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Omni Silicone Rubber TECHNICAL INFORMATION AMAZING AMAZING Introduction Omni silicone rubbers have been formulated using only the highest Omni quality raw materials sourced from many different countries; this ensures that Omni rubber has the highest Silicone Rubber performance characteristics. The Omni range has been developed in our Contents own laboratory where we have the very latest hi tech equipment for measuring all of the 1 Benefits of using Silicone Rubber critical properties of both the raw materials and finished products. 2 The Omni Silicone Rubber range Every batch of Omni silicone rubber we - Omni L.C. (Low Cost) manufacture ourselves, they are all tested - Omni – Sil before being allowed to be despatched to our - Omni L.T. (Low Temperature) customers as required by our ISO 9001 quality assurance system. 3 Specialist Mold Rubbers Our hi tech equipment allows us to test and 4 Preparing a Master Model control the following characteristics to their breaking point... 5 Packing the Mold Frame • Tear strength 6 Vulcanizing the Packed Mold Frame • Tensile strength 7 Mold Cutting • Elongation 8 Producing a mold using Separation Cream and Locating Pins 9 Calibrating the Vulcanizer 10 Storage & Shelf Life 11 Silicone Rubber Problem Solving 12 Silicone Rubber Material Safety Data Sheet 13 Mold Separation Cream Material Safety Data Sheet 1 The Benefits of using Omni Silicone Rubber Silicone rubber use in all of the discerning jewelry factories has grown dramatically over the past 5 years; silicone rubber is at the forefront of jewelry casting now and in the future. Omni silicone rubbers provide far better surfaces on wax patterns than natural rubber, they are comparable in cost but offer a much higher performance. Our rubber is easy to pack, vulcanize and cut; all of these attributes combine to make Omni Silicone Rubber the obvious choice. • Easier to pack the mold when compared to natural rubber • Glass like finish on the wax pattern, producing a better cast surface, therefore less finishing and polishing needed • Exceptional detail reproduction • Self lubricating, no need for sprays or talc • Easier to cut the mold • Greater flexibility particularly where intricate designs, cores or plugs are required • Can be used along with locator pins and separation cream • Produces a tighter seal and therefore reduces wax flashing • L.T. can be used to produce molds directly from RP/SLR patterns 2 Omni Soft Omni HTV Silicone Rubber Vulcanization Temp 165 - 175ºC 330 - 347ºF Range Shore A Hardness 28 - 30 Omni Omni Sil L.C. HTV HTV Vulcanization Temp 165 - 175ºC Vulcanization Temp 165 - 175ºC 330 - 347ºF 330 - 347ºF Shore A Hardness 38 - 40 Shore A Hardness 48 - 50 Omni Speedi L.T. - Cure LTV QCV Vulcanization Temp 72 - 82ºC Vulcanization Temp 85 - 95ºC 161 - 180ºF 185 - 203ºF Shore A Hardness 38 - 40 Shore A Hardness 38 - 40 3 Specialist Mold Rubbers Omni L.T. Because direct casting of a RP/SLR model is extremely difficult most all jewelry manufacturers now produce molds directly from the resin model and from the mold create their wax patterns to cast. Omni L.T. (Low Temperature) allows you to produce a mold directly from the RP/SLR pattern because it vulcanizes at between 162 and180°f (72 - 82°c) and does not therefore distort the pattern during vulcanization. Omni L.T. allows for an average sized mold to be packed, vulcanized, cut and ready to inject within 2 hours. Omni Speedi – Cure “Time is money” in particular in a jeweller’s work place Mold Size Quick Cure STD HTV Cure where a one-off casting is required instantly. Omni 12mm (1/2”) 10 mins 30 mins “Speedi – Cure” can help save precious time and a ¾” (20 mm) mold can be produced in 45 minutes. 19mm (3/4”) 15 mins 45 mins 25mm (1”) 20 mins 60 mins Omni “Speedi – Cure” has exactly the same mechanical properties as Omni – Sil and produces the exact same quality of pattern, it simply allows you to move faster. Using this type of rubber requires the vulcanizer to be calibrated regularly and at the correct set temperature. 