 30 - 300GHz, around 60 times the frequencies used by WiFi, cellphones and GPS. They can be thought of as being ‘insect scale.’
Prior to 2000, M-Rays were prohibitively expensive to generate outside of academia. However, an explosion in technological development has now made it possible to generate M-Rays using much smaller - and considerably cheaper - microchips. The number of patents involving them has surged, as have their uses. As M-Rays are extremely useful for detecting small objects and their most common use is in full-body scanners at airports. They also find use in rapid telecommunications and satellite applications, helped by the fact that they are not absorbed by water vapour.
Using M-Rays in insulation production
Electromagnetic waves slow down when they pass through materials other than a vacuum. In a vacuum the speed of light is 299,792,458m/s. However, in a glass fibre laminate material it is less than half as fast, around 142,758,313m/s. The wavelength also changes, becoming shorter. The frequency, i.e. how many times the wave oscillates per second, is unchanged.
This is extremely useful if we want to calculate the grammage of an insulation material for which the speed of light is known. We can simply arrange a transmitter to pass a beam through the material to a reflector and onto a detector. By measuring the time it takes to get back to the detector, it is possible to calculate the amount of material through which the M-Rays pass. As the M-Ray beam has a known area, we can then calculate the grammage, i.e.: the weight of the material over a given area (g/cm2).
This method has some key advantages compared to traditional methods that rely on radioactive sources. Firstly, the presence of radioactive isotopes or nuclear sources is entirely eliminated from the production line, along with the associated risks and handling protocols. Secondly, the time delay is linearly proportional to the grammage of the material. This means that there is no theoretical upper limit to the thickness of a material that can be measured. This is not the case with radioactive methods, which calculate thickness or grammage based on the number of particles that can pass through the material. At higher thicknesses, the number of particles is very low, sacrificing accuracy, which can only be regained with larger, more troublesome radioctive sources. Figure 3 shows a test with wood panels in which M-Rays exhibited strong linear correlation between time delay and grammage up to nearly 80,000g/m2 (80kg/m2). The test was only halted because the researchers had used up all the panels available.
From M-Rays to density
In glass/mineral-wool production one can easily convert grammages (g/cm2) into densities (g/cm3) thanks to the more stable thickness of the web. Thicknesses are generally under better control than the basis-weight or grammage in that market. In processes where thickness and grammage are both subject to variation, such as in the field of polyurethane panels, grammages can be converted into densities by means of laser-assistance for thickness measurement.
Insulation solutions
Hammer-IMS, established in 2016, has developed a number of M-Ray-based systems that incorporate multiple measurement points. These have been deployed to measure polystyrene, mineral wool, polyurethane, plastic, paper, coverings and more.
Hammer-IMS’ mineral/glass wool solution incorporates a 400mm measuring gap and up to 100% coverage. The system is easy to install, with low maintenance needs. Typically there will be multiple measuring points to ensure that fibres are equally distributed across the width of the production line. For mineral and glass wool, PTFE or composite guidance sheets assist the material through the system. It is also possible to compensate for inconsistencies in the guidance sheets using software.
For polystyrene, users are often happy with a single measuring head, as thickness can be carefully controlled. A popular approach is to use M-Rays to provide the weight, while a laser measurement tracks thicknesses. These are then combined to provide density data.
Software
As with other monitoring systems, M-Ray-based solutions are not intended to be watched over continually by human operators. Rather the systems assist operators in the identification of long-term trends to ensure quality remains on track. Hammer-IMS has also released a uniformity tool to track deviations in weight from the nominal weight as a function of position, making it possible to observe and track high and low density areas. This can help users differentiate between samples that are the same grammage according to a time of flight analysis but which may vary massively in terms of how the material is actually spread across the sample (Figure 6). This can also check for periodic changes in density.
Concluding remarks
M-Rays present a novel approach to measure the grammage and density of insulation materials. Hammer-IMS has launched a number of such systems to the market, as well as many other sectors, offering considerable advantages over conventional measuring techniques, not least radioactive-free technology. Online software analysis allows users to make process changes as required, enabling M-Ray users to improve quality, reduce waste and reduce production costs simultaneously. Combined, these advantages make them a ‘no brainer’ for insulation production plants around the world.
