POM Material Injection Molding

POM Material Injection Molding

by | Oct 1, 2018 | General Injection Molding

Polyoxymethylene (POM) is a thermoplastic material also known as acetal. POM-H (polyoxymethylene homopolymer), POM-K (polyoxymethylene copolymer) is a high density, high crystallinity thermoplastic engineering plastic with good physical, mechanical and chemical properties, especially with excellent friction resistance.

POM is a crystalline plastic with a sharp melting point. Once the melting point is reached, the melt viscosity drops rapidly. Decomposition occurs when the
temperature exceeds a certain limit or the melt is heated for too long.

Copper is a POM degradation catalyst. Copper should be avoided where it is in contact with the POM melt.

 1. Plastic processing

POM has a small water absorption, generally 0.2%-0.5%. Under normal circumstances, POM can be processed without drying, but it must be dried for wet
materials. The drying temperature is above 80℃ and the time is more than 2 hours. The specific conditions should be based on the supplier’s data.

The proportion of recycled materials used is generally not more than 20-30%. However, depending on the type of product and the end use, it can sometimes be up to 100%.

2. The selection of plastic machine

In addition to the requirement that the screw has no stagnant area, the POM has no special requirements for the injection molding machine, and generally
can be injection molded.

3. Mold and gate design

The common mold temperature is controlled to 80-90℃, the runner diameter is 3-6 mm, the gate length is 0.5 mm. The gate size depends on the thickness
of the wall, and the circular gate diameter should be at least 0.5-0.6 times the thickness of the product. The width of the rectangular gate is usually 2 times
or more of the thickness, the depth is 0.6 times the wall thickness, and the draft angle is between 40′-1º30′.

Exhaust system

POM-H thickness 0.01-0.02mm width 3mm

POM-K thickness 0.04mm width 3mm

4. Melting temperature

POM-H can be set to 215℃ (190℃ – 230℃)

POM-K can be set to 205℃ (190℃ – 210℃)

5. Injection speed

Medium speed. If too slow, it produces ripples. If too fast, it is easy to produce grain and shear overheating.

6. Back pressure

The lower the better, generally no more than 200bar

7. Stay time in barrel

POM-H can be held at 215℃ for 35 minutes

POM-K can stay in 205℃ for 20 minutes without decomposition.

POM-K can be retained for 7 minutes at 240℃. If the machine is shut down, the barrel temperature should be lowered to 150℃. If you want to stop for a
long time, you must clean the machine and turn off the heater.

8. After machine stops

The cleaning barrel must use PE or PP. Turn off the heating and push the screw in the front position. The barrel and screw must be kept clean. Impurities or dirt can change the thermal stability of the POM (especially POM-H).

9. Post processing

For very warm parts and high quality requirements, heat treatment is required.

The annealing treatment effect can be carried out by immersing the product in a hydrochloric acid solution having a concentration of 30% for 30 minutes,
and then visually discriminating whether cracks have residual stress.

UPVC Injection Molding Setting

UPVC Injection Molding Setting

by | Sep 17, 2018 | Injection molding machine setting

UPVC, also known as hard PVC, is an amorphous thermoplastic resin made by polymerizing vinyl chloride monomer with certain additives (such as stabilizers, lubricants, fillers, etc.).

In addition to the use of additives, the method of blending and modifying with other resins has been adopted, which has obvious practical value. These resins are CPVC, PE, ABS, EVA, MBS, etc.

UPVC has a high melt viscosity and poor fluidity. Even if the injection pressure and melt temperature are increased, the fluidity does not change much. The molding temperature is very close to the thermal decomposition temperature, so the temperature range is narrow. It is a difficult material of molding.

1. Plastic processing

After 24 hours at room temperature, the amount of water absorption is less than 0.02%, so there is no need to dry. If it must be dried, it can be placed in dryer at 60-70 °C for 3 hours, or at 80 ° C for 1-1.5 hours.

Recycled materials can be mixed with up to 20% of the new material, depending on the end use of the product. Abuse of recycled materials can cause injection molding to fail, not only because there are too many recycled components, but also because the materials are reprocessed many times.

