Chop Gun or Hand Lay

There's never a reasonable debate with Tunnels when he gets on his undefendable horse and starts off. He states application and user defined techniques, that have nothing to do with the physical attributes of the cured matrix.

Discontinuous and randomly oriented short fibers are no match to continuous, long and well oriented fiber arrangement in a laminate. It's simple physics, regardless of the experience of operators. It's precisely the same physical properties as the comparison of particle board against plywood. Particle board has it's very short fibers, randomly arranged, while conventional plywood has continuous, full panel length and with fiber arrangement. Both panels use the same adhesive and the same fibers, yet conventional plywood is stiffer and stronger for the same weight and thickness.

The same is true with laminates (of any kind), a chopper laminate uses the same resin, just at a higher ratio than other laminate types and it uses the same fibers, which are short, discontinuous and randomly arranged. A cloth or directional fiber laminate has long, continuous fibers, arranged along load paths.

The simple truth is the fibers bear the loads and short fibers do a very poor job of this, instead relying on the resin's bond to them, which is why they're weaker and the resin content has to be higher. Couple these short, randomly oriented fibers with a weak resin system, like polyester and you have a heavy, overly thick, weak end product. Now, this may be good enough for some things, but race cars, boats, aircraft or anything else, that needs high strength to weight properties and a chopper gun laminate is discounted out of hand, for obvious reasons, none of which have anything at all, with the skill of the operator or the laminate schedule of this type of laminate.

There isn't any debate to this, just fanatical ramblings of some users, that don't understand the realities or physics of the materials involved. So, discussion of the "anisotropic" features of composites, which can be used to good advantage in designs, with the majority of fibres being placed along the orientation of the main load paths, is fruitless, even if such construction considerations can minimize the amount of parasitic material, that is put in orientations where there is little or no load.

 

Was that a sarcastic dig???

 

JTF, you must remember he'll grasp at anything to help support his indefensible positions. He doesn't believe in engineering, nor science, just what his hands have touched over the years. He can't support his arguments with anything other then bluster - no facts, no statistics - no physics, just unsubstantiated seat of the pants BS, which considering his other "positions", should taken with not a grain of salt, but the whole salt shaker.

 

Again everything you are saying is workers and operator problems .
During the times we had a quality controller standing watching and recording weights and measures of Glass !!, resin !!, and catalyst!!!, at the end of each spray session the quantities had to tally with what was written and i was always a fraction under rather than over weight and it was a compatition i had set myself to do glass to resin ratios and catalyst percentages were spot on . and whan i say close in talking 0.1 of a kilo on a job that required maybe 25 kilos or more of glass !!again practice and knowing simply by looking at the work and seeing if its ok or what not right .

The guy i worked with at Bonito craft in nz was the same he could spray the same as i do and as for watering eyes and the like , if that the way you want to work thats your problem because there no need at all .

You start to spray and cover a area and the laminaters come in behind you and you spray away from where they are on a slight angle and all the fumes and sprap are going ahead of the operater not in all directions and over people working !!
I am right handed so i spray to the left all the time i just wear a tee shirt and protective trouses and boots and a resperator but there are times when you can work without a resperator as all the crap is going away from you .

As for pulling a stand out and running on one there again thats the type of equipment you using . all the guns i have worked on have 100% trigger control so the sound of the chopper motor is what you have burned in your brain !!higher pitch dry glass!! lower pitch wet glass !!!. its all controlled by squeeze of the trigger . like i said before i could be standing or walking in the next building and know what was happening simply by the sound of the chopper and the pulse of the pump working in time with each other also the length of time all this was going on as to the quantity of material being consumed and going on the job .

Maybe im a little more it touch with my job than most people ,all these things are just second nature for me and i act acordingly to what ever situation i happen to be in .

Making in ground swimming pools out in the hot sun with no cover was the greatest challenge i ever had !! Pulling 3 strands of glass and able to stand on the part you just sprayed and rolled in less than 10 minutes later !!

