How to Inject Silicone Molds

How to Inject Silicone Molds

·      Often castings of an object are made by injecting material into a mold. The mold may be made up of two or more pieces, which are closed before injection begins. The main benefits of this process are reduced seam lines in the product as well as allowing you to use only as much casting material as you need with little waste. When injecting material into a closed silicone mold, it is essential to take several steps to insure that the casting comes out right. If your mold was designed for this purpose with the holes already in place, begin at Step 6. 

1

Determine the best injection point in your mold. Ideally, this should be a place that is not easily seen on the cast, such as the back or bottom. Mark the point with a marker.

2

Determine the highest points in the cast. Mark these with the marker.

3

Drill a hole in the silicone at the injection point. The drill bit should be the same diameter as the tip of the syringe. Use an extremely sharp drill bit to prevent the rubber from grabbing onto the bit. It's a good idea to have a friend hold the mold in place just in case the bit grabs the silicone; otherwise the entire mold will spin and could cause injuries.

4

Drill small holes in the highest points. Use the smallest bit you have for these as they are simply to allow air to escape as you inject the casting material.

5

Mark the holes in the mold shell and drill it out as well.

6

Apply a thin coat of silicone mold release or hand soap to the entire inner mold surface with a paintbrush. Allow it to dry and buff out the excess with a paper towel.

7

Close the mold and strap or clamp it shut tightly.

8

Mix the casting material according to its instructions.

9

Pour the casting material into the syringe.

10

Insert the tip of the syringe into the injection hole and inject the casting material.

11

Allow the casting material to run out of the air release holes for a few seconds before plugging each one with a bit of clay. This allows any air bubbles in the casting material to escape the mold.

12

Once the mold is filled, remove the syringe and plug the injection hole with clay.

13

Allow the casting material to cure and dry.

14

Remove the cast from the mold.

15

Remove the knobs left by the holes with a razor blade and sandpaper if needed.

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Dangers of Injection Molding

Many plastic products are pressed by an injection molding machine.

Many common plastic items are created using an injection molding machine, and manufacturers point to the machine's efficiency and speed in pressing out plastic products. Much of the injection molding process is automated, and in many cases, the machine operator's role is merely to monitor it. While operation requires minimal training, there are several potential dangers to running an injection molding machine.

Heat

Depending on the type of material used, the melting point for plastic ranges from 250 to 650 degrees Fahrenheit. An injection molding machine will heat up enough to not just melt the plastic, but allow it to flow smoothly into the mold. Burns are a hazard, whether from the machine's heated surfaces, melted plastic or from the freshly molded product. In addition to eye and face protection, heat-resistant gloves may be needed while operating the machine.

Caught In the Press

On an injection molding machine, the platens join together to form the actual mold, and the plastic is molded under pressure before it is ejected. This constant movement creates a hazard, as fingers can be crushed or amputated in the press. Long hair and jewelry can also get hung up in the machinery, severely injuring the operator. Reaching into a molding machine to free up a stuck part is particularly dangerous.

Peripheral Machinery

While not part of the injection molding process, waste plastic is often thrown into a grinder that can shred the scraps--or anything else that gets into the grinder--in seconds.

Fumes

Plastics and polymers are made from different chemical compounds that, when melted, may give off hazardous fumes. An injection molding machine should only be operated in a well-ventilated area.

Flying Objects

While most products made via an injection molding machine are ejected in a controlled manner, there is still the possibility of flying objects. Eye and face protection should be worn when operating the machine.

Slipping and Falling

Good housekeeping is essential when running an injection molding machine. Scraps of plastic can quickly collect on the surrounding floor area quickly, and it is easy to lose your footing and fall. New plastic is often shipped in pellet form, which can be hazardous if spilled.

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The Plastic Manufacturing Process

1.                            Plastic Injection Molding Process

Injection molding is one of the main methods by which parts are manufactured from plastic. The first step in the injection molding process is to feed plastic pellets into the hopper, which then feeds the pellets into the barrel. The barrel is heated and contains a reciprocating screw or a ram injector. A reciprocating screw is typically found in machines that produce smaller parts. The reciprocating screw crushes the pellets, making it easier for the plastic to be liquefied. Toward the front of the barrel, the reciprocating screw propels the liquefied plastic forward, thereby injecting the plastic through a nozzle and into the empty mold. Unlike the barrel, the mold is kept cool to harden the plastic into the correct shape. The mold plates are held closed by a large plate (referred to as a movable platen). The movable platen is attached to a hydraulic piston, which puts pressure on the mold. Clamping the mold shut prevents plastic from leaking out, which would create deformities in the finished pieces.

