I am in the process of finishing my 2nd gunstock, a Cz walnut factory stock, so I can get some practice. Ive read all the posts by other experienced members, including Ray and Chip, and Im doing the re-finishing per recommended method: chemical stripping, de-whiskering, sanding etc; I have now stained the stock, with a spirit based red mahagony stain; and now I am sealing it with a mix of polyurethane+boiled linseed+mineral spirits for the first coat, and plan on subsequent coats of PRO Custom finish.
My problem is, when I fine sanded the stock with the sealer mix, some of the stain came off in some places. Do I start all over again, stripping it and going from there? any other approaches?
Also, I noted some ares are soaked with oil. I have heated the stock with a hair dryer and washed it with mineral spirits, without significan improvement. Any tips?
Thanks all!
And Merry Christmas and Eid to all!

Double, double toil and trouble;
Fire burn, and caldron bubble.
Fillet of a fenny snake,
In the caldron boil and bake;
Eye of newt, and toe of frog,
Wool of bat, and tongue of dog,
Adder's fork, and blind-worm's sting,
Lizard's leg, and owlet's wing,—
For a charm of powerful trouble,
Like a hell-broth boil and bubble.

Chemical engineers spent careers figuring out finishes that work, and you insist on mixing 'em up.

It's one thing to use a sealer from one mfg, and a finish from another....

But you gotta' cook up your own stew?

flaco

Just buff more stain into these areas but I would use very litle on the rag almost a dry buff.

As far as oil removeal mineral spirits is kind of an oil in itself. I had a stock that leeched oil and I used thinner on a rag to dry it up but it took several times of wipe and let set a day or two then wipe again.

I'm with the flaco on this one. Your "mix" doesn't sound like the greatest to me. If you brought the stock to me as it is and asked me to refinish it, I'd strip it back down to bare wood, stain it to your desired color/shade, and finish it with the Pro Custom Oil and be done with it. Sorry if I rained on your parade.

Someone tell me What idiot told you to mix boiled linseed oil with urethane ?.
With mineral spirits ok with linseed oil ???. For what possible reason ?. Tung oil maybe in the correct portion and adding a small amount of cobalt or Japan Drier .

I don't want to start anything but why why why ???. Linseed oil is OLD School Dribble just like Shellac or Varnish finishes .
Oil finishes are inferior protection for wood exposed to the elements . I have no problem with hand rubbed oil stocks they look great .

I prefer the look ! , but with urethane protection which can be done without all that nonsense . Ph.D. Organic Chemistry . Strip it start over an do it correctly Please !.

Shoot Straight Know Your Target . ...

If you want strictly an Oil finish then there are several very good products on the market .
Try Brownells . If one could still obtain Dura Seal Gymthane it was the BEST bar none hands down . Worked for the NBA on basketball courts before Real durable urethane was wide spread . In general your Floor Finishes offer the most durable wood finishes if one stops to think about it .

I didn't mean to sound like some condescending ass which I can be at times . Sorry Merry Christmas too ALL .

Shoot Straight Know Your Target . ...

Okay, okay... I stole that.

It's a bunch of witches speaking.

A long time ago.

Still, I really like the witches issue.... As it turns out, there's some kind of metaphysics in gunsmithing. Religion, witches, whatever.

If I ever get to the point where I'm turning barrels on the lathe, don't be surprised if you hear me mumbling an invocation to Combustibus--the Patron Saint of Rifles--before I begin a job.

To get to the point, you have a couple of issues.

You cannot expect to sand in a finish over a thin layer of stain.

Just won't work.

As you now know.

I'd look for a finish that needs no more than knocking down with steel wool between coats.

And there's no need to re-invent the wheel.

Although eye of newt sounds good.

Please settle on a good finish from a reputable mfg that goes well over stain.

flaco

Indlovu, try wiping the stock with an acetone soaked rag until it's evenly de-stained before breaking out the MeCl stripper.

Instead of making your own version of Tru-Oil (BLO, urethane, and driers), buy some T-O and thin it to suit.

Yeti,
and since we're spouting off about being paper-smart,
Chem E.
Orgo's for memory-machines who can't do real math

quote:

Originally posted by Dr.K:
Someone tell me What idiot told you to mix boiled linseed oil with urethane ?

if you go to home depot or lowes and read the ingredients you will see oil, urethane, and solvents mixed by all the major manufacturers. they are hardly idiots.

in fact, IIRC, phil pilkington's oil finish mix was similar.

you may think phil, behr, deft and all are idiots, but I would disagree.

instead, it sounds like our friend is on the right track and in good company.

quote:

Do I start all over again, stripping it and going from there?

I think you will end up doing just that.

instead of staining the wood, tint the finishing oil. can't sand through that.

Thanks for the suggestions, especially Wm Shakespeare! will try eye of newt next!
I think im going to strip it and do it all over again. Sand, stain, pro-custom. no hellacious urethane-(ULP!) linseed mixes, i promise!