As for making kart bodies !! there small size is not practical for chopper spray and in all reality you should be resin infusing not spraying or hand laying !! so you should be getting into Hermans pocket and then picking his brains for all the know how and seting up etc etc !!
If you have a lot to manufacture then make another mould or two and worked properly could be a full time ,one after the other job .
Could cnc cut all your materials with nesting software and get the absolute best usage and very little waste .
ITS almost automatic so while to sitting on the toilet thinking ,its still working and when you get back its finished cutting and siting ready and waiting for you to clear the table and stack your glass and draw out the next multi layers and away it goes again .Watched it cutting 6 layers of differant glasses in one go all perfect in shape and size . so for mass production an absolute nessesaty !!!
Absolutly beautiful to watch at the last composits show in shanghai a few months ago .

 

Acknowledging that fibers oriented 90 degrees or nearly 90 degrees to the ideal direction to carry a known load path are not "working" very hard and are dead weight (other than holding the working fibers together [?]) I'd like to see exploration of three areas:

1.) How does the efficiency of fibers change with angle to load in an epoxy or vinylester layup. For example, how effective are fibers oriented 5 degrees, 10 degrees, 15 degrees, 30 degrees, 45 degrees, and 90 degrees to the load path. How much additional glass weight at each orientation to a known load path is required to carry the same load.

2.) What length of fiber is long enough that additional length doesn't add strength in each type of resin.

3.) Summarizing a variety of areas of a typical boat from sides midbody to cockpit sole how much of the laminate is typically engineered for specific known load paths and how much fiber is there for forces which affect the laminate from "any and every direction."

 

Ok long strands have stretch and give and take so in a loaded situations they become more durable and will last and keep on working .
Short strands will give you ridgidity and siffness so its you choice what you us and how you us the glass
The angle of the strands needs to run across at right angles for efficency ,but in high loading and shock loading depending on what and how the loading is, then changing the angle of the glass makes it more durable and able to cope with the situation ,but as you change the angle an amount of stiffness can be lost ,which in reality is not a bad thing because stiff panels break and are supseptable to damage easyer than panels that have bend and give and flex to absorb shock and spring back again .
Resin is just the glue that holds all the fibres together dosent mater if its poly ,vinyl or over rated epoxy !!
I am into glass and polyester and vinylester resins only .

Carbon,kevlar and epoxy resins i am not interested in because the type of work i do they dont last !!

Sorry all this is possibly to simple for you to understand .
I know what works and what dosent ! its why boats i made using these really simple really basic principles are still going and in use even after 20 years while others designed ,engineered and spec-ed by the best minds in the industry ,made with twice as much glass were falling apart and broken now stacked behind a shed getting over grown with weeds .
When all esle fails pull the plug on the computer and get back to basics and think !!

 

Par,

You are the voice of reason and sanity.
Unfortunately as you said, tunnels will not attempt to learn anything, ever.

From now on I'm going to try and answer the original question, not tunnels.

Marc

 

You do realize that the OP stopped asking questions or responding back at post #10. As a matter of fact he said he's already ordered the system and will (hopefully) get back to us with his findings at some later date. This thread should then just quitely fade away rather then become yet another verbal battle ground. It's amusing but after a while it just gets damn boring.

MM

 

I'm certainly sorry for my part in it.

 

Tell it like it is !!

Tell it like it is!!! not exadurated twisted stories you heard from others !!. if you dont know first hand by doing the job yourself or being there at the time then say nothing !!

 

I understand fully Upchurchmr and Mike. I've made 4 contributions to this thread, each with an effort toward accuracy and a level of benevolence. This is my 5th post on this thread. Tunnels has (once again) bantered on, distorting reality, the OP's needs, ignored facts, physics, engineering and relied on his personal certifications in 3rd world outfits. For what it's worth, Tunnels has made 16 posts, prior to this and I suspect he'll continue ranting about what he doesn't know, but happily practices in blind ignorance. My problem with this sort of information transmission is it's fundamentally incorrect, which I real at generally and it's easily proven with some research on his part. He'd be a better laminator as a result and those seeking advise would get more accurate, reliable information, which is the whole point of contributions here, unless of course your Tunnels.

In regard to the OP's question, he'll find the chopper gun setup fast, but he'll have a great deal of difficulty, selling bodies that are on an order of magnitude heavier, than the competition. If he reduces the laminate thickness, to account for the excess weight, he'll have a weaker product, which again will sort itself out on the race track. I've built a small number of race car bodies and body parts over the years. All were light, strong and stiff, for their weight. None where chopper or CSM and all were directionally laid up with some finish cloth to make things pretty, except on the most serious pieces. My current tow vehicle has a custom hood that I laid up, 1/3 the weight of a replacement. Of course it's all biax with 2 ounce finish cloth on the outside. Not a single body builder, that offers competitive products, uses CSM or chopper gun bodies, except the classes, such as the Legend series, where all the bodies are the same and the weight problem is just assumed, to keep costs down.

