Correct formulations and product consistency depend on fast and accurate process weighing. Sean Ottewell reports.
Nobel Weighing has completed a successful weighing project for a German chemical company that manufactures chemicals for use in the pulp and paper industry.
An existing batching tank with a volume of approximately 3m3 needed to be modified to allow accurate weighing of the individual ingredients. The existing weighing equipment, which had been in use for a while and which utilised classic load cells, was not functioning properly due to thermal expansion of the vessel. The customer's expectation was that any replacement solution must provide system accuracy in the range of +/-0.1%.
Special measures were required to implement a functioning weighing system due to this thermal expansion of the batching tank. Several different solutions were under discussion: modification to load corners with shear beams and complicated mechanics or simple installation of field-proven KIS-8 load cells, which are particularly tolerant against thermal expansion, strong vibrations, and high lateral forces. The client chose the technically superior version - the KIS load cell. The solution was to install three KIS-8 20kN load cells and one G4 multi-channel weight controller.
Key features of the installation include: short installation time required thanks to the easy modification to KIS-8; excellent reliability and accurate weighing during heating and other operating conditions; and no maintenance required for many years.[Page Break]
"We are surprised by the high accuracy despite the thermal expansion of the vessel. With NOBEL KIS 8 load cells and G4 instrument the accuracy of the weighing system is now even better than required and the installation was very easy and fast," noted the customer.
MASK Polymers is one of the leading manufacturers of rubber and PTFE products for the chemical and automobile industries in India. These customer industries have continuously increasing expectations regarding the quality of the parts they purchase. The standard operating procedures MASK had in place were not appropriate to economically achieve these markets requests.
The batch formulas for the different rubber qualities (150 recipes based on 500 components) were kept in a handwritten recipe book. Each day began with a handwritten daily production plan handed over to the mixing department. After a complete batch had been weighed according to the recipe book, it was forwarded to the kneader and after kneading was completed it was transferred to the mixing mill where rubber sheets according to desired composition were finally produced.[Page Break]
The process was completely dependent on the skills set of the operator, without any accountability, leading to an unsatisfactorily high rate of batch rejection. Confronted with the increasing costs of quality and the difficulty in accessing new markets, MASK saw the necessity to introduce a different batch formulation philosophy, based on semiautomatic operating procedures.
With the help of METTLER TOLEDO specialists, a concept was developed, taking into account the economic constraints, the precision in batch formulation, the harsh environment and the need for simplicity of operation.
A computer-based production and recipe management system was introduced. The existing weighing equipment was connected to an IND690 terminal managing the communication with the central computer (batch orders are entered directly to the IND690) and the weighing equipment, and displaying clear instructions and targets to the operating personnel.
For this purpose the application package Form-XP was loaded to the IND690. The formulation reports are uploaded from the IND690 to the computer for inventory control, statistical evaluation, leading to new possibilities for procedures optimisation.[Page Break]
A significant reduction in the costs of batch rejection was rapidly achieved. The improved level of quality and the full traceability of each batch enabled MASK to introduce new product lines with complex recipes and higher requirements.
Key benefits of FormXP include: easier handling and less paper interaction results in higher productivity; enhanced traceability of recipes by assigning charge, lot and batch numbers; extended safety by capturing component data via barcode scanner, displaying messages while formulating and ensuring a fail proof working sequence; higher efficiency by reporting the stock of raw material and using the rescaling function when overfilling components; and quicker adaption to changing production requirements by using the PC-software FormToolXP.[Page Break]
Continuous gravimetric feeding
The Multigrav feed station from Schenck Process uses continuous gravimetric feeding to achieve the best mixing results. This is especially true for the simultaneous feeding of different components to produce a homogenous mix (Fig. 1).
The more challenging the feeding tasks, the more flexible the solutions need to be. This is a challenge for which the Multigrav feed station was designed.
Up to eight can be grouped together on a shared console for multi-ingredient batching. The feed station adapts perfectly to even the most challenging of tasks: powerful, reliable, versatile and very easy to maintain. It's an easily adapted feed station for quick, clean and easy product changes. And it's highly precise too. With an adjustment range of 1:80, the multiple feed station offers maximum precision and constant feed consistency. Another benefit is the compact design which allows the Multigrav to be fitted virtually anywhere, even in tight spaces. The console, the bottom of which is protected against heat radiation, remains freely accessible at all times.
Other benefits include: virtually maintenance free, low investment costs, optimum precision over a wide adjustment range, and nominal delivery rates of 0.3-400 kg/h.[Page Break]
Meanwhile Schenck's MULTIDOS F weigh feeder is aimed at gravimetric feeding tasks, or when mass flow needs to be recorded. It is particularly useful if the installation height is very low and gaps in transport need bridging because it is economical, space-saving and virtually maintenance-free.
In addition, the MULTIDOS F weigh feeder satisfies stringent hygienic requirements when these are important. For example, the weighing module is very easy to dismantle and assemble, saving time and effort for frequent cleaning intervals. Wet cleaning with a jet of steam is also easy. All relevant parts for cleaning are secured with easy-to-use plug connections. It is also available with a dust proof housing if requested by the customer.
Other benefits include: fixed drive technology outside the housing - no chain drive (plug-in coupling); modern MechaTronic drive with integrated frequency converter, fully configured and wired to electronics (plug and play); belt monitoring with automatic compensation for belt influences; high throughput rates of up to 170 m3/h, with high-precision measuring and feeding of between +/- 0.25 and +/- 0.5%; and batch operation with coarse/fine flow function and loading at the point of discharge.
Finally, the T16 load cell from Thames Side is aimed at dynamic weighing applications in the 5-35kg capacity where a simple and cost-effective solution is called for. It is particularly suited to high speed check-weighing applications. Features include: double bending beam load cell; 316 stainless steel housing; viscous damping especially for use in dynamic applications; standard IP66 protection with optional venting for wash down applications; integral single point load cell allows off-centre loading; integrated on-centre overload protection; and durable and chemical resistant polyurethane cable.
The new load cells joins others in the Thames Side stable, including the T21 viscous damped load cell assembly for dynamic weighing applications and the T34D digital compression load cell for truck scales and silo weighing.[Page Break]
Avery Weigh-Tronix acquires Central Weighing
Avery Weigh-Tronix, a business unit of Illinois Tool Works (ITW), has acquired Central Weighing. Both companies have their headquarters in the UK.
Central Weighing specialises in vehicle weighing, tracking and management systems. It also offers a novel web-based tracking and monitoring system developed for municipal vehicles and the waste industry marketed under the Exactrak name.
Avery Weigh-Tronix is a leading edge global manufacturer and supplier of high quality industrial weighing products and systems. The acquisition of Central Weighing will facilitate the pooling of technological resources, complimentary product and service capabilities of two market leaders. It also reinforces the commitment by Avery Weigh-Tronix to providing smarter innovative products and achieving greater reach to the global marketplace with expansion into both existing and growth markets.
"Avery Weigh-Tronix is one of the leading industrial scale and weighing system manufacturers in the world. The acquisition of Central Weighing will bring a new depth of innovative products, allowing us the opportunity to expand our global reach and bring added value to the market by leveraging existing distribution networks," said Peggi Trimble, general manager, Industrial Division at Avery Weigh-Tronix.
Avery Weigh-Tronix has its headquarters in Birmingham, England, with operations in North America, Ireland, Germany, India, Malaysia and China. Central Weighing is based in Kidderminster, England, and operates worldwide. ITW revenues in 2011 totalled US$17.8b (EUR14b) with more than half of these generated outside of the United States. The company consists of approximately 825 business units in 52 countries and employs 60,000 people.