Methods for processing plexiglass

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Currently, sheet acrylic (organic) glass is one of the most widely used sheet polymeric materials. Plexiglas is transparent, opaque or light-scattering sheets with varying degrees of light transmission with a perfectly glossy surface on both sides, with a thickness of 1.0 to 24 mm.

Plexiglass cutting

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Plexiglass can be cut with both the simplest tool, such as a hand saw for metal, and more complex ones, such as a laser. In most cases, a circular saw is used for straight cuts and a band saw or milling cutter for cutting curved shapes. A band saw is more suitable for cutting out blanks before forming, since with such cutting there is no need to obtain a clear cut (a band saw with a rotation speed of 700-800 m / min is used to cut cast acrylic). For a clear and smooth surface when cutting complex shapes, we recommend using a router bit. Circular saws allow making straight, accurate cuts with a clear cut (when cutting cast acrylic, a circular saw with carbide-reinforced teeth with a rotation speed of 800-1200 m / min is used). For small jobs, saws with a light metal blade can be used.

For more technological cutting it is preferable to use high-speed equipment. At a high cutting speed and a minimum feed rate, you can get a high-quality edge (when cutting extrusion plexiglass with high-speed circular saws, the recommended disk rotation speed is 4000 rpm). For processing, it is necessary to use discs with a diameter of 250 mm, made of high speed steel or reinforced with carbide. To avoid deformation, the saw teeth should not be set apart..

Laser cutting has a number of advantages: exceptional cutting accuracy, low waste, high quality cuts requiring little grinding. However, this method contributes to the appearance of high internal stress of the material, and further bonding of such surfaces is not recommended..

Cast plexiglass is easy to machine, but due to its low thermal conductivity it quickly heats up in the cutting zone. Therefore, processing should be carried out at the smallest depth of the cut layer, but at high cutting speeds.

Drilling plexiglass

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Drilling of extruded plexiglass is carried out using a stationary or mobile drilling machine using special drills for light metals from high-speed steel of increased productivity, specially sharpened for drilling extruded plexiglass. Care must be taken to ensure that the edges of the drilled hole are smooth to avoid cracking. In the case of deep drilling, it is recommended to raise the drill frequently in order to extract the chips and limit the heating of the material.

When drilling molded plexiglass, any metal twist drills are used. Correction factor for drill diameter +0.05 mm relative to hole diameter. To avoid internal stress during drilling, it is necessary to cool the cutting tool and the material with cooling lubricants or compressed air.

Plexiglass engraving

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In most cases, engraving is carried out using rippers mounted on pantographs and equipped with small diameter cutters (2-6 mm) of various profiles. Laser cutting machines can also be used, which allow engraving by limiting the deep action of the laser beam..

Plexiglass grinding

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Rough surfaces or surfaces with defects such as scratches are sanded with wet fine corundum sandpaper. After rough polishing, the surface should be treated with special agents (polishing pastes such as VIAM, tripoli, crocus, dispersed in wax). All operations are carried out either manually or on a polishing machine.

Plexiglass polishing

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Cut edges and a matt surface can be mechanically polished with high quality using diamond cutters. However, if this is not possible, for example, a curved cut, then flame polishing is recommended. This method consists of treating the items with a clean “hard” high temperature flame, but some precautions should be taken. So, for example, the surface to be sanded must be absolutely clean, and, in addition, this method creates significant stresses, which must be removed by annealing before gluing or applying paint..

Plexiglas molding

This type of processing allows you to give the material a variety of shapes. It consists of three stages:

  • Heat
  • Molding
  • Cooling
  • 1. Heat. If the resulting part does not conform to the desired shape, it can be reheated and then corrected. Cast acrylic has shape memory and can easily return to its original position when reheated. With extruded plexiglass, this is possible only if the material has not been stretched. Before heating, the protective film must be removed from the molded plastic and can be left on the extruded.

    Before forming, it is necessary to pre-dry the extruded plastic in order to avoid the formation of bubbles in the finished product at the folds. The need for drying arises due to the fact that during storage or transportation, a small amount of moisture can penetrate into the material. Drying is carried out either in a convection drying chamber with hot air circulation (at a temperature of 75-80 ° C for 1-2 hours per mm of thickness – as a rule, with a high moisture content, 24 hours of drying are sufficient), or using infrared radiation at a temperature from 75 to 80 ° C for 1-2 hours for each mm of thickness.

