1-How to select the appropriate injection molding machine size?

With respect to size and geometry of the part you are going to mold, required clamping force and shot weight are the two main factors which influence size of the appropriate injection molding machine.

Calculating exact magnitude of the required clamping force is an intricate process and needs in-depth knowledge of fluid mechanics and mathematics, but as a rough estimation you can calculate it by multiplying injection pressure by projected area of the molded parts. For a precise result you can call NBM.

Maximum shot weight of an injection molding machine is defined based on Polystyrene. For a different material you need to know its density which can be easily found on the internet.

C: (Polystyrene) Shot weight

B: Material density

m=CB/1.05

Example: Assume the maximum shot weight of an injection molding machine is 110 grams of Polystyrene, how many grams of Polypropylene can be injected?

m = (0.95*110)/1.05=99.5 gr

We recommend to conduct the molding at shot weight of 50-85% of the maximum injection capacity. For amorphous materials you can use slightly more than 85% of the maximum capacity, but for semi crystalline materials you must stick to the lower limits.

2- What are the types of injection molding machines?

There are different classifications for injection molding machines but the most common one classifies machines to vertical and horizontal based on their injection direction. Horizontal injection molding machines are for general purposes, but vertical machines are less prevalent and are used for specific purposes such as insert-injection molding.

Yizumi horizontal injection molding machine

 

Yizumi vertical injection molding machine

As another classification, injection molding machines are classified by the type of driving systems which could be hydraulic, electrical, or hybrid. Advantages and disadvantages of each type are discussed in the following:

Hydraulic injection molding machines:

Advantages:

• Lower price
• More available spare parts
• Lower cost of maintenance
• Hydraulic equipment are more resistant to corrosion
• High clamping forces are available

Disadvantages:

• High energy consumption
• Potential oil leakage
• Generate more heat thus more cooling capacity is needed
• Not recommended for producing medical and hygienic parts

Hybrid injection molding machines:

Advantages:

• Moderate price
• Low energy consumption (compared with hydraulic machines)
• Low heat generation
• Quick response times

Disadvantages:

• Still hydraulics exist, so oil leakage can mess the factory
• The maintenance technicians should master both of hydraulic and electrical systems
• Hybrid machines are usually custom-made and they have very diverse designs.

Full electric injection molding machines:

Advantages:

• Low cycle time
• Very clean thus appropriate for medical and hygienic parts
• Very low noise pollution
• Very low energy consumption
• Very precise
• High repeatability

Disadvantages:

• High price
• Not available in big sizes
• Spare parts are hard to find in the domestic market

Each type of injection molding machines has some advantages and disadvantages, for choosing the most appropriate type you should take many things including cost, product quality and availability into account.

We offer consulting services to make you able to select the right machineries which meet all of your needs.

• Why are there so many types reciprocating screw designs?

Each plastic materials may have different properties such as viscosity, crystalline structure, shear resistance and etc. Due to the variety of properties and behavior of plastics, different designs of reciprocating screw are developed.

• How to calculate production costs?

A product of service cost can be calculated by sum of direct material, direct labor (direct costs) and factory overheads (indirect costs). In some cases it is a simple task, however calculating production costs for a plastic part can be a lot more complicated, because to determine direct and indirect costs needs experience as well as some levels of financial knowledge. You can count on us for providing consulting services on this issue.

• A brief introduction to plastic properties and plasticizing parameters:

Polymer name	Density g/cm3	Melting temp. (Celsius)	Shrinkage (%)	Mold temp. (Celsius)	Cylinder temp. at different zones Celsius))
					Nozzle tip	Middle	Entry
PS	1.05	130-165	0.4	10-75	180-260	200-260	160-250
HIPS	1.4-1.06	130-165	0.4	5-75	220-270	190-260	160-250
ABS	1.06-1.1	130-160	0.6	50-80	190-250	180-240	170-240
LDPE	0.91-0.93	108-126	1.5-5	35-60	230-310	220-300	170-220
HDPE	0.94-0.97	126-137	2.0-5	35-60	230-310	220-300	170-220
PP	0.95	160-176	1-2.5	50-80	210-300	180-260	160-240
PVC	1.35	160-212	0.1-0.5	10-60	170-220	160-195	150-195
PMMA	1.18	160-210	0.5	50-90	180-230	160-240	140-220
PA6	1.13	210-215	0.8-1.5	50-60	210-230	210-230	200-210
PA66	1.14	250-265	2.25	50-80	250-280	240-280	220-280
CA	1.3	69-105	0.5	40-75	180-200	170-190	150-180
PC	1.2	215-265	0.8	80-99	250-320	260-340	280-350
POM	1.41-1.42	165-175	2	50-90	190-210	175-220	160-210

 

• What are the differences between hopper dryer and dehumidifier?

Hoper dryer is appropriate removing moisture out for non-hygroscopic polymers which absorb moisture only on their surface, but for hygroscopic polymers such as PET, PC and ABS you need to use dehumidifier.