The heart of industry, almost nothing can be manufactured without heat-treating. 我们最近采访了Bob Farrell (Hubbard-Hall的高级副总裁兼技术总监)，并向他询问了一些关于热处理市场的问题, 他在30年的经验中所看到的以及使用这些澳门威尼斯人网上赌场的制造商的前景.
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Why are metals heat treated?
Metals are crystalline materials; there are rare cases where they could be amorphous, but generally speaking, metals are crystalline materials. By heating a metal, 你可以改变这种金属的晶体结构，得到某些想要的特性，比如硬度. Most people are familiar with the Rockwell Hardness; for instance, you do a transformation crystalline transformation, and then you try to lock that in, or you try to cool it, so it transforms more to a different phase and lock that phase-in. You could get characteristics such as hardness or toughness; in some cases — although we’re not involved really in salts to do that — you can also infuse materials into the surface of the metal and form what’s called ‘the case.’ You could have a nitrogen case, a carbon case, Black oxide is the conversion of a base metal material to an oxide of that base metal material. A prime example would be Fe3O4, which is black iron oxide, otherwise known as magnetite; another is a CuO, or copper monoxide. 当化学物质与基础物质反应形成基础主要成分的氧化物时，就会发生这种反应. In the case of stainless steel, not only does it form oxides, but it also forms sulfides of the base materials that tend to be black as well. or a carbon nitride case. These types of surfaces could give lubricity too, but generally speaking, 你在做所谓的中性硬化，然后回火，以获得特定的晶体结构，从给定的金属中获得特定的特性.
What are heat-treating salts?
Salts are blends of common salts; for instance, what’s called a ‘high heat salt’ is a blend of potassium and sodium chloride. 如果它是一个熔点很高的盐你在更高的温度下工作你也可以在里面放氯化钡, 所以氯化钾钠和氯化钡存在于一种盐中这是一种中性盐它通常也被称为高温盐. You could have what’s called the tempering salt, which typically operates at temperatures below 1000°F but at least 50°F to 100°F above the melting point. Tempering salts are blends of sodium nitrite, sodium nitrate, and potassium nitrate. 有一种盐是卖给铝热处理的那就是硝酸钠和硝酸钾. You have your nitrate salts — which are your tempering salts — and you have your high heat salts, which are your chloride salts. What the salt is it’s a dry powdered blend, but you heat it to its melting point, and then it becomes a liquid. It’s a melt just like ice melts, and you have water; it’s the same thing with the salts.
Why use heat treat salts?
用于热处理金属的方法是盐或熔炉，你可以把零件放在传送带上进入高热熔炉, and it’s just air that’s around that heats the parts. So the parts will come out, 然后你做一个淬火来冷却它们，试图锁定一个结构，或者冷却它们，然后把它们加热到一个通常在300到800华氏度之间的范围, and temper back the metal. That can be done on a lot of parts that are fasteners, for instance, small parts. Where salts are really used are where you want very little distortion. As you know, if you heat something and you cool it rapidly, it could distort. 盐，因为它们是相对致密的液体，减少了热处理过程中的变形量. Therefore salts are used on things such as precision gears; lawnmower blades are a huge area where salts are used primarily for distortion purposes. What are salts doing when you look at molten salt? It’s used for two purposes: it’s used to add heat to a part or used to take heat away from a part, such as in a quench. If you remember thermodynamics, heat flows from hot to cold, so if you have a hot salt, the heat flows into the part to heat it up to a temperature to neutral harden it, and then that could go into a quench, and the salt is cooler than the part. As it goes in the heat goes from the part back to the salt. 盐吸收热量的程度和速度比空气要大得多如果你用空气淬灭的话, which some people do out of furnaces.
What types of heat-treating salts are there?
To summarize, 有三种基本类型的盐:回火盐是在300°F到900°F范围内工作的盐，这些盐通常用于加热部件，如果部件在该温度范围内发生相变，或者将部件冷却到该温度范围并锁定部件的晶体结构. 你有中性盐，通常在1000°F以上使用，更典型的是在1500°F到1800°F的范围内使用，可能高达2100°F，用于中性硬化. The third salt are the case hardening salts; you don’t see them used as frequently anymore, 但是如果你有一个零件你想要低变形但你想在零件上做碳或氮或碳氮结合的情况，这是一个非常薄的层，你可以使用渗碳或表面硬化盐. There are really three classes of salts that are still out there being used.
