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Accuracy and Payback of a Gravimetric Blender

2019-10-29


A wide variety of plastic products are manufactured either by the injection molding or extrusion molding process using specialized machines. The plastic raw material which is used as the input to the machines has to be mixed with a large number of other additives so that the finished plastic product has the desired physical and chemical properties. Most manufacturers have decided the right combination of the various ingredients which are being used after extensive research. Yet during manufacturing, the accuracy of the mixture which is being used and quality of the finished product depends to a large extent on the type of plastic blender which is being used.

There are different types of blenders available for plastic material before it can be used for manufacturing products. Volumetric blenders will mix the various materials based on the volume of each material. These blenders are using a mixture of sensors and timers, to calculate the quantity of each material being mixed. On the other hand gravimetric blenders are measuring the weight of each ingredient in the mixture. The volumetric blenders are usually cheaper than the gravimetric blenders, since they have a simpler design, yet increasingly manufacturers prefer gravimetric blenders due to their advantages which are discussed below.

The gravimetric blenders can be further divided into batch blenders and continuous blenders. In the batch blender, depending on the amount of plastic raw material required, all the other ingredients are added to the mixture in the desired weight. Load cells are used to ensure that each of the ingredients is of the weight desired. After the plastic material and the ingredients have been added to the batch blender, the material is blended so that the various ingredients are uniformly mixed. However using this method, there is no guarantee that the mixture will be completely uniform; some parts of the mixture may have a higher or lower concentration of the additives.

Hengju-Accuracy And Payback Of A Gravimetric Blender

For ensuring greater accuracy of the mixture, some manufacturers are using continuous blenders. There are a number of hoppers which contain the various raw materials required for manufacturing the plastic product in the plastic blender. Each of the hoppers has a load cell for monitoring the loss in the weight of the hopper as the material is being fed into the blender. The different ingredients in the plastic fall into the blender, where they are mixed together, before being transferred to the next part of the manufacturing process. This method ensures that the mixture created is uniform, since the desired proportions of the raw materials are present and being mixed.

Typically for making plastic products, plastic raw material and more expensive additives are used. While it is easier to uniformly blend materials which are similar in particle size and shape, if the ingredients are different like flakes and powder, the mixture may not be homogeneous. Since this will affect the quality of the finished product, most manufacturers are adding more of the additives to compensate for the lack of uniformity. These additives are more expensive than the plastic raw material and this adds to the cost of the finished product, since the raw materials used are more expensive.

For higher volumes it is observed that continuous gravimetric plastic blenders are the most accurate, ensuring that the mixture has the desired ingredients in the ratio required. When the volume of the plastic material used is less at approximately 5 kg per hour, studies indicate that the accuracy of both the batch type and continuous gravimetric blenders is similar. Both the gravimetric blender types are significantly more accurate compared to the volumetric blenders, so the additional amount of additive which is required to compensate for the lack of accuracy is less.

Typically due to the blending accuracy for each shot for a gravimetric plastic blender, the manufacturer will have to add 1% more additive. In comparison the amount of additive to be added for a volumetric mixer may be 3% more. Hence using a highly accurate gravimetric blender can help the manufacturer save a lot of money in expensive additive costs in the long term. Research has indicated that a well-designed gravimetric blender will pay back the higher price compared to other blenders in less than one year. So businesses who wish to reduce their manufacturing expenses should consider purchasing a high quality gravimetric blender.


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