The International Hobby Metal Casting ezine.
Brought To You By: Col Croucher.
Administrator of: www.myhomefoundry.com
Australia.
April 2006. Volume: 03. Number: 30.
Would you like to be featured in this ezine? All you need to do is drop us a line and we will do the rest. Or if you know of anybody with an interesting story to tell, let us know. Thank you to the people featured in the past three issues who have taken the time to submit some photographs and a short article about their hobby foundry & projects.
The ezine has also reached another milestone, we now have over one thousand subcribers from many countries around the globe, while that is not a large number as far as online ezines go, but remember that metal casting aint quite like other hobbies. A big thank you to the people who have been with us from day one. As with many free ezine subscriptions people come and go at will, so if you are amongst the first subscribers, and you are still here, thank you for staying with us, I hope you have enjoyed the journey.
This ezine was launched on 17-10-2003, there were several new subscribers who signed up on 28-10-2003.The first issue (text format) was emailed to 120 subcribers.
And while we are in celebration mode. Congratulations to Paul Smithling for being the lucky one thousandth ezine subscriber, you will be recieving the complete hobby foundry ebook package as part of the promotion we have been running on our web site for the past two or three weeks, we've had a lot of fun and there has been lots of new subscribers signing up, a big welcome to you if you have just joined us, we hope you enjoy what hobby foundry work can offer you.
Note: Paul has been notified and we are waiting for his reply.
OK, that's got the ezine history lesson and prize giving out of the way, let's see, what else has been happening of late. There is still a lot of casting activity going on out there... and there are many new people coming into hobby metal casting scene who are looking for guidance, and wanting to learn the special skills required for this age old craft. I have noticed that many people take quite a while to make the start with their metal casting, and I'm sure that much of the procrastination is due to lack of start up knowledge.
If you are an old hand at the game, with many years of foundry practice under your belt, you probably dont have to think twice about what the various steps and processes are in your foundry, but to a beginner, it can be quite overwhelming trying to work out the right way to do things. The very best way to learn, of course is to have one-on-one tuition i.e. have a mentor to show and teach you the tricks.
The next best way is to buy some books/ebooks to read - study & learn, this method followed up with some online mentoring is also a good way to learn, we've helped several people in this respect, and it has worked quite well. As an author and publisher the after sale mentoring is quite enjoyable, but there are also many people who dont seem to require much help at all, they read - learn - practice and seem to get the hang of moulding and casting pretty quick.
The publication date of this issue has fallen near Easter so I would like to take this opportunity to wish you a safe and happy Easter... wherever you may be. The short holiday break might also provide a good time to tidy up the workshop/foundry and get ready for some serious casting work in the next few weeks, that is my aim anyway.
Don't forget the foundry ebook specials on right now, take advantage of the ezine celebration price, plus the valuable bonus ebooks included in the package also... so if you have not taken the plunge yet, now just might be the right time.
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The Package:
3-Vol Metal Casting Made Easy.
Design Of Gates & Risers.
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Petro-Bond user Guide
How to build tongs.
How to build Mould Boxes.
How to build Hot Wire Foam Cutter.
RTV repro moulds & patterns.
*New*
How to build a Sand Muller.
Cam
McKeown's OZ Foundry.
Cam McKeown. Furnace uses a gas
pre-heat before switching to ATF oil fired Furnace Burner.
The burner set-up with gas & oil nozzles, plus air blast pipe
feeding into the burner tube. (See Oil burner success article below)
Making Patterns.
Next to knowing how to melt and cast metal, the next hurdle facing most hobby casters is the art of"Pattern Making". Recently on one of the forums a new member requested some info about materials to use for pattern making, there are several good materials you can use to make patterns, besides the traditional timbers that have been used through the ages. Many of the traditional timbers are getting very hard to obtain and can be expensive to buy.
Many years ago I discovered that MDF can be used to make excellent patterns in the home foundry. Wheel rim patterns were made by glueing blocks (25mm thick) of MDF together and then mounting the MDF block in the four jaw lathe chuck to machine the pattern, as Ron says below, MDF is very dusty to machine and sand, you need to wear a face mask.To sealing MDF pattern's I find that several layers of shellac with a good sanding in between each coat will produce a smooth durable foundry pattern. BUT, MDF patterns will also shrink & crack after a long period of time. When ever I need some MDF I go to the local joinery shop and collect all their offcuts out of the scrap bin for free.
What Is The Best Material For Patterns.
This posting was placed on a forum recently.
Hi all.
I am looking for the right timber to use in making patterns. I will be milling them with a CNC mill so need wood that wont splinter easily I guess. I did do a search first but it came up blank.