2. Injection molding machine selection

UPVC has a high viscosity and easy decomposition, and the decomposition products have a corrosive effect on iron. The screw and barrel is special designed, and extra fan on barrel may be required.

3. Mold and gate design

The mold temperature can be set 40°C. The length of the flow path is short and the diameter is large to reduce pressure loss and keep holding pressure. The shorter the gate, the better. The gate cross section should be round, the diameter is at least 6 mm, and the shape is conical, and the inner angle is 5° degree.

The runner cross section is also round and 7mm diameter.

The mold is stainless steel with a chromium content of at least 13%, preferably 16%, and a Rockwell hardness of at least 55. The mold can be chrome-plated to form protection against corrosion.

4. Melt temperature

It varies from 185-205 °C. The exact melt temperature of the UPVC can be known from the smoothness of the injected material. If the material is rough,  the material is not uniform (insufficient plasticization), indicating that the temperature is too low; if the foam is emitted after the injection and a large amount of smoke is emitted, the temperature is too high.

5. Injection speed

The injection speed need to be slow, otherwise excessive shearing will degrade the material. When UPVC is used to produce extremely smooth thick-walled products, multi-stage injection molding speed should be used.

6. Screw speed

Should be in accordance with the molding cycle. The screw surface speed should not exceed 0.15-0.2m/s

7. Back pressure

Up to 150 bar, but the lower the better. The common is 5 bar.

8. Material residence time in barrel

At 200 °C, the residence time can not exceed 5 minutes. When the temperature is 210 ° C, the residence time can not exceed 3 minutes.

Reach right plastic mold factory to get services and processes

Reach right plastic mold factory to get services and processes

by | Sep 7, 2018 | General Injection Molding

Plastic molds are important industrial products in order to shape and mold plastic before it results to a more viable and feasible product in the market. It commonly undergoes injection molding in various forms but the most popular technique is forcing a plastic liquid into a metal mold. The molding is made through the use of molten plastic that cools while it is inside the mold.

Plastic molds are used in order to lessen down the costs related to various manufacturing processes. This technology is favored because of the quick turnaround time in the procedure. A variation known as reaction injection molding is also used for fiberglass, epoxy and polymer plastic. Here are ideas on the services, processes and equipment design employed in the manufacture of these products.

Plastic molding services result from rotational molding, blow molding, thermoforming and compression molding. Other services include mold prototyping, insert molding, micro-molding, two- shot injection molding, machining and hot stamping. These services have characteristics that make them distinct from one another.

For instance, machining is that phase where the molds are removed through drilling, milling or turning. Micro-molding is known to use special and mini molding machines in order to produce small parts out of the process. The parts produced out of these services are commonly less than two grams in weight. In a two- shot injection, a plastic product is produced from two sets of raw materials through the use of only one operation.

Plastic molding processes

Plastic molds cannot be completed without undergoing some processes. First on the list is the development of a three-dimensional or 3D CAD model. The making of a computer model is that point when a manufacturer may ask a consumer for concepts and prototypes to see if they are good enough for the production of plastics.

Machines for injection molding, blow molding and thermoplastic injection are a few examples of plastic mold factory equipment designs. The basic outputs from these machines include insulated runners as well as CAM, encapsulating, stack and insert molds. This important aspect in manufacturing plastic molds is the fabrication of machineries to create the output. Barrels, liners, component and feeders are also created out of the equipment design. Along the process, special forms of equipment for different plastic mold services are formed.

Plastic molding, one of the most vital process required, is required to taken into utilize to shape plastic using a rigid frame or mould. Not to mention the way of using technique that allows for the creation of objects of all shapes and sizes with huge design flexibility for both simple and highly complex designs.

Reaching the right and reputed plastic mold factory is important where you will gt complete solutions for this process that is a popular manufacturing option – responsible for many car parts, containers, signs and other high volume items. There are a number of added features and benefits associated with it that will surely persuade you to reach the right factory that is involved in offering you complete and comprehensive solutions.