Improved Dry Vacuum Calibration Tables

Dry vacuum calibration tables were designed in response to the need to hold complex plastic material profiles to very tight tolerances while they were being cooled in the extrusion process. Tables had been developed to carry the calibration tooling needed to produce tight tolerances at high result rates and to allow for the easy changeover from one component to another. Even though calibration tooling is needed to accomplish this, it is very expensive and alternate strategies have been developed to increase rates without building much longer and much longer calibration tooling. Tables had to be modified to be able to cope with the alternate cooling strategies.

CALIBRATION TOOLING

The calibration tooling can be created from aluminum for better heat transfer but it is normally created from stainless steel for better life because of the abrasive nature of filled plastics rubbing on the polished surfaces. The internal surface area is cut in the shape of the required profile and very polished for low drag level of resistance. Cooling channels happen to be cut into the tooling for move of the critically important cooling water. Furthermore, channels are cut into the instrument for vacuum to draw the plastic portion out against the calibrator wall to make good contact to make sure cooling and obtaining the proper dimensions. Generally the tool is built to be ¡°dry¡± and therefore 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 water to do something as a lubricant between the part and the metallic surface. This may also improve the cooling efficiency.

The initial calibration tooling shall smooth the surface of the hot plastic material since it first enters the tooling. The primary job of the calibration tooling is to cool the component as it is controlling the decoration of the plastic. The length of the calibration tooling will change with the line quickness of the extruded part, the complexity of the account, and the dimensional tolerances needed of the profile. Raising any of the factors shall raise the required amount of the tooling. Calibrators are typically built-in sections of 4 to 15 inches long for ease of manufacture and handling. They're then found in sets to attain the needed length of calibration necessary for the account either with or without gaps between each calibration block. Calibration of 4 legs or more is not uncommon in complex home window profile lines.

Since the primary purpose of the calibration tooling is to cool the plastic as it is being held in shape, it is advisable to have water channels through the tooling in the proper location for uniform cooling and have adequate water flow to maintain the required processing temperature. Typically chilled water that's maintained at 50¡ã - 55¡ã F is used to circulate through the tooling. It is sometimes desirable for the first calibrator to be slightly warmer than the rest to raised impart a smooth area to the plastic and to reduce drag caused by shocking the plastic with the initial cooling. This warmer temperature in the first calibrator is generally attained by adjusting the move of water entering that first calibrator, on the other hand a temperature controlled device may be used to assure consistent plastic recycling extruder machine temperature.

CALIBRATION TABLES

Dry out vacuum calibration tables have already been developed and are provided by many companies that offer a convenient base which the calibration tooling could be mounted. They generally provide a heavy duty body with the vacuum and drinking water pumps along with all of the necessary plumbing, including filters, high temperature exchangers, etc., alongside necessary controls. They enable simple link with modular calibration tooling so that it can be changed out very easily. The tooling is usually mounted on some type of rail system for consistent alignment with itself. The table generally incorporates a tray system beneath the mounting rails to capture any leaking or stray water.

Alignment of the calibration tooling to the extrusion tooling is crucial so motion of the table is controlled by allowing adjustment of the positioning side to side and up and straight down. These linear activities are typically attained by a hand steering wheel traveling a gear system although a powered travel system may be used. Activity of the desk toward and from the extruder is normally driven as a result of magnitude of the modification that is needed.

AUXILIARY TANKS

An auxiliary container is usually installed on the calibration desk after the primary calibration tooling so as to offer more cooling for the account. These tanks are 6 to 12 feet lengthy typically. They are designed to keep forming plates that continue to hold the part straight as the applied vacuum holds the portion out against the forming plates to carry the size and dimensions. They are made to immerse the part in water with turbulent mixing to break up the insulating layer of water around your skin of the portion. The container itself is designed for water to be presented at the front end of the tank and the vacuum is definitely utilized at the downstream end of the container drawing the water through the tank. Turbulence is normally created by the placement of holes in the forming plates. Holes all around the part create some turbulence but alternating plates with holes above the portion and below the component increase turbulence and water flow over the part, raising cooling efficiency.

These types of tanks require a complete lot of water movement to attain the turbulence required for good cooling efficiency. That water is being slow of the tank by the vacuum applied at the downstream end of the container. This requires the use of liquid ring vacuum pumps that may handle both air needed to pull a vacuum along with the water that's being unveiled for cooling and has to be sucked out from the tank. Even so, the more water that the pumps have to approach reduces their productivity to pull vacuum pressure that is their primary purpose. Therefore, larger hp pumps and more of these are needed to make this operational system work. Commonly a 10-hp pump would be needed for each six to eight 8 foot of auxiliary tank in addition to the vacuum requirements of the calibration tooling. In many high output applications 10, 20 as well as 30 feet of auxiliary tanks happen to be needed to achieve the required cooling. All of these liquid band vacuum pumps operating at low productivity because they have to pull so much water create a greater capital expenditure up front and also higher on-going working and maintenance costs.

BETTER SOLUTION

A better solution would be to separate the normal water from the air in order that each can do it¡¯s intended job. The new air is needed to draw a vacuum while the water is needed for cooling. The employ of a high strength spray from nozzles that surround the portion all the way down the tank provide the necessary quantity of cool water for cooling without the need of abnormal volumes just to develop turbulence. The strength of the spray of cool water onto the top of part breaks up the level of warm water that can slow down cooling. This volume of drinking water drops to the bottom of the container where it can quickly be removed separately from the vacuum port. With this construction, the vacuum pump must handle a drastically lower volume of water and will therefore be much more efficient. Actually a liquid ring pump may not be required enabling the use of a 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 dried calibration to permit for the particular auxiliary tank. A fresh generation of hybrid dry calibration tables are getting made that separate normal water pumping and vacuum systems and offer variable lengths to install calibration tooling. This provides the versatility that a lot of processors require. This versatility can include adjusting spray intensity in different sections to optimize cooling as expected, or allowing for different degrees of vacuum or unique water temperatures in various parts of the tank even.

In conclusion, these new dry vacuum calibration systems can offer the control of dimensions and size that end users have come to anticipate at higher rates and lower energy costs that processors would like. Innovative calibration table designs make this both convenient and feasible.

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