Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1993-02-16
1994-06-28
Aftergut, Jeff H.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
156166, 156242, 156441, 156433, 264136, 264137, 264134, 264174, 264257, B29C 6714
Patent
active
053243773
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of pultruding parts including the reinforcement of the part with some longitudinally continuous fibers and some transverse fibers.
Pultrusion is a well known technique in which longitudinally continuous fibers are collated into a required shape, saturated with a resin and passed through a die in which the resin sets. The force to transmit the fibers and the resin through the die is applied as a pulling action downstream of the die on the finished set part. In many cases although not necessarily the resin is thermo setting and the fibers are glass fibers provided in rovings in which each fiber is continuous and extends longitudinally.
Some pultruded parts consist wholly of longitudinally fibers provided by the rovings. Other parts and particularly more complex parts require additional strength in the transverse direction since the tendency of the rovings or longitudinal fibers to split apart in the transverse direction does not provide sufficient transverse strength for the required complex part. The conventional technique is to apply in addition to the rovings a proportion of mat which comprises a plurality of fibers laid in generally random pattern in a two dimensional form with a bonding material to hold the fibers in the two dimensional pattern. The mat is then required to be slit to a required width for the part concerned and is then applied onto the part generally as an outer layer by bending and forming the mat to wrap around the already shaped rovings. The mat and the finished part provides fibers which extend transversely to the longitudinal direction and accordingly provide strength in the transverse direction.
The mat has however a number of serious problems which interfere with the efficiencies and economics of the pultrusion process.
Firstly, the mat is a rather expensive item relative to the cost of rovings in view of the additional operations necessary for the forming of a two dimensional mat, the additional bonding material and also the slitting and waste from slitting all of which significantly increased the cost.
Secondly, the mat is difficult to form into the required shapes. Thicker and stronger mats are available but these tend to be very stiff and very difficult to bend often in view of the heavy bonding layer so it is almost necessary to crack the bonding layer or binder before the bending action can take place. Hence is of course very difficult to bend the layer into complex shapes and to ensure that the shapes are held while the material enters the die.
Lighter weight mats are easier to form but then often have insufficient transverse strength in the finished part. In addition this lighter weight mat can have insufficient pull strength wet or dry to enter the die and accordingly can be pushed longitudinally and torn at the entrance to the die.
The choice of mat is therefore a compromise between the necessity for bending and the required strength and this of course seriously limits the effectiveness of the pultrusion action.
More recently mats have become available which are needled in a direction at right angles to the normal two dimensional form of the mat so as to provide loops which cooperate with the rovings and also to form a mat structure which is less dependent upon a bonding layer to provide necessary pull strength. This mat has a tendency to stretch and is very expensive thus seriously interfering with the economics of the pultrusion process.
U.S. Pat. No. 4,058,581 (Park) discloses an attempt to attach discontinuous fibers to the longitudinally continuous fibers by simply adding these into the bath of resin so that they maybe picked up by the longitudinal fibers as they pass through the resin. There is no statement that this leads to a layer of transverse fibers on the part and it is believed that any fibers so attached would simply be pulled straight and longitudinal by passage through the die.
It is one object of the present invention, therefore, to provide an improved method of pultrusion in which it is no longer necessary to apply a m
REFERENCES:
patent: 3702356 (1972-11-01), Hall
patent: 3769127 (1973-10-01), Goldsworthy
patent: 3993726 (1976-11-01), Moyer
patent: 4058581 (1977-11-01), Park
patent: 4296060 (1981-10-01), Killmeyer
patent: 4680224 (1987-07-01), O Connor
patent: 4695404 (1987-09-01), Kwong
patent: 4820366 (1989-04-01), Beever et al.
patent: 5120380 (1992-06-01), Strachan
Ade Stanley G.
Aftergut Jeff H.
Battison Adrian D.
Omniglass Ltd.
Thrift Murray E.
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