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3444 Dight Avenue So.
Minneapolis, MN 55406
Tel: 612.721.2911
Fax: 612.721.1009
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Casting Machine Information
This document contains information on casting machines that can be used in casting/molding process using liquid polyurethane materials, which include MDI/polyether/polyester based liquid components for elastomers and foams. We do not recommend particular machine manufacturers. This document helps to see the choices of the components assembly configuration based on your products, required production capacity, budget, material used, and other elements that you should see when selecting your casting machine. We recommend contacting the machine manufacturers and work with them to assemble the optimum machine for your operation.
Types of urethane material, molding procedure, and production rate or quantity are important aspects when you are choosing your casting machines. May of the manufacturers of casting machines have choices of parts based on these factors. This literature has basic information on the machines and choices of each part commonly available from these machine manufacturers. If you are already familiar with this type of machine and the parts, you can use the list of the manufacturers as reference for the suppliers. The meter-mixing/dispensing machines typically consist of the following parts.
Tank/material retaining container
A machine needs a container to feed the material from. A machine can be fed directly from drums, lined from tank, or carry its own holding tanks.
The holding tanks for the component materials need to have some pressure release mechanism as you dispense to counter-balance the pressure. Desiccant filter or nitrogen gas feeding is needed for isocyanate side for pressure balancing devise.
Heating capacity of the tank may be an option if you prefer to control the material temperature higher. If your material has phase separation issues, you may want to look at agitators in tanks to constantly agitate the material.
For high-performance class materials, heated tank is essential to retain the production parameters. However, for room-temperature-curable materials for lower performance end, drum feed is sometimes sufficient.
Lines
Depending on the type of process, you need to choose appropriate lines (tubes/pipes) to carry the component materials to the mixing head.
For elevated temperature process, line may have to be heated. Some materials freezes very quickly when the temperature is lower, which may cause the whole system to clog up.
Recirculation valve/line may help keeping the steady temperature of material. It circulates the component material back to the heated retaining tank, so when your machine is not dispensing the material, the material within the line does not freeze.
If you use corrosive material such as solvents, you may choose PTFE coated feeding lines. Some manufacturers also use rigid stainless steel tubing.
Piston mixing system (see below) typically needs to retain higher pressure than gear pump system. Gear pump/high pressure systems use the line as pressure buffer for steady flow of the material.
Driving Motor
In general, there are pneumatic and electric driven systems.
Electric motors have better power and can handle high viscosity materials better than pneumatic, but it is usually more expensive. Also, if you use some flammable material, it is more difficult to make it explosion proof.
Pneumatic driven systems, since they do not require electric motor, they could contribute to the explosion proof design of your equipment. However, when you use a high viscosity material, the out-put rate may vary depending on the viscosity. It may also be somewhat noisier to operate than electric.
You can choose to have individual motor to each pump and agitator, or have one motor to drive all by connecting them with shafts and gears.
If you need to handle high viscosity material to be metered with a good precision, you may want to choose electric. The unit cost of pneumatic is generally lower than electric.
Metering Pump
Metering pump is very important part, but they have various qualities/prices. It is important that you choose the pumps that are best-fit to your application. Cheap/low-quality pumps slip and do not keep a good/constant ratio. Commonly, gear pump systems and piston pump systems are used.
Gear pump system works at small output as well as a large out put. It is relatively low pressure system and dispenses the material continuously without pulse.
Piston metering system often relies on the back-pressure of the material in the line for constant ratio. There are continuous pulses as it dispenses, through-put control may become difficult. It is generally noisier than gear pump.
In general, gear pump system is often preferred for a common continuous casting operation. However, piston systems create much higher pressure comparing to a gear pump of same price range. This is why piston systems are widely used in high-pressure spray machines. If your material requires high pressure dispensing, such as a heavily filled material and a highly viscous prepolymer, you may consider piston system. Some, low cost machines use piston system, and it may suffice to cast low-end room-temperature curable materials if it does not need a high precision of constant mix ratio and output rate.
Mixing Head
The choices are between static mixing, dynamic mixing, dynamic-static mixing, and impingement mixing.
Static mixing will be easiest in terms of maintenance as you would dispose of the disposable plastic mixing tube each time. Static mixing heads are lower cost comparing to others. However, if the component materials are harder to mix, static mixing system may not blend the components sufficiently.
A dynamic mixing system mixes the components dynamically by mixing rods in the mixing chamber, so it mixes very well. It is higher price and for higher outputs. The maintenance will be more difficult as dynamic mixing rods are usually not disposable.
