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Paintball Gun Lubrication Primer

01 Feb 95
By: James "Bandit" McComber
Original Html conversion by: Jim Burke (jburke@bates.edu)

Editor's Note: The original version of this FAQ contained references to Teflon(R) brand PTFE, a material used in lubricants.  While PTFE is made by several companies, only PTFE manufactured by DuPont carries the Teflon(R) name.  After WARPIG, and some of WARPIG's sponsors received letters from the DuPont corporation threatening legal action in response to Mr. McComber's mentioning their product by name without listing the trademark registration, we have removed these references and simply replaced them with PTFE.

Teflon is a registered trademark of the DuPont corporation.


Disclaimer
This is my opinion, based on my own experience and research.

 Scope
This text covers some of the basic information concerning lubricants and their use in paintball guns. It is intended as a guide to help the owners of paintguns in their selection of proper lubricants. This is not a complete tribology text.


Contents


INTRODUCTION

When looking for a lubricant for your paintball gun, you should consider functional characteristics such as chemical compatibility, lubricity, viscosity, temperature range and oxidation stability. In addition to the above functional characteristics, you should also consider the safety properties, including toxicity and flammability.

 A description of some of the composite and synthetic materials used in paintguns is included, as well as a section on o-ring use.
 
 

COMPATIBILITY

When selecting a lubricant for use in a paintball gun, the issue of chemical stability becomes very important. Most paintguns manufactured today composite or plastic mechanical parts, as well as synthetic rubber seals of varying types. (see MATERIALS)

The non-metallic components are suseptible to chemical attack from solvents and incompatible oils and greases. The results of such attacks can cause damage in the form of deformation, deterioration, reduced service life, and accelerated failure rates. These types of damage to o-rings and plastic parts cause paintguns to develop abnormal operating characteristics such as sluggish actions, excessive drag of moving parts, CO2 leakage, valve malfunction, frequent ball breakage, as well as high maintenance. It is impossible to list all compatible and incompatible substances here, but here are a few common ones:
 
 

       O-RING/SEAL COMPOUND
            --------------------
               S - SILICONE (*)
               P - POLYURETHANE
               N - NITRILE
               T - PTFE

                  S   P   N   T     COMPATIBILITY RATING
LUBRICANT       +---------------    --------------------
  ---------     |
SILICONE GREASE | 3   1   1   1       1 - GOOD
      VASELINE  | 4   1   1   1       2 - FAIR
SEMI LUBE V.14  | 2   1   1   1       3 - DOUBTFUL
MOTOR OIL       | 4   1   1   1       4 - UNSATISFACTORY
KC TROUBLE FREE | 2   1   1   1       X - INSUFFICIENT DATA
WATER           | 4   1   2   1 
BRAKE FLUID     | 3   4   3   X

 CONSIDERATIONS: Temperature range, swelling, degradation,
                 seal integrity, both static and dynamic.

  (*) Silicone o-rings should not be used as dynamic seals, 
    and require special considerations.
     (see O-RING SEAL USE)

LUBRICITY

Obviously one of the important criteria to be looked at when selecting a lubricant, is its slipperiness. Ultimately you want all the moving parts to move smoothly, without excessive drag caused by the lubricant itself. The degree of slipperiness is relative to the surface finish of the parts being separated by the lubricant. Some lubricant oils and greases contain solid friction reducing ingredients such as PTFE powder, molybdenum disulfide, or graphite. Proprietary organic lubricants are becoming more commonly used to boost the performance of existing compounds. Most lube oils are slipperly enough for paintgun applications, however, viscosity should be considered next. (see VISCOSITY)

VISCOSITY

The primary purpose of the lubricant is to reduce friction and minimize wear by separating the lubricated surfaces with a thin film. This has to be done without imposing unnecessary viscous drag. Viscosity is a measure of a lubricant's resistance to flow. As temperature increases, viscosity decreases. Because of this the opposite is also true. Therefore, when you are selecting a lubricant for your paintgun, you must remember that CO2 is -54 deg. C in liquid state. A lube oil that is the consistancy of motor oil at room temperature, may become so thick during use in the paintgun, that it stops functioning due to viscous drag. (see TEMPERATURE RANGE)

One common measurement of viscosity is Kinematic. It is done by measuring the time it takes a fixed volume of oil to travel through a capillary tube with gravity, at a certain temperature. The unit of measure is called a Centistoke (cSt).

Not all oils respond to temperature in the way described above. The property of resisting changes in viscosity due to temperature change is expressed as Viscosity Index. The higher the V.I. of an oil, the less tendency for its viscosity to change with temperature. Look for a V.I. of at least 250.
 
 

TEMPERATURE RANGE

Some libricants don't list the viscosity index, but instead they just tell you the operating temperature range. This is fine provided it is truthful. For paintball guns, look for a temperature range like -55 to +50 deg. C.

OXIDATION STABILITY

Oxidation is a chemical reaction of the oil with oxygen and is a form of deterioration to which all petroleum oils are subject. It is accelerated by increased temperature, the presence of water and solid contaminants. As the oil oxidizes it forms degredation products such as sludge and organic acids.

