工业的核心，几乎没有任何东西可以不经过热处理而制造出来. We recently caught up with Bob Farrell (Senior Vice President and Technical Director at Hubbard-Hall) and asked him a few questions about the heat-treat market, what he has seen in his 30 years of experience and what lies ahead for manufactures using these applications.
金属为什么要热处理?
Metals are crystalline materials; there are rare cases where they could be amorphous, 但是一般来说, 金属是结晶材料. 通过加热金属, you could change the crystal structure of that metal and get certain desired characteristics such as hardness. Most people are familiar with the Rockwell Hardness; for instance, 你做一个转换结晶转换, 然后你试着锁定它, 或者你试着冷却它, 所以它更多地转变到一个不同的阶段，并锁定那个阶段. 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.你可以有一个氮的例子, 碳壳, 黑色氧化物是将贱金属材料转化为该贱金属材料的氧化物. 最典型的例子就是Fe3O4, 什么是黑色的氧化铁, otherwise known as magnetite; another is a CuO, 或者一氧化铜. It occurs when the chemicals react with a base material to form an oxide of the base’s primary constituent. 在不锈钢的情况下, 它不仅形成氧化物, 但它也会形成基材的硫化物，这些硫化物往往也是黑色的. 或者是氮化碳. 这些类型的表面也可以提供润滑性, 但是一般来说, you are doing what’s called neutral hardening and then tempering back to get in a specific crystal structure to get a specific characteristic out of a given metal.
什么是热处理盐?
Salts are blends of common salts; for instance, 所谓的“高温盐”是钾和氯化钠的混合物. It could also have if it’s a very high melting point salt you’re working at higher temperatures you put barium chloride in there as well, so you have potassium sodium and barium chlorides present in one salt — that’s a neutral salt — and that’s typically called a high-heat salt as well. 你可以加入回火盐, 通常在低于1000华氏度的温度下工作，但至少在熔点以上50华氏度到100华氏度. 回火盐是亚硝酸钠、硝酸钠和硝酸钾的混合物. There is one salt that’s sold for aluminum heat treating that’s just sodium nitrate and 硝酸钾. 有硝酸盐，也就是回火盐，还有高温盐, 哪些是你的氯盐. 盐是什么，是干粉末状混合物, 但是你把它加热到熔点, 然后变成液体. It’s a melt just like ice melts, and you have water; it’s the same thing with the salts.
为什么要用热处理盐?
The methods that are used to heat treat metals are salts or furnaces where you could have parts on a conveyor belt going into a high heat furnace, 只是周围的空气加热了这些部件. 部分就出来了, and then you do a quench to cool them down to try to lock in a structure or cool them down and then heat them back up to a range typically between 300°F and 800°F, 把金属回火. 这可以在很多零件上完成，比如紧固件，小零件. 真正使用盐的地方是你想要很少变形的地方. 如你所知，如果你加热某样东西然后迅速冷却，它就会变形. Salts because they are relatively dense liquids lessen the amount of distortion during the heat-treating process. Therefore salts are used on things such as precision gears; lawnmower blades are a huge area where salts are used primarily for distortion purposes. 当你观察熔盐时，盐在做什么? 它有两种用途:一种是给某个部位增加热量，另一种是把热量从某个部位带走, 如在淬火中. 如果你还记得热力学的话, 热量从热流向冷, 如果你有热盐, 热量流入零件，将其加热到中性硬化的温度, 然后它就会被冷却, 而且盐比零件更凉. 当它放进去的时候，热量从部分回到盐里. The salt will absorb heat to a much greater extent and much quicker than say air would if you did an air quench, 有些人是用炉子做的吗.
有哪些类型的热处理盐呢?
总结, there are three basic types of salts: tempering salts which are the salts that operate say from 300°F to 900°F range and those are typically used either to heat the part up if the part does a phase transition in that temperature range or to cool the part down to that range and lock in a crystal structure of the part. You have your neutral salts that are typically used above a 1000°F more typically used in a range of 1500°F to 1800°F — maybe as high as 2100°F– for the neutral hardening. The third salt are the case hardening salts; you don’t see them used as frequently anymore, but if you have a part where you want low distortion yet you want to do a carbon or nitrogen or a carbon-nitrogen combination case on the part — which is a very thin layer — you could use your carburizing or case hardening salt. 目前仍在使用的盐类有三种.
