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Rayite Machinable Media Sealers and Parting Compounds Parting compounds (also called "separators" or "releasers") are needed to prevent adhesion of Rayite Machinable Media to the porous surfaces of molds made from wood, wood composites, or any other material not impervious to moisture contamination. They also permit removal of the Rayite Machinable Media from the mold upon which it "sets up." Machine Rayite surfaces must also be sealed and a separating compound must be applied before being cast against. Sealing of Molds All porous molds must be sealed before the parting agent is applied. Sealing is particularly essential for wood patterns to prevent dampness from causing the wood to swell, which results in difficulty releasing the mold. Molds of metal, glass, plastic and other impervious materials do not require sealing. A quick-drying lacquer applied by brush or spray gun is an excellent sealer for wood or other porous substrates. Two coats of lacquer provide more resistance to moisture than shellac. Other sealants include polyurethane and acrylic sanding sealers. Mold Separators Satisfactory separating compounds must provide the following vital functions:
Listed below are acceptable mold separators: Stearic Acid and Kerosene (Stearine) - Formula: 1/4 lb. stearic acid shaved to flakes; 1 pt. kerosene. Melt stearic acid by warming: Remove from heat source and add kerosene with constant stirring until a uniform mixture is obtained. Apply to the sealed mold surface with a soft brush. Petroleum Jelly - Formula: 1 part petroleum jelly; 2 parts kerosene. Blend mixture by carefully heating and thoroughly stirring (Caution - Fire Hazard). Apply as a thin coat. Other mold separating compounds include:
Rayite Machinable Media Sealers It may be desirable to cast against a machined Rayite Machinable Media surface. Depending on the type of casting materials used, the surface of a machined Rayite pattern must be sealed and a separating agent must be applied to prevent adhesion and consequential damage to the Rayite Machined surface. Specifically, many thermosetting resins containing styrene can damage the surface of machined Rayite patterns. Sealing Rayite Machinable Media Machined Surfaces Rayite Machinable Media casts are quite dense, and therefore prevent proper saturation of most commercial "sealers". Also, many sealers may contain chemical solvents that are not compatible with some ingredients used in Rayite Machinable Media. Avoid sealers that include high-flash hydrocarbon carriers (MEK, acetone, etc.). The recommended application technique for low viscosity sealers is to flood the Rayite surface, allowing the sealer time to penetrate. Remove excess sealer with a rag. Let the surface air dry before applying a parting compound. Recommended Parting Compounds Wax based separators have proven to be the best products to use on Rayite casts. Common paste waxes are not only effective as separators, but are also cost effective. Avoid parting compounds that include high-flash hydrocarbon carriers (MEK, acetone, etc.) For best results, apply the separating compound in three steps. First, using a clean soft rag, apply a liberal coat of wax and let it "dry." The best results have been found by hand applying the wax. Buff with a soft, dry cloth to remove excess wax. Apply a second coat of wax and let dry. Again buff to remove excess wax. Apply a third liberal coating of wax; let dry but do not buff again. Rayite™ 100 Machinable
Media
Rayite 100 from United States Gypsum Company has revolutionized the rapid prototyping, model and pattern industries by being the first and only mineral-based product which surpasses industry standards and requirements. Others may claim to be "castable", buy only Rayite 100 can make claims so unique that USG has been granted a patent by the U.S. Patent Office. Features of Rayite 100:
Milling & Surface Finishing Rayite 100 Machinable Media is dimensionally stable and can be used after the slurry has set up for three hours or more. A Dimensional Stability Test was conducted representing a comprehensive seven step test in which changes in dimensions were measured after seven environmental immersions. The difference between the initial and the final dimensions were compared. Rayite™ 100 Machinable Media exhibited "excellent" dimensional stability (within 0.0019/lin. ft.). Recommended Cutting Lubricants It is recommended that each shop experiment with Rayite™ 100 Machinable Media and determine the most appropriate cutter designs based on the type of work being performed. Recommended Spindle Speeds and Table Feeds Through extensive research and field testing, an evaluation of spindle speeds and table feeds indicates that Rayite™ 100 Machinable Media is generally most efficient when spindle speeds are kept to a minimum RPM, while table feed rates are maximized. Specific spindle/table speed relationships are dependent upon cutter design, surface finish required and machine capability, as well as the degree of dryness within the Rayite 100 cast. For example, hogging operations can be run at higher feed rates with lower spindle speeds. Finish cuts can also be taken with high