Any ideas?
Thanks for any help provided.
Reply 01.
I've been a patternmaker for more than 30 years, studied under my grandfather, I used wood and plaster for most of that time but have been creeping into CNC the last few years.. For patterns I used to use a lot of Jelutong. It's getting harder to find but the hardwood store near me can order it in a pinch. Basswood works pretty good. Phillipine Mahogany makes very durable patterns and is much more stable than the south american stuff. I have some matchplates made by the Navy in the 60s from Sugar Pine that are still going strong, dimensions are still good and there's no cracking (they sealed them really well).
For CNC work I use Cherry wood or blocks of Acrylic.
Bill.
Reply 02.
I like MDF. It has no grain and machines really well. It is dusty, though. A vacuum nozzle near the tool works well. I use a 5 ° tapered ball end mill so draft and filets are automatic. MDF will absorb moisture from the air, so sealing is important. It can be bought at most building supply centers in large sheets
and in planks (look for shelf boards). It glues well, so it can be glued up into blocks of any size. If you need a long term pattern, you can make the original oversize and cast the permanent (production) pattern in aluminum or the metal of your choice.
Try it, you'll like it.
Ron .
In Australia, MDF (Medium Density Fibre board) was promoted as the wood craftsmans clay, and they are not far from wrong, MDF is a vesatile product which can be used in all kinds of applications. An excellent pattern making material for the hobby & pro worker alike.
Oil Burner Success.
What kind
of fuel source will you use to fire your furnace? It seems to be
a never ending debate amongst hobby foundry people. I must admit I've
always leaned toward the pro gas field simply because of it's ease of
use, cleanliness and efficient heating, that is, until I took notice of
the system that Cam Mckeown has set up. Cam lives in the Gippsland
Valley area of Victoria Australia. His furnace uses a combination of
both LP gas and oil. Gas to preheat the furnace for
a few minutes before switching over to fuel oil. Cam says the system is
easy to use and puts out an incredible amount of heat, infact he melts cast iron with his oil fired
furnace. One of the secrets to his success is a well designed set up
(see photos above) and he uses ATF
or Automatic Transmssion Fluid (Oil)
this seems to be much better than using old engine or sump oil, as we
call it out here in OZ. And the best part is you can get the ATF for
FREE. I think we could all take a closer look at the system that Cam
uses. To see how he has set his furnace up take a visit to his web site.
http://home.iprimus.com.au/cmckeown/oil_fired_furnace.htm
Thermocouple Tables. If
you want to learn more
about
thermocouples then spend some surfing time around the following
thermocouple
web site.
http://www.temperatures.com/tctables.html
The Worlds Fastest Indian.
Burt Munro. New Zealand Motor Cycle Speed Legend. (Screening Now)Here's a story of inspiration for anyone trying to achieve big things with little in the way of resources.
His methods, to say the least, were unorthodox. He used an old spoke for a micrometer and cast parts in old tins (sound familiar) although one American report has him casting pistons in the sand at the local beach! He built his own overhead four-cam design to replace the standard two-cam system and converted the engine to overhead valves.
He made his own barrels, flywheels, pistons, cams and followers and pressure lubrication system. In their final form he in effect hand-carved the con-rods from a Caterpillar tractor axle, and hardened and tempered
them to 143 tons tensile strength. Rumour has it that Burt made his engine barrels from pieces of cast iron gas pipe, which he scrounged from the gas company after they had been dug up for replacement.
He reasoned that, after some years in the ground, they were well seasoned. (Aged) He then made aluminium slices, which he shrunk over the pipe to make the cooling fins.
Burt Munro died in December 1978. The Indian, his for 57yrs is in the hands of an enthusiast in the South Island of NZ. As well as the bike he left behind a legend of skill, perseverance, and courage, which typifies the ingenuity and resilience of the New Zealand spirit, and of which all New Zealanders, motorcyclists or not, may be justly proud.
To read the whole story visit:
http://www.indianmotorbikes.com/features/munro/munro.htm
Or go see the movie The Worlds Fastest Indian at your nearest cinema, I've been to watch the movie and It is one of the best I have seen for many years, it is an amazing, fabulous story.
Aluminum Casting Processes.
Aluminum is one of the few metals that can be cast by all of the processes used in casting metals. These processes, in decreasing order of amount of aluminum casting, are: die casting, permanent mold casting, sand casting (green sand and dry sand), plaster casting, investment casting, and continuous casting. Other processes such as lost foam, squeeze casting, and hot isostatic pressing are also mentioned.