所有回火盐都兼容吗?
如果它们是以硝酸盐为基础的盐. The difference between the salts are the ratios; the ratios determine what the melting point is. 有一种盐有共析混合物，它的熔点精确到275华氏度. Then you could have salts such as the one that’s used for aluminum which is just potassium and sodium nitrate that melts at 420°F. 所有的硝酸盐盐都含有三种碱性氮, 也就是硝酸钠, 硝酸钾, 亚硝酸钠. 你可以, 在理论上, 同时使用它们, 但是你会改变熔点因为你的比例会改变. 它们可以是混合的, 但是它们不能给你精确的熔点，这很重要, 它还能改变热量, 在理论上, 同时使用它们, 但是你会改变熔点因为你的比例会改变 absorption or the heat transfer characteristics of the salt as well.
高热浴的整改是做什么的，又该怎么去加颗粒呢?
高温浴反应是因为它们与空气中的氧气和二氧化碳发生反应. 你可以 imagine you have this molten solution of salts; it’s glowing red, 它在浴缸中与二氧化碳和氧气反应形成碳酸盐, 但它也会在溶液中形成氧化物. 当你得到这些会发生什么呢?它会干扰热量传递, 这可能会给零件的冶金制造带来一些困难. 你要做的就是净化，去除那些氧化物, 这通常是用颗粒来完成的, 或者像过去那样，人们会在盐中泡出氯甲烷气体来纠正它. What the rectifier pellets are really doing is it’s eliminating those oxides that are built up in there and neutralizing the carbonate. 小球在盐中产生氨, 所以你要慢慢加入颗粒, 当然, 经过任何整改, 你可以在工作人员不在洗澡时进行整改. 你在进化氨它会中和碳酸盐并与氧化物反应. Make sure that’s done in a well-ventilated area as well so you get none of the gases that may be formed escaping into the work environment.
去除高温浴和回火锅的污泥的最好方法是什么?
The best way to de-sludge a bath would be to cool it down as close to the melting point as possible within 50°F to 100°F of the melting point. What you’re doing with desludging — and you see it more with the tempering salts — are you come out of a high heat bath that’s the chloride bath with salts that have melting points of 1000°F or higher, 然后你进入一个低于熔点的回火棒. 盐中性盐会在回火盐中脱落, 当然, 它们在回火浴的温度下不会融化, 所以这些盐会出来, 它会以雪撬的形式沉淀出来. 你要做的就是把回火浴冷却到275华氏度的温度, 把它冷却到350华氏度, 然后你进去, 然后舀出掉出来的污泥. 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, 把它拿出来. Contaminants that are dragged into high heat baths — say the work isn’t clean quite well enough or there’s a lot of grit and grime or particulate matter on there — you could also get these sludges forming in a neutral bath, 高温中性浴, 结果是一样的. 假设盐浴的熔点是1000华氏度, 你会把它冷却到1075华氏度，然后慢慢地，非常小心地, 当然, 进去，试着从盐浴的底部舀出污染物，把它们舀出来.
贵公司有能力对盐浴进行分析吗?
我们定期为客户做盐浴分析. 在某些情况下, 它是付费的, 在某些情况下, 这不是, 但是我们有能力做高温中性盐和回火盐.
你们提供的几种回火盐的区别和优点是什么?
真的没有太大的区别. 这都取决于你想在什么温度下操作. 除了用在铝上的盐, 这种盐是非常特殊的因为你不希望亚硝酸盐出现在用于铝的盐中. So, it really depends on the factors that come into play; 当然 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, 你可以用300华氏度的盐来代替, 但是一般来说, there’s not a lot of difference in the heat absorption or the heat conduction characteristics of the tempering salts when all is said and done.
我应该把样品送到哪里去测试?
我们在南卡罗来纳的英曼工厂进行测试. 他们会被送到. 道格拉斯·巴顿，他为我们做了所有的盐和盐分析.
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