Additive Handling

Containerized Additive Handling and Feeding for Polypropylene and Polyethylene Compounding Properties of Raw Ingredients Today’s producers and users of plastics require a multitude of ‘properties’ from their plastic compounds ranging from, resistance to ultraviolet radiation and inherent decay, rigidity, temperature and fire resistance, purity and colors to name but a few.

In order to achieve these differing properties, specific additives are "compounded" with the virgin feed stock. *Typical Plastic Additives* To achieve the desired properties of plastic compounds, a wide variety of raw ingredients are used. These additives are normally in powder or granular form and contain differing handling and flow characteristics. The following list is typical for polypropylene and/or polyethylene production: Amide E Irganox B215 Anti-Block Concentrate Irganox B225, Atmer122 Irganox 1010 Atmul 84K Millad 3905 Calcium Carbonate OABH Calcium Stearate Pigments (Various) Carbon black Sodium Benzoate Crodamide Sodium Stearate DSTDP Talc Ferro AM340 Titanium Dioxide Glycolube Topanol CA Ionox 330 *Business Requirements Set the Stage…* Producers of plastic compounds in today’s business environment are now required to maintain low inventory levels. It is therefore difficult to maintain stock levels of a high number of different compounds. This pressure, has forced the introduction of multi-purpose facilities which necessitate rapid change over from compound to compound, easy cleaning to avoid cross contamination and effective handling to ensure health and safety issues such as containment are maintained to the highest possible level. *Traditional Method for Batch Additives Handling & Feeding* Raw ingredients are typically delivered to the plastic compounding plant in super sacks, bags/sacks or drums.

These are then taken to a "Masterbatch Formulation" area of the plant facility, whereby they are weighed and dispensed into a Masterbatch mixer/blender. This dispensing process may be manual or automatic (via feed device). The additives are homogenously blended to form the "Masterbatch" that will be mixed or simultaneously added along with virgin plastic to the extruder.

*Traditional Method for Continuous Additives Handling and Feeding* Raw ingredients are typically delivered to the plastic compounding plant in super sacks, bags/sacks or drums.

These are then taken to the upper level of the compounding building, whereby they are manually dispensed into a series of loss in weight feeders that feed the various ingredients through an in-line mixer which consequently feeds the virgin feed stock and raw ingredients through to the barrel of the extruder.

*Process Difficulties With Traditional Methods.* These types of traditional processes allow for the manufacture of different grades of plastics but often yield low reliability and repeatability. The quality assurance may be unreliable, changeover from product to product is slow and it utilizes a high level of labor. Moreover, hygiene/cleanliness usually suffers with a large level of bag and drum opening/emptying at the beginning of the process. Utilizing traditional methods of dispensing the powders inherently means excessive dust, spillage or wastage of trapped materials in the sacks and bags, as many of the materials are cohesive with difficult flow characteristics. Sacks and bags are also susceptible to damage and/or moisture while in storage or transport. Product change means extensive clean down of the complete process system, with highly inefficient operator involvement and a slow down in production outputs. *Utilization of the Intermediate Bulk Container (IBC) System* Modern compounding manufacturing facilities are now often designed using Intermediate Bulk Container (IBC) systems for additive handling, formulation and dispensing, filling discharging and blending with the mixes fed to the extruders via loss-in-weight feeders either directly and/or by adopting pre-mix or master-batch techniques. *Refilling Gravimetric (Loss-In-Weight) Feeders* Most compounding facilities rely on gravimetric or volumetric feeders to deliver the correct recipe of additives to the extruder. Feeders simultaneously meter virgin plastic and additives into the extruder in a continuous mode to yield a continuous output of compounded plastic product.
	For consistent, accurate feeding of the additives into the extruder, it is often essential to use gravimetric (loss-in-weight) type feeders. This ensures a constant and highly accurate mass flow rate to the extruder on a second-by-second basis and ensures it is maintained throughout the production run. Experience has shown that loss-in-weight feeders are the most accurate units for this purpose. Since all feeders have a finite volume in their hoppers, they need to be filled and re-filled periodically (typically 6 to 12 refills per hour) based on the rate and the size of the feeder’s hopper (storage). Refilling is usually achieved from a secondary "refill hopper" located directly above the feeder to utilize flow by gravity into the unit as required. Although the feeder maintains a continuous feed into the extruder, it must be refilled on a "batch" basis, requiring special computer control software to facilitate the continuous "weight-loss" feed during a refill (whereas the feeder is actually gaining weight).
*IBC System for Continuous Additives Compounding* Most new continuous compounding facilities utilize bulk storage with discharger valve for the bulk virgin plastic and an IBC (containerized) system for the additives, whereby the additives are received from the supplier in the IBCs, or they are decanted in a separate (dust controlled) warehouse area from the bags/bulk-bags/drums into IBCs. These IBCs are often bar coded or marked for batch recording purposes and can then be controlled as part of the process facility’s inventory control system. Once filled, the IBCs are, typically stored (often with a blanket of inert gas to alleviate hygroscopicity and decomposition/degradation). When required, the IBCs are then taken to the compounding building/facility, and placed (either automatically or by forklift truck) onto a discharge station that is positioned directly above the LIW feeder. The discharge station, in turn, automatically discharges additive (on-demand) into to a loss in weight feeder which, typically, feeds additive (along with virgin resin) into a continuous in-line mixer and, subsequently, into the extruder. A typical continuous process may call for as many as 5 or 6 LIW feeders during any given compounding campaign.

