High Purity Graphite Molds
Traditional composite molds are typically made of metal. However, from the perspective of mold making and their intended use these types of molds have difficulty taking on complex shapes and working with composite materials. This is the result of incompatible thermal expansion coefficients between the mold itself and the materials positioned inside. Therefore, graphite has emerged as the first choice for mold making because of its desired physical and chemical properties. Jitai sells an enormous range of custom high purity graphite molds that can significantly reduce the per-part pricing for our clients.
Graphite is a crystalline form of the element carbon with the following characteristics:
1. Excellent thermal and electrical conductivity;
2. Resistant to chemical corrosion and does not react easily with a variety of metals
3. Low thermal expansion coefficient and good thermal stability
4. Ideal lubrication and wear resistance
5. Performs well in extreme heat (most copper metal matrix sintering temperatures are above 800℃). Strength increases concurrently with the increase of temperature
6. Good machining performance, can be used for molds with complex shapes and in situations where high precision is necessary.
1.Used for continuous and semi-continuous casting of non-ferrous metals. Due to its good thermal conductivity and self-lubricating quality of the material, the size of the ingot stays accurate, the surface remains smooth, and its crystalline structure stays uniform even after many firings. This allows for increased casting speeds, ensuring that the next process can begin immediately following. This greatly improves the yield rate and product quality.
2. Moulds for pressure casting: Artificial graphite has been successfully used for pressure casting of non-ferrous metals. For example, zinc alloy and copper alloy castings produced with pressure casting molds of artificial graphite materials are frequently used in automobile parts.
3. Graphite molds for centrifugal casting: Graphite molds have been successfully utilized in centrifugal casting. US companies have used artificial graphite molds with a wall thickness of more than 25mm to centrifugally cast bronze bushes, bushings, and sleeves.
4. Hot pressing molds: The artificial graphite used in hot pressing molds has two characteristics for pressure sintering of cemented carbides:
A) If the temperature during pressing is increased to 1350 to 1450℃, the required unit pressure can be reduced to 1/10th of what would be needed if the mould was cold.
B) Pressing and heating are performed concurrently, and a dense sintered body can be obtained after only a short time of sintering.
5. Molds for glass molding: Graphite material has become an indispensable mold material for working with glass. It can be used to make molds for glass tubes, elbows, funnels and a variety of other forms.
6. Sintering molds and other diamond sintering molds: Because of the low thermal expansion of artificial graphite, sintering molds and brackets for transistors can be manufactured. It is now widely used and has become an indispensable material for the development of the semiconductor industry.
Performance comparison of commonly used mold processing materials and composite materials
|
Material |
Bulk Density g/cm3 |
Thermal Expansion Coefficient 10-6/℃ |
|
Graphite |
1.7 |
2.7 |
|
Aluminum |
2.7 |
23 |
|
Steel |
7.86 |
12 |
|
Carbon Fibre/Epoxy |
1.6 |
0~2.7 |
|
Glass Fibre/Epoxy |
1.9 |
12.6~23 |
QUALITY CONTROL
Over the years we have finely tuned our multi-step process of ensuring every single component passes all quality and functionality tests, tests that begin even before raw materials are on-boarded. At this first stage, each shipment of raw materials undergoes an acceptance sampling method assortment which makes a determination about whether to accept the material. If such a determination is made, the entire shipment is cleaned, a full inspection is performed, minor imperfections are buffed and polished, and stock is then warehoused. The second stage is conducted immediately following the initial assembly and brazing stages. Every single product undergoes an individual visual inspection followed by a preliminary hermeticity test. For hermeticity we utilize a helium leak test that is adjusted to meet the exacting air tightness requirements of our clients. Following the plating stage, each batch undergoes a sampling inspection and a coating bonding degree analysis. Products that make it past this stage are then subjected to full inspection which includes scrutiny of appearance, construction, plating thickness, and a second helium tracer gas hermeticity test. Finally products are put through the full range of Factory Inspection trials. These include pin fatigue tests, a salt spray corrosion resistance test and analysis that relies on climate simulation equipment to test product performance. Once products are approved, they are individually vacuum-packed with a deoxidizing desiccant insert and ensconced in additional protective packaging before being shipped out. These efforts guarantee that every Jitai product delivered to you is of the same high quality as when it left the factory.