Mix all of the finish you want. I find it fun, and you can get finishes different from any commercial product. Talk to people who actually make stocks and get info from them. Play with the solutions and come up with what you like the best. Undertsand going in that there is no one universal "best." Depends on a lot of things, including the exact blank you use. Most finishes are "good enough" to work in every situation. But I also have friends who play with mixes to suit the blank. Same basic finish, but slightly different mixes. Depends on how anal you want to get about it.

Be very leery of self appointed experts who bash others and yet offer no concrete help, even when they are asked. Lots of professionals stake their reputations on concoctions they brew up and then field test on all of the contiennts. These are the people I owuld listen to if I were you. These topics are not covered in a theoretical and sterile classroom of higher education, and reality often throws egg in the center of the face of the self appointed experts. I can tell you, I have wiped egg off of my face more than one time. And you know what, I bet you I will do it again before I die!

I found this page on the web,don't know if it's good info or not. Concrete I would think so.

How to refinish a gunstock

OK, how about a little help for us non-stock makers. What is the best way to do a little touch up on a fine stock finish as it wears? I have a rifle that came out of the Martini-Hagn shop and it is getting some of the bumps and scrapes that are to be expected. I tried a tiny spot of Tru-oil and some Pilkingtons but neither acted like it would dry so I wiped them off.

Any help or should I call Hagn and get his advice?

Josh

Hello?

There's no need to consult other sites.

Some of the best stockmakers in the world post right here on AR, and they've been generous with advice.

I'd search posts by Duane, Chic, Bill Soverns, SDH, and in particular TC1 has used stain with great success.

flaco

Flaco-

Just to be sure you know (I am almost positive you do) you were not the self appointed expert I alluded to.

Josh-

Have you called M&H? Ralph Martini is incredibly giving of his metal working knowledge. I am sure they would tell you what they used on your stock when they made it.

Different finishes lend themselves to spot repairs to differing degrees. If it is oil, then the slacum from a Purdey's Worthog kit would be a good fit. Daly's Seafin or Laurel Mountain Forge (Permalyn) would be another couple of good things to try if you do not know exactly what they use.

In his latest book, Steve Hughes (SDH on this board) has a chapter devoted to stock refinsihing and touch up. He mentions Pete Mazur using "Pete's Mix 36", which is a finish of 1 part tung oil to 1 part linseed oil. I'll say this, Pete Mazur knows more than I will likely ever know about getting good finishes on wood and metal!

quote:

Originally posted by Dr.K:
Someone tell me What idiot told you to mix boiled linseed oil with urethane ?.........
Ph.D. Organic Chemistry . Strip it start over an do it correctly Please !.

Idiot??? I dont care if you have 5 PH.D.'s in all kinds of Chemistry. Thats uncalled for and really doesnt address his problem.


Indlovu - the blotches you are seeing are from you sanding back through the stain (and believe me I have done this myself...it doesnt take much). This is a difficult problem to fix without starting over. I avoid staining a stock unless I have to.

Yeti - gave the best advice to try and save the project from starting over.

Oh, and btw Dr K - that g33/40 rifle I just finished started with Permalyn, then Dalys Seafin, and then Slacum....which is linseed oil.

Great hearing from Bill on this one I also think a stock wipe down will do great.

WHY RED MAHOGANY to start with?
A good finish is work to fill the grain and I don't care what you use. Laurel Mountain stain and True Oil is still the best and easiest.
I have tried all of those magic grain fillers and they all leave more filling to be done anyway.
You want something that dries and dries fast, not months or years. Be prepared to do some work.
Any stain that is dissolved by the finish is junk. You want a color that penetrates deep so it is not rubbed off and Laurel Mountain fills that nicely.

Posted by delloro
if you go to home depot or lowes and read the ingredients you will see oil, urethane, and solvents mixed by all the major manufacturers. they are hardly idiots.

Have any clue as to how MANY OILS there are ?.

The simplest PU is linear in which the hydroxyl compound and the nitrogen compound each have a functionality of two. This can be represented by the following:

Isocyanate + Polyol = Polyurethane

The isocyanate can react with different chemical groups, so the final properties of the polymer will vary according to the reaction route taken.

Therefore the formulation of a PU must take into account every possible reactive constituent. PUs may have a very widely varying structure depending on the type of isocyanate and the type of reactive hydrogen components present in the formulation.

The presence or otherwise of the various groups along the urethane linkage will control the end properties of the polymer.

The curing of a PU can be regarded as the formation of a network, also called crosslinking, the extent or degree of cure is often expressed as the crosslink density.

