Dip molding (dip moulding) is a process used to manufacture plastic parts, products and components. As one might expect, manufacturers perform the dip molding process by dipping a mold into liquid plastic and allowing it to set before removing it from the plastic.
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The History of Dip Molding
The modern dip molding process got its start in the United States and the United Kingdom in the 1930s. While people used dip mold-like processes before the 20th century (ex. hot wax candle creation), it didn’t take off as an industrial process until around World War II. World War II jump started the dip mold industry because of its wide use of plastic and polymers. Around this time, manufacturers discovered that they could quickly and easily dip mold plastic shapes, which they could then use as containers, tool handles, and the like. Later, they discovered that, to get thicker walls, they could just dip and mold the product again and again.
For the first fifty years or so of its existence, most dip molding was done using either natural latex or PVC. However, when the FDA announced in 1993 that between 2% and 10% of the US population had a latex allergy, the industry, particularly the medical glove industry, had to begin diversifying. At that time, they added a finishing process that involved removing process powders. They also tried to remove some of the offending proteins from latex itself. Even more, the dip molding industry began working with other polymer products, like nitrile rubber, neoprene, polyurethane, and SBR (styrene butadiene rubber).
Today, the dip molding industry is booming. The plastic dip mold industry is particularly big. In the coming years, you can expect to see this trend continue, as automation becomes more prevalent, equipment becomes more efficient, tooling costs drop, and more and more polymer blends become available.
Advantages to Dip Molding
There are many advantages to dip molding, as well as dip coating. First, dip molding is suitable for fast prototyping because it has short lead times and, unlike other manufacturing methods, it has minimal setup costs. The latter fact is because both the equipment and process are basic. In addition, since the process is almost entirely automated, dip mold labor costs are also low. Plus, as the process is straightforward, it has relatively high turnaround times.
Furthermore, dip molded parts are highly flexible and malleable; therefore, manufacturers can easily strip even the most complex parts from the molds. Even better, dip molded products require little or no secondary processing. This ensures that there is minimal material wastage during the process.
In addition to providing a colorful and attractive finish to various products, plastic moldings and coatings provide corrosion resistance, scratch resistance, wear protection, and a smooth, tactile grip for safe and easy handling. Finally, dip molding and dip coating are both incredibly versatile. They offer a wide range of wall thicknesses, wall textures, and part sizes.
Applications of Dip Molding
Dip molding is an important plastic product formation process. The purpose of dip molding is both decorative and protective. For example, covering the handles of many everyday objects improves the comfort and grip, and can add an element of design to an object.
Dip molded parts and dipped products are popular for use in a wide variety of industries, including the consumer, medical, electronic and retail industries. In particular, dip mold products are important in the: biking, medical device, sanitation, appliance, and sports and recreation industries.
Dip Molding Products
Dip molding produces dipped mold parts such as: plastic caps, plastic plugs and other sorts of plastic closures, handles and grips (like pump grips) for appliances, handlebars, cap plugs, sports and recreational equipment, gloves, and countless small plastic products.
Materials Used for Dip Molding
Dip molding relies primarily on plastisol. However, the process can also be performed with materials like latex, neoprene, urethane, and epoxy.
- A vinyl (PVC) compound, is already a liquid at room temperature and therefore is an ideal material choice for the process of dip molding as it requires even less energy to undergo manufacturing. Plastisol also hardens permanently once heated, which makes plastisol dip molding, also known as PVC dip molding or vinyl dip molding, more perfect for plastic product manufacturing.
- Until the late 1980’s, latex dip molding was actually the most popular type of dip molding. Latex as a raw material is extractable from nature, but it can also be synthesized. In addition, it’s inexpensive and non-toxic. Unfortunately, some of the world’s population has an allergy to it, making it less popular and lucrative than it once was.
- Useful in dip molding because it offers properties of chemical resistance, ozone resistance, flexibility, and non-toxicity. It is quite similar to latex, but it is safe for those with latex allergies.
- Also known as polyurethane, is a polymer that offers properties of high resilience, durability, and light stability.
- Another great material for dip molding. It is known for its mechanical strength, chemical resistance, heat resistance, temperature resistance, and ability as an electrical insulator.