table feed rates, however spindle RPM's may need to be increased to improve surface quality. Surface Finishing The surface quality of Rayite™ 100 Machinable Media is directly proportional to the milling operation and the degree of dryness within the Rayite 100 cast. Machining can begin in as little as three hours from the start of mixing with Rayite™ 100 Machinable Media. However, a small amount of "free water" remains in the casting. Although this water does not affect the dimensional stability of the cast, it may affect the quality of the cut surface. The overall quality of a milled surface can be greatly improved by drying the surface prior to milling. If, for example, two operations were to be used, a "hog" or rough cut and a finish cut, it would be desirable to initiate surface drying during the rough cut operation. Under some shop conditions, this can be done quite simply by allowing the milled Rayite 100 cast to dry overnight. However, this form of drying may not be suitable under all shop conditions, i.e., warm, humid conditions will not promote drying.  Applying a stream of warm, dry air parallel to the surface
being cut is the most efficient means of drying Rayite 100 casts. Test conducted by USG
confirm that high velocity heated air is efficient in promoting surface drying (see
picture at left). Typically, high velocity, heated air can promote surface drying in as
little as 30 minutes from the start of the drying process.It is suggested that a high velocity blower direct air parallel to the surface of the block while being milled. Warmer temperatures will promote drying (up to 165°F). Apply heated air to the cut surface for a minimum of 30 minutes. A simple setup using a portable heat gun can be utilized. Using insulated flexible aluminum duct clamped around the nozzle of the heat gun, direct the opposite end of the duct toward the Rayite 100 casting. Caution: Hot surfaces may cause burns if allowed to come in contact with skin. Use sufficient insulation around duct. Maximum drying efficiency occurs when the air flow is parallel to the top surface of the block. Utilize maximum air velocity settings with air temperature settings not to exceed 165°F. This setting is best for the rough or "hog" cut. Maintain the air velocity but lower the heat setting to 100°F or less while milling the finish cut. It is not recommended that Rayite 100 casts be left on unprotected metal surfaces for long periods of time due to the moisture content from Rayite 100 casts. Use a barrier such as plastic or rubber sheets to isolate the cast from the metal surface. Surface Polishing Various degrees of surface "quality" can be achieved with Rayite 100 Machinable Media. A Class "A" finish can be accomplished with minimal labor through simple polishing. Using the correct tools will help to speed up and simplify the polishing process. The most efficient tools are pneumatic or electric oscillating sanders, although sanding by hand may be acceptable. Begin by sanding with a medium to fine sandpaper (silicone carbide) and continue with progressively finer grits. DO NOT use water to lubricate the sandpaper. Use mineral spirits, turpentine, boiled linseed oil, or any of the sealers recommended by USG. Apply a paste wax such as Johnson's Paste Wax to the surface once the required finish has been achieved. Mixing Procedures Successful mixing and use of Rayite™ 100 Machinable Media require the following specific standards and procedures. To obtain the full benefit of this product, shop practices and procedures must be standardized. An ideal Rayite 100 Machinable Media mix is one in which the powder particles are completely dispersed in the water to produce a uniform, homogeneous slurry. Such a mix should be the goal of every shop, and extreme care must be taken to control variables such as batch size, mixer design, mixing time, water purity, and water temperature. The following information will cover many of the factors that determine production of an ideal Rayite™ 100 Machinable Media mix. Water Purity Water used in mixing Rayite™ 100 Machinable Media should be as pure as possible. If water is drinkable, it probably is suitable for the mixing of Rayite 100 Slurries. In many cases, water for industrial use is taken from contaminated sources and is high in organic impurities that will lengthen the setting time of Rayite 100 Machinable Media. Other contaminates could negatively affect the slurry and ultimately the finished cast. Water Temperature Since Rayite™ 100 Machinable Media products have maximum solubility at about 100°F, variations in water temperature will affect setting time and can cause difficulty in the control of mixing time. The rule of thumb to remember is that cold water retards set, while warmer water accelerates set. It is recommended that the water temperature used, combined with Rayite™ 100 Machinable Media powder, have a slurry temperature between 65 and 80°F. Wide variations in water temperature can be corrected by using a tempering tank to balance extreme temperature differences. Tank types can range from an automatic system that blends hot and cold water to a simple container warmed by waste heat or by air temperature in the shop.
