Dip molding is the process of manufacturing plastic parts, products and
components by dipping a mold into liquid plastic and allowing it to set
before removing it from the plastic. The process is common in
manufacturing items for the consumer, medical, electronic and retail
industries, producing parts such as plastic caps, plastic plugs and
other sorts of plastic closures, handles and grips for appliances,
sports and recreational equipment, gloves and small plastic products.
Dip molding is an important plastic product formation process. Dip coating is 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. Plastic coatings are typically polymer coatings or vinyl coatings. The most common however are PVC coatings and plastisol coatings although other materials also used in dip molding include latex, neoprene, urethane, epoxy etc. Plastisol, a vinyl 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 is ideal for the manufacturing of many plastic products. Products used for outdoor applications use UV coating to protect products and surfaces from damaging ultraviolet rays.
During the process of dip molding, the polymer or vinyl is kept in a liquid state and heated if necessary to bring it to optimum viscosity. Two variables to be considered that can affect both the quality and appearance of the product are the temperature of the mold and the temperature of the material. Next, it is important to determine a consistent speed for dipping, or immersing, and withdrawing the mold from the liquid. Mandrels, or molds, are heated to ensure the adherence of the molten polymer to the surface of the mold. The mold is slowly lowered into the liquid plastic allowing for uniform surface coverage of the mold and even wall thickness. 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 dip molding. Once the desired "dwell time" has been reached, the mold is slowly removed from the liquid and allowed to harden. The mold has to be removed slowly and consistently to ensure a smooth finish on the surface, and to prevent wall thickness irregularities. Some polymers, such as plastisol, are further heat treated in an oven to fully set the mold. The polymer is then stripped from the mandrel and moved on to secondary finishing if necessary. However, dip molded products are relatively precise and do not often require extra finishing. A broad range of parts and products are made from this method including pump grips, plastic bags, handle bars, plugs and numerous small plastic parts.Dip coating
is a very similar process to dip molding, but it is used to provide a protective layer on the surface of an existing part. Some products and parts may be fully coated, such as plastic coated fences, wire forms or racks, while others are half coated to serve as grips, tool handles or electrical connectors. The purpose of dip molding or dip coating 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. Plastic can be manufactured in many different colors and by using different techniques, texture, hardness and surface appearance of the coatings can all be adjusted aesthetically. However, the more important reason for 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. Plastic coating also improves a product's noise reducing and vibration dampening properties, adds excellent thermal insulation and eliminates the needs for deburring as it 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.
There are many advantages to dip molding and dip coating and these processes are used commonly in plastics manufacturing. Dip molding is suitable for fast prototyping due to its short lead times and unlike other manufacturing methods, there are minimal setup costs because both the equipment and process are basic. Labor costs are low as the process is almost entirely automated, and as the process is straightforward, there are relatively high turnaround times. The parts being made are highly flexible and malleable and therefore even the most complex parts are able to be stripped easily from the molds. Dip molded products or coatings require little or no secondary processing due to the nature of dipping and removing, and this ensures that there is minimal material wastage during the process. In addition to providing a colorful and attractive finish to various products, plastic coatings provide corrosion resistance, scratch and wear protection and a smooth, tactile grip for safe and easy handling. A range of wall thicknesses are achievable through using controlled temperature, dip speed and time, and the rate at which a piece is removed from the plastisol.
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Dip Molding Types
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.
is 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.
- is the process of submersing an object in a tank full of coating material.
- is a thermal process by which metal molds are dipped and coated.
is the process in which an object is heated, dipped in plastisol and
then placed in a heated chamber where fusion takes place.
- are plastic covers formed through the process of dip molding.
- is a process in which metals are coated with plastic.
- are 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.
is 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.
is the method of completely immersing an object in liquid plastisol
and then letting it gel so that the object is totally covered.
- Vinyl coatings are wear resistant vinyl compounds that undergo dip coating processes to form rigid smooth or textured protective coatings over substrate surfaces, typically metals.
Dip Molding Terms
- A test that determines the ease
of removing air bubbles from plastisol.
- 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
- 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.
- A measure of the viscosity of plastisol.
- 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.
- 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
- Added materials used to reduce costs or modify the finished
- When plastisol becomes immobile after its liquid has
been absorbed by the resin.
- When plastisol travels out of fused or partially-fused
- 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.
- 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.
- 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.
- 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.
- Small particles of PVC that are mixed with
plasticizer to form plastisol.
- A measure of the viscosity of plastisol.
- Dark specks in fused plastisol of burnt resin caused by
- 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.
- 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.
- The tendency of plastisol to become more viscous
while in storage.