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.

 
Flow chart no. 1 - Degeneration of oil. 

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.

Flow chart no. 2 - Oil oxidation: chain cycle.

Oils therefore must be changed as per specified schedule.

Note: In this blog post I have explained the oxidation process of hydrocarbon/ mineral oils. In a different post, I shall explain how silicone oil degenerates.

                                                           

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Written by: Anshuman Punj.

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Evaporation Boat: How it is made

GENERAL PROPERTIES

Evaporation Boats are ceramic components required for vacuum deposition of various types of metals e.g. aluminum, copper, silver etc. over various substrates.

ALFA – Evaporation Boat (Supervac Industries)

They are of two types –

A) - 2 Component Boat – This type of boat is made with Titanium Diboride (Conductor) and Boron Nitride (Insulator).

B) - 3 Component Boat – This is made with Titanium Diboride (Conductor), Boron Nitride (Insulator) and Aluminum Nitride (Insulator).

Two Component boat is longer lasting and of better quality. In three component boat, Aluminum Nitride is added to bring down the cost. But consequently, it is lower in life and quality as well. Hence, users prefer 2 component boats to 3 component ones.

Production of Evaporation Boats is very expensive, involving heavy, costly machinery, raw materials and running energy costs. Also it is protected by patent laws. Therefore, very few companies in the world are producing it.

THE PROCESS

There are 5 basic steps in the production of Evaporation Boats:

1.     Preparing the powders – First of all, the powder particles are brought down to the desired size through milling.

2.     Blending of the raw materials – The powders are mixed together in the desired ratio and blended thoroughly for the sake of uniformity in the raw material.

3.     Hot-pressing – The blended raw material is then hot-pressed at a very high temperature (More than 1500⁰C) with a pressure of more than 150 tons. This delivers a big block of ceramic.

 

4.     Machining – The hot-pressed ceramic block is then cut into boats with a diamond cutter. Each boat is ground for a smooth finish and dimensional accuracy.  A cavity is ground into each boat.  

5.     Quality control – Each and every boat is measured for resistivity. After final inspection, boats are packed for shipping.

ALFA Boats come in various sizes and resistivity.

Supervac Industries make Evaporation Boats known with the trade name – ALFA ONE - are made in various sizes and resistivity as per the customer’s requirement. ALFA ONE boats come with Supervac Industries’ stamp of world- class quality and reliability.



                                                                                                       Written by: Anshuman Punj.

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Tips on Getting More Life Out of Your Diffusion Pump Oil

Diffusion Pump oil is of two types – Silicone and Hydrocarbon.

Most people these days prefer silicone DP oil because of the following reasons.

* Good quality silicone diffusion pump oil will have a high vapor point and therefore deliver a higher vacuum level.

* Will be thermally stable.

* Compared to Hydrocarbon oil, silicone DP oil will perform better over long periods of time with little to no degradation.

* This oil is also relatively safe from the standpoint of toxicity and flammability.

Diffusion pump oil is one of the costly consumables in a Metallizer. With a few precautions, its life can be prolonged considerably and much money saved.

Dos and Don’ts:

1)   Never open the pump when the oil inside is still hot. Doing so will affect the viscosity of the oil – it thickens and eventually turns into gel form.

2)   Care should be taken to top up the oil in the pump in a timely manner. In the absence of topping up, the reduced quantity of oil will accidently over heat and in extreme circumstances, can even crystallize into blue-grey powder or crystals.

3)   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.

4)   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.

5)   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.

6)   There should be no gross vacuum leaks as this will cause the pressure to drop. In a lay man’s language, this means that from some point air is getting inside the pump, not letting proper vacuum to form. Such leaks can be plugged by applying silicone vacuum grease to O rings and joints.

7)   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 corroded over time.

8)   Often back streaming of contaminants from the vacuum chamber takes place causing the oil to form sludge. This can   also happen if the Rotary vacuum pump is letting its vapors to escape into the diffusion pump. This is preventable by installing filters above the chevron baffle of the diffusion pump as well as on the line in between the rotary and the diffusion pump.

