||Dip Molding & Dip Coating - Frequently Asked Questions.
- What is the dip molding process?
Dip molding defines any process where a mold is dipped into a polymer for molding a part. This process is used to make everything from drink coolers to caps, grips and formed parts. The process begins with aluminum or steel mandrels (molds) situated on a handling rack. The rack is often dipped in a mold release solution to aid in stripping a finished part and then preheated. The mandrels (molds) are then dipped into the plastisol material for a specified time. The newly formed parts are then cured, dip-quenched and stripped off the mandrels (molds).
- What is the dip coating process?
Dip coating defines any process where a part is dipped into a polymer for applying a coating directly on the product. This process is used to provide cushioned grips for objects such as hand tools and to provide protective or decorative coatings on parts. The process begins with the parts situated on a handling rack. The rack can be dipped in a primer solution to aid in the adherence of the coating and then preheated. The parts are then dipped into the plastisol material for a specified time. The newly coated parts are then cured, dip-quenched and removed from the holding frame.
- What materials are used in dip molding and dip coating?
Foremost, plastisol is the most common dip molding material. But latex, neoprene, urethane, and other materials are also used.
- How much set-up time is required for part production?
In the past, level sensing systems did not account for vinyl displacement. This meant several test frames were run to establish accurate part length. Due to recent technological advances and the option of closed loop level sensing, our systems can be configured to dip proper length the first time and every time after.
- What is the most efficient way to heat forms for the molding process?
Depending on part configuration, high velocity convection air provides the most uniform preheat. A combination of infrared with convection air can be supplied to utilize the quick heat-up of infrared and the heat transfer uniformity of convection.
- How does the system ensure uniform part wall thickness?
Uniformly preheated molds/parts ensure consistent wall gauge. By utilizing high velocity convection air tightly controlled to equilibrium temperature, we ensure repeatable wall thickness. By maintaining temperatures close to the set point, cycle after cycle and day after day, consistency and repeatability are assured. As a result of the superior ovens, variables such as open oven doors or extended oven dwell times do not adversely affect system performance or part quality.
- Do dip tanks require cooling?
Generally, tanks do not require cooling. Old systems used poorly insulated ovens, spilling heat into the vinyl making the idea of cooling the tanks attractive. In fact, tank cooling is unnecessary for most applications on MCT machines.
- Is there a need to exhaust smoke or fumes from the vinyl dip station?
No, almost no smoke or fumes are present and therefore, no dip station exhaust is normally necessary. This again is the result of lower preheat temperatures. Only a slight waft of smoke normally rises when the mold enters the plastisol.
- Is an additional filter needed for exhaust or smoke?
No, additional filters are usually unnecessary. As a result of the high velocity convection, little smoke is generated and no special handling of exhaust is usually necessary. At temperatures below 450°F, normally only small amounts of plasticizer are exhausted. That small amount of plasticizer is dissipated by the volume of air exhausted.
- Is any treatment to quench water necessary?
No, treatment of the quench water is not normally necessary. A recirculation system using cold tap water is usually more than adequate. Chilled water can accelerate cooling by keeping the quench water temperature lower.
- What is the best stripping method?
We usually accommodate the customers' preferred method of stripping for their specific parts. These methods have generally been mechanical or pneumatic. We can provide automatic part stripping systems that will reduce operating costs in addition to the potential for repetitive motion injuries to operators.
- How much scrap or percentage of scrap should we expect?
You should expect almost no scrap. Our best recorded estimate is based on probe tips of 1/16" diameter and a tolerance of 0.005" and 100% QC. As you know, these are difficult parts. Before the installation of our machine, our customer was rejecting over 27%. After the installation of our machine, our customer was rejecting less than 3%.
- What safety features are included in an MCT system?
A number of safety features are standard on every MCT system.
Emergency Stop pushbuttons. Emergency Stop pushbuttons are provided at several points which immediately shut down the entire system. The oven burner is shut down immediately while the oven exhaust blowers continue to operate to quickly cool the ovens and prevent any potential fire hazard.
Pause/Resume pushbutton. A unique Pause/Resume pushbutton is also provided for the operator, which immediately "freezes" all motion without shutting down the ovens. If the operator merely wishes to clear a jammed stripper plate or check the tooling, the operator presses this pushbutton. When finished, the operator presses the pushbutton again to immediately resume production.
Safety Fencing. Safety Fencing encloses the vinyl dip, quench, and strip areas of the machine. An access opening is provided in the strip area for the operator. The opening is protected by a safety area sensor which stops motion when a beam is broken.
National Fire Protection Association Standards. The ovens are designed in accordance with National Fire Protection Association standard #86, with additional safety features that we consider sound design practice.
National Electrical Code and OSHA Safety Standards. The entire machine is designed in accordance with the National Electrical Code and OSHA Safety Standards as minimums. Sound engineering frequently requires that we exceed these minimums.
- Can you help us reduce our raw material costs?
There are a few ways to reduce your raw materials cost through formulation, ordering, and efficiency. To reduce cost through formulation, fillers or extenders may be added to extend the raw material. Dip molders and coaters normally avoid fillers and extenders due to problems with material handling and finish quality. As a result of our unique agitation approach in every MCT dip tank, our system can accommodate almost any formulation imaginable.
To reduce cost through ordering, choose totes rather than drums of commonly used material. Also, ordering standard material for an entire year in advance for storage and distribution from the supplier will reduce costs and provide protection from price increases.
To reduce cost through efficiency, every MCT system can very accurately control wall thickness to provide a reduction of material usage. One customer of caps and plugs has saved over $90,000 per year in raw material as a direct result of the accuracy of wall thickness on our system. To assist you even further, quality raw material suppliers can also be quite helpful.