Diamond, ruby, or sapphire?

By Hypertherm
Posted on 07/17/2014 in SPARK the blog, Waterjet cutting

No, we aren't planning to send you the gemstone of your choice, but rather are talking about the orifice for your waterjet system. People often wonder which of the three orifice types they should choose. There are a few factors that might play into your decision, but before we get to that, let's quickly review the options.

The first two options, sapphires and rubies, are actually one option. That’s because both come from the same mineral, corundum, and are nearly identical from a performance and cost standpoint. Both are quite hard (9 on a scale of 1 to 10) with a reasonable life expectancy of about 40 hours, and a cost of about $20.

While sapphires and rubies are hard, diamonds are even harder. Diamonds are a 10 on the Mohs hardness scale. You might be thinking "Oh, that's not much. It's only one point higher than a sapphire or ruby." In reality though, that 1 point is a lot. It translates into nearly 4 times the hardness, meaning a diamond is 4 times harder than a sapphire or ruby.

While a sapphire or ruby orifice will last for an average of 40 cutting hours, a diamond will last at least 1,000 hours! In addition to lasting longer, diamond orifices provide a more consistently shaped jet for a consistently better cut.

There is no question then that diamonds are the very best mineral for a cutting orifice. The problem though is that diamonds are prohibitively more expensive, costing upwards of $400. This makes a diamond orifice 30 times more expensive than its sapphire / ruby counterpart.

If you do the math and divide $20 by 40 hours, you’ll see that the sapphire or ruby costs about 50 cents per cutting hour and the diamond ($400 divided by 1,000 hours) about 40 cents. The diamond has a slightly better cost profile, but the difference is so small, it’s negligible. The real cost difference comes down to labor. It takes time to change out an orifice. Do you want to do it once a week or once every 6 months?

So diamonds last longer, provide better cut quality, and cost less in the long run. Does this mean you should buy a diamond orifice? In most cases, yes. This is especially critical for companies tasked with cutting very large, thick, or expensive parts (a specialized mirror or glass lens for an industrial telescope, titanium for an aircraft, etc.) Believe us, you don’t want your orifice to fail in the middle of a cut!

Also, companies running multiple cutting heads on their waterjet table should use diamond orifices. You may have assumed the opposite—more cutting heads means you should buy the less expensive orifices to save your accountant heartburn. However, sapphire and rubies don’t perform as consistently as diamonds. The 40 hour life expectancy is an average number. Some rubies may last 15 hours, some 30, some 45. Now, think about what this means if you’re running a table with three or four cutting heads. Rather than changing your orifices once or twice a year, you could find yourself changing out an orifice every couple of days.

Though diamonds are the ideal orifice in most cases, there is at least one instance when you might want to choose a sapphire or ruby. If you find yourself using a lot of different nozzle / orifice combinations because you have to cut a wide variety of material types, you may want to stick with sapphires or rubies. A job shop is a good example of a business that may be called upon to cut rubber, stone, and metal all in one day. If you’re using a lot of nozzle / orifice combinations there is a greater chance the operator may (a) accidently lose an orifice, (b) drop it into the water table, or (c) accidently introduce debris into the orifice which could cause serious damage. Most people would probably agree it is better to have one of the above happen to a $20 rather than $400 orifice.



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