The extent of cross linking may vary and will be reflected in the final properties of the PU, ranging from longer, linear chains of flexible elastomers and foams to the rigid, heavily cross linked polymers. Thermoplastic polyurethanes (TPUs) are a particular case. They are effectively co-polymers of a hard PU and a very flexible PU in which microphase segregation.
Pigments

Many PUs tend to yellow in the light albeit without any adverse affect on the physical properties. To produce coloured PUs pigmented pastes are added to the polyol formulation. The pigments, both inorganic and organic, improve the light stability of PU products.
Fillers

As with other polymers the use of fillers in PUs will yield products with modified performance. Calcium carbonate and glass fibres are most commonly used.




Polyurethanes – What Goes Into PUs?
Topics Covered

Background

Selection of a Polyurethane

Raw Materials

Isocyanates

Polyols

Polyethers

Polyesters

Pre Polymers

Common Additives

Catalysts

Chain Extenders

Blowing Agents

Flame Retardants

Pigments

Fillers

Basic Polyurethane Chemistry
Background

A PU is made by mixing together the ingredient chemicals (isocyanate and polyol see later) in predetermined proportions, which then react to form the polymer.

Uniquely, PUs utilise simultaneous polymerisation and shaping of the part.

The production of consistent end products depends on mixing, in precise ratio, the ingredient chemicals and maintenance of the appropriate processing temperatures. As the liquid isocyanate and polyol react to form the PU, the liquid mix becomes increasingly viscous eventually forming a solid mass. The reaction is exothermic and therefore heat is involved.

Other ingredients will be included in the polyol blend, for example the catalyst which controls the rate at which the liquid mixture reacts to become solid.

There are no hard and fast rules for obtaining the optimum PU end product, success is due to good formulation selection with well chosen and appropriate processing parameters and mould geometry. The process by which liquid polymers are converted to elastomeric or glassy solids is fundamental to the manufacture of PU products.
Selection of a Polyurethane

There are a number of steps:

Consider the requirements which the application will demand of the PU with respect to chemical and physical properties.

Based upon an understanding of what controls these properties select a few candidate PU systems. The properties of a PU are largely controlled by the chemical nature of the system and how it is processed so it is prudent to consult specialist suppliers and processors at this stage.

Establish that the converter can process the proposed system on existing plant. The important processing characteristics of the system will include viscosity, pot life, reactive mix ratio control, demould time and process temperature.

Undertake preliminary tests, make prototypes, conduct field trials and obtain customer approval.
Raw Materials
lsocyanates

Many commercial grades of isocyanates used for making PUs are aromatic in nature. Each isocyanate will give different properties to the end product, requiring different curing systems and, in most cases, different processing systems. An important property of an isocyanate is its functionality, i.e. the number of isocyanate groups (-NCO) per molecule. For cross linked PU applications the average functionality of the isocyanate is usually a little over two. The higher functionality isocyanates are used for special applications. When a di-functional isocyanate is used with a di-functional polyol a long linear PU molecule for elastomeric applications is formed. The common isocyanates used to make PUs are shown in figure 1.

Figure 1. Typical isocyanates

Many PU products, such as flexible foams, are made with toluene diisocyanate (TDI).

The other main isocyanate used is methylene diphenyl diisocyanate (MDI), the most widely used MDI product is `Crude MDI' with a functionality of about 2.8.

A monomeric derivative of MDI, called 'Pure MDI', with a functionality of 2 can be distilled from Crude MDI. `Pure MDI' is a solid at ambient temperatures and is usually modified to a liquid form for ease of handling.

The modified isocyanates and isocyanate pre-polymers with special reactivity characteristics are used when it is impractical to use the more conventional isocyanates. Such derivatives are formed from the reaction of the isocyanate with compounds such as amines, diols or triols.
Polyols

There are two main types of polyols used in the PU industry, polyethers and polyesters. Typical polyols used are shown in figure 2.



Figure 2. Typical polyols.
Polyethers

The more widely used polyethers have a relatively low molecular weight in the range of 500 to 3000 and are manufactured from propylene oxide (PO) and ethylene oxide (EO).

PO is the major constituent of the polyol, whereas EO is only included in small amounts to modify the properties of the polyol.

The functionality of the polyether polyol (number of active hydroxyl groups per molecule) can be varied and is normally 2 for elastomers, approximately 3 for flexible foams and up to 6 or more for rigid foams.
Polyesters

The polyester polyols are typically produced by the condensation reaction of a diol such as ethylene glycol with a dicarboxylic acid.

Polyester polyols tend to be more expensive, are usually more viscous and difficult to handle but develop PUs with superior tensile, abrasion, flexing and oil resistance properties. Consequently they are used to make PUs for more demanding applications.

A disadvantage of polyester based PUs is their lower hydrolysis resistance.
Pre polymers

In a pre polymer system, the polyol and isocyanate (either a polyester or a polyether) are reacted to give a pre polymer that may be either a liquid or a waxy solid.

The reactant ratios used ensure the pre polymer contains isocyanate groups at the chain ends. The pre polymer can, when required, be chain extended to give a high molecular weight cross linked product.
Common Additives
Catalysts

Catalysts have a key role in PU production being required to maintain a balance between the reaction of the isocyanate and polyol.

