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Molded Devices, Inc.
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What You May Not Know About Dip Molding and Dip Coating
The following article was contributed by Molded Devices, Inc.
Dip molding may not be a term that readily comes to mind when surgeons begin complicated procedures. Yet without this sophisticated, highly controllable process, many medical devices used daily in hospitals could not meet stringent certification requirements. Similarly, the dip coating process has been in use for decades, but many OEMs in various industries are unaware of the full scope of its capabilities.
Both processes--dip molding and dip coating--are offered by Molded Devices, Inc. (MDI), a Riverside, Calif.-based provider of custom dip molding, custom injection molding, and dip coating services. Founded in 1963, MDI is ISO 13485 certified for the manufacture of Plastisol (plasticized PVC) dip molded and dip coated components, protective caps, and protective covers for medical devices. The company offers dip coating and molding, fluidized bed powder coating, and custom injection molding in several facilities throughout the U.S., including in Tempe, Ariz., and Waterbury, Connecticut.
It also offers in-house secondary services that include printing and decorating; assembly; piercing, slitting, and die cutting; and packaging (www.moldeddevices.com).
Dip Molded Products Play Critical Role in Medical Equipment Design
Dip molding defines any process where a mold is dipped into a polymer for molding a part. The process begins with aluminum or steel mandrels, or molds, on a handling rack. The rack is preheated, then dipped into a substance such as Plastisol, latex, neoprene, urethane, or other material for a specified amount of time. The newly formed parts are then cured, dip-quenched, and stripped off the mandrels and delivered to medical equipment manufacturers in the quantity required.
The wide range of medical products made available through the dip molding process is growing and includes nasal cannulas, Y-connectors, dental dams, and tissue collection sacks. Quality stent covers, probe covers, tubes, diaphragms, and catheter balloons also benefit from this technique.
Tim Truitt, co-founder of Truer Medical, Inc. appreciates the critical role dip molding plays in the medical arena. His company supplies a proprietary line of products for airway management and temperature sensing used by anesthesiologists. One of Truer Medical's products is the esophageal stethoscope, which is used to monitor heart rate, breathing, and core body temperature during surgery.
These esophageal stethoscopes contain a critical dip molded component that is used to house the sensitive internal components and electronics required to monitor temperature and sound. The cuff also assists in the installation of the device into the patient by covering the sharp end of the extruded tubing and can be lubricated.
"It's important that the wall of the molded part is consistent and thin so that the temperature, as well as heart and breath sounds, can easily be picked up by the sensors inside the cuff," says Truitt.
The part is so critical, in fact, that Truitt says it receives 100% testing to ensure there are no pinhole leaks and the solvent bonding is secure so that upon removal, the cuff does not remain in the patient.
To meet these requirements, the cuff is dip molded in Plastisol, a liquid at room temperature that gels and remains a solid once it is exposed to specific elevated temperature. It can range in hardness from 33 (softest) to 96 (hardest) Shore A scale durometer, and offers temperature resistance from -20°F to 160°F. It is also ISO 1099 certified and approved by the USFDA.
Plastisol heads the list of dip moldable materials because of its long history of success, ease of processing, affordability, and prevalence in the industry. But latex, neoprene, urethane, and other materials may also be used.
"It's a long, difficult process to qualify a material for the medical device industry,” says Truitt. "That's why many medical equipment designers and manufacturers use Plastisol. It has successfully endured the testing process.”
For medical device applications, the Plastisol must meet Class VI testing by the United States Pharmacopeia (USP), a private non-governmental organization that promotes the public health by establishing state-of-the-art standards to ensure the quality of medicines and other health care technologies. The standards include six classes, of which Class VI is the most stringent.
For Truer Medical (www.truermedical.com), a dip molded cuff made from Plastisol had one potential negative drawback. In the hands of inexperienced dip molders used to less stringent tolerance requirements, dip molded parts could contain minute drip marks if not handled properly.
From a medical standpoint, this is problematic as drip marks could affect the thickness of the cuff's double-wall, which to be most effective is limited to 8 – 14 thousandths of an inch per wall. Any blemishes potentially diminish sound transmission and, as a result, possibly impede the physician's ability to accurately assess a patient's condition during surgery.
These types of medical devices are subject to the Code of Federal Regulations, Title 21, Part 11. The code defines the criteria under which electronic records and electronic signatures are considered to be trustworthy, reliable and equivalent to paper records and transmissions.