Variations in the water-to-Rayite 100 Machinable Media ratio will affect various performance characteristics of the final cast such as machinability, porosity and overall strength. It is important to control the water-to-Rayite ratio by carefully measuring each component. Soaking When manufactured, Rayite 100 Machinable Media particles are surrounded by an envelope of air. Part of this air is removed from the Rayite 100 powder particles during shipping and handling; part during soaking. In addition to removing air, soaking allows each Rayite 100 particle to be completely saturated with water so that it is easier to disperse. However, Rayite 100 Machinable Media particles are influenced by additives that may not easily disperse in water. It is recommended that Rayite 100 Machinable Media be allowed to soak for a minimum of 2 minutes. Any powder that does not sink into the water should be hand dispersed into the water prior to mixing.
The mixing of Rayite 100 Machinable Media is the most important step in producing casts with maximum strength, hardness and machining properties. Any changes in mixing procedures will have a greater effect on the finished product than any other phase of the entire operation. It is also vitally important to always weigh the water and Rayite powder. Incorrect water and Rayite powder ratios will negatively affect the quality of Rayite casts. Mixing disperses Rayite 100 particles in the water. Also, the strength of the Rayite 100 cast is partially determined in mixing since there is a direct relationship between energy input during mixing and strength development of the cast. Careful, efficient mixing also minimizes potential pitfalls such as air entrapment. Trapped air results in strength reduction within the cast as well as surface blemishes caused by air pockets exposed during the machining process.
Depending on actual batch size, adjustments can be made to the soaking and mixing cycles. Typically, larger batches may require slightly longer soaking and mixing cycles. Mixing Rayite 100 Machinable Media Sift or strew Rayite 100 Machinable Media into water slowly and evenly. Do not drop handfuls of Rayite 100 Machinable Media directly into water. Allow to soak for 2 to 4 minutes, then mix as required - generally 2 1/2 to 5 minutes - to obtain a creaming of the Rayite 100 slurry. Hand Mixing - Hand mixing is generally acceptable for small batches up to 3 pounds. It is important to use a vigorous stirring motion when hand mixing. Because optimum physical properties are in direct relation to energy input in mixing, hand mixing will not result in a Rayite 100 cast with the best properties.
Generally only one propeller is necessary, but where this does not provide enough turbulence, use two per shaft. Keep all equipment clean to avoid acceleration of Rayite 100 slurry setting time. Pouring Rayite 100 Machinable Media Using a steady rate, pour Rayite 100 Machinable Media into one corner of the mold and allow the slurry to rise and seek its own level. To avoid trapping air, vibrate or shake the mold or the surface onto which the mold is placed.
Rayite 100 Machinable Media products harden in approximately one hour. To aid in the drying and cooling down process, remove the hardened Rayite 100 cast from the mold, or loosen the mold walls and allow air to circulate the cast. Rayite 100 Machinable Media products can be used approximately three hours after set time. Volume and mix calculations This formula is useful in calculating the amount of Rayite 100 Machinable Media to be used in a mold of known dimension. Simply fill in the missing information and calculate where instructed. this format provides both the amount of water and the amount of Rayite 100 Machinable Media powder required. Step #1: Calculate volume of mold, V. If volume is calculated in in.³, convert in.³ to
ft.³. (V / 1728 = ?) Step #2: Calculate slurry requirement of mold, SW: (SW=V X 109) Step #3: Calculate Rayite 100 powder weight, PW: (PW=SW / 1.3) Step #4: Calculate water weight, WW: (WW=PW x 0.3) Mix it. Cast it. Machine it. Rayite 100 machinable Media is a new mineral-based material developed by United States gypsum Company for prototyping, mold making, tape proofing, models and tooling aids. Used with all machining processes, this super-tough material machines smooth with outstanding edge definition. The results are sharp, precise cuts with minimal loading on milling machines and cutting tools. Rayite 100 Machinable Media simplifies your preparation time by eliminating labor-intensive gluing and clamping of board-type machinable products. Just mix it, cast it and machine it.
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Water-To-Rayite 100 Machinable Media Ratio
Mixing
To
mix Rayite 100 Machinable Media properly for uniform casts, follow these easy steps:
Mechanical Mixing - For
best results, use the recommended mixer/mixer motor combination as indicated below. The
mixing shaft should be maintained at an angle 15° from vertical. The propeller or Jiffy®
mixer should clear the bottom of the container by 1 to 2 inches and the shaft should be
about half-way between the center and the side of the container. The propeller or Jiffy
mixer should force the mix downward.
When
the mold is filled, continue tapping or vibrating until no new air bubbles are seen rising
to the surface. Utilize vibration equipment (table or hand-held unit) where appropriate.
Help draw out trapped air by inserting and withdrawing a spatula or stirring stick in the
Rayite 100 slurry.