The model material classification and choice principles

In this lesson, the instruction content is model material classification and choice principles. “The model material classification and choice principle” is to classify based on the model 去·material’s physical and chemical characteristics. Then we choose special material to produce according to the production process requirement. However, all models produced are used for full mold casting, that is lost foam casting. By this way, the model application is limited--special use for lost foam casting. Mentioning lost foam model, we need to know the lost foam casting ’s special requirement for models. The related requirement is as follows:

  1.The vaporization is rapid and full with little residual.

 2. The model density is small. The strength and surface rigidity are good to make model not to be damaged in the production, carry and dry sand filling processes and to make sure stable model size and character.

3. The variety and specification are complete. These material can adapt to different material and structures of model production requirement.

So, what are the model materials? What are the different specifications, physical and chemical properties of these materials? How can we choose model material according to model characteristics?

2.1.1 Overview

Review the lost foam casting definition. The lost foam casting(also called full mold casting) is to produce full  mould same with casting structures and sizes by high polymer material(EPS, STMMA or EPMMA). By dipping refractory coating (it plays the roles of strengthening, bright and clean, permeability) and drying, they are buried in dry silica sand. By three-dimension vibration and modeling, the modeling sandbox for casting is poured by the molten liquid metal in the negative pressure state to make high molecule material model  gasify due to heating. Then it is replaced by liquid metal and forms the new casting production method  (after cooling and soldification)by the one-time modeling casting new process.

2.1.2 The model material classification

There are three kinds of foam beads special for lost foam casting

     ① About Expandable polystyrene beads (abbreviated as EPS), there are Longwang brand, Jiaxing brand and Xingda brand and so on in the current market. However, the Longwang brand performance is relatively stable(For following model, we take Longwang brand as an example to instruct).

   ② For the Expandable Methyl Methacrylate and Styrene Copolymer Resin Beads (abbreviated as STMMA),

   ③ Expandable Methyl Methacrylate Beads(abbreviated as EPMMA).

2.1.3 The model material type, characteristics and application range

1 EPS model classification

①E level of material--standard material

②H level of material--specially light material, high foaming ratio

③B level of material--fast plastic, energy-saving type

④ F level of material--flame resistance type

⑤FR level of material--pigment

⑥N level of material--impact resistance material

⑦FD level of material--food level of material

⑧G level of material--special material

According to EPS use requirement of lost foam casting, we only explain  H level of material in detail, that is very light material .

(1) H level of material characteristics

The repeated foaming performance--it can pre-foam 6 times. The foam beads are full with resilience.

The foaming performance--foaming material is dry and loose,the fluidity is good,; foaming rate is high; the curing time is short and saves steam.

The machining property--associativity is bad; the heating time is short; the molding range is wide.

The molding quality--smooth, bright, strong strength is good and adaptation is good.

The storage--The original grains can be stored for 6 months without any problem (in a cool and constant temperature environment, with room temperature no higher than 25℃, avoiding direct sunlight. Once opened, use them up as soon as possible. If not used up, seal them well. It is recommended that the retention time after opening be no more than 24 hours). The quality is stable.