Supervac Industries
Supervac Industries
Jhandewalan, New Delhi, Delhi


Evaporation Boat Get Your Moneys Worth Out Of It

In the present time of intense competition, it is natural that engineers are trying hard to optimize the use of every resource to reduce costs. In Metalizing, Evaporation Boats undoubtedly contribute most in variable cost. It is therefore important that maximum life is derived from Evaporation Boats without affecting the quality of Metalizing. Based on my knowledge of Engineering, experience of nearly 20 years in vacuum line and interaction with actual users, I have compiled a list of measures which if implemented can ‘enhance’ the life of Evaporation boats by about 25% so that you get your money’s worth out of it.  These have been summarized as under - 1)    Initial heating of the new boats also called “break in” must always be slow to get proper life from Boats. Reason? New boats will always have some absorbed moisture. If the boat is heated quickly in this condition, the moisture, converted into steam having much higher volume will have little time to escape and can cause cracks because of high pressure build up. 2)    At the end of the cycle it must be ensured that all the Aluminum or any other metal being metalized has evaporated completely before heating is switched off. Otherwise residual metal will seep into the pores of boats; now differential cooling rates of boat and metal will crack the boat. 3)    Care must be exercised that before the vacuum is broken, boats must have cooled down. This is because sudden contact with cold air can cause boat breakage. About 5 minutes is enough for boats to cool down. 4)    Worn out copper clamps also are a big reason for boats not performing to their full capacity. Non uniform wear of clamp causes sparking between clamp and boat; this overheats and cracks the boat. 
5)    A good quality graphite foil is very important factor in enhancing the life of Boat. To save money, sometimes Metalizers use poor quality plumbing grade graphite foil. This foil contains many impurities and binders and offers resistance to the flow of current. This causes the ends of boat to overheat and break. Supervac supplies 100% pure graphite foil free of binders. This is made with the patented process of Exfoliation. This foil gives you the following outstanding benefits – A)    Offers no resistance to the flow of current. B)    Saves costly power. C)    Enhances the life of Boats.6)    There is one more major factor inter linking the life of evaporation boat with graphite foil. Good quality graphite foil has good compressibility. This allows a proper electrical contact in boats and clamp before heating begins and expansion of boats in heated condition. Poor quality graphite foil on the other hand will not allow expansion of boats in heated condition putting additional stress and subsequent breakage of boats. 7)    Aluminum of purity 99% or more is required to avoid premature cracking. Impure aluminum will have impurities which will have different boiling temperatures; this will lead to an unstable pool of metal in boat cavity. This in turn results in non uniform heating of Evaporation Boat leading to thermal stress and breakage. 8)    Age of aluminum wire also affects boat life. With age, aluminum oxidizes and Aluminum oxide thus formed causes spitting and excessive heating of Boats. Freshly made or “cleaned” wire works best. 9)  Hardness of Aluminum should be maintained in proper range if required by tempering as a very hard wire is likely to puncture the boats.

Why Should Vacuum Oils be changed at specified intervals

In the present time of cut throat competition, users are under great pressure to reduce the cost of production. To achieve this objective, many times vacuum oils are not changed at specified intervals to get more “life” from them.This is a dangerous practice and can damage the vacuum system badly. Let us understand why-   Oils degenerate on account of oil oxidation. In Oxidation, oxygen reacts with the oil to form Hydro-peroxides. Hydro-peroxides are unstable and break down into Ketones. Ketones further oxidize to form Aldehydes and Carboxylic acid. Now Carboxylic acid attacks the pump metal parts as well as O rings, Oil seals etc. causing acid corrosion. That is not all. By products of oil oxidation in the presence of acid further react and combine to form larger molecular species which polymerize to form sludge.Sludge makes oil very viscous and can cause – ·         Jamming and breakage of vanes in the Rotary Vacuum Pump. ·        Overheating and damage to the pump interiors in the Diffusion Pump. What is even more damaging is that this process is like a nuclear chain reaction that keeps speeding up with time. With oxidation, oil thickens and this reduces lubrication, which in turn results in a higher temperature. At increased temperature the rate of oxidation further increases (Rate of oxidation doubles with every 100C rise of temperature as per Arrhenius rate rule).  This damages costly vacuum pumps in a short time.  