Dip Molding Process
The first step in the dip molding manufacture process is to warm the polymer or vinyl until it reaches a liquid state. Two variables to be considered that can affect both the quality and appearance of the product are the temperature of the mold part and the temperature of the material. That’s why, once at the right temperature, the polymer must be kept in this state, and if necessary, heated to optimum viscosity.
Next, manufacturers must determine a consistent speed for dipping, or immersing, and withdrawing the mold from the liquid. They use these determinations during the third step.
During step three, manufacturers heat mandrels, or molds, in order to ensure that the molten polymer will stick to their surfaces. Then, they slowly lower the molds into the liquid plastic, making sure to allow for uniform surface coverage and even wall thickness. Because the plastic has been heated, this is called a hot dip process. The longer a mold is allowed to be immersed in the liquid for, the thicker the wall of the product will be, and so it is important to consider this manufacturing aspect before undergoing plastic dip molding.
Once the desired "dwell time" has been reached, manufacturers slowly remove the mold from the liquid and let it harden. Like when they first immersed it, they must remove the mold slowly and consistently in order to ensure a smooth finish on the surface, and to prevent wall thickness irregularities.
After this, some polymers, like plastisol, are further heat treated in an oven to fully set the mold.
Finally, the polymer is then stripped from the mandrel. If necessary, manufacturers move it on to secondary finishing. However, because dip molded products are relatively precise, most do not require extra finishing.
Customization for Plastic Molding
When designing plastic molding projects, manufacturers think about the necessary textures, hardness levels, dimensions, etc. of the parts they plan to create. Fortunately, they have a lot of design freedom; plastic can be manufactured in many different colors, and by using different techniques, manufacturers can aesthetically adjust the respective textures, hardnesses and surface appearances of the coatings.
Dip Molding Types
- Cast Molding
- Involves dispensing plastisol into a mold, placing it in an oven and then heating it so the plastisol fuses into the finished part. This process is capable of producing multi-colored parts.
- Cold Dip Coating
- Used mostly for thin coatings of plastisol. In this process, the object is dipped in plastisol without preheating, and then placed in a heated chamber.
- Dip Coating
- The process of submerging an object in a tank full of coating material.
- Dip Molding
- A thermal process by which metal molds are dipped and coated.
- Hot Dip Coating
- The process in which an object is heated, dipped in plastisol and then placed in a heated chamber where fusion takes place.
- Plastic Caps
- Plastic covers formed through the process of dip molding.
- Plastic Dip Coating
- A process in which metals are coated with plastic.
- Plastic Plugs
- Plastic caps formed through the process of dip molding.
- Polymer Coatings
- Act as a protective covering in corrosive environments by enhancing the abrasion resistance of the component’s surface.
- Rotational Molding
- A method that involves placing a limited amount of plastisol in a mold and then rotating it as heating takes place so the liquid is equally distributed. This is used to create hollow products.
- Saturation Coating
- The method of completely immersing an object in liquid plastisol and then letting it gel so that the object is totally covered.
- Vinyl Coating
- Wear resistant vinyl compounds that undergo dip coating processes to form rigid smooth or textured protective coatings over substrate surfaces, typically metals.
Molding Machinery Used
There are a variety of different machines, systems, and tools used in dip molding processes.
- Automatic Rack Transfer System (ARTS) Station
- Used mostly with rotary dip molding machines in rotational molding. The advantages of this system are that: 1) it raises the amount of operator positions for reloading and unloading without taking the racks offline, and 2) it permits extra positions for cooling and priming metal parts. The latter is important for coating preparation or for automatically lubricating mandrels.
- Molding Blower
- A high temperature air mover that raises turbulence and heat transfer to the mandrel or tool in the preheat oven. It’s also used in the cure oven to accelerate curing and lower heat stratification.
- Closeable Dam
- A device used in dip molding. Manufacturers install it in the dip tank, where it completely stops the flow of plastisol over the weir during the dip cycle. The closeable dam must work in tandem with the dip tank agitation and the recirculation pump cycle.
- Molding Mandrel
- Or metal mold, forms the internal shape of a dip molded part. Typically, the mandrel is made of steel, aluminum or other alloys. To customize the dip molding process, manufacturers can mount multiple mandrels to a bar that is placed into a master rack, or they can mount them directly on the arm of a molding machine.
