Acrylic's mechanical performance—When a designer uses an acrylic sheet to make a light box sign, he must measure the mechanical properties of the material used. Instead of just considering the material properties of the acrylic sheet, he tries to achieve all the desired appearance of the logo.
When making a large light box, consider the wind load on the façade. Be sure to leave the expansion allowance. It is important not only to consider the normal conditions of use, but also to use it in the light box. National standards for building identification of wind-resistant carriers are in place in most countries.
For designers, when considering the use of traditional materials, such as metals, most design formulas should pay attention to the following points:
1, the material has a linear stress / tension curve
2, the deflection generated during the loading process is small
Many thermoplastic materials generally do not have a linear stress/tension curve, but acrylic is quite satisfactory at this point. Before designing a signboard, know the maximum expected operating temperature.
Design stress
The stress/tension curve of a standard acrylic sheet is substantially linear over the normal operating temperature range and the maximum tension is less than 1%. Because the recommended design stress is not too large even if creep is allowed, the nonlinear problem can be solved. However, some typical thermoplastic materials, such as acryl, have a large Young's modulus and produce large deflections during bending, which are not within the design stress considerations.
The following two methods can solve the problem of huge deflection:
1. First and foremost, the most obvious method is the use of deflection theory, but this method is quite complex, and in many applications, the formulas for thermoplastic materials are not all ready to use.
2. Secondly, it is also the preferred method, that is, using a simpler small deflection theory, first considering the possible deflection, limiting the allowable degree, rather than considering the design from the point of view of stress. It is caused by wind load. This method has the added advantage that the logo maintains a good appearance even under wind loads and is not easily detached from the mounting frame.
The rule is that the final deflection should not exceed the material thickness. Because in this low deflection state, the surface stress of the material under tension is small.
For the above reasons, it is recommended to use the small deflection theory when designing the acrylic sheet.
Deflection
Deflection can occur due to the static load of the wind-borne sheet itself. To avoid this effect, proper precautions are important.
Some of the acrylic sheets that have been accumulated over many years of experience suggest a design guide for thickness. Under maximum wind load conditions, a given size of light box sign can be applied directly without the need for frequent calculations.
Please note:
If the design is to make a larger light box sign or for economic reasons, the recommended sheet thickness cannot be used, the acrylic sheet must be reinforced to prevent excessive distortion or possible breakage when the gust is hit. The degree of reinforcement is difficult to describe accurately, but the support strips can be made of transparent acrylic slabs, spaced approximately 600 mm apart, and bonded to the back of the light box sign panel at the correct angle to provide additional stiffness. Huge shop signs or light boxes, such as the logo on the top of tall buildings, are easy to withstand large wind loads. Consider the back of the panel of the light box sign, and fix the anti-deformation bolts at regular intervals. Sign production
Water absorption
After a long period of time, the acrylic sheet can absorb up to 2% of moisture, which will change the size of the light box. The extent of water absorption and dimensional change depends on the relative humidity of the surrounding atmosphere and the initial moisture content of the board itself. Typically, 100% relative humidity increases the size by 0.3%, so a proper expansion allowance is required to prevent distortion of the marking.
Acrylic extruded sheets will vary slightly in size in wet conditions due to their lower initial moisture content.
Thermal expansion
The linear thermal expansion coefficient of thermoplastic materials is greater than most other materials, so if the marking is used for places with large temperature changes, leave enough room for thermal expansion.
Please note that when the acrylic sheet is used for outdoor light box signs, sufficient expansion and contraction allowance must be left in the design and manufacturing process.
Polyacrylamide (PAM) is a water-soluble polymer, which is insoluble in most organic solvents, has good flocculating properties, can reduce frictional resistance between liquids, Can be divided into non-ionic, anionic, cationic and amphoteric four types.
When PAM is used for flocculation, it is related to the surface properties of the species being flocculated, especially the potential, viscosity, turbidity, and pH of the suspension. The kinetic potential of the particle surface is the reason for particle inhibition. Can reduce the potential and condense.
Granular polyacrylamide flocculant cannot be directly added to sewage. It must be dissolved in water before use, and its aqueous solution are used to treat sewage.The water in which the particulate polymer is dissolved should be clean. Generally tap water is suitable for formulating polymer solutions. Strong ACID, strong alkali, high salt water is not suitable for preparation. Water at room temperature is ok, no necessary to heat. Dissolution is slow when the water temperature is below 5 ° C. Increasing the water temperature will accelerate the dissolution rate, but above 40 ° C will accelerate the degradation of the polymer and affect the use effect. The solution concentration is recommended to be 0.1% -0.3%.
Polyacrylamide
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