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Quá trình tạo khuôn đúc bằng cát:




The diagrams to the left shows the pattern on a flat board and a casting box called a ?~drag?T being placed over it.

 
 




Special casting sand will soon be packed around the pattern but to ensure to can be removed easily from the sand, parting powder is sprinkled over and around it. (parting powder is similar to talcum powder). It stops the casting sand sticking to the pattern and pulling away with it when the pattern is finally removed from the sand.

 
 




Casting sand is then shaken through a sieve (called riddled sand) so that only fine particles fall around the pattern. This is called facing sand and it must be fine so that detail on the pattern shows up on the final casting. Different types of sand are available. The safest is called petro-bond. This is a mixture of quality sand and oil. The cheapest is called green sand and this is mixed with water. Green sand must be mixed carefully as if too much water is added - when molten aluminium is poured into the mould an explosion can result

The drag is then packed with more casting sand. It is a good idea to sieve all the sand being placed above the pattern and then ram it down firmly using a ramming tool. The tool has two ends, one is cylindrical and is used for general packing down of the sand. The other end is quite pointed and this can be used for packing sand close up to the pattern.


When the drag is packed fully it is levelled off (called ?~strickled off?T) using a straight steel bar.

 




 
 

The entire drag and its contents are then turned over so that the base of the pattern can be seen.





 
 


A top box called a ?~copê?T is then placed on top of the drag and locating pins are put in position so that the casting boxes cannot move sideways.

 
 

Sprue pins are positioned. One usually on the back of the pattern and the other to the side. These will eventually provide an entrance and exit for the molten aluminium when it is poured into the sand.The sand is packed/rammed into the cope in the same way as the drag. Parting powder is first applied, followed by facing sand. The sprue pins should be taller than the box and stand out from the sand when it is levelled with a strickling bar.


Small depressions are dug into the sand at the top of the two sprue pins. These are useful when the aluminium is poured. The depressions are called the pouring basin and feeder.

 




 
 


The top box (the cope) is then removed and if all is well the cope with the sand inside should lift off the drag (bottom box) without the sand falling out. A small ?~gatê?T is cut below the position of one of the sprue pins. This will help the molten aluminium flow into the cavity left by the mould. Small tools are available or can easily be made to dig a variety of shapes in the casting sand. They are similar to small trowels.

 
 




 
 




The pattern is removed using a ?~spikê?T. The end of the spike can be threaded and so it can be screwed into the softwood pattern. Before removing the pattern it is a good idea to gently tap the spike so that it loosens the pattern from the sand. It can then be lifted away from the casting box (drag).

The cope (top casting box) is placed back on top of the drag and the locating pins put in position. Before this is done vents can be created using a thin piece of welding rod, pushing it through the sand . This allows gases to escape once the aluminium is poured.

 
 






 
 


The aluminium is poured with great care. This is discussed in detail on other information sheets. The aluminium is poured down the hole left by the first sprue pin (now called the ?~runner?T). As it runs down the runner it flows through the ?~gatê?T cut by the trowel, into the cavity left by the pattern and up the riser (the hole left by the second sprue pin). The casting should be left for at least an hour before removal from the sand.

 
 




 
 


When removed from the sand, the runner and riser are cut away and the casting is ready for machining.

Sách:
Foundry Technology, 719 trang
Nhà xuất bản: Butterworth-Heinemann; (September 26, 2001)
ISBN: 0750645679 |

Sách: Metalcasting
Tác giả : C. W. Ammen
Số trang: 432 pages ;
Nhà xuất bản: McGraw-Hill Professional; (September 30, 1999)
ISBN: 007134246X

Text
Cám ơn RW nhiều, nhưng sách VN có không?

Cái này xem ra hấp dẩn thật. Nếu có sẳn một mẩu vật thì ta có thể mô phỏng lại một cách tương đối mẩu vật bằng cách này .
Cái này em thấy làm chơi vui ở nhà thì được chứ trong thực tiển sản xuất em vẩn khoái khuôn đúc bằng silicon hơn .
Nhưng bác RW cho em hỏi tý , nhở em dùng vật liệu như sắt nhiệt độ nóng chảy rất cao liệu khi đổ vào nó có làm nóng chảy cả cát và làm hỏng khuôn đúc luôn không vậy ?

to kimtthanh:
tôi không rõ lắm về tình hình sách vở trong nước. bạn có thể tìm đến trường đại học Bách Khoa Hà Nội, khoa " Khoa học và công nghệ vật liệu ", hỏi bộ môn Công nghệ đúc xem có tài liệu gì tham khảo được không.
to Antey2500:
Cát thường có thành phần chính là SiO2. Nhiệt độ nóng chảy của SiO2 là 1700 độ C.
Tham khảo thêm nhiệt độ nóng chảy của một số vật liệu khác.
Sắt : 1200C
Thép: 1400C
Đồng : 600C
Nhôm: 658C
Như vậy ta không phải lo chuyện cái khuôn bị nóng chảy ra.