| 释义 |
▪ I. preform, v.|priːˈfɔːm|
[ad. L. præformāre: see pre- A. 1 and form v. So F. préformer (18th c. Bonnet in Littré).]
a. trans. To form or shape beforehand. (Chiefly in pa. pple.)
1601[see preformed]. 1793Holcroft Lavater's Physiogn. xxiv. 122 If the germ exists preformed in the mother. 1858Bushnell Nat. & Supernat. xi. (1864) 337 God's original scheme, taken as a whole, was so planned, or preformed. 1897Allbutt's Syst. Med. IV. 117 Bile pigments are not preformed in the blood.
(b) spec. To form (plastic or other moulding material) into a shape, usu. one resembling a desired final shape, before some further processing. Also absol.
1936H. W. Rowell Technol. Plastics xx. 148 A ‘tablet’..is made in a stock size of die and is not preformed to the approximate shape of the moulding. 1943D. W. Brown Handbk. Engin. Plastics i. 9 In order to reduce the size of the powder space required in moulds, the raw material is sometimes preformed into comparatively small pellets prior to being introduced into the mould. 1968L. K. Arnold Introd. Plastics (1969) ii. 41 The powder may be preformed, that is, pressed into pellets or disks of convenient size to reduce bulk density and facilitate charging the mold. 1975C. A. Harper Handbk. Plastics & Elastomers xii. 36 There are..transfer-type presses that will automatically feed the powder, preform, preheat, transfer, and complete the molding cycle.
b. To determine the form of beforehand; to furnish a mould or model of (a structure to be subsequently formed).
1890Cent. Dict. s.v., Bone preformed in cartilage. The fetal skeleton preforms that of the adult.
Hence preˈforming vbl. n.; also preˈformer, a press or similar device for preforming plastic.
1931Plastics & Molded Products VII. 705 (Advt.), Trouble-free preforming and more economical production with Stokes single punch and rotary preform presses. 1952J. Delmonte Plastics Molding viii. 193 Standard single⁓punch preformers are illustrated in Figs. 2 and 3, and a rotary-type preforming machine is illustrated in Fig. 4. 1966J. A. Brydson Plastics Materials x. 210 Preforming is carried out by compressing sieved powder that has been evenly loaded into a mould. 1968Encycl. Polymer Sci. & Technol. IX. 26 Preformers are basically compacting presses; they may be mechanical, hydraulic, pneumatic, or rotary cam-type machines.
▪ II. preform, n.|ˈpriːfɔːm|
1. [f. the vb.] A moulded object which has to receive further processing to produce the final shape, which it usu. resembles.
1931Plastics & Molded Products VII. 102 The test strip..is 73/4 in. long by 1 in. wide and is molded from four preforms composed of a very soft grade of phenol-plastic compound. 1935C. Ellis Chem. Synthetic Resins II. lxviii. 1317 Tablets or preforms are made from the molding powder by applying high pressure..quickly and without heat. 1945H. Barron Mod. Plastics vii. 166 Preforms are employed where the use of fairly bulky moulding powder is a disadvantage. 1962Gloss. Terms Glass Industry (B.S.I.) 33 Preform, a small glass product, normally employed in making glass-to-metal seals, formed by dry-pressing glass powder into shape in a die, the shape being fired to consolidate the glass particles into a non-porous component. 1968Encycl. Polymer Sci. & Technol. IX. 26 It is easier for an operator to pick up a preform and place it in a mold cavity or transfer pot than to have to weigh a charge of granular material. 1970New Scientist 12 Nov. 326/1 A precise quantity of [metal] powder is compacted and sintered so as to produce a preform which is approximately 85 per cent dense.
2. Philol. [pre- A. 2.] A linguistic form reconstructed from later evidence.
1939L. H. Gray Foundations of Lang. i. 3 If..one has such a series as English (he) bears, Old Icelandic berr, Gothic baíriþ.., Old High German birit, Old Irish berid, Modern Irish bheir..,..one may, by comparing and contrasting these forms in accordance with phonetic correspondences.., determine why they are here alike, and there unlike, and may perceive how they can all be derived from an hypothetical pre-form. 1972Language XLVIII. 409 There are two possibilities for reconstructing the gen. pl. preforms of the two attested nouns. |