Liquid Ring Vacuum Pump & Compressors for the Automotive Industry
From heat treatment of steel to lamination of wood veneer, no vacuum pump has worked quite as well for as long as the liquid ring vacuum pump for all types of materials processing in the automotive industry.
Vacuum impregnation is important for sealing any porous areas of metal that is to be used for automotive manufacturing, as any newly cast metal will have its fair share of microscopic pores. These pores contribute to the accelerated compromise of structural integrity due to the scaling that ambient air effects onto the metal.
Increased porosity translates into increased surface area upon which scaling can be inflicted. Impregnation is the process in which metal castings or powdered metal parts are impregnated under intense negative pressure with sealant to drastically reduce porosity. After this, excess sealant is removed and residual sealant is rinsed off of the metal. The sealant is then cured and removed from the impregnation chamber. This sealant is made from various resins that cure to become impermeable thermoset polymers that permanently seal the pores within the automotive parts. There are different ways to go about this; wet vacuum impregnation involves immersing the parts in the liquid sealant. The chamber is put into vacuum conditions by a wet-running vacuum pump to allow for proper deaeration. The sealant is then drained away and the parts are put into a centrifuge. This ensures that any excess sealant can be shaken off by centrifugal force or dripped off by gravity.
Vacuum coating provides marketability through aesthetics and protection against external elements such as rain and snow. This is achieved by vaporizing or ionizing metallic or ceramic-based coating material. The lower air density allows the microscopic layer to settle uniformly on the automotive part. Vaporized liquid paints can be applied in the same way, allowing for uniform color and better marketability. Vacuum coating can be split into two categories known as physical vapor deposition and chemical vapor deposition. These categories can be separated into subcategories and so on, so for the purposes of the literature the focus will be on one method of physical vapor deposition called cathodic arc deposition. An arc is created between a cathode and anode, which vaporizes the coating material and allows it to roam in the low-pressure chamber. The vapor condenses evenly on the automotive part.
Carbon fiber is commonly used in automotive parts for its lightweight and robust properties. To create carbon fiber parts, a process called the “wet layup/lamination process” is performed. Generally, there are three different methods of performing this process: wet layup, prepreg lamination, and resin transfer molding. All involve the infusing of resin into the microscopic meshes of carbon fiber before laminating and curing. In the wet layup method, carbon fiber is cut and set into a mold. Resin is poured in, and the fiber is pressed into the resin to “soak” it into its fibers. In another method, prepreg vacuum bag lamination, a roll of carbon fiber is run through a series of rollers. At a specific point, resin is poured into the fiber. The soaked fiber is set into a bag, which is set into the mold, and the resin cures as heat is applied. Vacuum is sucked in the bag, which creates intense low pressure within the bag. This causes atmospheric pressure to press on the carbon fiber with strong force, manipulating it into the mold.
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Applications of Liquid Ring Vacuum Pumps
Wet vacuum impregnation requires a wet-running pump that is able to provide constant, deep vacuum. The vacuum pressure required to perform thorough impregnation is quite deep, near perfect. Because of this, even momentary changes in the vacuum pressure will affect the quality of the yield. The pump needs to be strong and corrosion-resistant to protect itself against any abrasive chemical agents used to manufacture the sealant, and it needs to be able to pump away the vapors that hydrocarbon material such as resins are able to emit. Many resins are highly flammable, and any vapors that may be created must be transported very carefully. The liquid ring vacuum pump provides constant suction. The single-stage reaches 26” Hg while the two-stage reaches 28” Hg of vacuum. These pumps can be constructed with proper metallurgy to be explosion-proof for flammable vapors and corrosion-resistant for abrasive agents.
These qualities shine in vacuum coating applications as well. Such atomized powder coatings are extremely flammable. The liquid ring vacuum pump also boasts near-isothermal compression due to the high specific heat capacity of the liquid ring, which makes for gentle handling of flammable material. Vacuum impregnation of liquid dyes and paints especially makes use of the wet process specialization of the liquid ring vacuum pump.
Wet layup/vacuum bag lamination processes are inherently “wet” processes – the pump supplying pressure to the vacuum bag will inevitably process residual amounts of liquid resins. These resins can be abrasive, flammable, semi-solid, or just simply liquid, all of which can pose a potential threat to the operation at best, and an explosion with millions of dollars in damage at worst. All of the gentle and constant handling of material previously aforementioned makes the liquid ring vacuum pump perfect for lamination processes. The liquid ring vacuum pump can also process the small resin solids, liquid slugs of resin, and semi-solid slurries without so much as a fraction of an inch Hg in pressure lost over a fraction of a second.