- Master Rack
- A frame used in dip molding. It’s usually made of aluminum or steel, and it has pins or indentations symmetrically positioned for retaining adapter bars. Typically, the designs of master racks are customized for specific dip molding machines, and can be used with many similar tooling bars.
- Overhead Dip Station
- A dip station designed for constant, multiple dips, multiple colors, or multiple grades. It features two-axes. The vertical axis removes preheated racks of parts or tools from the machine, and then moves them laterally to any of up to four dip tanks.
- Molding Pawl
- A component of the overhead dip station. Typically used in pairs (but customizable), this J-shaped gripper is used to grab the rack of tools to be dip coated.
- Profile Dripping
- Used to control drip and thickness. It relies on programmed positions, speeds and dwell times to alter the dip speeds of a tool or mandrel. It can be customized to work with both traditional moving tank designs and overhead dip systems.
- Strip Heater
- An electric heater used in cure ovens. Airflow over these heaters moves the heat from the strip heater to the plastic coating to be cured. Most strip heaters are insulated by mica, but manufacturers can also customize them via different insulation types, such as mineral insulation or nickel-chromium insulation.
- Tubular Heater
- An electric heater with a high surface temperature, used in coating. It’s typically installed in the preheat section of the machine. With the help of customizable airflow and infrared radiation over the elements, the heater moves heat to the mandrel or to the tool to be coated.
Variations and Similar Processes of Dip Molding
To create the best product, manufacturers turn to many variations on and similar processes to the dip mold process. Learn more about them by reading the descriptions below.
- Dip Coating
- A similar service that is also offered by many dip molders that partially or fully coats products with a protective material. Dip coaters apply coatings to products in the same method as dip molding, by dipping them in liquid plastic or liquid plastisol. Plastic coatings are typically a polymer coating or a vinyl coating. The most common, however, are PVC coatings and plastisol coatings The biggest advantage of dip coating is its protective and insulative properties. For example, electrical wires and components such as jumper cables or extension cords are dip coated to provide electrical insulation. Also, both plastic coating and plastisol coating improve a product's noise reducing and vibration dampening properties, add excellent thermal insulation and eliminate the need for deburring (because coating reduces sharp edges on metal parts). Coating around wires and fences improves the corrosion resistance of the products and extends their lifespan, especially when used outdoors.
- Powder Coating
- A coating process that, instead of liquid plastic, uses a free-flowing, dry powder. Manufacturers apply the powder electrostatically, and then cure it under heat. One of the advantages of powder coating is that it does not require a solvent to keep the binder and filler parts in liquid suspension. Also, using powder coating, manufacturers can produce parts with much thicker walls without having to worry about sagging or running. Furthermore, powder coating allows for specialty effects that cannot be accomplished with conventional coating. Finally, powder coatings take less time to cure, and they release little or no Volatile Organic Compounds (VOCs) while doing so.
- Injection Molding
- A manufacturing process that, like dip molding, uses a mold and liquid material to form a part. Injection molding, though, uses a ram or screw-type plunger to force molten plastic material into a mold cavity, where it contours to the form of the mold, cools, and solidifies. Once solidified, it is a shape that has conformed to the contour of the mold. One of the most common types of injection molding is plastic injection molding. Injection molding is cost-effective, efficient, creates little waste, and produces a high yield of durable products.
- Blow Molding
- Another mold process that primarily works with plastic. Manufacturers use blow molding to make hollow plastic parts. The three main types of blow molding are: extrusion blow molding, injection blow molding, and injection stretch blow molding. During these processes, manufacturers start by melting down plastic. Then, they form it into a parison, or in the case of injection and injection stretch blow molding (ISB), a preform. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can pass. After that, they clamp the parison into a mold and blow air into it. The resulting air pressure pushes the plastic out until it matches the mold. Once the plastic cools and hardens, manufacturers can open the mold and eject the newly formed part. This dip molding service is popular for its low tool and dies costs, its fast production rates, and its ability to create complex parts.
- Silicone Dip Coating
- A subcategory of dip coating. Dip coating is a process during which manufacturers immerse finished metal products into a molten plastic or elastomer in order to coat them with a new exterior. Silicone is a synthetic rubber made up primarily of silicon, oxygen, hydrogen and carbon.