The combination of very complex PU chemistry and diverse processing and moulding conditions make great demands of the catalyst. Its main function is to exploit the diverse reactions to create a product with the desired properties.

There are two main classes of catalyst used in PU production.

Organometallics are used to accelerate the reaction and formation of urethane linkages and hence promote rapid curing.

The most popular organometallic catalysts are tinbutyltin dilaurate and stannous octoate. Tin catalysts are used to catalyse micro cellular elastomers and reaction injected moulded (RIM) systems.

Amines are the other major class of catalysts widely used in the making of PU foams. Some amine catalysts promote crosslinking whilst others assist in controlling the foam's cell structure.
Chain Extenders

Chain extenders are reactive low molecular weight di-functional compounds such as hydroxyl amines, glycols or diamines and are used to influence the end properties of the PU.

The chain-extender reacts with the isocyanate to affect the hard/soft segment relationship and therefore the modulus and glass transition temperature (Tg) of the polymer. The Tg provides a measure of the polymer's softening point and some indication of the safe upper limit of its working temperature range.
Blowing Agents

Cellular or foamed PUs are manufactured by using blowing agents to form gas bubbles in the reaction mixture as it polymerises. They are usually low boiling point liquids which are volatilised by the heat generated by the exothermic reaction between the isocyanate and polyol.

Rigid foams yield sufficient exothermic heat from the reaction to allow foam expansion in association with the blowing agent.

Flexible PU foams are usually blown by the C02 generated by the reaction of water and isocyanate (or in association with methylene chloride). Blowing of the foam can also be accomplished by the direct injection of air or gas into the foam. Chloroflurocarbons (CFCs) have been used as blowing agents but their effects on the ozone layer have led to restrictions of their use and they are being replaced by more environmentally acceptable alternatives such as pentane.
Flame retardants

Certain end use sectors now take greater account of possible 'worst scenarios' in materials selection.

These considerations will include the effects of smoke and toxic decomposition products on people, property and equipment. PU foams used in furniture are an example which spring to mind. Fire retardancy can be achieved by the addition of fluorine, chlorine, bromine or iodine compounds to the polyol. Solid compounds such as melamine and aluminium trihydrate are also important flame retardants.

Materials and products are continuously evolving and developing and the trends are now to lower smoke and fume generation, and in the much longer term `lower toxicity'. There is an increasing commitment to tougher requirements and in certain sectors of the PU industry this has led to the development of low or halogen free systems.
Pigments

Many PUs tend to yellow in the light albeit without any adverse affect on the physical properties. To produce coloured PUs pigmented pastes are added to the polyol formulation. The pigments, both inorganic and organic, improve the light stability of PU products.
Fillers

As with other polymers the use of fillers in PUs will yield products with modified performance. Calcium carbonate and glass fibres are most commonly used. The former primarily to make cheaper formulations, the latter are of growing interest in reaction injection moulding (RIM) technology (see later).
Basic Polyurethane Chemistry

The simplest PU is linear in which the hydroxyl compound and the nitrogen compound each have a functionality of two. This can be represented by the following:

Isocyanate + Polyol = Polyurethane

The isocyanate can react with different chemical groups, so the final properties of the polymer will vary according to the reaction route taken.

Therefore the formulation of a PU must take into account every possible reactive constituent. PUs may have a very widely varying structure depending on the type of isocyanate and the type of reactive hydrogen components present in the formulation.

The presence or otherwise of the various groups along the urethane linkage will control the end properties of the polymer.

The curing of a PU can be regarded as the formation of a network, also called crosslinking, the extent or degree of cure is often expressed as the crosslink density.

The extent of cross linking may vary and will be reflected in the final properties of the PU, ranging from longer, linear chains of flexible elastomers and foams to the rigid, heavily cross linked polymers. Thermoplastic polyurethanes (TPUs) are a particular case. They are effectively co-polymers of a hard PU and a very flexible PU in which microphase segregation of the hard phase occurs (figure 3).

Figure 3. Microphase separation of their hard segments.

The clusters of hard PU, shown as thicker lines, act as ‘pseudo cross-links’ and allow the material to behave as an elastomer. When the temperature is raised the clusters disassociate and the material can be made to flow, when subsequently cooled the clusters reform and the material again exhibits elastomeric properties.

Thus these materials show elastomeric behaviour at room temperature, but can be processed as thermoplastics. Hence the name of the material class, thermoplastic urethane elastomer.

Delloro: Your absolutely right WE are not IDIOTS !. Maybe I was little Harsh at my reaction to someone putting boiled linseed oil into Polyurethane . If I had done anything like that while employed by Akzo Nobel or Valspar ,I would have been fired on the spot !. I am one of those People who Consults for Deft aerospace coatings division along with several other coatings company .

