Insane Hydraulics
Bold and audacious blog about fluid power
What do I know about safety? Only the stuff I learned the hard way, I reckon. Hydraulic shops, unlike their electric counterparts, have avoided safety scrutinies since the dawn of time, and while this surely (or at least hopefully) is bound to change, I like to contribute the only way I know how - by sharing my most "flagrant" experiences.
Today, I want to tell you a story of how a hose-cutting machine nearly killed me because of my reckless actions. This is not a joke. Like all industrial mechanics, I've experienced a fair share of close calls and have scary stories to tell and scars to show, but if I were asked to pick a self-induced incident that brought me the closest to my death - this one would be my first choice (that is - so far, because, as we all know, stupidity has no limits, and I never cease to amaze myself in that regard).
I did something dumb, and as a result of that, I repeatedly (albeit heedlessly) put myself within a hair's breadth of suffering an incredibly graphic accident that most likely would have led to my demise (given the fact that we operate in a rural area and the nearest hospital is 50 km away). When the accident waiting to happen did happen, I skipped the Darwin award by sheer chance, and all I can say is that I am convinced now that destiny balances out "incredibly stupid" with "incredibly lucky" - or at least that's the only explanation that makes sense to me.
So, this here would be the star of today's show - our trusted hose cutter which we got brand-new back in 2012:
It's battered and old, sure, but it has been cutting hoses for twelve years now, so we can forgive the unpresentable looks. It has a 5.5 kW three-phase two-pole motor driving a 300-mm blade at 2900 rpm, which is more than enough for our hose-cutting needs.
The story I am about to tell you happened a long time ago - about a year after we got it. I actually thought I'd lost the pictures of the incident when the hard drive of our office computer kicked the bucket, but this week, I stumbled into a copy of the folder in an old archive that I apparently made - and now I can, finally, tell and show!
As soon as I began using our brand-new hose-cutting machine, I saw that something weird was happening to the cutting disc - it was slicing through R2AT hoses problem-free, but when I would need to cut through a tougher hose with four or more braids/spirals - it would get "wobbly" - that's the best I can do to describe what was happening. Not always, but quite often. You could see the disc oscillate laterally, and it would make a vibrating sound, and sometimes it would flatter so bad that it would touch the framing around it and produce a very loud metallic rattling sound. This would only last for a second, and then the disc would straighten out by itself, once again becoming a thin slice instead of a wide oscillating band.
Any sane person would have exchanged the blade - but not me! And that was the first stupid thing that I did. But the cutter worked fine for a month. Then - for another month. Then - for a year... I got so used to these "daily wobbles" that I didn't even consider them as something extraordinary anymore ."I guess that's just the way these disks work" - I would say, explaining to random startled witnesses the origin of the loud rattles.
Then, one day, I removed the front panel of the cutter. I forget what it was now - a screw got loose inside or something - but what matters is I removed the panel, put it against the wall, and then didn't put it back! I am sure most of you can relate to situations when there's something that you know you need to do, but since there's never enough time for anything, you just tell yourself - "No worries, I'll do it when I have a minute..." And so, for at least a couple of weeks, possibly more, I cut all the hoses with the front panel removed and the cutting disk exposed - wobbles and all. Just to give you an idea of how insane it was, here's how this machine looks without the front panel:
Scary, right? So, one day I came to work earlier than usual, looked at the cutter and then at the panel sitting next to it, and then spent exactly two minutes putting it back in place (all it took was tightening four screws). Two freaking minutes - that's all it took to remount the front cover - but that decision was probably the best decision of my life, because that very morning - and I kid you not - that very morning, when I cut into another piece of a 4SH hydraulic hose, the disk started wobbling, as usual, and then - BAM! - exploded into a thousand pieces with a loud bang!
We were renting two warehouses back then, and my wife was inside the office in the second warehouse, behind the closed door - but the bang was so loud that she heard it all the way from there and came running to see what happened! She later told me that she thought she'd heard a gunshot.
I was startled, shook-up, but unharmed. Now, take a look at the front panel and especially at this picture taken from the side:
The panel is made out of a 1-mm steel sheet, and one of the disk fragments was still able to cut through it! There were at least five fragments that were hurled in my direction with energy enough to dent the steel sheet - the impact spots are still apparent, even after I hammered the bulges out:
I asked my wife to take a picture of me cutting a hose today just to give you a perspective on where these fragments, or better - blades - would hit had the panel still been out:
Can you imagine? Lots of important stuff there. I reckon getting hit straight into the femoral artery with a sharp and heavy blade flying at 50 meters per second leaves about a couple of minutes before you bleed out and lose consciousness. You see now why I called this post "playing Russian roulette with a hose cutter" - because that's exactly what I did during all the time I worked with the cutting disk exposed and aimed at a selection of vital parts of my body.
Here's another argument for calling this a Russian roulette. A steel disk with a radius of 150 mm and width of 3 mm will have a mass of 1.67 kg (density of 7850 kg/m³). Its moment of inertia would be ½mr²= 0.5x1.67x0.0225 = 0.019 kgm², and its kinetic energy at 314 rad/second (3000 rpm) would be ½Iω² = 0.5x0.019x314² = 937 joules. That's a freaking .45ACP round right there!
This is the slotted disk type that I use now. It works great, and I have never seen it wobble:
So, my friends, if you ever hear a hose-cutting disk "do the wobbles" - don't gamble - replace it with a quality disk immediately, and you will be perfectly fine. And also - never in your life even think about turning such a machine on with the cutting disk exposed! Never!