Dry out vacuum calibration tables were made in response to the necessity to hold complex plastic material profiles to very tight tolerances while these were being cooled on the extrusion process. Tables had been developed to hold the calibration tooling had a need to produce limited tolerances at high outcome rates and to allow for the easy changeover from one portion to another. Although the calibration tooling is needed to gain this, it is very expensive and alternate methods have been developed to increase rates without building longer and much longer calibration tooling. Tables needed to be modified in order to deal with the alternate cooling strategies.
The calibration tooling could be made from aluminum for better heat transfer but it is normally made from stainless steel for better life due to the abrasive nature of filled plastics rubbing over the polished surfaces. The inner surface area is trim in the form of the required profile and highly polished for low drag level of resistance. Cooling channels will be cut in to the tooling for flow of the critically significant cooling water. Furthermore, channels are cut into the program for vacuum to pull the plastic portion out against the calibrator wall to create good contact to ensure cooling and acquiring the proper dimensions. Usually the tool is built to be dry meaning that no drinking water touches the extruded account in the calibrator. Some calibration was created to actually introduce handful of water or let leakage of cooling normal water to act as a lubricant between your part and the metal surface. This can also improve the cooling efficiency.
The original calibration tooling will smooth the surface of the hot plastic material as it first enters the tooling. The primary task of the calibration tooling is to cool the component as it is managing the decoration of the plastic. Along the calibration tooling will vary with the relative brand rate of the extruded part, the complexity of the profile, and the dimensional tolerances essential of the profile. Raising any of the factors shall raise the required length of the tooling. Calibrators are typically built-in parts of 4 to 15 inches long for ease of manufacture and handling. They are then found in sets to attain the needed amount of calibration needed for the account either with or without gaps between each calibration block. Calibration of 4 toes or more is not uncommon in complex screen profile lines.
Since the primary purpose of the calibration tooling is to cool the plastic since it is being held in form, it is critical to have water channels through the tooling in the proper location for uniform cooling and have adequate water flow to keep the required processing temperature. Typically chilled water that's maintained at 50 - 55 F is used to circulate through the tooling. Sometimes it is desirable for the first calibrator to be slightly warmer compared to the rest to raised impart a smooth surface to the plastic also to reduce drag caused by shocking the plastic material with the original cooling. This warmer temperature in the 1st calibrator is generally attained by adjusting the circulation of water going into that first calibrator, nevertheless a temperature controlled product can be used to assure consistent temperature.
Dry vacuum calibration tables have already been developed and are offered by many companies that offer a convenient base which the calibration tooling could be mounted. They generally give a heavy duty framework with the vacuum and drinking water pumps along with all the necessary plumbing, including filters, high temperature exchangers, etc., alongside necessary controls. They allow for simple connection to modular calibration tooling so that it could be changed out very easily. The tooling is certainly mounted on some type of rail program for reliable alignment with itself. The table usually incorporates a tray system beneath the mounting rails to get any leaking or stray water.
Alignment of the calibration tooling to the extrusion tooling is crucial so movement of the desk is controlled by allowing adjustment of the positioning side to side and up and straight down. These linear movements are typically attained by a hand wheel generating a gear system although a powered drive system can be used. Motion of the table toward and from the extruder is usually driven due to the magnitude of plastic extruder the change that is needed.
An auxiliary container is usually mounted on the calibration table after the preliminary calibration tooling to be able to offer additional cooling for the account. These tanks are usually 6 to 12 foot long. They are made to keep forming plates that continue to contain the part straight while the applied vacuum retains the component out against the forming plates to hold the size and sizes. They are designed to immerse the part in normal water with turbulent mixing to break up the insulating layer of water around the skin of the part. The tank itself is made for water to be launched at the front end end of the tank and the vacuum can be applied at the downstream end of the container drawing the water through the tank. Turbulence is created by the placement of holes in the forming plates usually. Holes all over the portion create some turbulence but alternating plates with holes above the part and below the component increase turbulence and drinking water flow across the part, increasing cooling efficiency.
These types of tanks need a complete large amount of water movement to achieve the turbulence required for good cooling efficiency. That water is being drawn out of the container by the vacuum used at the downstream end of the container. This requires the utilization of liquid ring vacuum pumps that may handle both air needed to pull a vacuum combined with the water that is being unveiled for cooling and has to be sucked from the tank. Nevertheless, the more drinking water that the pumps need to approach reduces their proficiency to pull a vacuum which is their primary goal. Therefore, larger hp pumps and more of them are needed to make this operational system work. Commonly a 10-hp pump would be required for each 6 to 8 8 toes of auxiliary tank as well as the vacuum requirements of the calibration tooling. In many high output applications 10, 20 and even 30 toes of auxiliary tanks happen to be needed to achieve the required cooling. All of these liquid band vacuum pumps operating at low effectiveness because they need to pull so many water create a much larger capital expenditure in advance and higher on-going functioning and maintenance costs.
A better solution would be to separate the normal water from the air so that each can do it s intended job. The atmosphere is needed to draw a vacuum while the water is necessary for cooling. The work with of a high intensity spray from nozzles that surround the portion all the way down the tank provide the necessary quantity of cold water for cooling with no need of unnecessary volumes just to produce turbulence. The intensity of the spray of cool water onto the top of part breaks up the level of heated water that can decelerate cooling. This level of normal water drops to underneath of the container where it can easily be taken away separately from the vacuum port. With this configuration, the vacuum pump needs to handle a considerably lower level of water and will therefore be much more efficient. In fact a liquid band pump is probably not required allowing the use of a far more efficient and lower horsepower Regenerative pump.
Early tables that utilized this technology had the drawback of having a fixed length of rail section for the dry calibration to permit for the specialised auxiliary tank. A new generation of hybrid dried out calibration tables are becoming made that separate drinking water pumping and vacuum devices and provide variable lengths to install calibration tooling. This adds the versatility that most processors require. This versatility range from adjusting spray strength in different sections to optimize cooling as required, or enabling different degrees of vacuum or several water temperatures in various sections of the tank even.
In conclusion, these new dry vacuum calibration systems can provide the control of dimensions and size that end users have come to expect at higher prices and lower energy costs that processors would like. Brand-new calibration table designs make this both convenient and feasible.