*IBC System for Masterbatched Additives Compounding* Modern batch compounding processes often utilize an IBC (containerized) System to not only store, handle and discharge masterbatches, but also to mix/blend the masterbatch ingredients inside the IBC. For this, the masterbatch ingredients are added (as required) directly into the IBC. Once formulated, the IBC is tumble-blended to produce a homogenous masterbatch that can be stored for use as required by the process. Again it is typical for masterbatch to be fed through an IBC discharger into a loss in weight feeder and, ultimately, into the extruder.




The Masterbatch is dispensed from the IBC (by the IBC discharge station) into a loss in weight feeder which is then blended with the virgin plastic from the bulk silo and compounded as with the other methods. Intermediate Bulk Containers Provide Process Flexibility Very few modern process facilities either operating or under construction are now dedicated to one single product or formulation. The increasing need for flexibility as a result of market forces and production schedules is now a priority for all Operation Managers. IBC's offer a complete flexible system and allow for immediate changes in formulation and recipes without the need to change the refill equipment. It also allows for plant expansion to meet increasing production demands. *IBC Cone Valve Technology* Most additive powders exhibit difficult flow characteristics. These can be very cohesive and often subject to ratholing and bridging in static hoppers/containers. Until recently, refill hoppers have almost always been static and in a few cases have used bulk bags. These have proved very unreliable due to the problems of extracting the material and dust creation problems around the discharge point due to inadequate sealing arrangements. Where static hoppers are used it is often necessary to provide external extraction devices to ensure that the powder discharges from the hopper. These can be in the form of vertical or horizontal agitators, air jets or external or internal vibrators. Often these may prove to be ineffective, noisy, degrade or segregate the product. It is very important that blended materials do not segregate during the filling and discharging operation. Where hand filling takes place into a static hopper dust and debris is created in the vicinity. Also the storage of bags and drums around the hopper area is an unnecessary hazard. This can be eliminated with the use of IBC systems. *Cone Discharger Valve as a LIW Feeder Refill Device* The Cone discharger valve offers many unique benefits over the use of normal valves or other discharging aids: · When signaled to operate, the cone valve will "lift" quickly and allow the discharge of material to begin immediately. · Due to the controlled "pulse" action of the cone valve, the refill rate can be controlled and prevents a sudden drop of material in to the hopper, which could damage the weigh scale. · With the use of the pulse timers and lift height adjustment, the controlled refill rate can be very easily adjusted to suit each individual LIW feeder without any compromise to the accuracy. · The cone discharger valve also acts as a shut off valve. No extra valve is required to be added between the Discharger outlet and the feeder inlet. · The cone valve is also an aid to powder extraction. There is no necessity for any other extraction device like an external or internal vibrator. The cone valve will ensure complete discharge of material in the bulk silo or IBC to the LIW feeder. · Isolation of the vibrating cone is via a bellows. There is no need to fit any extra isolation mounts between the discharger unit and the hopper / silo. · The profile of the valve is such that it has a minimum of headroom when fitted to the hopper. This reduces the overall height of the feed system. · The valve can have very high feed rates (1000’s of ft³ per hr) and is therefore particularly suited for refilling large flow rate LIW feeders or for feeding flow meters for powder handling. · Since they are pneumatically actuated, Cone Valves can operate in a hazardous area without any modification. This is very important particularly in plastics/chemical plants.
	*Contained IBC Discharge* For modern plastic compounding operations, dust containment is a major issue. The Matcon IBC provides dust free filling, storage and discharging of hard to handle, dusty additives in an easy to use package. Dust containment from an operator and environment point of view is important, as is dust containment for cross product contamination. *IBC Benefits in Plastic Compounding Applications:* · Eliminate the negatives of the static hopper. · Creates a clean and hazard free environment in the production area. · Reduces the maintenance and cleaning down time. · Improves the efficiency of the production operation.