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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How to Clean Chromed Plastic on Vehicles

·                               Chromed plastic is found on many locations of a vehicle such as grills, door handles and body mouldings. It becomes water spotted, can be discolored from acid rain or covered in bug residue. Using a glass cleaner to remove these contaminants is the safest way to clean the plastic without harming the adjacent painted areas. This process can be repeated as needed. However, since the glass cleaner dries to a spotless finish, usually no further cleaning is necessary. 

Instructions

1

Mix a bucket of soapy water using dish detergent and water as if preparing to hand-wash a car. Use the mixture with a kitchen sponge to clean the moulding of all road film and grime. Dry when complete with a chamois or kitchen-type towel.

2

Apply glass cleaner such as Windex to a kitchen towel or directly onto chrome and scrub chromed area with the kitchen towel. Chrome does not scratch easily, so use moderate pressure to scrub stains.

3

Repeat as necessary. Due to the majority of stains, such as tree sap or acid rain spots, being water-based contaminants, a water-based cleaner such as Windex is the best for cleaning. Although glass cleaner should remove all stains, rubbing compound with a terry cloth rag and elbow grease may be used for removing more difficult stains such as dried bird droppings or bug residue.

Chrome Vs. Nickel Plating

Chrome and nickel are metals used to plate machine parts, such as rollers and cylinders, with a scratch-resistant surface that protects them from wear and tear. They are also used on bathroom and kitchen fixtures.

1.                            Chrome

Chrome comes in standard and hard versions. It is applied in varying thicknesses according to the required purpose. Thinner coatings are used on objects that are not exposed to much abrasion. Thicker coatings offer more protection from abrasion and corrosion. If a machine part is frequently exposed to water, experts at Phoenix Electroplating recommend an undercoat of nickel plating, as chrome is porous.

Nickel

Nickel is used to prevent corrosion, particularly when applied prior to chrome plating on objects. It is also hard-wearing and is widely used on machine parts in the oil and gas industry, the automotive industry, in making molds for plastics and in food processing machines.

Bathroom and Kitchen Fixtures

According to Rejuvenation, suppliers of home fixtures, nickel was the standard finish for kitchen and bathroom fixtures made from the 1800s until the 1930s. Chrome then overtook nickel in popularity. Nickel is warmer in appearance and creates a more authentic, antique look, but Rejuvenation says the two finishes blend harmoniously in one room.

How to Clean Chrome Plated Plastic

Any chrome surfaces actually consist of an extremely thin layer of chrome plated onto another material. Regardless of what that other material is, from plastic to steel to aluminum, this chrome plated is what needs to be addressed when the time comes to clean it. You can always buy a special chrome cleaner, but there are several items in your home that work just as well and are far less expensive.

1.                            Toothpaste Method

1

Spread a thin layer of toothpaste on the surface of the chrome plating. Use the opaque white toothpaste, not one of the gel varieties.

2

Rub the toothpaste-covered chrome plating with a soft, clean cloth in small circular and swirling patterns. There is no need to apply a lot of force.

3

Take a fresh cloth and wipe away the toothpaste, revealing a shining, clean surface.

2.                            Vinegar Method

4

Pour undiluted distilled white vinegar into a spray bottle.

5

Spray the surface of the chrome plating with the undiluted vinegar.

6

Wipe down the surface with a clean cloth.

3.                            Baby Oil Method

7

Dampen a portion of a soft cloth with baby oil.

8

Rub the baby oil into the chrome plating in the same manner as you did with the toothpaste.

9

Wipe off excess baby oil with a fresh cloth or a still fresh portion of the same cloth.

10

Wipe down the newly cleaned area with soapy water to remove any greasy feeling from the baby oil, if desired.

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How to Chrome Plastic Parts

How to Chrome Plastic Parts

1

Take the part down to the bare plastic. You can do this by etching the parts with strong chromic acid, according to Atlas Chrome. This will give you a basic surface to begin working on.

2

Repair any cracks or splits in the plastic part. You can do this by using epoxy glue purchased at your local auto supply store.

3

Dip the plastic parts with silver so that that they will conduct electricity.

4

Layer a conventional plating process such as copper, nickel or chrome onto the plastic parts in several layers. You will most likely need to lightly sand and buff the plastic parts prior this process as well.