4 Preparing a Master Model To ensure the best results Masters should be cleaned before producing the rubber mold, the best method for this is to use the ultrasonic cleaning process. To achieve the best surface it is advised to rhodium plate masters, this will fill in any imperfections and give a perfect surface. After plating the master should be cleaned, again using an ultrasonic. Where brass is used to produce the master, it should be plated as brass may well react with the rubber. It is a fact that more time spent on perfecting the Master Pattern will save time on finishing of the casting. MASTER MODEL Is it made out of brass? Yes No Plate to stop Clean Plate mold reaction Make mold Clean Clean Make mold Make mold 5 Packing the Mold Frame Please note that the mold frames used for silicone rubber should not be used for Correctly Packed natural rubber, they are incompatible. Pack the mold frame base ensuring that all of the cavity is completely filled. The rubber in the mold Under-Packed frame should be slightly overfilled and be convex. This will ensure that the rubber flows completely around the master during vulcanization. If the mold is not completely packed they will almost certainly result in bubbles inside the cured mold. It is possible to use both Omni L.C. and Omni – Sil in the same mold, this method is often used where the pattern being created is highly detailed or intricate but the size requires a firm exterior. This process also leads to a longer life of the mold. Please DO NOT use Omni L.T. for this process it is not compatible with Omni L.C. or Omni – Sil. 6 Vulcanizing the packed Mold Frame It is advisable to turn the vulcanizer on at the required temperature 30 minutes before use; this will ensure that will have sufficient time at the correct temperature to achieve full vulcanization. For best results you should regularly calibrate your vulcanizer, the read out temperature can be as much as 60°f (15°c) below the required temperature which will result in an under cured mold. Defects where the mold is under cured are: • Bubbles in the Mold • Sticky Molds • Low Shore A Hardness • Poor Memory • Poor Tear Strength If you experience any of these defects in your molds we suggest that you check the calibration of your vulcanizer. 7 Mold Cutting There are so many different methods of mold cutting, many passed down from father to son and so on, cutting the rubber mold is by far the most effective way rather than using separation cream and locating pins. Cutting allows for a far more intricate wax pattern to be injected where cores, undercuts and spirals are required. When producing the rubber mold, and in particular where silicone rubber is used because of the high gloss surface of the rubber, the use of “Air Venting” is advisable. The vents are important to allow the flow of air out of the mold as the wax is injected. Venting also reduces the chance of wax flashing in the mold during injection. 8 Producing a mold using Separation Cream and Locating Pins This method is used generally speaking, where the pattern to be injected is very simple. 1 The mold is produced by packing the base of the frame with silicone rubber, placing the master onto the base and pressing it in. A thin layer of separation cream is applied over the surface (ensuring that the master is not covered) 2 Place the locating pins into each corner of the rubber mold. 3 Proceed to pack the remainder of the mold tightly. 4 Continue to vulcanize the mold at the recommended temperature and time as recommended. 5 Once the vulcanizing is completed remove the mold frame and allow it to cool, when cooled remove the mold from the frame and it will easily part allowing removal of the master. The mold is now ready to use. 9 Calibrating the Vulcanizer Regular calibration of the Vulcanizer is very important in ensuring that the rubber is fully cured, our recommendation would be for the re calibration every six months. For this you will need a thermometer with a “K” type thermocouple and a small block of wood, see instructions below. Where the mold is not fully cured you may well see the following mold problems... • Bubbles in the Mold • Sticky Molds • Low Tear Strength • Low Shore A Hardness. • Poor Mold Memory Steps to Calibrate the Vulcanizer 1 Close the vulcanizer platens, turn it on, set to the vulcanizing temperature (330°f - 165°c). Allow to stand for 30 minutes to achieve temperature. 2 Open the platens and place the wood in position, put the thermocouple on top of the wood and close the platens. 3 Leave to stabilize for 10 minutes then take the temperature reading; compare it to the desired temperature. 4 Where the temperature is too high or too low reduce or increase it on the dial and allow to settle, then take a second reading using the same method, continue until the two readings are in unison and correct. 5 Repeat the same exercise for the bottom platen The readings on the vulcanizer and thermocouple should not differ by more than +/- 5% 10 Storage & Shelf Life Silicone Rubber contains catalysts which HTV Shelf Life - Months are temperature activating, therefore it is 14 important that the rubber is stored away 12 from direct sunlight and at a temperature 10 below 72°F /22°C to obtain the maximum 8 shelf life.
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