If Tunnels was so good, why isn't a single racing team, purchasing their chopper bodies, at a fraction of the price of the hand laid, vacuum bagged or infused offerings? I see a wide open market for his special talents. Yep, he could build new F1 bodies at 1/100th the cost and pocket the difference. Yep, he's nuts, old and hasn't bothered to keep up with technology or industry advances in the last few decades, so you get what you get from him. Hell, I'm nuts and old, but I have kept up and still participate in industry advancement. Currently I'm running testing for three different companies on product viability and/or durability in the marine environment, plus two others for personal enlightenment for another forum member who specializes in just these products.

Tunnels, please try to keep up, you have some serious laminating skills. Maybe you can breeze through some information > http://www.gurit.com/files/documents/Gurit_Guide_to_Composites(1).pdf < Do a search for chopper gun and see what the industry thinks about it. If you don't like the result here, there are literally dozens of other sources for the exact same information (laminate properties). There's this new thing called G-O-O-G-L-E . . . try it, you'll be amazed.

 

Its not dig at all !!! just theres some one else out there that has exsperianced the same things i have .
Why do you people always twist things round so you only see the negitives and play on them continuosly cover and over :?:



Gurit used to be called High Moduals . Mr Richard Honey one of the origainal founding members i have known and worked with since the late 1970/80s ,during his early days during those times we spent lots times talking about glass and glassing and the basic principles that he laid out its what i have always used ever since those times and they all work .Its only when you try to step outside those basics that people get themselves into trouble and things dont work .

 

So, you agree with his assessment of chopper and CSM laminates? Would you like me to quote him on the subject?

Page 40:
"5.3.5.1 Chopped Strand Mat
Chopped strand mat (CSM) is a non-woven material which, as its name implies, consists of randomly orientated chopped strands of glass which are held together
- for marine applications - by a PVA emulsion or a powder binder. Despite the fact that PVA imparts superior draping handling and wetting out characteristics users in a marine environment should be wary of its use as it is affected by moisture and can lead to osmosis like blisters. Today, chopped strand mat is rarely used in high performance composite components as it is impossible to produce a laminate with a high fibre content and, by definition, a high strength-to-weight ratio."

Page 48:
"Description
Fibre is chopped in a hand-held gun and fed into a spray of catalysed resin directed at the mould. The deposited materials are left to cure under standard
atmospheric conditions.
Materials Options:
Resins: Primarily polyester.
Fibres: Glass roving only.
Cores: None. These have to be incorporated separately.
Main Advantages:
i) Widely used for many years.
ii) Low cost way of quickly depositing fibre and resin.
iii) Low cost tooling.
Main Disadvantages:
i) Laminates tend to be very resin-rich and therefore excessively heavy.
ii) Only short fibres are incorporated which severely limits the mechanical properties of the laminate.
iii) Resins need to be low in viscosity to be sprayable. This generally compromises their mechanical/thermal properties.
iv) The high styrene contents of spray lay-up resins generally means that they have the potential to be more harmful and their lower viscosity means that they have an increased tendency to penetrate clothing etc.
(v) Limiting airborne styrene concentrations to legislated levels is becoming increasingly difficult.
Typical Applications:
Simple enclosures, lightly loaded structural panels, e.g. caravan bodies, truck fairings, bathtubs, shower trays, some small dinghies."

Like I said, you can keep up, or wallow in what once was (decades ago) acceptable. The above, though not definitive or in depth on a technical level, certainly is in line with all (every single one) current testing and opinion in regard to chopper or chopped laminates (except for you Tunnels).

 

hi mrbcurry1, why not use vaccuum injection for youre go karts.
A friend of mine is crazy about composite materials, and made his own vaccuum injection system. If you have an old go kart, you can use it as a mould??

just a suggestion,

 

The guys orginal question was and i quote (I am just wondering if I switch using a chop gun system, does it hold up in same layer thickness ) so this personall attach and yet another put me down post is your answer to his question ??
my answer to his question was a simple yes !! it will hold up if the gun operater know what hes doing !!