5

Apply the chrome plating to the plastic parts for the final revamp. Do this by soaking them in a chrome plating solution for about five minutes

What Is the Blow Molding Process?

Blow molding is used to produce plastic bottles.

Blow molding is a method for making a variety of hollow plastic products. Molten plastic is extruded, in a tube shape, from a die, then a mold closes around it. The plastic is then inflated.

History

Blow molding first appeared late in the 1800s, but modern polyethylene bottle production did not commence until the early 1940s.

Types

The blow molding process can take four forms: reheat and blow molding, injection blow molding, stretch blow molding and extrusion blow molding. The machinery can vary significantly, though the major difference tends to be the point of plastic inflation.

Uses

The various processes are used to create a range of products, including bleach and milk bottles. Stretch blow molding is used in the production of PET (Polyethylene terephthalate) bottles, which are widely employed for carbonated beverages.

Plastics

The plastics used in the various blow molding processes can include HDPE (high density polyethylene), LDPE (low density polyethylene), PP (polypropylene), and PVC (polyvinyl chloride).

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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The Stages of Blow Moulding

today virtually all cast plastic parts are manufactured using blow molding technology.

Blow molding is a process used to cast plastic parts that are hollow. Since 1942 when the first polyethylene bottle was produced using blow molding technology, blow molding has become the standard manufacturing process for making cast plastic parts. Blow molding involves the fabrication of a tube made of molten plastic called parison. The next stage of the process is to shape the tube into the desired form using one of several blow molding processes.

Heating The Resin

The first step in any blow molding process is to heat the resin. Thermoplastic resin is heated to about 400 degrees. Once the resin reaches its molten state, it is extruded over a die head. The die head forces the thermoplastic resin to flow around it, thus creating a hollow center in the resin. The resin has now formed a tube called parison.

Molding

The parison is then placed inside a pre-determined mold. The interior shape of the mold cavity is what will ultimately determine the shape of the finished casting. The mold is then closed around the parison. At this point in the process, the parison is still very warm. The mold however, is cooled with water.

Inflation

Compressed air is then blown into the mold. The air fills the center of the parison tube and forces the sides to expand, thus conforming to the shape of the mold interior. The parison is still very warm at this point to allow it to expand without breaking. As the warm parison expands to meet the cold walls of the mold, it freezes off and becomes rigid.

Cooling

Once the warm parison has cooled off, it solidifies inside the mold. Once properly cooled, the parison will maintain the form in which it was cast. The mold can now be opened and the finished plastic component removed.

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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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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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How to Generate Runner Sizes for Plastic Injection Mold Design

The runner feeds the molten plastic from an injection machine into the mold to form the desired plastic part. The length of the runner is completely dependent on the part design, so there are no specific rules regarding overall length. It is the diameter of the runner that impacts part quality and cost and therefore it should be sized with some care. Once the runner freezes, no more plastic can be injected into the part. The runner should be sized to make sure that part receives sufficient plastic without excessive fractional heating, while freezing quickly enough to minimize cycle time.

Instructions

1.                            Calculating Runner Diameter

1

Determine thickest cross-section of the desired part.

2

Where part design allows, locate runner nearest to the thickest cross section of the part. If the part is of a uniform thickness, locate the runner near the center or along the longest edge, as part design allows.

3

Runner diameter should be between 75% to 100% of the part thickness where the runner is located.

4

Based on your injection machine type, determine the acceptable pressure drop for an injection cycle.

2.                            Calculate Injection Pressure Drop

5

Calculate runner volume. V = pi x r^2 x L, where pi = 3.14159, r = runner radius and L = runner length.

6

Calculate volumetric flow rate (Q) based upon your pre-determined fill time. The fill time is a function of material type, part thickness, and desired cycle time. The molder must know this independent of this exercise. Q = V/t, where t = seconds of fill time.

7

Calculate shear rate (S). S = 4Q/(pi x r^3)

8

Calculate the pressure drop (P). P = (S x m x 2L)/r, where m = melt viscosity of the plastic. The melt viscosity is a function of S, melt temperature, and the material. The molder must know this independent of this exercise, although many plastic suppliers can help with this.

9

Compare pressure drop to predetermined acceptable pressure drop. If improvement is desired, change the runner diameter and repeat the exercise. Repeat calculation until an acceptable runner diameter is found.

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