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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How to Make a Silicone Mold

Silicone molds are most often used in projects that require resin or other plastic casting, and can be seen in the creation of toys, collectible figurines, props, model parts and other small plastic casting projects. Silicone rubber is usually preferred because it can be used with many materials and it does not stick to itself or other objects, negating the need for a mold release agent or a separating wall during the molding process. The most common type of silicone mold is the two-part mold, which creates a seamless end product.

Instructions

1

Build a molding box for the model object you would like to make copies from. For smaller objects, make your box walls from Legos, and roll out a flat piece of modeling clay for the bottom of the box. For larger objects, build the box walls and bottom from sturdy cardboard or wood. Make sure that the box gives your model a clearance of at least 1/4 inch on all sides.

2

Mix together half a batch of silicone RTV rubber and catalyst, following the packaging directions for the brand of rubber you have. Make sure that the catalyst is completely blended into the rubber, creating a pale version of the catalyst's color.

3

Mark the halfway point on your molding box with a pencil or marker. Pour the batch of silicone rubber into the molding box, and stop at this halfway mark.

4

Press the model object into the siliconerubber until it is half covered and does not touch the sides of the molding box. Let this half of the mold cure, or dry, overnight or for 12 hours.

5

Mix together the rest of the silicone RTV rubber, and pour it into the molding box, covering the model object completely. Let the rubber cure overnight.

6

Take the molding box apart and separate the mold halves, removing the model object. Fit the mold halves back together and secure them with rubber bands.

7

Carve a pouring hole in the top of the mold at the joining line with a razor blade or utility knife. Cut the hole deep enough to penetrate through the rubber and reach the inside cavity.

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Disadvantages of Blow Molding

Blow molding is the process in which hollow, plastic containers are made. Air is blown into molds to form items such as thermoplastic bottles, tubing and milk jugs. While blow molding allows companies to manufacture high volumes of plastic containers, which are significantly cheaper than glass, there are a few disadvantages to the process. Some disadvantages include environmental hazards and a significant dependence on petroleum.

Environmental Disadvantages

Plastic products made by the process of blow molding aren't biodegradable, which presents an obvious environmental hazard, especially when empty containers find their way to landfills. When disposed of in landfills, plastic products are buried and remain in the earth forever. Their oil-based material then becomes part of the soil and runs the risk of threatening plant life, animals and groundwater.

Dependence on Petroleum

Aside from the gasoline industry, plastic manufacturers depend on millions of gallons of petroleum in their quest to produce blow-molded products. Because oil is the most important agent in thermoplastics and blow molding is becoming more streamlined and automated, the process plays an ongoing threat on a diminishing world oil supply.

Process and Material Limitations

Although blow molding has been automated and can produce mass quantities of products, the process is largely limited to hollow forms. These forms are delicate and contain various thicknesses which must be precise, which often results in wasted material in the process of arriving at containers with proper dimensions and specifications. In some cases, thermoplastic is stretched to save on material, which can lead to substandard containers.

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Steps of Injection Molding

·                                  

Many popular plastic items are produced by injection molding.

Injection molding has continued to grow since the late 19th century. Capable of producing small items such as combs, it is also used to create parts for airplanes and medical supplies. It is hard to imagine the world without the products it produces. The process was patented by John Wesley Hyatt and his brother Isaiah in 1872. Today, injection molding is used to produce about 30 percent of all plastic products. The process is relatively simple, but expensive. Thus it is usually only used to mass produce items.

Instructions

1

Clamp the mold shut. This will hold the mold in place while the mold is filled with melted plastic. It will also keep the mold still while the plastic cools.

2

Inject the melted plastic into the mold. The plastic starts out as polymer resin pellets which are poured into a large open-bottomed hopper. A motor turns the auger, feeding the pellets into the cylinder where they are melted and turned into molten plastic, then pushed into the mold. The auger injects the melted plastic into the mold at a pressure between 10,000-30,000 pounds per square inch. The auger then holds the plastic, forcing more plastic in to fill the mold completely. This guarantees that the final product will not contain any gaps. A gate closes keeping the plastic inside the mold while it cools. Molds are usually either water ic belting. 35+ years' experience.

3

Drill small holes into the mold, if it is cooled by water or another liquid. The cooling period accounts for about 85 percent of the molding process. The temperature of the water is usually between 33 and 60 degrees Fahrenheit. Water below freezing can be used. However, glycol, or a similar additive, needs to be used to keep the water from freezing. The major disadvantage to using water to cool the mold is the buildup of condensation.

