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Blending the raw materials is one of the most underrated aspects of
calendering technology. The reason, perhaps, is at U.S. manufacturers first
concentrated on flexible compounds rather than rigid ones. Blending flexible
compounds is done differently, usually in large batch blenders, first heated
and then cooled for better absorption and storage of masterbatched plasticizer
and pigment. So, when U.S. manufacturers finally under took compounding of
rigid PVC formulas, there was a tendency not to spend capital dollars on the
high-intensity mixers used extensively in Europe. Because of their high speed,
not only do they blend thoroughly and quickly but fuse ingredients in place
preventing separation. U.S. compounders had been relying on ribbon blenders,
which are much less efficient. Banburys, from the Farrel Corp, were used to
flux batch by batch and essential mixing was accomplished in the fluxing step.
But with the newer continuous fluxing machines, little effective mixing is
done after a compound leaves a blender. A blender is essentially a very simple piece of equipment, it consists of a
large container into which the plastic materials are fed, the bottom of which
is conical in shape to aid with emptying the material out after the blending
process is complete. A vertical screw feeds the plastic to the top of the
blender where it then spays onto the sides of the blender where foils further
disperse the material.How long this process takes depends on the quantity of
material and the speed of the screw.
| Pre-Blending |
When we purchase reground feedstocks from
sources other than our own recycling division, we blend the materials
before allocating them to production. This allows us to test a representative
sample of product to ensure it is not comtaminated with different polymer
types and also to obtain the physical properties for that batch of feedstock.
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| Blending |
For many years this has been a key stage
of production. Once our technical centre have formulated which materials
will provide the required specification for a product, they are blended
together. The purpose of blending at this stage is
again to create a homogenous batch of feedstock which will produce a
consistent quality compound. Without this uniformity you may need to
keep adjusting the settings of your molding equipment, which will reduce
cycle times, increase scrap rates and potentially affect the quality
of your product.
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| Post-Blending |
However careful we are to ensure consistency
of our finished compound it is still possible that minor fluctuations
throughout the compounding process will cause variations in physical
properties or colour of the resulting product.
Post-blending is (like the name suggests)
a post production process. If the finished compound does fluctuate through
the batch then we may blend different parts of the batch together to
obtain a more consistent product.
Once we have blended the material, further
quality assurance checks are performed to ensure that the compound meets
the required specification and quality criteria.
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Molding
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