We apply varying types of organic paints onto moving steel substrate by using coater heads. In this operation, paint is transferred to the moving strip with rotating rolls. There are at least two rolls of typical diameters 250-300mm that rotate at high speeds (typical line speed 50- 100 m/min).
Customers request a high number of different colors or different paint chemistries. After each customer order, coater heads need to be washed and cleaned to eliminate any color contamination or paint system contamination. Usually, operators use a solvent spray gun to wash the paint residue from the rolls, paint tray and piped paint delivery system. Solvent circulates around the rolls to remove the paint residue and a brush is usually used to assist cleaning, particularly on roll ends and journals. The rolls continue to rotate during this procedure however they are placed in a clean down mode before starting this cleaning operation. (See video footage capturing clean down procedure).
There are a number of safety risks associated with the coater head cleaning process. The focus of this design work is to eliminate any risk of hand injuries to operators carrying out this task.
The major risks are created by the moving parts of the coater heads that need cleaning which can cause arm/hand/finger injuries. Because of the rotation of the rolls, there is often at least one nip point (see figure 1 below). A nip point is a point of convergence between two rotating parts, or a rotating part and a stationary part, where all or part of the human body could become drawn in, trapped and injured. Nip points are very common on all coil coating lines. Coater head cleaning is routinely carried out by operators working close to the potential point of entrapment and historically there have been a number of severe injuries to hands being drawn into the nip point often resulting in permanent disability.
Link to Figure 1 - https://www.dropbox.com/s/tq61d1nv2y667mw/fig1.png?dl=0
The techniques deployed currently to minimize the entrapment risk during cleaning operations are:
- Rolls set to rotate so that there is an outgoing nip during washdowns. (The rolls rotate outwards so that it will not draw hands into the nip area between the rolls, roll rotation acts to throw a hand out from the nip point.)
- During roll wash downs the system is put in a clean down mode which reduces roll speeds to approximately 10m/ min, significantly slower than line run speed.
- Nip guards are installed to create a narrow gap that prevents fingers getting drawn into the roll nip. (See Figure 2)
Link to Figure 2 - https://www.dropbox.com/s/dycayg5j93pepzx/fig2.png?dl=0
- 100% Hands-free cleaning whereby the procedure dictates that operators do not physically touch the rotating rolls with their hand, but use solvent gun /circulation system, roll pressure and where required brushes.
- Low torque roll setting during wash down procedure so roll will trip if something gets caught in the nip.
The current procedures and training specify that all of the cleanings are done in "hands-free" mode, however, this is reliant on operators following the correct procedures and the risks associated are still not completely eliminated. Therefore, we are looking for solutions, which will completely eliminate risks associated with this process.
The solution should satisfy the following success criteria:-
- Zero harm (no injury): Operator’s hands should not get close to moving machinery while cleaning. The design must ensure that the operator is removed from the danger zone and prevents access to the rotating rolls and the pinch points these create.
- The solution must ensure that the applicator rolls and ancillary rolls in the coater head are cleaned to a level that ensure no contamination of the next scheduled product.
- The standard of the quality of the cleaning should be independent of human factors and not depend on the operator’s skill and physical effort.
- Consideration should be given to ensure the efficient use of solvent cleaning fluid, minimizing the operational cost being a key design criterion.
- Cleaning substances, such as solvents, must get transported and drained automatically from the coater head area.
- Explosive solvent fumes can build within the coater room which may cause an explosion, therefore any equipment must be ATEX rated and suitable to use in an explosive atmosphere created by the solvent fumes. The design must not create any potential ignition sources such as electrical systems exposed the coater house atmosphere.
- Solution identified must give consideration to the need for operators to view/inspect both the product and application of the paint (or offer alternatives). Operators must be able to view the coater rolls in service.
- The solution should be ergonomically designed so as to minimize any impact (or reduce) the time taken to carry out both cleaning and roll change operations. (Typical wash downtime should be 10-15 minutes depending on coater head configuration)
- The potential for Heat / Ignition / Spark generation (through friction or system failure) to be considered and eliminated. (Not just through use of ATEX approved equipment) but any cleaning pad, scraper, nozzle static or other parts of any proposed system design which may cause ignition etc.
- Significant redesign or replacement of the existing coaters should be avoided as cost prohibitive.
- The system should be capable of operating throughout the current range of an operating parameter (range of roll diameters) and also different coater roll setup (forward/ reverse/ 2 roll/ 3 rolls).