Vacuum brazing furnaces are incredibly useful in the automotive sector whether they are used by carmakers or manufacturers of commercial vehicles and motorcycles.
To be clear, therefore, brazing is a heating process which ensures two metals bond together with a metallic filler. So that a strong bond is made, the filler needs to have a lower melting temperature than either of the two sections of metal being connected.
In the automotive manufacturing sectors, different types of filler materials are used.
These could be thin plates, wired metal or even pastes.
Each has its advantages and disadvantages but the main thing to know is that when a high-quality bond is called for the more control there is in the brazing process the better.
Regardless of the type of join or filler being utilized, the reason for this is that stress and corrosion resistance will be improved if the working environment is controlled.
For example, exposure to dirt will often mean a brazed joint becomes less secure over time.
Indeed, even tiny particles in the air have the capacity to contaminate a brazing process, meaning that the join could wear out prematurely.
Since poor joins and corrosion are something that all carmakers - and others in the automotive sector - would prefer to avoid, controlling the environment around a brazing process is crucial. And, for the best results, creating a vacuum around the material being used will always be preferable. This is when the advanced technologies used in modern vacuum brazing furnaces come into their own.
A low-pressure atmosphere is ideal for brazing, especially when all airborne particulates have been removed from the environment.
Just as is the case in any precise engineering industry, such as aeronautics, creating a vacuum means generating more accuracy.
Ideally, a modern vacuum furnace will reduce any potential contamination of unwanted materials to all but nil.
As a result, the joined metal bonding will offer a high level of mechanical resistance and have a much greater lifespan.
Where complicated internal components are being manufactured, especially those which are oddly shaped, this can be an especially important consideration for carmakers to take into account.
Because the automotive sector needs numerous joining points of often quite small dimensions for its designs, vacuum furnace brazing is frequently a first-choice option.
Many in the industry will make use of water heat exchangers joints, for example, particularly when aluminum is used for this purpose. Various aluminum alloys might be used but the point is that they all possess a good level of thermal conductivity, making it an ideal choice across the sector.
Vacuum brazing furnaces are made up of three elements:
· furnace vessels,
· hot chambers and
· the vacuum pumping systems that lower the internal pressure.
Let's look at each of these, in turn, before moving on to the all-important loading and cooling stations that precise manufacturing processes demand these days.
To begin with, vessels are at the core of any heat process technology, whether you are talking about brazing or not.
Basically, a vessel separates the inside of the furnace from the outside.
The reason that this is important is that it prevents the external environment from impacting on the brazing process.
High-performance vessels will typically have an elliptical shape that extends along the horizontal which means they will be suitably sized for most automotive sector heating treatments.
Secondly, a hot chamber will be placed inside the heating furnace. Commonly made from stainless steel panels, the hot chamber should ideally have nickel-chrome resistors.
Advanced hot chambers are large enough to offer independently controlled heating zones for different brazing applications.
Once set, the temperature should remain constant with very little variance, even with repeated use, in either direction.
The other noteworthy vacuum furnace technology used today is the vacuum system itself.
This is the part of the vacuum brazing furnace that generates the vacuum, usually by pumping air out of the vessel.
As well as getting rid of airborne particles, such as dust, it is important that these pumps have the ability to get rid of undesirable humidity since this can impact negatively on the quality of all brazed bonding processes.
Finally, loading and cooling stations have different functions but can be lumped together because they offer one thing in common: greater convenience.
Essentially, a loading station is used to prepare the vacuum furnace for its next job.
In a manufacturing setting, this is crucial because it means that the next load can be put together even while the previous one is being processed within the vacuum furnace itself.
As soon as the furnace has been vacated by the previous load, the next one can be inserted directly from the adjoining loading station. Modern loading stations are able to handle loads upwards of 900 kg although the most impressive ones will be able to cope with two tonnes, or even more in some cases.
After a brazing heat treatment has finished, the internal load can be automatically transferred so that the vacuum furnace is ready to accept its next load. This means it should be placed in a cooling station chamber whereby it will cool at the desired rate, not too fast nor too slowly.
Ideally, the cooling station will allow the joined sections of metal and their filler to drop in temperature in a controlled way with recirculated air.