Silicone Vacuum Grease Explained

Grease is a lubricant in a semi-solid state. It is generally applied to those machinery parts where liquid lubricants would not stay and need to be applied only occasionally.It also works as a sealant to keep out moisture and other unwanted materials from the system.How is grease made?Grease is made with a base oil or lubricant mixed with a thickener. The quality and properties of grease are therefore primarily determined by the following factors-
  1. The base oil
  2. The thickener
  3. Special purpose additives, if any
How is the base oil in grease important?We all know that lubricants can oxidize. But do you know that greases can oxidize too? That is because of the base oil that makes up the grease.Good base oil = Good greaseLow Quality base oil = Low Quality greaseOxidized base oil = Oxidized greaseHydrocarbon base oil in grease, when oxidized, will produce carbonization leading to progressive hardening and crust formation. This can lead to substantial damage to the moving machine parts as well as permanently ruin the o-rings and seals.What is the Drop Point in grease?Generally, grease breaks down when subjected to temperatures that exceed its melting point or the Drop Point. This is that critical temperature where the gel structure of the grease breaks down and turns into liquid form. The base oil, thickener and the additives separate. This transformation is always irreversible. On cooling, it regains neither its consistency fully nor its former performance.  When heated beyond its Drop point, grease softens, leaks and bleeds into the system. For vacuum systems this spells disaster.So does it mean that the Drop Point of a grease is determined by its base oil’s boiling point?Yes, primarily. It also depends to an extent on the proportion and quality of the thickener used. How a particular grease will behave under extreme conditions like high pressure and temperature depends upon the properties of the base lubricant in it.Does the grease have a low temperature too?Yes, just like the melting or Drop point, grease has a low temperature too at which it stiffens. At this cold or low temperature grease becomes too hard to be of any use for the moving components. Instead of lubricating them, hardened grease can damage the o-rings and seals or the moving parts like bearings etc. by stiffening and jamming them.Again, the base oil determines the lowest temperature of grease. Are all greases alike?No, the difference in the components makes greases differ from one another. There are hydrocarbon greases as well as silicone greases. Then there are synthetic multi-purpose greases. Within these 3 categories too, greases differ based on the type and grade of the base oil used. Different industries require grease that caters to their specific needs. For example, Dielectric grease is used by the electrical industry; special automotive greases are used by the automotive industry;Food grade grease is required in machines where it is likely to come in contact with edible ingredients and so on.As the name suggests, the basic difference lies in the type of base oil in both. Hydrocarbon based greases are mineral oil based while silicone grease has silicone oil as the base oil. Hydrocarbon based grease is used primarily by the automotive industry and mechanisms requiring high frictional lubrication which makes use of grease’s thixotropic property. Silicone grease on the other hand is most suited for lubrication as well as a sealant because of its water resistant property.

Synthetic Rotary vacuum pump oil vs Mineral Rotary vacuum pump oil

Vacuum pumps are a small but extremely critical part in a much larger vacuum coating process. Oils meant for these vacuum pumps need to be very reliable since one doesn’t want unnecessary stops in the vacuum cycle. Apart from giving us the desired vacuum level, these oils should protect and preserve the pump interiors and not form oil sludge.Just a couple of decades ago, finding these qualities in vacuum pump oils would have been impossible by users. Back then, options to using mineral oils were nearly zero. These mineral oils could never deliver consistent vacuum; uniform viscosity levels were missing; oil changes had to be frequent as the oil oxidized pretty frequently; and formation of sludge in the pump was a constant headache for engineers. That was before the advent of synthetic vacuum pump oil.What are synthetic oils?Unlike mineral oils that are derived directly from crude oil, synthetic oils are lubricants with synthetic base stock plus other performance enhancing chemical compounds. Because of being artificially made, in synthetic oils it becomes possible to tweak certain parameters to better suit the application for which they are manufactured.Advantages of Synthetic oils:Just like advent of Silicone Diffusion Pump oils revolutionized the way Diffusion pumps worked (Hard to believe but it is true that about 15 years back all Diffusion Pumps worked on mineral diffusion pump oils). Same way Synthetic Rotary vacuum pump oils are enhancing efficiency of Rotary vacuum pumps to unbelievable levels. Synthetic oils make it possible for Rotary Pump to reach higher vacuum and faster! These oils make sure that there is hardly any pump maintenance requirements, they last longer and work out more economical and so on. You can easily infer this from table below which compares major properties and characteristics of these oils.  
 Synthetic Rotary Pump Oil  Mineral Rotary Pump Oil
1Synthetic base stockPetroleum base stock
2Has a high viscosity index because of which it can withstand extreme working temperaturesHas a low viscosity index because of which chances of it evaporating or turning to thick tar are high
3Better chemical stabilityNot very chemically stable
4High resistance to oxidationLow resistance to oxidation
5High resistance to process gasesDegrades faster when exposed to certain process gases

