The Appropriate Selection for Plastics Process Auxiliary Equipment—Dosing and Mixing

Volumetric Dosers SCM Series

Gravimetric Blenders SGB Series

Addition of color masterbatch, recycled material and additive is necessary in the plastics molding production. Thus the importance of metering & mixing equipment can not be ignored. Metering accuracy varies to some extent in accordance with different requirements of finished products. On one hand, Volume type metering error within ±3% is suitable for addition of additive or recycled material that is used upon low request. Manual correction must be finished before metering machine (like SHINI SCM series) is under operation or alteration of proportion. On the other hand, Weight type precision error within ±0.3%~±0.7% is suitable for addition of additive, color masterbatch or add to process upon high request, without manual correction while operating because controller will calculate metering automatically based on required proportion. Weight type metering machine can be divided into the weight loss type and weight increase type (like SHINI SGB series). For the former a dependent loading component is needed for each metering of ingredient therefore it costs a lot with a favorable precision.

There are two main considerations while selecting metering & mixing equipment: first one is that what the range of error value in the operation conditions is; second one is that what the process capability in the operation conditions is. Based on above two factors it will be likely to select an appropriate metering blender for use.

A metering & mixing equipment with proper function would increase excellent rate of finished product and save a few useful resources.

Model Selection of Volumetric Doser SCM Series

A client would like to select a volumetric doser SCM series with 300g injection molding, molding cycle 25s and 10s for per molding collosol. Doser proportion needed to add is 5%; doser material particle should be uniform with 2~3mm dimension and 1.2kg/L bulk density. What is the proper selection of SCM series?

This case is designed to calculate doser quantity needed per hour P (g/hr).

P=each injection molding weight×doser proportion×(3600÷molding cycle)÷(plasticizing time÷molding cycle)=300×5%×3600÷25÷(10÷25)=5400g/hr

Result: the doser weight needed per hour is 5.4kg/hr. By referring to Shini parameter table of SCM catalog, SCM75-14 output range is 0.2~8kg/hr, SCM38-12 output range is 0.3~10kg/hr, so we can choose SCM 75-14 or SCM37-12 two models.
Note: if the doser density selected by client disaccorded with that of catalogue, transform the data by means of formula between density and volume.

Bulk Density (ρ) = weight (m)×Volume (v)
Unit of Bulk Density (ρ): kg/L
Unit of weight (m): kg
Unit of Volume: L

For example, the bulk density of doser material used by client is ρ1 (0.8kg/L) and the required amount of doser after calculated is m1 (3kg/hr). Because it is the Volumetric Machine, its output volume remains unchanged. The output volume when it is converted as 1.2 kg/L doser is:
m/ρ=m1/ρ 1
So, m=(m1/ρ1)×(ρ=(3/0.8)×1.2 =4.5kg/hr. According to the catalog, doser with output capacity of 4.5kg/hr should be selected.

Table: SCM Output Capacity Reference

                            Note: 1. the results above are based on doser material with bulk density 1.2kg/L proportion.
                                      2. intermediate value is favorable in model selection.

Model Selection of Gravimetric Blenders SGB Series

A client provides parameters as follows:
Process capability per hour: 150kg/hr, Material A: 80%, Material B: 10%, Material C: 8% and Material D: 2%. These materials above are grain-shape; the question is what type of SHINI SGB series should be selected.

The question could be solved based on SGB gravimetric blender specifications. The parameters provided by client include process capability per hour of 150kg/hr and four kinds of material. Primary selection could be SGB-200-4.
Because mixture proportion of Material D is 2%, it needs to choose 1 set screw conveying. (Use auger micro feeder if mixture proportion is less than 5%).
Therefore type of appropriate machine is SGB-200-4-1R.
Note: SGB series can not be applied to deal with pulverulent materials because they would cause bridging and would not drop down. Powder leakage would take place with metering valve in normal state.