There are many factors that affect selection of a casting process for producing a specific aluminum alloy part. The most important factors for all casting processes are:
- Feasibility and cost factors
- Quality factors.
Quality factors are also important in the selection of a casting process. When applied to castings, the term quality refers to both degree of soundness (freedom from porosity, cracking, and surface imperfections) and levels of mechanical properties (strength and ductility).
However, it should be kept in mind that in die casting, although cooling rates are very high, air tends to be trapped in the casting, which gives rise to appreciable amounts of porosity at the center. Extensive research has been conducted to find ways of reducing such porosity; however, it is difficult if not impossible to eliminate completely, and die castings often are lower in strength than low-pressure or gravity-fed permanent mold castings, which are more sound in spite of slower cooling.
Die Casting
Alloys of aluminum are used in die casting more extensively than alloys of any other base metal. In the United States alone, about 2.5 billion dollars worth of aluminum alloy die castings is produced each year. The die casting process consumes almost twice as much tonnage of aluminum alloys as all other casting processes combined.Die casting is especially suited to production of large quantities of relatively small parts. Aluminum die castings weighing up to about 5 kg are common, but castings weighing as much as 50 kg are produced when the high tooling and casting-machine costs are justified.
Typical applications of die cast aluminum alloys include:
- Alloy 380.0 - Lawnmower housings, gear
- Alloy A380.0 - Streetlamps housings, typewriter frames, dental equipment
- Alloy 360.0 - Frying skillets, cover plates, instrument cases, parts requiring corrosion resistance.
- Alloy 413.0 - Outboard motor parts such as pistons, connecting rods, and housings
- Alloy 518.1 - Escalator parts, conveyor components, aircraft and marine hardware and lit tings.
Die castings are made by injection of molten metal into metal molds under substantial pressure. Rapid injection and rapid solidification under high pressure combine to produce a dense, fine-grain surface structure, which results in excellent wear and fatigue properties. Air entrapment and shrinkage, however, may result in porosity, and machine cuts should be limited to 1.0 mm to avoid exposing it.
Aluminum alloy die castings usually are not heat treated but occasionally are given dimensional and metallurgical stabilization treatments.
Die castings are not easily welded or heat treated because of entrapped gases. Special techniques and care in production are required for pressure-tight parts. The selection of an alloy with a narrow freezing range also is helpful. The use of vacuum for cavity venting is practiced in some die casting foundries for production of parts for some special applications.
Approximately 85% of aluminum alloy die castings are produced in aluminum-silicon-copper alloys (alloy 380.0 and its several modifications). This family of alloys provides a good combination of cost, strength, and corrosion resistance, together with the high fluidity and freedom from hot shortness that are required for ease of casting. Where better corrosion resistance is required, alloys lower in copper, such as 360.0 and 413.0 must be used.
Alloy 518.0 is occasionally specified when highest corrosion resistance is required. This alloy, however, has low fluidity and some tendency to hot shortness. It is difficult to cast, which is reflected in higher cost per casting.
Permanent mold casting
(This system can be used with a high success rate in the home hobby foundry)Permanent mold (gravity die) casting, like die casting, is suited to high-volume production. Permanent mold castings typically are larger than die castings. Maximum weight of permanent mold castings usually is about 10 kg, but much larger castings sometimes are made when costs of tooling and casting equipment are justified by the quality required for the casting.
Permanent mold castings are gravity-fed and pouring rate is relatively low, but the metal mold produces rapid solidification. Permanent mold castings exhibit excellent mechanical properties. Castings are generally sound, provided that the alloys used exhibit good fluidity and resistance to hot tearing.
Mechanical properties of permanent mold castings can be further improved by heat treatment. If maximum properties are required, the heat treatment consists of a solution treatment at high temperature followed by a quench and then natural or artificial aging. For small castings in which the cooling rate in the mold is very rapid or for less critical parts, the solution treatment and quench may be eliminated and the fast cooling in the mold relied on to retain in solution the compounds that will produce age hardening.
Some common aluminum permanent mold casting alloys, and typical products cast from them, are presented below.
- Alloy 366.0 - Automotive pistons
- Alloys 355.0, C355.0, A357.0 - Timing gears, impellers, compressors, and aircraft and missile components requiring high strength
- Alloys 356.0, A356.0 - Machine tool parts, aircraft wheels, pump parts, marine hardware, valve bodies
- Other aluminum alloys commonly used for permanent mold castings include 296.0, 319.0, and 333.0.
