Why Pre-mixing :
For the manufacturing of Powder Coatings there is required a pre-mix feedstock for the extruders that is a complete homogeneous mix of all the raw materials to be fed into the extruder. These raw materials in thermosetting systems comprise of polymers generally of low molecular weight, hardener, catalyst, cross-linking or curing agent, pigments and extenders and flow control additives in a range of particle sizes >10micro-<10mm .
Polymers: Solid grades of resin are used and these control properties such as meltingpoint, flow and film properties the resins having a softening point 68 - 1120C are mainly used for Powder Coatings and tend to be in flake or prill form.
Hardener: The choice of curing agent to be used with the particular type of polymer is influenced by its final application and cure and the properties required in the coating. The hardener should be unreactive at room temperature remaining latent up to1000C andshould react fully at 1800C this reaction time must be balanced within the constraints of good flow out of resin against the commercial considerations.
Pigment and extender: Pigments used in the manufacture of liquid systems are used for powder coatings provided they are heat resistant, chemically inert and fast to light. The exclusive use of Titanium dioxide for the manufacture of whites and light shades. Carbon organic and inorganic pigments are used for blacks and greys; although emphasis is now with the organic pigments as reduction in heavy metals is made. Inorganic extenders are now used and incorporated in formulations and are usually of high specific gravity.
Flow control additive: Formulations usually incorporate flow control agents to manage powder coatings finished film effects and appearance during curing without them surface defects would appear.
With the range of the above raw materials the formulations for modern powder coatings
can include less than twelve or more than twenty different materials in any one recipe. For good processing of the pre-mix in the extruder we have stated that this pre-mix should be homogeneous this requires a more intensely mixed reduced and dispersed uniform premix feedstock.
To obtain this homogeneity we must pre-mix the raw materials that have been previously weighed in their component parts to allow a dry mixing of all the materials so they will feed into the extruder feed system and provide consistent stream of mixed raw materials with minimum segregation.
Pre-mixing process :
1. Pre-weighing :
The batching together of all the raw materials necessary for one mix of the product formulation consisting in the main, of full bags (25Kg) of the bulk raw materials and weighed small amounts to make up the pigments and the small amounts of material above or below multiples of 25Kg. This material is pre-weighed and batched together ready for loading into the mixer or mix container. With bulk storage of some of the large volume materials the total amount may be weighed in with out batching the RM's, depending on the size of mix(er). Pre-batching is a longer process for each mix but gives the opportunity to double check each RM into the mixer or mix container so reducing the possibility of errors in loading.
2. Loading :
The physical input of the batch of weighed raw materials into the mixer or mixer container ready for mixing. It is good practice to load some of the bulk raw material first, resin or extender and then to add the small ingredients, pigments etc. and then the balance of the bulk materials. This insures that the pigments will be evenly dispersed at the start of the mixing sandwiched in the middle of the raw materials. Small amounts of pigment should be added with the extraction turned down to prevent loss of these additions into the system.
When loading containers it is important that all fine materials are sandwiched so when the container is inverted the fine materials are not exposed directly to the rotor blade seal.
3. Pre-mixing :
Portable container mixers have been around for many years as with tumble
blender the open top container can be attached to the mixing head for mixing of the batch of material. The mixing head after being raised and clamped in position then rotates 1800 to present the material in the container with the mixing rotor the mixer then works as a shear mixer. After mixing the container is inverted and lowered on to its trolley to be emptied or processed direct from the container downstream and reused for the next batch.
This minimises cleaning of the material contact surfaces of mixer head and container. The containers can be handled by overhead crane or by moving on the trolley wheels attached to each separate container. This gives the flexibility for rapid process change and increased utilisation of the mixer required in the modern powder coatings facility.
The portable container allows the next batch to be processed while waiting for quality check testing of previous batches. With a fixed mixer the batch would wait in the mixer until testing was completed with the container mixer the container is put to one side while waiting results and the mixer is free to be used.
There have been many designs of detachable container mixer with all types of separate integral container / trolley and methods of clamping and lifting the container to the mixing head. They include pneumatic lifting and clamping of the container using cylinders and belows all fitted with electronic switching for position / status indication and confirmation.
With the more complexity and number of electro-mechanical and pneumatic switches comes reliability and operation of the machine for each mixing cycle.
This type is the most robust, reliable and simple to operate for the Powder
Coatings Pre-mixing Process in the market today ,and widely applied and accepted by most powder coatings plants .
Container mixers main features :
· movable container clamped and fastened in fixed trolley mounted on two flexible Castors makes unit light-weighed and easy to operate .
· Manufactured by 304 pure stainless steel with internally well polished container as mirrors finishing .
· fitted with butterfly discharging valve with easy operating.
· qualified manufactured to meet existing container systems for standardization and interchangable ability with other containers.
· Manufactured by 304 pure stainless steel with mirror finishing.
· Internally well polished easy cleaning.
· Equipped with reliably easy to maintain durable sealing element .
· Extracting controling valve.
· Temperature sense setting and corresponding protection system.
· Dynamic balancing mixing tools.
· Cooling circulating available for mixing head and related tools.
Lifting and fastening & tilting
· Simple guidance to load portable container.
· Robust positive fastening system.
· Accurate sensing and fixing
· Cleaning location and levelling loading .
· interactive interlocking safe system.
· Change of position alarming device.
Mixing and tilting driving
· main gearbox designing for reliable operation.
· Tailor well made tilting gearbox robust and safety engineered.
· IP55 motors and controls safety stopping device.
Controling panels & systems
· Easy operational controlling.
· Fully controlled and temperaturing indication and over temperature protecting.
· Fully automatic and manual operation, PLC controlling system.
Transporting and Installing
· Well designed for containerization and minimum on site installation; single power supply to controling panel; sufficient compressed air and cooling water centrally well supplying .
· Fully instruction to provide; full Technical and Maintenance documents
Simply Operational and easy cleaning
· Easy to clean .
· Safe and reliable for operation.
· Larger volume container for low bulk density products.