# Hot plates and the lighting will not last



## Frankk12 (Aug 15, 2009)

I am wondering how Harold Heated his chemicals inside the fume hood and about light
Because hot plates will not last and lights 
Thanks


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## EDI Refining (Aug 15, 2009)

We made a tray for under our hot plate, with an air inlet, circulating air up (directing fumes away).

As for the light, just a simple clear plastic cover, would do the trick


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## goldsilverpro (Aug 15, 2009)

There are standard, moisture proof, incandescent bulb fixtures, made of PVC and glass.


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## Harold_V (Aug 16, 2009)

Frankk12 said:


> I am wondering how Harold Heated his chemicals inside the fume hood and about light
> Because hot plates will not last and lights
> Thanks


I used a three burner gas hotplate. I had no interest in using electricity, if for no other reason, I also incinerated in my fume hood and needed open flame. I was perfectly satisfied with the setup, and used it for the entire duration of my refining career. The one problem I had was ruining the valves from excessive heat, but they'd last a good long time, and were inexpensive to replace. 

Light?

I used an 18" fluorescent lamp that had a heat proof glass lens between the light fixture and the inside of the hood. The lamp mounted on the outside. You can see it in the picture, below. It was housed in a piece of stainless. The light is the item just above the opening of the hood. The top protrusion is the cover for the filter. 

Harold


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## Anonymous (Aug 16, 2009)

Harold,
Does that hood use a ventria effect to evacuate the fumes? I am trying to figure out how to build one that will suck the fumes out and pull them through sodium hydroxide solution to netualize them without having the fumes go through the pump.

I think I can have the venturi pull a vacuum on the sodium hydroxide solution with the supply from the fume hood fed in at the bottom of this soltuion.
I have a few blowers from 1/2 hp to 1 1/2 to choose from. 

thanks
jim


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## Harold_V (Aug 17, 2009)

No. My blower was dismantled and fully coated with an acid resisting epoxy. It is also a paddle wheel, not a squirrel cage. I ran that particular setup for about 10 years. In that time, I had to replace the blower assembly once. It was in good condition when I sold the refining business, and went with the sale, so if a good job of covering the components is accomplished, they have a very respectable life expectancy. Remember, I processed daily, and for long hours. 

While I filtered my exhaust, it was filtered to recover values, not to remove contaminants that are best recovered as you suggest. I am not able to provide any information in that regard, as it was not something I did at the time. I commend you for considering the removal of harmful substances. It's the right thing to do. 

Harold


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## golddie (Aug 17, 2009)

I went to google for this and I was not able to find much about it
Does anyone have a link
Thanks



> ventria effect to evacuate the fumes


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## golddie (Aug 17, 2009)

```
While I filtered my exhaust, it was filtered to recover values,
```

Hi Harold
How did you do this
Thanks


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## Harold_V (Aug 17, 2009)

golddie said:


> ```
> While I filtered my exhaust, it was filtered to recover values,
> ```
> 
> ...


The top cover you see in the picture exposes a slot when removed. The slot accommodated 20" x 25" furnace filters. When they got loaded, they were removed and incinerated. 

The fume hood was built with trapping values in mind. For lack of better description, the air flow worked much like an exponential horn in a sound system. The design of the hood, with a sloping interior, created a larger and larger area in which the air traveled, slowing it down so it could drop coarse particles. The very light particles got trapped by the filter. The sloping area created a void in which the solids could accumulate. 

Cleaning out the fume hood, which was done on a roughly two year schedule, never failed to yield less than 8 ounces of gold. 

Do keep in mind, I used my hood daily, and seldom turned off the blower. I also incinerated filters and polishing wastes regularly, which was the source of the solids in question. I processed thousands of ounces of gold, so the hobby refiner isn't likely to enjoy the same results. 

Harold


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## Anonymous (Aug 17, 2009)

Harold,
You really got a good head on your shoulders, I never even had the thaught cross my mind to take the blower appart and coat with an epoxy.
Thanks, that will simplify things allot. 