 The viscosity of the oil will increase as the oxidation progresses, as will the presence of sludge and acids. These sludges may deposit on sliding surfaces, causing them to stick or wear. The acids may be corrosive to metal components of the paintgun. The addition of an anti-oxidant to the oil's base component, will improve its resistance to oxidation.

TOXICITY

Many common "off the shelf" lubricants are highly toxic and damaging to the skin and eyes. Try to use only those lubricants which are non-toxic, and do not damage eye tissue. As pointed out in section 8.4, some quantity of the lubricant is likely to spray away from the paintgun during use.

FLAMMABILITY

Petroleum products being what they are, tend to be flammable. Materials with flash points below 93.3 deg. C. are considered combustable while those with a flash point below 37.8 deg. C. are considered flammable. Try to find non-flammable lubricants for use in paintguns, and don't smoke while applying oil to, or using your paintgun.

MATERIALS

This section describes some of the more common plastic and elastomer compounds found in paintball guns. It also contains information about how these materials interact with various lubricants.

Silicone is good at resisting acids and will operate over a very wide range of temperatures, however it is not a very good choice for use as seals in paintguns because of its susceptibility to damage from petroleum products. Silicone rubbers tend to absorb silicone fluids, resulting in swelling and softening of the compound. Silicone o-rings are usually blue-white, clear or rust-brown in colour.

Nitriles are one of the best choices for use in paintguns. O-rings with a high nitrile content are good at resisting chemicals and can be designed to endure wide temperature variations. Nitrile o-rings must contain some plasticizers in order for them to function at extreme temperatures. Silicone lubricants tend to remove the plasticizers from the nitrile, causing excessive hardening and/or shrinking. Almost all nitrile o-rings are black in colour.

Polyurethane o-rings are used in paintguns because they are resistant to petro-chemicals and wide ranging temperatures and weather. They offer very good performance in abrasive environments, but lack the ability to withstand acids, ketones and chlorinated hydrocarbons. Polyurethane o-rings range in colour from yellow to off-white.

Polycarbonate resins (Lexan) are not used in the mechanics of paintguns, however they they are worth mentioning here for safety reasons. When lexan comes in contact with most petroleum products, fine cracks begin to appear, called "crazing". Crazing weakens the polycarbonate and eventually leads to complete failure of the structure. This effect is most severe when the lexan is under stress. ALL PAINTBALL GOGGLE SYSTEMS USE POLYCARBONATE LENSES. Most paintguns, ESPECIALLY SEMI-AUTOMATICS, will at some level, spray lubricant out and away from the paintgun. CHECK YOUR GOGGLES FREQUENTLY FOR CRACKS, they tend to form at the edges of the lens, where the lens contacts the frame of the goggle.

Nylon like PTFE and delrin is mainly used as a structural component, and in some cases as a fastener. As a seal, nylon is used in washers for static crush type applications. It is generally compatible with petroleum fluids.

Delrin is used to produce machined composite parts, such as bolts, pump handles, ball indexing ramps, and other mechanical parts. It is used where weight savings and durability are are required. Delrin is a known as a "self-lubricating plastic". This is because the compound has built in friction reducing ingredients similiar to PTFE.

PTFE is used primarily as a structural component in areas that require smooth operation, like valve guides, and bolt/hammer connecting rod sleeves. As a o-ring seal, PTFE is too stiff to be used in anything except static, compression type seals. PTFE is almost completely non-absorbant, and will not hold enough oil to aid lubrication. It is also finely ground and added to some lubricating oils to enhance the oil's slipperiness. When used in this type of application, PTFE (PolyTetraFluoroEthylene) is typically used in resin form, . PTFE o-rings are usually white in colour.

O-RING SEAL USE

Paintball guns contain o-rings and other seals that have different functions, in both static and dynamic applications. O-ring compounds vary depending on the type of sealing they do.

Static seals like the one under the power-tube retaining cap on a Nelson- based valve system, uses nitrile because it doesn't move during use. The o-ring around the top of a CA tank is static during use, but the compound used is polyurethane. This is due to the abrasive threads that it must pass through during installation.

Dynamic, or moving seals like the o-rings around the bolt and/or hammer in a semi-auto paintgun generally are made of polyurethane. These seals need to be abrasion resistant, yet flexible due to the reciprocating action. Silicone o-rings should not be used as reciprocating dynamic seals because of their lack of shear strength, low abrasion resistance and high coefficient of friction.

 Another type of dynamic seal is the "cup" seal. These are not o-rings, but generally, made of the same polyurethane material. Silicone is sometimes used in brass "cup" seals.

SUMMARY

There are many things to consider when selecting the proper lubricant for use in a paintball gun. Many of the properties outline here are inter- related, and dependant on operating environment. Just because a lubricant is chemically compatible with the o-rings, doesn't mean it will keep your paintgun functioning properly. Also, a certain lube might have all the right characteristics to make the gun work, but might be too toxic to be safe.

 Here are a few tips: Use a lube that is non-toxic. If you play in cold, wet climates, use a lubricant that has a low viscosity, high V.I. and has good oxidation stability. Hot, dry climates dictate an higher viscosity or a very high V.I. rating. The best advice I can give is to use a lubricant designed for paintball guns, or one recommended by the paintgun manufacturer.
 
 

COPYRIGHT 1995

James McComber
xcalibre@freenet.vancouver.bc.ca


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