A manufacturer of epoxy resins was looking for a plant concept with which he could map a mixing process, including the dosed feeding of individual components in the production of synthetic resins. The subsequent drum filling of resin and hardener should also be integrated.
Since various of the customer’s production facilities already use a perfectly functioning mixing, conveying and filling system from Engelsmann, this proven solution was also the planning basis for the upcoming project.
Synthetic resins consist of two components, the pure epoxy resin and the corresponding hardener. Only when these two components are mixed together in a certain ratio do the respective molecules react with each other and the viscous mixture begins to harden.
The most important thing is to maintain the exact right mixing ratio between resin and hardener. If this is not the case, excess molecules of one component will not find a reaction partner. This has a negative effect in the cured state. A brittle or sticky surface is the result, combined with a significantly lower breaking strength. In the right mixing ratio, however, the synthetic resins harden into a stable material. The following practical example shows how such a system environment can look. At the heart of the solution are three JEL TRM drum mixers.
The JEL TRM drum mixer: compulsory mixer for three-dimensional rearrangement of the material to be mixed. Robust design, with extensive equipment and safety features. For fully automatic feeding and emptying.
Three production lines will be set up in the planned plant: one for resin and two for hardener production. The individual components such as aerosil, fillers and a special resin or hardener premix will be emptied from their respective storage containers and conveyed to a drum mixer.
The mixing process causes the individual substances to combine to a viscous mixture. The resin itself and the hardener components are produced. As these are sold as the end products, the dosed output from the drum mixer and the drum filling must also be mapped with the new system.
The process sounds simple at first, but it involves some difficulties, such as the different material properties of individual components:
The fillers used have good flow properties.
Aerosil, with its very low bulk density, tends to form dust as well as adhesions and slight agglomeration.
The resin and hardener premixes are in liquid form.
Resin and the hardener components as end products are viscous.
The different product properties and unit shapes have different requirements for the production equipment. This is already evident when emptying the drums and feeding the pre-products into the drum mixers.
First, the liquid premix is emptied from a storage tank via on-site pumps and pipelines and fed into the drum mixer. Then the solids are fed in. Both aerosil and the fillers are delivered in big bags, but must be emptied in different ways.
Emptying fillers from the big bag directly into the drum mixer
Thanks to their very good flowability, the fillers can be emptied directly from the big bag into the drum mixer – without an additional big bag emptying station or emptying aids. For this partial step, an emptying unit is placed in the centre of the drum mixer. For emptying, the full big bag is simply lifted with a crane track and lowered above the emptying unit. The operator, standing on a platform next to the mixer, clamps the discharge spout of the big bag into the discharge unit and actuates the locking mechanism. After the big bag outlet is opened, the fillers empty directly into the drum mixer virtually by themselves and without the use of a conveyor.
Emptying of the Aerosil with a big bag emptying station and transfer to the drum mixer
In order to empty the fine powder aerosil completely and without dust emissions, the use of a big bag emptying station was necessary. The station is loaded via an integrated crane track with chain hoist. At the push of a button, the big bag is moved into the emptying position and can be connected to the emptying unit.
To protect the operator and the plant environment from excessive dust exposure, this empty unit is double-sealed and designed in such a way that no product residues can escape even when the big bag is loosened. To prevent the fine aerosil from settling in the folds of the big bag, the station is also equipped with a spring tensioning and flexing device to ensure efficient and complete product discharge.
Feeding the mixer: Directly from the big bag into the mixer or alternatively – for the difficult-flowing aerosil – with the big bag emptying station.
The walk device consists of two support plates on which the big bag is placed. Pneumatically controlled, the plates raise and lower alternately during the emptying process. In doing so, they lift one side of the big bag. This improves the angle of repose and the product trickles into the discharge hopper. Here, the aerosil is pneumatically discharged, transported vertically upwards via pipelines and fed into the drum mixer via the inlet.
The big bag emptying station is also equipped with weighing cells so that the product feed can take place accurately in terms of weight. With the help of the electric control, the operator simply enters the amount of product to be transferred to the mixer and the emptying and conveying process starts. As soon as the desired quantity is reached, the material feed into the emptying hopper is interrupted by a pneumatic pinch valve and the diaphragm pump is switched off.
Now the most important process can start, the mixing of the individual resin and hardener components.
The cylindrical drum of the compulsory mixer can be designed in individual sizes according to requirements. For this practical example, JEL TRM drum mixers are used – with a capacity of 3,200 l for hardener production and 6,300 l for resin production.
The rotating T-blade mixer inside forces the mix into a three-dimensional movement. In this way, the components are intensively mixed together, even if they differ greatly in terms of quantity ratio, bulk density and grain size.
After just a few minutes in the drum mixer, the aerosil, fillers and liquid premix react with each other and combine to form a highly viscous resin or hardener. The T-blades are aligned in such a way that the mix is transported towards the outlet. However, due to the high viscosity of the product, residues would stick to the inner wall of the mixing chamber. In order to also remove these residues, the drum mixer was equipped with two scraper bars. These bars rotate at both ends of the mixer and loosen product adhesions, which are then fed back into the mixing process.
The drum mixer is equipped with two scrapers. These bars rotate at both ends of the mixer and loosen product build-up.
To ensure the perfect quality of the end product, it was also important that no air bubbles form in either the resin or the hardener during the mixing process. To avoid this, the drum mixers are each equipped with a filter dome. With the help of a vacuum pump, all air is extracted from the mixing container, thus preventing the formation of bubbles. Since the drum mixer is also equipped with a pressure sensor and a temperature sensor, the operator can always monitor these parameters via the integrated control system in order to be able to intervene if necessary in the event of irregularities.
After the mixing process is finished, the discharge flap of the mixing container opens and the finished resin or hardener component is conveyed by the now slowly rotating T-blades towards the discharge hopper and flows into the eccentric screw pump mounted below. This conveys the final product to the drum filling station, the last station of this system.
Since resins and hardeners are filled directly into their sales containers, this last process step is also metered. For this purpose, a weighing platform was integrated into the discharge pipe of the screw pump, consisting of a floor scale with a mounted turntable. With the help of a forklift, the operator places a pallet with 4 empty barrels on the turntable so that one of the barrels is positioned directly under the screw pump discharge pipe.
The filling of the product is started by pressing a button on the electrical control. The operator only has to enter the desired quantity and the filling process continues until the floor scale sends a signal to the electrical control that the filling quantity has been reached. Then the filling is stopped automatically by closing the discharge flap of the mixer and no more product is discharged into the eccentric screw.
To prevent product residues in the eccentric screw from flowing into the drum filling even after the material flow has stopped, the electrical control is set so that the eccentric screw also switches off when the filling weight is reached. This ensures that exactly the right quantity is always filled and sold.