There is no core in blow mould, comparatively low clamping and blowing pressure required, and thus, need not be made of high tensile strength material. However, good thermal conductivity is necessary to reduce the cycle time and to produce quality product.
The Advantages of Aluminium Moulds
Following are some of the main advantages, which can be obtained by using Aluminium alloys for moulds. Some are well-known, other perhaps less:
1. The importance of machinability: equal to lightness
2. Extremely high thermal exchange capability: rapid cooling of the injected thermoplastic product
3. Liberty when designing the thicknesses of the thermoplastic moulded part
4. Elimination of many electroerosion operations
5. Actual utilisation of HSC and VHSC systems with Al alloys
6. Elimination (or drastic reduction) of fitting time
7. Durability and good maintenance of polished surfaces
8. Considerable weight reduction: easy-to-handle Al moulds and simplification of investments in infrastructures
9. Re-design flexibility
For blow moulding HDPE parts, aluminium is typically used for the base material, with BeCu or stainless steel inserts in the pinch off areas. For PVC parts, BeCu, ampcoloy or stainless steel as employed as the base material, with A-2 or stainless steel inserts in the pinch off areas. And for PET parts, the base mould is usually made of aluminium or BeCu, with A-2 or stainless pinch-offs.
When it comes to injection mould & blow plastic mould materials nothing speeds production like Copper alloys. Mipalloy 100's thermal conductivity is almost 10 times greater than Tool Steels, so it offers faster, more uniform heat dissipation. That means more than 20% shorter cycle times. But speed of production is not the only factor. Current research at Western Michigan University shows Beryllium Copper cores exceed most production requirements. For extreme conditions such as long runs of 30% Glass-filled Nylon, Beryllium Copper lasts longer than P-20 Steel cores.
The plastics industry has proven Mipalloy 100 as a material of choice for injection moulding & blow moulding applications.
The injection moulding cycle is made up of a number of elements. They include the filling portion, the cooling portion & the mould open portion. The cooling portion is always the longest & is usually 65% of the overall cycle. Therefore the longest element in the overall cycle is where the greatest benefit can be obtained in improving the injection moulding cycle & where Beryllium Copper works best.
In addition to its superior thermal conductivity Mipalloy 100 offers the following advantages;
1. Maintains high surface finish.
2. Accepts etching & texturing.
3. Requires no additional heat treatment. Supplied in heat treated condition.
4. Can be readily machined using conventional machining practices as well as Electrical Discharge Machining (EDM).
Mipalloy manufactures & stocks Beryllium Copper in various shapes & sizes;
1. Round rod from 6mm diameter to 145mm diameter.
2. Rectangular & Square bars from 1square upwards.
3. Large forgings weighing more than 1000 kgs single piece.
Recommended blow mould applications;
Blow pins : High thermal conductivity for efficient heat removal, reducing cycle time.
Mould Inserts : Inserts at pinch off & neck areas of Aluminium mould increasing both hardness & conductivity.
Complete moulds : resistant to attack in PVC applications. Mipalloy 100 alone or with hardened pinch offs for use in moulds with complex parting lines.
Recommended injection mould applications;
Core pins, cavity areas, sprue bushings, ejector pins & sleeves, manifold systems.
Advantages include;
Improved control of post mould shrinkage.
Better heat dissipation in areas of heavy wall sections or limited water channel access.
Improved dimensional stability in multi cavity tools or in large flat walled parts.
Excellent wear life when mated with standard tool steels.
Mould Life - Cycle
In the Processing shop, it is clear moulds dont last forever. There are three basic failure modes to permanent mould tooling.
1. Thermal fatigue manifested in cracking primarily
2. Erosion manifested in dimensional errors and/or texture problems
3. Damage due to improper handling or maintenance.
Molds may be retired for many reasons such as obsolescence but they fail for one or more of the three reasons above. It is also clear that molds, even of the same design, do not last for exactly the same number of shots. So mould-tooling life is not characterized by a single factor.
Life, as the saying goes, is more complicated than that.
Mould life cycle is dependent on various factors, which are
1. Plastic material to be moulded
2. Type of moulding operation viz. Injection,Blow etc.,
3. Complexity of the part
4. Type of machine used for moulding
5. Operators care in moulding and maintenance / handling
6. Type of material used in the construction of the mould.
The table below lists the average number of moldings to be expected dependent on the mould material.
Q: What happens in heat treatment ?
In heat treatment mechanical properties are altered by :
Changing the size of the grains of what it is composed or by
Changing its micro constituents
Q: Purpose of heat treatment?
1. To Improve Machinability
2. To Relieve Internal Stresses
3. To Change or Refine Grain Size
4. To Improve Mechanical Properties
5. To Improve Resistance to wear, heat & corrosion
6. To Produce a hard surface on a ductile interior
7. To improve magnetic & electrical properties
Q: DIFFERENT PROCESS OF HEAT TREATMENT?
1. Annealing is generally used to soften the steel
2. Normalising is used to eliminate coarse grain structure obtained during forging rolling and stamping and produce fine grains.
3. Hardening is done to develop high hardness to resist wear and enable to cut other metals
The hardness produced by hardening depending upon the carbon content of steel. Steel containing less than 0.15% C does not respond to hardening treatment.
Tempering is done to reduce internal stresses and reduce some of the hardness produced during
Special Hardening Techniques:
1. Vaccum hardening
2. Laser hardening
3. Plasma hardening
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