4

Loosen the clamp and open the mold. Remove the plastic part that was just created. Then clean the part, removing any excess plastic.

How to Calculate Molding Machine Sizes

Producing quality plastic products requires a molding machine that has been properly sized.

Molding machines come in a wide variety of clamp tonnages. The clamp tonnage refers to the amount of force that the machine can exert on a mold while the molten plastic is being injected. The plastic is injected into the mold at high pressure in order to ensure that the mold is completely filled before the plastic hardens. The pressure of the injection when coupled with the surface area of the mold creates a force that must be counteracted by the molding machine. The molding machine must be sized to handle this force to produce acceptable products.

Instructions

1.                            Sizing a Molding Machine

1

Determine the surface area of the part that is being molded in square inches. If it is a multiple cavity mold, the surface area associated with each cavity along with the runners that feed each cavity should be included in the total surface area.

2

Determine the planned injection pressure in pounds per square inch (psi). The injection pressure will be a function of the material that you are using and the part wall thickness. A material supplier can help determine the injection pressure.

3

Determine the pressintensification ratio for the molding machine. This is a function of the machine's screw and the hydraulic piston that acts upon it. The machine supplier can provide this information if it is not already known.

4

Multiply the injection pressure by the intensification ratio. This provides the plastic packing pressure in psi.

5

Multiply the plastic packing pressure by the part surface area. This results in the total pounds of force that will be exerted on the mold in pounds.

6

Divide the pounds of force by 2,000 (2,000 pounds = 1 ton). This provides the tons of force required to be offset by the molding machine's clamp tonnage. This gives the minimum clamp tonnage size needed for a molding machine for the specific product in question.

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Using a Valve Gate for Injection Molding

How to Use a Valve Gate for Injection Molding

A hot runner system with a valve gate can lower the production cost of molded plastic parts.

A hot runner system offers some significant advantages in injection molding. A key component of such a system is the valve gate. The valve gate shuts off the flow of molten plastic to the mold at a specific time right at the part surface. This allows a part to be molded without a sprue or runner remaining on the part. Eliminating the sprue or runner improves the appearance of the part, may shorten cycle times, eliminates the need for a runner removal operation and eliminates the waste associated with a discarded runner or sprue.

How to use a Valve Gate in Molding

1

Size and select a valve gate in tandem with the hot runner system. The hot runner system provider will aid in the selection process. In many cases, the mold maker will coordinate this effort. The material to be molded and the overall part design will be the fundamental keys to sizing a valve gate.

2

Install the mold with a hot runner system and the valve gate in an injection press. The electronic controls for the valve gate will need to be tied to the press timer that times the injection cycle. Additionally, valve gates are often pneumatically or hydraulically actuated. Ensure that proper controls are set up to actuate the valve.

3

Determine the time in the injection cycle when the gate should be closed. This will be a function of the rate of material flow and the size of the part. Once the mold has been sufficiently filled by molten plastic to produce acceptable quality, there is no need for additional plastic to be injected. This is when the gate can be closed and the melt procedure for the next cycle can begin.

4

Set the actuator on the valve gate to shut when the injection timer reaches the time determined in the previous step.

5

Set the actuator on the valve gate to open when the injection timer is reset at the beginning of the next cycle.

6

Commence operating the injection press as per normal operating conditions.

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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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what's silicone molding?silicone mold, mold silicone

Silicone Mold

Silicone molds are produced crafts special mold rubber, silicone is characterized by high temperature, corrosion resistance, tear resistance and strong , high simulation fine , special molds for making all kinds of crafts .

 

Silicone mold materials

Silicone is good for its environmental performance and more and more people know and understand the silicone mold , let’s start form silicone raw materials .

1 , according to the performance of raw materials, silicone can be divided into ordinary silicone and The pure silica gel

Ordinary silica also known as precipitated silica ,

Color: translucent, milky white , pale yellow , gray and so on.

Hardness : 30 °, 40 °, 50 °, 60 °, 70 ° , commonly between 40 ° -70 °.

Density :1.1-1 .12g/cm ³

Elongation: 400%

Uses: more used on phone keypad, miscellaneous items, such as middle and low conductive silicone rubber products .

pure silicone rubber Color: Clear .