Are all tempering salt compatible?
They are if they’re nitrate-based salts. The difference between the salts are the ratios; the ratios determine what the melting point is. There’s a salt that has a eutectoid mixture, and it’s a very precise melting point at 275°F. 然后你可以有盐，比如用于铝的盐，它是钾和硝酸钠，在420华氏度融化. All the nitrate based salts contain the three basic nitrogen species, which are sodium nitrate, potassium nitrate, and sodium nitrite. You can, in theory, use them together, but you’re going to alter the melting point because your ratios are going to change. They could be mixed, but they don’t give you that precise melting point that’s important, and it also changes the heat You can, in theory, use them together, 但是你会改变熔点因为你的比例也会改变盐的吸收或者传热特性.
What does rectification of the high heat bath do, and how should a person go about adding pellets?
High heat baths react because they react with oxygen and CO2 in the air. You can imagine you have this molten solution of salts; it’s glowing red, it’s reacting with CO2 and oxygen to form carbonates in the bath, but it also forms oxides in the bath. What happens when you get those is it can interfere with the heat transfer, and it could lead to some difficulties with the metallurgy of the part. What you have to do is you have to rectify to remove those oxides, and that’s typically done with pellets, or as in days past people would bubble methyl chloride gas through a salt to rectify it. 整流器真正要做的是消除那些在那里形成的氧化物并中和碳酸盐. The pellets generate ammonia in the salt, so you want to add the pellets slowly, and of course, with any rectification, you may do the rectification when work is not in the bath. You’re evolving ammonia that reacts to neutralize the carbonates and react with the oxides. 确保在通风良好的地方进行，这样就不会有可能形成的气体逃逸到工作环境中.
What’s the best method of desludging a high heat bath and tempering pot?
去除污泥的最佳方法是将其冷却到尽可能接近熔点的温度，在熔点50°F到100°F之间. 你要做的是清除淤泥你在回火盐上看到的更多你从高温浴中出来那是氯化物浴，盐的熔点达到1000华氏度或更高, and you go into a tempering bat that’s operating below that melting point. The salt the neutral salts will come off in the tempering salt, and of course, they’re not melted at the temperature of the tempering bath, so those salts will come out, and it’ll precipitate out in the form of sledge. What you do is you cool that tempering bath down to if it’s a 275°F melt tempering bath, you cool it down to say 350°F, and then you go in, and you ladle out the sludge that’s falling out. It’s almost like snow falling; imagine your tempering salts in the atmosphere; the chloride salts the snow that falls down and accumulates at the bottom of the pot, and you take it out. 被拖进高温浴的污染物——比如工作不够干净，或者上面有很多沙砾、污垢或颗粒物质——也可能在中性浴中形成这些污泥, the high-temperature neutral bath, and see the same thing. Say the salt bath has a melting point of a 1000°F, you’d cool it down to maybe 1075°F and then slowly and very carefully, of course, go in and try to ladle out from the bottom of the salt bath the contaminates to get them out.
Does your company have the capability of performing analysis of the salt baths?
We routinely do salt bath analysis for customers. In some cases, it’s paid for, and in some cases, it’s not, but we do have the capability to do both the high heat neutral salts and the tempering salts.
What are the differences and advantages of the several tempering salts you provide?
There really isn’t much difference. It really is all predicated on what temperature you want to operate at. With the exception of the salt that’s used on aluminum, that salt is very specific because you don’t want nitrites in a salt that’s used on aluminum. So, it really depends on the factors that come into play; and of course the cost of the salt — sodium nitrite being the most expensive ingredient that’s typically in there — but it’s also the ingredient that gives you a lower melting point. I recommend a 275°F melt point; it’s a very precise melt point and it gives you an operating range of up to 1000°F. The salt could be used for a lot of applications; if you want a less expensive salt, you could go to a 300°F melt point salt and use that instead, but generally speaking, 总之，回火盐的吸热和热传导特性并没有太大的区别.
Where do I send samples for testing?
We do the testing down in our Inman, South Carolina facility. They’d be sent into the attention of Dr. Douglas Patton, and he does all the salt and salt analysis for us.
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