So it looks like I can do the Math !. Maybe I can't read but failed to see linseed oil ; Tung oil as well as others but not linseed oil !.

Happy Holidays to ALL OF YOU ...

I at least have the education to admit when I'm Wrong , which happens every so often . I'm not a Gun Smith nor a stock maker . I have how ever made several Blanks for Stock makers in a wide variety of Woods from around the world . I've also worked in wood finished wood for over 40 years . Before I obtained my Degrees and changed my vocation . I was an importer as well as installer of so many different wood projects I lost count .

All of you can thank Myself as well as 3 other colleagues of mine for the Flexible paint that's on vehicles bumpers !. MPDIOL GLYCOL which was patented by ARCO CHEMICAL . By the way that Aerospace , Automotive and Marine coatings are URETHANE !. All of which I've been involved with for 25 years and counting .

I sincerely apologize to any of you which were offended by my use of the word Idiot .

I shall refrain from using that terminology in the future and use the correct phrase " Mental Midget " !.

Again Merry Christmas and Happy Holidays to ALL of YOU . ...

ROTFLMAO

As my Dear old Dad was fond of saying, "If you can't dazzle them with brilliance, baffle them with bullshit."

quote:

All of you can thank Myself as well as 3 other colleagues of mine for the Flexible paint that's on vehicles bumpers !

So your the guy who did that I was just saying the other day....If I knew who that guy was I would thank him. Thank You, and remember YOU requested I do so!

quote:

Originally posted by Dr.K:
Have any clue as to how MANY OILS there are ?.

sure, lots. mineral, animal, vegetable, and many divisions within each. there is also that figurative oil associated with your unctuous insincerity.

[Kaaa-SNIP from azom.com re: useless stuff, incl. thermoplastics, not the point here]

quote:

Delloro: Your absolutely right WE are not IDIOTS !

I never stated that you were not an idiot. I wrote that there were many people who did mix solvents, linseed oil, and poly, who were not idiots. now, if you are seeking to fall within that group of people that I stated were not idiots, then you would have to be a person mixing those three things. which would make you, by your own words, an .....

quote:

Maybe I was little Harsh at my reaction to someone putting boiled linseed oil into Polyurethane .

no, you were not a little harsh, you were completely rude.

quote:

If I had done anything like that while employed by Akzo Nobel or Valspar ,I would have been fired on the spot !.

were you formulating wood finishes for gunstocks when you worked for those companies?

quote:

I am one of those People who Consults for Deft aerospace coatings division along with several other coatings company .

not for wood gunstock finishes?

quote:

So it looks like I can do the Math !. Maybe I can't read but failed to see linseed oil ; Tung oil as well as others but not linseed oil !.

so what

here's a cut-n-paste of my own

Oil and Varnish Blends

Danish Oil falls into this category, they are made by mixing a small amount of varnish with a larger amount of a curing oil such as tung or linseed, thinning with mineral spirits and adding metallic dryers.

These oils give you the best of both worlds, the protection of varnish and the ease of application of straight oil. They are not suitable for high wear items such as a kitchen table, but are excellent for end tables, beds, night tables or mirrors.

Apply as you would a straight oil, but only leave on for 10 to 15 minutes before wiping off the excess otherwise the varnish ingredient will become gummy. Allow 12 to 24 hours between coats.

Varnish

Varnish is a straight oil with resin added such as polyurethane, Spar or Marine varnish has a higher oil component making it more flexible. Outdoor products have UV inhibitors added to prolong the life of your outdoor furniture.

quote:

Originally posted by Dr.K:The simplest PU is linear in which the hydroxyl compound and the nitrogen compound each have a functionality of two. This can be represented by the following:

Isocyanate + Polyol = Polyurethane

The isocyanate can react with different chemical groups, so the final properties of the polymer will vary according to the reaction route taken.

Therefore the formulation of a PU must take into account every possible reactive constituent. PUs may have a very widely varying structure depending on the type of isocyanate and the type of reactive hydrogen components present in the formulation.

The presence or otherwise of the various groups along the urethane linkage will control the end properties of the polymer.

The curing of a PU can be regarded as the formation of a network, also called crosslinking, the extent or degree of cure is often expressed as the crosslink density.

The extent of cross linking may vary and will be reflected in the final properties of the PU, ranging from longer, linear chains of flexible elastomers and foams to the rigid, heavily cross linked polymers. Thermoplastic polyurethanes (TPUs) are a particular case. They are effectively co-polymers of a hard PU and a very flexible PU in which microphase segregation.
Pigments

Many PUs tend to yellow in the light albeit without any adverse affect on the physical properties. To produce coloured PUs pigmented pastes are added to the polyol formulation. The pigments, both inorganic and organic, improve the light stability of PU products.
Fillers

As with other polymers the use of fillers in PUs will yield products with modified performance. Calcium carbonate and glass fibres are most commonly used.