Hardness : 30 °, 40 °, 50 °, 60 °, 70 °, 80 ° , commonly between 40 ° -60 °.

Density :1.1-1 .12 g / c ㎡

Elongation: 600% -700 %

Features : Because this material is good transparency , strong tensile . High cost

Usage: silicone tube, protective cover and other high need high flexibility products .

2 , according to the physical properties of silicone raw materials, can be divided into solid silicone and liquid silicone .

Solid silicone is mainly used for molded products. For example: silicone case , silicone utensils , silicone molds, silicone keys , etc., mainly used for liquid silicone extrusion products, such as silicone nipple , silicone tubes.

Insulation silicone pad , excellent heat capacity , silicone ( food-grade silicone ) resistant to 200 ℃ high temperature and long-term use , the production of raw materials meet food grade standards , through FDA food-grade test , tasteless , non-toxic , mold manufacturers in accordance with production, color, shape can be customized .

 production process

Molding form and mold parting line is very important.  first, to take the easy mode , the second is the parting line should be selected without affecting the overall effect of the product, the third is not to affect product quality , such as mold line position waterscape series too high , sealing materials and more time to mold line of products prone to cracking ; fourth step is to reduce the flow of operations , such as opening half of the mold .

In order to prevent the flow around the silicone mold, use some slice for blocking the certain area , no gap , oil smooth surface . After completion of the above work to prepare , and then on the kinds of painted plaster mold or mold release agent on Vaseline or spray , smooth product requirements with a clean cotton cloth soaked in Vaseline evenly on the mold, the mold for 30 minutes species to fully absorb Vaseline , and then a clean cotton cloth to clean the surface of the mold require bright surface ; rather have the texture of the product as long as evenly coated with Vaseline on it will be better formulated silicone tune. When the direction of the irregular silica gel formulation should be agitated to mix the curing agent and silicone sufficiently minimize pumping to maintain a vacuum of the required air -0.1Mpa within the mixed rubber , smooth product is best when the adhesive coated first layer 7-8 seconds.

With a good silicone molding should be timely . The glue in a way trickle down to the highest parts of the mold , let it flow , where the flow is not in place with a painting brush in place, if it is not only full piece molded silicone brush evenly throughout the product but also on clay . Each item of each brush at least three silica layer thickness of silica 1mm, the brush process silica required to brush after each additional layer of the cured layer , the third layer when the brush is applied to the top of a second layer layers of gauze to increase the strength of the silica gel . Entire mold silicone products based in part on the size of the different requirements of thickness control in 3-4mm, width no greater than the product width 60 mm. Start silica gel solidification time was 20 minutes.

1 , clean and dry the female die, (brushing a layer of mold release wax release agent )

 2, 500-1000 grams of silicon rubber mold ( silicone molds , rubber molds , silicone rubber , silicone ) keep well for spare ;

3 , weight certain proportion hardener ( typically 1.5-2.5 % ), put in a container, mix and stir ;

4 , depending on the situation (especially for the first layer ) by adding a certain amount of silicone  dilution. Until thoroughly mixed up , usually 3-5 minutes.

5. Silicon rubber mold ( mold silicone mold , silicone rubber , silicone ) and the curing agent mixture , i.e. the reaction at room temperature , and the release of low molecular weight alcohol , the alcohol molecules from the colloid is required under the negative pressure discharge bulbs 1-3 minutes. Also available ( depending on the tool maker’s experience ) without the aid of equipment.

6 , multi- piece mold brushing should follow inner, middle and outer while curing appropriate. Curing agent is relatively low, the reaction time is lengthened , the reaction fully , like colloids , thus curing agent is preferably within a little more than outside . When brushing until the first layer ( inner layer ) dry and then brush a second layer . Operating time 30-50 minutes , removal time 10-15 hours. Curing time 24 hours . Note brushing first , the best use mold cloth , which can greatly improve die life ( but must not use the glass fiber cloth , or likely to cause mold scrap )

7 , three-dimensional perfusion mode , generally 10-15 hours curing as well.

8 , but also of the soft mold produced coat plaster or fiberglass to support soft silicone mold Note : 1 , analog line options: Choose the location does not affect the appearance of the product ; selection position after filling easy processing ; choose mold itself is easy to dismantle location mold ; select products easily deformed position 2 , the production schedule must not rush blindly to increase the amount of hardener , otherwise it will greatly reduce the silicone mold life.