Jim


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## Refiner232121 (Aug 17, 2009)

I wonder what this means when you use a scrubber


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## Harold_V (Aug 18, 2009)

Refiner232121 said:


> I wonder what this means when you use a scrubber


What it would mean to me is that anything that was harvested by the scrubber should be refined for values. All of this equipment can work together if you use the proper procedures. Keep in mind, some of the "losses" when refining consist of vapors that carry dissolved metals. If you introduce the discharge air to a wet scrubber, the values will be found there. Unless a pH change is accomplished, they may stay in solution. I believe some monitoring of the scrubber would be warranted to determine if and where values accumulate. 

As far as painting the blower with epoxy, one of the requirements is to sand blast the old covering (paint) until you are down to bright metal. Otherwise the remaining paint will lift, preventing a good bond of the epoxy. Any surfaces of steel or aluminum exposed to acid fumes will enjoy a very short life-span. 

Being a machinist, it was easy for me to blast the purchased blower (W.W. Grainger, one of the clog free types) in house. Those without a blast cabinet may have to hire the blasting done. Make damned sure they understand that NO paint can remain, that it must be blasted down to clean, white metal. Follow the instructions that come with the epoxy to the letter if you expect performance. Make sure the epoxy paint in question is suited to acid exposure. Not all are. Many do not require primer. 

For the blower, a ¼ horse is adequate for a nice fume hood. Moves about 900 cfm as I recall. I would not recommend anything larger, and you may consider smaller if it's available, especially if you have no designs on incinerating with your hood. Mine was constructed totally of asbestos, clear to the roof, where it discharged. No fear of fire. 

Harold


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## 4metals (Aug 20, 2009)

Harold,
Your modification of a standard Grainger blower with a clog free impeller is very interesting to me, considering you also did some burning in the same hood. Obviously the hood was made of something fireproof and acid resistant (ahhh the good ole days when asbestos was legal!) but the treatment of the blower (with epoxy) and it's longevity intrigues me, I know the impellers you are talking about and they are usually cast alloy with no hidden nooks where you couldn't coat with epoxy. The Grainger blowers usually pack more CFM than the PVC lab blowers but their corrosion resistance has always been an issue. You must have epoxy coated the inner shroud and the bearing shaft very well to seal it good enough to get that kind of life. Any preventative maintenance on the blower? (aside from greasing the bearings) 

As a point of reference, how many gallons of 70% nitric on average did you consume a day? This kind of implies the acid load the blower saw. Also how high was the stack? I assume you didn't have a scrubber as most blowers pull through a scrubber to lessen the load on the blower as well. Plus you had outside make-up air too, that can really slow things up in the winter! Did you use a blower in sync to provide make up air or did the exhaust draw provide it all? A-lot of questions I know and I apologize but your system seemed to have it together! 

When I posted on building a hood and scrubber a lot of members balked at the blower price for a corrosion resistant blower. This could be a cost effective alternative.


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## Anonymous (Aug 20, 2009)

Harold_V said:


> Refiner232121 said:
> 
> 
> > I wonder what this means when you use a scrubber
> ...



Harold, I get them for free, so I guess even if they do not last forever it would not matter much. I was thinking bigger because I was going, and still may, to use the venturi to pull a vacuum on the fume box. If I go with the direct drive I also can get 1/4 - 1/20 hp for free so that is not a problem. I do not do much so I really dont need a large hood. I was thinking like 2 ft square for the foot print about 3 ft high, so I could also include a pre filter to trap solid particulates. I have enamald sheet metal and all the plexiglass I could ever need. Would the enamald (stuff used on appliances and cookware) hold up? 

I am not just going to use mine for chemical, but also for grinding fingers and stuff to contain the fine particles before refining.

thanks
Jim


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## goldsilverpro (Aug 20, 2009)

I got them for cheap - there are jillions of good ones in scrap metal yards. I once had 2 ordinary belt-driven, 9" or 10" squirrel-cage blowers, in tandem, mounted inside of a 12' fume hood - the motor was on top of the hood. It took 3 or 4 years of daily acid work before they completely fell apart and stopped exhausting. Went to the scrap yard and got another pair.


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## dick b (Aug 20, 2009)

Hello:

Just for comparison, I'm making my fume hood 51 3/4" W X 25" D X 38" H. Similar in style to what you see on ebay for a lab hood.

