calculation of tip & die

Hi all,
How to calculate tip and Die for tube extrusion and pressure(vaccum) extrusion in PVC i.e

1 ) what should be the landing length of tip & die in tube extrusion
2) is there any need of landing in die of pressure extrusion.
3) what should be the DDR & DDB in both type.

Regards

Hello again Mr. Sharma,

1) Unfortunately what you are asking for in item 1 are processing parameters that have been developed by wire and cable companies over many years and usually, they consider them secret and a part of their intellectual property. I doubt if any wire and cable company is going to tell you exactly what they are doing. However, if you are really serious in properly developing your tooling designs, I suggest you work with a quality manufacturer of extrusion tooling like the B&H Tool Company, Inc. www.bhtool.com/index.html

Unfortunately you haven't told us whether you are referring to insulating or sheathing so we have assumed you are talking about sheathing. Likewise we have no idea as to whether you are referring to a commercial PVC or to an "in-house" manufactured PVC. Finally we have no understanding as to whether you are referring to a semi-rigid or a fully flexible PVC. You certainly don't make it easy for us.

In tubing, the tip land length is often variable with the die design. The land length of the die is often constant or a function of the die diameter and the polymer being extruded. The die land length serves to hold and stabilize the polymer pressure inside the crosshead.

Please see the B&H Tool Company, Inc.web page www.bhtool.com/advisor-article2.htm to view a drawing of a tubing tip and die. The classic tubing design has the tip and die land exits flush with each other at the exit of the crosshead as is shown in the drawing

In pressure extrusion there often no length of land on the tip but the die should still have its land length as discussed above. It is very easy to visualize the land length of the tip in the drawing above being cut back to various semi-tubing positions before removing the land entirely to create the full pressure condition.


2) The die will still have its length of land as discussed in (1) above

3) Typically the value of the Draw Down Ratio (DDR) for PVC should be around 1.5. while the value of the Draw Ratio Balance (DRB) should be close to 1 (+/-) (Source - Page 260 of the Concise Encyclopedia Of Plastics.)

For those who wish to better understand the concept of Draw Down Ratio (DDR) and the calculation of same , we suggest you visit this B&H Tool Company, Inc. web page www.bhtool.com/advisor-article2.htm

Likewise the Draw Down Ratio Balance or Draw Ratio Balance (DRB) can be found at www.bhtool.com/advisor-article3.htm