Written by Kerryn Caulfield, Executive Director, Composites Australia Inc.
No one could argue that 2020 is a year of massive change. For industrial composites manufacturer Marky Industries, 2020 is the year the company made the bold move to transform its entire production system from LRTM (Light Resin Transfer Moulding) to reusable silicone vacuum bags.
Blaise Visconti, Composite Technical Managerfor Marky Industries, is a closed moulding specialist who relocated from the UK to work for the company and its production transition in 2019. “We’ve done a lot of inhouse R&D on the system over the past two years. Our progression and improvements in the silicone bagging system mean we can now easily tackle moulds with difficult 3D geometry using additional locators built into the bags to assist with vacuum sealing and support the weight of the silicone.”
Blaise explained that the company’s efforts have resulted in the ability to maintain a better vacuum source for the entire cure period. It is done right at the heart of the infusion without losing resin and with a dry breather system that completely eliminates the requirement for catchpots. This has resulted in substantial improvement in material usage while producing a noticeably better consolidated laminate. The system overcomes the inherent flaw in the infusion process whereby a vacuum bag can slightly relax after fill when all perimeter breathers are choked off by the liquid resin.
“We have also improved the resin runner system making it far more user friendly and much quicker to install. The old system was very fiddly and demanded much work after being fitted to the bag. The new system has all the work moulded into the runner and is simply bonded into position. We have also created multiple runner junction types for building ready to go resin flow networks, whereas before you would need to cut and paste any junction features from the flimsy channel section.”
Another very important development is the relationship of the thickness of the bags verses resin exotherm. Marky’s development team discovered that thicker silicone bags actually work against you, especially with gelcoat finished parts, due to the thermal mass of the silicone. This can hold and insulate the heat from the resin exotherm causing gelcoat blister and rework. Marky now manufactures much thinner bags supported with more reinforcement mesh to alleviate this issue. The bags are lighter and easier the handle which in turn keeps costs lower and produces better quality parts.
“The system needs less resin and glass and makes stronger parts. We’ve improved part-to-part quality, cut down on consumables and reduced our waste stream. The system doesn’t require release agents and there is no maintenance. Turnaround times have also decreased significantly,” advised Blaise.
Blaise advises that the two types of silicone rubber are 1) Tin (condensation) cured and 2) Platinum (addition) cured silicone rubber. Both types have advantages and disadvantages and neither are compatible with one another. Silicone rubber is an excellent choice for making moulds in that it has excellent strength, flexibility, and is self-releasing.
The only thing RTV (room-temperature vulcanizing) silicone will stick to is silicone itself. Tin (condensation) cured silicone rubber uses tin salts as a catalyst and uses moisture in the air to transform from liquid to solid. Platinum (addition) cured silicone rubber uses a platinum catalyst and uses heat to transform from a liquid to a solid.
The company only uses the highest quality two-component platinum addition cured silicone which has a high chemical resistance to the aggressive components found in some resins and a high resistance to wear and tear. It has a high level of accuracy in reproducing detailed parts and is dimensionally stable over time with nondeformability. Its non-stick properties are also considerable at high temperatures, resistant to ageing and can sustain perfect negative pressure.
One product where the reusable silicone bag system has proved itself as an efficient and economic production system is the iconic swimming starting blocks that Marky manufactures for the export market.
The International Swimming Federation (FINA), sports bodies such as the Australian Institute of Sport (AIS) and pool equipment manufacturers have driven design changes to give swimmers a speed advantage when diving into the pool. The most significant development is the adjustable slanted footrest, allowing swimmers to use the crouch start with the rear leg at a 90 degree angle at the knee. The blocks are now designed to accommodate both the track start where the swimmer positions one foot in front of the block and one foot at the rear, as well as the standard start where the swimmer positions both feet and hands at the front of the block.
As Blaise says “The design, shape and materials of the starting blocks enable athletes to gain propulsive energy and underwater trajectory. And, as a superpower in the sport of swimming, it is realistic that an Australian company should manufacture state of the art aquatic equipment in a suburb halfway between Brisbane and the Gold Coast and export to the rest of the world.”