- UV Coating
- A process in which manufacturers apply UV curable coatings to products. These coatings render the products resistant to wear, scratch, fogging, chemicals, microbes, and, of course, damaging ultraviolet rays. UV coating is best used on outdoor products. They are mostly applied via spray, dip, roll, or flow processes. Because UV coating processes do not require heat, they are popular with formed plastic parts.
Things to Consider When Choosing Dip Molding
If you’re interested in investing in dip molding services, it’s important that you work with an experienced dip mold manufacturer that you can trust. While many suppliers offer dip molding and similar services, not all of them are equal, and not all of them are right for you. Find the right manufacturer for you by discussing your application at length with multiple dip mold companies. Make sure they understand your requirements and specifications, are willing and able to work within your budget and deadline, and, most importantly, that they’re dedicated to delivering you a high-quality solution. Get started by checking out the many excellent dip mold manufacturers that we have listed above.
Dip Molding Terms
- Air Release
- A test that determines the ease of removing air bubbles from plastisol.
- Automatic Rack Transfer System (ARTS) Station
- Used mostly with rotary dip molding machines. The advantage of this system is that it raises the amount of operator positions for reloading and unloading without taking the racks offline, and also permits extra positions for cooling and priming metal parts for coating preparation or for automatically lubricating mandrels.
- An irregularity on the surface of fused plastisol, caused by the contamination of water, air or solvents.
- A high temperature air mover that raises turbulence and heat transfer to the mandrel or tool in the preheat oven, also used in the cure oven to accelerate curing and lower heat stratification.
- Brookfield Viscosity
- A measure of the viscosity of plastisol.
- Closeable Dam
- A device in the dip tank that completely stops the flow of plastisol over the weir during the dip cycle. Its use requires synchronization with the dip tank agitation and recirculation pump cycle.
- Removal of trapped air from plastisol by using a vacuum during mixing or later in the process.
- Dip Line
- The uppermost edge of the dipped plastic coating.
- A material that upon being stretched to twice its length at room temperature will immediately snap back into place.
- A measure of how far fused plastisol can be stretched without breaking.
- Added materials used to reduce costs or modify the finished product.
- When plastisol becomes immobile after its liquid has been absorbed by the resin.
- When plastisol travels out of fused or partially-fused vinyl film.
- Forms the internal shape of a dip molded part, made of steel, aluminum or other alloys. Multiple mandrels are usually mounted to a bar that is placed into a master rack or mounted directly on the arm of a machine.
- Master Rack
- A frame of aluminum or steel with pins or indentations symmetrically positioned for retaining adapter bars. Typically, the designs of master racks are for specific dip molding machines and can be used with many similar bars of tooling.
- A plastisol into which solvent has been added.
- Overhead Dip Station
- Used for multiple dips or several colors or grades in a constant process. The two-axis design removes preheated racks of parts or tools from the machine by using the vertical axis, and then moves the parts laterally to any of up to four dip tanks.
- Overhead dip stations use this J-shaped gripper to grab the rack of tools to be dip coated. Typically these are used in pairs.
- Solids with low melting points or liquids with high boiling points that are used to give flexibility to PVC resins.
- A liquid substance made of a blend of polyvinyl chloride (PVC) resins and liquid plasticizers. It is a thermoplastic that can be used to produce coatings or moldings through a heat process.
- Profile Dripping
- Uses programmed positions, speeds and dwell times to alter the dip speeds of a tool or mandrel. This is for controlling the drip and the thickness, and may be used with traditional moving tank designs or with overhead dip systems.
- PVC Dispersion Resin
- Small particles of PVC that are mixed with plasticizer to form plastisol.
- Severs Viscosity
- A measure of the viscosity of plastisol.
- Dark specks in fused plastisol of burnt resin caused by overheating.
- Strip Heater
- An electric heater in most cure ovens that is typically mica insulated. Airflow over these heaters moves the heat from the strip heater to the plastic coating to be cured.
- An agent that is used in plastisol to reduce its viscosity and enhance air release.
- Tubular Heater
- An electric heater with a high surface temperature, typically in the preheat section of the machine. Air flow as well as infrared radiation over the elements moves the heat to the mandrel or tool to be coated.
- Viscosity Aging
- The tendency of plastisol to become more viscous while in storage.