I'm putting a rectangular glass window in the top so I can set a 4' flourescent light on top and plexiglass doors on the front, similar to a cabinet because I don't have a high enough ceiling to make it slide up like a regular lab hood.

I'm setting it on a cabinet with casters so I can move it around to clean up.

I decided to use 1/2" gypsum tile backer to make it out of. That way its acid and fire resistant. I am glueing all the parts together with polyurethane adhesive. 

It will have a filter and scrubber system similar to what was discussed in the post on building an acid resistant hood and scrubber by 4metals in this section.

When I get it all finished, I'm going to spray paint the inside with white epoxy appliance paint.

Won't be real soon, but I intend to take some pictures and post them for all to see.


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## PreciousMexpert (Aug 20, 2009)

Hi Dick b
I would like to see the pictures
You said they are on ebay
Can you give the link
Thanks


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## dick b (Aug 20, 2009)

Yes, just searh fume hood in lab equipment. Dickb
search this number 110426353403


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## Harold_V (Aug 23, 2009)

4metals said:


> You must have epoxy coated the inner shroud and the bearing shaft very well to seal it good enough to get that kind of life. Any preventative maintenance on the blower? (aside from greasing the bearings)


The entire blower housing was sand blasted and fully coated, inside and outside. The first replacement, which came several years after it was put in service, was the result of some of the inside corners beginning to lose the epoxy paint. The blower was still functioning well, but it was easier to replace it when it was down (for cleaning and examination). As far as service was concerned, the blower ran flawlessly. There was never any maintenance required. I insured that the motor had ball bearings. I also determined that my filtering system was doing an adequate job. There was very little on the impeller, or lining the stack, even after ten years. By sharp contrast, I would peel a thick layer off the inside of the fume hood in the air handling chamber, just before the filter. I did that on about a two year interval, and recovered no less than 8 ounces of gold for my trouble. 

As you alluded, the impeller was an alloy, aluminum in fact. I was concerned that it may not hold the epoxy, but it proved to hold it well. I did experience a little vibration, due to the uneven painting. Given the opportunity to do it again, I'd likely try to spin the impeller slowly while it was being painted with a spray gun. 

The only part of the motor that was exposed was the end of the shaft. I coated it with a little grease on assembly and never worried about how it would react. As it turned out, that was acceptable. 

Part of the success was due to using the hood for incineration. That would dry out the assembly, and I incinerated frequently. I expect I would have enjoyed less success had I not. 

The hood was made entirely of asbestos, using long stainless bolts with maximum thread exposure to the very weak asbestos board that was used. I was given a stack of 1¼" asbestos board, bonded with a plastic of sorts. The sheets were about 19" wide and 8' long, remnants of what was used for countertops of some description. I used this material for the sides of the hood. I still have a little of the board left, which I have targeted for the countertop material for my burnout oven for my investment casting room. 

I used a material known as Colorlith (not sure of the name) for the countertop where the hood stood. It, too, was asbestos. Having experienced carbonizing of wood beneath the burners, I put six inch high pieces of the board on edge, then mounted the working surface. That gave 6" of air space under the burners, beneath the working surface. While the compartment, which housed two drawers, would get quite warm when incinerating, it was never hot enough to be a concern. Front and back panels of the hood were made of 3/4" thick asbestos. 



> As a point of reference, how many gallons of 70% nitric on average did you consume a day? This kind of implies the acid load the blower saw.


My rather humble operation would be better judged by the liters that were consumed daily rather than gallons. Towards the end of my operation, I was buying thee drums of nitric annually. 



> Also how high was the stack?


The roof of the castle was a very low pitch, something like 14" in 15', so there wasn't much sticking out above the roof line, which was below the parapet. I'll have to make a guess on height, but it wouldn't have been more than about 8' from the top of the blower to the end of the stack. I fabricated a square cover that would prevent rain and snow from entering the stack. It was epoxied to the inside of the stack with four pieces of Transite, about ½" thick. 



> I assume you didn't have a scrubber as most blowers pull through a scrubber to lessen the load on the blower as well.


That's correct. I had thought of one time and again, but nothing ever came of the thoughts, then I decided to retire and sold the business. 