Polyurethanes – What Goes Into PUs?
Topics Covered

Background

Selection of a Polyurethane

Raw Materials

Isocyanates

Polyols

Polyethers

Polyesters

Pre Polymers

Common Additives

Catalysts

Chain Extenders

Blowing Agents

Flame Retardants

Pigments

Fillers

Basic Polyurethane Chemistry
Background

A PU is made by mixing together the ingredient chemicals (isocyanate and polyol see later) in predetermined proportions, which then react to form the polymer.

Uniquely, PUs utilise simultaneous polymerisation and shaping of the part.

The production of consistent end products depends on mixing, in precise ratio, the ingredient chemicals and maintenance of the appropriate processing temperatures. As the liquid isocyanate and polyol react to form the PU, the liquid mix becomes increasingly viscous eventually forming a solid mass. The reaction is exothermic and therefore heat is involved.

Other ingredients will be included in the polyol blend, for example the catalyst which controls the rate at which the liquid mixture reacts to become solid.

There are no hard and fast rules for obtaining the optimum PU end product, success is due to good formulation selection with well chosen and appropriate processing parameters and mould geometry. The process by which liquid polymers are converted to elastomeric or glassy solids is fundamental to the manufacture of PU products.
Selection of a Polyurethane

There are a number of steps:

Consider the requirements which the application will demand of the PU with respect to chemical and physical properties.

Based upon an understanding of what controls these properties select a few candidate PU systems. The properties of a PU are largely controlled by the chemical nature of the system and how it is processed so it is prudent to consult specialist suppliers and processors at this stage.

Establish that the converter can process the proposed system on existing plant. The important processing characteristics of the system will include viscosity, pot life, reactive mix ratio control, demould time and process temperature.

Undertake preliminary tests, make prototypes, conduct field trials and obtain customer approval.
Raw Materials
lsocyanates

Many commercial grades of isocyanates used for making PUs are aromatic in nature. Each isocyanate will give different properties to the end product, requiring different curing systems and, in most cases, different processing systems. An important property of an isocyanate is its functionality, i.e. the number of isocyanate groups (-NCO) per molecule. For cross linked PU applications the average functionality of the isocyanate is usually a little over two. The higher functionality isocyanates are used for special applications. When a di-functional isocyanate is used with a di-functional polyol a long linear PU molecule for elastomeric applications is formed. The common isocyanates used to make PUs are shown in figure 1.

Figure 1. Typical isocyanates

Many PU products, such as flexible foams, are made with toluene diisocyanate (TDI).

The other main isocyanate used is methylene diphenyl diisocyanate (MDI), the most widely used MDI product is `Crude MDI' with a functionality of about 2.8.

A monomeric derivative of MDI, called 'Pure MDI', with a functionality of 2 can be distilled from Crude MDI. `Pure MDI' is a solid at ambient temperatures and is usually modified to a liquid form for ease of handling.

The modified isocyanates and isocyanate pre-polymers with special reactivity characteristics are used when it is impractical to use the more conventional isocyanates. Such derivatives are formed from the reaction of the isocyanate with compounds such as amines, diols or triols.
Polyols

There are two main types of polyols used in the PU industry, polyethers and polyesters. Typical polyols used are shown in figure 2.



Figure 2. Typical polyols.
Polyethers

The more widely used polyethers have a relatively low molecular weight in the range of 500 to 3000 and are manufactured from propylene oxide (PO) and ethylene oxide (EO).

PO is the major constituent of the polyol, whereas EO is only included in small amounts to modify the properties of the polyol.

The functionality of the polyether polyol (number of active hydroxyl groups per molecule) can be varied and is normally 2 for elastomers, approximately 3 for flexible foams and up to 6 or more for rigid foams.
Polyesters

The polyester polyols are typically produced by the condensation reaction of a diol such as ethylene glycol with a dicarboxylic acid.

Polyester polyols tend to be more expensive, are usually more viscous and difficult to handle but develop PUs with superior tensile, abrasion, flexing and oil resistance properties. Consequently they are used to make PUs for more demanding applications.

A disadvantage of polyester based PUs is their lower hydrolysis resistance.
Pre polymers

In a pre polymer system, the polyol and isocyanate (either a polyester or a polyether) are reacted to give a pre polymer that may be either a liquid or a waxy solid.

The reactant ratios used ensure the pre polymer contains isocyanate groups at the chain ends. The pre polymer can, when required, be chain extended to give a high molecular weight cross linked product.
Common Additives
Catalysts

Catalysts have a key role in PU production being required to maintain a balance between the reaction of the isocyanate and polyol.

The combination of very complex PU chemistry and diverse processing and moulding conditions make great demands of the catalyst. Its main function is to exploit the diverse reactions to create a product with the desired properties.

There are two main classes of catalyst used in PU production.

Organometallics are used to accelerate the reaction and formation of urethane linkages and hence promote rapid curing.