Dynamic-static mixing system is something fairly new. It looks like a static mixing head, but the spiral fixture within the disposable mixing tube rotates and dynamically mixes the material. This mixes the component well and maintenance is easier than the dynamic system.
Impingement mixing is generally used for spray coating and RIM process. This usually requires high pressure (piston) pumps. The component materials are dispensed from nozzles with a high pressure and collide within a small mixing chamber or right outside of the nozzle, the mixed material is injected into a high pressure mold or sprayed directly on to a substrate. Impingement mixing has more restrictions to mixing ratios, output, and other processing parameters. Impingement systems are often used in spray, foam, and RIM systems and not used in liquid cast elastomer systems.
In most of polyurethane liquid casting, static mixing works sufficiently. There are a variety of tube sizes/lengths; you have some choice to higher output to lower output with higher mixing turbulence with some choices of lengths, which can be interpreted as mixing time. However, there is a limit to static mixing. If you are mixing a third component such as powder fillers, static mixing may not have capacity to mix. If A/B components have a large difference in their viscosities, mixing may become an issue. When the output requirement exceeds the capability of static mixing systems, you may also need to look at other mixing head options.
Output
The required output rate is one of the first questions the machine manufactures ask. You need to determine the range of output material you need per minute for your operation. Smaller machines are 1 – 2 pounds per minute. The larger one would be as much as hundreds of pounds per minute. In general, larger the output, more expensive the machine is. Also, if you need a very small precision output, it may take a special machine.
Other options
They have some options for on-off switches. You can probably choose from trigger, foot-switch, manual on-off, or shot-timer. If you need the portability, you may ask to put it on wheels. Some manufactures also provide design of automated production lines and fabrication lines.
Fixed Ratio vs. Variable Ratio
The most of piston pump systems are fixed ratio. Except for a few unique models, once you have a machine, you cannot change or adjust the mixing ratio unless switching the pumps. Piston pump systems are often lower cost, and it creates higher pressure than gear pump systems. Insulation foam machines and polyurea spray coating machines are often this type.
Advantage for gear/variable-ratio system is that you can use different materials in the same machine. Polyurethane and other resin systems are not all 1:1 or 1:2 systems. If you want to use a variety of materials with the same machine, variable ratio system gives better flexibility.
Also, all resin materials come with a small specification range that is accepted in the industry. However, some application requires tight hardness control. Even the material is within the specification range, you may need to calibrate your machine to obtain exact ratio. This calibration requires a variable mixing machine. By adjusting the actual mixing ratio slightly, you can get more precise chemical balance of the formulation.
The following section lists the suppliers of meter mixing/dispensing equipment. This list is for your reference only, and we do not guarantee the quality of their machines, parts, or the results of the operation with our materials using their machines. Please contact the manufacturer directly to discuss your application and evaluation procedure. This listing is not in a particular order.
Ashby Cross http://www.ashbycross.com/
Cannon http://www.cannon.com/
Edge-Sweets http://www.edge-sweets.com/
Graco http://www.graco.com/
Gusmer http://www.gusmer.com/
GlasCraft http://www.glascraft.com/
Liquid Control Decker http://www.deckerinc.com/about/aboutDecker.aspx
Max Machinery http://www.maxmachinery.com/
Michael Engineering http://www.michaelengineering.com/
Sheepscot http://www.sheepscotmachine.com/
Advance Process Technology http://advancedprocess.com/apt/index.html
Krauss-maffei http://www.krauss-maffei.de/
Sealant Equipment and Engineering http://www.sealantequipment.com/
I&T Fisnar Inc. http://www.ijfisnar.com/usa/meter_mix_index.htm
Northstar Polymers, LLC
3444 Dight Avenue South
Minneapolis, MN 55406
Tel: 612.721.2911
Fax: 612.721.1009
E-Mail: info@northstarpolymers.com
Notice: All of the statements, recommendations, suggestions, and data concerning the subject material are based on our laboratory results, and although we believe the same to be reliable, we expressly do not represent, warrant, or guarantee the accuracy, completeness, or reliability of same, or the material or the results to be obtained from the use thereof, neither do we warrant that any such use, either alone or in combination with other materials, shall be free of the rightful claim of any third party by way of INFRINGEMENT or the like, and NORTHSTAR POLYMERS DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, OF MERCHANTABILITY and FITNESS FOR A PARTICULAR PURPOSE.