What considerations should weigh on your mind when buying a vacuum furnace? (episode 1)

There are many sound reasons for investing in a professional vacuum furnace.

Each company that owns and operates one will have its own priorities and reasons for favouring one purchasing factor over another. However, anyone who is relatively new to the world of vacuum furnace technology may not realise just how much there is to consider with these sorts of furnaces.

In these three articles, we'll break down all of the most important purchasing considerations for you. Although we have identified that there are ten different considerations that you ought to weigh up before making an investment decision, which ones are most crucial will vary according to specific industrial needs.

There is no point saying that automation is the prime consideration for all buyers of vacuum furnaces, for example, because material considerations may be of more importance within certain sectors.

Rather, the idea is to gain a better understanding of all of the factors that should play their part in deciding which sort of vacuum furnace technology to go for.

After all, all business requirements change with time so something that might have seemed relatively unimportant when you first bought your vacuum furnace may become crucial as your technical requirements or customer needs alter over time. As such, it is worth considering all of the following ten points with equal care before making your investment decisions – even if one or more of the factors does not seem as though it is a high priority now.

Read on to find out more about some of the most important considerations for buying a vacuum furnace today in part one and then progress to the two following parts where you will discover much more about this fascinating technology.

Welding Points

When a vacuum furnace is manufactured, its weld points will be crucial to its reliability.

Welding is considered to be the simplest way of forming a join between two sections. Nevertheless, this simplicity belies the exacting rules that manufacturers must follow.

There are regulations laid down by the American Society of Mechanical Engineers as well as similar ones that European operators must adhere to.

The point about welding rules from a buyer's perspective is that they need to be followed. Buyers should consider that these regulations are essential to the safe operation of the furnace itself.

The regulatory framework manufacturers operate in attempts to deal with all of the potential dangers caused by the use of such joints. For example, typically the rules will state that a welding seam must be continuous and only performed on one side of the structure of the furnace. That said, further reinforcement of the join may be allowed with spot welding on the reverse side.

Whichever regulatory framework you happen to be talking about, the principle is that welding points should be sufficiently strong to prevent the unwanted formation of cracks.

Bear in mind that in vacuum furnaces, some of these cracks could be very small indeed and consequently tricky to identify without a great deal of expertise.

When a furnace is de-pressurised, such micro-cracking could lead to bigger fissures and, ultimately, a total system failure.

• A key question to ask of a furnace maker is what has been taken into account with welding at the design stage.
• What steps does the manufacturer have in place to prevent any welds from generating deformations in the product?
• How are tension states avoided, for example?

Another important aspect of welding is the thickness of the joints themselves – ideally, they will be no bigger than is needed and all of the same, uniform size. If excess filler material has been used, then it could lead to subsequent overheating.

Measurement Systems

Any vacuum furnace you purchase must be able to measure its level of vacuum, usually by gauging the work of the furnace's pumping system. Of course, there are a variety of different pumping systems that a furnace can be fitted with. These all have the same role of bringing the system to a de-pressurised state so that the final voids necessary for the heat treatment can be generated.

Like the pumping system itself, there are a variety of measurement systems that go with them.

For example, a diaphragm pressure gauge might offer you a mechanical indication of the pressure level. Equally, a measurement head indicating the thermal conductivity could be in use.

There again, some measurement systems make use of cold cathode ionisation heads.

It is worth exploring all of these technologies in greater depth before making a decision on a particular product since you may need one, two or even all three in your unit.

Bear in mind, too, that a vacuum furnace is generally a clean heat treatment system.

In other words, you should expect degassed surfaces to be present with only negligible amounts of water vapour present for later expulsion. Even if the workpieces going into a vacuum furnace for a heat treatment have been carefully cleaned prior to the process, there may be trace levels of condensates that remain present. If so, sludge or certain suspensions in the oil that diffusion or rotary pumping system may come about.

Measuring them may be crucial for ongoing work even though they are likely to be minimal in a high-quality system. It is, therefore, crucial that the manufacturer has considered the cycle times that will be involved with the furnace. If so, a smaller pumping unit can be used that is appropriate to the tasks at hand.

Leakage

In the main, the principal cause of vacuum furnace degradation and the consequential downturn in production efficiency during vacuum heat treatments is leakage.

Leaks are often traced back after a failure as having come about undetected during a straightforward operation. Therefore, buyers should carefully consider how much leakage they can expect from a furnace and, when it occurs, the costs involved in putting the matter right.

Typically, the elastomers used in seals will prematurely age due to their exposure to heat.

Sometimes this can be due to the normal wear and tear you would expect of dynamic seals as they are open and shut.

However, another important aspect to think about is where overheating has occurred, commonly the result of a reduced flow of coolant.

Whatever the reason for a leak to have occurred, what buyers ought to focus on is how they can be detected.

What you want is clear instrumentation that indicates a leak situation may be occurring at the earliest possible stage.

Such instruments need to be easily interpreted by the furnace's operators.

Overly complex instrumentation means that they cannot give their due attention to the problem of leakage.

After all, this is a question of system management because such problems will occur no matter what in the fullness of time. Ideally, there will be monitoring systems in place checking on the microporosity of sheets, any welding defects in the vacuum chamber or the heat exchanger as well as those monitoring static seals for non-conformity.

Of course, other factors may also be taken into account, such as monitoring defects in the feedthrough of any dielectric resins that might be used.

However, the point is that the leaks detection must be conducted with highly sensitive instruments on any insulated components.

You can find out more about the most important things to know before making a purchasing decision about which vacuum furnace technology to invest in by downloading our buyer's guide to vacuum furnaces.

Click here to download the guide, otherwise, simply head on to part two of this article.