9)   Silicone diffusion pump oil starts to decompose if it comes in contact with even trace elements of alkali metals (e.g., sodium, potassium, cesium etc.). Use of the latter should be avoided in the presence of silicone DP oil.  

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Graphite Foil/Tape - SV-GF

Supervac manufactures Graphite foil (SV-GF). These foils are manufactured by a patented process of EXFOLIATION and hot pressing: a technology which very few companies in the world possess. Because of its excellent electrical conductivity, anti-corrosion and thermal resistant properties coupled with compressibility and flexibility, SV-GF works outstandingly in various applications.

fig.1

As shown in fig.1, graphite foil is used as an electrically conducting gasket between the hot evaporation boat (up to 1500⁰ C) and the copper clamps. It serves various important functions here. 

1.    It has to let as much as 700 amps. of current pass without any resistance.

2.    On one side, it has to protect the expensive evaporation boat from getting over-heated and cracking.

3.    On the other side, it has to protect the copper clamp from overheating and melting.

Good quality graphite foil performs all these functions effortlessly. SV-GF’s pure, compressive strength packs in denser amounts of graphite per sq.cm.

If, for the sake of cost cutting, cheap plumbing grade graphite foil is used, it causes immense damage to the machinery, the process and the product involved. These low grade graphite foils contain various binders like rubber compounds, adhesives and resins etc. in them. Therefore they are not 100% pure. On being used inside the vacuum chamber, these binders release various gases which affect the vacuum adversely. Also, these gases adhere to the thin film being metalized and bring down the quality of metalizing. Because of binders conduction is not 100%. This causes current loss, sparking and overheating of Evaporation boats as well as of Copper Clamps.

Following are the properties of a good quality graphite foil -

• Should be very flexible

• Very compressible

• Very Pure – should contain no bonding agents like adhesives, rubber compounds or resins.

• Corrosion resistant

• Temperature resistant- in the absence of any binders, pure graphite SV-GF can withstand very low temperatures of cryogenic liquids like liquid oxygen to very high temperatures like those of molten metals like molten steel and aluminum.   

• High tensile strength for a paper-like product

• Should not melt even at very high temperatures

• Excellent sealing characteristics

• Excellent insulating barriers

• No cold flow or creep phenomenon

• Self-lubricating – should have a very low co-efficient of friction to prevent cleaving and grazing between machinery parts.

SV-GF comes with all the above qualities. It is available in all the sizes for the convenience of our valued customers.

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Diffusion Pump Maintenance

The entire process of vacuum deposition rests on the foundation of efficient working of Diffusion pump. Good quality Diffusion pumps are like work horses: they are capable of functioning effortlessly for long periods of time provided they are fed nicely and taken care of. For diffusion pumps, the fodder is diffusion pump oil.

Diffusion pump oils are of two types – hydrocarbon and silicone.

Most diffusion pump users these days prefer silicone oil to hydrocarbon because of many reasons; one of them being – easy maintenance of the pump in case of silicone diffusion pump oil. Unlike hydrocarbon oil, silicone diffusion pump oil does not leave any deposits – carbon or otherwise – on the jets of the diffusion pump. Hydrocarbon oil is chosen only where cost cutting is required.

Supervac Industries manufactures both types of diffusion pump oils – Ultra high vacuum Silicone diffusion pump oil (SV-Sigma) and Hydrocarbon Diffusion Pump oil (SV-Delta).

Silicone oil should never be mixed with hydrocarbon oil. In case a pump has been running on hydrocarbon oil but now needs to be run on silicone oil, the diffusion pump chamber should be opened up, cleaned thoroughly with alcohol, other solvents, soapy water and de-ionized water. After that the opened chamber of the pump should be left to dry completely in a closed, clean environment for at least 3-4 days.   

WARNING: There should be no residual alcohol or moisture left in the pump. Reason?

1.     This can contaminate the oil that will be charged after the cleaning.

2.     Residual vapors increase the vacuum time.

In normal circumstances, if a good quality Silicone Diffusion Pump oil is being used then  diffusion pump needs to be opened up for cleaning only once every 4-5 years. Unnecessary opening up of the pump (as some freelance ‘maintenance experts’ tend to advise gullible customers) can damage the pump as they are not meant to be opened repeatedly. Also, this is an absolute waste of useful machine time and money.