> Plus you had outside make-up air too, that can really slow things up in the winter!


Heh! Learned to wear a warm coat during the winter months, and did a lot of sweating in the summer. You may have looked at the picture. There is a 6" diameter tube leading to the side you see. That was the air supply, and it had a twin on the opposite side, each with a butterfly valve to control the intake air. I pulled air from a galvanized manifold I installed in the ceiling before hanging the drywall. Try as I might, I can't remember where I put the fresh air intake for the manifold, but I had it planned such that it would pretty much be assured it would get fresh air, not air that was being discharged from the stack. 



> Did you use a blower in sync to provide make up air or did the exhaust draw provide it all? A-lot of questions I know and I apologize but your system seemed to have it together!


I relied on the blower to pull fresh air, which it did with a vengeance. A pwered supply could prove troublsome in that I wanted to keep a negative pressure in the lab at all times, to keep fumes at a minumum. With acids in use in an ongoing basis, the atmosphere had to be constantly flushed. For that reason, the hood was rarely turned off. 

Needless to say, when I was incinerating I needed a huge air flow to keep things cool, but when I was evaporating it was very desirable to have just enough to keep the fumes moving in the right direction. As it turned out, the two 6" supply tubes introduced air at such a high velocity that it was troublesome. I would have been wise to go to larger pipe. Instead, I simply operated with the window open slightly, so a good portion of the air being discharged was pulled in from the window. It was only about two feet from the hood opening. That was the only part of the entire system I wasn't happy with, although it functioned well enough for me to never change. 

I could operate my hood with the opening closed off. I had a piece of tempered glass that fit the opening, so I could observe what was happening, and with the two butterfly valves, I could throttle down the air flow, but I typically had so many things going on at one time that I had to have access to the hood on a regular basis. As a result, I rarely used the cover. 



> When I posted on building a hood and scrubber a lot of members balked at the blower price for a corrosion resistant blower. This could be a cost effective alternative.



All depends on what you consider cost effective. As I recall, the epoxy I purchased sold for something like $180/gallon. The epoxy I used to build the transition for the blower, rectangular to round, 8" Transite, was also quite expensive, although I don't recall the price. It was a neat product, set by heat. It worked with a small applicator, such as one used for caulk, then the joints were heated by the hot plate. I had my doubts, but the epoxy held up better than the Transite. While I never had to replace anything made of asbestos, there was marked degradation, but it also had been in service over ten years. 

I likely would have gone a different route, but I knew how I'd use my hood, and had already had a fire, almost losing the house we owned before building the castle. Didn't want to take any chances with a faulty design setting yet another fire. 

All in all, the refining experience, for me, was very rewarding and revealing. I cherish the memories! I have no interest in refining now, but given the same set of circumstances, I'd do it all over again. 

Harold
edit: corrected format so one of the quotes would display properly. No change in content.


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## glorycloud (Aug 27, 2009)

I hope that you write a book one day about your refining and business experiences. Not so much for
the how-to's and where-for's of refining ( although that I greatly enjoy reading about certainly 8) )
but for the memories you just spoke about and the pleasure you derived by doing interesting work
and doing it well.

I love reading those kinds of musings! If you write it, I will buy a copy. :lol: 

Thanks Harold!!


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## golddie (Dec 1, 2009)

I found these asbestos tiles
http://cgi.ebay.com/Antique-1950s-Asbestos-Vinyl-Floor-Tiles-Green-Marble_W0QQitemZ130346986038QQcmdZViewItemQQptZTile_Flooring?hash=item1e59492a36

I said maybe i could make a hood like harolds with these 

should I make one layer of asbestos and on the outside layer have stanless steel
I can attach the asbestos with stanless steel bolts.
I was reading harold writting and I think this is how he did it.
But there will be gaps where the asbestos join togther.
I said maybe I could have the outer stanless steel cover welded so that smoke does not come into the room.
I hope you could understand what I said
Thanks


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## qst42know (Dec 1, 2009)

These tiles will not work. 

They are vinyl with asbestos fibers blended in for wear resistance. Not the same product at all.

They will certainly melt, and possibly burn.


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