    To heat the molded plexiglass before molding, use equipment that creates a uniform temperature field with a difference in the plane and sheet thickness of no more than ± 3 ° C. Cast glass is heated 3-4 min / mm thick to a temperature of 165-190 ° C. Block plexiglass quickly softens when heated, but its strength decreases slightly in comparison with extrusion. Cast and extruded acrylic plastics react differently to heat. In cast acrylic plastic, uniform shrinkage of a maximum of 2% is possible, the same in all directions (correspondingly, the sheet thickness increases). Extruded acrylic plastic has 3 to 6% in the extrusion direction and 1-2% in the transverse direction (for a 2 mx 3 m sheet, the extrusion direction is the 3 m side). Cast acrylic easily tolerates heating inhomogeneity of 10-15 ° C (overheated cast acrylic, unlike extrusion, does not crack or break when deformed), in the case of extruded, the difference in heating temperature can lead to significant stresses in the material.

    2. Molding. The behavior of these materials during hot forming is also different. To deform cast acrylic, considerable pressure must be applied, extruded acrylic is molded easily and effortlessly (recommended temperature range – 160-170 ° С; heating time – 3 minutes per 1 mm of material thickness).

    Molds (dies and punches) are made from various materials: wood, plaster, aluminum, steel. Hot molding can be carried out in simple ways, for example, by placing the plastic after heating on a convex or concave shape, where, under its own weight, it acquires its shape. Plastic molding can also be carried out by free retraction in a vacuum-tight chamber and free blowing with compressed air, both with the help of molds and without them.

    If it is necessary to bend a flat sheet in a straight line, then it is enough to conduct local heating of the plastic along the bending axis using one or more rectilinear heating elements, for example with a nichrome string.

    3. Cooling. In order to avoid internal stress, the cooling should be as long and uniform as possible. For the best preservation of the printed shape and to avoid deformation, the product must be left on the matrix until it cools down to a temperature of 60-70 ° C. Molded products must be thermally conditioned to reduce stress prior to contact with solvents, paint or self-adhesive films..

    Cold bending

    Plexiglas, both cast and extruded, is easy to cold bend, but a minimum bend radius must be observed to avoid stressing the boards. The minimum bending radius should be 230 times the plastic thickness.

    Welding

    In the case of injection molded plexiglass, it is recommended to use (as well as for extruded plexiglass) “related” adhesives, which allows achieving the most durable connection and its weather resistance. To obtain transparent, colorless seams when gluing with an overlap or butt with a one-sided overlay, it is preferable to use CMM glue based on polymethyl methacrylate.

    Before gluing, parts made of molded plexiglass must be annealed to relieve internal stress. The recommended annealing temperature is 65-80 ° C, depending on the softening temperature of the glass (90-120 ° C), after which natural cooling is preferred.

    Welding is also used to obtain blanks for molding non-standard products, for attaching linings and for forming bulges. Casting Plexiglas is welded at higher temperatures (up to 300 ° C). The finished part after mechanical treatment of the seam is subjected to heat treatment to relieve internal stresses.

    Welding methods:

  • Induction;
  • Radiation;
  • Ultrasonic soldering;
  • Vibration;
  • Hot gas.

Gluing

Extruded Plexiglas sheets can be glued to themselves and to other materials, thus obtaining a high-strength and durable seam. It is advisable to heat treatment before gluing.

Materials for bonding extrusion plexiglass:

  • Film type of glue: solution of polymethyl methacrylate in a volatile solvent;
  • Polymerizable type of glue: PMMA syrup with dimethylaniline (SMM), to which a polymerization initiator (benzoyl peroxide) is added at the time of gluing;
  • Other types of glue: epoxy, polyester, polyurethane and other brands AK-90, MP-88 (81), BF-2 (4,6);
  • Solvents: dichloroethane, methylene chloride.
  • After drying and solidification of the glue at room temperature, it is recommended to anneal for 2-5 hours at a temperature of 60 ° C.
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