All that is needed to be done for normal oil change is –

1.     Open the drain cock of the diffusion pump AFTER it has cooled down and let the oil flow out completely.

2.     Close the drain cock.

3.     Charge the new diffusion pump oil.

  

   

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BEWARE! DC-704 USERS

It is quite understandable that when a consumer is extremely satisfied with a product, he tends to ask for the same over and over again. In the vacuum world, DC-704 was the undisputed king of vacuum oils for a long time. Then, in 2012, Dow Corning, the American company manufacturing this oil; for reasons best known to them only; decided to stop the production of this oil and along with it – DC-702 and DC-705 also.

For a while this caused world-wide panic, leading to overstocking of these oils by the user companies.

Soon, the users, world over, acting wisely, found equal, in fact even better, options than this outdated oil. But for a few companies, this fascination, bordering on mania, for an ancient, though reliable product refuses to die down. Supervac Industries manufactures Ultra High Vacuum Silicone Diffusion Pump oil (SV-Sigma) which has proved its mettle against DC-704 time and again.

Even when DC-704 was readily available, most companies took into account SV-Sigma’s excellent performance plus its sensible price and converted to using Supervac’s Ultra High Vacuum Silicone Diffusion Pump Oil (SV-Sigma). Today these people make a loyal fan base for the company which is growing substantially.

Absence of DC-704 coupled with its still widespread demand has given an opportunity to many unscrupulous people to pass on spurious oil (often packed in tin cans) as DC-704. This so-called DC-704 oil is nothing but cheap recycled hydrocarbon oil distilled many times over to give it a light yellow color. Surprisingly, the innocent users fail to take into account that DC-704 used to be colorless silicone oil packed by Dow Corning in plastic cans. This spurious oil can cause serious damage to the costly plant and pumps.

Innocent, gullible people who are still hankering after DC-704 should give up their illogical love affair with a dead product.

Supervac Industries is successfully supplying their Ultra High Vacuum Silicone Diffusion Pump oil (SV-Sigma) not only within India but also to many other countries around the world for the last almost 9 years.

                                                                                                 

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Caution! Vacuum Pump Users

The role of Rotary vacuum pump (also called Roughing pump), in creating a smooth vacuum cycle cannot be stressed upon enough. In turn, this makes rotary/mechanical pump oil an important factor in the smooth running of the vacuum pump.

Unfortunately many vacuum pump users do not realize that rotary vacuum pump oil is not an ordinary lubricant. It is a special fluid, manufactured, keeping in mind the required thermal and oxidative stability and is absolutely different from motor oil.

Motor oils are lubricants made for car/scooter/truck engines. They have a different viscosity index and carry no vacuum properties.

 

Motor oils contain numerous additives like rust inhibitors, anti-corrosion compounds etc. that are indeed required for a motor engine. But the same elements present inside a vacuum pump can become potentially harmful. Inside a vacuum pump, under high temperature and low pressure, these additives get separated from the base fluid and stick to the interiors as gummy substances. This affects not only the vacuum pressure but also harms the pump.

Also when working temperature of Rotary Pump which is about 80⁰C is reached, motor oils start releasing vapors. This destroys the vacuum. Whereas Vacuum oils during manufacturing are heated to 300⁰C under high vacuum. So they do not release any vapors.

Supervac Silicone Rotary vacuum pump oil (SV-77) and Supervac Hydrocarbon rotary vacuum pump oil (SV-68) are free of such harmful agents.

They are also free of aromatic compounds. SV-77, a next generation, triple distilled, synthetic rotary pump oil is an excellent product manufactured by Supervac Industries. Along with excellent lubrication it delivers ultimate vacuum of 6x10‾⁴ Torr. Its life is almost 3 times that of ordinary lubricant/motor oil and does not turn to sludge, thereby, bringing down the requirement for pump maintenance. SV-77 has received tremendous positive response from the vacuum industry.

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