Extrusion Toolings

Good day!

I just want to ask, do we have any standard in calculating the diameter of the point/tip and the die for extrusion lines?
Like for example, for conductor size of 1.2 can we use 1.26 or 1.34? and the die will be 2.16 or 2.24? Some people are saying yes we could use the bigger diameter of tip but some say it will create off center.
I just want to ask the opinion of the experts.

Hello there,

Before we answer you, you must tell us some more information.

- What is the conductor? Solid annealed copper or 7 wire annealed (1+6 concentrically stranded) conductor. (Not bunched)

- What are the numbers in your question? Millimeters, Square millimeters? (If the conductor diameter is 1.2 mm (0.0472 inches), it is about 16.5 AWG)

- What is the insulation and process? (PE, PVC, XLPE Moisture Cure, XLPE Steam Cure) Likewise please confirm that this is pressure extrusion and not tubing.

- What is the purpose of this insulated conductor? (Example - House wiring at 220 Volt AC, 50 or 60 Hz?)

Thank you.

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com
519 641- 3212

Thank you again for the reply.

1. It is a stranded conductor (7wires for NYA and 19wires for THHN).
2. The values are in mm. The 1.2mm is for 18AWG in our company.
3. PVC and XLPE insulation and it is pressure tooling.
4. All for building wires. For THHN (19 wires) it is 600V and for NYA (7wires) it is 450/750V.

I could send you the conductor sizes we have if you want.
And also some people are saying that with bigger point diameter it will create a wire break.

Hello again,

The difference between your understanding (18 AWG) and my calculation (About 16.5 AWG) was due to fact that I assumed the conductor to be solid and not stranded, hence more copper. I imagine it is 18 AWG if your 7 wire strands have a diameter of (1.2) /3 = 0.4 mm and your 19 wire strands have a diameter of (1.2) / 5 = 0.24 mm.

Now on to your original questions.

Since you are using pressure extrusion, the inside bore of the die defines the outside diameter of the insulation. Increasing the die diameter is not required because you would be giving away plastic for nothing. The diameter of the die is therefore fixed.

Now as far as the tip is concerned, the clearance between the tip and the conductor or core should be sufficiently close enough to hold center without causing wire breaks or jamming of the core. For small stranded conductor, it should be three or four mils (Thousandths of an inch). If you are experiencing high spots on your strand, the issue is at stranding (Tension control, starting and stopping and so on.) and not at insulating. Check by installing a laser diameter on the bare conductor as it enters the cross head or at the stranding machine. Be sure however to protect the laser from damage or destruction if the wire breaks. If you are flying this bare stranded wire off at the extruder, do you have tight control as to the flying direction? I personally prefer live (driven) pay-off reels with no twisting at extrusion.

If your tips are plugging with copper dust, the problem is with the drawing lubricant and I personally would first suspect the emulsifier in the drawing lubricant. If you are having such a technical issue, contact your drawing lubricant supplier immediately. You should also be using deionized water to dilute the drawing lubricant plus you should use clean fresh water in the drawing machine annealer. (A lubricant is not necessary in my experience.) Please do not assume drawing lubricants are low tech nuisance you must have because this is not the case.

I have actually witnessed annealed, preheated, solid copper wire (24, 26 and 28 gauges) broken by high pressure plastic via diameter reduction of the conductor (Plastic pressure say in the area of 7500 psi.) but breaking a larger stranded conductor like yours by having too much clearance in the tip would be very unlikely. There are usually pressure gauges on primary, high speed extrusion lines after the breaker plate to make sure that the tooling in the cross head has been designed and installed correctly. Do you have an accurate procedure to set the position of the tip relative to the die or is this all fixed?

If you use a larger than recommended tip, always keep in mind that the conductor runs on the bottom inside surface of the tip, thus you will have to manually center the insulation by adjusting the position of the die holder (if possible).

This is really all the advice I can give from this side of the World and without inspecting your tooling, seeing the line set up and in operation.

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com
519 641- 3212

Thank you Mr. Peter for your adivce. Is this also applicable to Tube Toolings? I think for tube toolings, the diameter of the tip will be much bigger right?

Hello,

Generally speaking, tubing is used to pull down a plastic sheath by vacuum on to a rather uneven core so the tip clearance would be more in that particular situation. The tip also has a longer bearing than that in a pressure set up. In tubing, the sheath wall thickness is maintained without giving away excess plastic. For example, it is commonly used for sheathing PVC insulated, paired and cabled inside telephone cable.

The die however would have a larger diameter or bore because of the pull down of the plastic on to the core. (Drawdown Ratio) In extrusion, the ratio of the thickness of the die opening to the final thickness of the sheath is known as the drawdown ratio.

You are going to have to buy some books from the WAI Store if you need more information. For a start I suggest the Electrical Wire Handbook Set. It is remarkably economical.

www.wirenet.org/waistore/productdetail.cfm?productid=2

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com
519 641- 3212