Fortunately, Truitt has never had any kind of Medical Device Report (MDR) from a quality standpoint because he has maintained a long-term relationship with Molded Devices, Inc. Over the years, the full-service California-based firm has refined its dip molding process to eliminate drip marks and other similar flaws.
According to Truitt, Molded Devices is one of only a few companies in the United States that can offer dip molding, dip coating (a similar process in which a metal part is dipped directly into Plastisol or other material), and injection molding capabilities.
Truer Medical receives four different sized cuffs including 9Fr, 12fr, 18Fr and 24Fr, as well as an injection molded cap for the other end of its esophageal stethoscope.
Through a key acquisition in mid-2012, Molded Devices has added latex, neoprene, and Dermosol dip molding capabilities. Latex, in particular, is ideal for molded parts for the medical industry as it is more robust than Plastisol and can tolerate a wider high-to-low temperature range. It also allows for more elasticity and the ability to withstand more chemical abrasion.
OEMs Turn to Dip Coating for Products Large and Small
Dip coating defines any process where a part is dipped into a polymer, such as Plastisol, for applying a coating directly onto the product. The process is known to deliver non-slip cushioned gripping surfaces to products, protect against abrasion and corrosion, provide electrical insulation, and enhance a product's appearance for sales appeal.
The most identifiable application of dip coating is for the grips on many hardware store tools. But it has also been used for products as varied as toys and fitness equipment, as well as outdoor furniture and municipal bike racks. However, what many OEMs may not fully understand is the variety of products that can benefit from the process. Dip coating can be used to deliver just about any coating color imaginable, a variety of hardness profiles from relatively soft to hard, along with such properties as temperature resistance, static dissipation, and UV protection. Some dip coating manufacturers have expanded their operations to dip coat not just small parts, but products as large as 55 x 55 x 8 inches.
The Dip Coating Process
In the dip coating process, parts are typically arranged on a handling rack and then lowered into a tank of Plastisol. After being dipped for a specified time, the coated substrates or parts are then cured in large ovens, dip-quenched, and removed from the holding frame.
Plastisol is preferred for dip coating for the same reasons that it heads the list of dip moldable materials. It is also available to match color, hardness, finish, and such properties as high and low temperature resistance, static dissipation, and UV protection.
Dip Coating Large Bike Racks
Doug Devine, owner and general manager of Sunshine U-LOK Corporation (www.sunshineu-lok.com), was well acquainted with all the practical advantages of dip coating when he met for the first time with Molded Devices, Inc. Devine had been searching nearly 20 years for a company that could handle the kind of volume and quality required to service cities and colleges with his company's 5-foot-long, dip coated bicycle racks.
In the summer of 2011, Devine's son and Sunshine U-LOK manager, Christian, discovered MDI through the Internet. "I told MDI that we were looking for additional capability to build larger inventories," explains Devine. "They immediately expressed an interest, even though at the time, it meant investing in constructing tanks and ovens large enough to do the work."
As a result of this relationship, MDI expanded its production area and is currently one of the only dip coating manufacturers in the United States that can coat parts as large as 55 x 55 x 8 inches. Size was not the only issue, however. Devine wanted more color choices that might complement municipal, corporate, and campus architectural designs. Basic gray or black was not aesthetically pleasing in every environment.
According to Devine, MDI ran a dozen color samples and he ultimately selected six. "In the past, many customers would ask for specific colors, so we anticipate this will bring us more business."
Once they received their first shipment of dip-coated bike racks in September of 2011, Sunshine U-LOK Corporation quickly increased its inventory, and sales have been brisk. The productivity upgrade is due in part to MDI's ability to hold to schedule and meet deadlines.
"They bent over backwards to support our vision," explains Devine. "Their professionalism and quality control has been very impressive. Today, we have ten times the product we had before, and the quality and look of our bike racks is so much better."
Customers are happy, too. Last year, the City of Santa Monica, California acquired 500 bike racks in a variety of styles--the largest number Sunshine U-LOK ever installed in an American municipality.
In the past, city maintenance workers would have to re-paint the traditional steel, powder-coated bike racks three or four times a year. Now the crew simply wipes down the Sunshine U-LOK dip-coated racks with a cotton cloth and cleaning fluid.
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