Is my medieval hot hole puncher going to work?

[Alan314]

I need to melt holes in rubber sheets that are 20" wide by about 1/8" thick. The only way to punch the holes is with heat so they do not close back up. I know there are hot needle hole punch machines but I don't have $50,000 to buy one. So I'm considering building one myself.

This is how I plan to build it... I have a 24" section of 6" ID schedule 40 steel pipe. I need about 5 holes per square inch. I plan to drill about 800 holes in the pipe and put nails through each hole which in turn I will weld to the pipe. The nails will protrude about 1/4" out of the pipe. The nails are about 5/32" in diameter. I'll use a gas torch to shoot a flame into the pipe / drum to get the nails hot enough to melt and perforate the rubber sheets. The pipe will be on a shaft so it can rotate while the rubber sheets are fed between the hot spiked roller and a smooth roller so the rubber is perforated as it is fed through. I'd like to be able to perforate 6 feet of rubber per minute.

Does it sound like this will work? Would it be better to use short nails so inside the pipe the head of the nails are welded to the inner wall of the pipe, or would it be better to use longer nails so the nails inside the pipe can absorb more heat to transfer to the tips of the nails outside of the pipe? Would it be better to use some type of electric heating element instead of gas?

Please help. Thanks!!!!!!

 

[pmover]

not sure, but the roller with the nails will be hot too, so will the roller have any impact on the rubber - like softening/melting? if only the nails were at the elevated temps, then likely worth a trial test (heat a nail and try making the holes). somehow, the roller would need to be "insulated" from the applied heat.

electric heating elements for each nail seem ideal, but designing and implementing appears challenging. something to think about . . .

meanwhile, good luck.
-pmover

 

[Alan314]

I put in a couple nails and heated the area of the nails with a torch and rolled it over the material. It made good holes and the roller did not damage the rubber. However, that was heating just a very small area.

My primary concern is how hot am I going to have to get the drum to transfer heat 800 nails? Will it be efficient or will I need to use a huge amount of gas to heat it up? Between the pipe and nails the roller will weigh close to 45 pounds. There is also a lot of surface area losing heat. I have no idea how to calculate how many BTUs I need to keep it heated.

If the roller gets too hot I plan to weld a steel mesh with a small air gap above the roller to keep the roller from melting the rubber, but I hope I can minimize the contact of the roller with the rubber and just have the nails touching the rubber.

My biggest questions now are do I use short or long nails inside the drum, and how many BTUs to keep it heated?

 

[Compositepro]

Holes in rubber are usually made using hollow punches or or hollow core drills. Heat will leave the rubber with a smelly and gooey residue. In any case steel nails are very poor conductors of heat.

 

[rmw]

steel nails are very poor conductors of heat.

compared to what?

rmw

 

[Compositepro]

For the intended application. There is a tremendous difference between heating the tip of a nail red hot and the burning a hole compared to heating the head and burning with the tip. 5 holes per square inch at 6 ft per minute is a lot of heat flow.

 

[Alan314]

Even 3 feet per minute will do. I just tried it on a small scale using a 5" x 5" metal plate with nails through it (50 nails) and heating the back side of the plate with a torch. Imagine a branding iron to envision what the contraption looks like. There was no problem with residual smell or gooey residue. It does smoke some while punching the holes.

I know with enough heat applied to the drum anything is possible but I need to worry about cost. Ideally I need to keep the cost down to 10 cents pet foot that I perforate.

I'm concerned that after spending a lot of hours to build the drum that it will require so much energy to heat the nail tips that it will not be practical or economical to use.

If iron nails are a poor conductor what other spikes should I consider? If I use nails, long or short? Please help!

 

[dvd]

How many of the sheets do you need to make? Think about getting the sheets perf'ed by a laser or water jet contractor. By time you mess around perfecting (or even 'adequating') your process you could have paid someone to make your production run.

 

[MintJulep]

There's a reason a proper hot needle punch costs $50,000.

 

[Alan314]

DVD - I checked into it and the best thing for this material is hot needle perforation. A hollow puch system would also work but not ideal. Eventually i will end up buying a real machine (maybe 6 months out) but for now I really need to find a way to get orders out that is not too labor intensive.

Can anyone provide any tips as far as if nail length in the drum matters and approximately what capacity tourch would be needed to heat my monsterosity?

 

[chicopee]

Instead of nails use hollow punches as suggested by Compositepro. Instead of having a roller, you may want to use a flat plate to which a series of hollow punches are welded and stamp the rubber sheet with that assembly. Under the rubber sheet you may want a backing plate with holes aligned to the hollow punches in order to insure a perforated rubber sheet.

 

[chicopee]

You may also want to explore the use of aligned stubs instead of aligned holes in the backing plate.

 

[MintJulep]

How about just a single heated tip on an X-Y gantry.

 

[Alan314]

I need to keep the cost down and keep it low tech for now; has to be something I can build in a small shop in a couple days. We even considered the hot needle machine despite to cost but it takes close to 4 months for delivery of a unit. We need something by the end of next week.

I think I'm just going to wing it. Instead of 5 holes per square inch I'm going to go with 4 holes. That drops the nail count from 800 to 400 on the drum so it save me a lot of tine drilling and welding. We can run the sheets through twice if necessary to double up on the perforations.

