Vespel 是杜邦公司生產(chǎn)的一系列耐用高性能聚酰亞胺基塑料的商標(biāo)。

特點(diǎn)和應(yīng)用
Vespel 主要用于航空航天、半導(dǎo)體和運(yùn)輸技術(shù)。它結(jié)合了耐熱性、潤(rùn)滑性、尺寸穩(wěn)定性、耐化學(xué)性和抗蠕變性,可用于惡劣和 的環(huán)境條件。
與大多數(shù)塑料不同,即使在高溫下也不會(huì)產(chǎn)生明顯的釋氣,這使得它可用于輕質(zhì)隔熱罩和坩堝支撐。它在真空應(yīng)用中也表現(xiàn)良好,低至極低的低溫。然而,Vespel 往往會(huì)吸收少量的水,從而導(dǎo)致放置在真空中的泵時(shí)間更長(zhǎng)。

盡管在這些特性中,有些聚合物都超過了聚酰亞胺,但它們的結(jié)合是 Vespel 的主要優(yōu)勢(shì)。

熱物理性質(zhì)
Vespel 通常用作測(cè)試熱絕緣體的導(dǎo)熱性參考材料,因?yàn)樗哂懈咴佻F(xiàn)性和熱物理性能的一致性。例如,它可以承受高達(dá) 300 °C 的反復(fù)加熱,而不會(huì)改變其熱性能和機(jī)械性能。已經(jīng)發(fā)布了大量測(cè)量的熱擴(kuò)散率、比熱容和推導(dǎo)密度的表格,這些表格都是溫度的函數(shù)。
磁性
Vespel 用于 NMR 波譜的高分辨率探針,因?yàn)樗捏w積磁化率(Vespel SP-1 在 21.8 °C 時(shí)為 -9.02 ± 0.25×10?6[5])接近室溫下的水(20 °C 時(shí)為 -9.03×10?6 [6]) 負(fù)值表示兩種物質(zhì)都是抗磁性的.將NMR樣品周圍材料的體積磁化率與溶劑的體積磁化率相匹配,可以減少磁共振線的磁化率展寬。
制造應(yīng)用加工
Vespel 可以通過直接成型 (DF) 和等靜壓成型(基本形狀 - 板材、棒材和管材)進(jìn)行加工。對(duì)于原型數(shù)量,通常使用基本形狀以提高成本效益,因?yàn)?DF 零件的工具成本相當(dāng)高。對(duì)于大規(guī)模的CNC生產(chǎn),DF零件通常用于降低每個(gè)零件的成本,而犧牲的材料性能不如等靜壓生產(chǎn)的基本形狀。
類型
對(duì)于不同的應(yīng)用,特殊配方被混合/復(fù)合。形狀由三個(gè)標(biāo)準(zhǔn)過程生成:
壓縮成型(用于板材和環(huán));
等靜壓成型(棒材用);和
直接成型(用于大批量生產(chǎn)的小尺寸零件)。
與從壓縮成型或等靜壓形狀加工而成的零件相比,直接成型零件的性能特征較低。等靜壓形狀具有各向同性的物理性質(zhì),而直接成型和壓縮成型的形狀表現(xiàn)出各向異性的物理性質(zhì)。


Vespel is the trademark of a range of durable high-performance polyimide-based plastics made by DuPont.[1][2]

Characteristics and applications
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Vespel is mostly used in aerospace, semiconductor, and transportation technology. It combines heat resistance, lubricity, dimensional stability, chemical resistance, and creep resistance, and can be used in hostile and extreme environmental conditions.

Unlike most plastics,[3] it does not produce significant outgassing even at high temperatures, which makes it useful for lightweight heat shields and crucible support. It also performs well in vacuum applications,[4] down to extremely low cryogenic temperatures. However, Vespel tends to absorb a small amount of water, resulting in longer pump time while placed in a vacuum.

Although there are polymers surpassing polyimide in each of these properties, the combination of them is the main advantage of Vespel.

