Accurate process weighing improves plant performance

Paul Boughton

As chemical companies strive to reduce product give away and improve production yields, weighing is becoming an increasingly important part of the overall process. Eugene McCarthy reports.
Weighing technology and software from Avery Weigh-Tronix has reduced product giveaway and improved the yield from a batch of chemicals for Schlötter Ireland by five per cent.
Schlötter blends chemicals for a wide variety of industries including automative, microelectronics, metal finishing and medical devices. The cost of blended chemicals varies but can be up to €50/kg, so process efficiency was a key driver in the company’s lean manufacturing programme.
The company would normally fill 25-1000kg containers, but also offers product in 1-10kg bottles of the blended chemical, depending upon customer requirements.  
Previously the operator would place the drum or other container on to a floor scale and then fill it manually to the required level. In order never to short ship, the operator would overfill these containers so, for example, a 25kg drum could receive 1kg extra and sometimes as much as 2kg. Giveaway was even more extreme on the smaller four litre bottles - often up to 10 per cent extra. Typically, these chemicals are higher value products.
Another problem was that if there was any spillage or product left in the filling tank, then the company has to pay for its proper disposal as a hazardous waste, in line with its IPC licence.
Avery Weigh-Tronix installed and programmed its Evolution E1110 indicator to control the pump and filling head from the filling tanks in response to the weight readings from the existing floor scales. This new semi-automated system has reduced product giveaway and improved the company’s margins. It has also freed up operator time to concentrate on more value added activities.
“Moving from a manual to a semi-automated system has seen a huge improvement in our packaging performance. It has improved our yield and enables us to use our workforce more constructively. All the operator has to do is press a button, there is no need to monitor the filling process of large containers anymore,” says Don Chaplin, engineering manager for Schlötter Ireland.
“Avery Weigh-Tronix installed and commissioned the system in conjunction with our engineers. In time we may upgrade the system even further and incorporate data loggers so that the system also records the filling operation and feeds back the data. This will help us further improve our processes. We now have seven such systems operational at our facility in Newbridge, County Kildare. The capability of Avery Weigh-Tronix equipment and their engineers helped these projects come in on budget and on time in each instance,” he added. [Page Break]
Weighbridge: the liquid challenge
The weighing of liquids being transported in tank wagons is a particularly challenging task for measuring and weighing technology as these substances are in almost constant motion, so precisely gauging their weight requires special techniques and methods.
MULTIRAIL LiquidWeight from Schenck Process is the ideal solution for this difficult process: the company has developed this weighbridge specifically for the legal-for-trade weighing of liquids transported by rail (Fig. 1).
According to Schenck, it is now possible to obtain an outstandingly precise, verifiable (to OIML R106-1) reading of the weight of tank wagons and even of entire trains.   
Depending on a customer’s specific requirements, the weighbridge system can generate figures with an OIML accuracy class of 0.2 or 0.5 for wagons with a weight of up to 150 tonnes. MULTIRAIL LiquidWeight has been specially designed with a concrete weighing sleeper that is fitted with high-precision sensors which transmit all forces and moments and which provide an ultra-accurate reading of the vertical force components.
The novel feature of Schenck Process’s solution is how it is integrated into the track without the cutting of rails or use of foundations. This eliminates interference from unwanted wagon motion while they pass over the weighbridge – this represents a real advantage in the high-precision, in-motion weighing process of rolling stock, especially when transporting liquid goods.
Customers benefit in many different ways, such as reduced maintenance work and – above all – significantly faster weighing processes and lower manpower requirements.
Static weighing processes require tank wagons to be uncoupled and weighed one by one, but the in-motion system means coupled wagons can be weighed as a train passes over the Schenck Process weighbridge at a constant speed. This also does away with the obligatory waiting period necessary for static weighing processes. So with MULTIRAIL LiquidWeight, there is no need to wait for the liquid in tank wagons to almost come to a complete standstill.[Page Break]
A wireless set up
Owing to the impracticality of wired connections between load cells and their respective weight indicators for certain weighing applications, wireless setups can offer users a more viable alternative. In addition to improved flexibility, wireless systems negate the need to locate and replace cables in instances where they have become damaged. Such occurrences can be time consuming and costly, with system downtime providing a further burden.
Applied Weighing offers a wireless solution to problems associated with standard cabled setups. Whilst this technology has been primarily utilised by the company for overhead weighing applications, it also lends itself to other applications where cable runs would be an issue.
A transceiver module within the load cell transmits information between the load cell and a handheld weight indicator, enabling the user to manage as many as 12 load cells from a single hand held display. The wireless transmission of information between the devices is possible up to 120 metres and, for both the handheld display and load cell with transceiver module, battery life is typically five months based on six hours a day usage. A wireless printing option is also available.
Furthermore, the hand held display remotely ‘wakes’ and ‘sleeps’ the transceiver module in the load cell to conserve battery life. Crucially, the wireless connection between devices is possible with all Applied Weighing load cells, thereby offering users wireless solutions to a host of applications.
This includes use in hazardous areas, with a range of ATEX-certified load cells on offer.
Meanwhile, constant investment in R&D over the last 20 years has enabled DEM Weighing Systems to expand operations from Ireland to the UK and Israel. Current customers include Pfizers, Warner Lambert, Smithkline Beecham, Takeda and Rottapharm.
The company says its latest development, a novel direct liquid cooling (DLC) board, gives it the edge over competitors.
The DLC board fits straight into customers’ existing load cells on vessels and silos, converting them from analogue to digital. This, says the company, gives 10 times greater accuracy all at a fraction of the cost of digital load cells.
In addition, the in-house team of software engineers at DEM have developed the new touch screen JPC data capture terminal. This is essentially a harsh environment PC and the software can be written in-house to meet a customer’s requirements or alternatively it can be interfaced with an existing network. This product is proving very popular in the chemical/pharmaceutical industries and has been used successfully in applications that require multiple weighing stations connected to one central processing unit.
Free system handbook to integrate weigh modules
Mettler Toledo has issued a handbook for the design and application of load cells and weigh modules for tanks, silos, vessels, hoppers and conveyors. The document covers the fundamentals of designing, building and installing of customised solutions. It addresses engineers, designers and service people.
Using the correct weighing technology is the basis for achieving the required accuracy over the entire lifecycle of any weighing system. But it also depends on the design of the support structure since it deflects downwards as load is applied to it.
An undesirable vertical force results any time that piping or wiring is connected. Both effects can cause severe weighing errors by supporting some of the weight that should be applied to the weigh modules.
Mettler Toledo’s 150-page handbook, written in English, describes the planning and installation of such weighing systems. It offers practical guidelines for engineers, designers and service people to avoid common errors. It covers design calculations, thermal effects, piping connections, designing of support structures and calibration.
The company has experience on a global base in consulting, providing and installing tank, silo, vessel, hopper and conveyor weighing systems. It offers a comprehensive range of weigh modules, weight transmitters and terminals in various versions suitable for use in dry, wet or hazardous environments.
The handbook is free to download from HERE