2.                            Plastic Extrusion Molding Process

Extrusion molding is another method of manufacturing plastic components. Extrusion molding is very similar to injection molding and is used to make pipes, tubes, straws, hoses and other hollow pieces. Plastic resin is fed into a barrel where it is liquefied. A rotating screw propels the liquefied plastic into a mold, which contains a tube-shaped orifice. The size and shape of the tube determines the size and shape of the plastic piece. The liquefied plastic then cools and is fed through an extruder, which flattens the plastic and forms the piece into its final shape.

Issues That Arise in the Plastic Manufacturing Process

A number of complications can arise during the plastic manufacturing process, including burned parts, deformities, surface imperfections and brittle parts. Parts become burned when the molds are not kept cool or if the melting temperature in the barrel is too high. Additionally, if the reciprocating screw becomes jammed or is not rotating fast enough, liquefied resin will remain in the barrel too long and become scorched. Surface imperfections and deformities occur when the surface temperature of the mold is uneven, if the molds are not clamped tightly enough or if the melting temperature is too high. Brittle pieces are formed when not enough liquefied resin is injected into the mold or if the plastic hardens before the mold can be filled. Regular testing and calibration of injection and extrusion molding machines is critical to ensure that the process runs smoothly.

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Silicone Mold Problems

 

Frequent Questions

1 . Why silicone mold appear less turning model ?

In the process of making molds adding too much silicone oil, silicone oil destroys the molecular weight silicone , so the mold will be fewer non-durable turning model such phenomena . If molding more complex patterns products come with a large hardness silicone mold , there will be fewer turning model of the phenomenon , because silicone excellent time will be very brittle , easily broken . Conversely , if you do build a product to do with a small hardness silicone mold , the result would be equally unsatisfactory . Because the silicone is too soft, it will reduce the tensile and tear strength , made ​​out of the mold will be deformed , so turning model number will be reduced. Plastic mold itself is very good quality , silicone no good or bad , only suitable or unsuitable . We should adopt appropriate size product hardness silicone to make a mold.

2  Why silicone mold have burning phenomenon ?

Because unsaturated resin and resin product added peroxide curing agent after the reaction in case of resin will produce a lot of heat, general resin curing time of 3 minutes, three minutes after going to release soon , will prevent the silicone mold burning problem

3 Why silicone mold will appear in the table dry quit phenomenon ?

Silicone mold belongs condensation silicone , which is absorbed by the moisture in the air and cured silicone in the process of making , the water evaporated , while there is no transferred amount of water, this phenomenon occurs . Solution: This phenomenon does not belong to product quality issues , but because there is no control of moisture , silica gel to enhance shelf life , shelf life of these phenomena appear long , long time using silica gel , add amount of 0.05% water ,  the problem can be solved.

4 Why silicone mold appear poor tension phenomenon ?

Because the client in the production process of the mold in order to reduce the viscosity of silicone , silicone easy to make large amounts of silica in a silicone oil is added , this will become very soft silicone that produce intolerance pulling the tear strength is reduced , Rally deterioration phenomenon resulting mold is not durable , life is short, less turning and so on.

5 Why mold will appear oil flush?

Silicone mold itself have no oil flush problem , just because during operation adds composite silicone ( silicone oil with white mineral oil complex ligand ) as white mineral oils are petrochemical products, not silicone .

6 Why mold have aging phenomenon ?

In the process of making silicone molds , we recommend our customers the best without any oil, if necessary , the amount of silicone oil added up to no more than 5 % to 10 %. Because the addition of silicone oil will destroy the molecular weight silicone too , so do not come out of the mold will produce acid , intolerant aging phenomenon.

7. Why silicone mold have surface marks , stripes, not smooth and so on ?

This phenomenon is a product or a model to be replicated no grinding or polishing sake. Because in fact the model or the product itself is not enough to smooth or perfect , so the product or model to be copied if not polished or polished , even the best silicone molds will do pretty, is not smooth enough . Another case is , when playing a release agent , no uniform brushing can also cause mold surface problem.

8  you know the usage of mold silicone?

Silicone mold is mainly used for toy and gift industry , craft industry , furniture decoration industry , figures copied , building decoration industry , resin handicraft industry , unsaturated resin crafts industry , candle craft, Plastic toy industry ,Gifts stationery industry,Gypsum gifts industry, mold manufacturing industry, Bolero industrial , simulation plant and animal sculptures, Buddhist carvings crafts products and other industries copy and mold making .

Mainly in used in toys , gifts, floral fine products for packet mode , filling mold products , glass , lighting , candles , figures copy production molds , large products , open- slice mode , relief , statues , gifts making molds , sole model , perfusion mold, sand- casting.

A variety of different uses specific operations silicone mold is also not the same , what is required to achieve the specific operation must be based on a variety of different parameters.

 How to clean

General production mold clean up our way is the use of sandblasting ,place the silicone products mold into blasting machine, blasting head is aligned with the production of silicone products mold cavity , and then gradually Sort cavity by sandblasting .

 

 

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