Graphite Suspension vs Boron Nitride Suspension

Time and again, we are approached by users wanting to know which coating will be best for their application: graphite suspension or boron nitride suspension.  Often, the same vacuum system manufacturer who earlier recommended boron nitride suspension is now recommending graphite suspension or vice versa, as a coating inside the vacuum chamber. This has led to much confusion amongst the users. In this blog, I have attempted to address this confusion by stating the properties of both along with the pros and cons of their use. Either of the two can be selected based on one’s requirement.Properties of Graphite Suspension:
  1. This is made up of very fine graphite particles in either water based or solvent based suspension.  For vacuum coating purposes, water based suspensions are better suited since they do not release any vapours and thus do not hinder the vacuum formation process.
  2. Graphite suspension is electrically conductive.
  3. It is thermal resistant in nature.
  4. Coated graphite suspension provides an excellent barrier to the vacuum chamber walls against any chemical or process gases.
  5. Graphite suspension works as an excellent release agent.
  6. It is chemically inert; so does not react to any chemical or molten metal vapours.
  7. Excellent lubricating properties.
  8. Black in colour.
  9. This is a semi-metal material. Properties of Boron Nitride Suspension:
    1. BN suspension comprises of ultra fine particles of boron nitride in aqueous base or solvent base. Water based boron nitride suspension is always better than solvent based for vacuum coating purposes as the former releases no vacuum hindering vapours.
    2. It is electrically insulating.
    3. It has high thermal conductivity.
    4. It acts as an excellent protective barrier for the vacuum chamber walls against any chemical or process gases.
    5. BN suspension acts as a release agent, enabling stuck aluminium to be wiped off the vacuum chamber floor.
    6. It is chemically inert.
    7. Excellent lubricating properties.
    8. White in colour.
    9. This is an Advanced ceramic material.

How To Get Maximum Life From Your Diffusion Pump Oil

Diffusion Pump Oil is one of the costliest consumables required by vacuum users. In the present day scenario of cut throat competition, engineers are under a lot of pressure to reduce costs without compromising on quality. Based on my experience of almost 20 years in the vacuum line, I have compiled a list of do’s and don’ts as to how one can get maximum life from the diffusion pump oil. For the benefit of our valued customers, the facts are given below -   1.   Topping up at regular intervals is most important factor in getting maximum life from Diffusion Pump Oil. Care should be taken to top up the oil in the pump in a timely manner. In the absence of topping up, volume of oil in the Diffusion Pump reduces, whereas heaters keep producing the same amount of heat. This causes overheating and accelerated loss of DP oil. This further reduces the volume of oil, which in turn causes more overheating and loss of DP oil is further accelerated and so on. 
2.   Keep track of the water flow through the cooling lines. Check the inlet and outlet water temperature as well as the flow rate. Lines can become clogged or scaled over time. As Diffusion Pump oil vapor can only condense on coming in contact with cold walls of DP. Any reduction in cooling causes overheating and increase of pressure inside DP. This may result in loss of oil by back streaming.   3.   Strange as it may sound a very low fore- pressure can also cause loss of DP oil. This can be prevented by switching on heaters before fore pressure becomes too low.   4.   Faulty gauges for pressure/heater too, can cause accidental overheating of the oil or the oil not getting the required heating. Check that all the gauges are functioning properly.   5.   Silicone diffusion Pump Oils have a life of about 4 times that of Hydrocarbon Diffusion Pump Oils. Also Silicone Diffusion Pump oil does not blacken and clog the jets of DP so Silicone DP oil works out more economical in the long run.6.   Poorly working Rotary Pump will put extra burden on diffusion pump. It must be ensured that Rotary pump is working properly to get full life from Diffusion Pump Oil.   7.   Do not expose the oil to air when it is heated. Doing so will affect the viscosity of the oil – it thickens and vacuum reduces. To avoid air exposure valves must be checked from time to time.   8.   To avoid having the oil migrate into the vacuum chamber, a cold cap should be fitted at the top of the nozzle assembly inside the diffusion pump. This cold cap condenses the vapor in that area.   9.   A concentric circular chevron baffle should be present at the mouth of the pump. It allows air molecules to wander in, but traps the heavier oil vapors as they try to escape.   10. There should be no gross vacuum leaks as this will result in deterioration of oil quickly. Vacuum leaks also cause the pressure to drop and in extreme cases may cause stalling of Diffusion Pump. Stalling will cause loss and deterioration of diffusion pump oil. Such leaks can be plugged by applying silicone vacuum grease to O rings and joints.   11. Sometimes back streaming of contaminants from the vacuum chamber takes place causing the oil to form sludge. This is preventable by installing filters above the chevron baffle of the diffusion pump.   12.    Silicone diffusion pump oil starts to decompose if it comes in contact with even trace elements of alkali metals (e.g. hydroxides  of sodium, potassium, cesium etc.). If process requires use of these then care should be exercised to prevent them reaching silicone DP oil.  
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Anshuman Punj (CEO)
B-21, Flatted Factory Complex, Jhandewalan
New Delhi- 110055, Delhi, India

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