Whilst buying pre-blended coloured material has traditionally been the route of a lot of processors working with PVC and PVCu, you now have other options thanks to Vynacol. Clearly, buying pre-blended material is going to be more expensive than taking on the task yourself. It also has the potential to create difficulties if you need to change the blend recipe at short notice. Generally, the lead times for coloured compounds are significantly greater than for natural compounds or masterbatch and this creates more complex stock control issues for you.
Adding masterbatch into your blend yourself, for plastics processing presents you with a number of choices.
Firstly, you could pre-blend by hand. On initial thought, this can appear an easy, cheap option. However, due to the inaccuracy of the method, in the long term it can turn out to be the most expensive option. Habitually, masterbatches are added in larger amounts than are necessary, which is clearly wasting money and can also have an effect on the quality of the end product. This in turn can have an effect on customer satisfaction.
As keen as we might be to provide you with masterbatch, we are professional enough to want you to get the best you can from our products.
You may decide to Dose your masterbatch and ancillary machinery for this purpose is available in 2 types – Volumetric Dosers and Gravimetric Dosers.
Dosers introduce one material constituent, such as masterbatch, into the flow of material going into the processing machine. As an example, you can place a simple feeding unit at the throat of a processing machine and this will meter colour concentrate or liquid colour into the flow of virgin material being delivered from a hopper, situated above the throat of the machine. You can of course use this system for other additives, not just colour.
A Volumetric Doser generally relies completely on free flowing materials. It does need to be calibrated to achieve levels of accuracy and experience shows that operator reliant calibration is not always as precise as would be hoped. However, if you do favour this route, at least one manufacturer of these dosers provides a well-respected model which is specifically designed for feeding materials which cannot be considered to be free flowing, such as powders and prill. With this particular machine the hopper features an integral bridge breaker bar that sweeps the bottom of the hopper once every 2 turns of the auger. This bridge breaker serves to keep the flights of the auger full and assures accurate metering. The hopper capacity is restricted to about 1/2 cu. ft. (about 4.5 kilos). Keeping the capacity low avoids compaction and helps with metering. The hopper is stainless steel and removable for easy cleanout. The bridge breaker bar is belt driven by the auger feeder motor.
Gravimetric Dosers generally operate by measuring the weight of the hopper supplying the additive. Known as a “loss in weight” mode, this allows them to accurately monitor and keep on correcting the desired dosing level. This is an ideal solution if you are working with materials with a poor flow rate.
On the other hand, Blending controls not just the additive/masterbatch going into the plastics processing machine, but all of the necessary components. A recipe can consist of virgin material, regrind and colour which are all precisely blended together in a controlled and repeatable procedure.
Volumetric Blenders are typically seen as satisfactory if the proportions of regrind and additive you are using are not critical to the look or quality of the final product. Volumetric blenders depend on the timed dispensing of free flowing materials. If the free flow of the material is in any way compromised this will greatly upset the accuracy. Each component of the final blend must be calibrated because the Blender needs to know volume to weight ratios. Human intervention is required to adjust the flow rates as necessary and there is the possibility of using more virgin or additive than is necessary, which will of course impact on cost effectiveness.
Gravimetric Blenders, might have the highest initial purchase cost but achieve amazing results and a quick payback on the initial investment. These machines provide assurance that proportions of ingredients remain consistent. Once set up with the chosen recipe, most Gravimetric Blenders will run without interference, automatically calibrating to ensure both accurate proportions and mixing of the elements of the blend.
Gravimetric Blenders may be positioned onto the processing machine (a preferred option for many as it does not give blended material the chance to separate before being processed). Alternatively, they can be positioned on a stand on the floor beside the machine. It is also possible to mount smaller blenders on mobile stations, allowing flexibility between processing machines. A final option is often used by plastics processors running the same blend for the purpose of manufacturing large numbers of multiple products. The Blender is normally located in a central area, for example a mezzanine and connected to the processing machines by a central conveying system designed for the purpose.
A number of manufacturers have advanced control systems that will allow precise documentation of the blending process for the purposes of quality control. Each single metered dose of all the materials is verified by weight. Any variations in flow, density, time etc. are allowed for and as a result they probably deliver the best automatic blending accuracy. Gravimetric Blenders, dependent upon the model diversity from the different manufacturers, are available in a wide range of throughput sizes. From micro models for very small processing machines with the ability to blend up to 4 components right through to a throughput capacity of 5500kgs/hr and the ability to blend up to 12 ingredients.
Whilst we do not formally recommend any particular manufacturers of Dosing and Blending machinery, we do provide a link to the website of an established UK distributor of some of the most well respected machines. We hope that this will provide you with further information.