The most popular organometallic catalysts are tinbutyltin dilaurate and stannous octoate. Tin catalysts are used to catalyse micro cellular elastomers and reaction injected moulded (RIM) systems.

Amines are the other major class of catalysts widely used in the making of PU foams. Some amine catalysts promote crosslinking whilst others assist in controlling the foam's cell structure.
Chain Extenders

Chain extenders are reactive low molecular weight di-functional compounds such as hydroxyl amines, glycols or diamines and are used to influence the end properties of the PU.

The chain-extender reacts with the isocyanate to affect the hard/soft segment relationship and therefore the modulus and glass transition temperature (Tg) of the polymer. The Tg provides a measure of the polymer's softening point and some indication of the safe upper limit of its working temperature range.
Blowing Agents

Cellular or foamed PUs are manufactured by using blowing agents to form gas bubbles in the reaction mixture as it polymerises. They are usually low boiling point liquids which are volatilised by the heat generated by the exothermic reaction between the isocyanate and polyol.

Rigid foams yield sufficient exothermic heat from the reaction to allow foam expansion in association with the blowing agent.

Flexible PU foams are usually blown by the C02 generated by the reaction of water and isocyanate (or in association with methylene chloride). Blowing of the foam can also be accomplished by the direct injection of air or gas into the foam. Chloroflurocarbons (CFCs) have been used as blowing agents but their effects on the ozone layer have led to restrictions of their use and they are being replaced by more environmentally acceptable alternatives such as pentane.
Flame retardants

Certain end use sectors now take greater account of possible 'worst scenarios' in materials selection.

These considerations will include the effects of smoke and toxic decomposition products on people, property and equipment. PU foams used in furniture are an example which spring to mind. Fire retardancy can be achieved by the addition of fluorine, chlorine, bromine or iodine compounds to the polyol. Solid compounds such as melamine and aluminium trihydrate are also important flame retardants.

Materials and products are continuously evolving and developing and the trends are now to lower smoke and fume generation, and in the much longer term `lower toxicity'. There is an increasing commitment to tougher requirements and in certain sectors of the PU industry this has led to the development of low or halogen free systems.
Pigments

Many PUs tend to yellow in the light albeit without any adverse affect on the physical properties. To produce coloured PUs pigmented pastes are added to the polyol formulation. The pigments, both inorganic and organic, improve the light stability of PU products.
Fillers

As with other polymers the use of fillers in PUs will yield products with modified performance. Calcium carbonate and glass fibres are most commonly used. The former primarily to make cheaper formulations, the latter are of growing interest in reaction injection moulding (RIM) technology (see later).
Basic Polyurethane Chemistry

The simplest PU is linear in which the hydroxyl compound and the nitrogen compound each have a functionality of two. This can be represented by the following:

Isocyanate + Polyol = Polyurethane

The isocyanate can react with different chemical groups, so the final properties of the polymer will vary according to the reaction route taken.

Therefore the formulation of a PU must take into account every possible reactive constituent. PUs may have a very widely varying structure depending on the type of isocyanate and the type of reactive hydrogen components present in the formulation.

The presence or otherwise of the various groups along the urethane linkage will control the end properties of the polymer.

The curing of a PU can be regarded as the formation of a network, also called crosslinking, the extent or degree of cure is often expressed as the crosslink density.

The extent of cross linking may vary and will be reflected in the final properties of the PU, ranging from longer, linear chains of flexible elastomers and foams to the rigid, heavily cross linked polymers. Thermoplastic polyurethanes (TPUs) are a particular case. They are effectively co-polymers of a hard PU and a very flexible PU in which microphase segregation of the hard phase occurs (figure 3).

Figure 3. Microphase separation of their hard segments.

The clusters of hard PU, shown as thicker lines, act as ‘pseudo cross-links’ and allow the material to behave as an elastomer. When the temperature is raised the clusters disassociate and the material can be made to flow, when subsequently cooled the clusters reform and the material again exhibits elastomeric properties.

Thus these materials show elastomeric behaviour at room temperature, but can be processed as thermoplastics. Hence the name of the material class, thermoplastic urethane elastomer.

Dr. K

Just one question. Is the above authored by you?

The reason I ask is that in my science education, I was taught that I must give credit to the author when I use any portion of a text written by someone else. It is commonly called citing, and the (original) author must be listed. In my job, I would get fired for that mistake, and my reputation as a man of science would be tarnished.

Just wondering, as I would hate to have someone google "Polyurethanes - What Goes into PUs?" and come up with a paper that is written by someone else. Of course with your education and experience, that is surely not the case.

If, on the other hand you are the original author of the above, then it is an excellent overview, and I commend you.

Have a Merry Christmas, Sir.

Jim

No the Urethane dazzle is not BS nor was it
authored by me .Does it make it a lie ?.

In an obvious POOR attempt I was simply trying to show there is NO reason what so ever to use Linseed oil in any type of urethane .Simply foolish in my opinion it causes problems . After application is OK I guess but for what purpose ?.

