Dray and Lawrence screw

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... 

The Kim screw is basically an improvement of the Dray and Lawrence screw. A picture of the Kim screw is shown in Fig. 8.61. 

This means that the melting performance of the Kim screw is slightly lower than the Dray and Lawrence screw and the Barr screw. It has an advantage over the Dray and Lawrence screw in that the transition from feed to barrier section occurs more smoothly. However, at the end of the barrier section the same difficulty arises as with the Dray and Lawrence screw. 

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