A Very Fine Thing

Process numerous and different materials in one mill without retooling; do away with expensive cooling when working with difficult materials; produce better particle shapes; and, finally, offer high process reliability. These are the features that mills made by the Pallmann Group offer in response to demands of masterbatch producers and compounders.

Polycarbonate, ABS, polyamide, polyimide, EVA - milling these materials into top quality powders for masterbatches and the like, without special cooling, is possible. Energy saving does not begin with fiddling with design details, but rather by asking basic process questions: processor who want to eliminate expensive cooling of materials with liquid nitrogen or other media prior to grinding, who can carry out quicker and deeper cleaning, who can put more materials through a mill in quick succession, and who can accurately target important parameters of the final product, will come out on top with considerable energy, cost and quality advantages.

Cost and quality are the focal points of masterbatch production. Special design features developed for Pallmann’s PolyGrinder mills target these aspects.

The state of the art in virtually every other mill on the market allows only Hart PVC and polyethylene to be ground at room temperature. Because the material heats up during grinding, air cooling alone is insuffi-cient with other materials. In most cases, liquid nitrogen is used instead. Costly to generate, store and supply, liquid nitrogen adds around 5 to 10 cents per kilo to the cost of the product.

It doesn’t have to be that way. Pallmann’s patented mill design can process "difficult" materials such as Ethylene vinyl acetate (EVA) with a VA content of up to 20 percent into high quality particles, without any extra cooling. And depending on the composition, the PolyGrinder has no problem with a polypropylene copolymer that no other mill on the market can handle. Processing costs benefit from the lower complexity of the system as well as the elimination of costly nitrogen.

The milling of a very wide range of plastics without additional cooling and with a defined particle shape is possible thanks to the use of some very special grinding wheels: instead of being made in a single piece, the profiled areas are in segments, which are better able to give an even scissor-like cut over the entire grinding area, creating a lower energy input - and thus reduced warming. The special cutting shape achieved with this construction not only protects the processed material, but also the mill: the reduced wear considerably extends the lifetime of the segments. In addition, the segmentation provides for lower cost of resharpening and increased safety. Ring-shaped components common in other constructions tend to warp during annealing, causing assembly problems.

From the middle and in one piece

Engineers prefer symmetry – and that makes sense in most plant and equipment. In this case, however, the patented, special arrangement of the fixed and moving grinding wheels works in a simple way to yield an important effect: the automatic air flow that results in the grinding chamber ensures an even and optimal transport of the material. Despite the compact design, a so-called large-chamber effect is achieved.

In addition, the entire body of the mill is machined from a solid block of steel, rather than being welded together. This not only provides for the highest possible robustness of the housing and rotor support, but also offers advantages in daily operation: there are no seams, sharp corners or dead spots that make cleaning difficult. Fast cleaning and safety, and no contamination that can easily be overlooked, provide for fast and cost-effective – and safe - colour- and material changes. This makes Pallmann mills suitable for materials development too: fast switching between different types of materials with relatively low cleaning effort enables the economic production of smaller quantities.

This is even more the case because the whole system built around the PolyGrinder is extremely com-pact. A feeder dispenses the granules evenly into the mill, a blower downstream transfers the ground pow-der over an extremely short distance into the cyclone separator, a rotary air lock conveys the final product into a container. The automatic control of the complete system is done via an integrated control cabinet. All accessories required for operation and material changeover are positioned at a comfortable working height. The compact design of the entire high output system not only saves valuable floor space, but also it contributes very short tubes how far the material moves... very short ways... to fast and easy cleaning with low material loss.

Particle shape is critical for processing parameters

Bulk weight, particle size the fineness, particle shape and flowability of the milled material can have a significant impact on the quality of the final product. Masterbatch producers, for example, look for a large particle surface area with a narrow particle size distribution to get good binding with additives and to ensure an even distribution of the masterbatch in the final product.

Applications such as rotational molding may appear undemanding, but if one is capable of producing powder with a precisely specified particle size distribution and special geometry – and so generate very high fluidity - it may be possible to reduce the amount of material needed for a special part, without altering its mechanical properties. And these savings have a direct effect on the product costs - or the yield per part - in the overall cost calculation.

In both cases, and especially in masterbatch and compound production, developers are plagued with un-certainty about the performance of the powder, the quality achievable in the product, and the cost of grind-ing (the cooling required, part wear, and so on). For such cases, it makes sense to start trials in the world's largest pilot plant for size-reduction technology, at the Pallmann Group’s headquarters in Zweibrücken, Germany, to clarify in advance just what is technically and economically feasible - experience shows that is more than the average material developer suspects.

Cost and quality in focus

A variety of factors affect the cost of fine grinding: the absence of refrigerant, the quick and safe cleaning, as well as the durability and low maintenance with minimal downtime, all have a big effect on keeping costs down. Contract millers needing to process a wide range of materials in rapid succession can especially benefit from this. In addition, the ability to accurately influence, size, surface structure, bulk density and other parameters, provide further competitive advantages.

Reader enquiries

PALLMANN Group
Wolfslochstraße 51
66482 Zweibrücken
Germany

+49 6332 802-103

rolf.gren@​pallmann.eu

www.pallmann.eu