Sand casting
Sand casting, which in a general sense involves the forming of a casting mold with sand, includes conventional sand casting and evaporative pattern (lost-foam) casting.In conventional sand casting, the mold is formed around a pattern by ramming sand, mixed with the proper bonding agent, onto the pattern. Then the pattern is removed, leaving a cavity in the shape of the casting to be made. If the casting is to have internal cavities or undercuts, sand cores are used to make them. Molten metal is poured into the mold, and after it has solidified the mold is broken to remove the casting. In making molds and cores, various agents can be used for bonding the sand. The agent most often used is a mixture of clay and water.
Casting quality is determined to a large extent by foundry technique. Proper metal-handling practice is necessary for obtaining sound castings. Complex castings with varying wall thickness will be sound only if proper techniques are used.
Evaporative (lost-foam) pattern casting
Evaporative pattern casting (EPC) is a sand casting process that uses an unbounded sand mold with an expendable polystyrene pattern placed inside of the mold. This process is somewhat similar to investment casting in that an expendable material can be used to form relatively intricate patterns in a surrounding mold material. Unlike investment casting, however, evaporative pattern casting (EPC) involves a polystyrene foam pattern that vaporizes during the pouring of molten metal into a surrounding mold of unbounded sand.
Shell Mould Casting
In shell mold casting, the molten metal is poured into a shell of resin-bonded sand only 10 to 20 mm thick - much thinner than the massive molds commonly used in sand foundries. Shell mold castings surpass ordinary sand castings in surface finish and dimensional accuracy and cool at slightly higher rates; however, equipment and production are more expensive.Plaster Casting
In this method, either a permeable (aerated) or impermeable plaster is used for the mold. The plaster in slurry form is poured around a pattern, the pattern is removed and the plaster mold is baked before the casting is poured. The high insulating value of the plaster allows castings with thin wads to be poured.Minimum wall thickness of aluminum plaster castings typically is 1.5 mm. Plaster molds have high reproducibility, permitting castings to be made with fine details and close tolerances. Mechanical properties and casting quality depend on alloy composition and foundry technique. Slow cooling due to the highly insulating nature of plaster molds tends to magnify solidification-related problems, and thus solidification must be controlled carefully to obtain good mechanical properties.
Cost of basic equipment for plaster casting is low; however, because plaster molding is slower than sand molding, cost of operation is high. Aluminum alloys commonly used for plaster casting are 295.0, 355.0, C355.0, 356.0 and A356.0.
Investment casting
Investment casting of aluminum most commonly employs plaster molds and expendable patterns of wax or other fusible materials. Plaster slurry is "invested" around patterns for several castings, and the patterns are melted out as the plaster is baked.Investment casting produces precision parts; aluminum castings can have walls as thin as 0.40 to 0.75 mm. However, investment molding is often used to produce large quantities of intricately shaped parts requiring no further machining so internal porosity seldom is a problem. Because of porosity and slow solidification, mechanical properties are low.
Investment castings usually are small, and it is especially suited to production of jewelry and parts for precision instruments. Recent strong interest by the aerospace industry in the investment casting process has resulted in limited use of improved technology to produce premium quality castings. Combining this accurate dimensional control with the high and carefully controlled mechanical properties can, at times, justify casting costs and prices normally not considered practical.
Aluminum alloys commonly used for investment castings are 208.0, 295.0, 308.0, 355.0, 356.0, 443,0, 514.0, 535.0 and 712.0.
Centrifugal Casting
Centrifuging is another method of forcing metal into a mold. Steel baked sand, plaster, cast iron, or graphite molds and cores are used for centrifugal casting of aluminum. Metal dies or molds provide rapid chilling, resulting in a level of soundness and mechanical properties comparable or superior to that of gravity-poured permanent mold castings.Wheels, wheel hubs, and papermaking or printing rolls are examples of aluminum parts produced by centrifugal casting. Aluminum alloys suitable for permanent mold, sand, or plaster casting can be cast centrifugally.
Continuous Casting
Long shapes of simple cross section (such as round, square, and hexagonal rods) can be produced by continuous casting, which is done in a short, bottomless, water-cooled metal mold.The casting is continuously withdrawn from the bottom of the mold; because the mold is water cooled, cooling rate is very high. As a result of continuous feeding, castings generally are free of porosity. In most instances, however, the same product can be made by extrusion at approximately the same cost and with better properties, and thus use of continuous casting is limited. The largest application of continuous casting is production of ingot for rolling, extrusion, or forging.
Composite-Mold Casting
Many of the molding methods described above can be combined to obtain greater flexibility in casting. Thus, dry sand cores often are used in green sand molds, and metal chills can be used in sand molds to accelerate local cooling.Until Next Month.
Keep safe. Col Croucher. Australia.