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How do they get the hole in a thin, little hypodermic needle?

 

Our question, How do manufacturers make the tiny hole through a hypodermic needle? We have asked several people we thought might know, pharmacists, doctors, etc. and so far no one can explain it. It started out as a simple question but now we are on a quest to find the answer. We are junior high science students.

Carol Cornelius
- Guymon, Oklahoma


 

Hi Carol,

I believe that the only way to do this is to firstly make a much larger tube (using stainless for needles) and to FILL that tube with a material that can be easily, so-to-speak, removed. I think it was copper.

Why? Because if you cold extrude or cold size, and pass unfilled tubing through a range of ever decreasing dies to get very, very small tube diameters, you'll get ovality if not complete distortion and flattening.

In the rolling mill industry the super fine rolling mill design is called a Zenzimir (or a word sounding very much like that) but I don't think that by itself it can make hypo needles. But the initial tubing? Most probably.

The next problem is to try to remove the 'filler' material. Thousands and thousands of needles are placed in a nitric acid tank ... and not days, not weeks BUT months later the acid eventually leaches out all the copper. Presto, super fine holes in a super thin material. Ergo, you have your fine needle. OK? Aren't you lucky you are growing up in a world where, compared to Ye Olden Days, injections used to hurt!

Now you can go tell all your pharmacists and doctors HOW TO DO IT!

freeman newton portrait Freeman Newton
- White Rock, British Columbia, Canada
freeman newton died


 

Having been in the medical needle business for over 20 years, I can tell you how this is done. A flat, ( I believe it is about 1 1/2" in width) strip of 304 stainless steel is roll formed and welded at the joint into a tube. The tube is then annealed and drawn down through a series of dies with a floating mandrel on the inside of the tube that keeps the I.D. consistent. Where ever needed, additional annealing is performed to keep the desired physical properties and draw characteristics of the stainless steel. If you look at a relatively large needle under magnification, you can find the weld line! This is the beginning for every needle manufactured even down to a 30 gage.

For more information you can contact the tubing manufacturer K-Tube Corporation in San Diego California. I hope this helps!

Best regards,

Frank Blinkhorn
- Keene, NH, US


 

I would like to thank Frank for his accurate response to this posting. He is correct. These days, tubing is made on a tube mill by first forming then welding, either with a laser or TIG welding operation.

Gary A. Piazza
miniature stainless tubing - Poway, California, USA

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