If the torch blowing on the inside is not enough to heat it up then I guess I can put one on the outside too! We just need to get the sheets out next week so at this point anything goes.

In the end when we are done using it I can probably sell it to some gothic store. It will look rather ominous like a torture machine with all those nails sticking out of it. LOL.

Please keep the suggestions coming. Thanks!

 

[dvd]

First problem that I see is that the tip of your nail has a faster velocity than points closer to the wall of the pipe so when the nail enters the sheet it will move through more material than when the nail is directly below the centerline. I think that your holes are going to be oblong. Probably doesn't matter.

Next issue is stripping the perforated material off of the perforating roll. The material will want to follow the roll and a stripper plate would need to be outside of the swing radius of the nail tips. So you complete the oblong start when the punch entered, except the material follows a different path.

I haven't looked, but it would seem to me that there is thermophysical property data on rubber (what kind?) that should allow you to quantify your heat requirements. Add up the instantaneous volume of material removed and multiply accordingly.

Next problem is thermal expansion. How are you supporting the rotating pipe? If you fix bearings to some sort of journal there will be enough thermal growth to ruin your bearings. If you point a torch in one end, there will be an excess of heat on one side: it will be very difficult to maintain an even temperature distribution.

What are you doing with the smoke and combustion by-products?

How much of this sheet do you need to produce?

I don't understand what you mean when you say that you checked into it and hot needle punching is the best process. Did you have laser cut samples produced? I think that you could buy yourself some time by having your first production runs laser cut, or use some other process at a fabrication facility.

 

[Alan314]

First problem that I see is that the tip of your nail has a faster velocity than points closer to the wall of the pipe so when the nail enters the sheet it will move through more material than when the nail is directly below the centerline. I think that your holes are going to be oblong. Probably doesn't matter.

Yes, they are slightly oblong but barely. Cosmetics are not very important for application.

Next issue is stripping the perforated material off of the perforating roll.  The material will want to follow the roll and a stripper plate would need to be outside of the swing radius of the nail tips.  So you complete the oblong start when the punch entered, except the material follows a different path

I think the material is heavy enough to fall off the roller but if not I'll weld a stripper strip to dislodge the material from the roller. I'm putting a mesh slightly raised from the roller which should stay below the melting temp and prevent the material from melting to the roller.

I haven't looked, but it would seem to me that there is thermophysical property data on rubber (what kind?) that should allow you to quantify your heat requirements.  Add up the instantaneous volume of material removed and multiply accordingly.

I don't have a data sheet. Next time I get a chance I'll measure at what temp it melts.

Next problem is thermal expansion.  How are you supporting the rotating pipe. If you fix bearings to some sort of journal there will be enough thermal growth to ruin your bearings. If you point a torch in one end, there will be an excess of heat on one side: it will be very difficult to maintain an even temperature distribution.

I have 3" ID brass bushings I am using to support the drum. The center support pipe is slightly less than 3" OD and a loose fit so it should be ok considering the low speed rotation and no need for precision on the holes. 3" pipe is welded to main drum with 4 weld tabs. I have no idea yet if the heat will be evenly distributed...

What are you doing with the smoke and combustion by-products?

I plan to put an insulated dome / half pipe over the drum to cover most of the drum except for the bottom inch or so. This is to reduce the amount of heat radiating out onto the operator, and to help keep the nails hot after they punch the product. The material feels like rubber but I think it is vegetable based vs regular rubber that smokes like crazy when burned. This stuff produces some smoke but not too much. May put a vent pipe on the dome if smoke becomes an issue. Shop is in a desert area and will probably do the work outdoors.

How much of this sheet do you need to produce?

Need to get about 400 sheets out next week followed my maybe around 1,000 sheets early January. Not sure on volume after January but it could pick up.

I don't understand what you mean when you say that you checked into it and hot needle punching is the best process.  Did you have laser cut samples produced? I think that you could buy yourself some time by having your first production runs laser cut, or use some other process at a fabrication facility.

Customer checked and said it had to be hot punched. I checked with a manufacturer of all types of perforation machines and they said the same thing. Either hot needle or a hollow punch system. I don't think I could build a hollow punch machine so I'm going with fire and spikes for now! Good chance we'll order a real hot needle machine that can be regulated as to temp and speed once we are secure orders will continue to come in to justify the expense. Pretty sure now but a lot of money to spend if the orders don't follow through after the first couple runs.

 

[Wrenchbender]

Lots of moving parts to work out (e.g. feed, stripping sheet from the nail pickup, backing plate, plumbing, etc.) Addressing the original post, yes it sounds feasible. Just for the heck of it I would try to quantify things as much as possible before spending company money on a prototype, just to show that you've done your homework:
[a] What temperature do you need at the nail tip to make a clean hole. (Measure by experiment.)
Back calculate a temperature needed inside the pipe. Assume convective losses to the air over the nail length 'L'. Is it achievable? I would have to check a heat transfer book to get the coefficients, conductivity, Biot numbers and so on (ugh). You should also be able rank different alloys vs steel.
[c] Pick out nail protrusion and intrusion lengths.
[d] Heating element - I think electric is preferable to gas, just for efficiency.

My first thought was a reciprocating fixture of ganged soldering irons linked to a feed mechanism, but the hole interdistance is too close. It would take multiple passes, so I guess a rotary 'mill' is better. Oh, and if it works, don't use derogatory names; call it something like music box ?.