Maillefer screw

Mixing screws — S-shaped kneader, Eagle mixing. Turbine mixing, Cohen double-wave, or Maillefer screws with pin-, blister ring-, fluted-, barrier-screw. Dynamic Extentional Flow Mixer (DEEM), etc. 

The melting performance of the Maillefer screw geometry can be analyzed by a down-channel mass balance ... 

The right-hand term, the melting rate per unit down-channel distance, is given by Eq. 7.109(c). In the analysis of the melting performance, a complication arises in that the solid bed velocity cannot be assumed constant. This can be appreciated by comparing the solid bed width profile of a standard screw with constant channel depth to the channel width profile of the solids channel in a Maillefer screw. The width of the solid bed in a standard zero-compression screw as a function of down-channel distance z can be written as ... 

The width of the solids channel of the Maillefer screw can he written as ... 

By comparing the channel width profile, Fig. 8.57, to the solid bed width profile in a standard screw with constant solid bed velocity. Fig. 8.56, it is clear that the two profiles are considerably different. If the solid bed is to occupy the full width of the channel W,s in the Maillefer screw, the velocity of the solid bed will have to change along the barrier section. This may require substantial deformations in the solid bed, but it will be assumed that the solid bed is capable of undergoing the required... 

The advantage of the Maillefer screw is primarily the physical separation of the melt pool and the solid bed. As a result, there is less chance of formation of a melt film between the solid bed and the screw and, therefore, there is less chance of solid bed breakup. Thus, the melting process can occur in a more stable fashion but not necessarily at a higher rate. 

The initial part of the barrier section is the same as the Maillefer screw. However, when the melt channel is sufficiently wide, the barrier flight starts to run parallel to the main flight. 

The melting performance of the Barr screw can be analyzed by the same procedure followed for the Maillefer screw. The initial portion of the barrier section can be analyzed just as a Maillefer screw. If Zji is the length of the initial Maillefer portion of the barrier section, the solid bed velocity at z = Zj, is approximately ... 

If typical values are used for cpb and cpf, the melting length of the Dray and Lawrence screw will about 10 to 20% longer than the ideal compression screw. The melting performance of the Dray and Lawrence screw is thus about the same as the Barr screw and slightly better than the Maillefer screw. A patent on this barrier screw... 

Again, the melting performance can be analyzed by the procedure used for the Maillefer screw. Because of the continuously varying helix angle, the analysis is rather involved. Ingen Housz and Meijer [27] found for the total melting length of the Kim screw ... 

The characteristics of the various barrier screws are summarized in Table 8.1. The Maillefer screw has many desirable characteristics despite the fact that its melting performance is not quite as good as the other barrier screws. The Ingen Housz screw clearly has the best melting performance however, this is at the expense of geometrical simplicity. 

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