No matter which way one chooses to finish a stock or any other wood project .

Thermoplastics has nothing to do with wood or metal urethane finishes in this context!.

Dependant upon HOW urethane is formulated it can be reactive or not UV curable or Moisture or catalytic and several other combinations . Many other methods including the addition of other ingredients will produce pliable or rock solid foam compounds .Which also have nothing to do with stock finishing !.

The proper method IMO and it's just that .

Is to abrade a woods surface so as to slightly open surface tension , wipe the wood back with a solvent mineral spirits I don't like to oily .Then apply a soluble dye spirit type stain Alcohol , Lacquer type work better than water based . Water raises grain it also does not penetrate as deeply . Oil stains also work but again don't go deep enough and simply surface seal the wood .

By using a spirit or dye stain then using a diluted mixture of urethane or oil if you prefer I don't . This allows penetration or a surface incising of the wood . Now one can abrade the surface with tru oil and what ever grit paper they desire , and apply more oil or Watco , tung linseed what ever you want to .

I how ever don't . I simply apply more urethane with less dilution after a couple of coats full strength . After proper drying I simply use a felt pad and rotten stone knock the gloss off too a satin or apply a satin finish on top of the gloss . How ever I do still rub out the finial finish with an oil or wax .

My main objective is to WATERPROOF PROTECT and have an ease of finish to repair .

What I really prefer is to spray Two part or plural component for all you purist Urethane, Aliphatic, Isocyanate, For Aerospace .

Maybe I was little Harsh at my reaction to someone putting boiled linseed oil into Polyurethane .



no, you were not a little harsh, you were completely rude.

I also apologized for being a condescending ass !.

quote:
If I had done anything like that while employed by Akzo Nobel or Valspar ,I would have been fired on the spot !.



were you formulating wood finishes for gunstocks when you worked for those companies?

NO as these company's don't manufacture weapons of this type and are in the business of coatings for substrate protection .

Here we go again : Oil Varnish blends are not true urethanes !. There are hybrid products on the market which use the " Term " urethane or varnish so as to skate on VOC'S compliances .

I can tell you without hesitation if one wishes to use an EXCELLENT Varnish then use . Eiphanes products !.

The best two oil finishes commercially available products ( were ) when mixed at a 40/60 ratio ( Flood ) Dura Seal )CWF & GYMTHANE PERIOD !.

If all of you like the oil finishes let me save you a tremendous amount of time and do away with archaic nonsense like Linseed oil .

Simply purchase Amazon Golden Teak Oil or Starbright Teak Oil . Available from a Marine outlet store !.

Like the gentleman said ; I don't think their idiots !.

I will stick with Urethane Aliphatic, Isocyanate type 1 . Next lesson Ceramics anyone ?.

With a twinkle of his Eye and a twitch of his nose and trusty computer up he rose too all a Merry Christmas as they choose .

quote:

Originally posted by Dr.K:
Next lesson Ceramics anyone ?.

ugh, no, I never could get the clay to mix with the linseed oil.

Ind, If you are looking for the old red color, I have had great luck with Phil Pilkingtons pre 64 red. I just followed the directions included with the bottle. A couple of weeks ago there was someone who said they had the recipe? I sure would like to hear what it is. That aside there has been some folks who have contributed to this with a lot more experience than I have. I'm just a beginner who's had some good luck. DW

If it's colors of stain you wish to obtain then Mohawk is where you look for the least amount of pain . Purchase several mix and match till it's one that your eye might catch .

delloro ;
ugh, no, I never could get the clay to mix with the linseed oil. Good one !.

It tis a forum is it not Ideas is what it's all about some good then some better left too others .

Regardless of the road I take it's in the best interest of all at stake .

I shall how ever attempt to fly the high road and lessen my load . I shall cease to go forth with my lessor than elegant speech .

Too ALL a Happy New Year . ...

Thanks all, guys, including Dr K.
I have restripped the stock and am waiting for Midway to deliver Pilkingtons stuff.
Will post pics when done.
Appreciate all the input, including Dr K's somewhat harsh criticism!
But: tru oil is a mix of linseed and urethanes, as someone pointed out. I was trying to replicate tru oil with the materials at hand.

Many thanks to Duane, Customstoxx and others; I bought Stephen Hughes book, and re-did the stock; (this is a 60 yr old Husqvarna mod 46)used pilkingtons finish. here are the results



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A a truly beautiful stock profile.

Well done...

On putting this forum to the use to which it was intended.

Asking for advice, getting plenty--some of it no doubt well intended, but hardly welcome--and having the patience to learn.

Congratulations.

flaco

Who said you weren't a professional stock restorer ?. Nice JOB !.

I simply use what ever products are pre manufactured , I could easily make my own formulas but for what purpose and at what cost !?.

Shoot Straight Know Your Target . ...

THANKS guys! it was great getting a lot of direction on this forum.