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Grey Iron Framework

One friend asked some questions about grey iron framework, I shared some useful information about the casting process and technical issues to this product, and hope these information will be helpful to the other buyers. 

Q: I came across your Dandong Foundry website through Google earlier today. You appear to offer a wide range of casting techniques and types of iron which indicates that you are experts in your field. I have a number of specific questions relating to your capabilities and your business methods.  

I have a cast product (grey iron framework) which requires a relatively smooth surface finish with good dimensional accuracy and perfectly straight castings, no bowing or twisting allowed.

My questions are as follows: 

Given the above requirements what casting method would you propose to achieve accuracy and finish, green sand or lost wax?, product shape would not allow shell moulding.  

A: Firstly, shell moulding will get better surface quality and dimensions, but normally in China, over 400mm is too large to shooters, which is the machine used to make the resin shell or core. So, your products are not suitable to shell molding, but if some foundries have super large shooters, maybe it is possible.

Secondly, although resin sand has better dimensions, but they are too light to resin sand casting process, no one is willing to make them by resin sand because too light will cause too high costs to resin sand comparatively. Resin sand usually produce over 50kg per piece. 

Thirdly, almost, there is no foundry who can make them by lost wax process, because most of lost wax workshops in China produce steel castings, not grey iron castings. Moreover, because of pollution, the lost wax casting process is dieing in China. Only steel foundries with good pollution control can survive in the future. Even me, can not find a lost wax foundry to produce iron castings for you. 

Therefore, the last and suitable process is green sand. However, normal green sand can not produce your products very well, since you have very high surface and dimensions requirements. The foundries need to use very fine sand. Which means, the grains of sand are small and has similar size. 

Moreover, these products can be made by floor molding or molding machines, but can not be made by automatic molding line, because the hot castings need to stay in their sand molds for whole night, and cool slowly in molds in order to avoid the twist and deformation.  

Q: Is there any trade-off in terms of quality of surface finish if using ductile iron rather than grey iron. I understand ductile iron has greater resistance to fracture if dropped which would be advantageous but not if it reduces the surface finish or dimensional accuracy of the finished casting. Your website shows the relative cost difference between the two types of casting how accurate a guide are these prices for estimating cost of finished castings?   

A: Yes, you are correct. The ductile iron has better strength, and greater resistance to fracture. If your products need to have good tensile strength, then you should consider the ductile iron, otherwise, it will be necessary. Most of frames used in boilers and stoves are made by grey iron.  

The ductile iron has same surface quality with grey iron, for dimensions, ductile iron maybe is more difficult to control, however, your products are small, so it will not cause too much difference. 

Normally, the ductile iron is 0.1 USD/kg higher than grey iron. 

So, all in all, unless you really need very good strength, otherwise, the grey iron should be suitable. 

Q: What is the approximate cost difference per kg between castings produced by lost wax and resin green sand casting methods? 

A: I can give you an approximate average prices to these casting processes, so you could know their difference of USD per kg, the following is for grey iron of normal weight, complexity and annual demand. 

Green Sand: 1.07 USD/kg

Resin Sand: 1.21 USD/kg

Lost Wax: 1.71 USD/kg 

Q: The casting are used outdoors so need long term protection against corrosion. Can you offer surface treatment such as electro-galvanizing or spray zinc without loosing sharp definition of casting? Also because they will be finally painted here in our country. 

A: If you need further coating treatment, then I suggest you to use the anti-rust oil, which is the cheapest, and easy to be remove before your treatment. If oil affects your treatment, then anti-rust primer painting is the second choice, which is also cheap and easy to be removed. The zinc galvanized is not suitable for you although we can offer both electric galvanize and hop dip galvanize coating for you. Galvanize is expensive and difficult to be removed. It may affect your further coating treatment. 

Q: I assume Pattern Making is done within your Group, can you give me any indication as to what these might be from the information above? What material would you use for patterns, Aluminum, Resin or Wood based on initial order volumes indicated? 

A: For making the samples, we can try to use the wooden patterns. For the initial order, we can try to use the resin patterns. If the resin pattern can not meet the requirements, then the aluminum patterns will be necessary. Aluminum patterns are made by CNC machining, so have better surface quality, dimensions and lifetime. For your products, if you really want good castings, I suggest you to open the aluminum patterns. Pattern cost is one-time cost, you just need to pay one time, and they can make tens of thousands of good castings. Without your drawings, I can not assure more for now. 

Q: Do you have minimum order values / quantities per shipment? This is a long term business opportunity not a one-off order plus I have many casting requirements but Quality of casting is paramount.  

A: We do not have minimum order limitation, however, we calculate the transportation, packing, customs declaration and other miscellaneous fees based on one ton weight. So, we hope your each order has the total weight of over one ton. Less than one ton will mean we will lose some money for paying those costs. These costs have min. limitation.  

Q: What is your nearest sea port for international shipments? Are you prices ex works or FOB? 

A: Our nearest international port is Dalian port. We delivered from it to USA, UK and many other countries. We can agree to any delivery terms, but usually, most of our clients will choose the CIF delivery, and some choose the FOB delivery. EX works is easy for us, but it will cause too many trouble for you to arrange the inland transportation in China. 

Q: How stable are your casting prices in current market? How much have they changed in percentage terms over past two years?  

A: I can show you three key prices, as for the grey iron by green sand casting process, in the past three years, the highest price was 1314 USD/TON in July, 2008, and lowest price was 939 USD/TON in April 2009, for now, it is 1070 USD/TON. So, you can see the change is huge. The main effects to the prices are pig iron cost, exchange rate of USD to RMB and worker salaries. For now, the pig iron price is rising, salaries are rising, and exchange rate is reducing, therefore, this is very bad time for exporting business for now. The price of iron castings were rising from the early of 2009 to now, and will rise continuously.  

Herein, truly thank this friend to permit us to issue this modified letter in the blog of Dandong Foundry, and if you need to learn about some casting information about your products, please feel free to contact us, and we will tell you what we know. By the way, we will not reveal your information without your permission.

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