Thermophysical properties
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Vespel is commonly used as a thermal conductivity reference material for testing thermal insulators, because of high reproducibility and consistency of its thermophysical properties. For example, it can withstand repeated heating up to 300 °C without altering its thermal and mechanical properties.[citation needed] Extensive tables of measured thermal diffusivity, specific heat capacity, and derived density, all as functions of temperature, have been published.[citation needed]

Magnetic properties
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Vespel is used in high-resolution probes for NMR spectroscopy because its volume magnetic susceptibility (?9.02 ± 0.25×10?6 for Vespel SP-1 at 21.8 °C[5]) is close to that of water at room temperature (?9.03×10?6 at 20 °C [6]) Negative values indicate that both substances are diamagnetic. Matching volume magnetic susceptibilities of materials surrounding NMR sample to that of the solvent can reduce susceptibility broadening of magnetic resonance lines.

Processing for manufacturing applications
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Vespel can be processed by direct forming (DF) and isostatic molding (basic shapes – plates, rods and tubes). For prototype quantities, basic shapes are typically used for cost efficiency since tooling is quite expensive for DF parts. For large scale CNC production, DF parts are often used to reduce per part costs, at the expense of material properties which are inferior to those of isostatically produced basic shapes.[7]

Types
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For different applications, special formulations are blended/compounded. Shapes are produced by three standard processes:

compression molding (for plates and rings);
isostatic molding (for rods); and
direct forming (for small size parts produced in large volumes).
Direct-formed parts have lower performance characteristics than parts that have been machined from compression-molded or isostatic shapes. Isostatic shapes have isotropic physical properties, whereas direct formed and compression molded shapes exhibit anisotropic physical properties.

Some examples of standard polyimide compounds are:

SP-1 virgin polyimideprovides operating temperatures from cryogenic to 300 °C (570 °F), high plasma resistance, as well as a UL rating for minimal electrical and thermal conductivity. This is the unfilled base polyimide resin. It also provides high physical strength and maximal elongation, and the best electrical and thermal insulation values. Example: Vespel SP-1.15% graphite by weight, SP-21added to the base resin for increased wear resistance and reduced friction in applications such as plain bearings, thrust washers, seal rings, slide blocks and other wear applications. This compound has the best mechanical properties of the graphite-filled grades, but lower than the virgin grade. Example: Vespel SP-21.40% graphite by weight, SP-22for enhanced wear resistance, lower friction, improved dimensional stability (low coefficient of thermal expansion), and stability against oxidation. Example: Vespel SP-22.10% PTFE and 15% graphite by weight, SP-211added to the base resin for the lowest coefficient of friction over a wide range of operating conditions. It also has excellent wear resistance up to 149 °C (300 °F). Typical applications include sliding or linear bearings as well as many wear and friction uses listed above. Example: Vespel SP-211.15% moly-filled (molybdenum disulfide solid lubricant), SP-3for wear and friction resistance in vacuum and other moisture-free environments where graphite actually becomes abrasive. Typical applications include seals, plain bearings, gears, and other wear surfaces in outer space, ultra-high vacuum or dry gas applications. Example: Vespel SP-3.
Material properties data
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Material properties of Vespel[8] (produced by isostatic molding and machining)
Property Units Test
condition SP-1
(unfilled) SP-21
(15% graphite) SP-22
(40% graphite) SP-211
(10% PTFE,
15% graphite) SP-3
(15% MoS
2)
Specific gravity dimensionless 1.43 1.51 1.65 1.55 1.60
Thermal expansion
coefficient 10?6/K 211–296 K 45 34 27 [9]
296–573 K 54 49 38 54 52
Thermal conductivity W/mK at 313 K 0.35 0.87 1.73 0.76 0.47
Volume resistivity Ω·m at 296 K 1014–1015 1012–1013
Dielectric constant dimensionless at 100 Hz 3.62 13.53
at 10 kHz 3.64 13.28
at 1 MHz 3.55 13.87