试题与答案

试述实行稳定挤出过程的一些流变学考虑。

题型:问答题

题目:

试述实行稳定挤出过程的一些流变学考虑。

答案:

参考答案:

(1)为稳定挤出,首先要求尽量减少不稳定源。匀化计量段入口处的压力P1应尽可能保持稳定,这要求加料口供料速度必须均匀。

(2)要实现稳定挤出,在其它条件不变的情况下,应适当地减少螺槽深度h和减少机筒与螺杆突棱的间隙δ。

(3)调节机头流通系数可调节挤出过程的稳定性。一般小口径机头K值较小,u值较小,易实现稳定挤出。

(4)物料粘度越大,挤出不稳定系数u越小,因此在保证质量的前提下,适当降低挤出温度,有助于稳定挤出。

(5)适当增加螺杆长度L(即增加L/D.,也使不稳定系数u下降。由于被加工物料具有松弛特性,因此若在加料口处物料发生压力波动,但经过长螺杆L,至匀化计量段会得到较多的松弛、变弱,从而使挤出过程稳定。

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题型:阅读理解

Use your American Express Card to enjoy one-day privileges at four of America’s greatest museums. Note the participating museums, and their exciting special exhibitions that you will not want to miss, listed below.

Boston

Isabella Stewart Gardner Museum

Chairs

February 11 — May 8, 2005

Italian furniture expert Fausto Calderai and Indian photographer Dayanita Singh present an exhibition of chairs from the museum’s collection and “chair photographs” from around the world presented in a Venetisan-style hall housing world-famous masterpieces.

For more information:www.gardnermuseum.org

New York    

The Noguchi Museum

Noguchi and Graham

December 1, 2004 — May 1,2005

Noguchi’s long-term collaboration with dancer Martha Graham is regarded by many as a high point in the history of both modern dance and art. The exhibition highlights nine of the sets created through this collaboration.

For more information:www.noguchi.org

Philadephia

Pennsylvania Academy of the Fine Arts

In Full view:American Painting (1720 — 2005)

January 11 — April 10, 2005

Founded in 1805, the Pennsylvania Academy has been home to America’s artists for 200 years. The Academy collects and exhibits the works of famous American artists, and is well-known for training fine artists. 2005 at the Academy begins with the largest exhibition of the Academy’s distinguished American collection in the institution’s history.

For more information:www.pafa.org

Seattle

Seattle Museum of Glass

Murano:glass from the Olnick Spanu Collection

Through November 7, 2004

This exhibition includes over 200 pieces of beautiful glass from Murano, the island of glassblowers near Venice, Italy. Watch live glass-blowing shows in the Hot Shop and see other modern glass exhibitions.

For more information:www.museumofglass.org

小题1:Which of the following websites offers information about the furniture show?

A.www.pafa.org

B.www.museumofglass.org

C.www.noguchi.org

D.www.gardnermuseum.org小题2:We learn form the text that Martha Graham is ______.

A.a dancer

B.a glassblower

C.a painter

D.a photographer小题3:If you want to know the history of American painting, you may visit ______.

A.The Noguchi Museum

B.Seattle Museum of Glass

C.Isabella Stewart Gardner Museum

D.Pennsylvania Academy of the Fine Arts

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