Plastic and nonmetallic article shaping or treating: processes – Vacuum treatment of work – To degas or prevent gas entrapment
Patent
1994-05-13
1996-07-02
Thurlow, Jeffery R.
Plastic and nonmetallic article shaping or treating: processes
Vacuum treatment of work
To degas or prevent gas entrapment
264149, 26417113, 26417123, 26417317, 26417318, 264237, 425113, 4251311, 4253791, B29C 4702
Patent
active
055319475
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a process for the manufacture of pencils with a firm lead and at least one coating whereby Polymer is be used as a binding material and the lead material and the coating material are extruded. The invention also concerns an installation to implement this process with a lead extruder and at least one coating extruder connected with the coating nozzle.
BACKGROUND OF THE INVENTION
Several requirements are made of pencils, whereby the characteristics essentially depend on the quality of the lead. A pencil must be, among other things, easily sharpened, which depends, on one hand, on how hard the coating is and, on the other hand, because of the impacting torsion, on how brittle the lead is; it also depends on the adhesion between lead and coating material. Variations in the thickness of the lead also tend to be of a disadvantage. In addition, the lead in the coating material should not be subjected to varying tensions or show fractures, which can easily occur during the manufacturing process.
Pencils tend to be made increasingly of synthetics, whereby profiles are being extruded; they are subsequently cut to the length of a pencil. As binding material in the material of the lead and the coating various polymers are used, preferably SAN or ABS Polymers, to which, in turn, appropriate additional substances such as color, gliding and adhesive substances and possibly filling substances can be added.
Even though the characteristics of the pencils are basically determined by the materials used, it has become clear that the manufacturing process also has a significant influence on the characteristics of a pencil.
The DE-OS 20 30 578 shows a device to manufacture and/or coat skein profiles, in particular for pencils. According to an operational formula an already pre-fabricated skein profile such as a wire, a rope, a tube or a similar device is entered in the skein compression nozzle, where the coating of the skein profile takes place. This process is not suited for the manufacture of pencils because pre-fabricated lead breaks very easily and is difficult to handle. A further disadvantage is that the pre-fabricated lead also breaks easily when it is put into contact with the hot coating material, because the differences in temperature between the lead and the coating material inevitably cause tension in the lead material.
DE-OS 20 30 578 also suggests that, immediately prior to the coating, the skein profile, which is to be coated, should be extruded. The nozzle is formed in a manner that it serves simultaneously as a feed into a second skein compression nozzle. This process, however, has the disadvantage that the lead is still plastic when the coating is being extruded on to it. If the compression of the coating material is very strong, a deformation of the lead occurs. This can lead not only to variations in thickness, but also to a complete failure to produce the lead.
The DE-PS 38 27 968 shows a process where all lead components are at first ground to the size of grains of corn and subsequently mixed in a turbomixer. In the turbomixer, a set temperature control is required because the mixture has to be regranulated before it reaches the extruder. In the lead extruder, the mixture goes through a filling zone, a passage zone, a compression zone and a extruder-head zone, whereby the temperature increases up to the extrusion zone and then decreases somewhat at the extruder head. This process is complicated and not very flexible because of the preparation of the lead components when, for example, the hardness of the lead is to be changed.
The DE-AS 22 03 635 shows a pencil with synthetic coating. The manufacture of the lead occurs in two operational stages with the interposition of a drying stage. In the first stage, for example, a mixer thoroughly mixes ABS-resin powder, graphite powder and calcium stearate. After drying, the mixture is extruded at about 170 degree Celsius with the use of an extruder and then, while still hot, is cut to create the materials for the penc
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Metzger Burkhard
Ziolkowski Hans
Bednarek Michael D.
Bellaform Extrusionstechnik GmbH
Thurlow Jeffery R.
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